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| ARCHIVE | Monday, April 7th - Tumor Models in Drosophila |
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February 2025 January 2025 December 2024 November 2024 October 2024 September 2024 August 2024 July 2024 June 2024 May 2024 April 2024 March 2024 February 2024 January 2024 December 2023 November 2023 October 2023 September 2023 August 2023 July 2023 June 2023 May 2023 April 2023 March 2023 February 2023 January 2023 December 2022 December 2021 December 2020 December 2019 December 2018 | Church, S. J., Pulianmackal, A. J., Dixon, J. A., Loftus, L. V., Amend, S. R., Pienta, K., Cackowski, F. C., Buttitta, L. A. (2024). Oncogenic signaling in the adult Drosophila prostate-like accessory gland leads to activation of a conserved pro-tumorigenic program, in the absence of proliferation. bioRxiv, PubMed ID: 38853988
Summary: Drosophila models for tumorigenesis and metastasis have revealed conserved mechanisms of signaling that are also involved in mammalian cancer. Many of these models use the proliferating tissues of the larval stages of Drosophila development, when tissues are highly mitotically active, or stem cells are abundant. Fewer Drosophila tumorigenesis models use adult animals to initiate tumor formation when many tissues are largely terminally differentiated and postmitotic. The Drosophila accessory glands are prostate-like tissues and a model for some aspects of prostate tumorigenesis using this tissue has been explored. In this model, oncogenic signaling was induced during the proliferative stage of accessory gland development, raising the question of how oncogenic activity would impact the terminally differentiated and postmitotic adult tissue. Oncogenic signaling in the adult Drosophila accessory gland was shown to lead to activation of a conserved pro-tumorigenic program, similar to that observed in mitotic larval tissues, but in the absence of proliferation. Oncogenic signaling in the adult postmitotic gland leads to tissue hyperplasia with nuclear anaplasia and aneuploidy through endoreduplication, which increases polyploidy and occasionally results in non-mitotic neoplastic-like extrusions. Gene expression changes in the Drosophila model were compared with that of endocycling prostate cancer cells induced by chemotherapy, which potentially mediate tumor recurrence after treatment. Similar signaling pathways are activated in the Drosophila gland and endocycling cancer cells, suggesting the adult accessory glands provide a useful model for aspects of prostate cancer progression that do not involve cellular proliferation. | Pilesi, E., Tesoriere, G., Ferriero, A., Mascolo, E., Liguori, F., Argiro, L., Angioli, C., Tramonti, A., Contestabile, R., Volonte, C., Verni, F. (2024). Vitamin B6 deficiency cooperates with oncogenic Ras to induce malignant tumors in Drosophila. Cell Death Dis, 15(6):388 PubMed ID: 38830901
Summary: Vitamin B6 is a water-soluble vitamin which possesses antioxidant properties. Its catalytically active form, pyridoxal 5'-phosphate (PLP), is a crucial cofactor for DNA and amino acid metabolism. The inverse correlation between vitamin B6 and cancer risk has been observed in several studies, although dietary vitamin B6 intake sometimes failed to confirm this association. However, the molecular link between vitamin B6 and cancer remains elusive. Previous work has shown that vitamin B6 deficiency causes chromosome aberrations (CABs) in Drosophila and human cells, suggesting that genome instability may correlate the lack of this vitamin to cancer. This study provides evidence in support of this hypothesis. Firstly, PLP deficiency, induced by the PLP antagonists 4-deoxypyridoxine (4DP) or ginkgotoxin (GT), was shown to promote tumorigenesis in eye larval discs transforming benign RasV12 tumors into aggressive forms. In contrast, PLP supplementation reduced the development of tumors. Low PLP levels, induced by 4DP or by silencing the sgll(PNPO) gene involved in PLP biosynthesis, worsened the tumor phenotype in another Drosophila cancer model generated by concomitantly activating RasV12 and downregulating Discs-large (Dlg) gene. Moreover, Ras(V12) eye discs from larvae reared on 4DP displayed CABs, reactive oxygen species (ROS) and low catalytic activity of serine hydroxymethyltransferase (SHMT), a PLP-dependent enzyme involved in thymidylate (dTMP) biosynthesis, in turnRRQrfrebbbgg required for DNA replication and repair. Feeding Ras(V12) 4DP-fed larvae with PLP or ascorbic acid (AA) plus dTMP, rescued both CABs and tumors. The same effect was produced by overexpressing catalase in Ras(V12) Dlg(RNAi) 4DP-fed larvae, thus allowing to establish a relationship between PLP deficiency, CABs, and cancer. Overall, these data provide the first in vivo demonstration that PLP deficiency can impact on cancer by increasing genome instability, which is in turn mediated by ROS and reduced dTMP levels. |
| Vialat, M., Baabdaty, E., Trousson, A., Kocer, A., Lobaccaro, J. A., Baron, S., Morel, L., de Joussineau, C. (2024). Cholesterol Dietary Intake and Tumor Cell Homeostasis Drive Early Epithelial Tumorigenesis: A Potential Modelization of Early Prostate Tumorigenesis. JCancers, 16(11) PubMed ID: 38893271
Summary: Epidemiological studies point to cholesterol as a possible key factor for both prostate cancer incidence and progression. It could represent a targetable metabolite as the most aggressive tumors also appear to be sensitive to therapies designed to decrease hypercholesterolemia, such as statins. However, it remains unknown whether and how cholesterol, through its dietary uptake and its metabolism, could be important for early tumorigenesis. Oncogene clonal induction in the Drosophila melanogaster accessory gland allows reproduction of tumorigenesis from initiation to early progression, where tumor cells undergo basal extrusion to form extra-epithelial tumors. These tumors accumulate lipids, and especially esterified cholesterol, as in human late carcinogenesis. Interestingly, a high-cholesterol diet has a limited effect on accessory gland tumorigenesis. On the contrary, cell-specific downregulation of cholesterol uptake, intracellular transport, or metabolic response impairs the formation of such tumors. Furthermore, in this context, a high-cholesterol diet suppresses this impairment. Interestingly, expression data from primary prostate cancer tissues indicate an early signature of redirection from cholesterol de novo synthesis to uptake. Taken together, these results reveal that during early tumorigenesis, tumor cells strongly increase their uptake and use of dietary cholesterol to specifically promote the step of basal extrusion. Hence, these results suggest the mechanism by which a reduction in dietary cholesterol could lower the risk and slow down the progression of prostate cancer. | Leung, N. Y., Xu, C., Li, J. S. S., Ganguly, A., Meyerhof, G. T., Regimbald-Dumas, Y., Lane, E. A., Breault, D. T., He, X., Perrimon, N., Montell, C. (2024). Gut tumors in flies alter the taste valence of an anti-tumorigenic bitter compound.. Curr Biol, 34(12):2623-2632 PubMed ID: 38823383
Summary: The sense of taste is essential for survival, as it allows animals to distinguish between foods that are nutritious from those that are toxic. However, innate responses to different tastants can be modulated or even reversed under pathological conditions. This study examined whether and how the internal status of an animal impacts taste valence by using Drosophila models of hyperproliferation in the gut. In all three models where proliferation-inducing transgenes were expressed in intestinal stem cells (ISCs), hyperproliferation of ISCs caused a tumor-like phenotype in the gut. While tumor-bearing flies had no deficiency in overall food intake, strikingly, they exhibited an increased gustatory preference for aristolochic acid (ARI), which is a bitter and normally aversive plant-derived chemical. ARI had anti-tumor effects in all three gut hyperproliferation models. For other aversive chemicals tested that are bitter but do not have anti-tumor effects, gut tumors did not affect avoidance behaviors. Bitter-sensing gustatory receptor neurons (GRNs) in tumor-bearing flies respond normally to ARI. Therefore, the internal pathology of gut hyperproliferation affects neural circuits that determine taste valence postsynaptic to GRNs rather than altering taste identity by GRNs. Overall, these data suggest that increased consumption of ARI may represent an attempt at self-medication. Finally, although ARI's potential use as a chemotherapeutic agent is limited by its known toxicity in the liver and kidney, these findings suggest that tumor-bearing flies might be a useful animal model to screen for novel anti-tumor drugs (Leung, 2024). |
| Rawal, C. C., Loubiere, V., Butova, N. L., Gracia, J., Parreno, V., Merigliano, C., Martinez, A. M., Cavalli, G., Chiolo, I. (2024). Sustained inactivation of the Polycomb PRC1 complex induces DNA repair defects and genomic instability in epigenetic tumors. Histochemistry and cell biology, 162(1-2):133-147 PubMed ID: 38888809
Summary: Cancer initiation and progression are typically associated with the accumulation of driver mutations and genomic instability. However, recent studies demonstrated that cancer can also be driven purely by epigenetic alterations, without driver mutations. Specifically, a 24-h transient downregulation of polyhomeotic (ph-KD), a core component of the Polycomb complex PRC1, is sufficient to induce epigenetically initiated cancers (EICs) in Drosophila, which are proficient in DNA repair and characterized by a stable genome. Whether genomic instability eventually occurs when PRC1 downregulation is performed for extended periods of time remains unclear. This study shows that prolonged depletion of PH, which mimics cancer initiating events, results in broad dysregulation of DNA replication and repair genes, along with the accumulation of DNA breaks, defective repair, and widespread genomic instability in the cancer tissue. A broad misregulation of H2AK118 ubiquitylation and to a lesser extent of H3K27 trimethylation also occurs and might contribute to these phenotypes. Together, this study supports a model where DNA repair and replication defects accumulate during the tumorigenic transformation epigenetically induced by PRC1 loss, resulting in genomic instability and cancer progression. | Parreno, V., Loubiere, V., Schuettengruber, B., Fritsch, L., Rawal, C. C., Erokhin, M., Gyorffy, B., Normanno, D., Di Stefano, M., Moreaux, J., Butova, N. L., Chiolo, I., Chetverina, D., Martinez, A. M., Cavalli, G. (2024). Transient loss of Polycomb components induces an epigenetic cancer fate. Nature, 629(8012):688-696 PubMed ID: 38658752
Summary: Although cancer initiation and progression are generally associated with the accumulation of somatic mutations, substantial epigenomic alterations underlie many aspects of tumorigenesis and cancer susceptibility, suggesting that genetic mechanisms might not be the only drivers of malignant transformation. However, whether purely non-genetic mechanisms are sufficient to initiate tumorigenesis irrespective of mutations has been unknown. This study shows that a transient perturbation of transcriptional silencing mediated by Polycomb group proteins is sufficient to induce an irreversible switch to a cancer cell fate in Drosophila. This is linked to the irreversible derepression of genes that can drive tumorigenesis, including members of the JAK-STAT signalling pathway and zfh1, the fly homologue of the ZEB1 oncogene, whose aberrant activation is required for Polycomb perturbation-induced tumorigenesis. These data show that a reversible depletion of Polycomb proteins can induce cancer in the absence of driver mutations, suggesting that tumours can emerge through epigenetic dysregulation leading to inheritance of altered cell fates (Parreno, 2024). |
Friday, April 4th - Larval and Adult Development |
| Blackie, L., Gaspar, P., Mosleh, S., Lushchak, O., Kong, L., Jin, Y., Zielinska, A. P., Cao, B., Mineo, A., Silva, B., Ameku, T., Lim, S. E., Mao, Y., Prieto-Godino, L., Schoborg, T., Varela, M., Mahadevan, L., Miguel-Aliaga, I. (2024). The sex of organ geometry. Nature, 630(8016):392-400 PubMed ID: 38811741
Summary: Organs have a distinctive yet often overlooked spatial arrangement in the body. It is proposed that there is a logic to the shape of an organ and its proximitY to its neighbours. Here, by using volumetric scans of many Drosophila melanogaster flies, we develop methods to quantify three-dimensional features of organ shape, position and interindividual variability. Both the shapes of organs and their relative arrangement were consistent yet differ between the sexes, and identify unexpected interorgan adjacencies and left-right organ asymmetries. Focusing on the intestine, which traverses the entire body, this study investigate how sex differences in three-dimensional organ geometry arise. The configuration of the adult intestine is only partially determined by physical constraints imposed by adjacent organs; its sex-specific shape is actively maintained by mechanochemical crosstalk between gut muscles and vascular-like trachea. Indeed, sex-biased expression of a muscle-derived fibroblast growth factor-like ligand renders trachea sexually dimorphic. In turn, tracheal branches hold gut loops together into a male or female shape, with physiological consequences. Interorgan geometry represents a previously unrecognized level of biological complexity which might enable or confine communication across organs and could help explain sex or species differences in organ function. | Rigato, A., Meng, H., Chardes, C., Runions, A., Abouakil, F., Smith, R. S., LeGoff, L. (2024). A mechanical transition from tension to buckling underlies the jigsaw puzzle shape morphogenesis of histoblasts in the Drosophila epidermis. PLoS Biol, 22(6):e3002662 PubMed ID: 38870210
Summary: The polygonal shape of cells in proliferating epithelia is a result of the tensile forces of the cytoskeletal cortex and packing geometry set by the cell cycle. In the larval Drosophila epidermis, two cell populations, histoblasts and larval epithelial cells, compete for space as they grow on a limited body surface. They do so in the absence of cell divisions. A striking morphological transition of histoblasts was observed during larval development, where they change from a tensed network configuration with straight cell outlines at the level of adherens junctions to a highly folded morphology. The apical surface of histoblasts shrinks while their growing adherens junctions fold, forming deep lobules. Volume increase of growing histoblasts is accommodated basally, compensating for the shrinking apical area. The folded geometry of apical junctions resembles elastic buckling, and the imbalance between the shrinkage of the apical domain of histoblasts and the continuous growth of junctions triggers buckling. This model is supported by laser dissections and optical tweezer experiments together with computer simulations. This analysis pinpoints the ability of histoblasts to store mechanical energy to a much greater extent than most other epithelial cell types investigated so far, while retaining the ability to dissipate stress on the hours time scale. Finally, a possible mechanism is proposed for size regulation of histoblast apical size through the lateral pressure of the epidermis, driven by the growth of cells on a limited surface. Buckling effectively compacts histoblasts at their apical plane and may serve to avoid physical harm to these adult epidermis precursors during larval life. This work indicates that in growing nondividing cells, compressive forces, instead of tension, may drive cell morphology. |
| Petrosky, S. J., Williams, T. M., Rebeiz, M. (2024). A genetic screen of transcription factors in the Drosophila melanogaster abdomen identifies novel pigmentation genes. G3 (Bethesda), 14(9) PubMed ID: 38820091
Summary: Gene regulatory networks specify the gene expression patterns needed for traits to develop. Differences in these networks can result in phenotypic differences between organisms. Although loss-of-function genetic screens can identify genes necessary for trait formation, gain-of-function screens can overcome genetic redundancy and identify loci whose expression is sufficient to alter trait formation. Here, we leveraged transgenic lines from the Transgenic RNAi Project at Harvard Medical School to perform both gain- and loss-of-function CRISPR/Cas9 screens for abdominal pigmentation phenotypes. Measurable effects on pigmentation patterns in the Drosophila melanogaster abdomen were observed for 21 of 55 transcription factors in gain-of-function experiments and 7 of 16 tested by loss-of-function experiments. These included well-characterized pigmentation genes, such as bab1 and dsx, and transcription factors that had no known role in pigmentation, such as slp2. Finally, this screen was partially conducted by undergraduate students in a Genetics Laboratory course during the spring semesters of 2021 and 2022. This screen was found to be a successful model for student engagement in research in an undergraduate laboratory course that can be readily adapted to evaluate the effect of hundreds of genes on many different Drosophila traits, with minimal resources. | Kurogi, Y., Mizuno, Y., Kamiyama, T., Niwa, R. (2024). The intestinal stem cell/enteroblast-GAL4 driver, escargot-GAL4, also manipulates gene expression in the juvenile hormone-synthesizing organ of Drosophila melanogaster. Sci Rep, 14(1):9631 PubMed ID: 38671036
Summary: Intestinal stem cells (ISCs) of the fruit fly, Drosophila melanogaster, offer an excellent genetic model to explore homeostatic roles of ISCs in animal physiology. Among available genetic tools, the escargot (esg)-GAL4 driver, expressing the yeast transcription factor gene, GAL4, under control of the esg gene promoter, has contributed significantly to ISC studies. This driver facilitates activation of genes of interest in proximity to a GAL4-binding element, Upstream Activating Sequence, in ISCs and progenitor enteroblasts (EBs). While esg-GAL4 has been considered an ISC/EB-specific driver, recent studies have shown that esg-GAL4 is also active in other tissues, such as neurons and ovaries. Therefore, the ISC/EB specificity of esg-GAL4 is questionable. This study reveals esg-GAL4 expression in the corpus allatum (CA), responsible for juvenile hormone (JH) production. When driving the oncogenic gene, Ras(V12), esg-GAL4 induces overgrowth in ISCs/EBs as reported, but also increases CA cell number and size. Consistent with this observation, animals alter expression of JH-response genes. These data show that esg-GAL4-driven gene manipulation can systemically influence JH-mediated animal physiology, arguing for cautious use of esg-GAL4 as a "specific" ISC/EB driver to examine ISC/EB-mediated animal physiology. |
| Raja, K. K. B., Yeung, K., Li, Y., Chen, R., Mardon, G. (2024). A single cell RNA sequence atlas of the early Drosophila larval eye. BMC Genomics, 25(1):616 PubMed ID: 38890587
Summary: The Drosophila eye has been an important model to understand principles of differentiation, proliferation, apoptosis and tissue morphogenesis. However, a single cell RNA sequence resource that captures gene expression dynamics from the initiation of differentiation to the specification of different cell types in the larval eye disc is lacking. This study reports transcriptomic data from 13,000 cells that cover six developmental stages of the larval eye. The data show cell clusters that correspond to all major cell types present in the eye disc ranging from the initiation of the morphogenetic furrow to the differentiation of each photoreceptor cell type as well as early cone cells. We identify dozens of cell type-specific genes whose function in different aspects of eye development have not been reported. These single cell data will greatly aid research groups studying different aspects of early eye development and will facilitate a deeper understanding of the larval eye as a model system. | Ray, A., Rai, Y., Inamdar, M. S. (2024). The Endosomal Sorting Complex, ESCRT, has diverse roles in blood progenitor maintenance, lineage choice and immune response. Biol Open, 13(6) PubMed ID: 38828842
