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ARCHIVE | Wednesday January 8th - Evolution |
November 2024 October 2024 September 2024 August 2024 July 2024 June 2024 May 2024 April 2024 March 2024 February 2024 January 2024 December 2023 November 2023 October 2023 September 2023 August 2023 July 2023 June 2023 May 2023 April 2023 March 2023 February 2023 January 2023 December 2022 December 2021 December 2020 December 2019 December 2018 | Liu, J., Zheng, C., Duan, Y. (2024). New comparative genomic evidence supporting the proteomic diversification role of A-to-I RNA editing in insects. Mol Genet Genomics, 299(1):46 PubMed ID: 38642133
Summary: Adenosine-to-inosine (A-to-I) RNA editing, resembling A-to-G mutation, confers adaptiveness by increasing proteomic diversity in a temporal-spatial manner. This evolutionary theory named "proteomic diversifying hypothesis" has only partially been tested in very few organisms like Drosophila melanogaster, mainly by observing the positive selection on nonsynonymous editing events. To find additional genome-wide evidences supporting this interesting assumption, this study retrieved the genomes of four Drosophila species and collected 20 deep-sequenced transcriptomes of different developmental stages and neuron populations of D. melanogaster. The RNA editomes in these samples was systematically profiled and meticulous comparative genomic analyses was performed. Further evidences were found to support the diversifying hypothesis. (1) None of the nonsynonymous editing sites in D. melanogaster had ancestral G-alleles, while the silent editing sites had an unignorable fraction of ancestral G-alleles; (2) Only very few nonsynonymous editing sites in D. melanogaster had corresponding G-alleles derived in the genomes of sibling species, and the fraction of such situation was significantly lower than that of silent editing sites; (3) The few nonsynonymous editing with corresponding G-alleles had significantly more variable editing levels (across samples) than other nonsynonymous editing sites in D. melanogaster. The proteomic diversifying nature of RNA editing in Drosophila excludes the restorative role which favors an ancestral G-allele. The few fixed G-alleles in sibling species might facilitate the adaptation to particular environment and the corresponding nonsynonymous editing in D. melanogaster would introduce stronger advantage of flexible proteomic diversification. With multi-Omics data, this study consolidates the nature of evolutionary significance of A-to-I RNA editing sites in model insects. | De Lisle, S. P. (2024). Genotype-Environment interaction and the evolution of sexual dimorphism: adult nutritional environment mediates selection and expression of sex-specific genetic variance in Drosophila melanogaster. J Evol Biol, 37(7):770-778 PubMed ID: 38668688
Summary: Sexual conflict plays a key role in the dynamics of adaptive evolution in sexually reproducing populations, and theory suggests an important role for variance in resource acquisition in generating or masking sexual conflict over fitness and life history traits. This study used a quantitative genetic genotype-environment experiment in Drosophila melanogaster to test the theoretical prediction that variance in resource acquisition mediates variation in sex-specific component fitness. Holding larval conditions constant, this study found that adult nutritional environments characterized by high protein content resulted in reduced survival of both sexes and lower male reproductive success compared to an environment of lower protein content. Despite reduced mean fitness of both sexes in high protein environments, a sex*treatment interaction was found for the relationship between resource acquisition and fitness; estimates of the adaptive landscape indicate males were furthest from their optimum resource acquisition level in high protein environments, and females were furthest in low protein environments. Expression of genetic variance in resource acquisition and survival was highest for each sex in the environment it was best adapted to, although the treatment effects on expression of genetic variance eroded in the path from resource acquisition to total fitness. Cross-sex genetic correlations were strongly positive for resource acquisition, survival, and total fitness and negative for mating success, although estimation error was high for all. These results demonstrate that environmental effects on resource acquisition can have predictable consequences for the expression of sex-specific genetic variance but also that these effects of resource acquisition can erode through life history. |
Ye, D., Walsh, J. T., Junker, I. P., Ding, Y. (2024).. Changes in the cellular makeup of motor patterning circuits drive courtship song evolution in Drosophila. Curr Biol, 34(11):2319-2329.e2316 PubMed ID: 38688283
Summary: How evolutionary changes in genes and neurons encode species variation in complex motor behaviors is largely unknown. This study developed genetic tools that permit a neural circuit comparison between the model species Drosophila melanogaster and the closely related species D. yakuba, which has undergone a lineage-specific loss of sine song, one of the two major types of male courtship song in Drosophila. Neuroanatomical comparison of song-patterning neurons called TN1 across the phylogeny demonstrates a link between the loss of sine song and a reduction both in the number of TN1 neurons and the neurites supporting the sine circuit connectivity. Optogenetic activation confirms that TN1 neurons in D. yakuba have lost the ability to drive sine song, although they have maintained the ability to drive the singing wing posture. Single-cell transcriptomic comparison shows that D. yakuba specifically lacks a cell type corresponding to TN1A neurons, the TN1 subtype that is essential for sine song. Genetic and developmental manipulation reveals a functional divergence of the sex determination gene doublesex in D. yakuba to reduce TN1 number by promoting apoptosis. This work illustrates the contribution of motor patterning circuits and cell type changes in behavioral evolution and uncovers the evolutionary lability of sex determination genes to reconfigure the cellular makeup of neural circuits. | Scarpa, A., Pianezza, R., Wierzbicki, F., Kofler, R. (2024). Genomes of historical specimens reveal multiple invasions of LTR retrotransposons in Drosophila melanogaster during the 19th century. Proc Natl Acad Sci U S A, 121(15):e2313866121 PubMed ID: 38564639
Summary: Transposable element invasions have a profound impact on the evolution of genomes and phenotypes. It is thus an important open question how often such TE invasions occur. To address this question, the genomes of historical specimens, sampled about 200 y ago were used. The LTR retrotransposons Blood, Opus, and 412 were shown to spread in Drosophila melanogaster in the 19th century. These invasions constitute second waves, as degraded fragments were found for all three TEs. The composition of Opus and 412, but not of Blood, shows a pronounced geographic heterogeneity, likely due to founder effects during the invasions. Finally, species from the Drosophila simulans complex were identified as the likely origin of the TEs. In total, seven TE families invaded D. melanogaster during the last 200y, thereby increasing the genome size by up to 1.2Mbp. It is suggested that this high rate of TE invasions was likely triggered by human activity. Based on the analysis of strains and specimens sampled at different times, this study provides a detailed timeline of TE invasions, making D. melanogaster the first organism where the invasion history of TEs during the last two centuries could be inferred. |
Tian, S., Asano, Y., Banerjee, T. D., Wee, J. L. Q., Lamb, A., Wang, Y., Murugesan, S. N., Ui-Tei, K., Wittkopp, P. J., Monteiro, A. (2024). A micro-RNA is the effector gene of a classic evolutionary hotspot locus. bioRxiv, PubMed ID: 38659873
Summary: In Lepidoptera (butterflies and moths), the genomic region around the gene cortex is a 'hotspot' locus, repeatedly used to generate intraspecific melanic wing color polymorphisms across 100-million-years of evolution. However, the identity of the effector gene regulating melanic wing color within this locus remains unknown. This study shows that none of the four candidate protein-coding genes within this locus, including cortex, serve as major effectors. Instead, a micro-RNA (miRNA), mir-193, serves as the major effector across three deeply diverged lineages of butterflies, and its function is conserved in Drosophila. In Lepidoptera, mir-193 is derived from a gigantic long non-coding RNA, ivory, and it functions by directly repressing multiple pigmentation genes. This study shows that a miRNA can drive repeated instances of adaptive evolution in animals. | Cao, J., Luo, Y., Chen, Y., Wu, Z., Zhang, J., Wu, Y., Hu, W. (2024). Maternal mitochondrial function affects paternal mitochondrial inheritance in Drosophila. Genetics, 226(4) PubMed ID: 38290047
Summary: The maternal inheritance of mitochondria is a widely accepted paradigm, and mechanisms that prevent paternal mitochondria transmission to offspring during spermatogenesis and postfertilization have been described. Although certain species do retain paternal mitochondria, the factors affecting paternal mitochondria inheritance in these cases are unclear. More importantly, the evolutionary benefit of retaining paternal mitochondria and their ultimate fate are unknown. This study shows that transplanted exogenous paternal D. yakuba mitochondria can be transmitted to offspring when maternal mitochondria are dysfunctional in D. melanogaster. Furthermore, the preserved paternal mitochondria are shown to be functional, and can be stably inherited, such that the proportion of paternal mitochondria increases gradually in subsequent generations. This work has important implications that paternal mitochondria inheritance should not be overlooked as a genetic phenomenon in evolution, especially when paternal mitochondria are of significant differences from the maternal mitochondria or the maternal mitochondria are functionally abnormal. These results improve the understanding of mitochondrial inheritance and provide a new model system for its study. |
Tuesday January 7th - Adult Physiology and Metabolism |
Poidevin, M., Mazuras, N., Bontonou, G., Delamotte, P., Denis, B., Devilliers, M., Akiki, P., Petit, D., de Luca, L., Soulie, P., Gillet, C., Wicker-Thomas, C., Montagne, J. (2024). A fatty acid anabolic pathway in specialized-cells sustains a remote signal that controls egg activation in Drosophila. PLoS Genet, 20(3):e1011186 PubMed ID: 38483976
Summary: Egg activation, representing the critical oocyte-to-embryo transition, provokes meiosis completion, modification of the vitelline membrane to prevent polyspermy, and translation of maternally provided mRNAs. This transition is triggered by a calcium signal induced by spermatozoon fertilization in most animal species, but not in insects. In Drosophila melanogaster, mature oocytes remain arrested at metaphase-I of meiosis and the calcium-dependent activation occurs while the oocyte moves through the genital tract. This study discovered that the oenocytes of fruitfly females are required for egg activation. Oenocytes, cells specialized in lipid-metabolism, are located beneath the abdominal cuticle. In adult flies, they synthesize the fatty acids (FAs) that are the precursors of cuticular hydrocarbons (CHCs), including pheromones. The oenocyte-targeted knockdown of a set of FA-anabolic enzymes, involved in very-long-chain fatty acid (VLCFA) synthesis, leads to a defect in egg activation. Given that some but not all of the identified enzymes are required for CHC/pheromone biogenesis, this putative VLCFA-dependent remote control may rely on an as-yet unidentified CHC or may function in parallel to CHC biogenesis. Additionally, it was discovered that the most posterior ventral oenocyte cluster is in close proximity to the uterus. Since oocytes dissected from females deficient in this FA-anabolic pathway can be activated in vitro, this regulatory loop likely operates upstream of the calcium trigger. These findings provide the first evidence that a physiological extra-genital signal remotely controls egg activation. Moreover, this study highlights a potential metabolic link between pheromone-mediated partner recognition and egg activation. | Moon, S. J., Hu, Y., Dzieciatkowska, M., Kim, A. R., Chen, P. L., Asara, J. M., D'Alessandro, A., Perrimon, N. (2024). Identification of high sugar diet-induced dysregulated metabolic pathways in muscle using tissue-specific metabolic models in Drosophila. bioRxiv, PubMed ID: 38712132
Summary: Individual tissues perform highly specialized metabolic functions to maintain whole-body homeostasis. Although Drosophila serves as a powerful model for studying human metabolic diseases, a lack of tissue-specific metabolic models makes it challenging to quantitatively assess the metabolic processes of individual tissues and disease models in this organism. To address this issue, 32 tissue-specific genome-scale metabolic models (GEMs) were constructed using pseudo-bulk single cell transcriptomics data, revealing distinct metabolic network structures across tissues. Leveraging enzyme kinetics and flux analyses, we predicted tissue-dependent metabolic pathway activities, recapitulating known tissue functions and identifying tissue-specific metabolic signatures, as supported by metabolite profiling. Moreover, to demonstrate the utility of tissue-specific GEMs in a disease context, the effect of a high sugar diet (HSD) on muscle metabolism. Together with (13)C-glucose isotopic tracer studies, we identified was examined of glyceraldehyde 3-phosphate dehydrogenase (GAPDH) as a rate-limiting enzyme in response to HSD. Mechanistically, the decreased GAPDH activity was linked to elevated NADH/NAD(+) ratio, caused by disturbed NAD(+) regeneration rates, and oxidation of GAPDH. Furthermore, a pathway flux index was introduced to predict and validate additionally perturbed pathways, including fructose and butanoate metabolism. Altogether, these results represent a significant advance in generating quantitative tissue-specific GEMs and flux analyses in Drosophila, highlighting their use for identifying dysregulated metabolic pathways and their regulation in a human disease model. |
Luo, M., Yuan, Q., Xie, Y., Mai, M., Song, W., Wang, Y., Shi, H., Xia, E., Guo, H. (2024). Yo-Yo Dieting Delays Male Drosophila melanogaster Aging Through Enhanced Mitochondrial Function, Relative to Sustained High-Calorie Diet Feeding.. The journals of gerontology Series A, Biological sciences and medical sciences, 79(4) PubMed ID: 38198696
Summary: This study aimed to investigate the influence of Yo-yo dieting on the aging process in male Drosophila melanogaster that have been exposed to a high-calorie (HC) diet. Fruit flies were fed with either a consistent HC diet or an alternating regimen of HC and low-calorie diets every 3 days (referred to as "Yo-yo dieting") for a total of 24 days. Biochemical assays were utilized to quantify levels of oxidative stress and activities of the mitochondrial respiratory chain complexes. The frozen section staining method was employed to assess the presence of lipid droplets, reactive oxygen species, cellular viability, and mitochondrial abundance in tissues. Additionally, the expression of key regulators involved in mitochondrial dynamics and biogenic signaling pathways was examined. Yo-yo dieting resulted in an extension of the fruit flies' lifespan, concomitant with reduced body weight, decreased body protein content, and lower triglyceride levels compared to continuous a HC diet feeding. Furthermore, Yo-yo dieting ameliorated impairments in motility and intestinal barrier function. Importantly, it improved mitochondrial function and upregulated the expression of essential mitochondrial fusion proteins, namely mitofusin 1 and mitofusin 2, optic atrophy 1, and peroxisome proliferator-activated receptor-γ coactivator-1α. Therefore, the practice of Yo-yo dieting extends the lifespan of fruit flies by modulating mitochondrial dynamics and the associated biogenic signaling pathways. | Wesseltoft, J. B., Danielsen, C. D., Andersen, A. M., de Jonge, N., Olsen, A., Rohde, P. D., Kristensen, T. N. (2024). Feeding Drosophila gut microbiomes from young and old flies modifies the microbiome. Sci Rep, 14(1):7799 PubMed ID: 38565609
Summary: It is becoming increasingly evident that the myriad of microbes in the gut, within cells and attached to body parts (or roots of plants), play crucial roles for the host. Although this has been known for decades, recent developments in molecular biology allow for expanded insight into the abundance and function of these microbes. This study used the vinegar fly, Drosophila melanogaster, to investigate fitness measures across the lifetime of flies fed a suspension of gut microbes harvested from young or old flies, respectively. It was hypothesized that flies constitutively enriched with a 'Young microbiome' would live longer and be more agile at old age (i.e. have increased healthspan) compared to flies enriched with an 'Old microbiome'. Three major take home messages came out of this study: (1) the gut microbiomes of young and old flies differ markedly; (2) feeding flies with Young and Old microbiomes altered the microbiome of recipient flies and (3) the two different microbial diets did not have any effect on locomotor activity nor lifespan of the recipient flies, contradicting the working hypothesis. Combined, these results provide novel insight into the interplay between hosts and their microbiomes and clearly highlight that the phenotypic effects of gut transplants and probiotics can be complex and unpredictable. |
Yin, J., Chen, H. L., Grigsby-Brown, A., He, Y., Cotten, M. L., Short, J., Dermady, A., Lei, J., Gibbs, M., Cheng, E. S., Zhang, D., Long, C., Xu, L., Zhong, T., Abzalimov, R., Haider, M., Sun, R., He, Y., Zhou, Q., Tjandra, N., Yuan, Q. (2024). Glia-derived secretory fatty acid binding protein Obp44a regulates lipid storage and efflux in the developing Drosophila brain. bioRxiv, PubMed ID: 38645138
Summary: Glia derived secretory factors play diverse roles in supporting the development, physiology, and stress responses of the central nervous system (CNS). Through transcriptomics and imaging analyses, this study has identified Obp44a as one of the most abundantly produced secretory proteins from Drosophila CNS glia. Protein structure homology modeling and Nuclear Magnetic Resonance (NMR) experiments reveal Obp44a as a fatty acid binding protein (FABP) with a high affinity towards long-chain fatty acids in both native and oxidized forms. Further analyses demonstrate that Obp44a effectively infiltrates the neuropil, traffics between neuron and glia, and is secreted into hemolymph, acting as a lipid chaperone and scavenger to regulate lipid and redox homeostasis in the developing brain. In agreement with this essential role, deficiency of Obp44a leads to anatomical and behavioral deficits in adult animals and elevated oxidized lipid levels. Collectively, these findings unveil the crucial involvement of a noncanonical lipid chaperone to shuttle fatty acids within and outside the brain, as needed to maintain a healthy brain lipid environment. These findings could inspire the design of novel approaches to restore lipid homeostasis that is dysregulated in CNS diseases. | Haynes, P. R., Pyfrom, E. S., Li, Y., Stein, C., Cuddapah, V. A., Jacobs, J. A., Yue, Z., Sehgal, A. (2024). A neuron-glia lipid metabolic cycle couples daily sleep to mitochondrial homeostasis.Nat Neurosci, 27(4):666-678 PubMed ID: 38360946
Summary: Sleep is thought to be restorative to brain energy homeostasis, but it is not clear how this is achieved. This study shows that Drosophila glia exhibit a daily cycle of glial mitochondrial oxidation and lipid accumulation that is dependent on prior wake and requires the Drosophila APOE orthologs NLaz and GLaz, which mediate neuron-glia lipid transfer. In turn, a full night of sleep is required for glial lipid clearance, mitochondrial oxidative recovery and maximal neuronal mitophagy. Knockdown of neuronal NLaz causes oxidative stress to accumulate in neurons, and the neuronal mitochondrial integrity protein, Drp1, is required for daily glial lipid accumulation. These data suggest that neurons avoid accumulation of oxidative mitochondrial damage during wake by using mitophagy and passing damage to glia in the form of lipids. We propose that a mitochondrial lipid metabolic cycle between neurons and glia reflects a fundamental function of sleep relevant for brain energy homeostasis. |
Monday January 6th - Adult neural development, structure and function |
Mao, R., Yu, J., Deng, B., Dai, X., Du, Y., Du, S., Zhang, W., Rao, Y. (2024). Conditional chemoconnectomics (cCCTomics) as a strategy for efficient and conditional targeting of chemical transmission. Elife, 12 PubMed ID: 38686992
Summary: Dissection of neural circuitry underlying behaviors is a central theme in neurobiology. We have previously proposed the concept of chemoconnectome (CCT) to cover the entire chemical transmission between neurons and target cells in an organism and created tools for studying it (CCTomics) by targeting all genes related to the CCT in Drosophila. This study has created lines targeting the CCT in a conditional manner after modifying GFP RNA interference, Flp-out, and CRISPR/Cas9 technologies. All three strategies have been validated to be highly effective, with the best using chromatin-peptide fused Cas9 variants and scaffold optimized sgRNAs. As a proof of principle, a comprehensive intersection analysis of CCT genes expression profiles in the clock neurons, uncovering 43 CCT genes present in clock neurons. Specific elimination of each from clock neurons revealed that loss of the neuropeptide ,CNMamide (CNMa) in two posterior dorsal clock neurons (DN1ps) or its receptor (CNMaR) caused advanced morning activity, indicating a suppressive role of CNMa-CNMaR on morning anticipation, opposite to the promoting role of PDF-PDFR on morning anticipation. These results demonstrate the effectiveness of conditional CCTomics and its tools created here and establish an antagonistic relationship between CNMa-CNMaR and PDF-PDFR signaling in regulating morning anticipation. | Shang, X., Talross, G. J. S., Carlson, J. R. (2024). Exitron splicing of odor receptor genes in Drosophila. Proc Natl Acad Sci U S A, 121(13):e2320277121 PubMed ID: 38507450
Summary: Proper expression of odor receptor genes is critical for the function of olfactory systems. This study identified exitrons (exonic introns) in four of the 39 Odorant receptor (Or) genes expressed in the Drosophila antenna. Exitrons are sequences that can be spliced out from within a protein-coding exon, thereby altering the encoded protein. This study focused on Or88a, which encodes a pheromone receptor and found that exitron splicing of Or88a is conserved across five Drosophila species over 20 My of evolution. The exitron was spliced out in 15% of Or88a transcripts. Removal of this exitron creates a non-coding RNA rather than an RNA that encodes a stable protein. These results suggest the hypothesis that in the case of Or88a, exitron splicing could act in neuronal modulation by decreasing the level of functional Or transcripts. Activation of Or88a-expressing olfactory receptor neurons via either optogenetics or pheromone stimulation increased the level of exitron-spliced transcripts, with optogenetic activation leading to a 14-fold increase. A fifth Or can also undergo an alternative splicing event that eliminates most of the canonical open reading frame. Besides these cases of alternative splicing, alternative polyadenylation of four Ors and exposure of Or67c to its ligand ethyl lactate in the antenna downregulated all of its 3' isoforms. This study reveals mechanisms by which neuronal activity could be modulated via regulation of the levels of Or isoforms. |
Singh, B. N., Tran, H., Kramer, J., Kirichenko, E., Changela, N., Wang, F., Feng, Y., Kumar, D., Tu, M., Lan, J., Bizet, M., Fuks, F., Steward, R. (2024). Tet-dependent 5-hydroxymethyl-Cytosine modification of mRNA regulates axon guidance genes in Drosophila. PLoS One, 19(2):e0293894 PubMed ID: 38381741
Summary: Modifications of mRNA, especially methylation of adenosine, have recently drawn much attention. The much rarer modification, 5-hydroxymethylation of cytosine (5hmC), is not well understood and is the subject of this study. Vertebrate Tet proteins are 5-methylcytosine (5mC) hydroxylases and catalyze the transition of 5mC to 5hmC in DNA. These enzymes have recently been shown to have the same function in messenger RNAs in both vertebrates and in Drosophila. The Tet gene is essential in Drosophila as Tet knock-out animals do not reach adulthood. We describe the identification of Tet-target genes in the embryo and larval brain by mapping one, Tet DNA-binding sites throughout the genome and two, the Tet-dependent 5hmrC modifications transcriptome-wide. 5hmrC modifications are distributed along the entire transcript, while Tet DNA-binding sites are preferentially located at the promoter where they overlap with histone H3K4me3 peaks. The identified mRNAs are preferentially involved in neuron and axon development and Tet knock-out led to a reduction of 5hmrC marks on specific mRNAs. Among the Tet-target genes were the robo2 receptor and its slit ligand that function in axon guidance in Drosophila and in vertebrates. Tet knock-out embryos show overlapping phenotypes with robo2 and both Robo2 and Slit protein levels were markedly reduced in Tet KO larval brains. These results establish a role for Tet-dependent 5hmrC in facilitating the translation of modified mRNAs primarily in cells of the nervous system. | Yu, H., Liu, D., Zhang, Y., Tang, R., Fan, X., Mao, S., Lv, L., Chen, F., Qin, H., Zhang, Z., van Aalten, D. M. F., Yang, B., Yuan, K. (2024). Tissue-specific O-GlcNAcylation profiling identifies substrates in translational machinery in Drosophila mushroom body contributing to olfactory learning. Elife, 13 PubMed ID: 38619103
Summary: O-GlcNAcylation is a dynamic post-translational modification that diversifies the proteome. Its dysregulation is associated with neurological disorders that impair cognitive function, and yet identification of phenotype-relevant candidate substrates in a brain-region specific manner remains unfeasible. By combining an O-GlcNAc binding activity derived from Clostridium perfringens OGA (CpOGA) with TurboID proximity labeling in Drosophila, this study developed an O-GlcNAcylation profiling tool that translates O-GlcNAc modification into biotin conjugation for tissue-specific candidate substrates enrichment. The O-GlcNAc interactome in major brain regions of Drosophila was mapped, and components of the translational machinery, particularly ribosomal subunits, were found to be abundantly O-GlcNAcylated in the mushroom body of Drosophila brain. Hypo-O-GlcNAcylation induced by ectopic expression of active CpOGA in the mushroom body decreased local translational activity, leading to olfactory learning deficits that could be rescued by dMyc overexpression-induced increase of protein synthesis. This study provides a useful tool for future dissection of tissue-specific functions of O-GlcNAcylation in Drosophila, and suggests a possibility that O-GlcNAcylation impacts cognitive function via regulating regional translational activity in the brain. |
Bence, M., Jankovics, F., Kristo, I., Gyetvai, A., Vertessy, B. G., Erdelyi, M. (2024). Direct interaction of Su(var)2-10 via the SIM-binding site of the Piwi protein is required for transposon silencing in Drosophila melanogaster. Febs j, 291(8):1759-1779 PubMed ID: 38308815
Summary: Nuclear Piwi/Piwi-interacting RNA complexes mediate co-transcriptional silencing of transposable elements by inducing local heterochromatin formation. In Drosophila, sumoylation plays an essential role in the assembly of the silencing complex; however, the molecular mechanism by which the sumoylation machinery is recruited to the transposon loci is poorly understood. This study shows that the Drosophila E3 SUMO-ligase Su(var)2-10 directly binds to the Piwi protein. This interaction is mediated by the SUMO-interacting motif-like (SIM-like) structure in the C-terminal domain of Su(var)2-10. We demonstrated that the SIM-like structure binds to a special region found in the MID domain of the Piwi protein, the structure of which is highly similar to the SIM-binding pocket of SUMO proteins. Abrogation of the Su(var)2-10-binding surface of the Piwi protein resulted in transposon derepression in the ovary of adult flies. Based on these results, a model is proposed in which the Piwi protein initiates local sumoylation in the silencing complex by recruiting Su(var)2-10 to the transposon loci. | Eichler, K., Hampel, S., Alejandro-GarcIa, A., Calle-Schuler, S. A., Santana-Cruz, A., Kmecova, L., Blagburn, J. M., Hoopfer, E. D., Seeds, A. M. (2024). Somatotopic organization among parallel sensory pathways that promote a grooming sequence in Drosophila. Elife, 12 PubMed ID: 38634460
Summary: Mechanosensory neurons located across the body surface respond to tactile stimuli and elicit diverse behavioral responses, from relatively simple stimulus location-aimed movements to complex movement sequences. How mechanosensory neurons and their postsynaptic circuits influence such diverse behaviors remains unclear. It was previously discovered that Drosophila perform a body location-prioritized grooming sequence when mechanosensory neurons at different locations on the head and body are simultaneously stimulated by dust. This study identified nearly all mechanosensory neurons on the Drosophila head that individually elicit aimed grooming of specific head locations, while collectively eliciting a whole head grooming sequence. Different tracing methods were used to reconstruct the projections of these neurons from different locations on the head to their distinct arborizations in the brain. This provides the first synaptic resolution somatotopic map of a head, and defines the parallel-projecting mechanosensory pathways that elicit head grooming. |
Friday January 2nd - Cytoskeleton |
Jackson, J. A., Denk-Lobnig, M., Kitzinger, K. A., Martin, A. C. (2024). Change in RhoGAP and RhoGEF availability drives transitions in cortical patterning and excitability in Drosophila. Curr Biol, 34(10):2132-2146.e2135 PubMed ID: 38688282
Summary: Actin cortex patterning and dynamics are critical for cell shape changes. These dynamics undergo transitions during development, often accompanying changes in collective cell behavior. Although mechanisms have been established for individual cells' dynamic behaviors, the mechanisms and specific molecules that result in developmental transitions in vivo are still poorly understood. This study took advantage of two developmental systems in Drosophila melanogaster to identify conditions that altered cortical patterning and dynamics. A Rho guanine nucleotide exchange factor (RhoGEF) and Rho GTPase activating protein (RhoGAP) pair required for actomyosin waves in egg chambers. Specifically, depletion of the RhoGEF, Ect2, or the RhoGAP, RhoGAP15B, disrupted actomyosin wave induction, and both proteins relocalized from the nucleus to the cortex preceding wave formation. Furthermore, overexpression of a different RhoGEF and RhoGAP pair, RhoGEF2 and Cumberland gap (C-GAP or Rho GTPase activating protein at 71E), was found to result in actomyosin waves in the early embryo, during which RhoA activation precedes actomyosin assembly by ~4 s. C-GAP was recruited to actomyosin waves, and disrupting F-actin polymerization altered the spatial organization of both RhoA signaling and the cytoskeleton in waves. In addition, disrupting F-actin dynamics increased wave period and width, consistent with a possible role for F-actin in promoting delayed negative feedback. Overall, this study showed a mechanism involved in inducing actomyosin waves that is essential for oocyte development and is general to other cell types, such as epithelial and syncytial cells. | Okenve-Ramos, P., Gosling, R., Chojnowska-Monga, M., Gupta, K., Shields, S., Alhadyian, H., Collie, C., Gregory, E., Sanchez-Soriano, N. (2024). Neuronal ageing is promoted by the decay of the microtubule cytoskeleton. PLoS Biol, 22(3):e3002504 PubMed ID: 38478582
Summary: Natural ageing is accompanied by a decline in motor, sensory, and cognitive functions, all impacting quality of life. Ageing is also the predominant risk factor for many neurodegenerative diseases, including Parkinson's disease and Alzheimer's disease. It is therefore necessary to gain a better understanding of the cellular and physiological processes underlying age-related neuronal decay. However, gaining this understanding is a slow process due to the large amount of time required to age mammalian or vertebrate animal models. This study introduces a new cellular model within the Drosophila brain, in which classical ageing hallmarks previously observed in the primate brain appear. These hallmarks include axonal swellings, cytoskeletal decay, a reduction in axonal calibre, and morphological changes arising at synaptic terminals. In the fly brain, these changes begin to occur within a few weeks, ideal to study the underlying mechanisms of ageing. The decay of the neuronal microtubule (MT) cytoskeleton was shown to precede the onset of other ageing hallmarks. The MT-binding factors Tau, EB1, and Shot/MACF1, are necessary for MT maintenance in axons and synapses, and their functional loss during ageing triggers MT bundle decay, followed by a decline in axons and synaptic terminals. Furthermore, genetic manipulations that improve MT networks slowed down the onset of neuronal ageing hallmarks and confer aged specimens the ability to outperform age-matched controls. Our work suggests that MT networks are a key lesion site in ageing neurons and therefore the MT cytoskeleton offers a promising target to improve neuronal decay in advanced age. |
Gu, L., Sauceda, R., Brar, J., Fessahaye, F., Joo, M., Lee, J., Nguyan, J., Teng, M., Weng, M. (2024). A novel protein Moat prevents ectopic epithelial folding by limiting Bazooka/Par3-dependent adherens junctions. bioRxiv, PubMed ID: 38496457
Summary: Cortical myosin contraction and cell adhesion work together to promote tissue shape changes, but how they are modulated to achieve diverse morphogenetic outcomes remains unclear. Epithelial folding occurs via apical constriction, mediated by apical accumulation of contractile myosin engaged with adherens junctions, as in Drosophila ventral furrow formation. While levels of contractile myosin correlate with apical constriction, whether levels of adherens junctions modulate apical constriction is unknown. This study identified a novel Drosophila gene moat that maintains low levels of Bazooka/Par3-dependent adherens junctions and thereby restricts apical constriction to ventral furrow cells with high-level contractile myosin. In moat mutants, abnormally high levels of Bazooka/Par3-dependent adherens junctions promote ectopic apical constriction in cells with low-level contractile myosin, insufficient for apical constriction in wild type. Such ectopic apical constriction expands infolding behavior from ventral furrow to ectodermal anterior midgut, which normally forms a later circular invagination. In moat mutant ventral furrow, a perturbed apical constriction gradient delays infolding. These results indicate that levels of adherens junctions can modulate the outcome of apical constriction, providing an additional mechanism to define morphogenetic boundaries. | McParland, E. D., Butcher, T. A., Gurley, N. J., Johnson, R. I., Slep, K. C., Peifer, M. (2024). The Dilute domain in Canoe is not essential for linking cell junctions to the cytoskeleton but supports morphogenesis robustness. J Cell Sci, 137(6) PubMed ID: 38323935
Summary: Robust linkage between adherens junctions and the actomyosin cytoskeleton allows cells to change shape and move during morphogenesis without tearing tissues apart. The Drosophila multidomain protein Canoe and its mammalian homolog afadin are crucial for this, as in their absence many events of morphogenesis fail. To define the mechanism of action for Canoe, it is being taken apart. Canoe has five folded protein domains and a long intrinsically disordered region. The largest is the Dilute domain, which is shared by Canoe and myosin V. To define the roles of this domain in Canoe, we combined biochemical, genetic and cell biological assays. AlphaFold was used to predict its structure, providing similarities and contrasts with Myosin V. Biochemical data suggested one potential shared function - the ability to dimerize. Canoe mutants were generated with the Dilute domain deleted (CnoΔDIL). Surprisingly, they were viable and fertile. CnoΔDIL localized to adherens junctions and was enriched at junctions under tension. However, when its dose was reduced, CnoΔDIL did not provide fully wild-type function. Furthermore, canoeΔDIL mutants had defects in the orchestrated cell rearrangements of eye> development. This reveals the robustness of junction-cytoskeletal connections during morphogenesis and highlights the power of natural selection to maintain protein structure. |
Rinaldin, M., Kickuth, A., Dalton, B., Xu, Y., Di Talia, S., Brugues, J. (2024). Robust cytoplasmic partitioning by solving an intrinsic cytoskeletal instability. bioRxiv, PubMed ID: 38559072
Summary: Early development across vertebrates and insects critically relies on robustly reorganizing the cytoplasm of fertilized eggs into individualized cells. This intricate process is orchestrated by large microtubule structures that traverse the embryo, partitioning the cytoplasm into physically distinct and stable compartments. Despite the robustness of embryonic development, here we uncover an intrinsic instability in cytoplasmic partitioning driven by the microtubule cytoskeleton. Embryos circumvent this instability through two distinct mechanisms: either by matching the cell cycle duration to the time needed for the instability to unfold or by limiting microtubule nucleation. These regulatory mechanisms give rise to two possible strategies to fill the cytoplasm, which have been experimentally demonstrated in zebrafish and Drosophila embryos, respectively. In zebrafish embryos, unstable microtubule waves fill the geometry of the entire embryo from the first division. Conversely, in Drosophila embryos, stable microtubule asters resulting from reduced microtubule nucleation gradually fill the cytoplasm throughout multiple divisions. These results indicate that the temporal control of microtubule dynamics could have driven the evolutionary emergence of species-specific mechanisms for effective cytoplasmic organization. Furthermore, this study unveils a fundamental synergy between physical instabilities and biological clocks, uncovering universal strategies for rapid, robust, and efficient spatial ordering in biological systems. | Tran, N. V., Montanari, M. P., Lubenets, D., Fischbach, L. L., Antson, H., Okada, Y., Ishimoto, Y., Tonissoo, T., Shimmi, O. (2024). α-Spectrin regulates cell shape changes during disassembly of microtubule-driven protrusions in Drosophila wings. microPublication biology, 2024 PubMed ID: 38690064
Summary: The dynamics of microtubule-mediated protrusions, termed Interplanar Amida Network (IPAN) in Drosophila pupal wing, involve cell shape changes. The molecular mechanisms underlying these processes are yet to be fully understood. This study delineates the stages of cell shape alterations during the disassembly of microtubule protrusions and underscores the pivotal role of α-Spectrin in driving these changes by regulating both the microtubule and actomyosin networks. These findings also demonstrate that α-Spectrin is required for the apical relaxation of wing epithelia during protrusion disassembly, indicating its substantial contribution to the robustness of 3D tissue morphogenesis. |
Tuesday December 31st - Signaling |
Dominicci-Cotto, C., Vazquez, M., Marie, B. (2024). The Wingless planar cell polarity pathway is essential for optimal activity-dependent synaptic plasticity. Frontiers in synaptic neuroscience, 16:1322771 PubMed ID: 38633293
