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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. This study examined 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.
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Monday December 13th - Chromatin and DNA repaired |
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Koestler, S. A., Ball, M. L., Muresan, L., Dinakaran, V., White, R. (2024). Transcriptionally active chromatin loops contain both 'active' and 'inactive' histone modifications that exhibit exclusivity at the level of nucleosome clusters. Epigenetics & chromatin, 17(1):8 PubMed ID: 38528624
Summary:
Chromatin state is thought to impart regulatory function to the underlying DNA sequence. This can be established through histone modifications and chromatin organisation, but exactly how these factors relate to one another to regulate gene expression is unclear. In this study, super-resolution microscopy was used to image the Y loops of Drosophila melanogaster primary spermatocytes, which are enormous transcriptionally active chromatin fibres, each representing single transcription units that are individually resolvable in the nuclear interior. Previous work found that the Y loops consist of regular clusters of nucleosomes, with an estimated median of 54 nucleosomes per cluster with wide variation. This study reports that the histone modifications H3K4me3, H3K27me3, and H3K36me3 are also clustered along the Y loops, with H3K4me3 more associated with diffuse chromatin compared to H3K27me3. These histone modifications form domains that can be stretches of Y loop chromatin micrometres long, or can be in short alternating domains. The different histone modifications are associated with different sizes of chromatin clusters and unique morphologies. Strikingly, a single chromatin cluster almost always only contains only one type of the histone modifications that were labelled, suggesting exclusivity, and therefore regulation at the level of individual chromatin clusters. The active mark H3K36me3 is more associated with actively elongating RNA polymerase II than H3K27me3, with polymerase often appearing on what are assumed to be looping regions on the periphery of chromatin clusters.These results provide a foundation for understanding the relationship between chromatin state, chromatin organisation, and transcription regulation - with potential implications for pause-release dynamics, splicing complex organisation and chromatin dynamics during polymerase progression along a gene.
| Kamalyan, S., Kyrchanova, O., Klimenko, N., Babosha, V., Vasileva, Y., Belova, E., Fursenko, D., Maksimenko, O., Georgiev, P. (2024). The N-terminal dimerization domains of human and Drosophila CTCF have similar functionality. Epigenetics & chromatin, 17(1):9 PubMed ID: 38561749
Summary:
CTCF is highly likely to be the ancestor of proteins that contain large clusters of C2H2 zinc finger domains, and its conservation is observed across most bilaterian organisms. In mammals, CTCF is the primary architectural protein involved in organizing chromosome topology and mediating enhancer-promoter interactions over long distances. In Drosophila, CTCF (dCTCF) cooperates with other architectural proteins to establish long-range interactions and chromatin boundaries. CTCFs of various organisms contain an unstructured N-terminal dimerization domain (DD) and clusters comprising eleven zinc-finger domains of the C2H2 type. The Drosophila (dCTCF) and human (hCTCF) CTCFs share sequence homology in only five C2H2 domains that specifically bind to a conserved 15 bp motif. Previous work demonstrated that CTCFs from different organisms carry unstructured N-terminal dimerization domains (DDs) that lack sequence homology. This study used the CTCF(attP(mCh)) platform to introduce desired changes in the Drosophila CTCF gene and generated a series of transgenic lines expressing dCTCF with different variants of the N-terminal domain. The findings revealed that the functionality of dCTCF is significantly affected by the deletion of the N-terminal DD. Additionally, a strong impact was observed on the binding of the dCTCF mutant to chromatin upon deletion of the DD. However, chromatin binding was restored in transgenic flies expressing a chimeric CTCF protein with the DD of hCTCF. Although the chimeric protein exhibited lower expression levels than those of the dCTCF variants, it efficiently bound to chromatin similarly to the wild type (wt) protein. These findings suggest that one of the evolutionarily conserved functions of the unstructured N-terminal dimerization domain is to recruit dCTCF to its genomic sites in vivo.