Summary: Most hematological malignancies are associated with reduced expression of one or more components of the Endosomal Sorting Complex Required for Transport (ESCRT). However, the roles of ESCRT in stem cell and progenitor maintenance are not resolved. Parsing signaling pathways in relation to the canonical role of ESCRT poses a challenge. The Drosophila hematopoietic organ, the larval lymph gland, provides a path to dissect the roles of cellular trafficking pathways such as ESCRT in blood development and maintenance. Drosophila has 13 core ESCRT components. Knockdown of individual ESCRTs showed that only Vps28 and Vp36 were required in all lymph gland progenitors. Using the well-conserved ESCRT-II complex as an example of the range of phenotypes seen upon ESCRT depletion, this study showed that ESCRTs have cell-autonomous as well as non-autonomous roles in progenitor maintenance and differentiation. ESCRT depletion also sensitized posterior lobe progenitors to respond to immunogenic wasp infestation. Key heterotypic roles for ESCRT have been found in position-dependent control of Notch activation to suppress crystal cell differentiation. This study shows that the cargo sorting machinery determines the identity of progenitors and their adaptability to the dynamic microenvironment. These mechanisms for control of cell fate may tailor developmental diversity in multiple contexts. |
Thursday, April 3rd - Disease Models |
| Gunasekaran, M., Littel, H. R., Wells, N. M., Turner, J., Campos, G., Venigalla, S., Estrella, E. A., Ghosh, P. S., Daugherty, A. L., Stafki, S. A., Kunkel, L. M., Foley, A. R., Donkervoort, S., Bonnemann, C. G., Toledo-Bravo de Laguna, L., Nascimento, A., Benito, D. N., Draper, I., Bruels, C. C., Pacak, C. A., Kang, P. B. (2024). Effects of HMGCR deficiency on skeletal muscle development. bioRxiv, PubMed ID: 38903061
Summary: Pathogenic variants in HMGCR were recently linked to a limb-girdle muscular dystrophy (LGMD) phenotype. The protein product HMG CoA reductase (HMGCR) catalyzes a key component of the cholesterol synthesis pathway. The two other muscle diseases associated with HMGCR, statin-associated myopathy (SAM) and autoimmune anti-HMGCR myopathy, are not inherited in a Mendelian pattern. The mechanism linking pathogenic variants in HMGCR with skeletal muscle dysfunction is unclear. This study knocked down Hmgcr in mouse skeletal myoblasts, knocked down hmgcr in Drosophila, and expressed three pathogenic HMGCR variants (c.1327C>T, p.Arg443Trp; c.1522_1524delTCT, p.Ser508del; and c.1621G>A, p.Ala541Thr) in Hmgcr knockdown mouse myoblasts. Hmgcr deficiency was associated with decreased proliferation, increased apoptosis, and impaired myotube fusion. Transcriptome sequencing of Hmgcr knockdown versus control myoblasts revealed differential expression involving mitochondrial function, with corresponding differences in cellular oxygen consumption rates. Both ubiquitous and muscle-specific knockdown of hmgcr in Drosophila led to lethality. Overexpression of reference HMGCR cDNA rescued myotube fusion in knockdown cells, whereas overexpression of the pathogenic variants of HMGCR cDNA did not. These results suggest that the three HMGCR-related muscle diseases share disease mechanisms related to skeletal muscle development. | Zuniga, G., Katsumura, S., De Mange, J., Ramirez, P., Atrian, F., Morita, M., Frost, B. (2024). Pathogenic tau induces an adaptive elevation in mRNA translation rate at early stages of disease. Aging Cell:e14245 PubMed ID: 38932463
Summary: Alterations in the rate and accuracy of messenger RNA (mRNA) translation are associated with aging and several neurodegenerative disorders, including Alzheimer's disease and related tauopathies. Previous work showed that error-containing RNA that are normally cleared via nonsense-mediated mRNA decay (NMD), a key RNA surveillance mechanism, are translated in the adult brain of a Drosophila model of tauopathy. The current study found that newly-synthesized peptides and translation machinery accumulate within nuclear envelope invaginations that occur as a consequence of tau pathology, and that the rate of mRNA translation is globally elevated in early stages of disease in adult brains of Drosophila models of tauopathy. Polysome profiling from adult heads of tau transgenic Drosophila reveals the preferential translation of specific mRNA that have been previously linked to neurodegeneration. Unexpectedly, this study found that panneuronal elevation of NMD further elevates the global translation rate in tau transgenic Drosophila, as does treatment with rapamycin. As NMD activation and rapamycin both suppress tau-induced neurodegeneration, their shared effect on translation suggests that elevated rates of mRNA translation are an early adaptive mechanism to limit neurodegeneration. This work provides compelling evidence that tau-induced deficits in NMD reshape the tau translatome by increasing translation of RNA that are normally repressed in healthy cells. |
| Deb, W., Rosenfelt, C., Vignard, V., Papendorf, J. J., ...., McWalter, K., Lupski, J. R., Isidor, B., Bolduc, F. V., Bezieau, S., Kruger, E., Kury, S., Ebstein, F. (2024). PSMD11 loss-of-function variants correlate with a neurobehavioral phenotype, obesity, and increased interferon response. American journal of human genetics, 111(7):1352-1369 PubMed ID: 38866022
Summary: Primary proteasomopathies have recently emerged as a new class of rare early-onset neurodevelopmental disorders (NDDs) caused by pathogenic variants in the PSMB1, PSMC1, PSMC3, or PSMD12 proteasome genes. Proteasomes are large multi-subunit protein complexes that maintain cellular protein homeostasis by clearing ubiquitin-tagged damaged, misfolded, or unnecessary proteins. In this study, this study have identified PSMD11 as an additional proteasome gene in which pathogenic variation is associated with an NDD-causing proteasomopathy. PSMD11 loss-of-function variants caused early-onset syndromic intellectual disability and neurodevelopmental delay with recurrent obesity in 10 unrelated children. These findings demonstrate that the cognitive impairment observed in these individuals could be recapitulated in Drosophila melanogaster with depletion of the PMSD11 ortholog Rpn6, which compromised reversal learning. Investigations in subject samples further revealed that PSMD11 loss of function resulted in impaired 26S proteasome assembly and the acquisition of a persistent type I interferon (IFN) gene signature, mediated by the integrated stress response (ISR) protein kinase R (PKR). In summary, these data identify PSMD11 as an additional member of the growing family of genes associated with neurodevelopmental proteasomopathies and provide insights into proteasomal biology in human health. | Stojkovic, M., Petrovic, M., Capovilla, M., Milojevic, S., Makevic, V., Budimirovic, D. B., Corscadden, L., He, S., Protic, D. (2024). Using a Combination of Novel Research Tools to Understand Social Interaction in the Drosophila melanogaster Model for Fragile X Syndrome. Biology, 13(6) PubMed ID: 38927312
Summary: Fragile X syndrome (FXS), the most common monogenic cause of inherited intellectual disability and autism spectrum disorder, is caused by a full mutation (>200 CGG repeats) in the Fragile X Messenger Ribonucleoprotein 1 (FMR1) gene. Individuals with FXS experience various challenges related to social interaction (SI). Animal models, such as the Drosophila melanogaster model for FXS where the only ortholog of human FMR1 (dFMR1) is mutated, have played a crucial role in the understanding of FXS. The aim of this study was to investigate SI in the dFMR1B55 mutants (the groups of flies of both sexes simultaneously) using the novel Drosophila Shallow Chamber and a Python data processing pipeline based on social network analysis (SNA). In comparison with wild-type flies (w(1118)), SNA analysis in dFMR1B55 mutants revealed hypoactivity, fewer connections in their networks, longer interaction duration, a lower ability to transmit information efficiently, fewer alternative pathways for information transmission, a higher variability in the number of interactions they achieved, and flies tended to stay near the boundaries of the testing chamber. These observed alterations indicate the presence of characteristic strain-dependent social networks in dFMR1B55 flies, commonly referred to as the group phenotype. Finally, combining novel research tools is a valuable method for SI research in fruit flies. |
| Sujkowski, A., Ranxhi, B., Bangash, Z. R., Chbihi, Z. M., Prifti, M. V., Qadri, Z., Alam, N., Todi, S. V., Tsou, W. L. (2024). Progressive degeneration in a new Drosophila model of spinocerebellar ataxia type 7. Sci Rep, 14(1):14332 PubMed ID: 38906973
Summary: Spinocerebellar ataxia type 7 (SCA7) is a progressive neurodegenerative disorder resulting from abnormal expansion of an uninterrupted polyglutamine (polyQ) repeat in its disease protein, ataxin-7 (ATXN7). ATXN7 is part of Spt-Ada-Gcn5 acetyltransferase (SAGA), an evolutionarily conserved transcriptional coactivation complex with critical roles in chromatin remodeling, cell signaling, neurodifferentiation, mitochondrial health and autophagy. SCA7 is dominantly inherited and characterized by genetic anticipation and high repeat-length instability. Patients with SCA7 experience progressive ataxia, atrophy, spasticity, and blindness. There is currently no cure for SCA7, and therapies are aimed at alleviating symptoms to increase quality of life. This studhy reports novel Drosophila lines of SCA7 with polyQ repeats in wild-type and human disease patient range. ATXN7 expression has age- and polyQ repeat length-dependent reduction in fruit fly survival and retinal instability, concomitant with increased ATXN7 protein aggregation. These new lines will provide important insight on disease progression that can be used in the future to identify therapeutic targets for SCA7 patients. | Sevegnani, M., Lama, A., Girardi, F., Hess, M. W., Castelo, M. P., Pichler, I., Biressi, S., Piccoli, G. (2024). Parkin R274W mutation affects muscle and mitochondrial physiology. Biochimica et biophysica acta Molecular basis of disease. 1870(7):167302 PubMed ID: 38878834
Summary: Recessive mutations in the Parkin gene (PRKN) are the most common cause of young-onset inherited parkinsonism. Parkin is a multifunctional E3 ubiquitin ligase that plays a variety of roles in the cell including the degradation of proteins and the maintenance of mitochondrial homeostasis, integrity, and biogenesis. In 2001, the R275W mutation in the PRKN gene was identified in two unrelated families with a multigenerational history of postural tremor, dystonia and parkinsonism. Drosophila models of Parkin R275W showed selective and progressive degeneration of dopaminergic neuronal clusters, mitochondrial abnormalities, and prominent climbing defects. In the Prkn mouse orthologue, the amino acid R274 corresponds to human R275. Here we described an age-related motor impairment and a muscle phenotype in R274W +/+ mice. In vitro, Parkin R274W mutation correlates with abnormal myoblast differentiation, mitochondrial defects, and alteration in mitochondrial mRNA and protein levels. These data suggest that the Parkin R274W mutation may impact mitochondrial physiology and eventually myoblast proliferation and differentiation. |
Tuesday, April 1st - Signalling |
| Lee, G. G., Peterson, A. J., Kim, M. J., O'Connor, M. B., Park, J. H. (2024). Multiple isoforms of the Activin-like receptor baboon differentially regulate proliferation and conversion behaviors of neuroblasts and neuroepithelial cells in the Drosophila larval brain. PLoS One, 19(6):e0305696 PubMed ID: 38913612
Summary: In Drosophila coordinated proliferation of two neural stem cells, neuroblasts (NB) and neuroepithelial (NE) cells, is pivotal for proper larval brain growth that ultimately determines the final size and performance of an adult brain. The larval brain growth displays two phases based on behaviors of NB and NEs: the first one in early larval stages, influenced by nutritional status and the second one in the last larval stage, promoted by ecdysone signaling after critical weight checkpoint. Mutations of the baboon (babo) gene that produces three isoforms (BaboA-C), all acting as type-I receptors of Activin-type transforming growth factor β (TGF-β) signaling, cause a small brain phenotype due to severely reduced proliferation of the neural stem cells. This study show that loss of babo function severely affects proliferation of NBs and NEs as well as conversion of NEs from both phases. By analyzing babo-null and newly generated isoform-specific mutants by CRISPR mutagenesis as well as isoform-specific RNAi knockdowns in a cell- and stage-specific manner, the data support differential contributions of the isoforms for these cellular events with BaboA playing the major role. Stage-specific expression of EcR-B1 in the brain is also regulated primarily by BaboA along with function of the other isoforms. Blocking EcR function in both neural stem cells results in a small brain phenotype that is more severe than baboA-knockdown alone. In summary, this study proposes that the Babo-mediated signaling promotes proper behaviors of the neural stem cells in both phases and achieves this by acting upstream of EcR-B1 expression in the second phase. | Wodrich, A. P. K., Harris, B. T., Giniger, E. (2024). Changes in mitochondrial distribution occur at the axon initial segment in association with neurodegeneration in Drosophila. Biol Open, 13(7) PubMed ID: 38912559
Summary: Changes in mitochondrial distribution are a feature of numerous age-related neurodegenerative diseases. In Drosophila, reducing the activity of Cdk5 causes a neurodegenerative phenotype and is known to affect several mitochondrial properties. Therefore, this study investigated whether alterations of mitochondrial distribution are involved in Cdk5-associated neurodegeneration. Reducing Cdk5 activity did not alter the balance of mitochondrial localization to the somatodendritic versus axonal neuronal compartments of the mushroom body, the learning and memory center of the Drosophila brain. Changes in mitochondrial distribution were observed at the axon initial segment (AIS), a neuronal compartment located in the proximal axon involved in neuronal polarization and action potential initiation. Specifically, its was observed that mitochondria are partially excluded from the AIS in wild-type neurons, but that this exclusion is lost upon reduction of Cdk5 activity, concomitant with the shrinkage of the AIS domain that is known to occur in this condition. This mitochondrial redistribution into the AIS is not likely due to the shortening of the AIS domain itself but rather due to altered Cdk5 activity. Furthermore, mitochondrial redistribution into the AIS is unlikely to be an early driver of neurodegeneration in the context of reduced Cdk5 activity. |
| Sharma, V., Sachan, N., Sarkar, B., Mutsuddi, M., Mukherjee, A. (2024). E3 ubiquitin ligase Deltex facilitates the expansion of Wingless gradient and antagonizes Wingless signaling through a conserved mechanism of transcriptional effector Armadillo/β-catenin degradation. Elife, 12 PubMed ID: 38900140
Summary: The Wnt/Wg pathway controls myriads of biological phenomena throughout the development and adult life of all organisms across the phyla. Thus, an aberrant Wnt signaling is associated with a wide range of pathologies in humans. Tight regulation of Wnt/Wg signaling is required to maintain proper cellular homeostasis. This study reports a novel role of E3 ubiquitin ligase Deltex in Wg signaling regulation. Drosophila dx genetically interacts with wg and its pathway components. Furthermore, Dx LOF results in a reduced spreading of Wg while its over-expression expands the diffusion gradient of the morphogen. This change is attributed to change in Wg gradient to the endocytosis of Wg through Dx which directly affects the short- and long-range Wg targets. The role of Dx in regulating Wg effector Armadillo was demonstrated where Dx down-regulates Arm through proteasomal degradation. This study also showed the conservation of Dx function in the mammalian system where DTX1 is shown to bind with β-catenin and facilitates its proteolytic degradation, spotlighting a novel step that potentially modulates Wnt/Wg signaling cascade. | Wu, J., Bala Tannan, N., Vuong, L. T., Koca, Y., Collu, G. M., Mlodzik, M. (2024). Par3/bazooka binds NICD and promotes notch signaling during Drosophila development. Dev Biol, 514:37-49 PubMed ID: 38885804
Summary: The conserved bazooka (baz/par3) gene acts as a key regulator of asymmetrical cell divisions across the animal kingdom. Associated Par3/Baz-Par6-aPKC protein complexes are also well known for their role in the establishment of apical/basal cell polarity in epithelial cells. Here we define a novel, positive function of Baz/Par3 in the Notch pathway. Using Drosophila wing and eye development, we demonstrate that Baz is required for Notch signaling activity and optimal transcriptional activation of Notch target genes. Baz appears to act independently of aPKC in these contexts, as knockdown of aPKC does not cause Notch loss-of-function phenotypes. Using transgenic Notch constructs, these data positions Baz activity downstream of activating Notch cleavage steps and upstream of Su(H)/CSL transcription factor complex activity on Notch target genes. A biochemical interaction was demonstrated between NICD and Baz, suggesting that Baz is required for NICD activity before NICD binds to Su(H). Taken together, these data define a novel role of the polarity protein Baz/Par3, as a positive and direct regulator of Notch signaling through its interaction with NICD. |
| Singh, K., Das, S., Sutradhar, S., Howard, J., Ray, K. (2024). Insulin signaling accelerates the anterograde movement of Rab4 vesicles in axons through Klp98A/KIF16B recruitment via Vps34-PI3Kinase. bioRxiv, PubMed ID: 38895253
Summary: Rab4 GTPase organizes endosomal sorting essential for maintaining the balance between recycling and degradative pathways. Rab4 localizes to many cargos whose transport in neurons is critical for regulating neurotransmission and neuronal health. Furthermore, elevated Rab4 levels in the CNS are associated with synaptic atrophy and neurodegeneration in Drosophila and humans, respectively. However, how the transport of Rab4-associated vesicles is regulated in neurons remains unknown. Using in vivo time-lapse imaging of Drosophila larvae, this study showd that activation of insulin signaling via Dilp2 and dInR increases the anterograde velocity, run length, and flux of Rab4 vesicles in the axons. Molecularly, activation of neuronal insulin signaling further activates Vps34, elevates the levels of PI(3)P on Rab4-associated vesicles, recruits Klp98A (a PI(3)P-binding kinesin-3 motor) and activates their anterograde transport. Together, these observations delineate the role of insulin signaling in regulating axonal transport and synaptic homeostasis. | Malinauskas, T., Moore, G., Rudolf, A. F., Eggington, H., Belnoue-Davis, H. L., El Omari, K., Griffiths, S. C., Woolley, R. E., Duman, R., Wagner, A., Leedham, S. J., Baldock, C., Ashe, H. L., Siebold, C. (2024). Molecular mechanism of BMP signal control by Twisted gastrulation. Nat Commun, 15(1):4976 PubMed ID: 38862520
Summary: Twisted gastrulation (TWSG1) is an evolutionarily conserved secreted glycoprotein which controls signaling by Bone Morphogenetic Proteins (BMPs). TWSG1 binds BMPs and their antagonist Chordin to control BMP signaling during embryonic development, kidney regeneration and cancer. This study reports crystal structures of TWSG1 alone and in complex with a BMP ligand, Growth Differentiation Factor 5. TWSG1 is composed of two distinct, disulfide-rich domains. The TWSG1 N-terminal domain occupies the BMP type 1 receptor binding site on BMPs, whereas the C-terminal domain binds to a Chordin family member. TWSG1 inhibits BMP function in cellular signaling assays and mouse colon organoids. This inhibitory function is abolished in a TWSG1 mutant that cannot bind BMPs. The same mutation in the Drosophila TWSG1 ortholog Tsg fails to mediate BMP gradient formation required for dorsal-ventral axis patterning of the early embryo. These studies reveal the evolutionarily conserved mechanism of BMP signaling inhibition by TWSG1. |
Friday, March 29th - Adult Physiology and Metabolism |
| Nolan, R. B., Fan, J. Y., Price, J. L. (2024). Circadian rhythms in the Drosophila eye may regulate adaptation of vision to light intensity. Frontiers in neuroscience, 18:1401721 PubMed ID: 38872947