Summary: From fly to man, the Wingless (Wg)/Wnt signaling molecule is essential for both the stability and plasticity of the nervous system. The Drosophila neuromuscular junction (NMJ) has proven to be a useful system for deciphering the role of Wg in directing activity-dependent synaptic plasticity (ADSP), which, in the motoneuron, has been shown to be dependent on both the canonical and the noncanonical calcium Wg pathways. This study shows that the noncanonical planar cell polarity (PCP) pathway is an essential component of the Wg signaling system controlling plasticity at the motoneuron synapse. Evidence is presented that disturbing the PCP pathway leads to a perturbation in ADSP. A PCP-specific allele of disheveled (dsh) affects the de novo synaptic structures produced during ADSP. The Rho GTPases downstream of Dsh in the PCP pathway are also involved in regulating the morphological changes that take place after repeated stimulation. Finally, Jun kinase was shown to be essential for this phenomenon, whereas no indication was found of the involvement of the transcription factor complex AP1 (Jun/Fos). This work shows the involvement of the neuronal PCP signaling pathway in supporting ADSP. Because AP1 mutants can perform ADSP adequately, it is hypothesized that, upon Wg activation, the Rho GTPases and Jun kinase are involved locally at the synapse, in instructing cytoskeletal dynamics responsible for the appearance of the morphological changes occurring during ADSP. | Sekiguchi, M., Katoh, S., Yokosako, T., Saito, A., Sakai, M., Fukuda, A., Itoh, T. Q., Yoshii, T. (2024). The Trissin/TrissinR signaling pathway in the circadian network regulates evening activity in Drosophila melanogaster under constant dark conditions. Biochem Biophys Res Commun, 704:149705 PubMed ID: 38430699
Summary: The circadian clock in Drosophila is governed by a neural network comprising approximately 150 neurons, known as clock neurons, which are intricately interconnected by various neurotransmitters. The neuropeptides that play functional roles in these clock neurons have been identified; however, the roles of some neuropeptides, such as Trissin, remain unclear. Trissin is expressed in lateral dorsal clock neurons (LNds), while its receptor, TrissinR, is expressed in dorsal neuron 1 (DN1) and LNds. This study investigated the role of the Trissin/TrissinR signaling pathway within the circadian network in Drosophila melanogaster. Analysis involving our newly generated antibody against the Trissin precursor revealed that Trissin expression in the LNds cycles in a circadian manner. Behavioral analysis further demonstrated that flies with Trissin or TrissinR knockout or knockdown showed delayed evening activity offset under constant darkness conditions. Notably, this observed delay in evening activity offset in Trissin(RNAi) flies was restored via the additional knockdown of Ion transport peptide (ITP), indicating that the Trissin/TrissinR signaling pathway transmits information via ITP. Therefore, this pathway may be a key regulator of the timing of evening activity offset termination, orchestrating its effects in collaboration with the neuropeptide, ITP. |
Ehlers, S. F., Manikowski, D., Steffes, G., Ehring, K., Gude, F., Grobe, K. (2024). A Residual N-Terminal Peptide Enhances Signaling of Depalmitoylated Hedgehog to the Patched Receptor. Journal of developmental biology, 12(2) PubMed ID: 38651456
Summary: During their biosynthesis, Sonic hedgehog (Shh; see Drosophila Hedgehog) morphogens are covalently modified by cholesterol at the C-terminus and palmitate at the N-terminus. Although both lipids initially anchor Shh to the plasma membrane of producing cells, it later translocates to the extracellular compartment to direct developmental fates in cells expressing the Patched (Ptch) receptor. Possible release mechanisms for dually lipidated Hh/Shh into the extracellular compartment are currently under intense debate. This paper describes the serum-dependent conversion of the dually lipidated cellular precursor into a soluble cholesteroylated variant (Shh(C)) during its release. Although Shh(C) is formed in a Dispatched- and Scube2-dependent manner, suggesting the physiological relevance of the protein, the depalmitoylation of Shh(C) during release is inconsistent with the previously postulated function of N-palmitate in Ptch receptor binding and signaling. Therefore, this study analyzed the potency of Shh(C) to induce Ptch-controlled target cell transcription and differentiation in Hh-sensitive reporter cells and in the Drosophila eye. In both experimental systems, it was found that Shh(C) was highly bioactive despite the absence of the N-palmitate. The artificial removal of N-terminal peptides longer than eight amino acids inactivated the depalmitoylated soluble proteins in vitro and in the developing Drosophila eye. These results demonstrate that N-depalmitoylated Shh(C) requires an N-peptide of a defined minimum length for its signaling function to Ptch. | von Saucken, V. E., Windner, S. E., Baylies, M. K. (2024). Postsynaptic BMP signaling regulates myonuclear properties in Drosophila larval muscles. bioRxiv, PubMed ID: 38645063
Summary: The syncytial mammalian muscle fiber contains a heterogeneous population of (myo)nuclei. At the neuromuscular junction (NMJ), myonuclei have specialized positioning and gene expression. However, it remains unclear how myonuclei are recruited and what regulates myonuclear output at the NMJ. This study identified specific properties of myonuclei located near the Drosophila larval NMJ. These synaptic myonuclei have increased size in relation to their surrounding cytoplasmic domain (scaling), increased DNA content (ploidy), and increased levels of transcription factor pMad, a readout for BMP signaling activity. Genetic manipulations show local BMP signaling affects muscle size, nuclear size, ploidy, and NMJ size and function. In support, RNA sequencing analysis reveals that pMad regulates genes involved in muscle growth, ploidy (i.e., E2f1), and neurotransmission. These data suggest that muscle BMP signaling instructs synaptic myonuclear output that then positively shapes the NMJ synapse. This study deepens understanding of how myonuclear heterogeneity supports local signaling demands to fine tune cellular function and NMJ activity. |
Li, M., Ding, W., Deng, Y., Zhao, Y., Liu, Q., Zhou, Z. (2024). The AAA-ATPase Ter94 regulates wing size in Drosophila by suppressing the Hippo pathway. Communications biology, 7(1):533 PubMed ID: 38710747
Summary: Insect wing development is a fascinating and intricate process that involves the regulation of wing size through cell proliferation and apoptosis. This study found that Ter94, an AAA-ATPase, is essential for proper wing size dependently on its ATPase activity. Loss of Ter94 enables the suppression of Hippo target genes. When Ter94 is depleted, it results in reduced wing size and increased apoptosis, which can be rescued by inhibiting the Hippo pathway. Biochemical experiments reveal that Ter94 reciprocally binds to Mer, a critical upstream component of the Hippo pathway, and disrupts its interaction with Ex and Kib. This disruption prevents the formation of the Ex-Mer-Kib complex, ultimately leading to the inactivation of the Hippo pathway and promoting proper wing development. Finally, this study showed that hVCP, the human homolog of Ter94, is able to substitute for Ter94 in modulating Drosophila wing size, underscoring their functional conservation. In conclusion, Ter94 plays a positive role in regulating wing size by interfering with the Ex-Mer-Kib complex, which results in the suppression of the Hippo pathway. | Liu, A., O'Connell, J., Wall, F., Carthew, R. W. (2024). Scaling between cell cycle duration and wing growth is regulated by Fat-Dachsous signaling in Drosophila. bioRxiv, PubMed ID: 38645118
Summary: The atypical cadherins Fat and Dachsous (Ds) signal through the Hippo pathway to regulate growth of numerous organs, including the Drosophila wing. This study found that Ds-Fat signaling tunes a unique feature of cell proliferation found to control the rate of wing growth during the third instar larval phase. The duration of the cell cycle increases in direct proportion to the size of the wing, leading to linear-like growth during the third instar. Ds-Fat signaling enhances the rate at which the cell cycle lengthens with wing size, thus diminishing the rate of wing growth. This results in a complex but stereotyped relative scaling of wing growth with body growth in Drosophila. Finally, the dynamics of Fat and Ds protein distribution in the wing were examined, observing graded distributions that change during growth. However, the significance of these dynamics is unclear since perturbations in expression have negligible impact on wing growth. |
Monday December 30th - Gonads |
Barr, J., Diegmiller, R., Colonnetta, M. M., Ke, W., Imran Alsous, J., Stern, T., Shvartsman, S. Y., Schedl, P. (2024). To be or not to be: orb, the fusome and oocyte specification in Drosophila. Genetics, 226(4) PubMed ID: 38345426
Summary: In the fruit fly Drosophila melanogaster, two cells in a cyst of 16 interconnected cells have the potential to become the oocyte, but only one of these will assume an oocyte fate as the cysts transition through regions 2a and 2b of the germarium. The mechanism of specification depends on a polarized microtubule network, a dynein dependent Egl:BicD mRNA cargo complex, a special membranous structure called the fusome and its associated proteins, and the translational regulator orb. This work investigated the role of orb and the fusome in oocyte specification. Specification is shown to be a stepwise process. Initially, orb mRNAs accumulate in the two pro-oocytes in close association with the fusome. This association is accompanied by the activation of the orb autoregulatory loop, generating high levels of Orb. Subsequently, orb mRNAs become enriched in only one of the pro-oocytes, the presumptive oocyte, and this is followed, with a delay, by Orb localization to the oocyte. Fusome association of orb mRNAs is essential for oocyte specification in the germarium, is mediated by the orb 3' UTR, and requires Orb protein. The microtubule minus end binding protein Patronin is shown to function downstream of orb in oocyte specification. Finally, in contrast to a previously proposed model for oocyte selection, the choice of which pro-oocyte becomes the oocyte does not seem to be predetermined by the amount of fusome material in these two cells, but instead depends upon a competition for orb gene products. | Buglak, D. B., Holmes, K. H. M., Galletta, B. J., Rusan, N. M. (2024). The Proximal Centriole-Like Structure Anchors the Centriole to the Sperm Nucleus. bioRxiv, PubMed ID: 38712096
Summary: Proper connection between the sperm head and tail is critical for sperm motility and fertilization. The link between the head and tail is mediated by the Head-Tail Coupling Apparatus (HTCA), which secures the axoneme (tail) to the nucleus (head). However, the molecular architecture of the HTCA is not well understood. This study used Drosophila to create a high-resolution map of proteins and structures at the HTCA throughout spermiogenesis. Using structured illumination microscopy, it was demonstrated that key HTCA proteins Spag4 and http://flybase.org/reports/FBgn0045842.htm">Yuri form a 'Centriole Cap' that surrounds the centriole (or Basal Body) as it is inserted, or embedded into the surface of the nucleus. As development progresses, the centriole is laterally displaces to the side of the nucleus, during which time the HTCA expands under the nucleus, forming what we term the 'Nuclear Shelf.' It was next shown that the proximal centriole-like (PCL) structure is positioned under the Nuclear Shelf and functions as a critical stabilizer of the centriole-nuclear attachment. Together, these data indicate that the HTCA is complex, multi-point attachment site that simultaneously engages the PCL, the centriole, and the nucleus to ensure proper head-tail connection during late-stage spermiogenesis. |
Siddiqui, N. U., Karaiskakis, A., Goldman, A. L., Eagle, W. V. I., Low, T. C. H., Luo, H., Smibert, C. A., Gavis, E. R., Lipshitz, H. D. (2024). Smaug regulates germ plasm assembly and primordial germ cell number in Drosophila embryos. Sci Adv, 10(15):eadg7894 PubMed ID: 38608012
Summary: During Drosophila oogenesis, the Oskar (OSK) RNA binding protein (RBP) determines the amount of germ plasm that assembles at the posterior pole of the oocyte. This study identified mechanisms that subsequently regulate germ plasm assembly in the early embryo. The Smaug (SMG) RBP is transported into the germ plasm of the early embryo where it accumulates in the germ granules. SMG binds to and represses translation of the osk messenger RNA (mRNA) as well as the bruno 1 (bru1) mRNA, which encodes an RBP that is shown to promote germ plasm production. Loss of SMG or mutation of SMG's binding sites in the osk or bru1 mRNA results in excess translation of these transcripts in the germ plasm, accumulation of excess germ plasm, and budding of excess primordial germ cells (PGCs). Therefore, SMG triggers a posttranscriptional regulatory pathway that attenuates the amount of germ plasm in embryos to modulate the number of PGCs. | Nashchekin, D., Squires, I., Prokop, A., St Johnston, D. (2024). The Shot CH1 domain recognises a distinct form of F-actin during Drosophila oocyte determination. Development, 151(7) PubMed ID: 38564309
Summary: In Drosophila, only one cell in a multicellular female germline cyst is specified as an oocyte and a similar process occurs in mammals. The symmetry-breaking cue for oocyte selection is provided by the fusome, a tubular structure connecting all cells in the cyst. The Drosophila spectraplakin Short stop (Shot localises to the fusome and translates its asymmetry into a polarised microtubule network that is essential for oocyte specification, but how Shot recognises the fusome is unclear. This study demonstrates that the actin-binding domain (ABD) of Shot is necessary and sufficient to localise Shot to the fusome and mediates Shot function in oocyte specification together with the microtubule-binding domains. The calponin homology domain 1 of the Shot ABD recognises fusomal F-actin and requires calponin homology domain 2 to distinguish it from other forms of F-actin in the cyst. By contrast, the ABDs of utrophin, Fimbrin, Filamin, Lifeact and F-tractin do not recognise fusomal F-actin. It is therefore proposed that Shot propagates fusome asymmetry by recognising a specific conformational state of F-actin on the fusome. |
Herriage, H. C., Calvi, B. R. (2024). Premature endocycling of Drosophila follicle cells causes pleiotropic defects in oogenesis. Genetics, 226(4) PubMed ID: 38302115
Summary: Endocycling cells grow and repeatedly duplicate their genome without dividing. Cells switch from mitotic cycles to endocycles in response to developmental signals during the growth of specific tissues in a wide range of organisms. The purpose of switching to endocycles, however, remains unclear in many tissues. Additionally, cells can switch to endocycles in response to conditional signals, which can have beneficial or pathological effects on tissues. However, the impact of these unscheduled endocycles on development is underexplored. This study used Drosophila ovarian somatic follicle cells as a model to examine the impact of unscheduled endocycles on tissue growth and function. Follicle cells normally switch to endocycles at mid-oogenesis. Inducing follicle cells to prematurely switch to endocycles resulted in the lethality of the resulting embryos. Analysis of ovaries with premature follicle cell endocycles revealed aberrant follicular epithelial structure and pleiotropic defects in oocyte growth, developmental gene amplification, and the migration of a special set of follicle cells known as border cells. Overall, these findings reveal how unscheduled endocycles can disrupt tissue growth and function to cause aberrant development. | Xu, D., Pan, J., Fang, Y., Zhao, L., Su, Y. (2024). RpS25 is required for sperm elongation and individualization during Drosophila spermatogenesis. Biochem Biophys Res Commun, 702:149633 PubMed ID: 38341921
Summary: Ribosomal protein 25 (RPS25) has been related to male fertility diseases in humans. However, the role of RPS25 in spermatogenesis has yet to be well understood. RpS25 is evolutionarily highly conserved from flies to humans through sequence alignment and phylogenetic tree construction. This study found that RpS25 plays a critical role in Drosophila spermatogenesis and its knockdown leads to male sterility. Examination of each stage of spermatogenesis from RpS25-knockdown flies showed that RpS25 was not required for initial germline cell divisions, but was required for spermatid elongation and individualization. In RpS25-knockdown testes, the average length of cyst elongation was shortened, the spermatid nuclei bundling was disrupted, and the assembly of individualization complex from actin cones failed, resulting in the failure of mature sperm production. These data revealed an essential role of RpS25 during Drosophila spermatogenesis through regulating spermatid elongation and individualization. |
Friday December 27th - Adult Neural Structure, Development, and Function |
Sears, J. C., Broadie, K. (2024). Use-Dependent, Untapped Dual Kinase Signaling Localized in Brain Learning Circuitry. J Neurosci, 44(12) PubMed ID: 38267256
Summary: Imaging brain learning and memory circuit kinase signaling is a monumental challenge. The separation of phases-based activity reporter of kinase (SPARK) biosensors allow circuit-localized studies of multiple interactive kinases in vivo, including protein kinase A (PKA) and extracellular signal-regulated kinase (ERK) signaling. In the precisely-mapped Drosophila brain learning/memory circuit, this study found PKA and ERK signaling differentially enriched in distinct Kenyon cell connectivity nodes. Potentiating normal circuit activity was found to induce circuit-localized PKA and ERK signaling, expanding kinase function within new presynaptic and postsynaptic domains. Activity-induced PKA signaling shows extensive overlap with previously selective ERK signaling nodes, while activity-induced ERK signaling arises in new connectivity nodes. Targeted synaptic transmission blockade in Kenyon cells was found to elevate circuit-localized ERK induction in Kenyon cells with normally high baseline ERK signaling, suggesting lateral and feedback inhibition. Overexpression of the pathway-linking Meng-Po (human SBK1) serine/threonine kinase was found to improve learning acquisition and memory consolidation results in dramatically heightened PKA and ERK signaling in separable Kenyon cell circuit connectivity nodes, revealing both synchronized and untapped signaling potential. Finally, a mechanically-induced epileptic seizure model (easily shocked "bang-sensitive" mutants) has strongly elevated, circuit-localized PKA and ERK signaling. Both sexes were used in all experiments, except for the hemizygous male-only seizure model. Hyperexcitable, learning-enhanced, and epileptic seizure models have comparably elevated interactive kinase signaling, suggesting a common basis of use-dependent induction. It is concluded that PKA and ERK signaling modulation is locally coordinated in use-dependent spatial circuit dynamics underlying seizure susceptibility linked to learning/memory potential. | Nelson, N., Vita, D. J., Broadie, K. (2024). Experience-dependent glial pruning of synaptic glomeruli during the critical period. Sci Rep, 14(1):9110 PubMed ID: 38643298
Summary: Critical periods are temporally-restricted, early-life windows when sensory experience remodels synaptic connectivity to optimize environmental input. In the Drosophila juvenile brain, critical period experience drives synapse elimination, which is transiently reversible. Within olfactory sensory neuron (OSN) classes synapsing onto single projection neurons extending to brain learning/memory centers, glia were found to mediate experience-dependent pruning of OSN synaptic glomeruli downstream of critical period odorant exposure. Glial projections were found that infiltrate brain neuropil in response to critical period experience, and use Draper (MEGF10) engulfment receptors to prune synaptic glomeruli. Downstream, antagonistic Basket (JNK) and Puckered (DUSP) signaling was found to be required for the experience-dependent translocation of activated Basket into glial nuclei. Dependent on this signaling, critical period experience was found to drives expression of the F-actin linking signaling scaffold Cheerio (FLNA), which is absolutely essential for the synaptic glomeruli pruning. Cheerio was found to mediate experience-dependent regulation of the glial F-actin cytoskeleton for critical period remodeling. These results define a sequential pathway for experience-dependent brain synaptic glomeruli pruning in a strictly-defined critical period; input experience drives neuropil infiltration of glial projections, Draper/MEGF10 receptors activate a Basket/JNK signaling cascade for transcriptional activation, and Cheerio/FLNA induction regulates the glial actin cytoskeleton to mediate targeted synapse phagocytosis. |
Gorko, B., Siwanowicz, I., Close, K., Christoforou, C., Hibbard, K. L., Kabra, M., Lee, A., Park, J. Y., Li, S. Y., Chen, A. B., Namiki, S., Chen, C., Tuthill, J. C., Bock, D. D., Rouault, H., Branson, K., Ihrke, G., Huston, S. J. (2024). Motor neurons generate pose-targeted movements via proprioceptive sculpting. Nature, 628(8008):596-603 PubMed ID: 38509371
Summary: Motor neurons are the final common pathway through which the brain controls movement of the body, forming the basic elements from which all movement is composed. Yet how a single motor neuron contributes to control during natural movement remains unclear. This study anatomically and functionally characterized the individual roles of the motor neurons that control head movement in the fly, Drosophila melanogaster. Counterintuitively, activity in a single motor neuron was found to rotate the head in different directions, depending on the starting posture of the head, such that the head converges towards a pose determined by the identity of the stimulated motor neuron. A feedback model predicts that this convergent behaviour results from motor neuron drive interacting with proprioceptive feedback. A single class of proprioceptive neuron was identified and genetically suppressed that changes the motor neuron-induced convergence as predicted by the feedback model. These data suggest a framework for how the brain controls movements: instead of directly generating movement in a given direction by activating a fixed set of motor neurons, the brain controls movements by adding bias to a continuing proprioceptive-motor loop. | Schretter, C. E., Sten, T. H., Klapoetke, N., Shao, M., Nern, A., Dreher, M., Bushey, D., Robie, A. A., Taylor, A. L., Branson, K. M., Otopalik, A., Ruta, V., Rubin, G. M. (2024). Social state gates vision using three circuit mechanisms in Drosophila. bioRxiv, PubMed ID: 38559111
Summary: Animals are often bombarded with visual information and must prioritize specific visual features based on their current needs. The neuronal circuits that detect and relay visual features have been well-studied. Yet, much less is known about how an animal adjusts its visual attention as its goals or environmental conditions change. During social behaviors, flies need to focus on nearby flies. How the flow of visual information is altered when female Drosophila enter an aggressive state was studied. From the connectome, three state-dependent circuit motifs were identified poised to selectively amplify the response of an aggressive female to fly-sized visual objects: convergence of excitatory inputs from neurons conveying select visual features and internal state; dendritic disinhibition of select visual feature detectors; and a switch that toggles between two visual feature detectors. Using cell-type-specific genetic tools, together with behavioral and neurophysiological analyses, this study shows that each of these circuit motifs function during female aggression. Features of this same switch operate in males during courtship pursuit, suggesting that disparate social behaviors may share circuit mechanisms. This work provides a compelling example of using the connectome to infer circuit mechanisms that underlie dynamic processing of sensory signals. |
Mallick, A., Tan, H. L., Epstein, J. M., Gaudry, Q., Dacks, A. M. (2024). Serotonin acts through multiple cellular targets during an olfactory critical period. bioRxiv, PubMed ID: 38645269
Summary: Serotonin (5-HT) is known to modulate early development during critical periods when experience drives heightened levels of plasticity in neurons.This study took advantage of the genetically tractable olfactory system of Drosophila to investigate how 5-HT modulates critical period plasticity in the CO2 sensing circuit of fruit flies. This study reveals that 5HT modulation of multiple neuronal targets is necessary for experience-dependent structural changes in an odor processing circuit. The olfactory conditioned place preference (CPP) is known to involve local inhibitory networks and, consistent with this, knocking down 5-HT7 receptors in a subset of GABAergic local interneurons was sufficient to block CPP, as was knocking down GABA receptors expressed by olfactory sensory neurons (OSNs). Additionally, direct modulation of OSNs via 5-HT2B expression in the cognate OSNs sensing CO2 is also essential for CPP. Furthermore, 5-HT1B expression by serotonergic neurons in the olfactory system is also required during the critical period. This study reveals that 5-HT modulation of multiple neuronal targets is necessary for experience-dependent structural changes in an odor processing circuit. | Perry, S., Clark, J. T., Ngo, P., Ray, A. (2024). Receptors underlying an odorant's valence across concentrations in Drosophila larvae. The Journal of experimental biology, 227(9) PubMed ID: 38511428
Summary: Odorants interact with receptors expressed in specialized olfactory neurons, and neurons of the same class send their axons to distinct glomeruli in the brain. The stereotypic spatial glomerular activity map generates recognition and the behavioral response for the odorant. The valence of an odorant changes with concentration, typically becoming aversive at higher concentrations. Interestingly, in Drosophila larvae, the odorant (E)-2-hexenal is aversive at low concentrations and attractive at higher concentrations. This study investigated the molecular and neural basis of this phenomenon, focusing on how activities of different olfactory neurons conveying opposing effects dictate behaviors. The repellant neuron in the larvae was identified as one expressing the olfactory receptor Or7a, whose activation alone at low concentrations of (E)-2-hexenal elicits an avoidance response in an Or7a-dependent manner. Avoidance can be overcome at higher concentrations by activation of additional neurons that are known to be attractive, most notably odorants that are known activators of Or42a and Or85c. These findings suggest that in the larval stage, the attraction-conveying neurons can overcome the aversion-conveying channels for (E)-2-hexenal. |
Thursday December 26th - Vesicles and synapsey |
Wilson, E. L., Yu, Y., Leal, N. S., Woodward, J. A., Patikas, N., Morris, J. L., Field, S. F., Plumbly, W., Paupe, V., Chowdhury, S. R., Antrobus, R., Lindop, G. E., Adia, Y. M., Loh, S. H. Y., Prudent, J., Martins, L. M., Metzakopian, E. (2024). Genome-wide CRISPR/Cas9 screen shows that loss of GET4 increases mitochondria-endoplasmic reticulum contact sites and is neuroprotective. Cell Death Dis, 15(3):203 PubMed ID: 38467609
Summary: Organelles form membrane contact sites between each other, allowing for the transfer of molecules and signals. Mitochondria-endoplasmic reticulum (ER) contact sites (MERCS) are cellular subdomains characterized by close apposition of mitochondria and ER membranes. They have been implicated in many diseases, including neurodegenerative, metabolic, and cardiac diseases. Although MERCS have been extensively studied, much remains to be explored. To uncover novel regulators of MERCS, a genome-wide, flow cytometry-based screen was conducted using an engineered MERCS reporter cell line. 410 genes were found whose downregulation promotes MERCS, and 230 genes were found whose downregulation decreases MERCS. From these, 29 genes were selected from each population for arrayed screening and 25 were validated from the high population and 13 from the low population. GET4 and BAG6 were highlighted as the top 2 genes that upon suppression increased MERCS from both the pooled and arrayed screens, and these were subjected to further investigation. Multiple microscopy analyses confirmed that loss of GET4 or BAG6 increased MERCS. GET4 and BAG6 were also observed to interact with the known MERCS proteins, inositol 1,4,5-trisphosphate receptors (IP3R) and glucose-regulated protein 75 (GRP75). In addition, loss of GET4 was found to increase mitochondrial calcium uptake upon ER-Ca(2+) release and mitochondrial respiration. Finally, loss of GET4 rescues motor ability was shown to improve lifespan and prevent neurodegeneration in a Drosophila model of Alzheimer's disease (Aβ42Arc). Together, these results suggest that GET4 is involved in decreasing MERCS and that its loss is neuroprotective. | Dong, W., Song, C. Y., Liu, M. Q., Gao, Y. H., Zhao, Z. W., Zhang, X. B., Moussian, B., Zhang, J. Z. (2024). Osiris17 is essential for stable integrin localization and function during insect wing epithelia remodeling.. International journal of biological macromolecules, 263(Pt 2):130245 PubMed ID: 38367779
Summary: The dynamic adhesion between cells and their extracellular matrix is essential for the development and function of organs. During insect wing development, two epithelial sheets contact each other at their basal sites through the interaction of βPS integrins with the extracellular matrix. This study reports that Osiris17 contributes to the maintenance of βPS integrins localization and function in developing wing of Drosophila and locust. In flies with reduced Osiris17 expression the epithelia sheets fail to maintain the integrity of basal cytoplasmic junctional bridges and basal adhesion. In contrast to the continuous basal integrin localization in control wings, this localization is disrupted during late stages of wing development in Osiris17 depleted flies. In addition, the subcellular localization revealed that Osiris17 co-localizes with the endosomal markers Rab5 and Rab11. This observation suggests an involvement of Osiris17 in endosomal recycling of integrins. Indeed, Osiris17 depletion reduced the numbers of Rab5 and Rab11 positive endosomes. Moreover, overexpression of Osiris17 increased co-localization of Rab5 and βPS integrins and partially rescued the detachment phenotype in flies with reduced βPS integrins. Taken together, these data suggest that Osiris17 is an endosome related protein that contributes to epithelial remodeling and morphogenesis by assisting basal integrins localization in insects. |
Iwanaga, R., Yahagi, N., Hakeda-Suzuki, S., Suzuki, T. (2024). Cell adhesion and actin dynamics factors promote axonal extension and synapse formation in transplanted Drosophila photoreceptor cells. Dev Growth Differ, 66(3):205-218 PubMed ID: 38403285
Summary: Vision is formed by the transmission of light stimuli to the brain through axons extending from photoreceptor cells. Damage to these axons leads to loss of vision. Despite research on neural circuit regeneration through transplantation, achieving precise axon projection remains challenging. To achieve optic nerve regeneration by transplantation, this study employed the Drosophila visual system. A transplantation method for Drosophila was previously established utilizing photoreceptor precursor cells extracted from the eye disc. However, little axonal elongation of transplanted cells into the brain, the lamina, was observed. Axonal elongation to the lamina was verified by modifying the selection process for transplanted cells. Moreover, focus was placed on N-cadherin (Ncad), a cell adhesion factor, and Twinstar (Tsr), which has been shown to promote actin reorganization and induce axon elongation in damaged nerves. Overexpression of Ncad and tsr promoted axon elongation to the lamina, along with presynaptic structure formation in the elongating axons. Furthermore, overexpression of Neurexin-1 (Nrx-1), encoding a protein identified as a synaptic organizer, was found to not only promote presynapse formation but also enhance axon elongation. By introducing Ncad, tsr, and Nrx-1, not only was axonal projection of transplanted cells to the brain beyond the retina achieved, but the projection of transplanted cells into a deeper ganglion, the medulla was also confirmed. The present study offers valuable insights to realize regeneration through transplantation in a more complex nervous system. | Shi, L., Yang, C., Zhang, M., Li, K., Wang, K., Jiao, L., Liu, R., Wang, Y., Li, M., Wang, Y., Ma, L., Hu, S., Bian, X. (2024). Dissecting the mechanism of atlastin-mediated homotypic membrane fusion at the single-molecule level. Nat Commun, 15(1):2488 PubMed ID: 38509071
Summary: Homotypic membrane fusion of the endoplasmic reticulum (ER) is mediated by dynamin-like GTPase Atlastin (ATL). This fundamental process relies on GTP-dependent domain rearrangements in the N-terminal region of ATL (ATL(cyto)), including the GTPase domain and three-helix bundle (3HB). However, its conformational dynamics during the GTPase cycle remain elusive. This study combine single-molecule FRET imaging and molecular dynamics simulations to address this conundrum. Different from the prevailing model, ATL(cyto) can form a loose crossover dimer upon GTP binding, which is tightened by GTP hydrolysis for membrane fusion. Furthermore, the α-helical motif between the 3HB and transmembrane domain, which is embedded in the surface of the lipid bilayer and self-associates in the crossover dimer, is required for ATL function. To recycle the proteins, Pi release, which disassembles the dimer, activates frequent relative movements between the GTPase domain and 3HB, and subsequent GDP dissociation alters the conformational preference of the ATL(cyto) monomer for entering the next reaction cycle. Finally, this study found that two disease-causing mutations affect human ATL1 activity by destabilizing GTP binding-induced loose crossover dimer formation and the membrane-embedded helix, respectively. These results provide insights into ATL-mediated homotypic membrane fusion and the pathological mechanisms of related disease. |
Cui, M. Y., Xu, M. B., Wang, Y. X., Bai, B. Y., Chen, R. S., Liu, L., Li, M. X. (2024). Long noncoding RNA LRG modulates Drosophila locomotion by sequestering Synaptotagmin 1 protein. Insect Sci, PubMed ID: 38480526
Summary: Apparently, the genomes of many organisms are pervasively transcribed, and long noncoding RNAs (lncRNAs) make up the majority of cellular transcripts. LncRNAs have been reported to play important roles in many biological processes; however, their effects on locomotion are poorly understood. This study presents a novel lncRNA, Locomotion Regulatory Gene (LRG), which participates in locomotion by sequestering Synaptotagmin 1 (SYT1). LRG deficiency resulted in higher locomotion speed which could be rescued by pan-neuronal overexpression but not by limited ellipsoid body, motoneuron or muscle-expression of LRG. At the molecular level, the synaptic vesicles (SVs) release and movement-related SYT1 protein was recognized as LRG-interacting protein candidate. Furthermore, LRG had no effects on SYT1 expression. Genetically, the behavioral defects in LRG mutant could be rescued by pan-neuronal knock-down of Syt1. Taken together, all the results suggested LRG exerts regulatory effects on locomotion via sequestering SYT1 thereby blocking its function without affecting its expression. This work displays a new function of lncRNA and provides insights for revealing the pathogenesis of neurological diseases with motor disorders. | Wahiduzzaman, Tindell, S. J., Alexander, E., Hackney, E., Kharel, K., Schmidtke, R., Arkov, A. L. (2024). Drosophila germ granules are assembled from protein components through different modes of competing interactions with the multi-domain Tudor protein. FEBS letters, 598(7):774-786 PubMed ID: 38499396
Summary: Membraneless organelles are RNA-protein assemblies which have been implicated in post-transcriptional control. Germ cells form membraneless organelles referred to as germ granules, which contain conserved proteins including Tudor domain-containing scaffold polypeptides and their partner proteins that interact with Tudor domains. This study shows that in Drosophila, different germ granule proteins associate with the multi-domain Tudor protein using different numbers of Tudor domains. Furthermore, these proteins compete for interaction with Tudor in vitro and, surprisingly, partition to distinct and poorly overlapping clusters in germ granules in vivo. This partition results in minimization of the competition. The data suggest that Tudor forms structurally different configurations with different partner proteins which dictate different biophysical properties and phase separation parameters within the same granule. |
Monday December 23rd - Gonads |
Ferveur, J. F., Cortot, J., Moussian, B., Cobb, M., Everaerts, C. (2024). Replenishment of Drosophila Male Pheromone After Mating. Journal of chemical ecology, 50(3-4):100-109 PubMed ID: 38270733
Summary: Insect exocrine gland products can be involved in sexual communication, defense, territory labelling, aggregation and alarm. In the vinegar fly Drosophila melanogaster the ejaculatory bulb synthesizes and releases 11-cis-Vaccenyl acetate (cVa). This pheromone, transferred to the female during copulation, affects aggregation, courtship and male-male aggressive behaviors. To determine the ability of male flies to replenish their cVa levels, males of a control laboratory strain and from the desat1 pheromone-defective mutant strain were allowed to mate successively with several females. Mating frequency, duration and latency, the amount of cVa transferred to mated females and the residual cVa in tested males. Mating duration remained constant with multiple matings were mesured, but it was found that the amount of cVa transferred to females declined with multiple matings, indicating that, over short, biologically-relevant periods, replenishment of the pheromone does not keep up with mating frequency, resulting in the transfer of varying quantities of cVa. Adult responses to cVa are affected by early developmental exposure to this pheromone; this revelation of quantitative variation in the amount of cVa transferred to females in the event of multiple matings by a male suggests variable responses to cVa shown by adults produced by such matings. This implies that the natural role of this compound may be richer than suggested by laboratory experiments that study only one mating event and its immediate behavioral or neurobiological consequences. | Hermant, C., Matias, N. R., Michel-Hissier, P., Huynh, J. R., Mathieu, J. (2024). Lethal Giant Disc is a target of Cdk1 and regulates ESCRT-III localization during germline stem cell abscission. evelopment, 151(8) PubMed ID: 38546617
Summary: Abscission is the final step of cytokinesis that allows the physical separation of sister cells through the scission of the cellular membrane. This deformation is driven by ESCRT-III proteins, which can bind membranes and form dynamic helices. A crucial step in abscission is the recruitment of ESCRT-III proteins at the right time and place. Alix is one of the best characterized proteins that recruits ESCRT-III proteins from yeast to mammals. However, recent studies in vivo have revealed that pathways acting independently or redundantly with Alix are also required at abscission sites in different cellular contexts. This study shows that Lgd acts redundantly with Alix to properly localize ESCRT-III to the abscission site in germline stem cells (GSCs) during Drosophila oogenesis. It was further demonstrated that Lgd is phosphorylated at multiple sites by the CycB/Cdk1 kinase. These phosphorylation events potentiate the activity of Shrub, a Drosophila ESCRT-III, during abscission of GSCs. This study reveals that redundancy between Lgd and Alix, and coordination with the cell cycle kinase Cdk1, confers robust and timely abscission of Drosophila germline stem cells. |
Tu, R., Ping, Z., Liu, J., Tsoi, M. L., Song, X., Liu, W., Xie, T. (2024). Niche Tet maintains germline stem cells independently of dioxygenase activity. The EMBO journal, 43(8):1570-1590 PubMed ID: 38499787