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Graham, E. L., Fernandez, J., Gandhi, S., Choudhry, I., Kellam, N., LaRocque, J. R. (2024). The impact of developmental stage, tissue type, and sex on DNA double-strand break repair in Drosophila melanogaster. PLoS Genet, 20(4):e1011250 PubMed ID: 38683763
Summary:
Accurate repair of DNA double-strand breaks (DSBs) is essential for the maintenance of genome integrity, as failure to repair DSBs can result in cell death. The cell has evolved two main mechanisms for DSB repair: non-homologous end-joining (NHEJ) and homology-directed repair (HDR), which includes single-strand annealing (SSA) and homologous recombination (HR). While certain factors like age and state of the chromatin are known to influence DSB repair pathway choice, the roles of developmental stage, tissue type, and sex have yet to be elucidated in multicellular organisms. To examine the influence of these factors, DSB repair in various embryonic developmental stages, larva, and adult tissues in Drosophila melanogaster was analyzed through molecular analysis of the DR-white assay using Tracking across Indels by DEcomposition (TIDE). The proportion of HR repair was highest in tissues that maintain the canonical (G1/S/G2/M) cell cycle and suppressed in both terminally differentiated and polyploid tissues. To determine the impact of sex on repair pathway choice, repair in different tissues in both males and females was analyzed. When molecularly examining tissues containing mostly somatic cells, males and females demonstrated similar proportions of HR and NHEJ. However, when DSB repair was analyzed in male and female premeiotic germline cells utilizing phenotypic analysis of the DR-white assay, there was a significant decrease in HR in females compared to males. This study describes the impact of development, tissue-specific cycling profile, and, in some cases, sex on DSB repair outcomes, underscoring the complexity of repair in multicellular organisms.
| Melnikova, L. S., Molodina, V. V., Georgiev, P. G., Golovnin, A. K. (2024). Role of Mod(mdg4)-67.2 Protein in Interactions between Su(Hw)-Dependent Complexes and Their Recruitment to Chromatin. Biochemistry (Mosc), 89(4):626-636 PubMed ID: 38831500
Summary:
Su(Hw) belongs to the class of proteins that organize chromosome architecture, determine promoter activity, and participate in formation of the boundaries/insulators between the regulatory domains. This protein contains a cluster of 12 zinc fingers of the C2H2 type, some of which are responsible for binding to the consensus site. The Su(Hw) protein forms complex with the Mod(mdg4)-67.2 and the CP190 proteins, where the last one binds to all known Drosophila insulators. To further study functioning of the Su(Hw)-dependent complexes, the previously described su(Hw)(E8) mutation was used with inactive seventh zinc finger, which produces mutant protein that cannot bind to the consensus site. The present work shows that the Su(Hw)(E8) protein continues to directly interact with the CP190 and Mod(mdg4)-67.2 proteins. Through interaction with Mod(mdg4)-67.2, the Su(Hw)(E8) protein can be recruited into the Su(Hw)-dependent complexes formed on chromatin and enhance their insulator activity. These results demonstrate that the Su(Hw) dependent complexes without bound DNA can be recruited to the Su(Hw) binding sites through the specific protein-protein interactions that are stabilized by Mod(mdg4)-67.2.
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Manning, S. A., Kroeger, B., Deng, Q., Brooks, E., Fonseka, Y., Hinde, E., Harvey, K. F. (2024). The Drosophila Hippo pathway transcription factor Scalloped and its co-factors alter each other's chromatin binding dynamics and transcription in vivo. Dev Cell, 59(13):1640-1654. PubMed ID: 38670104
Summary:
he Hippo pathway is an important regulator of organ growth and cell fate. The major mechanism by which Hippo is known to control transcription is by dictating the nucleo-cytoplasmic shuttling rate of Yorkie, a transcription co-activator, which promotes transcription with the DNA binding protein Scalloped. The nuclear biophysical behavior of Yorkie and Scalloped, and whether this is regulated by the Hippo pathway, remains unexplored. Using multiple live-imaging modalities on Drosophila tissues, this study found that Scalloped interacts with DNA on a broad range of timescales, and enrichment of Scalloped at sites of active transcription is mediated by longer DNA dwell times. Further, Yorkie increased Scalloped's DNA dwell time, whereas the repressors Nervous fingers 1 (Nerfin-1) and Tondu-domain-containing growth inhibitor (Tgi) decreased it. Therefore, the Hippo pathway influences transcription not only by controlling nuclear abundance of Yorkie but also by modifying the DNA binding kinetics of the transcription factor Scalloped.