Summary: The sensitivity of the eye at night would lead to complete saturation of the eye during the day. Therefore, the sensitivity of the eye must be down-regulated during the day to maintain visual acuity. In the Drosophila eye, the opening of and TRPL channels leads to an influx of Ca(++) that triggers down-regulation of further responses to light, including the movement of the TRPL channel and G&alpha proteins out of signaling complexes found in actin-mediated microvillar extensions of the photoreceptor cells (the rhabdomere). The eye also exhibits a light entrained-circadian rhythm, and we have recently observed that one component of this rhythm (BDBT) becomes undetectable by antibodies after exposure to light even though immunoblot analyses still detect it in the eye. BDBT is necessary for normal circadian rhythms, and in several circadian and visual mutants this eye-specific oscillation of detection is lost. Many phototransduction signaling proteins (e.g., Rhodopsin, TRP channels and Gα) also become undetectable shortly after light exposure, most likely due to a light-induced compaction of the rhabdomeric microvilli. The circadian protein BDBT might be involved in light-induced changes in the rhabdomere, and if so this could indicate that circadian clocks contribute to the daily adaptations of the eye to light. Likewise, circadian oscillations of clock proteins are observed in photoreceptors of the mammalian eye and produce a circadian oscillation in the ERG. Disruption of circadian rhythms in the eyes of mammals causes neurodegeneration in the eye, demonstrating the importance of the rhythms for normal eye function. | Meyerhof, G. T., Easwaran, S., Bontempo, A. E., Montell, C., Montell, D. J. (2024). Altered circadian rhythm, sleep, and rhodopsin 7-dependent shade preference during diapause in Drosophila melanogaster. Proc Natl Acad Sci U S A, 121(27):e2400964121 PubMed ID: 38917005
Summary: To survive adverse environments, many animals enter a dormant state such as hibernation, dauer, or diapause. Various Drosophila species undergo adult reproductive diapause in response to cool temperatures and/or short day-length. While flies are less active during diapause, it is unclear how adverse environmental conditions affect circadian rhythms and sleep. This study shows that in diapause-inducing cool temperatures, Drosophila melanogaster exhibit altered circadian activity profiles, including severely reduced morning activity and an advanced evening activity peak. Consequently, the flies have a single activity peak at a time similar to when nondiapausing flies take a siesta. Temperatures ≤15 °C, rather than photoperiod, primarily drive this behavior. At cool temperatures, flies rapidly enter a deep-sleep state that lacks the sleep cycles of flies at higher temperatures and require high levels of stimulation for arousal. Furthermore, at 25 °C, flies prefer to siesta in the shade, a preference that is virtually eliminated at 10 °C. Resting in the shade is driven by an aversion to blue light that is sensed by Rhodopsin 7 outside of the eyes. Flies at 10 °C show neuronal markers of elevated sleep pressure, including increased expression of Bruchpilot and elevated Ca(2+) in the R5 ellipsoid body neurons. Therefore, sleep pressure might overcome blue light aversion. Thus, at the same temperatures that cause reproductive arrest, preserve germline stem cells, and extend lifespan, D. melanogaster are prone to deep sleep and exhibit dramatically altered, yet rhythmic, daily activity patterns. |
| Byrns, C. N., Perlegos, A. E., Miller, K. N., Jin, Z., Carranza, F. R., Manchandra, P., Beveridge, C. H., Randolph, C. E., Chaluvadi, V. S., Zhang, S. L., Srinivasan, A. R., Bennett, F. C., Sehgal, A., Adams, P. D., Chopra, G., Bonini, N. M. (2024). Senescent glia link mitochondrial dysfunction and lipid accumulation. Nature, 630(8016):475-483 PubMed ID: 38839958
Summary: Senescence is a cellular state linked to ageing and age-onset disease across many mammalian species. Acutely, senescent cells promote wound healing and prevent tumour formation; but they are also pro-inflammatory, thus chronically exacerbate tissue decline. Whereas senescent cells are active targets for anti-ageing therapy, why these cells form in vivo, how they affect tissue ageing and the effect of their elimination remain unclear. This study identified naturally occurring senescent glia in ageing Drosophila brains and decipher their origin and influence. Using Activator protein 1 (AP1) activity to screen for senescence, this study determine that senescent glia can appear in response to neuronal mitochondrial dysfunction. In turn, senescent glia promote lipid accumulation in non-senescent glia; similar effects are seen in senescent human fibroblasts in culture. Targeting AP1 activity in senescent glia mitigates senescence biomarkers, extends fly lifespan and health span, and prevents lipid accumulation. However, these benefits come at the cost of increased oxidative damage in the brain, and neuronal mitochondrial function remains poor. Altogether, these results map the trajectory of naturally occurring senescent glia in vivo and indicate that these cells link key ageing phenomena: mitochondrial dysfunction and lipid accumulation. | Singh, A., Abhilasha, K. V., Acharya, K. R., Liu, H., Nirala, N. K., Parthibane, V., Kunduri, G., Abimannan, T., Tantalla, J., Zhu, L. J., Acharya, J. K., Acharya, U. R. (2024). A nutrient responsive lipase mediates gut-brain communication to regulate insulin secretion in Drosophila. Nat Commun, 15(1):4410 PubMed ID: 38782979
Summary: Pancreatic β cells secrete insulin in response to glucose elevation to maintain glucose homeostasis. A complex network of inter-organ communication operates to modulate insulin secretion and regulate glucose levels after a meal. Lipids obtained from diet or generated intracellularly are known to amplify glucose-stimulated insulin secretion, however, the underlying mechanisms are not completely understood. This study showed that a Drosophila secretory lipase, Vaha (CG8093), is synthesized in the midgut and moves to the brain where it concentrates in the insulin-producing cells in a process requiring Lipid Transfer Particle, a lipoprotein originating in the fat body. In response to dietary fat, Vaha stimulates insulin-like peptide release (ILP), and Vaha deficiency results in reduced circulatory ILP and diabetic features including hyperglycemia and hyperlipidemia. Our findings suggest Vaha functions as a diacylglycerol lipase physiologically, by being a molecular link between dietary fat and lipid amplified insulin secretion in a gut-brain axis. |
| Shin, M., Chang, E., Lee, D., Kim, N., Cho, B., Cha, N., Koranteng, F., Song, J. J., Shim, J. (2024). Drosophila immune cells transport oxygen through PPO2 protein phase transition. Nature, 631(8020):350-359 PubMed ID: 38926577
Summary: Insect respiration has long been thought to be solely dependent on an elaborate tracheal system without assistance from the circulatory system or immune cells. This study describes that Drosophila crystal cells-myeloid-like immune cells called haemocytes-control respiration by oxygenating Prophenoloxidase 2 (PPO2) proteins. Crystal cells direct the movement of haemocytes between the trachea of the larval body wall and the circulation to collect oxygen. Aided by copper and a neutral pH, oxygen is trapped in the crystalline structures of PPO2 in crystal cells. Conversely, PPO2 crystals can be dissolved when carbonic anhydrase lowers the intracellular pH and then reassembled into crystals in cellulo by adhering to the trachea. Physiologically, larvae lacking crystal cells or PPO2, or those expressing a copper-binding mutant of PPO2, display hypoxic responses under normoxic conditions and are susceptible to hypoxia. These hypoxic phenotypes can be rescued by hyperoxia, expression of arthropod haemocyanin or prevention of larval burrowing activity to expose their respiratory organs. Thus, it id proposed that insect immune cells collaborate with the tracheal system to reserve and transport oxygen through the phase transition of PPO2 crystals, facilitating internal oxygen homeostasis in a process that is comparable to vertebrate respiration. | Rai, M., Li, H., Policastro, R. A., Zentner, G. E., Nemkov, T., D'Alessandro, A., Tennessen, J. M. (2024). Glycolytic Disruption Triggers Interorgan Signaling to Nonautonomously Restrict Drosophila Larval Growth. bioRxiv, PubMed ID: 38895259
Summary: Drosophila larval growth requires efficient conversion of dietary nutrients into biomass. Lactate Dehydrogenase (Ldh) and Glycerol-3-phosphate dehydrogenase (Gpdh1) support larval biosynthetic metabolism by maintaining NAD(+)/NADH redox balance and promoting glycolytic flux. Consistent with the cooperative functions of Ldh and Gpdh1, the loss of both enzymes, but neither single enzyme, induces a developmental arrest. However, Ldh and Gpdh1 exhibit complex and often mutually exclusive expression patterns, suggesting that the Gpdh1; Ldh double mutant lethal phenotype could be mediated nonautonomously. This study find that the developmental arrest displayed by the double mutants extends beyond simple metabolic disruption and instead stems, in part, from changes in systemic growth factor signaling. Specifically, this synthetic lethality is linked to the upregulation of Upd3, a cytokine involved in the Jak/Stat signaling pathway. Moreover, either loss of the Upd3 or dietary administration of the steroid hormone 20-hydroxyecdysone (20E) rescue the synthetic lethal phenotype of Gpdh1; Ldh double mutants. Together, these findings demonstrate that metabolic disruptions within a single tissue can nonautonomously modulate interorgan signaling to ensure synchronous developmental growth. |
Wednesday, March 26th - Adult neural structure, development, and function |
| Nguyen, P. K., Cheng, L. Y. (2024). Drosophila medulla neuroblast termination via apoptosis, differentiation, and gliogenic switch is scheduled by the depletion of the neuroepithelial stem cell pool. Elife, 13 PubMed ID: 38905123
Summary: The brain is consisted of diverse neurons arising from a limited number of neural stem cells. Drosophila neural stem cells called neuroblasts (NBs) produces specific neural lineages of various lineage sizes depending on their location in the brain. In the Drosophila visual processing centre - the optic lobes (OLs), medulla NBs derived from the neuroepithelium (NE) give rise to neurons and glia cells of the medulla cortex. The timing and the mechanisms responsible for the cessation of medulla NBs are so far not known. In this study, we show that the termination of medulla NBs during early pupal development is determined by the exhaustion of the NE stem cell pool. Hence, altering NE-NB transition during larval neurogenesis disrupts the timely termination of medulla NBs. Medulla NBs terminate neurogenesis via a combination of apoptosis, terminal symmetric division via Prospero, and a switch to gliogenesis via Glial Cell Missing (Gcm); however, these processes occur independently of each other. It waws also shown that temporal progression of the medulla NBs is mostly not required for their termination. As the Drosophila OL shares a similar mode of division with mammalian neurogenesis, understanding when and how these progenitors cease proliferation during development can have important implications for mammalian brain size determination and regulation of its overall function. | Sturner, T., Brooks, P., Capdevila, L. S., Morris, B. J., ...., Card, G. M., Costa, M., Jefferis, G., Eichler, K. (2024). Comparative connectomics of the descending and ascending neurons of the Drosophila nervous system: stereotypy and sexual dimorphism. bioRxiv, PubMed ID: 38895426
Summary: In most complex nervous systems there is a clear anatomical separation between the nerve cord, which contains most of the final motor outputs necessary for behaviour, and the brain. In insects, the neck connective is both a physical and information bottleneck connecting the brain and the ventral nerve cord (VNC, spinal cord analogue) and comprises diverse populations of descending (DN), ascending (AN) and sensory ascending neurons, which are crucial for sensorimotor signalling and control. Integrating three separate EM datasets, complete connectomic description is provided of the ascending and descending neurons of the female nervous system of Drosophila and compare them with neurons of the male nerve cord. Proofread neuronal reconstructions have been matched across hemispheres, datasets and sexes. Crucially, 51% of DN cell types was matched to light level data defining specific driver lines as well as classifying all ascending populations. We use these results to reveal the general architecture, tracts, neuropil innervation and connectivity of neck connective neurons. Cnnected chains of descending and ascending neurons were found spanning the neck, that may subserve motor sequences. A complete description of sexually dimorphic DN and AN populations is provided, with detailed analysis of circuits implicated in sex-related behaviours, including female ovipositor extrusion (DNp13), male courtship (DNa12/aSP22) and song production (AN hemilineage 08B). This work represents the first EM-level circuit analyses spanning the entire central nervous system of an adult animal. |
| Sen, E., El-Keredy, A., Jacob, N., Mancini, N., Asnaz, G., Widmann, A., Gerber, B., Thoener, J. (2024). Cognitive limits of larval Drosophila: testing for conditioned inhibition, sensory preconditioning, and second-order conditioning. Learn Mem, 31(5) PubMed ID: 38862170
Summary: Drosophila larvae are an established model system for studying the mechanisms of innate and simple forms of learned behavior. They have about 10 times fewer neurons than adult flies, and it was the low total number of their neurons that allowed for an electron microscopic reconstruction of their brain at synaptic resolution. Regarding the mushroom body, a central brain structure for many forms of associative learning in insects, it turned out that more than half of the classes of synaptic connection had previously escaped attention. Understanding the function of these circuit motifs, subsequently confirmed in adult flies, is an important current research topic. In this context, larval Drosophila were tested for their cognitive abilities in three tasks that are characteristically more complex than those previously studied. The data provide evidence for (i) conditioned inhibition, as has previously been reported for adult flies and honeybees. Unlike what is described for adult flies and honeybees, however, the data do not provide evidence for (ii) sensory preconditioning or (iii) second-order conditioning in Drosophila larvae. The methodological features of these experiments are discussed as well as four specific aspects of the organization of the larval brain that may explain why these two forms of learning are observed in adult flies and honeybees, but not in larval Drosophila. | Azevedo, A., Lesser, E., Phelps, J. S., Mark, B., Elabbady, L., Kuroda, S., Sustar, A., Moussa, A., Khandelwal, A., Dallmann, C. J., Agrawal, S., Lee, S. J., Pratt, B., Cook, A., Skutt-Kakaria, K., Gerhard, S., Lu, R., Kemnitz, N., Lee, K., Halageri, A., Castro, M., Ih, D., Gager, J., Tammam, M., Dorkenwald, S., Collman, F., Schneider-Mizell, C., Brittain, D., Jordan, C. S., Dickinson, M., Pacureanu, A., Seung, H. S., Macrina, T., Lee, W. A., Tuthill, J. C. (2024). Connectomic reconstruction of a female Drosophila ventral nerve cord. Nature, 631(8020):360-368 PubMed ID: 38926570
Summary: A deep understanding of how the brain controls behaviour requires mapping neural circuits down to the muscles that they control. This study applied automated tools to segment neurons and identify synapses in an electron microscopy dataset of an adult female Drosophila melanogaster ventral nerve cord (VNC), which functions like the vertebrate spinal cord to sense and control the body. The fly VNC contains roughly 45 million synapses and 14,600 neuronal cell bodies. To interpret the output of the connectome, the muscle targets of leg and wing motor neurons were mapped using genetic driver lines and X-ray holographic nanotomography. With this motor neuron atlas, neural circuits were identified that coordinate leg and wing movements during take-off. This study provides the reconstruction of VNC circuits, the motor neuron atlas and tools for programmatic and interactive access as resources to support experimental and theoretical studies of how the nervous system controls behaviour. |
| Benchorin, G., Cho, R. J., Li, M. J., Molotkova, N., Kohwi, M. (2024). Dan forms condensates in neuroblasts and regulates nuclear architecture and progenitor competence in vivo. Nat Commun, 15(1):5097 PubMed ID: 38877037
Summary: Genome organization is thought to underlie cell type specific gene expression, yet how it is regulated in progenitors to produce cellular diversity is unknown. In Drosophila, a developmentally-timed genome reorganization in neural progenitors terminates competence to produce early-born neurons. These events require downregulation of Distal antenna (Dan), part of the conserved pipsqueak DNA-binding superfamily. Dan was found to form liquid-like condensates with high protein mobility, and whose size and subnuclear distribution are balanced with its DNA-binding. Further, a LARKS domain, a structural motif associated with condensate-forming proteins was identified. Deleting just 13 amino acids from LARKS abrogates Dan's ability to retain the early-born neural fate gene, hunchback, in the neuroblast nuclear interior and maintain competence in vivo. Conversely, domain-swapping with LARKS from known phase-separating proteins rescues Dan's effects on competence. Together, in vivo evidence is provided for condensate formation and the regulation of progenitor nuclear architecture underlying neuronal diversification. | Morano, N. C., Lopez, D. H., Meltzer, H., Sergeeva, A. P., Katsamba, P. S., Rostam, K. D., Gupta, H. P., Becker, J. E., Bornstein, B., Cosmanescu, F., Schuldiner, O., Honig, B., Mann, R. S., Shapiro, L. (2024). Cis inhibition of co-expressed DIPs and Dprs shapes neural development. bioRxiv, PubMed ID: 38895375
Summary: In Drosophila , two interacting adhesion protein families, Dprs and DIPs, coordinate the assembly of neural networks. While intercellular DIP/Dpr interactions have been well characterized, DIPs and Dprs are often co-expressed within the same cells, raising the question as to whether they also interact in cis . In cultured cells and in vivo, that DIP-α and DIP-δ can interact in cis with their ligands, Dpr6/10 and Dpr12, respectively. When co-expressed in cis with their cognate partners, these Dprs regulate the extent of trans binding, presumably through competitive cis interactions. The neurodevelopmental effects of cis inhibition in fly motor neurons and in the mushroom body are demonstrated. It was further shown that a long disordered region of DIP-&alpna; at the C-terminus is required for cis but not trans interactions, likely because it alleviates geometric constraints on cis binding. Thus, the balance between cis and trans interactions plays a role in controlling neural development. |
Tuesday, March 25th - Genes and Protein |
| Zhou, T., Wu, W., Ma, S., Chen, J., Huang, J., Qiao, X. (2024). Effects of RDL GABA Receptor Point Mutants on Susceptibility to Meta-Diamide and Isoxazoline Insecticides in Drosophila melanogaster. Insects, 15(5) PubMed ID: 38786890
Summary: Ionotropic γ-aminobutyric acid (GABA) receptors in insects, specifically those composed of the RDL (resistant to dieldrin) subunit, serve as important targets for commonly used synthetic insecticides. These insecticides belong to various chemical classes, such as phenylpyrazoles, cyclodienes, meta-diamides, and isoxazolines, with the latter two potentially binding to the transmembrane inter-subunit pocket. However, the specific amino acid residues that contribute to the high sensitivity of insect RDL receptors to these novel insecticides remain elusive. This study investigated the susceptibility of seven distinct Drosophila melanogaster Rdl point mutants against four meta-diamide and isoxazoline insecticides: isocycloseram, fluxametamide, fluralaner, and broflanilide. The findings indicate that, despite exhibiting increased sensitivity to fluralaner in vitro, the Rdl(I276C) mutant showed resistance to isocycloseram and fluxametamide. Similarly, the double-points mutant Rdl(I276F+G279S) also showed decreased sensitivity to the tested isoxazolines. On the other hand, the Rdl(G335M) mutant displayed high levels of resistance to all tested insecticides. Molecular modeling and docking simulations further supported these findings, highlighting similar binding poses for these insecticides. In summary, this research provides robust in vivo evidence supporting the idea that the inter-subunit amino acids within transmembrane M1 and M3 domains form the binding site crucial for meta-diamide and isoxazoline insecticide interactions. This study highlights the complex interplay between mutations and insecticide susceptibility, paving the way for more targeted pest control strategies. | Monch, T. C., Smylla, T. K., Brandle, F., Preiss, A., Nagel, A. C. (2024). Novel Genome-Engineered H Alleles Differentially Affect Lateral Inhibition and Cell Dichotomy Processes during Bristle Organ Development. Genes, 15(5) PubMed ID: 38790181