Summary: Ten-eleven translocation (TET) proteins are dioxygenases that convert 5-methylcytosine (5mC) into 5-hydroxylmethylcytosine (5hmC) in DNA and RNA. However, their involvement in adult stem cell regulation remains unclear. This study identified a novel enzymatic activity-independent function of Tet in the Drosophila germline stem cell (GSC) niche. Tet activates the expression of Dpp, the fly homologue of BMP, in the ovary stem cell niche, thereby controlling GSC self-renewal. Depletion of Tet disrupts Dpp production, leading to premature GSC loss. Strikingly, both wild-type and enzyme-dead mutant Tet proteins rescue defective BMP signaling and GSC loss when expressed in the niche. Mechanistically, Tet interacts directly with Bap55 and Stat92E, facilitating recruitment of the Polybromo Brahma associated protein (PBAP) complex to the dpp enhancer and activating Dpp expression. Furthermore, human TET3 can effectively substitute for Drosophila Tet in the niche to support BMP signaling and GSC self-renewal. These findings highlight a conserved novel catalytic activity-independent role of Tet as a scaffold protein in supporting niche signaling for adult stem cell self-renewal. | Kurogi, Y., Mizuno, Y., Okamoto, N., Barton, L., Niwa, R. (2024). The seminal vesicle is a juvenile hormone-responsive tissue in adult male Drosophila melanogaster. ioRxiv, PubMed ID: 38562788
Summary: Juvenile hormone (JH) is one of the most essential hormones controlling insect metamorphosis and physiology. While it is well known that JH affects many tissues throughout the insects life cycle, the difference in JH responsiveness and the repertoire of JH-inducible genes among different tissues has not been fully investigated. In this study, JH responsiveness in vivo was monitored using transgenic Drosophila melanogaster flies carrying a JH response element-GFP (JHRE-GFP) construct. Our data highlight the high responsiveness of the epithelial cells within the seminal vesicle, a component of the male reproductive tract, to JH. Specifically, an elevation was observed in the JHRE-GFP signal within the seminal vesicle epithelium upon JH analog administration, while suppression occurs upon knockdown of genes encoding the intracellular JH receptors, Methoprene-tolerant and germ cell-expressed. Starting from published transcriptomic and proteomics datasets, Lactate dehydrogenase was indentifed as a JH-response gene expressed in the seminal vesicle epithelium, suggesting insect seminal vesicles undergo metabolic regulation by JH. Together, this study sheds new light on biology of the insect reproductive regulatory system. |
Kaur, R., McGarry, A., Shropshire, J. D., Leigh, B. A., Bordenstein, S. R. (2024). Prophage proteins alter long noncoding RNA and DNA of developing sperm to induce a paternal-effect lethality. Science, 383(6687):1111-1117 PubMed ID: 38452081
Summary: The extent to which prophage proteins interact with eukaryotic macromolecules is largely unknown. This work shows that cytoplasmic incompatibility factor A (CifA) and B (CifB) proteins, encoded by prophage WO of the endosymbiont Wolbachia, alter long noncoding RNA (lncRNA) and DNA during Drosophila sperm development to establish a paternal-effect embryonic lethality known as cytoplasmic incompatibility (CI). CifA is a ribonuclease (RNase) that depletes a spermatocyte lncRNA important for the histone-to-protamine transition of spermiogenesis. Both CifA and CifB are deoxyribonucleases (DNases) that elevate DNA damage in late spermiogenesis. lncRNA knockdown enhances CI, and mutagenesis links lncRNA depletion and subsequent sperm chromatin integrity changes to embryonic DNA damage and CI. Hence, prophage proteins interact with eukaryotic macromolecules during gametogenesis to create a symbiosis that is fundamental to insect evolution and vector control. | Clemot, M., D'Alterio, C., Kwang, A. C., Jones, D. L. (2024). mTORC1 is required for differentiation of germline stem cells in the Drosophila melanogaster testis. PLoS One, 19(3):e0300337 PubMed ID: 38512882
Summary: Metabolism participates in the control of stem cell function and subsequent maintenance of tissue homeostasis. How this is achieved in the context of adult stem cell niches in coordination with other local and intrinsic signaling cues is not completely understood. The Target of Rapamycin (TOR) pathway is a master regulator of metabolism and plays essential roles in stem cell maintenance and differentiation. In the Drosophila male germline, mTORC1 is active in germline stem cells (GSCs) and early germ cells. Targeted RNAi-mediated downregulation of mTor in early germ cells causes a block and/or a delay in differentiation, resulting in an accumulation of germ cells with GSC-like features. These early germ cells also contain unusually large and dysfunctional autolysosomes. In addition, downregulation of mTor in adult male GSCs and early germ cells causes non-autonomous activation of mTORC1 in neighboring cyst cells, which correlates with a disruption in the coordination of germline and somatic differentiation. This study identifies a previously uncharacterized role of the TOR pathway in regulating male germline differentiation. |
Friday December 20th - Disease Models |
Brockett, J. S., Manalo, T., Zein-Sabatto, H., Lee, J., Fang, J., Chu, P., Feng, H., Patil, D., Davidson, P., Ogan, K., Master, V. A., Pattaras, J. G., Roberts, D. L., Bergquist, S. H., Reyna, M. A., Petros, J. A., Lerit, D. A., Arnold, R. S. (2024). A missense SNP in the tumor suppressor SETD2 reduces H3K36me3 and mitotic spindle integrity in Drosophila. Genetics, 226(4) PubMed ID: 38290049
Summary: Mutations in SETD2 are among the most prevalent drivers of renal cell carcinoma (RCC). This study identified a novel single nucleotide polymorphism (SNP) in SETD2, E902Q, within a subset of RCC patients, which manifests as both an inherited or tumor-associated somatic mutation. To determine if the SNP is biologically functional, CRISPR-based genome editing was used to generate the orthologous mutation within the Drosophila melanogaster Set2 gene. In Drosophila, the homologous amino acid substitution, E741Q, reduces H3K36me3 levels comparable to Set2 knockdown, and this loss is rescued by reintroduction of a wild-type Set2 transgene. Significant defects in spindle morphogenesis were similarly uncovered, consistent with the established role of SETD2 in methylating α-Tubulin during mitosis to regulate microtubule dynamics and maintain genome stability. These data indicate the Set2 E741Q SNP affects both histone methylation and spindle integrity. Moreover, this work further suggests the SETD2 E902Q SNP may hold clinical relevance. | Dark, C., Ali, N., Golenkina, S., Dhyani, V., Blazev, R., Parker, B. L., Murphy, K. T., Lynch, G. S., Senapati, T., Millard, S. S., Judge, S. M., Judge, A. R., Giri, L., Russell, S. M., Cheng, L. Y. (2024). Mitochondrial fusion and altered beta-oxidation drive muscle wasting in a Drosophila cachexia model. EMBO reports, 25(4):1835-1858 PubMed ID: 38429578
Summary: Cancer cachexia is a tumour-induced wasting syndrome, characterised by extreme loss of skeletal muscle. Defective mitochondria can contribute to muscle wasting; however, the underlying mechanisms remain unclear. Using a Drosophila larval model of cancer cachexia, enlarged and dysfunctional muscle mitochondria were observed. Morphological changes were accompanied by upregulation of beta-oxidation proteins and depletion of muscle glycogen and lipid stores. Muscle lipid stores were also decreased in Colon-26 adenocarcinoma mouse muscle samples, and expression of the beta-oxidation gene CPT1A was negatively associated with muscle quality in cachectic patients. Mechanistically, mitochondrial defects result from reduced muscle insulin signalling, downstream of tumour-secreted insulin growth factor binding protein (IGFBP) homologue ImpL2. Strikingly, muscle-specific inhibition of Forkhead box O (FOXO), mitochondrial fusion, or beta-oxidation in tumour-bearing animals preserved muscle integrity. Finally, dietary supplementation with nicotinamide or lipids, improved muscle health in tumour-bearing animals. Overall, this work demonstrates that muscle FOXO, mitochondria dynamics/beta-oxidation and lipid utilisation are key regulators of muscle wasting in cancer cachexia. |
Sultanakhmetov, G., Kato, I., Asada, A., Saito, T., Ando, K. (2024). Microtubule-affinity regulating kinase family members distinctively affect tau phosphorylation and promote its toxicity in a Drosophila model. Genes to cells : devoted to molecular & cellular mechanisms, 29(4):337-346 PubMed ID: 38329182
Summary: Accumulation of abnormally phosphorylated tau and its aggregation constitute a significant hallmark of Alzheimer's disease (AD). Tau phosphorylation at Ser262 and Ser356 in the KXGS motifs of microtubule-binding repeats plays a critical role in its physiological function and AD disease progression. Major tau kinases to phosphorylate tau at Ser262 and Ser356 belong to the Microtubule Affinity Regulating Kinase family (MARK1-4), which are considered one of the major contributors to tau abnormalities in AD. However, whether and how each member affects tau toxicity in vivo is unclear. Transgenic Drosophila was used as a model to compare the effect on tau-induced neurodegeneration among MARKs in vivo. MARK4 specifically promotes tau accumulation and Ser396 phosphorylation, which yields more tau toxicity than was caused by other MARKs. Interestingly, MARK1, 2, and 4 increased tau phosphorylation at Ser262 and Ser356, but only MARK4 caused tau accumulation, indicating that these sites alone did not cause pathological tau accumulation. These results revealed MARKs are different in their effect on tau toxicity, and also in tau phosphorylation at pathological sites other than Ser262 and Ser356. Understanding the implementation of each MARK into neurodegenerative disease helps to develop more target and safety therapies to overcome AD and related tauopathies. | Brown, J. C., McMichael, B. D., Vandadi, V., Mukherjee, A., Salzler, H. R., Matera, A. G. (2024). Lysine-36 of Drosophila histone H3.3 supports adult longevity. G3 (Bethesda), 14(4) PubMed ID: 38366796
Summary: Aging is a multifactorial process that disturbs homeostasis, increases disease susceptibility, and ultimately results in death. Although the definitive set of molecular mechanisms responsible for aging remain to be discovered, epigenetic change over time is proving to be a promising piece of the puzzle. Several post-translational histone modifications have been linked to the maintenance of longevity. This study focused on lysine-36 of the replication-independent histone protein, H3.3 (H3.3K36). To interrogate the role of this residue in Drosophila developmental gene regulation, a lysine-to-arginine mutant was generated that blocks the activity of its cognate-modifying enzymes. An H3.3BK36R mutation was shown to cause a significant reduction in adult lifespan, accompanied by dysregulation of the genomic and transcriptomic architecture. Transgenic co-expression of wild-type H3.3B completely rescues the longevity defect. Because H3.3 is known to accumulate in nondividing tissues, transcriptome profiling was carried out of young vs aged adult fly heads. The data show that loss of H3.3K36 results in age-dependent misexpression of NF-kappaB and other innate immune target genes, as well as defects in silencing of heterochromatin. It is proposed that H3.3K36 maintains the postmitotic epigenomic landscape, supporting longevity by regulating both pericentric and telomeric retrotransposons and by suppressing aberrant immune signaling. |
Zhang, P., Catterson, J. H., Gronke, S., Partridge, L. (2024). Inhibition of S6K lowers age-related inflammation and increases lifespan through the endolysosomal system. Journal and Nature aging, 4(4):491-509 PubMed ID: 38413780
Summary: Suppression of target of rapamycin complex 1 (TORC1) by rapamycin ameliorates aging in diverse species. S6 kinase (S6K) is an essential mediator, but the mechanisms involved are unclear. This study shows that activation of S6K specifically in Drosophila fat-body blocked extension of lifespan by rapamycin, induced accumulation of multilamellar lysosomes and blocked age-associated hyperactivation of the NF-kappaB-like immune deficiency (IMD) pathway, indicative of reduced inflammaging. Syntaxin 13 mediated the effects of TORC1-S6K signaling on lysosome morphology and inflammaging, suggesting they may be linked. Inflammaging depended on the IMD receptor regulatory isoform PGRP-LC, and repression of the IMD pathway from midlife extended lifespan. Age-related inflammaging was higher in females than in males and was not lowered in males by rapamycin treatment or lowered S6K. Rapamycin treatment also elevated Syntaxin 12/13 levels in mouse liver and prevented age-related increase in noncanonical NF-kappaB signaling, suggesting that the effect of TORC1 on inflammaging is conserved from flies to mammals. | Baassiri, A., Ghais, A., Kurdi, A., Rahal, E., Nasr, R., Shirinian, M. (2024). The molecular signature of BCR::ABL(P210) and BCR::ABL(T315I) in a Drosophila melanogaster chronic myeloid leukemia model. iScience, 27(4):109538 PubMed ID: 38585663
Summary: Chronic myeloid leukemia (CML) is a clonal hematopoietic stem cell disorder resulting from a balanced translocation leading to BCR::ABL1 oncogene with increased tyrosine kinase activity. Despite the advancements in the development of tyrosine kinase inhibitors (TKIs), the T315I gatekeeper point mutation in the BCR::ABL1 gene remains a challenge. A previous study reported in a Drosophila CML model an increased hemocyte count and disruption in sessile hemocyte patterns upon expression of BCR::ABL1(p210) and BCR::ABL1(T315I) in the hemolymph. In this study, RNA sequencing was performed to determine if there is a distinct gene expression that distinguishes BCR::ABL1(p210) and BCR::ABL1(T315I). Six genes are reported that were consistently upregulated in the fly CML model and validated in adult and pediatric CML patients and in a mouse cell line expressing BCR::ABL1(T315I). This study provides a comprehensive analysis of gene signatures in BCR::ABL1(p210) and BCR::ABL1(T315I), laying the groundwork for targeted investigations into the role of these genes in CML pathogenesis. |
Thursday December 19th - Genes, enzymes and protein expression, evolution, structure, and function |
Dzaki, N., Alenius, M. (2024). A cilia-bound unconventional secretory pathway for Drosophila odorant receptors. BMC Biol, 22(1):84 PubMed ID: 38610043
Summary: Post-translational transport is a vital process which ensures that each protein reaches its site of function. Though most do so via an ordered ER-to-Golgi route, an increasing number of proteins are now shown to bypass this conventional secretory pathway. In the Drosophila olfactory sensory neurons (OSNs), odorant receptors (ORs) are trafficked from the ER towards the cilia. This study shows that Or22a, a receptor of various esters and alcoholic compounds, reaches the cilia partially through unconventional means. Or22a frequently present as puncta at the somatic cell body exit and within the dendrite prior to the cilia base. These rarely coincide with markers of either the intermediary ER-Golgi-intermediate-compartment (ERGIC) or Golgi structures. ERGIC and Golgi also displayed axonal localization biases, a further indication that at least some measure of OR transport may occur independently of their involvement. Additionally, neither the loss of several COPII genes involved in anterograde trafficking nor ERGIC itself affected puncta formation or Or22a transport to the cilium. Instead, the consistent colocalization was observed of Or22a puncta with Grasp65, the sole Drosophila homolog of mammalian GRASP55/Grh1, a marker of the unconventional pathway. The numbers of both Or22a and Grasp65-positive puncta were furthermore increased upon nutritional starvation, a condition known to enhance Golgi-bypassing secretory activity. These results demonstrate an alternative route of Or22a transport, thus expanding the repertoire of unconventional secretion mechanisms in neurons. | Lawler, C. D., Nunez, A. K. P., Hernandes, N., Bhide, S., Lohrey, I., Baxter, S., Robin, C. (2024).. The haplolethal gene wupA of Drosophila exhibits potential as a target for an X-poisoning gene drive. G3 (Bethesda), 14(4) PubMed ID: 38306583
Summary: A synthetic gene drive that targets haplolethal genes on the X chromosome can skew the sex ratio toward males. Like an "X-shredder," it does not involve "homing", and that has advantages including the reduction of gene drive resistance allele formation. This studey examine this "X-poisoning" strategy by targeting 4 of the 11 known X-linked haplolethal/haplosterile genes of Drosophila melanogaster with CRISPR/Cas9. Targeting the wupA gene during spermatogenesis was shown to skew the sex ratio so fewer than 14% of progeny are daughters. That is unless the mutagenic males were crossed to to X^XY female flies that bear attached-X chromosomes, which reverses the inheritance of the poisoned X chromosome so that sons inherit it from their father, in which case only 2% of the progeny are sons. These sex ratio biases suggest that most of the CRISPR/Cas9 mutants induced in the wupA gene are haplolethal but some are recessive lethal. The males generating wupA mutants do not suffer from reduced fertility; rather, the haplolethal mutants arrest development in the late stages of embryogenesis well after fertilized eggs have been laid. This provides a distinct advantage over genetic manipulation strategies involving sterility which can be countered by the remating of females. The wupA mutants that destroy the nuclear localization signal of shorter isoforms are not haplolethal as long as the open reading frame remains intact. Like D. melanogaster, wupA orthologs of Drosophila suzukii and Anopheles mosquitos are found on X chromosomes making wupA a viable X-poisoning target in multiple species. |
Gatti, J. L., Lemauf, S., Belghazi, M., Arthaud, L., Poirie, M. (2024). In Drosophila Hemolymph, Serine Proteases Are the Major Gelatinases and Caseinases. Insects, 15(4) PubMed ID: 38667364
Summary: After separation on gel zymography, Drosophila melanogaster hemolymph displays gelatinase and caseinase bands of varying sizes, ranging from over 140 to 25 kDa. Qualitative and quantitative variations in these bands were observed during larval development and between different D. melanogaster strains and Drosophila species. The activities of these Drosophila hemolymph gelatinase and caseinase were strongly inhibited by serine protease inhibitors, but not by EDTA. Mass spectrometry identified over 60 serine proteases (SPs) in gel bands corresponding to the major D. melanogaster gelatinases and caseinases, but no matrix metalloproteinases (MMPs) were found. The most abundant proteases were tequila and members of the Jonah and trypsin families. However, the gelatinase bands did not show any change in the tequila null mutant. Additionally, no clear changes could be observed in D. melanogaster gel bands 24 h after injection of bacterial lipopolysaccharides (LPS) or after oviposition by Leptopilina boulardi endoparasitoid wasps. It can be concluded that the primary gelatinases and caseinases in Drosophila larval hemolymph are serine proteases (SPs) rather than matrix metalloproteinases (MMPs). Furthermore, the gelatinase pattern remains relatively stable even after short-term exposure to pathogenic challenges. | Stephan, T., Stoldt, S., Barbot, M., Carney, T. D., Lange, F., Bates, M., Bou Dib, P., Inamdar, K., Shcherbata, H. R., Meinecke, M., Riedel, D., Dennerlein, S., Rehling, P., Jakobs, S. (2024). Drosophila MIC10b can polymerize into cristae-shaping filaments. Life science alliance, 7(4) PubMed ID: 38253420
Summary: Cristae are invaginations of the mitochondrial inner membrane that are crucial for cellular energy metabolism. The formation of cristae requires the presence of a protein complex known as MICOS, which is conserved across eukaryotic species. One of the subunits of this complex, MIC10, is a transmembrane protein that supports cristae formation by oligomerization. In Drosophila melanogaster, three MIC10-like proteins with different tissue-specific expression patterns exist. This study demonstrated that CG41128/MINOS1b/DmMIC10b is the major MIC10 orthologue in flies. Its loss destabilizes MICOS, disturbs cristae architecture, and reduces the life span and fertility of flies. DmMIC10b has a unique ability to polymerize into bundles of filaments, which can remodel mitochondrial crista membranes. The formation of these filaments relies on conserved glycine and cysteine residues, and can be suppressed by the co-expression of other Drosophila MICOS proteins. These findings provide new insights into the regulation of MICOS in flies, and suggest potential mechanisms for the maintenance of mitochondrial ultrastructure. |
Tsukamoto, Y., Tsukamoto, N., Saiki, W., Tashima, Y., Furukawa, J. I., Kizuka, Y., Narimatsu, Y., Clausen, H., Takeuchi, H., Okajima, T. (2024). Characterization of galactosyltransferase and sialyltransferase genes mediating the elongation of the extracellular O-GlcNAc glycans. Biochem Biophys Res Commun, 703:149610 PubMed ID: 38359610
Summary: O-GlcNAc is a unique post-translational modification found in cytoplasmic, nuclear, and mitochondrial proteins. In a limited number of extracellular proteins, O-GlcNAc modifications occur through the action of EGF-domain O-GlcNAc transferase (Eogt), which specifically modifies subsets of epidermal growth factor-like (EGF) domain-containing proteins such as Notch receptors. The abnormalities due to EOGT mutations in mice and humans and the increased EOGT expression in several cancers signify the importance of EOGT pathophysiology and extracellular O-GlcNAc. Unlike intracellular O-GlcNAc monosaccharides, extracellular O-GlcNAc extends to form elongated glycan structures. However, the enzymes involved in the O-GlcNAc glycan extension have not yet been reported. This study comprehensively screened potential galactosyltransferase and sialyltransferase genes related to the canonical O-GlcNAc glycan pathway and revealed the essential roles of B4GALT1 and ST3GAL4 in O-GlcNAc glycan elongation in human HEK293 cells. These findings were confirmed by sequential glycosylation of Drosophila EGF20 in vitro by EOGT, β4GalT-1, and ST3Gal-IV. Thus, the findings from this study throw light on the specific glycosyltransferases that mediate O-GlcNAc glycan elongation in human HEK293 cells. | Tikhonova, E. A., Georgiev, P. G., Maksimenko, O. G. (2024). Functional Role of C-terminal Domains in the MSL2 Protein of Drosophila melanogaster. Biochemistry (Mosc), 89(4):663-673 PubMed ID: 38831503
Summary: Dosage compensation complex (DCC), which consists of five proteins and two non-coding RNAs roX, specifically binds to the X chromosome in males, providing a higher level of gene expression necessary to compensate for the monosomy of the sex chromosome in male Drosophila compared to the two X chromosomes in females. The MSL2 protein contains the N-terminal RING domain, which acts as an E3 ligase in ubiquitination of proteins and is the only subunit of the complex expressed only in males. Functional role of the two C-terminal domains of the MSL2 protein, enriched with proline (P-domain) and basic amino acids (B-domain), was investigated. As a result, it was shown that the B-domain destabilizes the MSL2 protein, which is associated with the presence of two lysines ubiquitination of which is under control of the RING domain of MSL2. The unstructured proline-rich domain stimulates transcription of the roX2 gene, which is necessary for effective formation of the dosage compensation complex. |
Tuesday December 17th - Evolution |
Bladen, J., Cooper, J. C., Ridges, J. T., Guo, P., Phadnis, N. (2024). A new hybrid incompatibility locus between Drosophila melanogaster and Drosophila sechellia. Genetics, 226(3) PubMed ID: 38184848
Summary: Despite the fundamental importance of hybrid incompatibilities to the process of speciation, there are few cases where the evolution and genetic architecture of hybrid incompatibilities are understood. One of the longest studied hybrid incompatibilities causes F1 hybrid male inviability in crosses between Drosophila melanogaster females and males from the Drosophila simulans clade of species-Drosophila simulans, Drosophila mauritiana, and Drosophila sechellia. This study discovered dramatic differences in the manifestation of this lethal hybrid incompatibility among the D. simulans clade of species. In particular, F1 hybrid males between D. melanogaster and D. sechellia are resistant to hybrid rescue through RNAi knockdown of an essential hybrid incompatibility gene. To understand the genetic basis of this inter-species difference in hybrid rescue, a triple-hybrid mapping method was developed. The results show that 2 discrete large effect loci and many dispersed small effect changes across the genome underlie D. sechellia aversion to hybrid rescue. The large effect loci encompass a known incompatibility gene Lethal hybrid rescue (Lhr) and previously unknown factor, Sechellia aversion to hybrid rescue (Satyr). These results show that the genetic architecture of F1 hybrid male inviability is overlapping but not identical in the 3 inter-species crosses. These results raise questions about whether new hybrid incompatibility genes can integrate into an existing hybrid incompatibility thus increasing in complexity over time, or if the continued evolution of genes can gradually strengthen an existing hybrid incompatibility. | Bastide, H., Legout, H., Dogbo, N., Ogereau, D., Prediger, C., Carcaud, J., Filee, J., Garnery, L., Gilbert, C., Marion-Poll, F., Requier, F., Sandoz, J. C., Yassin, A. (2024). The genome of the blind bee louse fly reveals deep convergences with its social host and illuminates Drosophila origins. Curr Biol, 34(5):1122-1132. PubMed ID: 38309271
Summary: Social insects' nests harbor intruders known as inquilines, which are usually related to their hosts. However, distant non-social inquilines may also show convergences with their hosts, although the underlying genomic changes remain unclear. This study analyzed the genome of the wingless and blind bee louse fly Braula coeca, an inquiline kleptoparasite of the western honey bee, Apis mellifera. Using large phylogenomic data, recent accounts were confirmed that the bee louse fly is a drosophilid and showed that it had likely evolved from a sap-breeder ancestor associated with honeydew and scale insects' wax. Unlike many parasites, the bee louse fly genome did not show significant erosion or strict reliance on an endosymbiont, likely due to a relatively recent age of inquilinism. However, a horizontal transfer was observed of a transposon and a striking parallel evolution in a set of gene families between the honey bee and the bee louse fly. Convergences included genes potentially involved in metabolism and immunity and the loss of nearly all bitter-tasting gustatory receptors, in agreement with life in a protective nest and a diet of honey, pollen, and beeswax. Vision and odorant receptor genes also exhibited rapid losses. Only genes whose orthologs in the closely related Drosophila melanogaster respond to honey bee pheromone components or floral aroma were retained, whereas the losses included orthologous receptors responsive to the anti-ovarian honey bee queen pheromones. Hence, deep genomic convergences can underlie major phenotypic transitions during the evolution of inquilinism between non-social parasites and their social hosts. |
Ridgway, A. M., Hood, E. J., Jimenez, J. F., Nunes, M. D. S., McGregor, A. P. (2024). Sox21b underlies the rapid diversification of a novel male genital structure between Drosophila species. Curr Biol, 34(5):1114-1121.e1117 PubMed ID: 38309269
Summary: The emergence and diversification of morphological novelties is a major feature of animal evolution. However, relatively little is known about the genetic basis of the evolution of novel structures and the mechanisms underlying their diversification. The epandrial posterior lobes of male genitalia. are a novelty of particular Drosophila species. The lobes grasp the female ovipositor and insert between her abdominal tergites and, therefore, are important for copulation and species recognition. The posterior lobes likely evolved from co-option of a Hox-regulated gene network from the posterior spiracles and have since diversified in morphology in the D. simulans clade, in particular, over the last 240,000 years, driven by sexual selection. The genetic basis of this diversification is polygenic but none of the causative genes have been identified. Identifying the genes underlying the diversification of these secondary sexual structures is essential to understanding the evolutionary impact on copulation and species recognition. This study shows that Sox21b negatively regulates posterior lobe size. This is consistent with expanded Sox21b expression in D. mauritiana, which develops smaller posterior lobes than D. simulans. This was tested by generating reciprocal hemizygotes and changes in Sox21b were confirmed to underlie posterior lobe evolution between these species. Furthermore, it was found that posterior lobe size differences caused by the species-specific allele of Sox21b significantly affect copulation duration. Taken together, this study reveals the genetic basis for the sexual-selection-driven diversification of a novel morphological structure and its functional impact on copulatory behavior. | Chen, J., Liu, C., Li, W., Zhang, W., Wang, Y., Clark, A. G., Lu, J. (2024). From sub-Saharan Africa to China: Evolutionary history and adaptation of Drosophila melanogaster revealed by population genomics. Sci Adv, 10(16):eadh3425 PubMed ID: 38630810
Summary: Drosophila melanogaster is a widely used model organism for studying environmental adaptation. However, the genetic diversity of populations in Asia is poorly understood, leaving a notable gap in knowledge of the global evolution and adaptation of this species. Genomes of 292 D. melanogaster strains were sequenced from various ecological settings in China and they were analyzed along with previously published genome sequences. Six global genetic ancestry groups were identified, despite the presence of widespread genetic admixture. The strains from China represent a unique ancestry group, although detectable differentiation exists among populations within China. The global migration and demography of D. melanogaster was deciphered, and i widespread signals of adaptation were identified, including genetic changes in response to insecticides. The effects of insecticide resistance variants using population cage trials and deep sequencing. This work highlights the importance of population genomics in understanding the genetic underpinnings of adaptation, an effort that is particularly relevant given the deterioration of ecosystems. |
Pianezza, R., Scarpa, A., Narayanan, P., Signor, S., Kofler, R. (2024). Spoink, a LTR retrotransposon, invaded D. melanogaster populations in the 1990s. PLoS Genet, 20(3):e1011201 PubMed ID: 38530818
Summary: During the last few centuries D. melanogaster populations were invaded by several transposable elements, the most recent of which was thought to be the P-element between 1950 and 1980. Here we describe a novel TE, which was named Spoink, that has invaded D. melanogaster. It is a 5216nt LTR retrotransposon of the Ty3/gypsy superfamily. Relying on strains sampled at different times during the last century this study showed that Spoink invaded worldwide D. melanogaster populations after the P-element between 1983 and 1993. This invasion was likely triggered by a horizontal transfer from the D. willistoni group, much as the P-element. Spoink is probably silenced by the piRNA pathway in natural populations and about 1/3 of the examined strains have an insertion into a canonical piRNA cluster such as 42AB. Given the degree of genetic investigation of D. melanogaster it is perhaps surprising that Spoink was able to invade unnoticed. | Li, T., Zhang, R. S., True, J. R. (2024). Genetic variation for sexual dimorphism in developmental traits in Drosophila melanogaster. G3 (Bethesda), 14(4) PubMed ID: 38427952
Summary: Sexual dimorphism in traits of insects during the developmental stages could potentially be the direct or indirect result of sex-specific selection provided that genetic variation for sexual dimorphism is present. This study investigated genetic variation in sexual dimorphism in a set of Drosophila melanogaster inbred lines for 2 traits: egg to adult development time and pupation site preference. Considerable genetic variation was found in sexual dimorphism among lines in both traits. The sexual dimorphic patterns remained relatively consistent across multiple trials, despite both traits being sensitive to environmental conditions. Additionally, 2 sexually dimorphic adult morphological traits were measured in 6 sampled lines, and correlations were investigated in the sexual dimorphism patterns with the 2 developmental traits. The abundance of genetic variation in sexual dimorphism for D. melanogaster developmental traits demonstrated in this study provides evidence for a high degree of evolvability of sex differences in preadult traits in natural populations. |
Monday December 16th - Signalling |
Schweibenz, C. K., Placentra, V. C., Moberg, K. H. (2024). The Drosophila EcR-Hippo component Taiman promotes
epithelial cell fitness by control of the Dally-like glypican and Wg gradient. bioRxiv, PubMed ID: 38617327
Summary: Rapidly dividing cells can eliminate slow growing neighbors through the apoptotic process of cell competition. This process ensures that only high fitness cells populate embryonic tissues and is proposed to underlie the ability of oncogene-transformed cells to progressively replace normal cells within a tissue. Patches of cells in the Drosophila wing disc overexpressing the oncogenic Taiman (Tai) transcriptional coactivator kill normal neighbors by secreting Spatzle ligands that trigger pro-apoptotic Toll signaling in receiving cells. However, extracellular signaling mechanisms responsible for elimination of slow growing cells by normal neighbors remain poorly defined. This study shows that slow growing cells with reduced Tai (Tai(low)) are killed by normal neighbors through a mechanism involving competition for the Wingless (Wg/Wnt) ligand. Elevated Wg signaling significantly rescues elimination of Tai(low) cells in multiple organs, suggesting that Tai may normally promote Wg activity. Examining distribution of Wg components reveals that Tai promotes extracellular spread of the Wg ligand from source cells across the wing disc, thus ensuring patterned expression of multiple Wg-regulated target genes. Tai controls Wg spread indirectly through the extracellular glypican Dally-like protein (Dlp), which binds Wg and promotes its extracellular diffusion and capture by receptors. Data indicate that Tai likely controls Dlp at two levels: transcription of dlp mRNA and Dlp intracellular trafficking. Overall, these data indicate that the Tai acts through Dlp to enable Wg transport and signaling, and that cell competition in the Tai(low) model arises due to inequity in the ability of epithelial cells to sequester limiting amounts of the Wg growth factor. | Cavieres-Lepe, J., Amini, E., Zabel, M., Nassel, D. R., Stanewsky, R., Wegener, C., Ewer, J. (2024). Timed receptor tyrosine kinase signaling couples the central and a peripheral circadian clock in Drosophila. Proc Natl Acad Sci U S A, 121(11):e2308067121 PubMed ID: 38442160
Summary: Circadian clocks impose daily periodicities to behavior, physiology, and metabolism. This control is mediated by a central clock and by peripheral clocks, which are synchronized to provide the organism with a unified time through mechanisms that are not fully understood. This study characterized in Drosophila the cellular and molecular mechanisms involved in coupling the central clock and the peripheral clock located in the prothoracic gland (PG), which together control the circadian rhythm of emergence of adult flies. The time signal from central clock neurons is transmitted via small neuropeptide F (sNPF) to neurons that produce the neuropeptide Prothoracicotropic Hormone (PTTH), which is then translated into daily oscillations of Ca(2+) concentration and PTTH levels. PTTH signaling is required at the end of metamorphosis and transmits time information to the PG through changes in the expression of the PTTH receptor tyrosine kinase (RTK), TORSO, and of ERK phosphorylation, a key component of PTTH transduction. In addition to PTTH, this study demonstrated that signaling mediated by other RTKs contributes to the rhythmicity of emergence. Interestingly, the ligand to one of these receptors (Pvf2) plays an autocrine role in the PG, which may explain why both central brain and PG clocks are required for the circadian gating of emergence. These findings show that the coupling between the central and the PG clock is unexpectedly complex and involves several RTKs that act in concert and could serve as a paradigm to understand how circadian clocks are coordinated. |
Li, Y., Lu, T., Dong, P., Chen, J., Zhao, Q., Wang, Y., Xiao, T., Wu, H., Zhao, Q., Huang, H. (2024). A single-cell atlas of Drosophila trachea reveals glycosylation-mediated Notch signaling in cell fate specification. Nat Commun, 15(1):2019 PubMed ID: 38448482
Summary: The Drosophila tracheal system is a favorable model for investigating the program of tubular morphogenesis. This system is established in the embryo by post-mitotic cells, but also undergoes remodeling by adult stem cells. This study provides a comprehensive cell atlas of Drosophila trachea using the single-cell RNA-sequencing (scRNA-seq) technique. The atlas documents transcriptional profiles of tracheoblasts within the Drosophila airway, delineating 9 major subtypes. Further evidence gained from in silico as well as genetic investigations highlight a set of transcription factors characterized by their capacity to switch cell fate. Notably, the transcription factors Pebbled, Blistered, Knirps, Spalt and aut are influenced by Notch signaling and determine tracheal cell identity. Moreover, Notch signaling orchestrates transcriptional activities essential for tracheoblast differentiation and responds to protein glycosylation that is induced by high sugar diet. Therefore, this study yields a single-cell transcriptomic atlas of tracheal development and regeneration, and suggests a glycosylation-responsive Notch signaling in cell fate determination. | David, S. B., Ho, K. Y. L., Tanentzapf, G., Zaritsky, A. (2024). Formation of recurring transient Ca(2+)-based intercellular communities during Drosophila hematopoiesis. Journal and Proc Natl Acad Sci U S A, 121(16):e2318155121 PubMed ID: 38602917
Summary: Tiissue development occurs through a complex interplay between many individual cells. Yet, the fundamental question of how collective tissue behavior emerges from heterogeneous and noisy information processing and transfer at the single-cell level remains unknown. This study reveals that tissue scale signaling regulation can arise from local gap-junction mediated cell-cell signaling through the spatiotemporal establishment of an intermediate-scale of transient multicellular communication communities over the course of tissue development. This intermediate scale of emergent signaling using cCa(2+) signaling in the intact, ex vivo cultured, live developing Drosophila hematopoietic organ, the lymph gland. Recurrent activation of these transient signaling communities defined self-organized signaling "hotspots" that gradually formed over the course of larva development. These hotspots receive and transmit information to facilitate repetitive interactions with nonhotspot neighbors. Overall, this work bridges the scales between single-cell and emergent group behavior providing key mechanistic insight into how cells establish tissue-scale communication networks. |
Tan, Q. H., Otgonbaatar, A., Kaur, P., Ga, A. F., Harmston, N. P., Tolwinski, N. S. (2024). The Wnt Co-Receptor PTK7/Otk and Its Homolog Otk-2 in Neurogenesis and Patterning. Journal and Cells, 13(5) PubMed ID: 38474329
Summary: Wnt signaling is a highly conserved metazoan pathway that plays a crucial role in cell fate determination and morphogenesis during development. Wnt ligands can induce disparate cellular responses. The exact mechanism behind these different outcomes is not fully understood but may be due to interactions with different receptors on the cell membrane. PTK7/Otk is a transmembrane receptor that is implicated in various developmental and physiological processes including cell polarity, cell migration, and invasion. Here, we examine two roles of Otk-1 and Otk-2 in patterning and neurogenesis. Otk-1 was found to bve a positive regulator of signaling and Otk-2 functions as its inhibitor. It is proposed that PTK7/Otk functions in signaling, cell migration, and polarity contributing to the diversity of cellular responses seen in Wnt-mediated processes. | Castro, K., Muradyan, V., Flota, P., Guanzon, J., Poole, N., Urrutia, H., Eivers, E. (2024). Drosophila Smad2 degradation occurs independently of linker phosphorylations. microPublication biology, 2024 PubMed ID: 38601902