| Carlson, J., Neidviecky, E., Cook, I., Cross, B., Deng, H. (2024). Interaction with B-type lamin reveals the function of Drosophila Keap1 xenobiotic response factor in nuclear architecture. Molecular biology reports, 51(1):556 PubMed ID: 38642177
Summary:
The -Nrf2 pathway serves as a central regulator that mediates transcriptional responses to xenobiotic and oxidative stimuli. Recent studies have shown that Keap1 and Nrf2 can regulate transcripts beyond antioxidant and detoxifying genes, yet the underlying mechanisms remain unclear. This research has uncovered that Drosophila Keap1 (dKeap1) and Nrf2 (CncC) proteins can control high-order chromatin structure, including heterochromatin. In this study, the molecular interaction was identified between dKeap1 and lamin Dm0, the Drosophila B-type lamin responsible for the architecture of nuclear lamina and chromatin. Ectopic expression of dKeap1 led to an ectopic localization of lamin to the intra-nuclear area, corelated with the spreading of the heterochromatin marker H3K9me2 into euchromatin regions. Additionally, mis-regulated dKeap1 disrupted the morphology of the nuclear lamina. Knocking down of dKeap1 partially rescued the lethality induced by lamin overexpression, suggesting their genetic interaction during development. The discovered dKeap1-lamin interaction suggests a novel role for the Keap1 oxidative/xenobiotic response factor in regulating chromatin architecture.
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Friday January 10th - Larval and Adult Development |
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Turingan, M. J., Li, T., Wright, J., Sharma, A., Ding, K., Khan, S., Lee, B., Grewal, S. S. (2024). Hypoxia delays steroid-induced developmental maturation in Drosophila by suppressing EGF signaling. PLoS Genet, 20(4):e1011232 PubMed ID: 38669270
Summary:
Animals often grow and develop in unpredictable environments where factors like food availability, temperature, and oxygen levels can fluctuate dramatically. To ensure proper sexual maturation into adulthood, juvenile animals need to adapt their growth and developmental rates to these fluctuating environmental conditions. Failure to do so can result in impaired maturation and incorrect body size. This study describes a mechanism by which Drosophila larvae adapt their development in low oxygen (hypoxia). During normal development, larvae grow and increase in mass until they reach critical weight (CW), after which point a neuroendocrine circuit triggers the production of the steroid hormone ecdysone from the prothoracic gland (PG), which promotes maturation to the pupal stage. However, when raised in hypoxia (5% oxygen), larvae slow their growth and delay their maturation to the pupal stage. Although hypoxia delays the attainment of CW, the maturation delay occurs mainly because of hypoxia acting late in development to suppress ecdysone production. This suppression operates through a distinct mechanism from nutrient deprivation, occurs independently of HIF-1 alpha and does not involve dilp8 or modulation of Ptth, the main neuropeptide that initiates ecdysone production in the PG. Instead, this study found that hypoxia lowers the expression of the EGF ligand, Spitz, and that the delay in maturation occurs due to reduced EGFR/ERK signaling in the PG. This study sheds light on how animals can adjust their development rate in response to changing oxygen levels in their environment. Given that hypoxia is a feature of both normal physiology and many diseases, these findings have important implications for understanding how low oxygen levels may impact animal development in both normal and pathological situations.
| Beno, M., Benova-Liszekova, D., Kostic, I., Sery, M., Mentelova, L., Prochazka, M., Soltys, J., Trusinova, L., Ritomsky, M., Orovcik, L., Jerigova, M., Velic, D., Machata, P., Omastova, M., Chase, B. A., Farkas, R. (2024). Gross morphology and adhesion-associated physical properties of Drosophila larval salivary gland glue secretion. Sci Rep, 14(1):9779 PubMed ID: 38684688
Summary:
One of the major functions of the larval salivary glands (SGs) of many Drosophila species is to produce a massive secretion during puparium formation. This so-called proteinaceous glue is exocytosed into the centrally located lumen, and subsequently expectorated, serving as an adhesive to attach the puparial case to a solid substrate during metamorphosis. Although this was first described almost 70 years ago, a detailed description of the morphology and mechanical properties of the glue is largely missing. Its main known physical property is that it is released as a watery liquid that quickly hardens into a solid cement. This study provides a detailed morphological and topological analysis of the solidified glue. It forms a distinctive enamel-like plaque that is composed of a central fingerprint surrounded by a cascade of laterally layered terraces. The solidifying glue rapidly produces crystals of KCl on these alluvial-like terraces. Since the properties of the glue affect the adhesion of the puparium to its substrate, and so can influence the success of metamorphosis, this study evaluated over 80 different materials for their ability to adhere to the glue to determine which properties favor strong adhesion. The alkaline Sgs-glue was found to adhere strongly to wettable and positively charged surfaces but not to neutral or negatively charged and hydrophobic surfaces. Puparia formed on unfavored materials can be removed easily without leaving fingerprints or cascading terraces. For successful adhesion of the Sgs-glue, the material surface must display a specific type of triboelectric charge. Interestingly, the expectorated glue can move upwards against gravity on the surface of freshly formed puparia via specific, unique and novel anatomical structures present in the puparial's lateral abdominal segments that as been named bidentia.