Summary: Hairless (H) encodes the major antagonist in the Notch signaling pathway, which governs cellular differentiation of various tissues in Drosophila. By binding to the Notch signal transducer Suppressor of Hairless (Su(H)), H assembles repressor complexes onto Notch target genes. Using genome engineering, three new H alleles, H(FA), H(LLAA) and H(WA) were generated and a phenotypic series was established by several parameters, reflecting the residual H-Su(H) binding capacity. Occasionally, homozygous H(WA) flies develop to adulthood. They were compared with the likewise semi-viable H(NN) allele affecting H-Su(H) nuclear entry. The H homozygotes were short-lived, sterile and flightless, yet showed largely normal expression of several mitochondrial genes. Typical for H mutants, both H(WA) and H(NN) homozygous alleles displayed strong defects in wing venation and mechano-sensory bristle development. Strikingly, however, H(WA) displayed only a loss of bristles, whereas bristle organs of H(NN) flies showed a complete shaft-to-socket transformation. Apparently, the impact of H(WA) is restricted to lateral inhibition, whereas that of H(NN) also affects the respective cell type specification. Notably, reduction in Su(H) gene dosage only suppressed the H(NN) bristle phenotype, but amplified that of H(WA). These differences are interpreted as to the role of H regarding Su(H) stability and availability. |
| Zhang, L., Ge, R., Yang, Y., Chen, K., Li, C. (2024). The zona pellucida protein piopio regulates the metamorphosis and reproduction in Tribolium castaneum. Archives of insect biochemistry and physiology, 116(1):e22122 PubMed ID: 38783685
Summary: The zona pellucida domain protein Piopio (Pio) was reported to mediate only the adhesion of the apical epithelial surface and the overlying apical extracellular matrix in Drosophila melanogaster, but the developmental roles of Pio were poorly understood in insects. To address this issue, this study comprehensively analyzed the function of Pio in Tribolium castaneum. Phylogenetic analysis indicated that pio exhibited one-to-one orthologous relationship among insects. T. castaneum pio had a 1236-bp ORF and contained eight exons. During development pio was abundantly expressed from larva to adult and lowly expressed at the late stage of embryo and adult, while it had more transcripts in the head, epidermis, and gut but fewer in the fat body of late-stage larvae. Knockdown of pio inhibited the pupation, eclosion, and reproduction of T. castaneum. The expression of vitellogenin 1 (Vg1), Vg2, and Vg receptor (VgR) largely decreased in pio-silenced female adults. Silencing pio increased the 20-hydroxyecdysone titer by upregulating phantom and spo expression but decreased the juvenile hormone (JH) titer through downregulating JHAMT3 and promoting JHE, JHEH-r4, and JHDK transcription. These results suggested that Pio might regulate the metamorphosis and reproduction via modulating the ecdysone and JH metabolism in T. castaneum. This study found the novel roles of pio in insect metamorphosis and reproduction, and provided the new insights for analyzing other zona pellucida proteins functions in insects. | Bose, A., Schuster, K., Kodali, C., Sonam, S., Smith-Bolton, R. (2024). The pioneer transcription factor Zelda facilitates the exit from regeneration and restoration of patterning in Drosophila. bioRxiv, PubMed ID: 38854062
Summary: For a damaged tissue to regenerate, the injured site must repair the wound, proliferate, and restore the correct patterning and cell types. Zelda, a pioneer transcription factor largely known for its role in embryonic zygotic genome activation, is dispensable for normal wing development but crucial for wing disc patterning during regeneration. Impairing Zelda function during disc regeneration resulted in adult wings with a plethora of cell fate errors, affecting the veins, margins, and posterior compartment identity. Using CUT&RUN, this study identified and validated targets of Zelda including the cell fate genes cut, Delta and achaete, which failed to return to their normal expression patterns upon loss of Zelda. In addition, Zelda controls expression of factors previously established to preserve cell fate during regeneration like taranis and osa, which stabilizes engrailed expression during regeneration, thereby preserving posterior identity. Finally, Zelda ensures proper expression of the integrins encoded by multiple edematous wings and myospheroid during regeneration to prevent blisters in the resuting adult wing. Thus, Zelda is crucial for maintaining cell fate and structural architecture of the regenerating tissue. |
| Webb, J. A., Farrow, E., Cain, B., Yuan, Z., Yarawsky, A. E., Schoch, E., Gagliani, E. K., Herr, A. B., Gebelein, B., Kovall, R. A. (2024). Cooperative Gsx2-DNA binding requires DNA bending and a novel Gsx2 homeodomain interface. Nucleic Acids Res, 52(13):7987-8002 PubMed ID: 38874471
Summary: The conserved Gsx homeodomain (HD) transcription factors (see Ind) specify neural cell fates in animals from flies to mammals. Like many HD proteins, Gsx factors bind A/T-rich DNA sequences prompting the following question: How do HD factors that bind similar DNA sequences in vitro regulate specific target genes in vivo? Prior studies revealed that Gsx factors bind DNA both as a monomer on individual A/T-rich sites and as a cooperative homodimer to two sites spaced precisely 7 bp apart. However, the mechanistic basis for Gsx-DNA binding and cooperativity is poorly understood. This study used biochemical, biophysical, structural and modeling approaches to (i) show that Gsx factors are monomers in solution and require DNA for cooperative complex formation, (ii) define the affinity and thermodynamic binding parameters of Gsx2/DNA interactions, (iii) solve a high-resolution monomer/DNA structure that reveals that Gsx2 induces a 20° bend in DNA, (iv) identify a Gsx2 protein-protein interface required for cooperative DNA binding and (v) determine that flexible spacer DNA sequences enhance Gsx2 cooperativity on dimer sites. Altogether, these results provide a mechanistic basis for understanding the protein and DNA structural determinants that underlie cooperative DNA binding by Gsx factors. | 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. |
Monday, March 24th - RNAs |
| Petrauskas, A., Fortunati, D. L., Kandi, A. R., Pothapragada, S. S., Agrawal, K., Singh, A., Huelsmeier, J., Hillebrand, J., Brown, G., Chaturvedi, D., Lee, J., Lim, C., Auburger, G., VijayRaghavan, K., Ramaswami, M., Bakthavachalu, B. (2024). Structured and disordered regions of Ataxin-2 contribute differently to the specificity and efficiency of mRNP granule formation. PLoS Genet, 20(5):e1011251 PubMed ID: 38768217
Summary: Ataxin-2 (ATXN2) is a gene implicated in spinocerebellar ataxia type II (SCA2), amyotrophic lateral sclerosis (ALS and Parkinsonism. The encoded protein is a therapeutic target for ALS and related conditions. ATXN2 (or Atx2 in insects) can function in translational activation, translational repression, mRNA stability and in the assembly of mRNP-granules, a process mediated by intrinsically disordered regions (IDRs). Previous work has shown that the LSm (Like-Sm) domain of Atx2, which can help stimulate mRNA translation, antagonizes mRNP-granule assembly. This study advances these findings through a series of experiments on Drosophila and human Ataxin-2 proteins. Results of Targets of RNA Binding Proteins Identified by Editing (TRIBE), co-localization and immunoprecipitation experiments indicate that a polyA-binding protein (PABP) interacting, PAM2 motif of Ataxin-2 may be a major determinant of the mRNA and protein content of Ataxin-2 mRNP granules. Experiments with transgenic Drosophila indicate that while the Atx2-LSm domain may protect against neurodegeneration, structured PAM2- and unstructured IDR- interactions both support Atx2-induced cytotoxicity. Taken together, the data lead to a proposal for how Ataxin-2 interactions are remodelled during translational control and how structured and non-structured interactions contribute differently to the specificity and efficiency of RNP granule condensation as well as to neurodegeneration. | Makhijani, K., Mar, J., Gaziova, I., Bhat, K. M. (2024). Posttranscriptional regulation of the T-box gene midline via the 3'UTR in Drosophila is complex and cell- and tissue-dependent. Genetics, 227(4) PubMed ID: 38805187
Summary: The T-box (Tbx) proteins have a 180-230 amino acid DNA-binding domain, first reported in the Brachyury (T) protein. They are highly conserved among metazoans. They regulate a multitude of cellular functions in development and disease. This study reports posttranscriptional and translational regulation of midline (mid), a Tbx member in Drosophila. The 3'UTR of mid was found to have mRNA degradation elements and AT-rich sequences. In Schneider S2 cells, mid-mRNA could be detected only when the transgene was without the 3'UTR. Similarly, the 3'UTR linked to the Renilla luciferase reporter significantly reduced the activity of the Luciferase, whereas deleting only the degradation elements from the 3'UTR resulted in reduced activity, but not as much. Overexpression of mid in MP2, an embryonic neuroblast, showed no significant difference in the levels of mid-mRNA between the 2 transgenes, with and without the 3'UTR, indicating the absence of posttranscriptional regulation of mmid in MP2. Moreover, while elevated mid-RNA was detected in MP2 in nearly all hemisegments, only a fifth of those hemisegments had elevated levels of the protein. Overexpression of the 2 transgenes resulted in MP2-lineage defects at about the same frequency. These results indicate a translational/posttranslational regulation of mid in MP2. The regulation of ectopically expressed mmid in the wing imaginal disc was complex. In the wing disc, where b is not expressed, the ectopic expression of the transgene lacking the 3'UTR had a higher level of mid-RNA and the protein had a stronger phenotypic effect. These results indicate that the 3'UTR can subject mid-mRNA to degradation in a cell- and tissue-specific manner. A balancer-mediated transgenerational modifier effect was detected on the expression and gain of function effects of the 2 transgenes. |
| Crane, A. B., Jetti, S. K., Littleton, J. T. (2024). A stochastic RNA editing process targets a limited number of sites in individual Drosophila glutamatergic motoneurons. bioRxiv, PubMed ID: 38798345
Summary: RNA editing is a post-transcriptional source of protein diversity and occurs across the animal kingdom. Given the complete profile of mRNA targets and their editing rate in individual cells is unclear, this study analyzed single cell RNA transcriptomes from Drosophila larval tonic and phasic glutamatergic motoneuron subtypes to determine the most highly edited targets and identify cell-type specific editing. From ∼15,000 genes encoded in the genome, 316 high confidence A-to-I canonical RNA edit sites were identified, with 102 causing missense amino acid changes in proteins regulating membrane excitability, synaptic transmission, and cellular function. Some sites showed 100% editing in single neurons as observed with mRNAs encoding mammalian AMPA receptors. However, most sites were edited at lower levels and generated variable expression of edited and unedited mRNAs within individual neurons. Together, these data provide insights into how the RNA editing landscape alters protein function to modulate the properties of two well-characterized neuronal populations in Drosophila. | 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. We show that a miRNA can drive repeated instances of adaptive evolution in animals. |
| Fingerhut, J. M., Lannes, R., Whitfield, T. W., Thiru, P., Yamashita, Y. M. (2024). Co-transcriptional splicing facilitates transcription of gigantic genes. PLoS Genet, 20(6):e1011241 PubMed ID: 38870220
Summary: Although introns are typically tens to thousands of nucleotides, there are notable exceptions. In flies as well as humans, a small number of genes contain introns that are more than 1000 times larger than typical introns, exceeding hundreds of kilobases (kb) to megabases (Mb). It remains unknown why gigantic introns exist and how cells overcome the challenges associated with their transcription and RNA processing. The Drosophila Y chromosome contains some of the largest genes identified to date: multiple genes exceed 4Mb, with introns accounting for over 99% of the gene span. This study demonstrates that co-transcriptional splicing of these gigantic Y-linked genes is important to ensure successful transcription: perturbation of splicing led to the attenuation of transcription, leading to a failure to produce mature mRNA. Cytologically, defective splicing of the Y-linked gigantic genes resulted in disorganization of transcripts within the nucleus suggestive of entanglement of transcripts, likely resulting from unspliced long RNAs. It is proposed that co-transcriptional splicing maintains the length of nascent transcripts of gigantic genes under a critical threshold, preventing their entanglement and ensuring proper gene expression. study reveals a novel biological significance of co-transcriptional splicing. | Zhang, Q., Fan, X., Fu, F., Zhu, Y., Luo, G., Chen, H. (2024). Adar Regulates Drosophila melanogaster Spermatogenesis via Modulation of BMP Signaling. Int J Mol Sci, 25(11) PubMed ID: 38891830
Summary: The dynamic process of Drosophila spermatogenesis involves asymmetric division, mitosis, and meiosis, which ultimately results in the production of mature spermatozoa. Disorders of spermatogenesis can lead to infertility in males. ADAR (Adenosine deaminase acting on RNA) mutations in Drosophila cause male infertility, yet the causative factors remain unclear. In this study, immunofluorescence staining was employed to visualize endogenous ADAR proteins and assess protein levels via fluorescence-intensity analysis. In addition, the early differentiation disorders and homeostatic alterations during early spermatogenesis in the testes were examined through quantification of transit-amplifying region length, counting the number of GSCs (germline stem cells), and fertility experiments. The findings suggest that deletion of ADAR causes testicular tip transit-amplifying cells to accumulate and become infertile in older male Drosophila. By overexpressing ADAR in early germline cells, male infertility can be partially rescued. Transcriptome analysis showed that ADAR maintained early spermatogenesis homeostasis through the bone-morphogenetic-protein (BMP) signaling pathway. Taken together, these findings have the potential to help explore the role of ADAR in early spermatogenesis. |
Thursday, March 20th - Adult Neural Structure, Development and Function |
| Zhang, X., Sun, D., Wong, K., Salkini, A., Najafi, H., Kim, W. J. (2024). The astrocyte-enriched gene deathstar plays a crucial role in the development, locomotion, and lifespan of D. melanogaster. Fly (Austin), 18(1):2368336 PubMed ID: 38884422
Summary: The Drosophila melanogaster brain is a complex organ with various cell types, orchestrating the development, physiology, and behaviors of the fly. While each cell type in Drosophila brain is known to express a unique gene set, their complete genetic profile is still unknown. Advances in the RNA sequencing techniques at single-cell resolution facilitate identifying novel cell type markers and/or re-examining the specificity of the available ones. In this study, exploiting a single-cell RNA sequencing data of Drosophila optic lobe, the cells were wcategorized based on their expression pattern for known markers, then the genes with enriched expression in astrocytes were identified. CG11000 (Deathstar) was identified as a gene with a comparable expression profile to the Eaat1 gene, an astrocyte marker, in every individual cell inside the Drosophila optic lobe and midbrain, as well as in the entire Drosophila brain throughout its development. Consistent with these bioinformatics data, immunostaining of the brains dissected from transgenic adult flies showed co-expression of CG11000 with Eaat1 in a set of single cells corresponding to the astrocytes in the Drosophila brain. Physiologically, inhibiting CG11000 through RNA interference disrupted the normal development of male D. melanogaster, while having no impact on females. Expression suppression of CG11000 in adult flies led to decreased locomotion activity and also shortened lifespan specifically in astrocytes, indicating the gene's significance in astrocytes. This gene was designated as 'deathstar' due to its crucial role in maintaining the star-like shape of glial cells, astrocytes, throughout their development into adult stage. | Coban, B., Poppinga, H., Rachad, E. Y., Geurten, B., Vasmer, D., Rodriguez Jimenez, F. J., Gadgil, Y., Deimel, S. H., Alyagor, I., Schuldiner, O., Grunwald Kadow, I. C., Riemensperger, T. D., Widmann, A., Fiala, A. (2024). The caloric value of food intake structurally adjusts a neuronal mushroom body circuit mediating olfactory learning in Drosophila. JLearn Mem, 31(5) PubMed ID: 38862177
Summary: Associative learning enables the adaptive adjustment of behavioral decisions based on acquired, predicted outcomes. The valence of what is learned is influenced not only by the learned stimuli and their temporal relations, but also by prior experiences and internal states. This study used the fruit fly Drosophila melanogaster to demonstrate that neuronal circuits involved in associative olfactory learning undergo restructuring during extended periods of low-caloric food intake. Specifically, a decrease was observed in the connections between specific dopaminergic neurons (DANs) and Kenyon cells at distinct compartments of the mushroom body. This structural synaptic plasticity was contingent upon the presence of allatostatin A receptors in specific DANs and could be mimicked optogenetically by expressing a light-activated adenylate cyclase in exactly these DANs. Importantly, this rearrangement in synaptic connections was found to influence aversive, punishment-induced olfactory learning but did not impact appetitive, reward-based learning. Whether induced by prolonged low-caloric conditions or optogenetic manipulation of cAMP levels, this synaptic rearrangement resulted in a reduction of aversive associative learning. Consequently, the balance between positive and negative reinforcing signals shifted, diminishing the ability to learn to avoid odor cues signaling negative outcomes. These results exemplify how a neuronal circuit required for learning and memory undergoes structural plasticity dependent on prior experiences of the nutritional value of food. |
| Sukumar, S. K., Antonydhason, V., Molander, L., Sandakly, J., Kleit, M., Umapathy, G., Mendoza-Garcia, P., Masudi, T., Schlosser, A., Nässel, D. R., Wegener, C., Shirinian, M., Palmer, R. H. (2024). The Alk receptor tyrosine kinase regulates Sparkly, a novel activity regulating neuropeptide precursor in the Drosophila central nervous system. Elife, 12 PubMed ID: 38904987
Summary: Numerous roles for the Alk receptor tyrosine kinase have been described in Drosophila, including functions in the central nervous system (CNS), however the molecular details are poorly understood. To gain mechanistic insight, this study employed Targeted DamID (TaDa) transcriptional profiling to identify targets of Alk signaling in the larval CNS. TaDa was employed in larval CNS tissues, while genetically manipulating Alk signaling output. The resulting TaDa data were analyzed together with larval CNS scRNA-seq datasets performed under similar conditions, identifying a role for Alk in the transcriptional regulation of neuroendocrine gene expression. Further integration with bulk and scRNA-seq datasets from larval brains in which Alk signaling was manipulated identified a previously uncharacterized Drosophila neuropeptide precursor encoded by CG4577 as an Alk signaling transcriptional target. CG4577, which we named Sparkly (Spar), is expressed in a subset of Alk-positive neuroendocrine cells in the developing larval CNS, including circadian clock neurons. In agreement with our TaDa analysis, overexpression of the Drosophila Alk ligand Jeb resulted in increased levels of Spar protein in the larval CNS. Spar protein is expressed in circadian (clock) neurons, and flies lacking Spar exhibit defects in sleep and circadian activity control. In summary, this study reports a novel activity regulating neuropeptide precursor gene that is regulated by Alk signaling in the Drosophila CNS. | Ehweiner, A., Duch, C., Brembs, B. (2024). Wings of Change: aPKC/FoxP-dependent plasticity in steering motor neurons underlies operant self-learning in Drosophila. F1000Research, 13:116 PubMed ID: 38779314