Summary: TGF-β signals are important for proliferation, differentiation, and cell fate determination during embryonic development and tissue homeostasis in adults. Drosophila Activin/TGF-β signals are transduced intracellularly when its transcription factor dSmad2 (also called Smad on X or Smox) is C-terminally phosphorylated by pathway receptors. Recently, it has been shown that receptor-activated dSmad2 undergoes bulk degradation, however, the mechanism of how this occurs is unknown. This study investigated if two putative linker phosphorylation sites are involved in dSmad2 degradation. Degradation of activated-dSmad2 was was shown to occur independently of threonine phosphorylation at linker sites 252 and 277. dSmad2 degradation was also shown not to be carried out by cellular proteasomes. |
Friday December 13th - Stress |
Everman, E. R., Macdonald, S. J. (2024). Gene expression variation underlying tissue-specific responses to copper stress in Drosophila melanogaster. G3 (Bethesda), 14(3) PubMed ID: 38262701
Summary: Copper is one of a handful of biologically necessary heavy metals that is also a common environmental pollutant. Under normal conditions, copper ions are required for many key physiological processes. However, in excess, copper results in cell and tissue damage ranging in severity from temporary injury to permanent neurological damage. Because of its biological relevance, and because many conserved copper-responsive genes respond to nonessential heavy metal pollutants, copper resistance in Drosophila melanogaster is a useful model system with which to investigate the genetic control of the heavy metal stress response. Because heavy metal toxicity has the potential to differently impact specific tissues, this study genetically characterized the control of the gene expression response to copper stress in a tissue-specific manner in this study. The copper stress response was assessed in head and gut tissue of 96 inbred strains from the Drosophila Synthetic Population Resource using a combination of differential expression analysis and expression quantitative trait locus mapping. Differential expression analysis revealed clear patterns of tissue-specific expression. Tissue and treatment specific responses to copper stress were also detected using expression quantitative trait locus mapping. Expression quantitative trait locus associated with MtnA, Mdr49, Mdr50, and Sod3 exhibited both genotype-by-tissue and genotype-by-treatment effects on gene expression under copper stress, illuminating tissue- and treatment-specific patterns of gene expression control. Together, these data build a nuanced description of the roles and interactions between allelic and expression variation in copper-responsive genes, provide valuable insight into the genomic architecture of susceptibility to metal toxicity, and highlight candidate genes for future functional characterization. | Chen, Y., McDonald, J. A. (2024). Collective cell migration relies on PPP1R15-mediated regulation of the endoplasmic reticulum stress response. Curr Biol 34(7):1390-1402 PubMed ID: 38428416
Summary: Collective cell migration is integral to many developmental and disease processes. Previous work discovered that protein phosphatase 1 (Pp1) promotes border cell collective migration in the Drosophila ovary. This study now reports that the Pp1 phosphatase regulatory subunit dPPP1R15 is a critical regulator of border cell migration. dPPP1R15 is an ortholog of mammalian PPP1R15 proteins that attenuate the endoplasmic reticulum (ER) stress response. In collectively migrating border cells, dPPP1R15 phosphatase restrains an active physiological protein kinase R-like ER kinase- (PERK)-eIF2α-activating transcription factor 4 (ATF4) stress pathway. RNAi knockdown of dPPP1R15 blocks border cell delamination from the epithelium and subsequent migration, increases eIF2α phosphorylation, reduces translation, and drives expression of the stress response transcription factor ATF4. Similar defects were observed upon overexpression of ATF4 or the eIF2α kinase PERK. Furthermore, it was shown that normal border cells express markers of the PERK-dependent ER stress response and require PERK and ATF4 for efficient migration. In many other cell types, unresolved ER stress induces initiation of apoptosis. In contrast, border cells with chronic RNAi knockdown of dPPP1R15 survive. Together, our results demonstrate that the PERK-eIF2ãalpha;-ATF4 pathway, regulated by dPPP1R15 activity, counteracts the physiological ER stress that occurs during collective border cell migration. It is proposed td2hat in vivo collective cell migration is intrinsically "stressful," requiring tight homeostatic control of the ER stress response for collective cell cohesion, dynamics, and movement. |
Stankovic, D., Tain, L. S., Uhlirova, M. (2024). Xrp1 governs the stress response program to spliceosome dysfunction. Nucleic Acids Res, 52(5):2093-2111 PubMed ID: 38303573
Summary: Co-transcriptional processing of nascent pre-mRNAs by the spliceosome is vital to regulating gene expression and maintaining genome integrity. This study showns that the deficiency of functional U5 small nuclear ribonucleoprotein particles (snRNPs) in Drosophila imaginal cells causes extensive transcriptome remodeling and accumulation of highly mutagenic R-loops, triggering a robust stress response and cell cycle arrest. Despite compromised proliferative capacity, the U5 snRNP-deficient cells increased protein translation and cell size, causing intra-organ growth disbalance before being gradually eliminated via apoptosis. This study identified the Xrp1-Irbp18 heterodimer as the primary driver of transcriptional and cellular stress program downstream of U5 snRNP malfunction. Knockdown of Xrp1 or Irbp18 in U5 snRNP-deficient cells attenuated JNK and p53 activity, restored normal cell cycle progression and growth, and inhibited cell death. Reducing Xrp1-Irbp18, however, did not rescue the splicing defects, highlighting the requirement of accurate splicing for cellular and tissue homeostasis. thousands work provides novel insights into the crosstalk between splicing and the DNA damage response and defines the Xrp1-Irbp18 heterodimer as a critical sensor of spliceosome malfunction and mediator of the stress-induced cellular senescence program. | Geng, J., Li, S., Li, Y., Wu, Z., Bhurtel, S., Rimal, S., Khan, D., Ohja, R., Brandman, O., Lu, B. (2024). Stalled translation by mitochondrial stress upregulates a CNOT4-ZNF598 ribosomal quality control pathway important for tissue homeostasis. Nat Commun, 15(1):1637 PubMed ID: 38388640
Summary: Translational control exerts immediate effect on the composition, abundance, and integrity of the proteome. Ribosome-associated quality control (RQC) handles ribosomes stalled at the elongation and termination steps of translation, with ZNF598 in mammals and Hel2 in yeast serving as key sensors of translation stalling and coordinators of downstream resolution of collided ribosomes, termination of stalled translation, and removal of faulty translation products. The physiological regulation of RQC in general and ZNF598 in particular in multicellular settings is underexplored. This study shows that ZNF598 undergoes regulatory K63-linked ubiquitination in a CNOT4-dependent manner and is upregulated upon mitochondrial stresses in mammalian cells and Drosophila. ZNF598 promotes resolution of stalled ribosomes and protects against mitochondrial stress in a ubiquitination-dependent fashion. In Drosophila models of neurodegenerative diseases and patient cells, ZNF598 overexpression aborts stalled translation of mitochondrial outer membrane-associated mRNAs, removes faulty translation products causal of disease, and improves mitochondrial and tissue health. These results shed lights on the regulation of ZNF598 and its functional role in mitochondrial and tissue homeostasis. |
Grmai, L., Michaca, M., Lackner, E., Nampoothiri, V. P. N., Vasudevan, D. (2024). Integrated stress response signaling acts as a metabolic sensor in fat tissues to regulate oocyte maturation and ovulation. Cell Rep, 43(3):113863 PubMed ID: 38457339
Summary: Reproduction is an energy-intensive process requiring systemic coordination. However, the inter-organ signaling mechanisms that relay nutrient status to modulate reproductive output are poorly understood.T his study used Drosophila melanogaster as a model to establish the integrated stress responses (ISR) transcription factor, Atf4, as a fat tissue metabolic sensor that instructs oogenesis. Atf4 was shown to regulates lipase activity to mediate yolk lipoprotein synthesis in the fat body. Depletion of Atf4 in the fat body also blunts oogenesis recovery after amino acid deprivation and re-feeding, suggestive of a nutrient-sensing role for Atf4. It was also discovered that Atf4 promotes secretion of a fat-body-derived neuropeptide, CNMamide, which modulates neural circuits that promote egg-laying behavior (ovulation). Thus, it is positted that ISR signaling in fat tissue acts as a "metabolic sensor" that instructs female reproduction-directly by impacting yolk lipoprotein production and follicle maturation and systemically by regulating ovulation. | Islam, A., Shaukat, Z., Hussain, R., Ricos, M. G., Dibbens, L. M., Gregory, S. L. (2024). Aneuploidy is Linked to Neurological Phenotypes Through Oxidative Stress. Journal of molecular neuroscience : MN, 74(2):50 PubMed ID: 38693434
Summary: Aneuploidy, having an aberrant genome, is gaining increasing attention in neurodegenerative diseases. It gives rise to proteotoxic stress as well as a stereotypical oxidative shift which makes these cells sensitive to internal and environmental stresses. A growing body of research from numerous laboratories suggests that many neurodegenerative disorders, especially Alzheimer's disease and frontotemporal dementia, are characterised by neuronal aneuploidy and the ensuing apoptosis, which may contribute to neuronal loss. Using Drosophila as a model, this study investigated the effect of induced aneuploidy in GABAergic neurons. An increased proportion of aneuploidy was found due to Mad2 depletion in the third-instar larval brain and increased cell death. Depletion of Mad2 in GABAergic neurons also gave a defective climbing and seizure phenotype. Feeding animals an antioxidant rescued the climbing and seizure phenotype. These findings suggest that increased aneuploidy leads to higher oxidative stress in GABAergic neurons which causes cell death, climbing defects, and seizure phenotype. Antioxidant feeding represents a potential therapy to reduce the aneuploidy-driven neurological phenotype. |
Thursday December 12th - Disease Models |
Thorpe, H. J., Owings, K. G., Aziz, M. C., Haller, M., Coelho, E., Chow, C. Y. (2024). Drosophila models of phosphatidylinositol glycan biosynthesis class A congenital disorder of glycosylation (PIGA-CDG) mirror patient phenotypes. G3 (Bethesda), 14(3) PubMed ID: 38124489
Summary: Mutations in the phosphatidylinositol glycan biosynthesis class A (PIGA) gene cause a rare, X-linked recessive congenital disorder of glycosylation. Phosphatidylinositol glycan biosynthesis class A congenital disorder of glycosylation (PIGA-CDG) is characterized by seizures, intellectual and developmental delay, and congenital malformations. The PIGA gene encodes an enzyme involved in the first step of glycosylphosphatidylinositol (GPI) anchor biosynthesis. There are over 100 GPI-anchored proteins that attach to the cell surface and are involved in cell signaling, immunity, and adhesion. Little is known about the pathophysiology of PIGA-CDG. This study describes the first Drosophila model of PIGA-CDG and demonstrates that loss of PIG-A function in Drosophila accurately models the human disease. As expected, complete loss of PIG-A function is larval lethal. Heterozygous null animals appear healthy but, when challenged, have a seizure phenotype similar to what is observed in patients. To identify the cell-type specific contributions to disease, neuron- and glia-specific knockdown of PIG-A were generated. Neuron-specific knockdown resulted in reduced lifespan and a number of neurological phenotypes but no seizure phenotype. Glia-knockdown also reduced lifespan and, notably, resulted in a very strong seizure phenotype. RNA sequencing analyses demonstrated that there are fundamentally different molecular processes that are disrupted when PIG-A function is eliminated in different cell types. In particular, loss of PIG-A in neurons resulted in upregulation of glycolysis, but loss of PIG-A in glia resulted in upregulation of protein translation machinery. This study demonstrates that Drosophila is a good model of PIGA-CDG and provides new data resources for future study of PIGA-CDG and other GPI anchor disorders. | Kinnart, I., Manders, L., Heyninck, T., Imberechts, D., Praschberger, R., Schoovaerts, N., Verfaillie, C., Verstreken, P., Vandenberghe, W. (2024). TElevated alpha-synuclein levels inhibit mitophagic flux. Journal and PubMed IDNPJ Parkinson's disease, 10(1):80 PubMed ID: 38594264
Summary: The pathogenic effect of SNCA gene multiplications indicates that elevation of wild-type α-synuclein levels is sufficient to cause Parkinson's disease (PD). Mitochondria have been proposed to be a major target of α-synuclein-induced damage. PINK1/parkin/DJ-1-mediated mitophagy is a defense strategy that allows cells to selectively eliminate severely damaged mitochondria. This study quantified mitophagic flux and non-mitochondrial autophagic flux in three models of increased α-synuclein expression: 1) Drosophila melanogaster that transgenically express human wild-type and mutant α-synuclein in flight muscle; 2) human skin fibroblasts transfected with α-synuclein or β-synuclein; and 3) human induced pluripotent stem cell (iPSC)-derived neurons carrying an extra copy of wild-type SNCA under control of a doxycycline-inducible promoter, allowing titratable α-synuclein upregulation. In each model, elevated α-synuclein levels potently suppressed mitophagic flux, while non-mitochondrial autophagy was preserved. In human neurons, a twofold increase in wild-type α-synuclein was already sufficient to induce this effect. PINK1 and parkin activation and mitochondrial translocation of DJ-1 after mitochondrial depolarization were not affected by α-synuclein upregulation. Overexpression of the actin-severing protein cofilin or treatment with CK666, an inhibitor of the actin-related protein 2/3 (Arp2/3) complex, rescued mitophagy in neurons with increased α-synuclein, suggesting that excessive actin network stabilization mediated the mitophagy defect. In conclusion, elevated α-synuclein levels inhibit mitophagic flux. Disruption of actin dynamics may play a key role in this effect. |
Sardina, F., Carsetti, C., Giorgini, L., Fattorini, G., Cestra, G., Rinaldo, C. (2024). Cul-4 inhibition rescues spastin levels and reduces defects in hereditary spastic paraplegia models. Brain : a journal of neurology, PubMed ID: 38551087
Summary: >Hereditary spastic paraplegias (HSPs) are degenerative motor neuron diseases characterized by progressive spasticity and weakness in the lower limbs. The most common form of HSP is due to SPG4 gene haploinsufficiency. SPG4 encodes the microtubule severing enzyme spastin. Although, there is no cure for SPG4-HSP, strategies to induce a spastin recovery are emerging as promising therapeutic approaches. Spastin protein levels are regulated by poly-ubiquitination and proteasomal-mediated degradation, in a neddylation-dependent manner. However, the molecular players involved in this regulation are unknown. This study shows that the Cullin-4-Ring E3 ubiquitin ligase complex (CRL4) regulates spastin stability. Inhibition of CRL4 increases spastin levels by preventing its poly-ubiquitination and subsequent degradation in spastin-proficient and in patient derived SPG4 haploinsufficient cells. To evaluate the role of CRL4 complex in spastin regulation in vivo, a Drosophila melanogaster model of SPG4 haploinsufficiency was developed which shows alterations of synapse morphology and locomotor activity, recapitulating phenotypical defects observed in patients. Downregulation of the CRL4 complex, highly conserved in Drosophila, rescues spastin levels and the phenotypical defects observed in flies. As a proof of concept of possible pharmacological treatments, a recovery of spastin levels and amelioration of the SPG4-HSP-associated defects ertr demonstrated both in the fly model and in patient-derived cells by chemical inactivation of the CRL4 complex with NSC1892. Taken together, these findings show that CRL4 contributes to spastin stability regulation and that it is possible to induce spastin recovery and rescue of SPG4-HSP defects by blocking the CRL4-mediated spastin degradation. | >Shen, N. X., Qu, X. C., Yu, J., Fan, C. X., Min, F. L., Li, L. Y., Zhang, M. R., Li, B. M., Wang, J., He, N., Liao, W. P., Shi, Y. W., Li, W. B. (2024). NUS1 Variants Cause Lennox-Gastaut Syndrome Related to Unfolded Protein Reaction Activation. Molecular neurobiology, PubMed ID: 38520610
Summary: NUS1 encodes the Nogo-B receptor, a critical regulator for unfolded protein reaction (UPR) signaling. Although several loss-of-function variants of NUS1 have been identified in patients with developmental and epileptic encephalopathy (DEE), the role of the NUS1 variant in Lennox-Gastaut syndrome (LGS), a severe child-onset DEE, remains unknown. This study identified two de novo variants of NUS1, a missense variant and a splice site variant, in two unrelated LGS patients using trio-based whole-exome sequencing performed in a cohort of 165 LGS patients. Both variants were absent in the gnomAD population and showed a significantly higher observed number of variants than expected genome-wide. The R290C variant was predicted to damage NUS1 and decrease its protein stability. The c.792-2 A > G variant caused premature termination of the protein. Knockdown of NUS1 activated the UPR pathway, resulting in apoptosis of HEK293T cells. Supplementing cells with expression of wild-type NUS1, but not the mutant (R290C), rescued UPR activation and apoptosis in NUS1 knockdown cells. Compared to wild-type Drosophila, seizure-like behaviors and excitability in projection neurons were significantly increased in Tango14 (homolog of human NUS1) knockdown and Tango14(R290C/+) knock-in Drosophila. Additionally, abnormal development and a small body size were observed in both mutants. Activated UPR signaling was also detected in both mutants. Thus, NUS1 is a causative gene for LGS with dominant inheritance. The pathogenicity of these variants is related to the UPR signaling activation, which may be a common pathogenic mechanism of DEE. |
Fukuda, J., Kosuge, S., Satoh, Y., Sekiya, S., Yamamura, R., Ooshio, T., Hirata, T., Sato, R., Hatanaka, K. C., Mitsuhashi, T., Nakamura, T., Matsuno, Y., Hatanaka, Y., Hirano, S., Sonoshita, M. (2024). Concurrent targeting of GSK3 and MEK as a therapeutic strategy to treat pancreatic ductal adenocarcinoma. Cancer science, 115(4):1333-1345 PubMed ID: 38320747
Summary: Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal malignancies worldwide. However, drug discovery for PDAC treatment has proven complicated, leading to stagnant therapeutic outcomes. This atidu identified Glycogen synthase kinase 3 (GSK3) as a therapeutic target through a whole-body genetic screening utilizing a '4-hit' Drosophila model mimicking the PDAC genotype. Reducing the gene dosage of GSK3 in a whole-body manner or knocking down GSK3 specifically in transformed cells suppressed 4-hit fly lethality, similar to Mitogen-activated protein kinase kinase (MEK), the therapeutic target in PDAC. Consistently, a combination of the GSK3 inhibitor CHIR99021 and the MEK inhibitor trametinib suppressed the phosphorylation of Polo-like kinase 1 (PLK1) as well as the growth of orthotopic human PDAC xenografts in mice. Additionally, reducing PLK1 genetically in 4-hit flies rescued their lethality. These results reveal a therapeutic vulnerability in PDAC that offers a treatment opportunity for patients by inhibiting multiple targets. | Park, Y. J., Lu, T. C., Jackson, T., Goodman, L. D., Ran, L., Chen, J., Liang, C. Y., Harrison, E., Ko, C., Hsu, A. L., Yamamoto, S., Qi, Y., Bellen, H. J., Li, H. (2024). Whole organism snRNA-seq reveals systemic peripheral changes in Alzheimer's Disease fly models. bioRxiv, PubMed ID: 38559164
Summary: Peripheral tissues become disrupted in Alzheimer's Disease (AD). However, a comprehensive understanding of how the expression of AD-associated toxic proteins, Aβ42 and Tau, in neurons impacts the periphery is lacking. Using Drosophila, a prime model organism for studying aging and neurodegeneration, the Alzheimer's Disease Fly Cell Atlas (AD-FCA) was generated: whole-organism single-nucleus transcriptomes of 219 cell types from adult flies neuronally expressing human Aβ42 or Tau. In-depth analyses and functional data reveal impacts on peripheral sensory neurons by Aβ42 and on various non-neuronal peripheral tissues by Tau, including the gut, fat body, and reproductive system. This novel AD atlas provides valuable insights into potential biomarkers and the intricate interplay between the nervous system and peripheral tissues in response to AD-associated proteins. |
Wednesday December 11th - Embryonic Development |
Thorpe, H. J., Owings, K. G., Aziz, M. C., Haller, M., Coelho, E., Chow, C. Y. (2024). Drosophila models of phosphatidylinositol glycan biosynthesis class A congenital disorder of glycosylation (PIGA-CDG) mirror patient phenotypes. G3 (Bethesda), 14(3) PubMed ID: 38124489
Summary: Mutations in the phosphatidylinositol glycan biosynthesis class A (PIGA) gene cause a rare, X-linked recessive congenital disorder of glycosylation. Phosphatidylinositol glycan biosynthesis class A congenital disorder of glycosylation (PIGA-CDG) is characterized by seizures, intellectual and developmental delay, and congenital malformations. The PIGA gene encodes an enzyme involved in the first step of glycosylphosphatidylinositol (GPI) anchor biosynthesis. There are over 100 GPI-anchored proteins that attach to the cell surface and are involved in cell signaling, immunity, and adhesion. Little is known about the pathophysiology of PIGA-CDG. This study describes the first Drosophila model of PIGA-CDG and demonstrates that loss of PIG-A function in Drosophila accurately models the human disease. As expected, complete loss of PIG-A function is larval lethal. Heterozygous null animals appear healthy but, when challenged, have a seizure phenotype similar to what is observed in patients. To identify the cell-type specific contributions to disease, neuron- and glia-specific knockdown of PIG-A were generated. Neuron-specific knockdown resulted in reduced lifespan and a number of neurological phenotypes but no seizure phenotype. Glia-knockdown also reduced lifespan and, notably, resulted in a very strong seizure phenotype. RNA sequencing analyses demonstrated that there are fundamentally different molecular processes that are disrupted when PIG-A function is eliminated in different cell types. In particular, loss of PIG-A in neurons resulted in upregulation of glycolysis, but loss of PIG-A in glia resulted in upregulation of protein translation machinery. This study demonstrates that Drosophila is a good model of PIGA-CDG and provides new data resources for future study of PIGA-CDG and other GPI anchor disorders. | Kinnart, I., Manders, L., Heyninck, T., Imberechts, D., Praschberger, R., Schoovaerts, N., Verfaillie, C., Verstreken, P., Vandenberghe, W. (2024). TElevated alpha-synuclein levels inhibit mitophagic flux. Journal and PubMed IDNPJ Parkinson's disease, 10(1):80 PubMed ID: 38594264
Summary: The pathogenic effect of SNCA gene multiplications indicates that elevation of wild-type α-synuclein levels is sufficient to cause Parkinson's disease (PD). Mitochondria have been proposed to be a major target of α-synuclein-induced damage. PINK1/parkin/DJ-1-mediated mitophagy is a defense strategy that allows cells to selectively eliminate severely damaged mitochondria. This study quantified mitophagic flux and non-mitochondrial autophagic flux in three models of increased α-synuclein expression: 1) Drosophila melanogaster that transgenically express human wild-type and mutant α-synuclein in flight muscle; 2) human skin fibroblasts transfected with α-synuclein or β-synuclein; and 3) human induced pluripotent stem cell (iPSC)-derived neurons carrying an extra copy of wild-type SNCA under control of a doxycycline-inducible promoter, allowing titratable α-synuclein upregulation. In each model, elevated α-synuclein levels potently suppressed mitophagic flux, while non-mitochondrial autophagy was preserved. In human neurons, a twofold increase in wild-type α-synuclein was already sufficient to induce this effect. PINK1 and parkin activation and mitochondrial translocation of DJ-1 after mitochondrial depolarization were not affected by α-synuclein upregulation. Overexpression of the actin-severing protein cofilin or treatment with CK666, an inhibitor of the actin-related protein 2/3 (Arp2/3) complex, rescued mitophagy in neurons with increased α-synuclein, suggesting that excessive actin network stabilization mediated the mitophagy defect. In conclusion, elevated α-synuclein levels inhibit mitophagic flux. Disruption of actin dynamics may play a key role in this effect. |
Sardina, F., Carsetti, C., Giorgini, L., Fattorini, G., Cestra, G., Rinaldo, C. (2024). Cul-4 inhibition rescues spastin levels and reduces defects in hereditary spastic paraplegia models. Brain : a journal of neurology, PubMed ID: 38551087
Summary: >Hereditary spastic paraplegias (HSPs) are degenerative motor neuron diseases characterized by progressive spasticity and weakness in the lower limbs. The most common form of HSP is due to SPG4 gene haploinsufficiency. SPG4 encodes the microtubule severing enzyme spastin. Although, there is no cure for SPG4-HSP, strategies to induce a spastin recovery are emerging as promising therapeutic approaches. Spastin protein levels are regulated by poly-ubiquitination and proteasomal-mediated degradation, in a neddylation-dependent manner. However, the molecular players involved in this regulation are unknown. This study shows that the Cullin-4-Ring E3 ubiquitin ligase complex (CRL4) regulates spastin stability. Inhibition of CRL4 increases spastin levels by preventing its poly-ubiquitination and subsequent degradation in spastin-proficient and in patient derived SPG4 haploinsufficient cells. To evaluate the role of CRL4 complex in spastin regulation in vivo, a Drosophila melanogaster model of SPG4 haploinsufficiency was developed which shows alterations of synapse morphology and locomotor activity, recapitulating phenotypical defects observed in patients. Downregulation of the CRL4 complex, highly conserved in Drosophila, rescues spastin levels and the phenotypical defects observed in flies. As a proof of concept of possible pharmacological treatments, a recovery of spastin levels and amelioration of the SPG4-HSP-associated defects ertr demonstrated both in the fly model and in patient-derived cells by chemical inactivation of the CRL4 complex with NSC1892. Taken together, these findings show that CRL4 contributes to spastin stability regulation and that it is possible to induce spastin recovery and rescue of SPG4-HSP defects by blocking the CRL4-mediated spastin degradation. | Shen, N. X., Qu, X. C., Yu, J., Fan, C. X., Min, F. L., Li, L. Y., Zhang, M. R., Li, B. M., Wang, J., He, N., Liao, W. P., Shi, Y. W., Li, W. B. (2024). NUS1 Variants Cause Lennox-Gastaut Syndrome Related to Unfolded Protein Reaction Activation. Molecular neurobiology, PubMed ID: 38520610
Summary: NUS1 encodes the Nogo-B receptor, a critical regulator for unfolded protein reaction (UPR) signaling. Although several loss-of-function variants of NUS1 have been identified in patients with developmental and epileptic encephalopathy (DEE), the role of the NUS1 variant in Lennox-Gastaut syndrome (LGS), a severe child-onset DEE, remains unknown. This study identified two de novo variants of NUS1, a missense variant and a splice site variant, in two unrelated LGS patients using trio-based whole-exome sequencing performed in a cohort of 165 LGS patients. Both variants were absent in the gnomAD population and showed a significantly higher observed number of variants than expected genome-wide. The R290C variant was predicted to damage NUS1 and decrease its protein stability. The c.792-2 A > G variant caused premature termination of the protein. Knockdown of NUS1 activated the UPR pathway, resulting in apoptosis of HEK293T cells. Supplementing cells with expression of wild-type NUS1, but not the mutant (R290C), rescued UPR activation and apoptosis in NUS1 knockdown cells. Compared to wild-type Drosophila, seizure-like behaviors and excitability in projection neurons were significantly increased in Tango14 (homolog of human NUS1) knockdown and Tango14(R290C/+) knock-in Drosophila. Additionally, abnormal development and a small body size were observed in both mutants. Activated UPR signaling was also detected in both mutants. Thus, NUS1 is a causative gene for LGS with dominant inheritance. The pathogenicity of these variants is related to the UPR signaling activation, which may be a common pathogenic mechanism of DEE. |
Fukuda, J., Kosuge, S., Satoh, Y., Sekiya, S., Yamamura, R., Ooshio, T., Hirata, T., Sato, R., Hatanaka, K. C., Mitsuhashi, T., Nakamura, T., Matsuno, Y., Hatanaka, Y., Hirano, S., Sonoshita, M. (2024). Concurrent targeting of GSK3 and MEK as a therapeutic strategy to treat pancreatic ductal adenocarcinoma. Cancer science, 115(4):1333-1345 PubMed ID: 38320747
Summary: Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal malignancies worldwide. However, drug discovery for PDAC treatment has proven complicated, leading to stagnant therapeutic outcomes. This atidu identified Glycogen synthase kinase 3 (GSK3) as a therapeutic target through a whole-body genetic screening utilizing a '4-hit' Drosophila model mimicking the PDAC genotype. Reducing the gene dosage of GSK3 in a whole-body manner or knocking down GSK3 specifically in transformed cells suppressed 4-hit fly lethality, similar to Mitogen-activated protein kinase kinase (MEK), the therapeutic target in PDAC. Consistently, a combination of the GSK3 inhibitor CHIR99021 and the MEK inhibitor trametinib suppressed the phosphorylation of Polo-like kinase 1 (PLK1) as well as the growth of orthotopic human PDAC xenografts in mice. Additionally, reducing PLK1 genetically in 4-hit flies rescued their lethality. These results reveal a therapeutic vulnerability in PDAC that offers a treatment opportunity for patients by inhibiting multiple targets. | Park, Y. J., Lu, T. C., Jackson, T., Goodman, L. D., Ran, L., Chen, J., Liang, C. Y., Harrison, E., Ko, C., Hsu, A. L., Yamamoto, S., Qi, Y., Bellen, H. J., Li, H. (2024). Whole organism snRNA-seq reveals systemic peripheral changes in Alzheimer's Disease fly models. bioRxiv, PubMed ID: 38559164
Summary: Peripheral tissues become disrupted in Alzheimer's Disease (AD). However, a comprehensive understanding of how the expression of AD-associated toxic proteins, Aβ42 and Tau, in neurons impacts the periphery is lacking. Using Drosophila, a prime model organism for studying aging and neurodegeneration, the Alzheimer's Disease Fly Cell Atlas (AD-FCA) was generated: whole-organism single-nucleus transcriptomes of 219 cell types from adult flies neuronally expressing human Aβ42 or Tau. In-depth analyses and functional data reveal impacts on peripheral sensory neurons by Aβ42 and on various non-neuronal peripheral tissues by Tau, including the gut, fat body, and reproductive system. This novel AD atlas provides valuable insights into potential biomarkers and the intricate interplay between the nervous system and peripheral tissues in response to AD-associated proteins. |
Wednesday December 11th - Embryonic Development |
Fischer, F., Ernst, L., Frey, A., Holstein, K., Prasad, D., Weichselberger, V., Balaji, R., Classen, A. K. (2024). A mismatch in the expression of cell surface molecules induces tissue-intrinsic defense against aberrant cells. Curr Biol, 34(5):980-996 PubMed ID: 38350446
Summary: Tissue-intrinsic error correction enables epithelial cells to detect abnormal neighboring cells and facilitate their removal from the tissue. One of these pathways, "interface surveillance," is triggered by cells with aberrant developmental and cell-fate-patterning pathways. It remains unknown which molecular mechanisms provide cells with the ability to compare fate between neighboring cells. Drosophila imaginal discs were demonstrated express an array of cell surface molecules previously implicated in neuronal axon guidance processes. They include members of the Robo, Teneurin, Ephrin, Toll-like, or atypical cadherin families. Importantly, a mismatch in expression levels of these cell surface molecules between adjacent cells is sufficient to induce interface surveillance, indicating that differences in expression levels between neighboring cells, rather than their absolute expression levels, are crucial. Specifically, a mismatch in Robo2 and Robo3, but not Robo1, induces enrichment of actin, myosin II, and Ena/Vasp, as well as activation of JNK and apoptosis at clonal interfaces. Moreover, Robo2 can induce interface surveillance independently of its cytosolic domain and without the need for the Robo-ligand ccSlit. The expression of Robo2 and other cell surface molecules, such as Teneurins or the Ephrin receptor is regulated by fate-patterning pathways intrinsic and extrinsic to the wing disc, as well as by expression of oncogenic Ras(V12). Combined, we demonstrate that neighboring cells respond to a mismatch in surface code patterns mediated by specific transmembrane proteins and reveal a novel function for these cell surface proteins in cell fate recognition and removal of aberrant cells during development and homeostasis of epithelial tissues. | Cupo, C., Allan, C., Ailiani, V., Kasza, K. E. (2024). Signatures of structural disorder in developing epithelial tissues. bioRxiv, PubMed ID: 38405955
Summary: Epithelial cells generate functional tissues in developing embryos through collective movements and shape changes. In some morphogenetic events, a tissue dramatically reorganizes its internal structure - often generating high degrees of structural disorder - to accomplish changes in tissue shape. However, the origins of structural disorder in epithelia and what roles it might play in morphogenesis are poorly understood. This question was examined in the Drosophila germband epithelium, which undergoes dramatic changes in internal structure as cell rearrangements drive elongation of the embryo body axis. Using two order parameters that quantify volumetric and shear disorder, structural disorder was shown to increase during body axis elongation and is strongly linked with specific developmental processes. Both disorder metrics begin to increase around the onset of axis elongation, but then plateau at values that are maintained throughout the process. Notably, the disorder plateau values for volumetric disorder are similar to those for random cell packings, suggesting this may reflect a limit on tissue behavior. In mutant embryos with disrupted external stresses from the ventral furrow, both disorder metrics reach wild-type maximum disorder values with a delay, correlating with delays in cell rearrangements. In contrast, in mutants with disrupted internal stresses and cell rearrangements, volumetric disorder is reduced compared to wild type, whereas shear disorder depends on specific external stress patterns. Together, these findings demonstrate that internal and external stresses both contribute to epithelial tissue disorder and suggest that the maximum values of disorder in a developing tissue reflect physical or biological limits on morphogenesis. |
Drewell, R. A., Klonaros, D., Dresch, J. M. (2024). Transcription factor expression landscape in Drosophila embryonic cell lines. BMC Genomics, 25(1):307 PubMed ID: 38521929
Summary: Large-scale studies over the last two decades have helped shed light on the complex network of TFs that regulate development in Drosophila melanogaster. This study presents a detailed characterization of expression of all known and predicted Drosophila TFs in two well-established embryonic cell lines, Kc167 and S2 cells. Using deep coverage RNA sequencing approaches this study investigated the transcriptional profile of all 707 TF coding genes in both cell types. Only 103 TFs have no detectable expression in either cell line and 493 TFs have a read count of 5 or greater in at least one of the cell lines. The 493 TFs belong to 54 different DNA-binding domain families, with significant enrichment of those in the zf-C2H2 family. 123 differentially expressed genes were identified, with 57 expressed at significantly higher levels in Kc167 cells than S2 cells, and 66 expressed at significantly lower levels in Kc167 cells than S2 cells. Network mapping reveals that many of these TFs are crucial components of regulatory networks involved in cell proliferation, cell-cell signaling pathways, and eye development. A reference TF coding gene expression dataset was produced in the extensively studied Drosophila Kc167 and S2 embryonic cell lines, and insight was gained into the TF regulatory networks that control the activity of these cells. | Matthew, J., Vishwakarma, V., Le, T. P., Agsunod, R. A., Chung, S. (2024). Coordination of cell cycle and morphogenesis during organ formation. Elife, 13 PubMed ID: 38275142
Summary: Organ formation requires precise regulation of cell cycle and morphogenetic events. Using the Drosophila embryonic salivary gland (SG) as a model, this stud uncoveedr the role of the SP1/KLF transcription factor Huckebein (Hkb) in coordinating cell cycle regulation and morphogenesis. The hkb mutant SG exhibits defects in invagination positioning and organ size due to the abnormal death of SG cells. Normal SG development involves distal-to-proximal progression of endoreplication (endocycle), whereas hkb mutant SG cells undergo abnormal cell division, leading to cell death. Hkb represses the expression of key cell cycle and pro-apoptotic genes in the SG. Knockdown of cyclin E or cyclin-dependent kinase 1, or overexpression of fizzy-related rescues most of the morphogenetic defects observed in the hkb mutant SG. These results indicate that Hkb plays a critical role in controlling endoreplication by regulating the transcription of key cell cycle effectors to ensure proper organ formation. |
Athilingam, T., Nelanuthala, A. V. S., Breen, C., Karedla, N., Fritzsche, M., Wohland, T., Saunders, T. E. (2024). Long-range formation of the Bicoid gradient requires multiple dynamic modes that spatially vary across the embryo. Development, 151(3) PubMed ID: 38345326
Summary: Morphogen gradients provide essential positional information to gene networks through their spatially heterogeneous distribution, yet how they form is still hotly contested, with multiple models proposed for different systems. This study focused on the transcription factor Bicoid (Bcd), a morphogen that forms an exponential gradient across the anterior-posterior (AP) axis of the early Drosophila embryo. Using fluorescence correlation spectroscopy it was found that there are spatial differences in Bcd diffusivity along the AP axis, with Bcd diffusing more rapidly in the posterior. Such spatially varying differences in Bcd dynamics were established to be are sufficient to explain how Bcd can have a steep exponential gradient in the anterior half of the embryo and yet still have an observable fraction of Bcd near the posterior pole. In the nucleus, Bcd dynamics were demonstrated to be impacted by binding to DNA. Addition of the Bcd homeodomain to eGFP::NLS qualitatively replicates the Bcd concentration profile, suggesting this domain regulates Bcd dynamics. These results reveal how a long-range gradient can form while retaining a steep profile through much of its range. | Gallois, M., Menoret, D., Marques-Prieto, S., Montigny, A., Valenti, P., Moussian, B., Plaza, S., Payre, F., Chanut-Delalande, H. (2024). Pri peptides temporally coordinate transcriptional programs during epidermal differentiation.. Sci Adv, 10(6):eadg8816 PubMed ID: 38335295