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Puli, O. R., Gogia, N., Chimata, A. V., Yorimitsu, T., Nakagoshi, H., Kango-Singh, M., Singh, A. (2024). Genetic mechanism regulating diversity in the placement of eyes on the head of animals. Proc Natl Acad Sci U S A, 121(16):e2316244121 PubMed ID: 38588419
Summary:
Despite the conservation of genetic machinery involved in eye development, there is a strong diversity in the placement of eyes on the head of animals. Morphogen gradients of signaling molecules are vital to patterning cues. During Drosophila eye development, Wingless (Wg), a ligand of Wnt/Wg signaling, is expressed anterolaterally to form a morphogen gradient to determine the eye- versus head-specific cell fate. The underlying mechanisms that regulate this process are yet to be fully understood. This study characterized defective proventriculus (dve) (Drosophila ortholog of human SATB1), a K50 homeodomain transcription factor, as a dorsal eye gene, which regulates Wg signaling to determine eye versus head fate. Across Drosophila species, Dve is expressed in the dorsal head vertex region where it regulates wg transcription. Second, Dve suppresses eye fate by down-regulating retinal determination genes. Third, the dve-expressing dorsal head vertex region is important for Wg-mediated inhibition of retinal cell fate, as eliminating the Dve-expressing cells or preventing Wg transport from these dve-expressing cells leads to a dramatic expansion of the eye field. Together, these findings suggest that Dve regulates Wg expression in the dorsal head vertex, which is critical for determining eye versus head fate. Gain-of-function of SATB1 exhibits an eye fate suppression phenotype similar to Dve. These data demonstrate a conserved role for Dve/SATB1 in the positioning of eyes on the head and the interocular distance by regulating Wg. This study provides evidence that dysregulation of the Wg morphogen gradient results in developmental defects such as hypertelorism in humans where disproportionate interocular distance and facial anomalies are reported.
| Mehaffey, T. M., Hecht, C. A., White, J. S., Hutson, M. S., Page-McCaw, A. (2024). Live imaging basement membrane assembly under the pupal notum epithelium. microPublication biology. PubMed ID: 38525127
Summary:
Basement membranes are sheet-like extracellular matrices containing Collagen IV, and they are conserved across the animal kingdom. Basement membranes usually line the basal surfaces of epithelia, where they contribute to structure, maintenance, and signaling. Although adult epithelia contact basement membranes, in early embryos the epithelia contact basement membranes only after basement membranes are assembled in embryogenesis. In Drosophila , the pupal notum epithelium is a useful model for live imaging epithelial cell behaviors, yet it is unclear when the basement membrane assembles in the pupa, as pupae are undergoing metamorphosis, similar to embryogenesis. To characterize the basement membrane in the pupal notum, spinning disk fluorescent microscopy was used to visualize Collagen IV subunit Vkg-GFP and adherens junction protein p120ctnRFP. Bright punctae of Vkg-GFP were observed in the X-Y plane, possibly representing Vkg-containing cells. A thin continuous Vkg-containing basement membrane was evident at 14 h APF, which became more enriched with Vkg-GFP over the next 6 h, indicating the basement membrane is still assembling during that time. Live imaging of the pupal notum during this time could provide insight into formation, assembly, and repair of the basement membranes.