Summary: Motor learning is central to human existence, such as learning to speak or walk, sports moves, or rehabilitation after injury. Evidence suggests that all forms of motor learning share an evolutionarily conserved molecular plasticity pathway. This study presents novel insights into the neural processes underlying operant self-learning, a form of motor learning in the fruit fly Drosophila. Wild type and transgenic Drosophila fruit flieswere operantly trained, tethered at the torque meter, in a motor learning task that required them to initiate and maintain turning maneuvers around their vertical body axis (yaw torque). This behavioral experiment was combined with transgenic peptide expression, CRISPR/Cas9-mediated, spatio-temporally controlled gene knock-out and confocal microscopy. Expression of atypical protein kinase C (aPKC) in direct wing steering motoneurons co-expressing the transcription factor FoxP was found to be necessary for this type of motor learning and that aPKC likely acts via non-canonical pathways. It takes more than a week for CRISPR/Cas9-mediated knockout of FoxP in adult animals to impair motor learning, suggesting that adult FoxP expression is required for operant self-learning. These experiments suggest that, for operant self-learning, a type of motor learning in Drosophila, co-expression of atypical protein kinase C (aPKC) and the transcription factor FoxP is necessary in direct wing steering motoneurons. Some of these neurons control the wing beat amplitude when generating optomotor responses, and modulation of optomotor behavior was found after operant self-learning. aPKC likely acts via non-canonical pathways and that FoxP expression is also required in adult flies. |
| Lottes, E. N., Ciger, F., Bhattacharjee, S., Timmins, E. A., Tete, B., Tran, T., Matta, J., Patel, A. A., Cox, D. N. (2024). CCT and Cullin1 Regulate the TORC1 Pathway to Promote Dendritic Arborization in Health and Disease. Cells, 13(12) PubMed ID: 38920658
Summary: The development of cell-type-specific dendritic arbors is integral to the proper functioning of neurons within their circuit networks. This study examined the regulatory relationship between the cytosolic chaperonin CCT, key insulin pathway genes, and an E3 ubiquitin ligase (Cullin1) in dendritic development. CCT loss of function (LOF) results in dendritic hypotrophy in Drosophila Class IV (CIV) multi-dendritic larval sensory neurons, and CCT has recently been shown to fold components of the TOR (Target of Rapamycin) complex 1 (TORC1) in vitro. Through targeted genetic manipulations, this study confirm that an LOF of CCT and the TORC1 pathway reduces dendritic complexity, while overexpression of key TORC1 pathway genes increases the dendritic complexity in CIV neurons. Furthermore, both CCT and TORC1 LOF significantly reduce microtubule (MT) stability. CCT has been previously implicated in regulating proteinopathic aggregation, thus, this study examined CIV dendritic development in disease conditions as well. The expression of mutant Huntingtin leads to dendritic hypotrophy in a repeat-length-dependent manner, which can be rescued by Cullin1 LOF. Together, these data suggest that Cullin1 and CCT influence dendritic arborization through the regulation of TORC1 in both health and disease. | Vaikakkara Chithran, A., Allan, D. W., O'Connor, T. P. (2024). Adult expression of the cell adhesion protein Fasciclin 3 is required for the maintenance of adult olfactory interneurons. J Cell Sci, 137(12) PubMed ID: 38934299
Summary: The proper functioning of the nervous system is dependent on the establishment and maintenance of intricate networks of neurons that form functional neural circuits. Once neural circuits are assembled during development, a distinct set of molecular programs is likely required to maintain their connectivity throughout the lifetime of the organism. This study demonstrates that Fasciclin 3 (Fas3), an axon guidance cell adhesion protein, is necessary for the maintenance of the olfactory circuit in adult Drosophila. The TARGET system was used to spatiotemporally knockdown Fas3 in selected populations of adult neurons. The findings show that Fas3 knockdown results in the death of olfactory circuit neurons and reduced survival of adults. It was also demonstrated that Fas3 knockdown activates caspase-3-mediated cell death in olfactory local interneurons, which can be rescued by overexpressing baculovirus p35, an anti-apoptotic protein. This work adds to the growing set of evidence indicating a crucial role for axon guidance proteins in the maintenance of neuronal circuits in adults. |
Wednesday, March 19th - Disease Models |
| Au, W. H., Miller-Fleming, L., Sanchez-Martinez, A., Lee, J. A., Twyning, M. J., Prag, H. A., Raik, L., Allen, S. P., Shaw, P. J., Ferraiuolo, L., Mortiboys, H., Whitworth, A. J. (2024). Activation of the Keap1/Nrf2 pathway suppresses mitochondrial dysfunction, oxidative stress, and motor phenotypes in C9orf72 ALS/FTD models. Life science alliance, 7(9) PubMed ID: 38906677
Summary: Mitochondrial dysfunction is a common feature of C9orf72 amyotrophic lateral sclerosis/frontotemporal dementia (ALS/FTD); however, it remains unclear whether this is a cause or consequence of the pathogenic process. Analysing multiple aspects of mitochondrial biology across several Drosophila models of C9orf72-ALS/FTD, this study found morphology, oxidative stress, and mitophagy are commonly affected, which correlated with progressive loss of locomotor performance. Notably, only genetic manipulations that reversed the oxidative stress levels were also able to rescue C9orf72 locomotor deficits, supporting a causative link between mitochondrial dysfunction, oxidative stress, and behavioural phenotypes. Targeting the key antioxidant Keap1/Nrf2 pathway, genetic reduction of Keap1 or pharmacological inhibition by dimethyl fumarate significantly was found to rescue the C9orf72-related oxidative stress and motor deficits. Finally, mitochondrial ROS levels were also elevated in C9orf72 patient-derived iNeurons and were effectively suppressed by dimethyl fumarate treatment. These results indicate that mitochondrial oxidative stress is an important mechanistic contributor to C9orf72 pathogenesis, affecting multiple aspects of mitochondrial function and turnover. Targeting the Keap1/Nrf2 signalling pathway to combat oxidative stress represents a therapeutic strategy for C9orf72-related ALS/FTD. | Zhou, C., Li, Z., Li, Y., Li, Y., Wang, W., Shang, W., Liu, J. P., Wang, L., Tong, C. (2024). TRABD modulates mitochondrial homeostasis and tissue integrity.. Cell Rep, 43(6):114304 PubMed ID: 38843396
Summary: High TRABD expression is associated with tau pathology in patients with Alzheimer's disease; however, the function of TRABD is unknown. Human TRABD encodes a mitochondrial outer-membrane protein. The loss of TRABD resulted in mitochondrial fragmentation, and TRABD overexpression led to mitochondrial clustering and fusion. The C-terminal tail of the TRABD anchored to the mitochondrial outer membrane and the TraB domain could form homocomplexes. Additionally, TRABD forms complexes with MFN2, MIGA2, and PLD6 to facilitate mitochondrial fusion. Flies lacking dTRABD are viable and have normal lifespans. However, aging flies exhibit reduced climbing ability and abnormal mitochondrial morphology in their muscles. The expression of dTRABD is increased in aged flies. dTRABD overexpression leads to neurodegeneration and enhances tau toxicity in fly eyes. The overexpression of dTRABD also increased reactive oxygen species (ROS), ATP production, and protein turnover in the mitochondria. This study suggested that TRABD-induced mitochondrial malfunctions contribute to age-related neurodegeneration. |
| Sidisky, J. M., Winters, A., Caratenuto, R., Babcock, D. T. (2024). Synaptic defects in a drosophila model of muscular dystrophy. Frontiers in cellular neuroscience, 18:1381112 PubMed ID: 38812789
Summary: Muscular dystrophies are a devastating class of diseases that result in a progressive loss of muscle integrity. Duchenne Muscular Dystrophy, the most prevalent form of Muscular Dystrophy, is due to the loss of functional Dystrophin. While much is known regarding destruction of muscle tissue in these diseases, much less is known regarding the synaptic defects that also occur in these diseases. Synaptic defects are also among the earliest hallmarks of neurodegenerative diseases, including the neuromuscular disease Amyotrophic Lateral Sclerosis (ALS). The current study investigates synaptic defects within adult muscle tissues as well as presynaptic motor neurons in Drosophila dystrophin mutants. The progressive, age-dependent loss of flight ability in dystrophin mutants is accompanied by disorganization of Neuromuscular Junctions (NMJs), including impaired localization of both presynaptic and postsynaptic markers. These synaptic defects, including presynaptic defects within motor neurons, are due to the loss of Dystrophin specifically within muscles. These results should help to better understand the early synaptic defects preceding cell loss in neuromuscular disorders. | Banerjee, S., Vernon, S., Ruchti, E., Limoni, G., Jiao, W., Asadzadeh, J., Van Campenhoudt, M., McCabe, B. D. (2024). Trio preserves motor synapses and prolongs motor ability during aging. Cell Rep, 43(6):114256 PubMed ID: 38795343
Summary: The decline of motor ability is a hallmark feature of aging and is accompanied by degeneration of motor synaptic terminals. Consistent with this, Drosophila motor synapses undergo characteristic age-dependent structural fragmentation co-incident with diminishing motor ability. Motor synapse levels of Trio, an evolutionarily conserved guanine nucleotide exchange factor (GEF), decline with age. Increasing Trio expression in adult Drosophila can abrogate age-dependent synaptic structural fragmentation, postpone the decline of motor ability, and maintain the capacity of motor synapses to sustain high-intensity neurotransmitter release. This preservative activity is conserved in transgenic human Trio, requires Trio Rac GEF function, and can also ameliorate synapse degeneration induced by depletion of miniature neurotransmission. These results support a paradigm where the structural dissolution of motor synapses precedes and promotes motor behavioral diminishment and where intervening in this process can postpone the decline of motor function during aging. |
| Zakharenko, L. P., Bobrovskikh, M. A., Gruntenko, N. E., Petrovskii, D. V., Verevkin, E. G., Putilov, A. A. (2024). Two Old Wild-Type Strains of Drosophila melanogaster Can Serve as an Animal Model of Faster and Slower Aging Processes. Insects, 15(5) PubMed ID: 38786885
Summary: Drosophila melanogaster provides a powerful platform to study the physiology and genetics of aging, i.e., the mechanisms underpinnings healthy aging, age-associated disorders, and acceleration of the aging process under adverse environmental conditions. This study tested the responses of daily rhythms to age-accelerated factors in two wild-type laboratory-adapted strains, Canton-S and Harwich. On the example of the 24 h patterns of locomotor activity and sleep, the responses of these two strains to such factors as aging, high temperature, carbohydrate diet, and diet were documented with different doses of caffeine-benzoate sodium. The strains demonstrated differential responses to these factors. Moreover, compared to Canton-S, Harwich showed a reduced locomotor activity, larger amount of sleep, faster rate of development, smaller body weight, lower concentrations of main sugars, lower fecundity, and shorter lifespan. It might be recommended to use at least two strains, one with a relatively fast and another with a relatively slow aging process, for the experimental elaboration of relationships between genes, environment, behavior, physiology, and health. | Li, M., Shou, H., Martínez Corrales, G., Svermova, T., Franco, A. V., Alic, N. (2024). Xbp1 targets canonical UPR(ER) and non-canonical pathways in separate tissues to promote longevity. iScience, 27(6):109962 PubMed ID: 38832022
Summary: Transcription factors can reprogram gene expression to promote longevity. Here, we investigate the role of Drosophila Xbp1. Xbp1 is activated by splicing of its primary transcript, Xbp1(u), to generate Xbp1(s), a key activator of the endoplasmic reticulum unfolded protein response (UPR(ER)). Xbp1(s) induces the conical UPR(ER) in the gut, promoting longevity from the resident stem cells. In contrast, in the fat body, Xbp1(s) does not appear to trigger UPR(ER) but alters metabolic gene expression and is still able to extend lifespan. In the fat body, Xbp1(s) and dFOXO impinge on the same target genes, including the PGC-1α orthologue Srl, and dfoxo requires Xbp1 to extend lifespan. Interestingly, unspliceable version of the Xbp1 mRNA, Xbp1(u) can also extend lifespan, hinting at roles in longevity for the poorly characterized Xbp1(u) transcription factor. These findings reveal the diverse functions of Xbp1 in longevity in the fruit fly. |
Thursday, March 13th - Evolution |
| Barerra, T. S., Sattolo, M. L., Kwok, K. E., Agrawal, A. F., Rundle, H. D. (2024). Mating environments mediate the evolution of behavioral isolation during ecological speciation. Evolution letters, 8(3):448-454 PubMed ID: 38818417
Summary: The evolution of behavioral isolation is often the first step toward speciation. While past studies show that behavioral isolation will sometimes evolve as a by-product of divergent ecological selection, a more nuanced understanding of factors that may promote or hamper its evolution is lacking. The environment in which mating occurs may be important in mediating whether behavioral isolation evolves for two reasons. Ecological speciation could occur as a direct outcome of different sexual interactions being favored in different mating environments. Alternatively, mating environments may vary in the constraint they impose on traits underlying mating interactions, such that populations evolving in a "constraining" mating environment would be less likely to evolve behavioral isolation than populations evolving in a less constraining mating environment. In the latter, mating environment is not the direct cause of behavioral isolation but rather permits its evolution only if other drivers are present. These ideas were tested with a set of 28 experimental fly populations, each of which evolved under one of two mating environments and one of two larval environments. Counter to the prediction of ecological speciation by mating environment, behavioral isolation was not maximal between populations evolved in different mating environments. Nonetheless, mating environment was an important factor as behavioral isolation evolved among populations from one mating environment but not among populations from the other. Though one mating environment was conducive to the evolution of behavioral isolation, it was not sufficient: assortative mating only evolved between populations adapting to different-larval environments within that mating environment, indicating a role for ecological speciation. Intriguingly, the mating environment that promoted behavioral isolation is characterized by less sexual conflict compared to the other mating environment. These results suggest that mating environments play a key role in mediating ecological speciation via other axes of divergent selection. | Whittle, C. A., Extavour, C. G. (2024). Gene Protein Sequence Evolution Can Predict the Rapid Divergence of Ovariole Numbers in the Drosophila melanogaster Subgroup. Genome biology and evolution, 16(7) PubMed ID: 38848313
Summary: Ovaries play key roles in fitness and evolution: they are essential female reproductive structures that develop and house the eggs in sexually reproducing animals. In Drosophila, the mature ovary contains multiple tubular egg-producing structures known as ovarioles. Ovarioles arise from somatic cellular structures in the larval ovary called terminal filaments (TFs), formed by TF cells and subsequently enclosed by sheath (SH) cells. As in many other insects, ovariole number per female varies extensively in Drosophila. At present, however, there is a striking gap of information on genetic mechanisms and evolutionary forces that shape the well-documented rapid interspecies divergence of ovariole numbers. To address this gap, genes associated with Drosophila melanogaster ovariole number were studied for functions based on recent experimental and transcriptional datasets from larval ovaries, including TFs and SH cells, and their rates and patterns of molecular evolution were assessed in five closely related species of the melanogaster subgroup that exhibit species-specific differences in ovariole numbers. From comprehensive analyses of protein sequence evolution (dN/dS), branch-site positive selection, expression specificity (tau), and phylogenetic regressions (phylogenetic generalized least squares), evidence is reported of 42 genes that showed signs of playing roles in the genetic basis of interspecies evolutionary change of Drosophila ovariole number. These included the signaling genes upd2 and Ilp5 and extracellular matrix genes vkg and Col4a1, whose dN/dS predicted ovariole numbers among species. Together, we propose a model whereby a set of ovariole-involved gene proteins have an enhanced evolvability, including adaptive evolution, facilitating rapid shifts in ovariole number among Drosophila species. |
| Hsu, S. K., Lai, W. Y., Novak, J., Lehner, F., Jaksic, A. M., Versace, E., Schlotterer, C. (2024). Reproductive isolation arises during laboratory adaptation to a novel hot environment. Genome Biol, 25(1):141 PubMed ID: 38807159
Summary: Reproductive isolation can result from adaptive processes (e.g., ecological speciation and mutation-order speciation) or stochastic processes such as "system drift" model. Ecological speciation predicts barriers to gene flow between populations from different environments, but not among replicate populations from the same environment. In contrast, reproductive isolation among populations independently adapted to the same/similar environment can arise from both mutation-order speciation or system drift. In experimentally evolved populations adapting to a hot environment for over 100 generations, this study found evidence for pre- and postmating reproductive isolation. On one hand, an altered lipid metabolism and cuticular hydrocarbon composition pointed to possible premating barriers between the ancestral and replicate evolved populations. On the other hand, the pronounced gene expression differences in male reproductive genes may underlie the postmating isolation among replicate evolved populations adapting to the same environment with the same standing genetic variation. This study confirms that replicated evolution experiments provide valuable insights into the mechanisms of speciation. The rapid emergence of the premating reproductive isolation during temperature adaptation showcases incipient ecological speciation. The potential evidence of postmating reproductive isolation among replicates gave rise to two hypotheses: (1) mutation-order speciation through a common selection on early fecundity leading to an inherent inter-locus sexual conflict; (2) system drift with genetic drift along the neutral ridges. | Ribeiro, T. D. S., Lollar, M. J., Sprengelmeyer, Q. D., Huang, Y., Benson, D. M., Orr, M. S., Johnson, Z. C., Corbett-Detig, R. B., Pool, J. E. (2024). Recombinant inbred line panels inform the genetic architecture and interactions of adaptive traits in Drosophila melanogaster. bioRxiv, PubMed ID: 38798433
Summary: The distribution of allelic effects on traits, along with their gene-by-gene and gene-by-environment interactions, contributes to the phenotypes available for selection and the trajectories of adaptive variants. Nonetheless, uncertainty persists regarding the effect sizes underlying adaptations and the importance of genetic interactions. Herein, we aimed to investigate the genetic architecture and the epistatic and environmental interactions involving loci that contribute to multiple adaptive traits using two new panels of Drosophila melanogaster recombinant inbred lines (RILs). To better fit these data, functions from R/qtl were reimplemented using additive genetic models. We found 14 quantitative trait loci (QTL) underlying melanism, wing size, song pattern, and ethanol resistance. By combining our mapping results with population genetic statistics, potential new genes were identified related to these traits. None of the detected QTLs showed clear evidence of epistasis, and the power analysis indicated that at least one significant interaction was seen if sign epistasis or strong positive epistasis played a pervasive role in trait evolution. In contrast, roles for gene-by-environment interactions were found involving pigmentation traits. Overall, the data suggest that the genetic architecture of adaptive traits often involves alleles of detectable effect, that strong epistasis does not always play a role in adaptation, and that environmental interactions can modulate the effect size of adaptive alleles. |