Summary: To achieve a highly differentiated state, cells undergo multiple transcriptional processes whose coordination and timing are not well understood. In Drosophila embryonic epidermal cells, polished-rice (Pri) smORF peptides act as temporal mediators of ecdysone to activate a transcriptional program leading to cell shape remodeling. This study shows that the ecdysone/Pri axis concomitantly represses the transcription of a large subset of cuticle genes to ensure proper differentiation of the insect exoskeleton. The repression relies on the transcription factor Ken and persists for several days throughout early larval stages, during which a soft cuticle allows larval crawling. The onset of these cuticle genes normally awaits the end of larval stages when the rigid pupal case assembles, and their premature expression triggers abnormal sclerotization of the larval cuticle. These results uncovered a temporal switch to set up distinct structures of cuticles adapted to the animal lifestyle and which might be involved in the evolutionary history of insects. |
Monday December 9th - Adult Physiology and Metabolism |
Wodrich, A. P. K., Harris, B. T., Giniger, E. (2024). Manipulating mitochondrial reactive oxygen species alters survival in unexpected ways in a Drosophila model of neurodegeneration. bioRxiv, PubMed ID: 38585927
Summary: Reactive oxygen species (ROS) are associated with aging and neurodegeneration, but the significance of this association remains obscure. Here, using a Drosophila model of age-related neurodegeneration, this relationship was probbed in the pathologically relevant tissue, the brain, by quantifying three specific mitochondrial ROS and manipulating these redox species pharmacologically. The goal is to ask whether pathology-associated changes in redox state are detrimental for survival, whether they may be beneficial responses, or whether they are simply covariates of pathology that do not alter viability. Surprisingly, it was found that increasing mitochondrial H(2)O(2) correlates with improved survival. Evidence was also found that drugs that alter the mitochondrial glutathione redox potential modulate survival primarily through the compensatory effects they induce rather than through their direct effects on the final mitochondrial glutathione redox potential per se. The response to treatment with a redox-altering drug was found to vary dramatically depending on the age at which the drug is administered, the duration of the treatment, and the genotype of the individual receiving the drug. These data have important implications for the design and interpretation of studies investigating the effect of redox state on health and disease as well as on efforts to modify the redox state to achieve therapeutic goals. | Poidevin, M., Mazuras, N., Bontonou, G., Delamotte, P., Denis, B., Devilliers, M., Akiki, P., Petit, D., de Luca, L., Soulie, P., Gillet, C., Wicker-Thomas, C., Montagne, J. (2024). A fatty acid anabolic pathway in specialized-cells sustains a remote signal that controls egg activation in Drosophila. PLoS Genet, 20(3):e1011186 PubMed ID: 38483976
Summary: Egg activation, representing the critical oocyte-to-embryo transition, provokes meiosis completion, modification of the vitelline membrane to prevent polyspermy, and translation of maternally provided mRNAs. This transition is triggered by a calcium signal induced by spermatozoon fertilization in most animal species, but not in insects. In Drosophila melanogaster, mature oocytes remain arrested at metaphase-I of meiosis and the calcium-dependent activation occurs while the oocyte moves through the genital tract. This study discovered that the oenocytes of fruitfly females are required for egg activation. Oenocytes, cells specialized in lipid-metabolism, are located beneath the abdominal cuticle. In adult flies, they synthesize the fatty acids (FAs) that are the precursors of cuticular hydrocarbons (CHCs), including pheromones. The oenocyte-targeted knockdown of a set of FA-anabolic enzymes, involved in very-long-chain fatty acid (VLCFA) synthesis, leads to a defect in egg activation. Given that some but not all of the identified enzymes are required for CHC/pheromone biogenesis, this putative VLCFA-dependent remote control may rely on an as-yet unidentified CHC or may function in parallel to CHC biogenesis. Additionally, it was discovered that the most posterior ventral oenocyte cluster is in close proximity to the uterus. Since oocytes dissected from females deficient in this FA-anabolic pathway can be activated in vitro, this regulatory loop likely operates upstream of the calcium trigger. These findings provide the first evidence that a physiological extra-genital signal remotely controls egg activation. Moreover, this study highlights a potential metabolic link between pheromone-mediated partner recognition and egg activation. |
Matsuka, M., Otsune, S., Sugimori, S., Tsugita, Y., Ueda, H., Nakagoshi, H. (2024). Fecundity is optimized by levels of nutrient signal-dependent expression of Dve and EcR in Drosophila male accessory gland. Dev Biol, 508:8-23 PubMed ID: 38199580 Steroid hormones play various physiological roles including metabolism and reproduction. Steroid hormones in insects are ecdysteroids, and the major form in Drosophila melanogaster is ecdysone. In Drosophila males, the accessory gland is responsive to nutrient-dependent regulation of fertility/fecundity. The accessory gland is composed of two types of binucleated epithelial cells: a main cell and a secondary cell (SC). The transcription factors Defective proventriculus (Dve), Abdominal-B, and Ecdysone receptors (EcRs) are strongly expressed in adult SCs. This EcR expression is regulated by parallel pathways of nutrient signaling and the Dve activity. Induction of Dve expression is also dependent on nutrient signaling, and it becomes nutrient signal-independent during a restricted period of development. Forced dve expression during the restricted period significantly increased the number of SCs. This study provides evidence that the level of nutrient signal-dependent Dve expression during the restricted period determines the number of SCs, and that ecdysone signaling is also crucial to optimize male fecundity through nutrient signal-dependent survival and maturation of SCs. | Ahmad, M., Wu, S., Guo, X., Perrimon, N., He, L. (2024). Sensing of dietary amino acids and regulation of calcium dynamics in adipose tissues through Adipokinetic hormone in Drosophila. bioRxiv, PubMed ID: 38496667
Summary: Nutrient sensing and the subsequent metabolic responses are fundamental functions of animals, closely linked to diseases such as type 2 diabetes /a >and various obesity-related diseases. Drosophila melanogaster has emerged as an excellent model for investigating metabolism and its associated disorders. This study used live-cell imaging to demonstrate that the fly functional homolog of mammalian glucagon, Adipokinetic hormone (AKH), secreted from AKH hormone-producing cells (APCs) in the corpora cardiaca, stimulates intracellular Ca (2+) waves in the larval fat body/adipose tissue to promote lipid metabolism. Further, it was shown that specific dietary amino acids activate the APCs, leading to increased intracellular Ca (2+) and subsequent AKH secretion. Finally, a comparison of Ca (2+) dynamics in larval and adult fat bodies revealed different mechanisms of regulation, highlighting the interplay of pulses of AKH secretion, extracellular diffusion of the hormone, and intercellular communication through gap junctions. This study underscores the suitability of Drosophila as a powerful model for exploring real-time nutrient sensing and inter-organ communication dynamics. |
Martelli, F., Lin, J., Mele, S., Imlach, W., Kanca, O., Barlow, C. K., Paril, J., Schittenhelm, R. B., Christodoulou, J., Bellen, H. J., Piper, M. D. W., Johnson, T. K. (2024). Identifying potential dietary treatments for inherited metabolic disorders using Drosophila nutrigenomics. JCell Rep, 43(3):113861 PubMed ID: 38416643
Summary: Inherited metabolic disorders are a group of genetic conditions that can cause severe neurological impairment and child mortality. Uniquely, these disorders respond to dietary treatment; however, this option remains largely unexplored because of low disorder prevalence and the lack of a suitable paradigm for testing diets. This study screened 35 Drosophila amino acid disorder models for disease-diet interactions and found 26 with diet-altered development and/or survival. Using a targeted multi-nutrient array, the interaction was examine in a model of isolated sulfite oxidase deficiency, an infant-lethal disorder. We show that dietary cysteine depletion normalizes their metabolic profile and rescues development, neurophysiology, behavior, and lifelong fly survival, thus providing a basis for further study into the pathogenic mechanisms involved in this disorder. Our work highlights the diet-sensitive nature of metabolic disorders and establishes Drosophila as a valuable tool for nutrigenomic studies for informing potential dietary therapies. | Hoxha, V., Shrestha, G., Baloch, N., Collevechio, S., Laszczyk, R., Roman, G. (2024). TBI and Tau Loss of Function Both Affect Naive Ethanol Sensitivity in Drosophila. Int J Mol Sci, 25(6) PubMed ID: 38542275
Summary: Traumatic brain injury (TBI) is associated with alcohol abuse and higher ethanol sensitivity later in life. Currently, it is poorly understood how ethanol sensitivity changes with time after TBI and whether there are sex-dependent differences in the relationship between TBI and ethanol sensitivity. This study uses the fruit fly Drosophila melanogaster to investigate how TBI affects alcohol sensitivity and whether the effects are sex-specific. The results indicate that flies have a significantly higher sensitivity to the intoxicating levels of ethanol during the acute phase post-TBI, regardless of sex. The increased ethanol sensitivity decreases as time progresses; however, females take longer than males to recover from the heightened ethanol sensitivity. Dietary restriction does not improve the negative effects of alcohol post-TBI. tau mutant flies exhibit a similar ethanol sensitivity to TBI flies. However, TBI increased the ethanol sensitivity of dtau(KO) mutants, suggesting that TBI and dtau loss of function have additive effects on ethanol sensitivity. |
Friday December 6th - Adult Neural Sevelopment, Structure and Function |
Weiss, J. T., Blundell, M. Z., Singh, P., Donlea, J. M. (2024). Sleep deprivation drives brain-wide changes in cholinergic presynapse abundance in Drosophila melanogaster. Proc Natl Acad Sci U S A, 121(13):e2312664121 PubMed ID: 38498719
Summary: Sleep is an evolutionarily conserved state that supports brain functions, including synaptic plasticity, in species across the animal kingdom. Hhis study examine the neuroanatomical and cell-type distribution of presynaptic scaling in the fly brain after sleep loss. Previous work showed that sleep loss drives accumulation of the active zone scaffolding protein Bruchpilot (BRP) within cholinergic Kenyon cells of the Drosophila melanogaster mushroom body (MB), but not in other classes of MB neurons. To test whether similar cell type-specific trends in plasticity occur broadly across the brain, flp-based genetic reporter was used to label presynaptic BRP in cholinergic, dopaminergic, GABAergic, or glutamatergic neurons. Then whole-brain confocal image stacks of BRP intensity were collected to systematically quantify BRP, a marker of presynapse abundance, across 37 neuropil regions of the central fly brain. The results indicate that sleep loss, either by overnight (12-h) mechanical stimulation or chronic sleep disruption in insomniac mutants, broadly elevates cholinergic synapse abundance across the brain, while synapse abundance in neurons that produce other neurotransmitters undergoes weaker, if any, changes. Extending sleep deprivation to 24 h drives brain-wide upscaling in glutamatergic, but not other, synapses. Finally, overnight male-male social pairings induce increased BRP in excitatory synapses despite male-female pairings eliciting more waking activity, suggesting experience-specific plasticity. Within neurotransmitter class and waking context, BRP changes are similar across the 37 neuropil domains, indicating that similar synaptic scaling rules may apply across the brain during acute sleep loss and that sleep need may broadly alter excitatory-inhibitory balance in the central brain. | Schulz, J., Franz, H. R., Deimel, S. H., Widmann, A. (2024). Exploring neonicotinoid effects on Drosophila: insights into olfactory memory, neurotransmission, and synaptic connectivity. Frontiers in physiology, 15:1363943 PubMed ID: 38550256
Summary: Neonicotinoid insecticides interfere with cholinergic neurotransmission by binding to the nicotinic acetylcholine receptor, impairing cognitive functions such as olfaction and related behaviors, with a particular emphasis on olfactory memory due to its ecological impact. This study focuses on Drosophila. The aim of this Saturday is to establish the fruit fly as a valuable model organism for studying the effects of neonicotinoids on behavior and neuronal circuitry. Experiments were conducted to investigate the effects of short-term exposure to sublethal doses of the neonicotinoid imidacloprid, mimicking realistic environmental insecticide exposure, on the formation of odor memories. Additionally, synaptic contacts and cholinergic neurotransmission were evaluated within the mushroom body, the primary memory network of insects. The results showed significant impairments in odor memory formation in flies exposed to imidacloprid, with exposure during the adult stage showing more pronounced effects than exposure during the larval stage. Additionally, functional studies revealed a decrease in synaptic contacts within the intrinsic olfactory projection neurons and the mushroom body. Furthermore, another experiment showed an odor-dependent reduction in cholinergic neurotransmission within this network. In summary, employing Drosophila as a model organism provides a robust framework for investigating neonicotinoid effects and understanding their diverse impacts on insect physiology and behavior. Our study initiates the establishment of the fruit fly as a pivotal model for exploring neonicotinoid influences, shedding light on their effects on olfactory memory, neuronal integrity, and synaptic transmission. |
Le, J. Q., Ma, D., Dai, X., Rosbash, M. (2024). Light and dopamine impact two circadian neurons to promote morning wakefulness. bioRxiv, PubMed ID: 38496661
Summary: In both mammals and flies, circadian brain neurons orchestrate physiological oscillations and behaviors like wake and sleep; these neurons can be subdivided by morphology and by gene expression patterns. Recent single-cell sequencing studies identified 17 Drosophila circadian neuron groups. One of these include only two lateral neurons (LNs), which are marked by the expression of the neuropeptide ion transport peptide (ITP). Although these two ITP(+) LNs have long been grouped with five other circadian evening activity cells, inhibiting the two neurons alone strongly reduces morning activity; this indicates that they are prominent morning neurons. As dopamine signaling promotes activity in Drosophila like in mammals, dopamine might influence this morning activity function. Moreover, the ITP(+) LNs express higher mRNA levels than other LNs of the type 1-like dopamine receptor Dop1R1. Consistent with the importance of Dop1R1, CRISPR/Cas9 mutagenesis of this receptor only in the two ITP(+) LNs renders flies significantly less active in the morning, and ex vivo live imaging shows that dopamine increases cAMP levels in these two neurons; cell-specific mutagenesis of Dop1R1 eliminates this cAMP response to dopamine. Notably, the response is more robust in the morning, reflecting higher morning Dop1R1 mRNA levels in the two neurons. As morning levels are not elevated in constant darkness, this suggests light-dependent upregulation of morning Dop1R1 transcript levels. Taken together with enhanced morning cAMP response to dopamine, the data indicate how light stimulates morning wakefulness in flies, which mimics the important effect of light on morning wakefulness in humans. | Lv, M., Cai, R., Zhang, R., Xia, X., Li, X., Wang, Y., Wang, H., Zeng, J., Xue, Y., Mao, L., Li, Y. (2024). An octopamine-specific GRAB sensor reveals a monoamine relay circuitry that boosts aversive learning. bioRxiv, PubMed ID: 38559104
Summary: Octopamine (OA), analogous to norepinephrine in vertebrates, is an essential monoamine neurotransmitter in invertebrates that plays a significant role in various biological functions, including olfactory associative learning. However, the spatial and temporal dynamics of OA in vivo remain poorly understood due to limitations associated with the currently available methods used to detect it. To overcome these limitations, this study developed a genetically encoded GPCR activation-based (GRAB) OA sensor called GRAB(OA1.0). This sensor is highly selective for OA and exhibits a robust and rapid increase in fluorescence in response to extracellular OA. Using GRAB(OA1.0), OA release was monitored in the Drosophila mushroom body (MB), the fly's learning center, and found that OA is released in response to both odor and shock stimuli in an aversive learning model. This OA release requires acetylcholine (ACh) released from Kenyon cells, signaling via nicotinic ACh receptors. Finally, it was discovered that OA amplifies aversive learning behavior by augmenting dopamine-mediated punishment signals via Oct&bta;1R in dopaminergic neurons, leading to alterations in synaptic plasticity within the MB. Thus, this new GRAB(OA1.0) sensor can be used to monitor OA release in real-time under physiological conditions, providing valuable insights into the cellular and circuit mechanisms that underlie OA signaling. |
Kitamata, M., Otake, Y., Kitagori, H., Zhang, X., Maki, Y., Boku, R., Takeuchi, M., Nakagoshi, H. (2024). Functional opsin patterning for Drosophila color vision is established through signaling pathways in adjacent object-detection neurons. Development, 151(6) PubMed ID: 38421315
Summary: Vision is mainly based on two different tasks, object detection and color discrimination, carried out by photoreceptor (PR) cells. The Drosophila compound eye consists of ~800 ommatidia. Every ommatidium contains eight PR cells, six outer cells (R1-R6) and two inner cells (R7 and R8), by which object detection and color vision are achieved, respectively. Expression of opsin genes in R7 and R8 is highly coordinated through the instructive signal from R7 to R8, and two major ommatidial subtypes are distributed stochastically; pale type expresses Rh3/Rh5 and yellow type expresses Rh4/Rh6 in R7/R8. The homeodomain protein Defective proventriculus (Dve) is expressed in yellow-type R7 and in six outer PRs, and it is involved in Rh3 repression to specify the yellow-type R7. dve mutant eyes exhibited atypical coupling, Rh3/Rh6 and Rh4/Rh5, indicating that Dve activity is required for proper opsin coupling. Surprisingly, Dve activity in R1 is required for the instructive signal, whereas activity in R6 and R7 blocks the signal. These results indicate that functional coupling of two different neurons is established through signaling pathways from adjacent neurons that are functionally different. | Diamandi, J. A., Duckhorn, J. C., Miller, K. E., Weinstock, M., Leone, S., Murphy, M. R., Shirangi, T. R. (2024). Developmental remodeling repurposes larval neurons for sexual behaviors in adult Drosophila. Curr Biol, 34(6):1183-1193.e1183 PubMed ID: 38377996
Summary: Most larval neurons in Drosophila are repurposed during metamorphosis for functions in adult life, but their contribution to the neural circuits for sexually dimorphic behaviors is unknown. This study identified two interneurons in the nerve cord of adult Drosophila females that control ovipositor extrusion, a courtship rejection behavior performed by mated females. This study shows that these two neurons are present in the nerve cord of larvae as mature, sexually monomorphic interneurons. During pupal development, they acquire the expression of the sexual differentiation gene, doublesex; undergo doublesex-dependent programmed cell death in males; and are remodeled in females for functions in female mating behavior. These results demonstrate that the neural circuits for courtship in Drosophila are built in part using neurons that are sexually reprogrammed from former sex-shared activities in larval life. |
Thursday, December 5th - Evolution |
Perlmutter, J. I., Chapman, J. R., Wilkinson, M. C., Nevarez-Saenz, I., Unckless, R. L. (2024).. A single amino acid polymorphism in natural Metchnikowin alleles of Drosophila results in systemic immunity and life history tradeoffs. PLoS Genet, 20(3):e1011155 PubMed ID: 38466751
Summary: Antimicrobial peptides (AMPs) are at the interface of interactions between hosts and microbes and are therefore expected to be rapidly evolving in a coevolutionary arms race with pathogens. In contrast, previous work demonstrated that insect AMPs tend to evolve more slowly than the genome average. Metchikowin (Mtk) is a Drosophila AMP that has a single amino acid residue that segregates as either proline (P) or arginine (R) in populations of four different species, some of which diverged more than 10 million years ago. These results suggest that there is a distinct functional importance to each allele. The most likely hypotheses are driven by two main questions: does each allele have a different efficacy against different specific pathogens (specificity hypothesis)? Or, is one allele a more potent antimicrobial, but with a host fitness cost (autoimmune hypothesis)? To assess their functional differences, D. melanogaster lines were created with the P allele, R allele, or Mtk null mutation using CRISPR/Cas9 genome editing and a series of life history and infection assays was performed to assess them. In males, testing of systemic immune responses to a repertoire of bacteria and fungi demonstrated that the R allele performs as well or better than the P and null alleles with most infections. Females show some results that contrast with males, with Mtk alleles either not contributing to survival or with the P allele outperforming the R allele. In addition, measurements of life history traits demonstrate that the R allele is more costly in the absence of infection for both sexes. These results are consistent with both the specificity hypothesis (either allele can perform better against certain pathogens depending on context), and the autoimmune hypothesis (the R allele is generally the more potent antimicrobial in males, and carries a fitness cost). These results provide strong in vivo evidence that differential fitness with or without infection and sex-based functional differences in alleles may be adaptive mechanisms of maintaining immune gene polymorphisms in contrast with expectations of rapid evolution. Therefore, a complex interplay of forces including pathogen species and host sex may lead to balancing selection for immune genotypes. Strikingly, this selection may act on even a single amino acid polymorphism in an AMP. | Vesala, L., Basikhina, Y., Tuomela, T., Nurminen, A., Siukola, E., Vale, P. F., Salminen, T. S. (2024). Mitochondrial perturbation in immune cells enhances cell-mediated innate immunity in Drosophila. BMC Biol, 22(1):60 PubMed ID: 38475850 ID
Summary: Mitochondria participate in various cellular processes including energy metabolism, apoptosis, autophagy, production of reactive oxygen species, stress responses, inflammation and immunity. However, the role of mitochondrial metabolism in immune cells and tissues shaping the innate immune responses are not yet fully understood. This study investigated the effects of tissue-specific mitochondrial perturbation on the immune responses at the organismal level. Genes for oxidative phosphorylation (OXPHOS) complexes cI-cV were knocked down in the fruit fly Drosophila melanogaster, targeting the two main immune tissues, the fat body and the immune cells (hemocytes). While OXPHOS perturbation in the fat body was detrimental, hemocyte-specific perturbation led to an enhanced immunocompetence. This was accompanied by the formation of melanized hemocyte aggregates (melanotic nodules), a sign of activation of cell-mediated innate immunity. Furthermore, the hemocyte-specific OXPHOS perturbation induced immune activation of hemocytes, resulting in an infection-like hemocyte profile and an enhanced immune response against parasitoid wasp infection. In addition, OXPHOS perturbation in hemocytes resulted in mitochondrial membrane depolarization and upregulation of genes associated with the mitochondrial unfolded protein response. Overall, this study showed that while the effects of mitochondrial perturbation on immune responses are highly tissue-specific, mild mitochondrial dysfunction can be beneficial in immune-challenged individuals and contributes to variation in infection outcomes among individuals. |
Wang, L., Zhang, G., Li, Q., Lu, F., Yang, K., Dai, X. (2024).. Carrageenan oligosaccharide alleviates intestinal damage via gut microflora through activating IMD/relish pathway in female Drosophila melanogaster. Faseb j, 38(3):e23455 PubMed ID: 38308636
Summary: Recent evidence suggests the anti-inflammatory effect of carrageenan oligosaccharides (COS). The effects of COS on intestinal injury induced by 0.6% sodium dodecyl sulfate (SDS) and the molecular mechanisms involved were investigated in this study. 0.625, 1.25, and 2.5 mg/mL COS in diet had no toxic effect in flies, and they could all prolong SDS-treated female flies' survival rate. 1.25 mg/mL COS prevented the development of inflammation by improving the intestinal barrier integrity and maintaining the intestinal morphology stability, inhibited the proliferation of intestine stem cells (ISCs), and the production of lysosomes induced by SDS, accompanied by a decrease in the expression of autophagy-related genes. Moreover, COS decreased the active oxygen species (ROS) content in gut and increased the antioxidant activity in SDS-induced female flies, while COS still played a role in increasing survival rate and decreasing intestinal leakage in CncC-RNAi flies. The improvement of anti-inflammation capacity may be associated with the regulation of intestinal microflora with COS supplementation for Drosophila melanogaster. COS changed the gut microbiota composition, and COS had no effect on germ-free (GF) flies. It is highlighted that COS could not work in Relish-RNAi flies, indicating relish is required for COS to perform beneficial effects. These results provide insights into the study of gut microbiota interacting with COS to modulate intestinal inflammation in specific hosts. | Xiong, P., Wang, W. W., Liu, X. S., Wang, Y. F., Wang, J. L. (2024). A CTL - Lys immune function maintains insect metamorphosis by preventing gut bacterial dysbiosis and limiting opportunistic infections. BMC Biol, 22(1):54 PubMed ID: 38448930
Summary: Gut bacteria are beneficial to the host, many of which must be passed on to host offspring. During metamorphosis, the midgut of holometabolous insects undergoes histolysis and remodeling, and thus risks losing gut bacteria. Strategies employed by holometabolous insects to minimize this risk are obscure. How gut bacteria affect host insects after entering the hemocoel and causing opportunistic infections remains largely elusive. This study used holometabolous Helicoverpa armigera as a model and found low Lactobacillus load, high level of a C-type lectin (CTL) gene CD209 antigen-like protein 2 (CD209) and its downstream lysozyme 1 (Lys1) in the midgut of the wandering stage. CD209 or Lys1 depletion increased the load of midgut Lactobacillus, which further translocate to the hemocoel. In particular, CD209 or Lys1 depletion, injection of Lactobacillus plantarum, or translocation of midgut L. plantarum into the hemocoel suppressed 20-hydroxyecdysone (20E) signaling and delayed pupariation. Injection of L. plantarum decreased triacylglycerol and cholesterol storage, which may result in insufficient energy and 20E available for pupariation. Further, Lysine-type peptidoglycan, the major component of gram-positive bacterial cell wall, contributed to delayed pupariation and decreased levels of triacylglycerols, cholesterols, and 20E, in both H. armigera and Drosophila melanogaster. A mechanism by which (Lactobacillus-induced) opportunistic infections delay insect metamorphosis was found, namely by disturbing the homeostasis of lipid metabolism and reducing 20E production. Moreover, the immune function of CTL - Lys was characterized for insect metamorphosis by maintaining gut homeostasis and limiting the opportunistic infections. |
Gao, B., Li, P., Zhu, S. (2024). Single Deletion Unmasks Hidden Anti-Gram-Negative Bacterial Activity of an Insect Defensin-Derived Peptide. Journal of medicinal chemistry, 67(4):2512-2528 PubMed ID: 38335999
Summary: Insect defensins are a large family of antimicrobial peptides primarily active against Gram-positive bacteria. This study explored their hidden anti-Gram-negative bacterial potential via a nature-guided strategy inspired by natural deletion variants of Drosophila defensins. Referring to these variants, the equivalent region of an insect defensin with the first cysteine-containing N-terminus was deleted, and the last three cysteine-containing C-terminal regions remained. This 15-mer peptide exhibits low solubility and specifically targets Gram-positive bacteria. Further deletion of alanine-9 remarkably improves its solubility, unmasks its hidden anti-Gram-negative bacterial activity, and alters its states in different environments. Intriguingly, compared with the oxidized form, the 14-mer reduced peptide shows increased activity on Gram-positive and Gram-negative bacteria through a membrane-disruptive mechanism. The broad-spectrum activity and tolerance to high-salt environments and human serum, together with no toxicity to mammalian or human cells, make it a promising candidate for the design of new peptide antibiotics against Gram-negative bacterial infections. | Deichsel, S., Gahr, B. M., Mastel, H., Preiss, A., Nagel, A. C. (2024). Numerous Serine/Threonine Kinases Affect Blood Cell Homeostasis in Drosophila melanogaster. Cells, 13(7) PubMed ID: 38607015
Summary: Blood cells in Drosophila serve primarily innate immune responses. Various stressors influence blood cell homeostasis regarding both numbers and the proportion of blood cell types. The principle molecular mechanisms governing hematopoiesis are conserved amongst species and involve major signaling pathways like Notch, Toll, JNK, JAK/Stat or RTK. Albeit signaling pathways generally rely on the activity of protein kinases, their specific contribution to hematopoiesis remains understudied. This study assessed the role of Serine/Threonine kinases with the potential to phosphorylate the transcription factor Su(H) in crystal cell homeostasis. Su(H) is central to Notch signal transduction, and its inhibition by phosphorylation impedes crystal cell formation. Overall, nearly twenty percent of all Drosophila Serine/Threonine kinases were studied in two assays, global and hemocyte-specific overexpression and downregulation, respectively. Unexpectedly, the majority of kinases influenced crystal cell numbers, albeit only a few were related to hematopoiesis so far. Four kinases appeared essential for crystal cell formation, whereas most kinases restrained crystal cell development. This group comprises all kinase classes, indicative of the complex regulatory network underlying blood cell homeostasis. The rather indiscriminative response we observed opens the possibility that blood cells measure their overall phospho-status as a proxy for stress-signals, and activate an adaptive immune response accordingly. |
Tuesday, December 3rd - Chromatin |
Hendricks, E. L., Liebl, F. L. W. (2024). The CHD family chromatin remodeling enzyme, Kismet, promotes both clathrin-mediated and activity-dependent bulk endocytosis. JPLoS One, 19(3):e0300255 PubMed ID: 38512854
Summary: Chromodomain helicase DNA binding domain (CHD) proteins, including CHD7 and CHD8, remodel chromatin to enable transcriptional programs. Both proteins are important for proper neural development as heterozygous mutations in Chd7 and Chd8 are causative for CHARGE syndrome and correlated with autism spectrum disorders, respectively. The Drosophila homolog of CHD7 and CHD8, Kismet (Kis), promotes neurotransmission, endocytosis, and larval locomotion. Endocytosis is essential in neurons for replenishing synaptic vesicles, maintaining protein localization, and preserving the size and composition of the presynaptic membrane. Several forms of vesicles have been identified including clathrin-mediated endocytosis, which is coupled with neural activity and is the most prevalent form of synaptic endocytosis, and activity-dependent bulk endocytosis, which occurs during periods of intense stimulation. Kis modulates the expression of gene products involved in endocytosis including promoting shaggy/GSK3β expression while restricting PI3K92E. kis mutants electrophysiologically phenocopy a liquid facets mutant in response to paradigms that induce clathrin-mediated endocytosis and activity-dependent bulk endocytosis. Further, kis mutants do not show further reductions in endocytosis when activity-dependent bulk endocytosis or clathrin-mediated endocytosis are pharmacologically inhibited. Kis is important in postsynaptic "../aimorph/mesoderm.htm">muscl/e for proper endocytosis but the ATPase domain of Kis is dispensable for endocytosis. Collectively, these data indicate that Kis promotes both clathrin-mediated endocytosis and activity-dependent bulk endocytosis possibly by p sromoting transcription of several endocytic genes and maintaining the size of the synaptic vesicle pool. | Smith, I. R., Hendricks, E. L., Latcheva, N. K., Marenda, D. R., Liebl, F. L. W. (2024). The CHD Protein Kismet Restricts the Synaptic Localization of Cell Adhesion Molecules at the Drosophila Neuromuscular Junction. Int J Mol Sci, 25(5) PubMed ID: 38474321
Summary: The appropriate expression and localization of cell surface cell adhesion molecules must be tightly regulated for optimal synaptic growth and function. How neuronal plasma membrane proteins, including cell adhesion molecules, cycle between early endosomes and the plasma membrane is poorly understood. This study shows that the Drosophila homolog of the chromatin remodeling enzymes CHD7 and CHD8, Kismet, represses the synaptic levels of several cell adhesion molecules. Neuroligins 1 and 3 and the integrins αPS2 and βPS are increased at kismet mutant synapses but Kismet only directly regulates transcription of neuroligin 2. Kismet may therefore regulate synaptic CAMs indirectly by activating transcription of gene products that promote intracellular vesicle trafficking including endophilin B (endoB) and/or rab11. Knock down of EndoB in all tissues or neurons increases synaptic FasII while knock down of EndoB in kis mutants does not produce an additive increase in FasII. In contrast, neuronal expression of Rab11, which is deficient in kis mutants, leads to a further increase in synaptic FasII in kis mutants. These data support the hypothesis that Kis influences the synaptic localization of FasII by promoting intracellular vesicle trafficking through the early endosome. |
Crain, A. T., Butler, M. B., Hill, C. A., Huynh, M., McGinty, R. K., Duronio, R. J. (2024). Drosophila melanogaster Set8 and L(3)mbt function in gene expression independently of histone H4 lysine 20 methylation. bioRxiv, PubMed ID: 38559189
Summary: Mono-methylation of Lysine 20 of histone H4 (H4K20me1) is catalyzed by Set8 and thought to play important roles in many aspects of genome function that are mediated by H4K20me-binding proteins. This study interrogated this model in a developing animal by comparing in parallel the transcriptomes of Set8null, H4 (K20R/A) , and l(3)mbt mutant Drosophila melanogaster We found that the gene expression profiles of H4K20A and H4K20R larvae are markedly different than Set8 (null) larvae despite similar reductions in H4K20me1. Set8null mutant cells have a severely disrupted transcriptome and fail to proliferate in vivo , but these phenotypes are not recapitulated by mutation of H4K20 indicating that the developmental defects of Set8null animals are largely due to H4K20me1-independent effects on gene expression. Further, the H4K20me1 binding protein L(3)mbt is recruited to the transcription start sites of most genes independently of H4K20me even though genes bound by L(3)mbt have high levels of H4K20me1. Moreover, both Set8 and L(3)mbt bind to purified H4K20R nucleosomes in vitro. It is concluded that gene expression changes in Set8null and H4K20 mutants cannot be explained by loss of H4K20me1 or L(3)mbt binding to chromatin, and therefore that H4K20me1 does not play a large role in gene expression. | Yamamoto-Hino, M., Ariura, M., Tanaka, M., Iwasaki, Y. W., Kawaguchi, K., Shimamoto, Y., Goto, S. (2024). PIGB maintains nuclear lamina organization in skeletal muscle of Drosophila. J Cell Biol, 223(2) PubMed ID: 38261271
Summary: The nuclear lamina (NL) plays various roles and participates in nuclear integrity, chromatin organization, and transcriptional regulation. Lamin proteins, the main components of the NL, form a homogeneous meshwork structure under the nuclear envelope. Lamins are essential, but it is unknown whether their homogeneous distribution is important for nuclear function. This study found that PIGB, an enzyme involved in glycosylphosphatidylinositol (GPI) synthesis, is responsible for the homogeneous lamin meshwork in Drosophila. Loss of PIGB resulted in heterogeneous distributions of B-type lamin and lamin-binding proteins in larval muscles. These phenotypes were rescued by expression of PIGB lacking GPI synthesis activity. The PIGB mutant exhibited changes in lamina-associated domains that are large heterochromatic genomic regions in the NL, reduction of nuclear stiffness, and deformation of muscle fibers. These results suggest that PIGB maintains the homogeneous meshwork of the NL, which may be essential for chromatin distribution and nuclear mechanical properties. |
Mukherjee, A., Fallacaro, S., Ratchasanmuang, P., Zinski, J., Boka, A., Shankta, K., Mir, M. (2024).. A fine kinetic balance of interactions directs transcription factor hubs to genes. bioRxiv, PubMed ID: 38659757
Summary: Eukaryotic gene regulation relies on the binding of sequence-specific transcription factors (TFs). TFs bind chromatin transiently yet occupy their target sites by forming high-local concentration microenvironments (hubs and condensates) that increase the frequency of binding events. Despite their ubiquity, such microenvironments have been difficult to study in endogenous contexts due to technical limitations. This study overcome these limitations and investigated how hubs drive TF occupancy at their targets. Using a DNA binding perturbation to a hub-forming TF, Zelda, in Drosophila embryos, hub properties, including the stability and frequencies of associations to targets, were found to be key determinants of TF occupancy. These data suggest that the targeting of these hubs is driven not just by specific DNA motif recognition, but also by a fine-tuned kinetic balance of interactions between TFs and their co-binding partners. | McKowen, J. K., Dassanayake, M., Hart, C. M. (2024). . The Tofu mutation restores female fertility to Drosophila with a null BEAF mutation. bioRxiv, PubMed ID: 38405992
Summary: Compensatory mutations offer clues to deciphering the role of a particular protein in cellular processes. This study investigated an unknown compensatory mutation, present in the BEAFNP6377 fly line, that provides sufficient rescue of the defective ovary phenotype caused by null BEAF alleles to allow maintenance of fly stocks lacking the chromatin domain insulator proteins Boundary Element-Associated Factors BEAF-32A and BEAF-32B. This mutation was called Tofu. Both classical genetics and genomic sequencing were used to attempt to identify the mutation. Evidence was found that points to a mutation in a predicted Polycomb response element upstream of the ribbon gene, which may lead to aberrant rib expression. |
Friday, November 29th - Cell Cycle |
Matsuura, Y., Kaizuka, K., Inoue, Y. H. (2024). Essential Role of COPII Proteins in Maintaining the Contractile Ring Anchoring to the Plasma Membrane during Cytokinesis in Drosophila Male Meiosis. Int J Mol Sci, 25(8) PubMed ID: 38674111