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Krejcva, G., Danielovq, A., Sehadovq, H., Dydka, F., Kubasek, J., Moos, M., Bajgar, A. (2024). Macrophages play a nutritive role in post-metamorphic maturation in Drosophila. Development, 151(7) PubMed ID: 38456486
Summary:
In the body of multicellular organisms, macrophages play an indispensable role in maintaining tissue homeostasis by removing old, apoptotic and damaged cells. In addition, macrophages allow significant remodeling of body plans during embryonic morphogenesis, regeneration and metamorphosis. Although the huge amount of organic matter that must be removed during these processes represents a potential source of nutrients, their further use by the organism has not yet been addressed. This study documented that, during metamorphosis, Drosophila larval adipose tissue is infiltrated by macrophages, which remove dying adipocytes by efferocytosis and engulf leaking RNA-protein granules and lipids. Consequently, the infiltrating macrophages transiently adopt the adipocyte-like metabolic profile to convert remnants of dying adipocytes to lipoproteins and storage peptides that nutritionally support post-metamorphic development. This process is fundamental for the full maturation of ovaries and the achievement of early fecundity of individuals. Whether macrophages play an analogous role in other situations of apoptotic cell removal remains to be elucidated.
| Sun, X., Decker, J., Sanchez-Luege, N., Rebay, I. (2024). Inter-plane feedback coordinates cell morphogenesis and maintains 3D tissue organization in the Drosophila pupal retina. Development, 151(6) PubMed ID: 38533736
Summary:
How complex organs coordinate cellular morphogenetic events to achieve three-dimensional (3D) form is a central question in development. The question is uniquely tractable in the late Drosophila pupal retina, where cells maintain stereotyped contacts as they elaborate the specialized cytoskeletal structures that pattern the apical, basal and longitudinal planes of the epithelium. This study combined cell type-specific genetic manipulation of the cytoskeletal regulator Abelson (Abl) with 3D imaging to explore how the distinct cellular morphogenetic programs of photoreceptors and interommatidial pigment cells (IOPCs) organize tissue pattern to support retinal integrity. These experiments show that photoreceptor and IOPC terminal differentiation is unexpectedly interdependent, connected by an intercellular feedback mechanism that coordinates and promotes morphogenetic change across orthogonal tissue planes to ensure correct 3D retinal pattern. It is proposed that genetic regulation of specialized cellular differentiation programs combined with inter-plane mechanical feedback confers spatial coordination to achieve robust 3D tissue morphogenesis.
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Wednesday January 8th - Evolution |
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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.
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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.
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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.
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Tuesday January 7th - Adult Physiology and Metabolism |
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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, tissue-dependent metabolic pathway activities were predicted, 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, glyceraldehyde 3-phosphate dehydrogenase (GAPDH) was identified 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.
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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.
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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. A mitochondrial lipid metabolic cycle between neurons and glia is proposed to reflect a fundamental function of sleep relevant for brain energy homeostasis.
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Monday January 6th - Adult neural development, structure and function |
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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. The concept of chemoconnectome (CCT) was previously proposed 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.
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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. This study describes 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.
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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. The SIM-like structure was demonstrated to bind 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.
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Friday January 2nd - Cytoskeleton |
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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.
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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, Biochemical, genetic and cell biological assays were combined. 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.
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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, this study 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.
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Tuesday December 31st - Signaling |
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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.
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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.
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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.
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Monday December 30th - Gonads |
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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 is termed 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.
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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.
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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.
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Friday December 27th - Adult Neural Structure, Development, and Function |
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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.
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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.
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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.
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Thursday December 26th - Vesicles and synapsey |
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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.
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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.
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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.
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Monday December 23rd - Gonads |
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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.
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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.
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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.
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Friday December 20th - Disease Models |
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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.
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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.
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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.
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Thursday December 19th - Genes, enzymes and protein expression, evolution, structure, and function |
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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.
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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.
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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.
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Tuesday December 17th - Evolution |
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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.
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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.
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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. This study describes 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.
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Monday December 16th - Signalling |
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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.
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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.
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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. This study examined 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.
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Friday December 13th - Stress |
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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.
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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.
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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.
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Thursday December 12th - Disease Models |
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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.
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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.
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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.
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Wednesday December 11th - Embryonic Development |
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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.
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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.
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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.
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Wednesday December 11th - Embryonic Development |
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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, this study demonstrated 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.
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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.
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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.
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Monday December 9th - Adult Physiology and Metabolism |
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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.
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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.
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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. Dietary cysteine depletion was shown to normalize 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.
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Friday December 6th - Adult Neural Sevelopment, Structure and Function |
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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.
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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.
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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.
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Thursday, December 5th - Evolution |
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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.
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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.
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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 opens the possibility that blood cells measure their overall phospho-status as a proxy for stress-signals, and activate an adaptive immune response accordingly.
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Tuesday, December 3rd - Chromatin |
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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.
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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 The gene expression profiles of H4K20A and H4K20R larvae was shown to be 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.
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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.
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