| Bladen, J., Nam, H. J., Phadnis, N. (2024). Transformation of meiotic drive into hybrid sterility in Drosophila. bioRxiv, PubMed ID: 38798315
Summary: Hybrid male sterility is one of the fastest evolving intrinsic reproductive barriers between recently isolated populations. A leading explanation for the evolution of hybrid male sterility involves genomic conflicts with meiotic drivers in the male germline. There are, however, few examples directly linking meiotic drive to hybrid sterility. This study reports that the Sex-Ratio chromosome of Drosophila pseudoobscura, which causes X-chromosome drive within the USA subspecies, causes near complete male sterility when moved into the genetic background of the Bogota subspecies. In addition, this new form of sterility is genetically distinct from the sterility of F1 hybrid males in crosses between USA males and Bogota females. Our observations provide a tractable study system where non-cryptic drive within species is transformed into strong hybrid sterility between very young subspecies. | Li, X. C., Gandara, L., Ekelof, M., Richter, K., Alexandrov, T., Crocker, J. (2024). Rapid response of fly populations to gene dosage across development and generations. Nat Commun, 15(1):4551 PubMed ID: 38811562
Summary: Although the effects of genetic and environmental perturbations on multicellular organisms are rarely restricted to single phenotypic layers, current understanding of how developmental programs react to these challenges remains limited. This study has examined the phenotypic consequences of disturbing the bicoid. regulatory network in early Dwrosophila embryos. Flies with two extra copies of bicoid, which causes a posterior shift of the network's regulatory outputs and a decrease in fitness. These flies were subjected to EMS mutagenesis, followed by experimental evolution. After only 8-15 generations, experimental populations have normalized patterns of gene expression and increased survival. Using a phenomics approach, this study found that populations were normalized through rapid increases in embryo size driven by maternal changes in metabolism and ovariole development. The results were extended to additional populations of flies, demonstrating predictability. Together, these w=== results necessitate a broader view of regulatory network evolution at the systems level. |
Tuesday, March 11th - Adult Neural Development, Structure and Development |
| Kim, H., Zhong, Z., Cui, X., Sung, H., Agrawal, N., Jiang, T., Dus, M., Yapici, N. (2024). HisCl1 regulates gustatory habituation in sweet taste neurons and mediates sugar ingestion in Drosophila. bioRxiv, PubMed ID: 38765964
Summary: Similar to other animals, the fly, Drosophila melanogaster, reduces its responsiveness to tastants with repeated exposure, a phenomenon called gustatory habituation. Previous studies have focused on the circuit basis of gustatory habituation in the fly chemosensory system. However, gustatory neurons reduce their firing rate during repeated stimulation, suggesting that cell-autonomous mechanisms also contribute to habituation. This study used deep learning-based pose estimation and optogenetic stimulation to demonstrate that continuous activation of sweet taste neurons causes gustatory habituation in flies. A transgenic RNAi screen was conducted to identify genes involved in this process, and knocking down Histamine-gated chloride channel subunit 1 (HisCl1) in the sweet taste neurons was found to significantly reduced gustatory habituation. Anatomical analysis showed that HisCl1 is expressed in the sweet taste neurons of various chemosensory organs. Using single sensilla electrophysiology, this study showed that sweet taste neurons reduced their firing rate with prolonged exposure to sucrose. Knocking down HisCl1 in sweet taste neurons suppressed gustatory habituation by reducing the spike frequency adaptation observed in these neurons during high-concentration sucrose stimulation. Finally, flies lacking HisCl1 in sweet taste neurons were shown to increase their consumption of high-concentration sucrose solution at their first meal bout compared to control flies. Together, these results demonstrate that HisCl1 tunes spike frequency adaptation in sweet taste neurons and contributes to gustatory habituation and food intake regulation in flies. Since HisCl1 is highly conserved across many dipteran and hymenopteran species, these findings open a new direction in studying insect gustatory habituation. | Long, T., Mohapatra, P., Ballou, S., Menuz, K. (2024). Odorant receptor co-receptors affect expression of tuning receptors in Drosophila. Frontiers in cellular neuroscience, 18:1390557 PubMed ID: 38832356
Summary: Insects detect odorants using two large families of heteromeric receptors, the xOdorant Receptors (ORs) and Ionotropic Receptors (IRs). Most OR and IR genes encode odorant-binding "tuning" subunits, whereas four (Orco, Ir8a, Ir25a, andIr76b) encode co-receptor subunits required for receptor function. This study examined the role of co-receptors on olfactory neuron survival in Drosophila. Consistent with olfactory neuron degeneration, expression of many OR-family tuning receptors is decreased in Orco mutants relative to controls, and transcript loss is progressive with age. The effects of Orco are highly receptor-dependent, with expression of some receptor transcripts nearly eliminated and others unaffected. Surprisingly, further studies revealed that olfactory neuron classes with reduced tuning receptor expression generally survive in Orco mutant flies. Furthermore, there is little apoptosis or neuronal loss in the antenna of these flies. Yhe effects of IR family co-receptor mutants was investigated using similar approaches, and expression of IR tuning receptors was found to decrease in the absence of Ir8a and Ir25a, but not Ir76b. As in Orco mutants, Ir8a-dependent olfactory neurons mostly endure despite near-absent expression of associated tuning receptors. Finally, differential expression analysis was used to identify other antennal genes whose expression is changed in IR and OR co-receptor mutants. Taken together, these data indicate that odorant co-receptors are necessary for maintaining expression of many tuning receptors at the mRNA level. Further, most Drosophila olfactory neurons persist in OR and IR co-receptor mutants, suggesting that the impact of co-receptors on neuronal survival may vary across insect species. |
| Medeiros, A. M., Hobbiss, A. F., Borges, G., Moita, M., Mendes, C. S. (2024). Mechanosensory bristles mediate avoidance behavior by triggering sustained local motor activity in Drosophila melanogaster. Curr Biol, 34(13):2812-2830.e2815 PubMed ID: 38861987
Summary: During locomotion, most vertebrates-and invertebrates such as Drosophila melanogaster-are able to quickly adapt to terrain irregularities or avoid physical threats by integrating sensory information along with motor commands. Key to this adaptability are leg mechanosensory structures, which assist in motor coordination by transmitting external cues and proprioceptive information to motor centers in the central nervous system. Nevertheless, how different mechanosensory structures engage these locomotor centers remains poorly understood. This study tested the role of mechanosensory structures in movement initiation by optogenetically stimulating specific classes of leg sensory structures. timulation of leg mechanosensory bristles (MsBs) and the femoral chordotonal organ (ChO) is sufficient to initiate forward movement in immobile animals. While the stimulation of the ChO required brain centers to induce forward movement, unexpectedly, brief stimulation of leg MsBs triggered a fast response and sustained motor activity dependent only on the ventral nerve cord (VNC). Moreover, this leg-MsB-mediated movement lacked inter- and intra-leg coordination but preserved antagonistic muscle activity within joints. Finally, leg-MsB activation was shown to mediate strong avoidance behavior away from the stimulus source, which is preserved even in the absence of a central brain. Overall, these data show that mechanosensory stimulation can elicit a fast motor response, independently of central brain commands, to evade potentially harmful stimuli. In addition, it sheds light on how specific sensory circuits modulate motor control, including initiation of movement, allowing a better understanding of how different levels of coordination are controlled by the VNC and central brain locomotor circuits. | Schnaitmann, C., Pagni, M., Meyer, P. B., Steinhoff, L., Oberhauser, V., Reiff, D. F. (2024). Horizontal-cell like Dm9 neurons in Drosophila modulate photoreceptor output to supply multiple functions in early visual processing. Frontiers in molecular neuroscience, 17:1347540 PubMed ID: 38813436
Summary: Dm9 neurons in the Drosophila optic lobe have been proposed as functional homologs of horizontal cells in the outer retina of vertebrates. This study combined genetic dissection of neuronal circuit function, two-photon calcium imaging in Dm9 and inner photoreceptors, and immunohistochemical analysis to reveal novel insights into the functional role of Dm9 in early visual processing. These experiments show that Dm9 receive input from all four types of inner photoreceptors R7p, R7y, R8p, and R8y. Histamine released from all types R7/R8 directly inhibits Dm9 via the histamine receptor Ort, and outweighs simultaneous histamine-independent excitation of Dm9 by UV-sensitive R7. Dm9 in turn provides inhibitory feedback to all R7/R8, which is sufficient for color-opponent processing in R7 but not R8. Color opponent processing in R8 requires additional synaptic inhibition by R7 of the same ommatidium via axo-axonal synapses and the second Drosophila histamine receptor HisCl1. Notably, optogenetic inhibition of Dm9 prohibits color opponent processing in all types of R7/R8 and decreases intracellular calcium in photoreceptor terminals. The latter likely results from reduced release of excitatory glutamate from Dm9 and shifts overall photoreceptor sensitivity toward higher light intensities. In summary, these results underscore a key role of Dm9 in color opponent processing in Drosophila and suggest a second role of Dm9 in regulating light adaptation in inner photoreceptors. These novel findings on Dm9 are indeed reminiscent of the versatile functions of horizontal cells in the vertebrate retina. |
| Vilimelis Aceituno, P., Dall'Osto, D., Pisokas, I. (2024). Theoretical principles explain the structure of the insect head direction circuit. Elife, 13 PubMed ID: 38814703
Summary: To navigate their environment, insects need to keep track of their orientation. Previous work has shown that insects encode their head direction as a sinusoidal activity pattern around a ring of neurons arranged in an eight-column structure. However, it is unclear whether this sinusoidal encoding of head direction is just an evolutionary coincidence or if it offers a particular functional advantage. To address this question, the basic mathematical requirements were established for direction encoding and it was shown to be performed by many circuits, all with different activity patterns. Among these activity patterns, this study proved that the sinusoidal one is the most noise-resilient, but only when coupled with a sinusoidal connectivity pattern between the encoding neurons. This predicted optimal connectivity pattern was compared with anatomical data from the head direction circuits of the locust and the fruit fly, finding that the theory agrees with experimental evidence. Furthermore, the predicted circuit was shown to emerge using Hebbian plasticity, implying that the neural connectivity does not need to be explicitly encoded in the genetic program of the insect but rather can emerge during development. Finally, in this theory, the consistent presence of the eight-column organisation of head direction circuits across multiple insect species is not a chance artefact but instead can be explained by basic evolutionary principles. | Brown, M., Sciascia, E., Ning, K., Adam, W., Veraksa, A. (2024). Regulation of brain development by the Minibrain/Rala signaling network. bioRxiv, PubMed ID: 38766038
Summary: The human dual specificity tyrosine phosphorylation regulated kinase 1A (DYRK1A) is implicated in the pathology of Down syndrome, microcephaly, and cancer, however the exact mechanism through which it functions is unknown. The role was studied of the Drosophila ortholog of DYRK1A, Minibrain (Mnb), in brain development. The neuroblasts (neural stem cells) that eventually give rise to differentiated neurons in the adult brain are formed from a specialized tissue in the larval optic lobe called the neuroepithelium, in a tightly regulated process. Molecular marker analysis of mnb mutants revealed alterations in the neuroepithelium and neuroblast regions of developing larval brains. Using affinity purification-mass spectrometry (AP-MS), the novel Mnb binding partners Ral interacting protein (Rlip) and RALBP1 associated Eps domain containing (Reps) were identified. Rlip and Reps physically and genetically interact with Mnb, and the three proteins may form a ternary complex. Mnb phosphorylates Reps, and human DYRK1A binds to the Reps orthologs REPS1 and REPS2. Furthermore, Mnb engages the small GTPase Ras-like protein A (Rala) to regulate brain and wing development. This work uncovers a previously unrecognized early role of Mnb in the neuroepithelium and defines the functions of the Mnb/Reps/Rlip/Rala signaling network in brain development. |
Monday, March 10th - Chromatin |
| Salzler, H. R., Vandadi, V., Matera, A. G. (2024). Set2 and H3K36 regulate the Drosophila male X chromosome in a context-specific manner, independent from MSL complex spreading. bioRxiv, PubMed ID: 38766267
Summary: Dosage compensation in Drosophila involves upregulating male X-genes two-fold. This process is carried out by the MSL (male-specific lethal) complex, which binds high-affinity sites and spreads to surrounding genes. Current models of MSL spreading focus on interactions of MSL3 (male-specific lethal 3) with histone marks; in particular, Set2-dependent H3 lysine-36 trimethylation (H3K36me3). However, Set2 might affect DC via another target, or there could be redundancy between canonical H3.2 and variant H3.3 histones. Further, it is difficult to parse male-specific effects from those that are simply X-specific. To discriminate among these possibilities, we employed genomic approaches in H3K36 (residue) and Set2 (writer) mutants. The results confirm a role for Set2 in X-gene regulation, but show that expression trends in males are often mirrored in females. Instead of global male-specific reduction of X-genes in Set2/H3K36 mutants, the effects were heterogeneous. Cohorts of genes were identified whose expression was significantly altered following loss of H3K36 or Set2, but the changes were in opposite directions, suggesting that H3K36me states have reciprocal functions. In contrast to H4(K16R) controls, analysis of combined H3.2(K36R)/H3.3(K36R) mutants neither showed consistent reduction in X-gene expression, nor any correlation with MSL3 binding. Examination of other developmental stages/tissues revealed additional layers of context-dependence. These studies implicate BEAF-32 and other insulator proteins in Set2/H3K36-dependent regulation. Overall, the data are inconsistent with the prevailing model wherein H3K36me3 directly recruits the MSL complex. It is proposed that Set2 and H3K36 support DC indirectly, via processes that are utilized by MSL but common to both sexes. | Snir, O., Elgart, M., Gnainsky, Y., Goldsmith, M., Ciabrelli, F., Dagan, S., Aviezer, I., Stoops, E., Cavalli, G., Soen, Y. (2024). Organ transformation by environmental disruption of protein integrity and epigenetic memory in Drosophila. PLoS Biol, 22(5):e3002629 PubMed ID: 38805504
Summary: Despite significant progress in understanding epigenetic reprogramming of cells, the mechanistic basis of "organ reprogramming" by (epi-)gene-environment interactions remained largely obscure. This study used the ether-induced haltere-to-wing transformations in Drosophila as a model for epigenetic "reprogramming" at the whole organism level. The findings support a mechanistic chain of events explaining why and how brief embryonic exposure to ether leads to haltere-to-wing transformations manifested at the larval stage and on. Ether interferes with protein integrity in the egg, leading to altered deployment of Hsp90 and widespread repression of Trithorax-mediated establishment of active H3K4me3 chromatin marks throughout the genome. Despite this global reduction, Ubx targets and wing development genes preferentially retain higher levels of H3K4me3 that predispose these genes for later up-regulation in the larval haltere disc, hence the wing-like outcome. Consistent with compromised protein integrity during the exposure, the penetrance of bithorax transformations increases by genetic or chemical reduction of Hsp90 function. Moreover, joint reduction in Hsp90 and trx gene dosage can cause bithorax transformations without exposure to ether, supporting an underlying epistasis between Hsp90 and trx loss-of-functions. These findings implicate environmental disruption of protein integrity at the onset of histone methylation with altered epigenetic regulation of developmental patterning genes. The emerging picture provides a unique example wherein the alleviation of the Hsp90 "capacitor function" by the environment drives a morphogenetic shift towards an ancestral-like body plan. The morphogenetic impact of chaperone response during a major setup of epigenetic patterns may be a general scheme for organ transformation by environmental cues. |
| Vorobyeva, N. E., Krasnov, A. N., Erokhin, M., Chetverina, D., Mazina, M. (2024). Su(Hw) interacts with Combgap to establish long-range chromatin contacts. Epigenetics & chromatin, 17(1):17 PubMed ID: 38773468
Summary: Insulator-binding proteins (IBPs) play a critical role in genome architecture by forming and maintaining contact domains. While the involvement of several IBPs in organising chromatin architecture in Drosophila has been described, the specific contribution of the Suppressor of Hairy wings (Su(Hw)) insulator-binding protein to genome topology remains unclear. This study provides evidence for the existence of long-range interactions between chromatin bound Su(Hw) and Combgap, which was first characterised as Polycomb response elements binding protein. Loss of Su(Hw) binding to chromatin results in the disappearance of Su(Hw)-Combgap long-range interactions and in a decrease in spatial self-interactions among a subset of Su(Hw)-bound genome sites. These findings suggest that Su(Hw)-Combgap long-range interactions are associated with active chromatin rather than Polycomb-directed repression. Furthermore, the majority of transcription start sites that are down-regulated upon loss of Su(Hw) binding to chromatin were observed to be located within 2 kb of Combgap peaks and exhibit Su(Hw)-dependent changes in Combgap and transcriptional regulators' binding. This study demonstrates that Su(Hw) insulator binding protein can form long-range interactions with Combgap, Polycomb response elements binding protein, and that these interactions are associated with active chromatin factors rather than with Polycomb dependent repression. | Sokolov, V., Kyrchanova, O., Klimenko, N., Fedotova, A., Ibragimov, A., Maksimenko, O., Georgiev, P. (2024). New Drosophila promoter-associated architectural protein Mzfp1 interacts with CP190 and is required for housekeeping gene expression and insulator activity. Nucleic Acids Res, 52(12):6886-6905 PubMed ID: 38769058
Summary: In Drosophila, a group of zinc finger architectural proteins recruits the CP190 protein to the chromatin, an interaction that is essential for the functional activity of promoters and insulators. This study describes a new architectural C2H2 protein called Madf and Zinc-Finger Protein 1 (Mzfp1) that interacts with CP190. Mzfp1 has an unusual structure that includes six C2H2 domains organized in a C-terminal cluster and two tandem MADF domains. Mzfp1 predominantly binds to housekeeping gene promoters located in both euchromatin and heterochromatin genome regions. In vivo mutagenesis studies showed that Mzfp1 is an essential protein, and both MADF domains and the CP190 interaction region are required for its functional activity. The C2H2 cluster is sufficient for the specific binding of Mzfp1 to regulatory elements, while the second MADF domain is required for Mzfp1 recruitment to heterochromatin. Mzfp1 binds to the proximal part of the Fub boundary that separates regulatory domains of the Ubx and abd-A genes in the Bithorax complex. Mzfp1 participates in Fub functions in cooperation with the architectural proteins Pita and Su(Hw). Thus, Mzfp1 is a new architectural C2H2 protein involved in the organization of active promoters and insulators in Drosophila. |