Summary: Coatomer Protein Complex-II (COPII) mediates anterograde vesicle transport from the endoplasmic reticulum (ER) to the Golgi apparatus. This study reports that the COPII coatomer complex is constructed dependent on a small GTPase, Sar1, in spermatocytes before and during Drosophila male meiosis. COPII-containing foci co-localized with transitional endoplasmic reticulum (tER)-Golgi units. They showed dynamic distribution along astral microtubules and accumulated around the spindle pole, but they were not localized on the cleavage furrow (CF) sites. The depletion of the four COPII coatomer subunits, Sec16, or Sar1 that regulate COPII assembly resulted in multinucleated cell production after meiosis, suggesting that cytokinesis failed in both or either of the meiotic divisions. Although contractile actomyosin and anilloseptin rings (Anillin, and septin filaments collectively) were formed once plasma membrane ingression was initiated, they were frequently removed from the plasma membrane during furrowing. This study explored the factors conveyed toward the CF sites in the membrane via COPII-mediated vesicles. DE-cadherin-containing vesicles were formed depending on Sar1 and were accumulated in the cleavage sites. Furthermore, COPII depletion inhibited de novo plasma membrane insertion. These findings suggest that COPII vesicles supply the factors essential for the anchoring and/or constriction of the contractile rings at cleavage sites during male meiosis in Drosophila. | Khodaverdian, V., Sano, T., Maggs, L., Tomarchio, G., Dias, A., Clairmont, C., Tran, M., McVey, M. (2024). REV1 Coordinates a Multi-Faceted Tolerance Response to DNA Alkylation Damage and Prevents Chromosome Shattering in Drosophila melanogaster. bioRxiv, PubMed ID: 38405884
Summary: When replication forks encounter damaged DNA, cells utilize DNA damage tolerance mechanisms to allow replication to proceed. These include translesion synthesis at the fork, postreplication gap filling, and template switching via fork reversal or homologous recombination. The extent to which these different damage tolerance mechanisms are utilized depends on cell, tissue, and developmental context-specific cues, the last two of which are poorly understood. To address this gap, this study has investigated damage tolerance responses following alkylation damage in Drosophila melanogaster. Translesion synthesis, rather than template switching, was shown to be the preferred response to alkylation-induced damage in diploid larval tissues. Furthermore, it was shown that the REV1 protein plays a multi-faceted role in damage tolerance in Drosophila. Drosophila larvae lacking REV1 are hypersensitive to methyl methanesulfonate (MMS) and have highly elevated levels of gamma-H2Av foci and chromosome aberrations in MMS-treated tissues. Loss of the REV1 C-terminal domain (CTD), which recruits multiple translesion polymerases to damage sites, sensitizes flies to MMS. In the absence of the REV1 CTD, DNA polymerase eta and zeta become critical for MMS tolerance. In addition, flies lacking REV3, the catalytic subunit of polymerase zeta, require the deoxycytidyl transferase activity of REV1 to tolerate MMS. Together, these results demonstrate that Drosophila prioritize the use of multiple translesion polymerases to tolerate alkylation damage and highlight the critical role of REV1 in the coordination of this response to prevent genome instability. |
Pazhayam, N. M., Frazier, L. K., Sekelsky, J. (2024). Centromere-proximal suppression of meiotic crossovers in Drosophila is robust to changes in centromere number, repetitive DNA content, and centromere-clustering. Genetics, 226(3) PubMed ID: 38150397 and PubMed ID
Summary: Accurate segregation of homologous chromosomes during meiosis depends on both the presence and the regulated placement of crossovers (COs). The centromere effect, or CO exclusion in pericentromeric regions of the chromosome, is a meiotic CO patterning phenomenon that helps prevent nondisjunction, thereby protecting against chromosomal disorders and other meiotic defects. Despite being identified nearly a century ago, the mechanisms behind this fundamental cellular process remain unknown, with most studies of the Drosophila centromere effect focusing on local influences of the centromere and pericentric heterochromatin. This study sought to investigate whether dosage changes in centromere number and repetitive DNA content affect the strength of the centromere effect, using phenotypic recombination mapping. Additionally, he effects of repetitive DNA function on centromere effect strength was studied using satellite DNA-binding protein mutants displaying defective centromere-clustering in meiotic nuclei. Despite what previous studies suggest, the results show that the Drosophila centromere effect is robust to changes in centromere number, repetitive DNA content, as well as repetitive DNA function. This study suggests that the centromere effect is unlikely to be spatially controlled, providing novel insight into the mechanisms behind the Drosophila centromere effect. | Sun, S., Defosse, T., Boyd, A., Sop, J., Verderose, F., Surray, D., Aziz, M., Howland, M., Wu, S., Changela, N., Jang, J., Schindler, K., Xing, J., McKim, K. S. (2024). Whole transcriptome screening for novel genes involved in meiosis and fertility in Drosophila melanogaster. Sci Rep, 14(1):3602 PubMed ID: 38351116
Summary: Reproductive success requires the development of viable oocytes and the accurate segregation of chromosomes during meiosis. Failure to segregate chromosomes properly can lead to infertility, miscarriages, or developmental disorders. A variety of factors contribute to accurate chromosome segregation and oocyte development, such as spindle assembly and sister chromatid cohesion. However, many proteins required for meiosis remain unknown. This study aimed to develop a screening pipeline for identifying novel meiotic and fertility genes using the genome of Drosophila melanogaster. To accomplish this goal, genes upregulated within meiotically active tissues were identified. More than 240 genes with no known function were silenced using RNA interference (RNAi) and the effects on meiosis and fertility were assessed. 94 genes were identified that when silenced caused infertility and/or high levels of chromosomal nondisjunction. The vast majority of these genes have human and mouse homologs that are also poorly studied. Through this screening process, novel genes were identified that are crucial for meiosis and oocyte development but have not been extensively studied in human or model organisms. Understanding the function of these genes will be an important step towards the understanding of their biological significance during reproduction. |
Joshi, J. N., Changela, N., Mahal, L., Defosse, T., Jang, J., Wang, L. I., Das, A., Shapiro, J. G., McKim, K. (2024). Meiosis-specific functions of kinetochore protein SPC105R required for chromosome segregation in Drosophila oocytes. bioRxiv. PubMed ID: 38559067
Summary: The reductional division of meiosis I requires the separation of chromosome pairs towards opposite poles. Previous work has implicated the outer kinetochore protein SPC105R/KNL1 in driving meiosis I chromosome segregation through lateral attachments to microtubules and co-orientation of sister centromeres. To identify the domains of SPC105R that are critical for meiotic chromosome segregation, an RNAi-resistant gene expression system was developed. SPC105R's C-terminal domain (aa 1284-1960) was found to be necessary and sufficient for recruiting NDC80 to the kinetochore and building the outer kinetochore. Furthermore, the C-terminal domain recruits BUBR1, which in turn recruits the cohesion protection proteins MEI-S332 and PP2A. Of the remaining 1283 amino acids, the first 473 were found most important for meiosis. The first 123 amino acids of the N-terminal half of SPC105R contain the conserved SLRK and RISF motifs that are targets of PP1 and Aurora B kinase and are most important for regulating the stability of microtubule attachments and maintaining metaphase I arrest. The region between amino acids 124 and 473 are required for two activities that are critical for accurate chromosome segregation in meiosis I, lateral microtubule attachments and bi-orientation of homologs. | Wood, B. W., Shi, X., Weil, T. T. (2024). F-actin coordinates spindle morphology and function in Drosophila meiosis. PLoS Genet, 20(1):e1011111 PubMed ID: 38206959
Summary: Meiosis is a highly conserved feature of sexual reproduction that ensures germ cells have the correct number of chromosomes prior to fertilization. A subset of microtubules, known as the spindle, are essential for accurate chromosome segregation during meiosis. Building evidence in mammalian systems has recently highlighted the unexpected requirement of the actin cytoskeleton in chromosome segregation; a network of spindle actin filaments appear to regulate many aspects of this process. Thisa study shows that Drosophila oocytes also have a spindle population of actin that appears to regulate the formation of the microtubule spindle and chromosomal movements throughout meiosis. Genetic and pharmacological disruption of the actin cytoskeleton was demonstrated to have a significant impact on spindle morphology, dynamics, and chromosome alignment and segregation during maturation and the metaphase-anaphase transition. A role was revealed for calcium in maintaining the microtubule spindle and spindle actin. Together, these data highlights potential conservation of morphology and mechanism of the spindle actin during meiosis. |
Tuesday, November 26th - Metabolism and Physiology |
Hunter-Manseau, F., Cormier, S. B., Strang, R., Pichaud, N. (2024). Fasting as a precursor to high-fat diet enhances mitochondrial resilience in Drosophila melanogaster. Insect Sci, PubMed ID: 38514255
Summary: Changes in diet type and nutrient availability can impose significant environmental stress on organisms, potentially compromising physiological functions and reproductive success. In nature, dramatic fluctuations in dietary resources are often observed and adjustments to restore cellular homeostasis are crucial to survive this type of stress. This study exposed male Drosophila melanogaster to two modulated dietary treatments: one without a fasting period before exposure to a high-fat diet and the other with a 24-h fasting period. Then mitochondrial metabolism and molecular responses to these treatments was investigated. Exposure to a high-fat diet without a preceding fasting period resulted in disrupted mitochondrial respiration, notably at the level of complex I. On the other hand, a short fasting period before the high-fat diet maintained mitochondrial respiration. Generally, transcript abundance of genes associated with mitophagy, heat-shock proteins, mitochondrial biogenesis, and nutrient sensing pathways increased either slightly or significantly following a fasting period and remained stable when flies were subsequently put on a high-fat diet, whereas a drastic decrease of almost all transcript abundances was observed for all these pathways when flies were exposed directly to a high-fat diet. Moreover, mitochondrial enzymatic activities showed less variation after the fasting period than the treatment without a fasting period. Overall, this study sheds light on the mechanistic protective effects of fasting prior to a high-fat diet and highlights the metabolic flexibility of Drosophila mitochondria in response to abrupt dietary changes and have implication for adaptation of species to their changing environment. | Aziz, R. A., Ramesh, P., Suchithra, K. V., Stothard, P., Narayana, V. K., Raghu, S. V., Shen, F. T., Young, C. C., Prasad, T. S. K., Hameed, A. (2024). Comprehensive insights into the impact of bacterial indole-3-acetic acid on sensory preferences in Drosophila melanogaster. Sci Rep, 14(1):8311 PubMed ID: 38594449
Summary: Several bacteria of environmental and clinical origins, including some human-associated strains secrete a cross-kingdom signaling molecule indole-3-acetic acid (IAA). IAA is a tryptophan (trp) derivative mainly known for regulating plant growth and development as a hormone. However, the nutritional sources that boost IAA secretion in bacteria and the impact of secreted IAA on non-plant eukaryotic hosts remained less explored. This study demonstrated significant trp-dependent IAA production in Pseudomonas juntendi NEEL19 when provided with ethanol as a carbon source in liquid cultures. IAA was further characterized to modulate the odor discrimination, motility and survivability in Drosophila melanogaster. A detailed analysis of IAA-fed fly brain proteome using high-resolution mass spectrometry showed significant alteration in the proteins governing neuromuscular features, audio-visual perception and energy metabolism as compared to IAA-unfed controls. Sex-wise variations in differentially regulated proteins were witnessed despite having similar visible changes in chemo perception and psychomotor responses in IAA-fed flies. This study not only revealed ethanol-specific enhancement in trp-dependent IAA production in P. juntendi, but also showed marked behavioral alterations in flies for which variations in an array of proteins governing odor discrimination, psychomotor responses, and energy metabolism are held responsible. This study provided novel insights into disruptive attributes of bacterial IAA that can potentially influence the eukaryotic gut-brain axis having broad environmental and clinical implications. |
Gururaja Rao, S., Lam, A., Seeley, S., Park, J., Aruva, S., Singh, H. (2024). . The BK(Ca) (slo) channel regulates the cardiac function of Drosophila. Physiological reports, 12(7):e15996 PubMed ID: 38561252
Summary: The large conductance, calcium, and voltage-active potassium channels (BK(Ca)) were originally discovered in Drosophila melanogaster as slowpoke (slo). They are extensively characterized in fly models as ion channels for their roles in neurological and muscular function, as well as aging. BK(Ca) is known to modulate cardiac rhythm and is localized to the mitochondria. Activation of mitochondrial BK(Ca) causes cardioprotection from ischemia-reperfusion injury, possibly via modulating mitochondrial function in adult animal models. However, the role of BK(Ca) in cardiac function is not well-characterized, partially due to its localization to the plasma membrane as well as intracellular membranes and the wide array of cells present in mammalian hearts. This study demonstrates for the first time a direct role for BK(Ca) in cardiac function and cardioprotection from IR injury using the Drosophila model system. It was also discovered that the BK(Ca) channel plays a role in the functioning of aging hearts. This study establishes the presence of BK(Ca) in the fly heart and ascertains its role in aging heart function. | Jiang, N. J., Dong, X., Veit, D., Hansson, B. S., Knaden, M. (2024). Elevated ozone disrupts mating boundaries in drosophilid flies. Nat Commun, 15(1):2872 PubMed ID: 38605003
Summary: Animals employ different strategies to establish mating boundaries between closely related species, with sex pheromones often playing a crucial role in identifying conspecific mates. Many of these pheromones have carbon-carbon double bonds, making them vulnerable to oxidation by certain atmospheric oxidant pollutants, including ozone. This study investigated whether increased ozone compromises species boundaries in drosophilid flies. We show that short-term exposure to increased levels of ozone degrades pheromones of Drosophila melanogaster, D. simulans, D. mauritiana, as well as D. sechellia, and induces hybridization between some of these species. As many of the resulting hybrids are sterile, this could result in local population declines. However, hybridization between D. simulans and D. mauritiana as well as D. simulans and D. sechellia results in fertile hybrids, of which some female hybrids are even more attractive to the males of the parental species. Our experimental findings indicate that ozone pollution could potentially induce breakdown of species boundaries in insects. |
van Heerwaarden, B., Sgro, C., Kellermann, V. M. (2024). Threshold shifts and developmental temperature impact trade-offs between tolerance and plasticity. Proceedings Biological sciences, 291(2016):20232700 PubMed ID: 38320612
Summary: Mounting evidence suggests that ectotherms are already living close to their upper physiological thermal limits. Phenotypic plasticity has been proposed to reduce the impact of climate change in the short-term providing time for adaptation, but the tolerance-plasticity trade-off hypothesis predicts organisms with higher tolerance have lower plasticity. Empirical evidence is mixed, which may be driven by methodological issues such as statistical artefacts, nonlinear reaction norms, threshold shifts or selection. This study examined whether threshold shifts (organisms with higher tolerance require stronger treatments to induce maximum plastic responses) influence tolerance-plasticity trade-offs in hardening capacity for desiccation tolerance and critical thermal maximum (CT(MAX)) across Drosophila species with varying distributions/sensitivity to desiccation/heat stress. Evidence was found for threshold shifts in both traits; species with higher heat/desiccation tolerance required longer hardening treatments to induce maximum hardening responses. Species with higher heat tolerance also showed reductions in hardening capacity at higher developmental acclimation temperatures. Trade-off patterns differed depending on the hardening treatment used and the developmental temperature flies were exposed to. Based on these findings, studies that do not consider threshold shifts, or that estimate plasticity under a narrow set of environments, will have a limited ability to assess trade-off patterns and differences in plasticity across species/populations more broadly. | Zhu, H., Ludington, W. B., Spradling, A. C. (2024). Cellular and molecular organization of the Drosophila foregut. Proc Natl Acad Sci U S A, 121(11):e2318760121 PubMed ID: 38442150
Summary: The animal foregut is the first tissue to encounter ingested food, bacteria, and viruses. This study characterized the adult Drosophila foregut using transcriptomics to better understand how it triages consumed items for digestion or immune response and manages resources. Cell types were assigned and validated using GFP-tagged and Gal4 reporter lines. Foregut-associated neuroendocrine cells play a major integrative role by coordinating gut activity with nutrition, the microbiome, and circadian cycles; some express clock genes. Multiple epithelial cell types comprise the proventriculus, the central foregut organ that secretes the peritrophic matrix (PM) lining the gut. Analyzing cell types synthesizing individual PM layers revealed abundant mucin production close to enterocytes, similar to the mammalian intestinal mucosa. The esophagus and salivary gland express secreted proteins likely to line the esophageal surface, some of which may generate a foregut commensal niche housing specific gut microbiome species. Overall, these results imply that the foregut coordinates dietary sensing, hormonal regulation, and immunity in a manner that has been conserved during animal evolution. |
Monday, November 25th - Evolution |
Cavigliasso, F., Savitsky, M., Koval, A., Erkosar, B., Savary, L., Gallart-Ayala, H., Ivanisevic, J., Katanaev, V. L., Kawecki, T. J. (2024). Cis-regulatory polymorphism at fiz ecdysone oxidase contributes to polygenic evolutionary response to malnutrition in Drosophila. PLoS Genet, 20(3):e1011204 PubMed ID: 38452112
Summary: This study investigated the contribution of a candidate gene, fezzik (fiz), to complex polygenic adaptation to juvenile malnutrition in Drosophila melanogaster. Experimental populations maintained for >250 generations of experimental evolution to a nutritionally poor larval diet (Selected populations) evolved several-fold lower fiz expression compared to unselected Control populations. This divergence in fiz expression is shown to be mediated by a cis-regulatory polymorphism. This polymorphism, originally sampled from a natural population in Switzerland, is distinct from a second cis-regulatory SNP previously identified in non-African D. melanogaster populations, implying that two independent cis-regulatory variants promoting high fiz expression segregate in non-African populations. Enzymatic analyses of Fiz protein expressed in E. coli demonstrate that it has ecdysone oxidase activity acting on both ecdysone and 20-hydroxyecdysone. Four of five fiz paralogs annotated to ecdysteroid metabolism also show reduced expression in Selected larvae, implying that malnutrition-driven selection favored general downregulation of ecdysone oxidases. Finally, as an independent test of the role of fiz in poor diet adaptation, fiz knockdown by RNAi was shown to result in faster larval growth on the poor diet, but at the cost of greatly reduced survival. These results imply that downregulation of fiz in Selected populations was favored by selection on the nutritionally poor diet because of its role in suppressing growth in response to nutrient shortage. However, they suggest that fiz downregulation is only adaptive in combination with other changes evolved by selected populations, which ensure that the organism can sustain the faster growth promoted by fiz downregulation. | Nunes, W. V. B., Oliveira, D. S., Dias, G. R., Carvalho, A. B., Caruso I, P., Biselli, J. M., Guegen, N., Akkouche, A., Burlet, N., Vieira, C., Carareto, C. M. A. (2024). A comprehensive evolutionary scenario for the origin and neofunctionalization of the Drosophila speciation gene Odysseus (OdsH). G3 (Bethesda), 14(3) PubMed ID: 38156703
Summary: Odysseus (OdsH) was the first speciation gene described in Drosophila related to hybrid sterility in offspring of mating between Drosophila mauritiana and Drosophila simulans. Its origin is attributed to the duplication of the gene unc-4 in the subgenus Sophophora. By using a much larger sample of Drosophilidae species, this study showed that contrary to what has been previously proposed, OdsH origin occurred 62 MYA. Evolutionary rates, expression, and transcription factor-binding sites of OdsH evidence that it may have rapidly experienced neofunctionalization in male sexual functions. Furthermore, the analysis of the OdsH peptide allowed the identification of mutations of D. mauritiana that could result in incompatibility in hybrids. In order to find if OdsH could be related to hybrid sterility, beyond Sophophora,the expression of OdsH was explored in Drosophila arizonae and Drosophila mojavensis, a pair of sister species with incomplete reproductive isolation. The data indicated that OdsH expression is not atypical in their male-sterile hybrids. In conclusion, it is proposed that the origin of OdsH occurred earlier than previously proposed, followed by neofunctionalization. These results also suggested that its role as a speciation gene might be restricted to D. mauritiana and D. simulans. |
Mishra, P., Rundle, H. D., Agrawal, A. F. (2024). The evolution of sexual dimorphism in gene expression in response to a manipulation of mate competition.. Evolution, 78(4):746-757 PubMed ID: 38270064
Summary: Many genes are differentially expressed between males and females and patterns of sex-biased gene expression (SBGE) vary among species. Some of this variation is thought to have evolved in response to differences in mate competition among species that cause varying patterns of sex-specific selection.This study used experimental evolution to test this by quantifying SBGE and sex-specific splicing in 15 Drosophila melanogaster populations that evolved for 104 generations in mating treatments that removed mate competition via enforced monogamy, or allowed mate competition in either small, simple, or larger, structurally more complex mating environments. Consistent with sex-specific selection affecting SBGE, initially sex-biased genes diverged in expression more among treatments than unbiased genes, and there was greater expression divergence for male- than female-biased genes. It has been suggested the transcriptome should be "feminized" under monogamy because of the removal of sexual selection on males; this was not observe, likely because selection differs in additional ways between monogamy vs. polygamy. Significant divergence in average expression dimorphism between treatments was observed and, in some treatment comparisons, the direction of the divergence differed across different sex-bias categories. There was not a generalized reduction in expression dimorphism under enforced monogamy. | Pennell, T. M., Sharma, M. D., Sutter, A., Wilson, D. T., House, C. M., Hosken, D. J. (2024). The condition-dependence of male genital size and shape. Ecology and evolution 14(3):e11180 PubMed ID: 38495435
Summary: The male genitals of internal fertilisers evolve rapidly and divergently, and sexual selection is generally responsible for this. Many sexually selected traits are condition-dependent-with their expression dependent upon the resources available to be allocated to them-as revealed by genetic or environmental manipulations of condition. However, it is not clear whether male genitals are also condition-dependent. This study manipulated conditions in two ways (via inbreeding and diet) to test the condition-dependence of the genital arch of Drosophila simulans. Genital size but not genital shape was found to suffer from inbreeding depression, whereas genital size and shape were affected by dietary manipulation of condition. The differential effects of these treatments likely reflect underlying genetic architecture that has been shaped by past selection: inbreeding depression is only expected when traits have a history of directional selection, while diet impacts traits regardless of historical selection. Nonetheless, these results suggest genitals can be condition-dependent like other sexually selected traits. |
Liu, G. Y., Jouandin, P., Bahng, R. E., Perrimon, N., Sabatini, D. M. (2024). An evolutionary mechanism to assimilate new nutrient sensors into the mTORC1 pathway. Nat Commun, 15(1):2517 PubMed ID: 38514639
Summary: Animals sense and respond to nutrient availability in their environments, a task coordinated in part by the mTOR complex 1 (mTORC1) pathway. mTORC1 regulates growth in response to nutrients and, in mammals, senses specific amino acids through specialized sensors that bind the GATOR1/2 signaling hub. Given that animals can occupy diverse niches, it was hypothesized that the pathway might evolve distinct sensors in different metazoan phyla. Whether such customization occurs, and how the mTORC1 pathway might capture new inputs, is unknown. This study identified the Drosophila melanogaster protein Unmet expectations (CG11596) as a species-restricted methionine sensor that directly binds the fly GATOR2 complex in a fashion antagonized by S-adenosylmethionine (SAM). Tn Dipterans GATOR2 was found to rapidly evolve the capacity to bind Unmet and to thereby repurpose a previously independent methyltransferase as a SAM sensor. Thus, the modular architecture of the mTORC1 pathway allows it to co-opt preexisting enzymes to expand its nutrient sensing capabilities, revealing a mechanism for conferring evolvability on an otherwise conserved system. | Ertl, H. A., Bayala, E. X., Siddiq, M. A., Wittkopp, P. J. (2024). Divergence of Grainy head affects chromatin accessibility, gene expression, and embryonic viability in Drosophila melanogaster. bioRxiv, PubMed ID: 38645200
Summary: Pioneer factors are critical for gene regulation and development because they bind chromatin and make DNA more accessible for binding by other transcription factors. The pioneer factor Grainy head (Grh) is present across metazoans and has been shown to retain a role in epithelium development in fruit flies, nematodes, and mice despite extensive divergence in both amino acid sequence and length. This study investigated the evolution of Grh function by comparing the effects of the fly (Drosophila melanogaster) and worm (Caenorhabditis elegans) Grh orthologs on chromatin accessibility, gene expression, embryonic development, and viability in transgenic D. melanogaster.The Caenorhabditis elegans ortholog rescued cuticle development but not full embryonic viability in Drosophila melanogaster grh null mutants. At the molecular level, the C. elegans ortholog only partially rescued chromatin accessibility and gene expression. Divergence in the disordered N-terminus of the Grh protein contributes to these differences in embryonic viability and molecular phenotypes. These data show how pioneer factors can diverge in sequence and function at the molecular level while retaining conserved developmental functions at the organismal level. |
Friday, November 22nd - Gonads |
Rinehart, L., Stewart, W. E., Luffman, N., Wawersik, M., Kerscher, O. (2024). Chigno/CG11180 and SUMO are Chinmo-interacting proteins with a role in Drosophila testes somatic support cells. PeerJ, 12:e16971 PubMed ID: 38495765
Summary: Stem cells are critical for replenishment of cells lost to death, damage or differentiation. Drosophila testes are a key model system for elucidating mechanisms regulating stem cell maintenance and differentiation. An intriguing gene identified through such studies is the transcription factor, chronologically inappropriate morphogenesis (Chinmo). Chinmo is a downstream effector of the Jak-STAT signaling pathway that acts in testis somatic stem cells to ensure maintenance of male stem cell fate and sexual identity. Defects in these processes can lead to infertility and the formation of germ cell tumors. While Chinmo's effect on testis stem cell behavior has been investigated in detail, there is still much to be learned about its structure, function, and interactions with other proteins. Using a two-hybrid screen, this study found that Chinmo interacts with itself, the small ubiquitin-like modifier SUMO, the novel protein CG11180, and four other proteins (CG4318, Ova (ovaries absent), Taf3 (TBP-associated factor 3), and CG18269). Since both Chinmo and CG11180 contain sumoylation sites and SUMO-interacting motifs (SIMs), their interaction was studied in more detail. Using site-directed mutagenesis of a unique SIM in CG11180, this study demonstrate that Chinmo's interaction with CG11180 is SUMO-dependent. Furthermore, to assess the functional relevance of both SUMO and CG11180, RNAi-mediated knockdown of both proteins was perfomed in somatic cells of the Drosophila testis. Using this approach, it was fond that CG11180 and SUMO are required in somatic cells of adult testes, and that reduction of either protein causes formation of germ cell tumors. Overall, this work suggests that SUMO may be involved in the interaction of Chinmo and CG11180 and that these genes are required in somatic cells of the adult Drosophila testis. Consistent with the CG11180 knockdown phenotype in male testes, and to underscore its connection to Chinmo, the name Chigno (Childless Gambino) for CG11180 is proposed. | Chen, J., Li, C., Sheng, Y., Zhang, J., Pang, L., Dong, Z., Wu, Z., Lu, Y., Liu, Z., Zhang, Q., Guan, X., Chen, X., Huang, J. (2024). Communication between the stem cell niche and an adjacent differentiation niche through miRNA and EGFR signaling orchestrates exit from the stem cell state in the Drosophila ovary. PLoS Biol, 22(3):e3002515 PubMed ID: 38512963
Summary: The signaling environment, or niche, often governs the initial difference in behavior of an adult stem cell and a derivative that initiates a path towards differentiation. The transition between an instructive stem cell niche and differentiation niche must generally have single-cell resolution, suggesting that multiple mechanisms might be necessary to sharpen the transition. This study examined the Drosophila ovary and found that Cap cells, which are key constituents of the germline stem cell (GSC) niche, express a conserved microRNA (miR-124). Surprisingly, loss of miR-124 activity in Cap cells leads to a defect in differentiation of GSC derivatives. Evidence is presented that the direct functional target of miR-124 in Cap cells is the epidermal growth factor receptor (EGFR) and that failure to limit EGFR expression leads to the ectopic expression of a key anti-differentiation BMP signal in neighboring somatic escort cells (ECs), which constitute a differentiation niche. It was further found that Notch signaling connects EFGR activity in Cap cells to BMP expression in ECs. It was deduced that the stem cell niche communicates with the differentiation niche through a mechanism that begins with the selective expression of a specific microRNA and culminates in the suppression of the major anti-differentiation signal in neighboring cells, with the functionally important overall role of sharpening the spatial distinction between self-renewal and differentiation environments. |
Hikawa, N., Kashio, S., Miura, M. (2024). Mating-induced increase of kynurenine in Drosophila ovary enhances starvation resistance of progeny. J Biol Chem, 300(3):105663 PubMed ID: 38246353
Summary: The maternal nutritional environment can impact progeny development, stress tolerance, and longevity. Such phenotypic variation of offspring resulting from the maternal environment is often referred to as the 'maternal effect' and is observed across taxa, including in humans. While some mechanisms behind maternal effects have been revealed, such as histone modification, many studies rely on drastic genetic or nutritional manipulation in describing these mechanisms. This study aimed to reveal how the maternal environment is regulated under physiological conditions to affect the progeny. Specifically, metabolic regulation in oocytes in response to mating is detailed using Drosophila melanogaster. Using liquid chromatography-mass spectrometry, it was found that upon mating, the ovary metabolites shifted, predominantly toward increasing amino acids and the tryptophan/kynurenine (Kyn) pathway. This mating-induced increase in ovary Kyn was driven by increased Kyn production in the fat body, a functional counterpart of the mammalian liver and white adipose tissue and the source of Kyn storage for the ovary after mating. Furthermore, maternal Kyn repression was shown to decrease the starvation resistance of progeny and that administering exogenous Kyn to the maternal generation enhanced the starvation resistance of female progeny. Taken together, these findings point to a previously unidentified role of fat body Kyn distribution during reproduction on progeny survival. | Uttekar, B., Verma, R. K., Tomer, D., Rikhy, R. (2024). Mitochondrial morphology dynamics and ROS regulate apical polarity and differentiation in Drosophila follicle cells. Development, 151(5) PubMed ID: 38345270
Summary: Mitochondrial morphology dynamics regulate signaling pathways during epithelial cell formation and differentiation. The mitochondrial fission protein Drp1 affects the appropriate activation of EGFR and Notch signaling-driven differentiation of posterior follicle cells in Drosophila oogenesis. The mechanisms by which Drp1 regulates epithelial polarity during differentiation are not known. In this study, we show that Drp1-depleted follicle cells are constricted in early stages and present in multiple layers at later stages with decreased levels of apical polarity protein aPKC. These defects are suppressed by additional depletion of mitochondrial fusion protein . Opa1 depletion leads to mitochondrial fragmentation and increased reactive oxygen species (ROS) in follicle cells. Increasing ROS by depleting the ROS scavengers, mitochondrial SOD2 and catalase also leads to mitochondrial fragmentation. Further, the loss of Opa1, SOD2 and catalase partially restores the defects in epithelial polarity and aPKC, along with EGFR and Notch signaling in Drp1-depleted follicle cells. These results show a crucial interaction between mitochondrial morphology, ROS generation and epithelial cell polarity formation during the differentiation of follicle epithelial cells in Drosophila oogenesis. |
Zelinger, E., Brumfeld, V., Rechav, K., Waiger, D., Kossovsky, T., Heifetz, Y. (2024). Three-dimensional correlative microscopy of the Drosophila female reproductive tract reveals modes of communication in seminal receptacle sperm storage. Communications biology, 7(1):155 PubMed ID: 38321098
Summary: In many taxa, females store sperm in specialized storage organs. Most insect sperm storage organs have a tubular structure, typically consisting of a central lumen surrounded by epithelial cells. These specialized tubules perform the essential tasks of transporting sperm through the female reproductive tract and supporting long-term sperm survival and function. Little is known about the way in which female sperm storage organs provide an environment conducive to sperm survival. This was addressed using a combined light microscopy, micro computed tomography (microCT), and Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) approach for high-resolution correlative three-dimensional imaging to advance our understanding of sperm-female interactions in Drosophila melanogaster. Using this multimodal approach, it was possible to scan the lower female reproductive tract and distal portion of the seminal receptacle at low magnification, and to subsequently zoom in for further analysis on an ultrastructural level. The findings highlight aspects of the way in which the seminal receptacle keeps sperm viable in the lumen, and set the stage for further studies. The methods developed are suitable not only for Drosophila but also for other organisms with soft, delicate tissues. | Heaney, J., Zhao, J., Casagranda, F., Loveland, K. L., Siddall, N. A., Hime, G. R. (2024). Drosophila Importin Alpha 1 (Dα1) Is Required to Maintain Germline Stem Cells in the Testis Niche. Cells, 13(6) PubMed ID: 38534338
Summary: Stem cell maintenance and differentiation can be regulated via the differential activity of transcription factors within stem cells and their progeny. For these factors to be active, they need to be transported from their site of synthesis in the cytoplasm into the nucleus. A tissue-specific requirement for factors involved in nuclear importation is a potential mechanism to regulate stem cell differentiation. This study has undertaken a characterization of male sterile importin alpha 1 (Dα1) null alleles in Drosophila and found that Dα1 is required for maintaining germline stem cells (GSCs) in the testis niche. The loss of GSCs can be rescued by ectopic expression of Dα1 within the germline but the animals are still infertile, indicating a second role for Dα1 in spermatogenesis. Expression of a Dα1 dominant negative transgene in GSCs confirmed a functional requirement for Dα1 in GSC maintenance but expression of the transgene in differentiating spermatogonia did not exhibit a phenotype indicating a specific role for Dα1 within GSCs. Our data indicate that Dα1 is utilized as a regulatory protein within GSCs to facilitate nuclear importation of proteins that maintain the stem cell pool. |
Thursday, November 21st - Adult Development |
Guo, X., Wang, C., Zhang, Y., Wei, R., Xi, R. (2024). Cell-fate conversion of intestinal cells in adult Drosophila midgut by depleting a single transcription factor. Nat Commun, 15(1):2656 PubMed ID: 38531872
Summary: The manipulation of cell identity by reprograming holds immense potential in regenerative medicine, but is often limited by the inefficient acquisition of fully functional cells. This problem can potentially be resolved by better understanding the reprogramming process using in vivo genetic models, which are currently scarce. This study reports that both enterocytes (ECs) and enteroendocrine cells (EEs) in adult Drosophila midgut show a surprising degree of cell plasticity. Depleting the transcription factor Tramtrack in the differentiated ECs can initiate Prospero-mediated cell transdifferentiation, leading to EE-like cells. On the other hand, depletion of Prospero in the differentiated EEs can lead to the loss of EE-specific transcription programs and the gain of intestinal progenitor cell identity, allowing cell cycle re-entry or differentiation into ECs. Intestinal progenitor cells, ECs, and EEs were found to have a similar chromatin accessibility profile, supporting the concept that cell plasticity is enabled by pre-existing chromatin accessibility with switchable transcription programs. Further genetic analysis with this system reveals that the NuRD chromatin remodeling complex, cell lineage conflict, and age act as barriers to EC-to-EE transdifferentiation. The establishment of this genetically tractable in vivo model should facilitate mechanistic investigation of cell plasticity at the molecular and genetic level. | Rodriguez, A., Foronda, D., Cordoba, S., Felipe-Cordero, D., Baonza, A., Miguez, D. G., Estella, C. (2024). Cell proliferation and Notch signaling coordinate the formation of epithelial folds in the Drosophila leg. Development, 151(8) PubMed ID: 38512712