| Willnow, P., Teleman, A. A. (2024). Nuclear position and local acetyl-CoA production regulate chromatin state. Nature, 630(8016):466-474 PubMed ID: 38839952
Summary: Histone acetylation regulates gene expression, cell function and cell fate. The pattern of histone acetylation was studied in the epithelial tissue of the Drosophila wing disc. H3K18ac, H4K8ac and total lysine acetylation are increased in the outer rim of the disc. This acetylation pattern is controlled by nuclear position, whereby nuclei continuously move from apical to basal locations within the epithelium and exhibit high levels of H3K18ac when they are in proximity to the tissue surface. These surface nuclei have increased levels of acetyl-CoA synthase, which generates the acetyl-CoA for histone acetylation. The carbon source for histone acetylation in the rim is fatty acid β-oxidation, which is also increased in the rim. Inhibition of fatty acid β-oxidation causes H3K18ac levels to decrease in the genomic proximity of genes involved in disc development. In summary, there is a physical mark of the outer rim of the wing and other imaginal epithelia in Drosophila that affects gene expression. | 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. |
Saturday, March 9th - Cell Cycle |
| Haseeb, M. A., Bernys, A. C., Dickert, E. E., Bickel, S. E. (2024). An RNAi screen to identify proteins required for cohesion rejuvenation during meiotic prophase in Drosophila oocytes. G3 (Bethesda), 14(8) PubMed ID: 38849129
Summary: Accurate chromosome segregation during meiosis requires the maintenance of sister chromatid cohesion, initially established during premeiotic S phase. In human oocytes, DNA replication and cohesion establishment occur decades before chromosome segregation and deterioration of meiotic cohesion is one factor that leads to increased segregation errors as women age. Previous work has led to a proposal that a cohesion rejuvenation program operates to establish new cohesive linkages during meiotic prophase in Drosophila oocytes and depends on the cohesin loader Nipped-B and the cohesion establishment factor Eco. In support of this model, recent work has demonstrated that chromosome-associated cohesin turns over extensively during meiotic prophase and failure to load cohesin onto chromosomes after premeiotic S phase results in arm cohesion defects in Drosophila oocytes. To identify proteins required for prophase cohesion rejuvenation but not S phase establishment, a Gal4-UAS inducible RNAi screen was conducted that utilized two distinct germline drivers. Using this strategy, 29 gene products were identifed for which hairpin expression during meiotic prophase, but not premeiotic S phase, significantly increased segregation errors. Prophase knockdown of Brahma or Pumilio, two positives with functional links to the cohesin loader, caused a significant elevation in the missegregation of recombinant homologs, a phenotype consistent with premature loss of arm cohesion. Moreover, fluorescence in situ hybridization confirmed that Brahma, Pumilio, and Nipped-B are required during meiotic prophase for the maintenance of arm cohesion. These data support the model that Brahma and Pumilio regulate Nipped-B-dependent cohesin loading during rejuvenation. Future analyses will better define the mechanism(s) that govern meiotic cohesion rejuvenation and whether additional prophase-specific positives function in this process. | Vicars, H., Karg, T., Mills, A., Sullivan, W. (2024). Acentric chromosome congression and alignment on the metaphase plate via kinetochore-independent forces in Drosophila.. bioRxiv, PubMed ID: 38798431
Summary: Chromosome congression and alignment on the metaphase plate involves lateral and microtubule plus-end interactions with the kinetochore. Here we take advantage of our ability to efficiently generate a GFP-marked acentric X chromosome fragment in Drosophila neuroblasts to identify forces acting on chromosome arms that drive congression and alignment. We find acentrics efficiently align on the metaphase plate, often more rapidly than kinetochore-bearing chromosomes. Unlike intact chromosomes, the paired sister acentrics oscillate as they move to and reside on the metaphase plate in a plane distinct and significantly further from the main mass of intact chromosomes. Consequently, at anaphase onset acentrics are oriented either parallel or perpendicular to the spindle. Parallel-oriented sisters separate by sliding while those oriented perpendicularly separate via unzipping. This oscillation, together with the fact that in monopolar spindles acentrics are rapidly shunted away from the poles, indicates that distributed plus-end directed forces are primarily responsible for acentric migration. This conclusion is supported by the observation that reduction of EB1 preferentially disrupts acentric alignment. In addition, reduction of http://Klp3a activity, a gene required for the establishment of pole-to-pole microtubules, preferentially disrupts acentric alignment. Taken together these studies suggest that plus-end forces mediated by the outer pole-to-pole microtubules are primarily responsible for acentric metaphase alignment. Surprisingly, this study found that a small fraction of sister acentrics are anti-parallel aligned indicating that the kinetochore is required to ensure parallel alignment of sister chromatids. Finally, induction of acentric chromosome fragments was found to result in a global reorganization of the congressed chromosomes into a torus configuration. |
| Marshall, W. F., Fung, J. C. (2024). Modeling homologous chromosome recognition via nonspecific interactions. Proc Natl Acad Sci U S A, 121(20):e2317373121 PubMed ID: 38722810
Summary: In many organisms, most notably Drosophila, homologous chromosomes associate in somatic cells, a phenomenon known as somatic pairing, which takes place without double strand breaks or strand invasion, thus requiring some other mechanism for homologs to recognize each other. Several studies have suggested a "specific button" model, in which a series of distinct regions in the genome, known as buttons, can associate with each other, mediated by different proteins that bind to these different regions. This study used computational modeling to evaluate an alternative "button barcode" model, in which there is only one type of recognition site or adhesion button, present in many copies in the genome, each of which can associate with any of the others with equal affinity. In this model, buttons are nonuniformly distributed, such that alignment of a chromosome with its correct homolog, compared with a nonhomolog, is energetically favored; since to achieve nonhomologous alignment, chromosomes would be required to mechanically deform in order to bring their buttons into mutual register. By simulating randomly generated nonuniform button distributions, many highly effective button barcodes can be easily found, some of which achieve virtually perfect pairing fidelity. This model is consistent with existing literature on the effect of translocations of different sizes on homolog pairing. It is conclude that a button barcode model can attain highly specific homolog recognition, comparable to that seen in actual cells undergoing somatic homolog pairing, without the need for specific interactions. This model may have implications for how meiotic pairing is achieved. | Hughes, S. E., Price, A., Briggs, S., Staber, C., James, M., Anderson, M., Hawley, R. S. (2024). A transcriptomics-based RNAi screen for regulators of meiosis and early stages of oocyte development in Drosophila melanogaster.G3 (Bethesda), 14(4) PubMed ID: 38333961
Summary: A properly regulated series of developmental and meiotic events must occur to ensure the successful production of gametes. In Drosophila melanogaster ovaries, these early developmental and meiotic events include the production of the 16-cell cyst, meiotic entry, synaptonemal complex (SC) formation, recombination, and oocyte specification. In order to identify additional genes involved in early oocyte development and meiosis, 3 published single-cell RNA-seq datasets from Drosophila ovaries were analyzed, using vasa (germline) together with c(3)G, cona, and corolla (SC) as markers. This analysis generated a 526 available RNAi lines containing shRNA constructs were in germline-compatible vectors representing 331 of the top 500 genes.Targeted ovaries were assessed for SC formation and maintenance, oocyte specification, cyst development, and double-strand break dynamics. Six uncharacterized genes exhibited early developmental defects. SC and developmental defects were observed for additional genes not well characterized in the early ovary. Interestingly, in some lines with developmental delays, meiotic events could still be completed once oocyte specificity occurred indicating plasticity in meiotic timing. These data indicate that a transcriptomics approach can be used to identify genes involved in functions in a specific cell type in the Drosophila ovary. |
| Vasavan, B., Das, N., Kahnamouei, P., Trombley, C., Swan, A. (2024). Skp2-Cyclin A Interaction Is Necessary for Mitotic Entry and Maintenance of Diploidy. J Mol Biol, 436(8):168505 PubMed ID: 38423454
Summary: Skp2, the substrate recognition component of the SCF(Skp2) ubiquitin ligase, has been implicated in the targeted destruction of a number of key cell cycle regulators and the promotion of S-phase. One of its critical targets is the Cyclin dependent kinase (Cdk) inhibitor p27 (Drosophila Dacapo), and indeed the overexpression of Skp2 in a number of cancers is directly correlated with the premature degradation of p27. Skp2 was first identified as a protein that interacts with Cyclin A in transformed cells, but its role in this complex has remained unclear. This paper demonstrates that Skp2 interacts with Cyclin A in Drosophila and is required to maintain Cyclin A levels and permit mitotic entry. Failure of mitotic entry in Skp2 mutant cells results in polyploidy. If these cells enter mitosis again they are unable to properly segregate their chromosomes, leading to checkpoint dependent cell cycle arrest or apoptosis. Thus, Skp2 is required for mitosis and for maintaining diploidy and genome stability. | Huang, Y. T., Hesting, L. L., Calvi, B. R. (2024). An unscheduled switch to endocycles induces a reversible senescent arrest that impairs growth of the Drosophila wing disc bioRxiv, PubMed ID: 38559130
Summary: A programmed developmental switch to G / S endocycles results in tissue growth through an increase in cell size. Unscheduled, induced endocycling cells (iECs) promote wound healing but also contribute to cancer. Much remains unknown, however, about how these iECs affect tissue growth. Using the D. melanogaster wing disc as model, this study found that populations of iECs initially increase in size but then subsequently undergo a heterogenous arrest that causes severe tissue undergrowth. iECs acquired DNA damage and activated a Jun N-terminal kinase (JNK) pathway, but, unlike other stressed cells, were apoptosis-resistant and not eliminated from the epithelium. Instead, iECs entered a JNK-dependent and reversible senescent-like arrest. Senescent iECs promoted division of diploid neighbors, but this compensatory proliferation did not rescue tissue growth. This study has uncovered unique attributes of iECs and their effects on tissue growth that have important implications for understanding their roles in wound healing and cancer. |
Thursday, March 6th - Disease Models |
| Polet, S. S., de Koning, T. J., Lambrechts, R. A., Tijssen, M. A. J., Sibon, O. C. M., Gorter, J. A. (2024). Conventional and novel anti-seizure medications reveal a particular role for GABA(A) in a North Sea progressive myoclonus Epilepsy Drosophila model. Epilepsy research, 203:107380 PubMed ID: 38781737
Summary: North Sea Progressive Myoclonus Epilepsy (NS-PME) is a rare genetic disorder characterized by ataxia, myoclonus and seizures with a progressive course. Although the cause of NS-PME is known, namely a homozygous mutation in the GOSR2 gene (c.430 G>T; p. Gly144Trp), sufficient treatment is lacking. Despite combinations of on average 3-5 anti-seizure medications (ASMs), debilitating myoclonus and seizures persist. This study aimed to gain insight into the most effective anti-convulsive target in NS-PME by evaluating the individual effects of ASMs in a NS-PME Drosophila model. A previously generated Drosophila model for NS-PME was used displaying progressive heat-sensitive seizures. This model was used to test 1. a first-generation ASM (sodium barbital), 2. common ASMs used in NS-PME (clonazepam, valproic acid, levetiracetam, ethosuximide) and 3. a novel third-generation ASM (ganaxolone) with similar mode of action to sodium barbital. Compounds were administered by adding them to the food in a range of concentrations. After 7 days of treatment, the percentage of heat-induced seizures was determined and compared to non-treated but affected controls. As previously reported in the NS-PME Drosophila model, sodium barbital resulted in significant seizure suppression, with increasing effect at higher dosages. Of the commonly prescribed ASMs, clonazepam and ethosuximide resulted in significant seizure suppression, whereas both valproic acid and levetiracetam did not show any changes in seizures. Interestingly, ganaxolone did result in seizure suppression as well. Of the six drugs tested, three of the four that resulted in seizure suppression (sodium barbital, clonazepam, ganaxolone) are primary known for their direct effect on GABA(A) receptors. This suggests that GABA(A) could be a potentially important target in the treatment of NS-PME. Consequently, these findings add rationale to the exploration of the clinical effect of ganaxolone in NS-PME and other progressive myoclonus epilepsies. | Dubey, P. K., Singh, S., Khalil, H., Kommini, G. K., Bhat, K. M., Krishnamurthy, P. (2024). Obg-like ATPase 1 Genetic Deletion Leads to Dilated Cardiomyopathy in Mice and Structural Changes in Drosophila Heart. bioRxiv, PubMed ID: 38854005
Summary: Cardiomyopathy, disease of the heart muscle, is a significant contributor to heart failure. The pathogenesis of cardiomyopathy is multifactorial and involves genetic, environmental, and lifestyle factors. Identifying and characterizing novel genes that contribute to cardiac pathophysiology are crucial for understanding cardiomyopathy and effective therapies. This study investigated the role of a novel gene, Obg-like ATPase 1 ( Ola1 ), in cardiac pathophysiology using a cardiac-specific knockout mouse model as well as a Drosophila model (see CG1354). Previous work demonstrated that OLA1 modulates the hypertrophic response of cardiomyocytes through the GSK-beta/beta-catenin signaling pathway. Furthermore, recent studies have suggested that OLA1 plays a critical role in organismal growth and development. For example, Ola1 null mice exhibit increased heart size and growth retardation. It is not known, however, if loss of function for Ola1 leads to dilated cardiomyopathy. Cardiac-specific Ola1 knockout mice (OLA1-cKO) were generated to evaluate the role of OLA1 in cardiac pathophysiology. Ola1-cKO in mice leads to dilated cardiomyopathy (DCM) and left ventricular (LV) dysfunction. These mice developed severe LV dilatation, thinning of the LV wall, reduced LV function, and, in some cases, ventricular wall rupture and death. In Drosophila, RNAi-mediated knock-down specifically in developing heart cells led to the change in the structure of pericardial cells from round to elongated, and abnormal heart function. This also caused significant growth reduction and pupal lethality. Thus, these findings suggest that OLA1 is critical for cardiac homeostasis and that its deficiency leads to dilated cardiomyopathy and dysfunction. Furthermore, this study highlights the potential of the Ola1 gene as a therapeutic target for dilated cardiomyopathy and heart failure. |
| Lewis, S. A., Forstrom, J., Tavani, J., Schafer, R., Tiede, Z., Padilla-Lopez, S. R., Kruer, M. C. (2024). eIF2alpha phosphorylation evokes dystonia-like movements with D2-receptor and cholinergic origin and abnormal neuronal connectivity. bioRxiv, PubMed ID: 38798458
Summary: Dystonia is the 3(rd) most common movement disorder. Dystonia is acquired through either injury or genetic mutations, with poorly understood molecular and cellular mechanisms. Eukaryotic initiation factor alpha (eIF2α) controls cell state including neuronal plasticity via protein translation control and expression of ATF4. Dysregulated eIF2α phosphorylation (eIF2α-P) occurs in dystonia patients and models including DYT1 (Drosophila Torsin), but the consequences are unknown. This study increased/decreased eIF2α-P and tested motor control and neuronal properties in a Drosophila model. Bidirectionally altering eIF2α-P produced dystonia-like abnormal posturing and dyskinetic movements in flies. These movements were also observed with expression of the DYT1 risk allele. Cholinergic and D2-receptor neuroanatomical origins were identified of these dyskinetic movements caused by genetic manipulations to dystonia molecular candidates eIF2α-P, ATF4, or DYT1, with evidence for decreased cholinergic release. In vivo, increased and decreased eIF2α-P increase synaptic connectivity at the NMJ with increased terminal size and bouton synaptic release sites. Long-term treatment of elevated eIF2α-P with ISRIB restored adult longevity, but not performance in a motor assay. Disrupted eIF2α-P signaling may alter neuronal connectivity, change synaptic release, and drive motor circuit changes in dystonia. | Yuan, Y., Yu, L., Zhuang, X., Wen, D., He, J., Hong, J., Xie, J., Ling, S., Du, X., Chen, W., Wang, X. (2025). Drosophila models used to simulate human ATP1A1 gene mutations that cause Charcot-Marie-Tooth type 2 disease and refractory seizures. Neural Regen Res, 20(1):265-276 PubMed ID: 38767491
Summary: Certain amino acids changes in the human Na+/K+-ATPase pump, ATPase Na+/K+ transporting subunit alpha 1 (ATP1A1), cause Charcot-Marie-Tooth disease type 2 (CMT2) disease and refractory seizures. To develop in vivo models to study the role of Na+/K+-ATPase in these diseases, the Drosophila gene homolog, Atpα, was modified to mimic the human ATP1A1 gene mutations that cause CMT2. Mutations located within the helical linker region of human ATP1A1 (I592T, A597T, P600T, and D601F) were simultaneously introduced into endogenous Drosophila Atpα by CRISPR/Cas9-mediated genome editing, generating the AtpαTTTF model. In addition, the same strategy was used to generate the corresponding single point mutations in flies (AtpαI571T, AtpαA576T, AtpαP579T, and AtpαD580F). Moreover, a deletion mutation (Atpαmut) that causes premature termination of translation was generated as a positive control. Of these alleles, two were found that could be maintained as homozygotes (AtpαI571T and AtpαP579T). Three alleles (AtpαA576T, AtpαP579 and AtpαD580F) can form heterozygotes with the Atpαmut allele. The Atpα allele carrying these CMT2-associated mutations showed differential phenotypes in Drosophila. Flies heterozygous for AtpαTTTF mutations have motor performance defects, a reduced lifespan, seizures, and an abnormal neuronal morphology. These Drosophila models will provide a new platform for studying the function and regulation of the sodium-potassium pump. |
| Sodders, M. J., Avila-Pacheco, J., Okorie, E. C., Shen, M., Kumari, N., Marathi, A., Lakhani, M., Bullock, K., Pierce, K., Dennis, C., Jeanfavre, S., Sarkar, S., Scherzer, C. R., Clish, C., Olsen, A. L. (2024). Genetic screening and metabolomics identify glial adenosine metabolism as a therapeutic target in Parkinson's disease. bioRxiv, PubMed ID: 38798570