Summary: The formation of complex three-dimensional organs during development requires precise coordination between patterning networks and mechanical forces. In particular, tissue folding is a crucial process that relies on a combination of local and tissue-wide mechanical forces. This study investigated the contribution of cell proliferation to epithelial morphogenesis using the Drosophila leg tarsal folds as a model. Tissue-wide compression forces generated by cell proliferation, in coordination with the Notch signaling pathway, were revealed to be essential for the formation of epithelial folds in precise locations along the proximo-distal axis of the leg. As cell numbers increase, compressive stresses arise, promoting the folding of the epithelium and reinforcing the apical constriction of invaginating cells. Additionally, the Notch target dysfusion plays a key function specifying the location of the folds, through the apical accumulation of F-actin and the apico-basal shortening of invaginating cells. These findings provide new insights into the intricate mechanisms involved in epithelial morphogenesis, highlighting the crucial role of tissue-wide forces in shaping a three-dimensional organ in a reproducible manner. |
Parasram, K., Zuccato, A., Shin, M., Willms, R., DeVeale, B., Foley, E., Karpowicz, P. (2024). The emergence of circadian timekeeping in the intestine. Nat Commun, 15(1):1788 PubMed ID: 38413599
Summary: The circadian clock is a molecular timekeeper, present from cyanobacteria to mammals, that coordinates internal physiology with the external environment. The clock has a 24-h period however development proceeds with its own timing, raising the question of how these interact. Using the intestine of Drosophila melanogaster as a model for organ development, this study tracked how and when the circadian clock emerges in specific cell types. The circadian clock was found to begin abruptly in the adult intestine and gradually synchronizes to the environment after intestinal development is complete. This delayed start occurs because individual cells at earlier stages lack the complete circadian clock gene network. As the intestine develops, the circadian clock is first consolidated in intestinal stem cells with changes in Ecdysone and Hnf4 signalling influencing the transcriptional activity of Clk/cyc to drive the expression of tim, Pdp1, and vri. In the mature intestine, stem cell lineage commitment transiently disrupts clock activity in differentiating progeny, mirroring early developmental clock-less transitions. These data show that clock function and differentiation are incompatible and provide a paradigm for studying circadian clocks in development and stem cell lineages. | Terry, D., Schweibenz, C., Moberg, K. (2024). Local ecdysone synthesis in a wounded epithelium sustains developmental delay and promotes regeneration in Drosophila. bioRxiv, PubMed ID: 38464192 ID
Summary: Regenerative ability often declines as animals mature past embryonic and juvenile stages, suggesting that regeneration requires redirection of growth pathways that promote developmental growth. Intriguingly, the Drosophila larval epithelia require the hormone ecdysone (Ec) for growth but require a drop in circulating Ec levels to regenerate. Examining Ec dynamics more closely, this study found that transcriptional activity of the Ec-receptor (EcR) drops in uninjured regions of wing discs, but simultaneously rises in cells around the injury-induced blastema. In parallel, blastema depletion of genes encoding Ec biosynthesis enzymes blocks EcR activity and impairs regeneration but has no effect on uninjured wings. Local Ec/EcR signaling was found to be required for injury-induced pupariation delay following injury and that key regeneration regulators upd3 and Ets21c respond to Ec levels. Collectively, these data indicate that injury induces a local source of Ec within the wing blastema that sustains a transcriptional signature necessary for developmental delay and tissue repair. |
Pandey, A., Roy, J. K. (2024). The insc-GAL4 driver marks distinct cell types in Drosophila midgut. Exp Cell Res, 435(2):113953 PubMed ID: 38278285
Summary: Drosophila geneticists frequently employ the binary GAL4-UAS system of conditional gene expression to direct expression of the desired transgene in tissues of interest. The inscuteable -GAL4 driver (insc-GAL4) expresses in the type 1 and type 2 neuroblasts of Drosophila larval brain, a frequent target tissue in many investigations. This GAL4 line additionally displayed its expression in the midgut. This study examined the expression of the UAS-mCD8GFP reporter under the command of the insc-GAL4 driver and observed that this driver expresses exclusively to intestinal stem cells (ISCs) of the Drosophila adult midgut as well as adult midgut precursors (AMPs) of the larval midgut besides its expression in larval brain. Additionally, using the G-TRACE method, it was observed that AMPs in the larval midgut consistently expressed insc-GAL4 in real-time, and the lineage expression of this GAL4 was observed in the enterocyte cells. This study reveals for the first time that insc-GAL4 is specific to larval AMPs and adult ISCs of the midgut. | Kumar, N., Rangel Ambriz, J., Tsai, K., Mim, M. S., Flores-Flores, M., Chen, W., Zartman, J. J., Alber, M. (2024). Balancing competing effects of tissue growth and cytoskeletal regulation during Drosophila wing disc development. Nat Commun, 15(1):2477 PubMed ID: 38509115
Summary: How a developing organ robustly coordinates the cellular mechanics and growth to reach a final size and shape remains poorly understood. Through iterations between experiments and model simulations that include a mechanistic description of interkinetic nuclear migration, this study shows that the local curvature, height, and nuclear positioning of cells in the Drosophila wing imaginal disc are defined by the concurrent patterning of actomyosin contractility, cell-ECM adhesion, ECM stiffness, and interfacial membrane tension. Increasing cell proliferation via different growth-promoting pathways results in two distinct phenotypes. Triggering proliferation through increases basal curvature, but an increase in growth through Dpp signaling and Myc causes tissue flattening. These distinct phenotypic outcomes arise from differences in how each growth pathway regulates the cellular cytoskeleton, including contractility and cell-ECM adhesion. The coupled regulation of proliferation and cytoskeletal regulators is a general strategy to meet the multiple context-dependent criteria defining tissue morphogenesis. |
Wednesday November 20th - Transcriptional Regulation |
Tendolkar, A., Mazo-Vargas, A., Livraghi, L., Hanly, J. J., Van Horne, K. C., Gilbert, L. E., Martin, A. (2024). Cis-regulatory modes of Ultrabithorax inactivation in butterfly forewings. Elife, 12 PubMed ID: 38261357
Summary: Hox gene clusters encode transcription factors that drive regional specialization during animal development: for example the Hox factor Ubx is expressed in the insect metathoracic (T3) wing appendages and differentiates them from T2 mesothoracic identities. Hox transcriptional regulation requires silencing activities that prevent spurious activation and regulatory crosstalks in the wrong tissues, but this has seldom been studied in insects other than Drosophila, which shows a derived Hox dislocation into two genomic clusters that disjoined Antennapedia (Antp) and Ultrabithorax (Ubx). This study investigated how Ubx is restricted to the hindwing in butterflies, amidst a contiguous Hox cluster. By analysing Hi-C and ATAC-seq data in the butterfly Junonia coenia, a Topologically Associated Domain (TAD) was shown to maintain a hindwing-enriched profile of chromatin opening around Ubx. This TAD is bordered by a Boundary Element (BE) that separates it from a region of joined wing activity around the Antp locus. CRISPR mutational perturbation of this BE releases ectopic Ubx expression in forewings, inducing homeotic clones with hindwing identities. Further mutational interrogation of two non-coding RNA encoding regions and one putative cis-regulatory module within the Ubx TAD cause rare homeotic transformations in both directions, indicating the presence of both activating and repressing chromatin features. A series of spontaneous forewing homeotic phenotypes obtained in Heliconius butterflies is described, their possible mutational basis is discussed. By leveraging the extensive wing specialization found in butterflies, this initial exploration of Ubx regulation demonstrates the existence of silencing and insulating sequences that prevent its spurious expression in forewings. | Ko, B. S., Han, M. H., Kwon, M. J., Cha, D. G., Ji, Y., Park, E. S., Jeon, M. J., Kim, S., Lee, K., Choi, Y. H., Lee, J., Torras-Llort, M., Yoon, K. J., Lee, H., Kim, J. K., Lee, S. B. (2024). Baf-mediated transcriptional regulation of teashirt is essential for the development of neural progenitor cell lineages. Experimental & molecular medicine, 56(2):422-440 PubMed ID: 38374207
Summary: Accumulating evidence hints heterochromatin anchoring to the inner nuclear membrane as an upstream regulatory process of gene expression. Given that the formation of neural progenitor cell lineages and the subsequent maintenance of postmitotic neuronal cell identity critically rely on transcriptional regulation, it seems possible that the development of neuronal cells is influenced by cell type-specific and/or context-dependent programmed regulation of heterochromatin anchoring. This possibility was explored by genetically disrupting the evolutionarily conserved barrier-to-autointegration factor (Baf) in the Drosophila nervous system. Through single-cell RNA sequencing, it was demonstrated that Baf knockdown induces prominent transcriptomic changes, particularly in type I neuroblasts. Among the differentially expressed genes, genetic analyses identified teashirt (tsh), a transcription factor that interacts with beta-catenin, to be closely associated with Baf knockdown-induced phenotypes that were suppressed by the overexpression of tsh or beta-catenin. It was also found that Baf and tsh colocalized in a region adjacent to heterochromatin in type I NBs. Notably, the subnuclear localization pattern remained unchanged when one of these two proteins was knocked down, indicating that both proteins contribute to the anchoring of heterochromatin to the inner nuclear membrane. Overall, this study reveals that the Baf-mediated transcriptional regulation of teashirt is a novel molecular mechanism that regulates the development of neural progenitor cell lineages. |
Tikhonova, E., Revel-Muroz, A., Georgiev, P., Maksimenko, O. (2024). Interaction of MLE with CLAMP zinc finger is involved in proper MSL proteins binding to chromosomes in Drosophila. Open biology, 14(3):230270 PubMed ID: 38471568
Summary: The Drosophila male-specific lethal (MSL) complex binds to the male X chromosome to activate transcription. It comprises five proteins (MSL1, MSL2, MSL3, Male absent on the first (MOF), and Maleless (MLE)) and two long noncoding RNAs (lncRNAs; roX1 and roX2/). The MLE helicase remodels the roX lncRNAs, enabling the lncRNA-mediated assembly of the Drosophila dosage compensation complex. MSL2 is expressed only in males and interacts with the N-terminal zinc finger of the transcription factor chromatin-linked adapter for MSL proteins (CLAMP), which is important for the specific recruitment of the MSL complex to the male X chromosome. This study found that MLE's unstructured C-terminal region interacts with the sixth zinc-finger domain of CLAMP. In vitro, 4-5 zinc fingers are critical for the specific DNA-binding of CLAMP with GA repeats, which constitute the core motif at the high affinity binding sites for MSL proteins. Deleting the CLAMP binding region in MLE decreases the association of MSL proteins with the male X chromosome and increases male lethality. These results suggest that interactions of unstructured regions in MSL2 and MLE with CLAMP zinc finger domains are important for the specific recruitment of the MSL complex to the male X chromosome. | Lin, S., Lim, B. (2024). Multifaceted effects on even-skipped transcriptional dynamics upon Kruppel dosage changes. Development, 151(5) PubMed ID: 38345298
Summary: Although fluctuations in transcription factor (TF) dosage are often well tolerated, TF dosage modulation can change the target gene expression dynamics and result in significant non-lethal developmental phenotypes. Using MS2/MCP-mediated quantitative live imaging in early Drosophila embryos, this study analyzed how changing levels of the gap gene Krü,ppel (Kr) affects transcriptional dynamics of the pair-rule gene even-skipped (eve). Halving the Kr dosage leads to a transient posterior expansion of the eve stripe 2 and an anterior shift of stripe 5. Surprisingly, the most significant changes are observed in eve stripes 3 and 4, the enhancers of which do not contain Kr-binding sites. In Kr heterozygous embryos, both stripes 3 and 4 display narrower widths, anteriorly shifted boundaries and reduced mRNA production levels. Kr dosage indirectly affects stripe 3 and 4 dynamics by modulating other gap gene dynamics. Moderate body segment phenotypes of Kr heterozygotes were quantively corrolated with spatiotemporal changes in eve expression. These results indicate that nonlinear relationships between TF dosage and phenotypes underlie direct TF-DNA and indirect TF-TF interactions. |
Gibson, T. J., Larson, E. D., Harrison, M. M. (2024). Protein-intrinsic properties and context-dependent effects regulate pioneer factor binding and function. Nat Struct Mol Biol, 31(3):548-558 PubMed ID: 38365978
Summary: Chromatin is a barrier to the binding of many transcription factors. By contrast, pioneer factors access nucleosomal targets and promote chromatin opening. Despite binding to target motifs in closed chromatin, many pioneer factors display cell-type-specific binding and activity. The mechanisms governing pioneer factor occupancy and the relationship between chromatin occupancy and opening remain unclear. Three Drosophila transcription factors with distinct DNA-binding domains and biological functions were studied: Zelda, Grainy head and Twist. The level of chromatin occupancy was demonstrated to be a key determinant of pioneering activity. Multiple factors regulate occupancy, including motif content, local chromatin and protein concentration. Regions outside the DNA-binding domain are required for binding and chromatin opening. These results show that pioneering activity is not a binary feature intrinsic to a protein but occurs on a spectrum and is regulated by a variety of protein-intrinsic and cell-type-specific features. | Pollex, T., Rabinowitz, A., Gambetta, M. C., Marco-Ferreres, R., Viales, R. R., Jankowski, A., Schaub, C., Furlong, E. E. M. (2024). Enhancer-promoter interactions become more instructive in the transition from cell-fate specification to tissue differentiation. Nat Genet, 56(4):686-696 PubMed ID: 38467791
Summary: To regulate expression, enhancers must come in proximity to their target gene. However, the relationship between the timing of enhancer-promoter (E-P) proximity and activity remains unclear, with examples of uncoupled, anticorrelated and correlated interactions. To assess this, 600 characterized enhancers or promoters were chosen with tissue-specific activity in Drosophila embryos and Capture-C was performed in FACS-purified myogenic or neurogenic cells during specification and tissue differentiation. This enabled direct comparison between E-P proximity and activity transitioning from OFF-to-ON and ON-to-OFF states across developmental conditions. This showed remarkably similar E-P topologies between specified muscle and neuronal cells, which are uncoupled from activity. During tissue differentiation, many new distal interactions emerge where changes in E-P proximity reflect changes in activity. The mode of E-P regulation therefore appears to change as embryogenesis proceeds, from largely permissive topologies during cell-fate specification to more instructive regulation during terminal tissue differentiation, when E-P proximity is coupled to activation. |
Monday November 18th - Cytoskeleton |
Singh, A., Thale, S., Leibner, T., Lamparter, L., Ricker, A., Nusse, H., Klingauf, J., Galic, M., Ohlberger, M., Matis, M. (2024). Dynamic interplay of microtubule and actomyosin forces drive tissue extension. Nat Commun, 15(1):3198 PubMed ID: 38609383
Summary: In order to shape a tissue, individual cell-based mechanical forces have to be integrated into a global force pattern. Over the last decades, the importance of actomyosin contractile arrays, which are the key constituents of various morphogenetic processes, has been established for many tissues. Recent studies have demonstrated that the microtubule cytoskeleton mediates folding and elongation of the epithelial sheet during Drosophila morphogenesis, placing microtubule mechanics on par with actin-based processes. While these studies establish the importance of both cytoskeletal systems during cell and tissue rearrangements, a mechanistic understanding of their functional hierarchy is currently missing. This study dissected the individual roles of these two key generators of mechanical forces during epithelium elongation in the developing Drosophila wing. Wing extension, which entails columnar-to-cuboidal cell shape remodeling in a cell-autonomous manner, is driven by anisotropic cell expansion caused by the remodeling of the microtubule cytoskeleton from apico-basal to planarly polarized. Importantly, cell and tissue elongation is not associated with Myosin activity. Instead, Myosin II exhibits a homeostatic role, as actomyosin contraction balances polarized microtubule-based forces to determine the final cell shape. Using a reductionist model, this study confirmed that pairing microtubule and actomyosin-based forces is sufficient to recapitulate cell elongation and the final cell shape. These results support a hierarchical mechanism whereby microtubule-based forces in some epithelial systems prime actomyosin-generated forces. | Li, S., Liu, Z. Y., Li, H., Zhou, S., Liu, J., Sun, N., Yang, K. F., Dougados, V., Mangeat, T., Belguise, K., Feng, X. Q., Liu, Y., Wang, X. (2024). Basal actomyosin pulses expand epithelium coordinating cell flattening and tissue elongation. Nat Commun, 15(1):3000 PubMed ID: 38589403
Summary: Actomyosin networks constrict cell area and junctions to alter cell and tissue shape. However, during cell expansion under mechanical stress, actomyosin networks are strengthened and polarized to relax stress. Thus, cells face a conflicting situation between the enhanced actomyosin contractile properties and the expansion behaviour of the cell or tissue. To address this paradoxical situation, late Drosophila oogenesis was studied; an unusual epithelial expansion wave behaviour was revealed. Mechanistically, Rac1 and Rho1 integrate basal pulsatile actomyosin networks with ruffles and focal adhesions to increase and then stabilize basal area of epithelial cells allowing their flattening and elongation. This epithelial expansion behaviour bridges cell changes to oocyte growth and extension, while oocyte growth in turn deforms the epithelium to drive cell spreading. Basal pulsatile actomyosin networks exhibit non-contractile mechanics, non-linear structures and F-actin/Myosin-II spatiotemporal signal separation, implicating unreported expanding properties. Biophysical modelling incorporating these expanding properties well simulates epithelial cell expansion waves. This work thus highlights actomyosin expanding properties as a key mechanism driving tissue morphogenesis. |
Osaka, J., Ishii, A., Wang, X., Iwanaga, R., Kawamura, H., Akino, S., Sugie, A., Hakeda-Suzuki, S., Suzuki, T. (2024). Complex formation of immunoglobulin superfamily molecules Side-IV and Beat-IIb regulates synaptic specificity. Cell Rep, 43(2):113798 PubMed ID: 38381608
Summary: Neurons establish specific synapses based on the adhesive properties of cell-surface proteins while also retaining the ability to form synapses in a relatively non-selective manner. However, comprehensive understanding of the underlying mechanism reconciling these opposing characteristics remains incomplete. This study has identified Side-IVBeat-IIb, members of the Drosophila immunoglobulin superfamily, as a combination of cell-surface recognition molecules inducing synapse formation. The Side-IV/Beat-IIb combination transduces bifurcated signaling with Side-IV's co-receptor, Kirre, and a synaptic scaffold protein, Dsyd-1. Genetic experiments and subcellular protein localization analyses showed the Side-IV/Beat-IIb/Kirre/Dsyd-1 complex to have two essential functions. First, it narrows neuronal binding specificity through Side-IV/Beat-IIb extracellular interactions. Second, it recruits synapse formation factors, Kirre and Dsyd-1, to restrict synaptic loci and inhibit miswiring. This dual function explains how the combinations of cell-surface molecules enable the ranking of preferred interactions among neuronal pairs to achieve synaptic specificity in complex circuits in vivo. | Sato, Y., Yamagishi, M., Yajima, J. (2024). Effect of temperature on actin filament corkscrewing driven by nonprocessive myosin IC. Biochem Biophys Res Commun, 703:149597 PubMed ID: 38367512
Summary: Myosin family proteins are ATP-driven, actin filament-based motor proteins that generate force along actin filaments. In in vitro actin filament gliding assays, certain myosins generate rotation of gliding actin filaments around their long axes. This study assessed the effects of temperature on the corkscrewing motion of actin filaments, including factors like gliding and rotational velocities and corkscrewing pitch. The corkscrewing motion was driven by a nonprocessive, full-length single-headed Drosophila myosin IC attached to an antibody adsorbed onto a cover glass. An in vitro actin filament corkscrewing assay was performed at temperatures ranging from 25 °C to 35 °C. The gliding and rotational velocities and the pitch of corkscrewing actin filaments generated by myosin IC molecules was found to increase with increasing temperature. Since the pitch is determined by dividing the gliding velocity by the rotational velocity, an increase in the pitch indicates that the gliding velocity increased faster than the rotational velocity with increasing temperature. These results suggest that temperature has distinct effects on the gliding and rotational forces produced by myosin IC, with implications for interpreting the temperature effect on torque-generation mechanisms driven by myosins on actin filaments at physiological temperatures. |
de-Carvalho, J., Tlili, S., Saunders, T. E., Telley, I. A. (2024). The positioning mechanics of microtubule asters in Drosophila embryo explants. Elife, 12 PubMed ID: 38426416
Summary: Microtubule asters are essential in localizing the action of microtubules in processes including mitosis and organelle positioning. In large cells, such as the one-cell sea urchin embryo, aster dynamics are dominated by hydrodynamic pulling forces. However, in systems with more densely positioned nuclei such as the early Drosophila embryo, which packs around 6000 nuclei within the syncytium in a crystalline-like order, it is unclear what processes dominate aster dynamics. This study take advantage of a cell cycle regulation Drosophila mutant to generate embryos with multiple asters, independent from nuclei. An ex vivo assay was used to further simplify this biological system to explore the forces generated by and between asters. Through live imaging, drug and optical perturbations, and theoretical modeling, it was demonstrate that these asters likely generate an effective pushing force over short distances. | McGory, J. M., Verma, V., Barcelos, D. M., Maresca, T. J. (2024). Multimerization of a disordered kinetochore protein promotes accurate chromosome segregation by localizing a core dynein module. J Cell Biol, 223(3) PubMed ID: 38180477
Summary: Kinetochores connect chromosomes and spindle microtubules to maintain genomic integrity through cell division. Crosstalk between the minus-end directed motor dynein and kinetochore-microtubule attachment factors promotes accurate chromosome segregation by a poorly understood pathway. This study identified a linkage between the intrinsically disordered protein Spc105 (KNL1 orthologue) and dynein using an optogenetic oligomerization assay. Core pools of the checkpoint protein BubR1 and the adaptor complex RZZ contribute to the linkage. Furthermore, a minimal segment of Spc105 with a propensity to multimerize and which contains protein binding motifs is sufficient to link Spc105 to RZZ/dynein. Deletion of the minimal region from Spc105 compromises the recruitment of its binding partners to kinetochores and elevates chromosome missegregation due to merotelic attachments. Restoration of normal chromosome segregation and localization of BubR1 and RZZ requires both protein binding motifs and oligomerization of Spc105. Together, our results reveal that higher-order multimerization of Spc105 contributes to localizing a core pool of RZZ that promotes accurate chromosome segregation. |
Friday November 15th - Adult neural development, structure, and function |
Takagi, S., Sancer, G., Abuin, L., Stupski, S. D., Arguello, J. R., Prieto-Godino, L. L., Stern, D. L., Cruchet, S., Alvarez-Ocana, R., Wienecke, C. F. R., van Breugel, F., Jeanne, J. M., Auer, T. O., Benton, R. (2024). Sensory neuron population expansion enhances odor tracking without sensitizing projection neurons. bioRxiv, PubMed ID: 37745467
Summary: The evolutionary expansion of sensory neuron populations detecting important environmental cues is widespread, but functionally enigmatic. This study investigated this phenomenon through comparison of homologous neural pathways of Drosophila melanogaster and its close relative Drosophila sechellia, an extreme specialist for Morinda citrifolia noni fruit. D. sechellia has evolved species-specific expansions in select, noni-detecting olfactory sensory neuron (OSN) populations, through multigenic changes. Activation and inhibition of defined proportions of neurons demonstrate that OSN population increases contribute to stronger, more persistent, noni-odor tracking behavior. These sensory neuron expansions result in increased synaptic connections with their projection neuron (PN) partners, which are conserved in number between species. Surprisingly, having more OSNs does not lead to greater odor-evoked PN sensitivity or reliability. Rather, pathways with increased sensory pooling exhibit reduced PN adaptation, likely through weakened lateral inhibition. This work reveals an unexpected functional impact of sensory neuron expansions to explain ecologically-relevant, species-specific behavior. | Abubaker, M. B., Hsu, F. Y., Feng, K. L., Chu, L. A., de Belle, J. S., Chiang, A. S. (2024). Asymmetric neurons are necessary for olfactory learning in the Drosophila brain. Curr Biol, 34(5):946-957.e944 PubMed ID: 38320552
Summary: Animals have complementary parallel memory systems that process signals from various sensory modalities. In the brain of the fruit fly Drosophila melanogaster, mushroom body (MB) circuitry is the primary associative neuropil, critical for all stages of olfactory memory. These findings suggest that active signaling from specific asymmetric body (AB) neurons is also crucial for this process. These AB neurons respond to odors and electric shock separately and exhibit timing-sensitive neuronal activity in response to paired stimulation while leaving a decreased memory trace during retrieval. These experiments also show that rutabaga-encoded adenylate cyclase, which mediates coincidence detection, is required for learning and short-term memory in both AB and MB. Additive effects were observed when manipulating rutabaga co-expression in both structures. Together, these results implicate the AB in playing a critical role in associative olfactory learning and short-term memory. |
Li, H., Li, Z., Yuan, X., Tian, Y., Ye, W., Zeng, P., Li, X. M., Guo, F. (2024). Dynamic encoding of temperature in the central circadian circuit coordinates physiological activities. Nat Commun, 15(1):2834 PubMed ID: 38565846
Summary: The circadian clock regulates animal physiological activities. How temperature reorganizes circadian-dependent physiological activities remains elusive. Using in-vivo two-photon imaging with the temperature control device, this study investigated the response of the Drosophila central circadian circuit to temperature variation and identified that DN1as serves as the most sensitive temperature-sensing neurons. The circadian clock gate DN1a's diurnal temperature response. Trans-synaptic tracing, connectome analysis, and functional imaging data reveal that DN1as bidirectionally targets two circadian neuronal subsets: activity-related E cells and sleep-promoting DN3s. Specifically, behavioral data demonstrate that the DN1a-E cell circuit modulates the evening locomotion peak in response to cold temperature, while the DN1a-DN3 circuit controls the warm temperature-induced nocturnal sleep reduction. These findings systematically and comprehensively illustrate how the central circadian circuit dynamically integrates temperature and light signals to effectively coordinate wakefulness and sleep at different times of the day, shedding light on the conserved neural mechanisms underlying temperature-regulated circadian physiology in animals. | Lillvis, J. L., Wang, K., Shiozaki, H. M., Xu, M., Stern, D. L., Dickson, B. J. (2024). Nested neural circuits generate distinct acoustic signals during Drosophila courtship. Curr Biol, 34(4):808-824.e806 PubMed ID: 38295797
Summary: Many motor control systems generate multiple movements using a common set of muscles. How are premotor circuits able to flexibly generate diverse movement patterns? This study characterizes the neuronal circuits that drive the distinct courtship songs of Drosophila melanogaster. Male flies vibrate their wings toward females to produce two different song modes-pulse and sine song-which signal species identity and male quality. Using cell-type-specific genetic reagents and the connectome, a cellular and synaptic map is provided of the circuits in the male ventral nerve cord that generate these songs and examine how activating or inhibiting each cell type within these circuits affects the song. The data reveal that the song circuit is organized into two nested feedforward pathways with extensive reciprocal and feedback connections. The larger network produces pulse song, the more complex and ancestral song form. A subset of this network produces sine song, the simpler and more recent form. Such nested organization may be a common feature of motor control circuits in which evolution has layered increasing flexibility onto a basic movement pattern. |
Agi, E., Reifenstein, E. T., Wit, C., Schneider, T., Kauer, M., Kehribar, M., Kulkarni, A., von Kleist, M., Hiesinger, P. R. (2024). Axonal self-sorting without target guidance in Drosophila visual map formation.. Science, 383(6687):1084-1092 PubMed ID: 38452066
Summary: The idea of guidance toward a target is central to axon pathfinding and brain wiring in general. This work shows how several thousand axonal growth cones self-pattern without target-dependent guidance during neural superposition wiring in Drosophila. Ablation of all target lamina neurons or loss of target adhesion prevents the stabilization but not the development of the pattern. Intravital imaging at the spatiotemporal resolution of growth cone dynamics in intact pupae and data-driven dynamics simulations reveal a mechanism by which >30,000 filopodia do not explore potential targets, but instead simultaneously generate and navigate a dynamic filopodial meshwork that steers growth directions. Hence, a guidance mechanism can emerge from the interactions of the axons being guided, suggesting self-organization as a more general feature of brain wiring. | Tao, L., Ayembem, D., Barranca, V. J., Bhandawat, V. (2024). Neurons underlying aggressive actions that are shared by both males and females in Drosophila. bioRxiv, PubMed ID: 38464020
Summary: Aggression involves both sexually monomorphic and dimorphic actions. How the brain implements these two types of actions is poorly understood. This study found that a set of neurons, which are called CL062, previously shown to mediate male aggression also mediate female aggression. These neurons elicit aggression acutely and without the presence of a target. Although the same set of actions is elicited in males and females, the overall behavior is sexually dimorphic. The CL062 neurons do not express fruitless, a gene required for sexual dimorphism in flies, and expressed by most other neurons important for controlling fly aggression. Connectomic analysis suggests that these neurons have limited connections with fruitless expressing neurons that have been shown to be important for aggression, and signal to different descending neurons. Thus, CL062 is part of a monomorphic circuit for aggression that functions parallel to the known dimorphic circuits. |
Tuesday November 12th - Disease Models |
Chaurasia, R., Ayajuddin, M., Ratnaparkhi, G. S., Lingadahalli, S. S., Yenisetti, S. C. (2024). A Simple Immunofluorescence Method to Characterize Neurodegeneration and Tyrosine Hydroxylase Reduction in Whole Brain of a Drosophila Model of Parkinson's Disease. Bio Protoc, 14(4):e4937 PubMed ID: 38405079
Summary: Dopaminergic (DAergic) neurodegeneration in the substantia nigra pars compacta of the human brain is the pathological feature associated with Parkinson's disease (PD). Drosophila also exhibits mobility defects and diminished levels of brain dopamine on exposure to neurotoxicants mimicking PD. This study demonstrates in a Drosophila model of sporadic PD that there is no decrease in DAergic neuronal number; instead, there is a significant reduction in tyrosine hydroxylase (TH) fluorescence intensity (FI). This study presents a sensitive assay based on the quantification of FI of the secondary antibody (ab). As the FI is directly proportional to the amount of TH synthesis, its reduction under PD conditions denotes the decrease in the TH synthesis, suggesting DAergic neuronal dysfunction. Therefore, FI quantification is a refined and sensitive method to understand the early stages of DAergic neurodegeneration. FI quantification is performed using the ZEN 2012 SP2 single-user software. This method will be of good use to biologists, as it can also be used with little modification to characterize the extent of degeneration and changes in the level of degeneration in response to drugs in different cell types. Unlike the expensive and cumbersome confocal microscopy, the present method will be an affordable option for fund-constrained neurobiology laboratories. | Imomnazarov, K., Lopez-Scarim, J., Bagheri, I., Joers, V., Tansey, M. G., Martin-Pena, A. (2024). Biochemical Fractionation of Human alpha-Synuclein in a Drosophila Model of Synucleinopathies. Int J Mol Sci, 25(7) PubMed ID: 38612454
Summary: Synucleinopathies are a group of central nervous system pathologies that are characterized by the intracellular accumulation of misfolded and aggregated α-synuclein in proteinaceous depositions known as Lewy Bodies (LBs). The transition of α-synuclein from its physiological to pathological form has been associated with several post-translational modifications such as phosphorylation and an increasing degree of insolubility, which also correlate with disease progression in post-mortem specimens from human patients. Neuronal expression of α-synuclein in model organisms, including Drosophila melanogaster, has been a typical approach employed to study its physiological effects. Biochemical analysis of α-synuclein solubility via high-speed ultracentrifugation with buffers of increasing detergent strength offers a potent method for identification of α-synuclein biochemical properties and the associated pathology stage. Unfortunately, the development of a robust and reproducible method for the evaluation of human α-synuclein solubility isolated from Drosophila tissues has remained elusive. This study tested different detergents for their ability to solubilize human α-synuclein carrying the pathological mutation A53T from the brains of aged flies. The effect of sonication on the solubility of human α-synuclein was assessed, and a protocol was optimized to discriminate the relative amounts of soluble/insoluble human α-synuclein from dopaminergic neurons of the Drosophila brain. The data established that, using a 5% SDS buffer, the three-step protocol separates cytosolic soluble, detergent-soluble and insoluble proteins in three sequential fractions according to their chemical properties. This protocol shows that sonication breaks down α-synuclein insoluble complexes from the fly brain, making them soluble in the SDS buffer and thus enriching the detergent-soluble fraction of the protocol. |
Li, Y., Liu, D., Zhang, X., Rimal, S., Lu, B., Li, S. (2024). RACK1 and IRE1 participate in the translational quality control of amyloid precursor protein in Drosophila models of Alzheimer's disease. J Biol Chem, 300(3):105719 PubMed ID: 38311171
Summary: Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by dysregulation of the expression and processing of the amyloid precursor protein (APP). Protein quality control systems are dedicated to remove faulty and deleterious proteins to maintain cellular protein homeostasis (proteostasis). Identifying mechanisms underlying APP protein regulation is crucial for understanding AD pathogenesis. However, the factors and associated molecular mechanisms regulating APP protein quality control remain poorly defined. This study shows that mutant APP with its mitochondrial-targeting sequence ablated exhibited predominant endoplasmic reticulum (ER) distribution and led to aberrant ER morphology, deficits in locomotor activity, and shortened lifespan. Regulators were sought that could counteract the toxicity caused by the ectopic expression of this mutant APP. Genetic removal of the ribosome-associated quality control (RQC) factor RACK1 resulted in reduced levels of ectopically expressed mutant APP. By contrast, gain of RACK1 function increased mutant APP level. Additionally, overexpression of the ER stress regulator (IRE1) resulted in reduced levels of ectopically expressed mutant APP. Mechanistically, the RQC related ATPase VCP/p97 and the E3 ubiquitin ligase Hrd1 were required for the reduction of mutant APP level by IRE1. These factors also regulated the expression and toxicity of ectopically expressed wild type APP, supporting their relevance to APP biology. THESE results reveal functions of RACK1 and IRE1 in regulating the quality control of APP homeostasis and mitigating its pathogenic effects, with implications for the understanding and treatment of AD. | Loreto, J. S., Ferreira, S. A., de Almeida, P., da Rocha, J. B. T., Barbosa, N. V. (2024). Screening for Differentially Expressed Memory Genes on a Diabetes Model Induced by High-Sugar Diet in Drosophila melanogaster: Potential Markers for Memory Deficits. Molecular neurobiology, 61(3):1225-1236 PubMed ID: 37698834
Summary: Type 2 diabetes mellitus (T2DM) has been shown to affect a series of cognitive processes including memory, increasing the risk for dementia, particularly Alzheimer's disease (AD). Although increasing evidence has supported that both diseases share common features, the pathophysiological mechanisms connecting these two disorders remain to be fully elucidated. This study used Drosophila melanogaster fed on a high-sugar diet (HSD) to mimic T2DM, and investigate its effects on memory as well as identify potential molecular players associated with the memory deficits induced by HSD. Flies hatched from and reared on HSD for 7Â days had a substantial decrease in short-term memory (STM). The screening for memory-related genes using transcriptome data revealed that HSD altered the expression of 33% of memory genes in relation to the control. Among the differentially expressed genes (DEGs) with a fold change (FC) higher than two, were five genes, related to synapse and memory trace formation, that could be considered strong candidates to underlie the STM deficits in HSD flies: Abl tyrosine kinase (Abl), bruchpilot (Brp), minibrain (Mnb), shaker (Sh), and gilgamesh (Gish). We also analyzed genes from the dopamine system, one of the most relevant signaling pathways for olfactory memory. Interestingly, the flies fed on HSD presented a decreased expression of the Tyrosine hydroxylase (Ple) and Dopa decarboxylase (Ddc) genes, signals of a possible dopamine deficiency. This work presents promising biomarkers to investigate molecular networks shared between T2DM and AD. |
Liao, J. Z., Chung, H. L., Shih, C., Wong, K. K. L., Dutta, D., Nil, Z., Burns, C. G., Kanca, O., Park, Y. J., Zuo, Z., Marcogliese, P. C., Sew, K., Bellen, H. J., Verheyen, E. M. (2024). Cdk8/CDK19 promotes mitochondrial fission through Drp1 phosphorylation and can phenotypically suppress pink1 deficiency in Drosophila. Nat Commun, 15(1):3326 PubMed ID: 38637532
Summary: Cdk8 in Drosophila is the orthologue of vertebrate CDK8 and CDK19. These proteins have been shown to modulate transcriptional control by RNA polymerase II. This study found that neuronal loss of Cdk8 severely reduces fly lifespan and causes bang sensitivity. Remarkably, these defects can be rescued by expression of human CDK19, found in the cytoplasm of neurons, suggesting a non-nuclear function of CDK19/Cdk8. This study showed that Cdk8 plays a critical role in the cytoplasm, with its loss causing elongated mitochondria in both muscles and neurons. Endogenous GFP-tagged Cdk8 can be found in both the cytoplasm and nucleus. Cdk8 was shown to promote the phosphorylation of Drp1 at S616, a protein required for mitochondrial fission. Interestingly, Pink1, a mitochondrial kinase implicated in Parkinson's disease, also phosphorylates Drp1 at the same residue. Indeed, overexpression of Cdk8 significantly suppresses the phenotypes observed in flies with low levels of Pink1, including elevated levels of ROS, mitochondrial dysmorphology, and behavioral defects. In summary, it is proposed that Pink1 and Cdk8 perform similar functions to promote Drp1-mediated fission. | Chang, Y. J., Lin, K. T., Shih, O., Yang, C. H., Chuang, C. Y., Fang, M. H., Lai, W. B., Lee, Y. C., Kuo, H. C., Hung, S. C., Yao, C. K., Jeng, U. S., Chen, Y. R. (2024). Sulfated disaccharide protects membrane and DNA damages from arginine-rich dipeptide repeats in ALS. Sci Adv, 10(8):eadj0347 PubMed ID: 38394210
Summary: Hexanucleotide repeat expansion in C9ORF72 (C9) is the most prevalent mutation among amyotrophic lateral sclerosis (ALS) patients. The patients carry over ~30 to hundreds or thousands of repeats translated to dipeptide repeats (DPRs) where poly-glycine-arginine (GR) and poly-proline-arginine (PR) are most toxic. The structure-function relationship is still unknown. This study examined the minimal neurotoxic repeat number of poly-GR and found that extension of the repeat number led to a loose helical structure disrupting plasma and nuclear membrane. Poly-GR/PR bound to nucleotides and interfered with transcription. A sulfated disaccharide was screened and identified that bound to poly-GR/PR and rescued poly-GR/PR-induced toxicity in neuroblastoma and C9-ALS-iPSC-derived motor neurons. The compound rescued the shortened life span and defective locomotion in poly-GR/PR expressing Drosophila model and improved motor behavior in poly-GR-injected mouse model. Overall, these results reveal structural and toxicity mechanisms for poly-GR/PR and facilitate therapeutic development for C9-ALS. |
Monday November 11th - Behavior |
Schwarz, J. E., Sengupta, A., Guevara, C., Barber, A. F., Hsu, C. T., Zhang, S. L., Weljie, A., Sehgal, A. (2024). Age-regulated cycling metabolites are relevant for behavior. Aging Cell, 23(4):e14082 PubMed ID: 38204362
Summary: Circadian cycles of sleep:wake and gene expression change with age in all organisms examined. Metabolism is also under robust circadian regulation, but little is known about how metabolic cycles change with age and whether these contribute to the regulation of behavioral cycles. To address this gap, cycling of metabolites in young and old Drosophila was compared and major age-related variations were found. A significant model separated the young metabolic profiles by circadian timepoint, but could not be defined for the old metabolic profiles due to the greater variation in this dataset. Of the 159 metabolites measured in fly heads, 17 were found that cycle by JTK analysis in young flies and 17 in aged. Only four metabolites overlapped in the two groups, suggesting that cycling metabolites are distinct in young and old animals. Among our top cyclers exclusive to young flies were components of the pentose phosphate pathway (PPP). As the PPP is important for buffering reactive oxygen species, and overexpression of glucose-6-phosphate dehydrogenase (G6PD), a key component of the PPP, was previously shown to extend lifespan in Drosophila, it was asked if this manipulation also affects sleep:wake cycles. Overexpression in circadian clock neurons was found to decrease sleep in association with an increase in cellular calcium and mitochondrial oxidation, suggesting that altering PPP activity affects neuronal activity. These findings elucidate the importance of metabolic regulation in maintaining patterns of neural activity, and thereby sleep:wake cycles. | Thiem, J., Viskadourou, M., Gaitanidis, A., Stravopodis, D. J., Strauß, R., Duch, C., Consoulas, C. (2024). Biological aging of two innate behaviors of Drosophila melanogaster: Escape climbing versus courtship learning and memory. PLoS One, 19(4):e0293252 PubMed ID: 38593121
Summary: Motor and cognitive aging can severely affect life quality of elderly people and burden health care systems. In search for diagnostic behavioral biomarkers, it has been suggested that walking speed can predict forms of cognitive decline, but in humans, it remains challenging to separate the effects of biological aging and lifestyle. This study examined a possible association of motor and cognitive decline in Drosophila, a genetic model organism of healthy aging. Long term courtship memory is present in young male flies but absent already during mid life (4-8 weeks). By contrast, courtship learning index and short term memory (STM) are surprisingly robust and remain stable through mid (4-8 weeks) and healthy late life (>8 weeks), until courtship performance collapses suddenly at ~4.5 days prior to death. By contrast, climbing speed declines gradually during late life (>8 weeks). The collapse of courtship performance and short term memory close to the end of life occur later and progress with a different time course than the gradual late life decline in climbing speed. Thus, during healthy aging in male Drosophila, climbing and courtship motor behaviors decline differentially. Moreover, cognitive and motor performances decline at different time courses. Differential behavioral decline during aging may indicate different underlying causes, or alternatively, a common cause but different thresholds for defects in different behaviors. |
Jiang, X., Sun, M., Chen, J., Pan, Y. (2024). Sex-Specific and State-Dependent Neuromodulation Regulates Male and Female Locomotion and Sexual Behaviors. Research (Washington, DC), 7:0321 PubMed ID: 38390306
Summary: Males and females display dimorphic behaviors that often involve sex-specific locomotor patterns. How the sexually dimorphic locomotion is mediated is poorly understood. This study identify a neuropeptide that oppositely regulates locomotion for efficient sexual behaviors in Drosophila males and females. Males are less active than females if isolated. However, when sexually aroused through activating homologous but sexually dimorphic pC1 neurons, males exhibit higher activity levels than females. Diuretic hormone 44 (DH44), that functions in pC1 neurons in a sex-specific way, was found to inhibit male locomotion and promote female locomotion. Surprisingly, DH44 exerts opposite effects in sexually aroused flies to promote male locomotion and suppress female locomotion, which is crucial for successful male courtship and female receptivity. These findings demonstrate sexually dimorphic and state-dependent control of locomotor activity by pC1 neuronal activity and DH44 modulation. | Zhao, H., Jiang, X., Ma, M., Xing, L., Ji, X., Pan, Y. (2024). A neural pathway for social modulation of spontaneous locomotor activity (SoMo-SLA) in Drosophila. Proc Natl Acad Sci U S A, 121(9):e2314393121 PubMed ID: 38394240
Summary: Social enrichment or social isolation affects a range of innate behaviors, such as sex, aggression, and sleep, but whether there is a shared mechanism is not clear. This study reports a neural mechanism underlying social modulation of spontaneous locomotor activity (SoMo-SLA), an internal-driven behavior indicative of internal states. Social enrichment specifically reduces spontaneous locomotor activity in male flies. We identify neuropeptides Diuretic hormone 44 (DH44) and Tachykinin (TK) to be up- and down-regulated by social enrichment and necessary for SoMo-SLA. A sexually dimorphic neural circuit was further demonstrate, in which the male-specific P1 neurons encoding internal states form positive feedback with interneurons coexpressing doublesex (dsx) and Tk to promote locomotion, while P1 neurons also form negative feedback with interneurons coexpressing dsx and DH44 to inhibit locomotion. These two opposing neuromodulatory recurrent circuits represent a potentially common mechanism that underlies the social regulation of multiple innate behaviors. |
Jagannathan, S. R., Jeans, T., Van De Poll, M. N., van Swinderen, B. (2024). Multivariate classification of multichannel long-term electrophysiology data identifies different sleep stages in fruit flies. Sci Adv, 10(8):eadj4399 PubMed ID: 38381836
Summary: Identifying different sleep stages in humans and other mammals has traditionally relied on electroencephalograms. Such an approach is not feasible in certain animals such as invertebrates, although these animals could also be sleeping in stages. In this study long-term multichannel local field potential recordings were performed in the brains of behaving flies undergoing spontaneous sleep bouts. Aonsistent spatial recordings were acquired of local field potentials across multiple flies, allowing comparison of brain activity across awake and sleep periods. Using machine learning, distinct temporal stages of sleep were uncover and the associated spatial and spectral features across the fly brain were explored. Further, the electrophysiological correlates were analyzed of microbehaviors associated with certain sleep stages. The existence was confirmed of a distinct sleep stage associated with rhythmic proboscis extensions, and spectral features of this sleep-related behavior was shown to differ significantly from those associated with the same behavior during wakefulness, indicating a dissociation between behavior and the brain states wherein these behaviors reside. | Panos, P., Chan, T., Gowda, N., Hong, J., Kansal, R., Shen, K., McLean, E. (2024). Sex Differences in Sociability for Drosophila melanogaster with Altered Gut Microbiomes. microPublication biology, 2024 PubMed ID: 38481554
Summary: In Drosophila melanogaster the gut microbiome has been shown to influence multiple behaviors, including aggressive social behavior. This study investigated the effect of the Drosophila microbiome on pro-social behavior. It was predicted that reducing the microbiome would lead to a decrease in pro-social behavior in adult flies. After altering the flies' microbiomes, virgin male flies with reduced microbiomes were significantly less social than virgin male control flies (t=3.09, p=0.006). This difference was not observed in virgin female flies (t=0.344, p=0.73), or mated flies of either sex (males: t=0.456, p=0.66; females: t=0.271, p=0.79). These results suggest that the role of the Drosophila microbiome in pro-social behavior is dependent on both sex and previous social experience. |
Saturday November 9th - Evolution |
Jarvis, W. M. C., Arthur, N. J., Rundle, H. D., Dyer, K. A. (2024). An experimental test of the evolutionary consequences of sympatry in Drosophila subquinaria. Evolution, 78(3):555-565 PubMed ID: 38153840
Summary: Prezygotic isolation is often stronger between sympatric as opposed to allopatric taxa, but the underlying cause can be difficult to infer from comparative studies alone. Experimental evolution, where evolutionary responses to treatments manipulating the presence/absence of heterospecific individuals are tracked, can provide a powerful complementary approach. This study used experimental evolution to investigate a naturally occurring pattern of reproductive character displacement in the mushroom-feeding fly, Drosophila subquinaria. In nature, female D. subquinaria from populations sympatric with the closely related Drosophila recens discriminate more strongly against heterospecific males than do females from allopatric populations. Starting with 16 replicate allopatric populations of D. subquinaria, the presence/absence of D. recens during mating (experimental sympatry vs. control) was manipulated and, when present, hybrids were allowed to live or they were killed each generation. Across 12 generations, heterospecific offspring production from no-choice mating trials between D. subquinaria females and D. recens males declined in both experimental sympatry treatments relative to the control, suggesting increased sexual isolation. Male cuticular hydrocarbon profiles also evolved, but only in the hybrids killed treatment. These results strongly imply that the existing reproductive character displacement in wild D. subquinaria populations was an evolutionary response to selection arising from secondary contact with D. recens. | Urum, A., Rice, G., Glassford, W., Yanku, Y., Shklyar, B., Rebeiz, M., Preger-Ben Noon, E. (2024). A developmental atlas of male terminalia across twelve species of Drosophila. Frontiers in cell and developmental biology, 12:1349275 PubMed ID: 38487271
Summary: How complex morphologies evolve is one of the central questions in evolutionary biology. Observing the morphogenetic events that occur during development provides a unique perspective on the origins and diversification of morphological novelty. One can trace the tissue of origin, emergence, and even regression of structures to resolve murky homology relationships between species. This study traced the developmental events that shape some of the most diverse organs in the animal kingdom-the male terminalia (genitalia and analia) of Drosophilids. Male genitalia are known for their rapid evolution with closely related species of the Drosophila genus demonstrating vast variation in their reproductive morphology. Confocal microscopy was used to monitor terminalia development during metamorphosis in twelve related species of Drosophila. From this comprehensive dataset, a new staging scheme is proposed for pupal terminalia development based on shared developmental landmarks, which allows one to align developmental time points between species. It was possible to trace the origin of different substructures, find new morphologies and suggest possible homology of certain substructures. Additionally, it was demonstrated that posterior lobe is likely originated prior to the split between the Drosophila melanogaster and the Drosophila yakuba clade. This dataset opens up many new directions of research and provides an entry point for future studies of the Drosophila male terminalia evolution and development. |
Padilla Perez, D. J. (2024). Geographic and seasonal variation of the for gene reveal signatures of local adaptation in Drosophila melanogaster. J Evol Biol, 37(2):201-211 PubMed ID: 38301664
Summary: In the early 1980s, the observation that Drosophila melanogaster larvae differed in their foraging behaviour laid the foundation for the work that would later lead to the discovery of the foraging gene (for) and its associated foraging phenotypes, rover and sitter. Since then, the molecular characterization of the for gene and understanding of the mechanisms that maintain its phenotypic variants in the laboratory have progressed enormously. However, the significance and dynamics of such variation are yet to be investigated in nature. With the advent of next-generation sequencing, it is now possible to identify loci underlying the adaptation of populations in response to environmental variation. This study presents the results of a genotype-environment association analysis that quantifies variation at the for gene among samples of D. melanogaster structured across space and time. These samples consist of published genomes of adult flies collected worldwide, and at least twice per site of collection (during spring and fall). Both an analysis of genetic differentiation based on Fsâ¢t values and an analysis of population structure revealed an east-west gradient in allele frequency. This gradient may be the result of spatially varying selection driven by the seasonality of precipitation. These results support the hypothesis that different patterns of gene flow as expected under models of isolation by distance and potentially isolation by environment are driving genetic differentiation among populations. Overall, this study is essential for understanding the mechanisms underlying the evolution of foraging behaviour in D. melanogaster. | Janzen, A., Pothula, R., Sychla, A., Feltman, N. R., Smanski, M. J. (2024). Predicting thresholds for population replacement gene drives. BMC Biol, 22(1):40 PubMed ID: 38369493
Summary: Threshold-dependent gene drives (TDGDs) could be used to spread desirable traits through a population, and are likely to be less invasive and easier to control than threshold-independent gene drives. Engineered Genetic Incompatibility (EGI) is an extreme underdominance system previously demonstrated in Drosophila melanogaster that can function as a TDGD when EGI agents of both sexes are released into a wild-type population. This study used a single generation fitness assay to compare the fecundity, mating preferences, and temperature-dependent relative fitness to wild-type of two distinct genotypes of EGI agents. Significant differences were found in the behavior/performance of these EGI agents that would not be predicted a priori based on their genetic design. A surprising temperature-dependent change is reported in the predicted threshold for population replacement in an EGI agent that drives ectopic expression of the developmental morphogen pyramus. The single-generation fitness assay presented here could reduce the amount of time required to estimate the threshold for TDGD strategies for which hybrid genotypes are inviable. Additionally, this work underscores the importance of empirical characterization of multiple engineered lines, as behavioral differences can arise in unique genotypes for unknown reasons. |
Clifton, B. D., Hariyani, I., Kimura, A., Luo, F., Nguyen, A., Ranz, J. M. (2023). Paralog transcriptional differentiation in the D. melanogaster-specific gene family Sdic across populations and spermatogenesis stages. Communications biology, 6(1):1069 PubMed ID: 37864070
Summary: How recently originated gene copies become stable genomic components remains uncertain as high sequence similarity of young duplicates precludes their functional characterization. The tandem multigene family Sdic is specific to Drosophila melanogaster and has been annotated across multiple reference-quality genome assemblies. This study shows the existence of a positive correlation between Sdic copy number and total expression, plus vast intrastrain differences in mRNA abundance among paralogs, using RNA-sequencing from testis of four strains with variable paralog composition. Single cell and nucleus RNA-sequencing data expose paralog expression differentiation in meiotic cell types within testis from third instar larva and adults. Additional RNA-sequencing across synthetic strains only differing in their Y chromosomes reveal a tissue-dependent trans-regulatory effect on Sdic: upregulation in testis and downregulation in male accessory gland. By leveraging paralog-specific expression information from tissue- and cell-specific data, these results elucidate the intraspecific functional diversification of a recently expanded tandem gene family. | Harris, M., Kim, B. Y., Garud, N. (2024). Enrichment of hard sweeps on the X chromosome compared to autosomes in six Drosophila species. Genetics, 226(4) PubMed ID: 38366786
Summary: The X chromosome, being hemizygous in males, is exposed one-third of the time increasing the visibility of new mutations to natural selection, potentially leading to different evolutionary dynamics than autosomes. Recently, an enrichment was found of hard selective sweeps over soft selective sweeps on the X chromosome relative to the autosomes in a North American population of Drosophila melanogaster. To understand whether this enrichment is a universal feature of evolution on the X chromosome, diversity patterns were analyzed across 6 commonly studied Drosophila species. An increased proportion was found of regions with steep reductions in diversity and elevated homozygosity on the X chromosome compared to autosomes. To assess if these signatures are consistent with positive selection, a wide variety of evolutionary scenarios was simulated spanning variations in demography, mutation rate, recombination rate, background selection, hard sweeps, and soft sweeps; the diversity patterns observed on the X are most consistent with hard sweeps. These findings highlight the importance of sex chromosomes in driving evolutionary processes and suggest that hard sweeps have played a significant role in shaping diversity patterns on the X chromosome across multiple Drosophila species. |
Wednesday November 6th - Synapse and Vesicles |
Son, S., Jeong, H., Lee, G., Park, J. H., Yoo, S. (2024). Biogenesis of circular RNAs in vitro and in vivo from the Drosophila Nk2.1 / scarecrow gene. bioRxiv, PubMed ID: 38463984
Summary: scarecrow (scro) encodes a fly homolog of mammalian Nkx2.1 that is vital for early fly development as well as for optic lobe development. Interestingly, scro was reported to produce a circular RNA (circRNA). This study identified 12 different scro circRNAs, which are either mono- or multi-exonic forms. The most abundant forms are circE2 carrying the second exon only and bi-exonic circE3-E4. Levels of circE2 show an age-dependent increase in adult heads, supporting a general trend of high accumulation of circRNAs in aged fly brains. Aligning sequences of introns flanking exons uncovered two pairs of intronic complementary sequences (ICSs); one pair residing in introns 1 and 2 and the other in introns 2 and 4. The first pair was demonstrated to be essential for the circE2 production in cell-based assays; furthermore, deletion of the region including potential ICS components in the intron-2 reduced in vivo production of circE2 and circE3-E4 by 80%, indicating them to be essential for the biogenesis of these isoforms. Besides the ICS, the intron regions immediately abutting exons seemed to be responsible for a basal level of circRNA formation. Moreover, the replacement of scro-ICS with those derived from laccase2 was comparably effective in scro-circRNA production, buttressing the importance of the hairpin-loop structure formed by ICS for the biogenesis of circRNA. Lastly, overexpressed scro affected outcomes of both linear and circular RNAs from the endogenous scro locus, suggesting that Scro plays a direct or indirect role in regulating expression levels of either or both forms. | Bernard, E. I. M., Towler, B. P., Rogoyski, O. M., Newbury, S. F. (2024). Characterisation of the in-vivo miRNA landscape in Drosophila ribonuclease mutants reveals Pacman-mediated regulation of the highly conserved let-7 cluster during apoptotic processes. Front Genet, 15:1272689 PubMed ID: 38444757
Summary: The control of gene expression is a fundamental process essential for correct development and to maintain homeostasis. Many post-transcriptional mechanisms exist to maintain the correct levels of each RNA transcript within the cell. Controlled and targeted cytoplasmic RNA degradation is one such mechanism with the 5'-3' exoribonuclease Pacman (XRN1) and the 3'-5' exoribonuclease Dis3L2 playing crucial roles. Loss of function mutations in either Pacman or Dis3L2 have been demonstrated to result in distinct phenotypes, and both have been implicated in human disease. One mechanism by which gene expression is controlled is through the function of miRNAs which have been shown to be crucial for the control of almost all cellular processes. Although the biogenesis and mechanisms of action of miRNAs have been comprehensively studied, the mechanisms regulating their own turnover are not well understood. This study characterised the miRNA landscape in a natural developing tissue, the Drosophila melanogaster wing imaginal disc, and assess the importance of Pacman and Dis3L2 on the abundance of miRNAs. A complex landscape of miRNA expression was revealed, and it whilst a null mutation in dis3L2 has a minimal effect on the miRNA expression profile, loss of Pacman has a profound effect with a third of all detected miRNAs demonstrating Pacman sensitivity. A role was revealed for Pacman in regulating the highly conserved let-7 cluster (containing miR-100, let-7 and miR-125), and a genetic model is presented outlining a positive feedback loop regulated by Pacman which enhances understanding of the apoptotic phenotype observed in Pacman mutants. |
Ilık, I, A., Jaglarzar, P., Tse, K., Brandl, B., Meierhofer, D., Muller, F. J., Smith, Z. D., Aktas, T. (2024). Autonomous transposons tune their sequences to ensure somatic suppression. Nature, 626(8001):1116-1124 PubMed ID: 38355802
Summary: Transposable elements (TEs) are a major constituent of human genes, occupying approximately half of the intronic space. During pre-messenger RNA synthesis, intronic TEs are transcribed along with their host genes but rarely contribute to the final mRNA product because they are spliced out together with the intron and rapidly degraded. Paradoxically, TEs are an abundant source of RNA-processing signals through which they can create new introns, and also functional or non-functional chimeric transcripts. The rarity of these events implies the existence of a resilient splicing code that is able to suppress TE exonization without compromising host pre-mRNA processing. This study shows that SAFB proteins protect genome integrity by preventing retrotransposition of L1 elements while maintaining splicing integrity, via prevention of the exonization of previously integrated TEs. This unique dual role is possible because of L1's conserved adenosine-rich coding sequences that are bound by SAFB proteins. The suppressive activity of SAFB extends to tissue-specific, giant protein-coding cassette exons, nested genes and Tigger DNA transposons. Moreover, SAFB also suppresses LTR/ERV elements in species in which they are still active, such as mice and flies. A significant subset of splicing events suppressed by SAFB in somatic cells are activated in the testis, coinciding with low SAFB expression in postmeiotic spermatids. Reminiscent of the division of labour between innate and adaptive immune systems that fight external pathogens, our results uncover SAFB proteins as an RNA-based, pattern-guided, non-adaptive defence system against TEs in the soma, complementing the RNA-based, adaptive Piwi-interacting RNA pathway of the germline. | Saedi, H., Waro, G., Giacchetta, L., Tsunoda, S. (2024). miR-137 regulates PTP61F, affecting insulin signaling, metabolic homeostasis, and starvation resistance in Drosophila. Proc Natl Acad Sci U S A, 121(5):e2319475121 PubMed ID: 38252824
Summary: miR-137 is a highly conserved brain-enriched microRNA (miRNA) that has been associated with neuronal function and proliferation. This study shows that Drosophila miR-137 null mutants display increased body weight with enhanced triglyceride content and decreased locomotor activity. In addition, when challenged by nutrient deprivation, miR-137 mutants exhibit reduced motivation to feed and prolonged survival. Genetic epistasis and rescue experiments show that this starvation resistance is due to a disruption in insulin signaling. These studies further show that miR-137 null mutants exhibit a drastic reduction in levels of the phosphorylated/activated Insulin receptor, InR (InR-P). Whether this is due to the predicted miR-137 target, Protein Tyrosine Phosphatase 61F (PTP61F), ortholog of mammalian TC-PTP/PTP1B, which are known to dephosphorylate InR-P. Indeed, levels of an endogenously tagged GFP-PTP61F are significantly elevated in miR-137 null mutants, and overexpression of PTP61F alone was shown to be sufficient to mimic many of the metabolic phenotypes of miR-137 mutants. Finally, elevated levels of PTP61F in the miR-137 null mutant background were knocked-down and this rescues levels of InR-P, restores normal body weight and triglyceride content, starvation sensitivity, as well as attenuates locomotor and starvation-induced feeding defects. This study supports a model in which miR-137 is critical for dampening levels of PTP61F, thereby maintaining normal insulin signaling and energy homeostasis. |
Crawford, B. I., Talley, M. J., Russman, J., Riddle, J., Torres, S., Williams, T., Longworth, M. S. (2024). Condensin-mediated restriction of retrotransposable elements facilitates brain development in Drosophila melanogaster. Nat Commun, 15(1):2716 PubMed ID: 38548759
Summary: Neural stem and progenitor cell (NSPC) maintenance is essential for ensuring that organisms are born with proper brain volumes and head sizes. Microcephaly is a disorder in which babies are born with significantly smaller head sizes and cortical volumes. Mutations in subunits of the DNA organizing complex condensin have been identified in microcephaly patients. However, the molecular mechanisms by which condensin insufficiency causes microcephaly remain elusive. Previous work has identified conserved roles for condensins in repression of retrotransposable elements (RTEs). This study shows that condensin subunit Cap-d3 knockdown in NSPCs of the Drosophila larval central brain increases RTE expression and mobility which causes cell death, and significantly decreases adult head sizes and brain volumes. These findings suggest that unrestricted RTE expression and activity may lead to improper brain development in condensin insufficient organisms, and lay the foundation for future exploration of causative roles for RTEs in other microcephaly models. | Rajeev, R., Mishra, R. K., Khosla, S. (2024). DNMT3L interacts with Piwi and modulates the expression of piRNAs in transgenic Drosophila. Epigenomics, 16(6):375-388 PubMed ID: 38440884
Summary: This study explored the role of Piwi protein and piRNAs in DNMT3L-mediated epigenetic inheritance. Transgenic Drosophila were used to examine the effect of ectopically expressed DNMT3L on the profile of piRNAs by sequencing of small RNAs. Previous work showed accumulation and inheritance of epimutations across multiple generations in transgenic DNMT3L Drosophila. This study shows interaction of DNMT3L with Piwi and a significant alteration in the piRNA profile across multiple generations in transgenic Drosophila. In the light of its interaction with histone H1, it is proposed that in addition to its role of modulating core histone modifications, DNMT3L allows for inheritance of epigenetic information through its collaboration with Piwi, piRNAs and histone H1. |
Tuesday November 5th - Synapse and Vesicles |
Beckers, C. J., Mrestani, A., Komma, F., Dannhauser, S. (2024). Versatile Endogenous Editing of GluRIIA in Drosophila melanogaster. Cells, 13(4) PubMed ID: 38391936
Summary: Glutamate receptors at the postsynaptic side translate neurotransmitter release from presynapses into postsynaptic excitation. They play a role in many forms of synaptic plasticity, e.g., homeostatic scaling of the receptor field, activity-dependent synaptic plasticity and the induction of presynaptic homeostatic potentiation (PHP). The latter process has been extensively studied at Drosophila melanogaster neuromuscular junctions (NMJs). The genetic removal of the glutamate receptor subunit IIA (GluRIIA) leads to an induction of PHP at the synapse. So far, mostly imprecise knockouts of the GluRIIA gene have been utilized. Furthermore, mutated and tagged versions of GluRIIA have been examined in the past, but most of these constructs were not expressed under endogenous regulatory control or involved the mentioned imprecise GluRIIA knockouts. This study performed CRISPR/Cas9-assisted gene editing at the endogenous locus of GluRIIA. This enabled the investigation of the endogenous expression pattern of GluRIIA using tagged constructs with an EGFP and an ALFA tag for super-resolution immunofluorescence imaging, including structured illumination microscopy (SIM) and direct stochastic optical reconstruction microscopy (dSTORM). All GluRIIA constructs exhibited full functionality and PHP could be induced by philanthotoxin at control levels. By applying hierarchical clustering algorithms to analyze the dSTORM data, postsynaptic receptor cluster areas of ~0.15 μm(2) were detected. Consequently, these constructs are suitable for ultrastructural analyses of GluRIIA. | Delgado, M. G., Delgado, R. (2024). Transient Synaptic Enhancement Triggered by Exogenously Supplied Monocarboxylate in Drosophila Motoneuron Synapse. Neuroscience, 539:66-75 PubMed ID: 38220128
Summary: Current evidence suggests that glial cells provide C3 carbon sources to fuel neuronal activity; however, this notion has become challenged by biosensor studies carried out in acute brain slices or in vivo, showing that neuronal activity does not rely on the import of astrocyte-produced L-lactate. Rather, stimulated neurons become net lactate exporters, as it was also shown in Drosophila neurons, in which astrocyte-provided lactate returns as lipid droplets to be stored in glial cells. In this view, this study investigated whether exogenously supplied monocarboxylates can support Drosophila motoneuron neurotransmitter release (NTR). By assessing the excitatory post-synaptic current (EPSC) amplitude under voltage-clamp as NTR indicative, both pyruvate and L-lactate (as the only carbon sources in the synapses bathing-solution) cause a large transient NTR enhancement, which declines to reach a synaptic depression state, from which the synapses do not recover. The FM1-43 (a fluorescent styryl dye that stains nerve terminals in an activity-dependent fashion) pre-synaptic loading ability , however, is maintained under monocarboxylate, suggesting that SV cycling should not contribute to the synaptic depression state. The NTR recovery was reached by supplementing the monocarboxylate medium with sucrose. However, monocarboxylate addition to sucrose medium does not enhance NTR, but it does when the disaccharide concentration becomes too reduced. Thus, when pyruvate concentrations become too reduced, exogenously supplied L-lactate could be converted to pyruvate and metabolized by the neural mitochondria, triggering the NTR enhancement. |
Dutta, D., Kanca, O., Shridharan, R. V., Marcogliese, P. C., Steger, B., Morimoto, M., Frost, F. G., Macnamara, E., Wangler, M. F., Yamamoto, S., Jenny, A., Adams, D., Malicdan, M. C., Bellen, H. J. (2024). Loss of the endoplasmic reticulum protein Tmem208 affects cell polarity, development, and viability. Proc Natl Acad Sci U S A, 121(9):e2322582121 PubMed ID: 38381787
Summary: Nascent proteins destined for the cell membrane and the secretory pathway are targeted to the endoplasmic reticulum (ER) either posttranslationally or cotranslationally. The signal-independent pathway, containing the protein TMEM208, is one of three pathways that facilitates the translocation of nascent proteins into the ER. The in vivo function of this protein is ill characterized in multicellular organisms. This study generated a CRISPR-induced null allele of the fruit fly ortholog CG8320/Tmem208 by replacing the gene with the Kozak-GAL4 sequence. Tmem208 was shown to be broadly expressed in flies and that its loss causes lethality, although a few short-lived flies eclose. These animals exhibit wing and eye developmental defects consistent with impaired cell polarity and display mild ER stress. Tmem208 physically interacts with Frizzled (Fz), a planar cell polarity (PCP) receptor, and is required to maintain proper levels of Fz. Moreover, this study identified a child with compound heterozygous variants in TMEM208 who presents with developmental delay, skeletal abnormalities, multiple hair whorls, cardiac, and neurological issues, symptoms that are associated with PCP defects in mice and humans. Additionally, fibroblasts of the proband display mild ER stress. Expression of the reference human TMEM208 in flies fully rescues the loss of Tmem208, and the two proband-specific variants fail to rescue, suggesting that they are loss-of-function alleles. In summary, this study uncovers a role of TMEM208 in development, shedding light on its significance in ER homeostasis and cell polarity. | Szenci, G., Glatz, G., Takaes, S., Juhasz, G. (2024). The Ykt6-Snap29-Syx13 SNARE complex promotes crinophagy via secretory granule fusion with Lamp1 carrier vesicles. Sci Rep, 14(1):3200 PubMed ID: 38331993
Summary: n the Drosophila larval salivary gland, developmentally programmed fusions between lysosomes and secretory granules (SGs) and their subsequent acidification promote the maturation of SGs that are secreted shortly before puparium formation. Subsequently, ongoing fusions between non-secreted SGs and lysosomes give rise to degradative crinosomes, where the superfluous secretory material is degraded. Lysosomal fusions control both the quality and quantity of SGs, however, its molecular mechanism is incompletely characterized. This study identified the R-SNARE Ykt6 as a novel regulator of crinosome formation, but not the acidification of maturing SGs. We show that Ykt6 localizes to Lamp1+carrier vesicles, and forms a SNARE complex with Syntaxin 13 and Snap29 to mediate fusion with SGs. These Lamp1 carriers represent a distinct vesicle population that are functionally different from canonical Arl8+, Cathepsin L+ lysosomes, which also fuse with maturing SGs but are controlled by another SNARE complex composed of Syntaxin 13, Snap29 and Vamp7. Ykt6- and Vamp7-mediated vesicle fusions also determine the fate of SGs, as loss of either of these SNAREs prevents crinosomes from acquiring endosomal PI3P. These results highlight that fusion events between SGs and different lysosome-related vesicle populations are critical for fine regulation of the maturation and crinophagic degradation of SGs. |
Drogalin, A., Monteiro, L. S., Alves, M. J., Castro, T. G. (2024). Golgi α-mannosidase: opposing structures of Drosophila melanogaster and novel human model using molecular dynamics simulations and docking at different pHs. Journal of biomolecular structure & dynamics, 42(5):2714-2725 PubMed ID: 37158092
Summary: The search for Golgi αmannosidase II (GMII) potent and specific inhibitors has been a focus of many studies for the past three decades since this enzyme is a key target for cancer treatment. α-Mannosidases, such as those from Drosophila melanogaster or Jack bean, have been used as functional models of the human Golgi α-mannosidase II (hGMII) because mammalian mannosidases are difficult to purify and characterize experimentally. Meanwhile, computational studies have been seen as privileged tools able to explore assertive solutions to specific enzymes, providing molecular details of these macromolecules, their protonation states and their interactions. Thus, modelling techniques can successfully predict hGMII 3D structure with high confidence, speeding up the development of new hits. In this study, Drosophila melanogaster Golgi mannosidase II (dGMII) and a novel human model, developed in silico and equilibrated via molecular dynamics simulations, were both opposed for docking. These findings highlight that the design of novel inhibitors should be carried out considering the human model's characteristics and the enzyme operating pH. A reliable model is evidenced, showing a good correlation between K(i)/IC(50) experimental data and theoretical ΔG(binding) estimations in GMII, opening the possibility of optimizing the rational drug design of new derivatives. | Gao, Z., Huang, E., Wang, W., Xu, L., Xu, W., Zheng, T., Rui, M. (2024). Patronin regulates presynaptic microtubule organization and neuromuscular junction development in Drosophila. iScience, 27(2):108944 PubMed ID: 38318379
Summary: Synapses are fundamental components of the animal nervous system. Synaptic cytoskeleton is essential for maintaining proper neuronal development and wiring. Perturbations in neuronal microtubules (MTs) are correlated with numerous neuropsychiatric disorders. Despite discovering multiple synaptic MT regulators, the importance of MT stability, and particularly the polarity of MT in synaptic function, is still under investigation. This study identified Patronin, an MT minus-end-binding protein, for its essential role in presynaptic regulation of MT organization and neuromuscular junction (NMJ) development. Analyses indicate that Patronin regulates synaptic development independent of Klp10A. Subsequent research elucidates that it is Short stop (Shot), a member of the Spectraplakin family of large cytoskeletal linker molecules, works synergistically with Patronin to govern NMJ development. This study further raise the possibility that normal synaptic MT polarity contributes to proper NMJ morphology. Overall, this study demonstrates an unprecedented role of Patronin, and a potential involvement of MT polarity in synaptic development. |
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