Summary: Parkinson's disease (PD) is the second most common neurodegenerative disorder and lacks disease-modifying therapies. A Drosophila model has been developed for identifying novel glial-based therapeutic targets for PD. Human alpha-synuclein is expressed in neurons and individual genes are independently knocked down in glia. A forward genetic screen was conducted, knocking down the entire Drosophila kinome in glia in alpha-synuclein expressing flies. Among the top hits were five genes (9Ak1, (Ak6, Adk1, Adk2, and awd) involved in adenosine metabolism. Knockdown of each gene improved locomotor dysfunction, rescued neurodegeneration, and increased brain adenosine levels. It was determined that the mechanism of neuroprotection involves adenosine itself, as opposed to a downstream metabolite. Deeper undersrtanding was obtained into the mechanism for one gene, Ak1, finding rescue of dopaminergic neuron loss, alpha-synuclein aggregation, and bioenergetic dysfunction after glial Ak1 knockdown. Metabolomics was performed in Drosophila and in human PD patients, allowing comprehensive characterization of changes in purine metabolism and potential biomarkers of dysfunctional adenosine metabolism were identified in people. These experiments support glial adenosine as a novel therapeutic target in PD. | Chauvin, S. D., Ando, S., Holley, J. A., ..., Onodera, O., Kato, T., Miner, J. J. (2024). Inherited C-terminal TREX1 variants disrupt homology-directed repair to cause senescence and DNA damage phenotypes in Drosophila, mice, and humans. Nat Commun, 15(1):4696 PubMed ID: 38824133
Summary: Age-related microangiopathy, also known as small vessel disease (SVD), causes damage to the brain, retina, liver, and kidney. Based on the DNA damage theory of aging, it was reasoned that genomic instability may underlie an SVD caused by dominant C-terminal variants in TREX1, the most abundant 3'-5' DNA exonuclease in mammals. C-terminal TREX1 variants cause an adult-onset SVD known as retinal vasculopathy with cerebral leukoencephalopathy (RVCL or RVCL-S). In RVCL, an aberrant, C-terminally truncated TREX1 mislocalizes to the nucleus due to deletion of its ER-anchoring domain. Since RVCL pathology mimics that of radiation injury, it was reasoned that nuclear TREX1 would cause DNA damage. This study shows that RVCL-associated TREX1 variants trigger DNA damage in humans, mice, and Drosophila, and that cells expressing RVCL mutant TREX1 are more vulnerable to DNA damage induced by chemotherapy and cytokines that up-regulate TREX1, leading to depletion of TREX1-high cells in RVCL mice. RVCL-associated TREX1 mutants inhibit homology-directed repair (HDR), causing DNA deletions and vulnerablility to PARP inhibitors. In women with RVCL, early-onset breast cancer was observed, similar to patients with BRCA1/2 variants. These results provide a mechanistic basis linking aberrant TREX1 activity to the DNA damage theory of aging, premature senescence, and microvascular disease. |
Wednesday, March 5th - Adult physiology and metabolism |
| Wilkin, M. B., Whiteford, R., Akbar, T., Hosseini-Alghaderi, S., Revici, R., Carbery, A. M., Baron, M. (2024). The First Defined Null Allele of the Notch Regulator, a Suppressor of Deltex: Uncovering Its Novel Roles in Drosophila melanogaster Oogenesis. Biomolecules, 14(5) PubMed ID: 38785929
Summary: Suppressor of deltex (Su(dx)) is a Drosophila melanogaster member of the NEDD4 family of the HECT domain E3 ubiquitin ligases. Su(dx) acts as a regulator of Notch endocytic trafficking, promoting Notch lysosomal degradation and the down-regulation of both ligand-dependent and ligand-independent signalling, the latter involving trafficking through the endocytic pathway and activation of the endo/lysosomal membrane. Mutations of Su(dx) result in developmental phenotypes in the Drosophila wing that reflect increased Notch signalling, leading to gaps in the specification of the wing veins, and Su(dx) functions to provide the developmental robustness of Notch activity to environmental temperature shifts. The full developmental functions of Su(dx) are unclear; however, this is due to a lack of a clearly defined null allele. This study reports the first defined null mutation of Su(dx), generated by P-element excision, which removes the complete open reading frame. The mutation is recessive-viable, with the Notch gain of function phenotypes affecting wing vein and leg development. New roles were uncovered for Su(dx) in Drosophila oogenesis, where it regulates interfollicular stalk formation, egg chamber separation and germline cyst enwrapment by the follicle stem cells. Interestingly, while the null allele exhibited a gain in Notch activity during oogenesis, the previously described Su(dx)(SP) allele, which carries a seven amino acid in-frame deletion, displayed a Notch loss of function phenotypes and an increase in follicle stem cell turnover. This is despite both alleles displaying similar Notch gain of function in wing development. This unexpected context-dependent outcome of Su(dx)(sp) is thought to being due to the partial retention of function by the intact C2 and WW domain regions of the protein. These results extend understanding of the developmental role of Su(dx) in the tissue renewal and homeostasis of the Drosophila ovary and illustrate the importance of examining an allelic series of mutations to fully understand developmental functions. | Hemba-Waduge, R. U., Liu, M., Li, X., Sun, J. L., Budslick, E. A., Bondos, S. E., Ji, J. Y. (2024). Metabolic control by the Bithorax Complex-Wnt signaling crosstalk in Drosophila. bioRxiv, PubMed ID: 38853890
Summary: Adipocytes distributed throughout the body play crucial roles in lipid metabolism and energy homeostasis. Regional differences among adipocytes influence normal function and disease susceptibility, but the mechanisms driving this regional heterogeneity remain poorly understood. This study reports a genetic crosstalk between the Bithorax Complex ( BX-C ) genes and Wnt/Wingless signaling that orchestrates regional differences among adipocytes in Drosophila larvae. Abdominal adipocytes, characterized by the exclusive expression of abdominal A ( abd-A )and Abdominal B ( Abd-B ), exhibit distinct features compared to thoracic adipocytes, with Wnt signaling further amplifying these disparities. Depletion of BX-C genes in adipocytes reduces fat accumulation, delays larval-pupal transition, and eventually leads to pupal lethality. Depleting Abd-A or Abd-B reduces Wnt target gene expression, thereby attenuating Wnt signaling-induced lipid mobilization. Conversely, Wnt signaling stimulated abd-A transcription, suggesting a feedforward loop that amplifies the interplay between Wnt signaling and BX-C in adipocytes. These findings elucidate how the crosstalk between cell-autonomous BX-C gene expression and Wnt signaling define unique metabolic behaviors in adipocytes in different anatomical regions of fat body, delineating larval adipose tissue domains. |
| Zhang, T., Zhou, Q., Jusic, N., Lu, W., Pignoni, F., Neal, S. J. (2024). Mitf, with Yki and STRIPAK-PP2A, is a key determinant of form and fate in the progenitor epithelium of the Drosophila eye. European journal of cell biology, 103(2):151421 PubMed ID: 38776620
Summary: The Microphthalmia-associated Transcription Factor (MITF) governs numerous cellular and developmental processes. In mice, it promotes specification and differentiation of the retinal pigmented epithelium (RPE), and in humans, some mutations in MITF induce congenital eye malformations. This study explored the function and regulation of Mitf in Drosophila eye development, and two roles were uncovered. Knockdown of Mitf results in retinal displacement (RDis), a phenotype associated with abnormal eye formation. Mitf functions in the peripodial epithelium (PE), a retinal support tissue akin to the RPE, to suppress RDis, via the effector Yorkie (Yki). Yki physically interacts with Mitf and can modify its transcriptional activity in vitro. Severe loss of Mitf, instead, results in the de-repression of retinogenesis in the PE, precluding its development. This activity of Mitf requires the protein phosphatase 2 A holoenzyme STRIPAK-PP2A, but not Yki; Mitf transcriptional activity is potentiated by STRIPAK-PP2A in vitro and in vivo. Knockdown of STRIPAK-PP2A results in cytoplasmic retention of Mitf in vivo and in its decreased stability in vitro, highlighting two potential mechanisms for the control of Mitf function by STRIPAK-PP2A. Thus, Mitf functions in a context-dependent manner as a key determinant of form and fate in the Drosophila eye progenitor epithelium. | Zhai, C., Wang, Y., Qi, S., Yang, M., Wu, S. (2024). Yki stability and activity are regulated by Ca(2+)-calpains axis in Drosophila. J Genet Genomics, PubMed ID: 38663479
Summary: Yorkie (Yki) is a key effector of the Hippo pathway that activates the expression of targets by associating with the transcription factor Scalloped. Various upstream signals, such as cell polarity and mechanical cues, control transcriptional programs by regulating Yki activity. Searching for Yki regulatory factors has far-reaching significance for studying the Hippo pathway in animal development and human diseases. This study identified Calpain-A (CalpA) and Calpain-B (CalpB), two calcium (Ca(2+))-dependent modulatory proteases of the calpain family, as critical regulators of Yki in Drosophila that interact with Yki, respectively. Ca(2+) induces Yki cleavage in a CalpA/CalpB-dependent manner, and the protease activity of CalpA/CalpB is pivotal for the cleavage. Furthermore, overexpression of CalpA or CalpB in Drosophila partially restores the large wing phenotype caused by Yki overexpression, and F98 of Yki is an important cleavage site by the Ca(2+)-calpains axis. This study uncovers a unique mechanism whereby the Ca(2+)-calpain axis modulates Yki activity through protein cleavage. |
| Nuga, O., Richardson, K., Patel, N. C., Wang, X., Pagala, V., Stephan, A., Peng, J., Demontis, F., Todi, S. V. (2024). Linear poly-ubiquitin remodels the proteome and influences hundreds of regulators in Drosophila. G3 (Bethesda), 14(11) PubMed ID: 39325835
Summary: Ubiquitin controls many cellular processes via its post-translational conjugation onto substrates. Its use is highly variable due to its ability to form poly-ubiquitin with various topologies. Among them, linear chains have emerged as important regulators of immune responses and protein degradation. Previous studies in Drosophila melanogaster found that expression of linear poly-ubiquitin that cannot be dismantled into single moieties leads to their own ubiquitination and degradation or, alternatively, to their conjugation onto proteins. However, it remains largely unknown which proteins are sensitive to linear poly-ubiquitin. To address this question, this study expanded the toolkit to modulate linear chains and conducted ultra-deep coverage proteomics from flies that express non-cleavable, linear chains comprising 2, 4, or 6 moieties. These chains were found to regulate shared and distinct cellular processes in Drosophila by impacting hundreds of proteins. Theseresults provide key insight into the proteome subsets and cellular pathways that are influenced by linear poly-ubiquitin with distinct lengths and suggest that the ubiquitin system is exceedingly pliable. | Terry, D., Schweibenz, C., Moberg, K. (2024). Local Ecdysone synthesis in a wounded epithelium sustains developmental delay and promotes regeneration in Drosophila. Development, 151(12) PubMed ID: 38775023
Summary: Regenerative ability often declines as animals mature past embryonic and juvenile stages, suggesting that regeneration requires redirection of growth pathways that promote developmental growth. Intriguingly, the Drosophila larval epithelia require the hormone ecdysone (Ec) for growth but require a drop in circulating Ec levels to regenerate. Examining Ec dynamics more closely, this study found that transcriptional activity of the Ec-receptor (EcR) drops in uninjured regions of wing discs, but simultaneously rises in cells around the injury-induced blastema. In parallel, blastema depletion of genes encoding Ec biosynthesis enzymes blocks EcR activity and impairs regeneration but has no effect on uninjured wings. Local Ec/EcR signaling was found to be required for injury-induced pupariation delay following injury and that key regeneration regulators upd3 and Ets21c respond to Ec levels. Collectively, these data indicate that injury induces a local source of Ec within the wing blastema that sustains a transcriptional signature necessary for developmental delay and tissue repair. |
Tuesday, March 4th - Spermatogenesis |
| Tian, S., Nguyen, H., Ye, Z., Rouskin, S., Thirumalai, D., Trcek, T. (2024). The Folding of Germ Granule mRNAs Controls Intermolecular Base Pairing in Germ Granules and Maintains Normal Fly Development. bioRxiv, PubMed ID: 38853845
Summary: Drosophila germ granules enrich mRNAs critical for fly development. Within germ granules, mRNAs form multi-transcript clusters marked by increased mRNA concentration, creating an elevated potential for intermolecular base pairing. However, the type and abundance of intermolecular base pairing in mRNA clusters is poorly characterized. Using single-molecule super-resolution microscopy, chemical probing for base accessibility, phase separation assays, and simulations, mRNAs were demonstrated t remain well-folded upon localization to germ granules. While most base pairing is intramolecular, mRNAs still display the ability for intermolecular base pairing, facilitating clustering without high sequence complementarity or significant melting of secondary structure. This base pairing among mRNAs is driven by scattered and discontinuous stretches of bases appearing on the surface of folded RNAs, providing multivalency to clustering but exhibits low probability for sustained interactions. Notably, engineered germ granule mRNAs with exposed GC-rich complementary sequences (CSs) presented within stable stem loops induce sustained base pairing in vitro and enhanced intermolecular interactions in vivo. However, the presence of these stem loops alone disrupts fly development, and the addition of GC-rich CSs exacerbates this phenotype. Although germ granule mRNAs contain numerous GC-rich CSs capable of stable intermolecular base pairing, they are primarily embedded by RNA folding. This study emphasizes the role of RNA folding in controlling the type and abundance of intermolecular base pairing, thereby preserving the functional integrity of mRNAs within the germ granules. | Chao, C. F., Pesch, Y. Y., Yu, H., Wang, C., Aristizabal, M. J., Huan, T., Tanentzapf, G., Rideout, E. (2024). An important role for triglyceride in regulating spermatogenesis. Elife, 12 PubMed ID: 38805376
Summary: Drosophila is a powerful model to study how lipids affect spermatogenesis. Yet, the contribution of neutral lipids, a major lipid group which resides in organelles called lipid droplets (LD), to sperm development is largely unknown. Emerging evidence suggests LD are present in the testis and that loss of neutral lipid- and LD-associated genes causes subfertility; however, key regulators of testis neutral lipids and LD remain unclear. This stuey shows LD are present in early-stage somatic and germline cells within the Drosophila testis. A role was identified for triglyceride lipase brummer (bmm) in regulating testis LD; whole-body loss of bmm leads to defects in sperm development. Importantly, these represent cell-autonomous roles for bmm in regulating testis LD and spermatogenesis. Because lipidomic analysis of bmm mutants revealed excess triglyceride accumulation, and spermatogenic defects in bmm mutants were rescued by genetically blocking triglyceride synthesis, these data suggest that bmm-mediated regulation of triglyceride influences sperm development. This identifies triglyceride as an important neutral lipid that contributes to Drosophila sperm development, and reveals a key role for bmm in regulating testis triglyceride levels during spermatogenesis. |
| Roach, T. V., Lenhart, K. F. (2024). Mating-induced Ecdysone in the testis disrupts soma-germline contacts and stem cell cytokinesis. Development, 151(11) PubMed ID: 38832826
Summary: Germline maintenance relies on adult stem cells to continually replenish lost gametes over a lifetime and respond to external cues altering the demands on the tissue. Mating worsens germline homeostasis over time, yet a negative impact on stem cell behavior has not been explored. Using extended live imaging of the Drosophila testis stem cell niche, short periods of mating in young males was found to disrupt cytokinesis in germline stem cells (GSCs). This defect leads to failure of abscission, preventing release of differentiating cells from the niche. GSC abscission failure is caused by increased Ecdysone hormone signaling induced upon mating, which leads to disrupted somatic encystment of the germline. Abscission failure is rescued by isolating males from females, but recurs with resumption of mating. Importantly, reiterative mating also leads to increased GSC loss, requiring increased restoration of stem cells via symmetric renewal and de-differentiation. Together, these results suggest a model whereby acute mating results in hormonal changes that negatively impact GSC cytokinesis but preserves the stem cell population. | He, L., Sun, F., Wu, Y., Li, Z., Fu, Y., Huang, Q., Li, J., Wang, Z., Cai, J., Feng, C., Deng, X., Gu, H., He, X., Yu, J., Sun, F. (2024). L(1)10Bb serves as a conservative determinant for soma-germline communications via cellular non-autonomous effects within the testicular stem cell niche. Molecular and cellular endocrinology, 591:112278 PubMed ID: 38795826
Summary: The testicular stem cell niche is the central regulator of spermatogenesis in Drosophila melanogaster. However, the underlying regulatory mechanisms arwe unclear. This study demonstrated the crucial role of lethal (1) 10Bb [l(1)10Bb] in regulating the testicular stem cell niche. Dysfunction of l(1)10Bb in early-stage cyst cells led to male fertility disorders and compromised cyst stem cell maintenance. Moreover, the dysfunction of l(1)10Bb in early-stage cyst cells exerted non-autonomous effects on germline stem cell differentiation, independently of hub signals. Notably, this study highlights the rescue of testicular defects through ectopic expression of L(1)10Bb and the human homologous protein BUD31 homolog (BUD31). In addition, l(1)10Bb dysfunction in early-stage cyst cells downregulated the expression of spliceosome subunits in the Sm and the precursor RNA processing complexes. Collectively, these findings established l(1)10Bb as a pivotal factor in the modulation of Drosophila soma-germline communications within the testicular stem cell niche. |
| Su, Q., Xu, B., Chen, X., Rokita, S. E. (2024). Misregulation of bromotyrosine compromises fertility in male Drosophila. Proc Natl Acad Sci U S A, 121(21):e2322501121 PubMed ID: 38748578
Summary: Biological regulation often depends on reversible reactions such as phosphorylation, acylation, methylation, and glycosylation, but rarely halogenation. A notable exception is the iodination and deiodination of thyroid hormones. This study reports detection of bromotyrosine and its subsequent debromination during Drosophila spermatogenesis. Bromotyrosine is not evident when Drosophila express a native flavin-dependent dehalogenase that is homologous to the enzyme responsible for iodide salvage from iodotyrosine in mammals. Deletion or suppression of the dehalogenase-encoding condet (cdt) gene in Drosophila allows bromotyrosine to accumulate with no detectable chloro- or iodotyrosine. The presence of bromotyrosine in the cdt mutant males disrupts sperm individualization and results in decreased fertility. Transgenic expression of the cdt gene in late-staged germ cells rescues this defect and enhances tolerance of male flies to bromotyrosine. These results are consistent with reversible halogenation affecting Drosophila spermatogenesis in a process that had previously eluded metabolomic, proteomic, and genomic analyses. | Shao, Z., Hu, J., Jandura, A., Wilk, R., Jachimowicz, M., Ma, L., Hu, C., Sundquist, A., Das, I., Samuel-Larbi, P., Brill, J. A., Krause, H. M. (2024). Spatially revealed roles for lncRNAs in Drosophila spermatogenesis, Y chromosome function and evolution. Nat Commun, 15(1):3806 PubMed ID: 38714658
Summary: Unlike coding genes, the number of lncRNA genes in organism genomes is relatively proportional to organism complexity. From plants to humans, the tissues with highest numbers and levels of lncRNA gene expression are the male reproductive organs. To learn why, a genome-wide analysis was initiated of Drosophila lncRNA spatial expression patterns in these tissues. The numbers of genes and levels of expression observed greatly exceed those previously reported, due largely to a preponderance of non-polyadenylated transcripts. In stark contrast to coding genes, the highest numbers of lncRNAs expressed are in post-meiotic spermatids. Correlations between expression levels, localization and previously performed genetic analyses indicate high levels of function and requirement. More focused analyses indicate that lncRNAs play major roles in evolution by controlling transposable element activities, Y chromosome gene expression and sperm construction. A new type of lncRNA-based particle found in seminal fluid may also contribute to reproductive outcomes. |
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