What's hot today:
Current papers in developmental biology and gene function


Sunday, April 30th, 2017

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Keais, G. L., Hanson, M. A., Gowen, B. E. and Perlman, S. J. (2017). X chromosome drive in a widespread Palearctic woodland fly, Drosophila testacea. J Evol Biol [Epub ahead of print]. PubMed ID: 28402000
Selfish genes that bias their own transmission during meiosis can spread rapidly in populations, even if they contribute negatively to the fitness of their host. Driving X chromosomes provide a clear example of this type of selfish propagation. These chromosomes have important evolutionary and ecological consequences, and can be found in a broad range of taxa including plants, mammals, and insects. This study reports a new case of X chromosome drive (X drive) in a widespread woodland fly, Drosophila testacea. Males carrying the driving X (SR males) sire 80-100% female offspring, and possess a diagnostic X chromosome haplotype that is perfectly associated with the sex ratio distortion phenotype. The majority of sons produced by SR males are sterile and appear to lack a Y chromosome, suggesting that meiotic defects involving the Y chromosome may underlie X drive in this species. Abnormalities in sperm cysts of SR males reflect that some spermatids are failing to develop properly, confirming that drive is acting during gametogenesis. By screening wild-caught flies using progeny sex ratios and a diagnostic marker, it was demonstrated that the driving X is present in wild populations at a frequency of ~10% and that suppressors of drive are segregating in the same population. The testacea species group appears to be a hotspot for X drive, and D. testacea is a promising model to compare driving X chromosomes in closely related species, some of which may even be younger than the chromosomes themselves.
Yang, B. and Wittkopp, P. J. (2017). Structure of the Transcriptional Regulatory Network Correlates with Regulatory Divergence in Drosophila. Mol Biol Evol [Epub ahead of print]. PubMed ID: 28333240
Transcriptional control of gene expression is regulated by biochemical interactions between cis-regulatory DNA sequences and trans-acting factors that form complex regulatory networks. Genetic changes affecting both cis- and trans-acting sequences in these networks have been shown to alter patterns of gene expression as well as higher-order organismal phenotypes. This study investigated how the structure of these regulatory networks relates to patterns of polymorphism and divergence in gene expression. To do this, a transcriptional regulatory network inferred for Drosophila melanogaster was compared to differences in gene regulation observed between two strains of D. melanogaster as well as between two pairs of closely related species: Drosophila sechellia and Drosophila simulans, and D. simulans and D. melanogaster. The number of transcription factors predicted to directly regulate a gene ("in-degree") was negatively correlated with divergence in both gene expression (mRNA abundance) and cis-regulation. This observation suggests that the number of transcription factors directly regulating a gene's expression affects the conservation of cis-regulation and gene expression over evolutionary time. The hypothesis that transcription factors regulating more target genes (higher "out-degree") are less likely to evolve changes in their cis-regulation and expression (presumably due to increased pleiotropy) was also tested, but little support was found for this predicted relationship. Taken together, these data show how the architecture of regulatory networks can influence regulatory evolution.
Simoes, P., Fragata, I., Seabra, S. G., Faria, G. S., Santos, M. A., Rose, M. R., Santos, M. and Matos, M. (2017).. Predictable phenotypic, but not karyotypic, evolution of populations with contrasting initial history. Sci Rep 7(1): 913. PubMed ID: 28424494
The relative impact of selection, chance and history will determine the predictability of evolution. There is a lack of empirical research on this subject, particularly in sexual organisms. This study used experimental evolution to test the predictability of evolution. The real-time evolution was analyzed of Drosophila subobscura populations derived from contrasting European latitudes placed in a novel laboratory environment. Each natural population was sampled twice within a three-year interval. Evolutionary responses at both phenotypic (life-history, morphological and physiological traits) and karyotypic levels were studied for around 30 generations of laboratory culture. The results show (1) repeatable historical effects between years in the initial state, at both phenotypic and karyotypic levels; (2) predictable phenotypic evolution with general convergence except for body size; and (3) unpredictable karyotypic evolution. It is concluded that the predictability of evolution is contingent on the trait and level of organization, highlighting the importance of studying multiple biological levels with respect to evolutionary patterns.
Shahrestani, P., Burke, M. K., Birse, R., Kezos, J. N., Ocorr, K., Mueller, L. D., Rose, M. R. and Bodmer, R. (2017). Experimental evolution and heart function in Drosophila. Physiol Biochem Zool 90(2): 281-293. PubMed ID: 28277957
Drosophila melanogaster is a good model species for the study of heart function. However, most previous work on D. melanogaster heart function has focused on the effects of large-effect genetic variants. This study compared heart function among 18 D. melanogaster populations that have been selected for altered development time, aging, or stress resistance. Populations with faster development and faster aging were found to have increased heart dysfunction, measured as percentage heart failure after electrical pacing. Experimental evolution of different triglyceride levels, by contrast, has little effect on heart function. Evolved differences in heart function correlate with allele frequency changes at many loci of small effect. Genomic analysis of these populations produces a list of candidate loci that might affect cardiac function at the intersection of development, aging, and metabolic control mechanisms.

Saturday, April 29th

Ferguson, G. B. and Martinez-Agosto, J. A. (2017). The TEAD family transcription factor Scalloped regulates blood progenitor maintenance and proliferation in Drosophila through PDGF/VEGFR receptor (Pvr) signaling. Dev Biol. PubMed ID: 28322737
The Drosophila lymph gland is a well-characterized hematopoietic organ in which a population of multipotent stem-like progenitors is maintained by a combination of signals from different cellular populations within the organ. This study demonstrates a requirement for the TEAD transcription factor Scalloped in the maintenance and proliferation of hematopoietic progenitors. A novel population of hemocytes in the early lymph gland was identified by the expression of Hand, Scalloped, and the PVR ligand PVF2. In this unique population, Scalloped maintains PVF2 expression, which is required for hemocyte proliferation and achievement of normal lymph gland size. STAT signaling was demonstrated to marks actively proliferating hemocytes in the early lymph gland, and inhibition of this pathway causes decreased lymph gland growth similar to loss of Scalloped and PVF2, demonstrating a requirement for PVR/STAT signaling in the regulation of lymph gland size. Finally, it was demonstrate that Scalloped regulates PVR expression and the maintenance of progenitors downstream of PVR/STAT/ADGF signaling. These findings further establish the role of the TEAD family transcription factors in the regulation of important signaling molecules, and expand mechanistic insight into the balance between progenitor maintenance and proliferation required for the regulation of lymph gland homeostasis.
Goodwin, K., Lostchuck, E. E., Cramb, K. M., Zulueta-Coarasa, T., Fernandez-Gonzalez, R. and Tanentzapf, G. (2017). Cell-cell and cell-ECM adhesions cooperate to organize actomyosin networks and maintain force transmission during dorsal closure. Mol Biol Cell [Epub ahead of print]. PubMed ID: 28331071
Tissue morphogenesis relies on the coordinated action of actin networks, cell-cell adhesions, and cell-ECM adhesions. Such coordination can be achieved through crosstalk between cell-cell and cell-ECM adhesions. Drosophila Dorsal Closure (DC), a morphogenetic process wherein an extra-embryonic tissue called the amnioserosa contracts and ingresses to close a discontinuity in the dorsal epidermis of the embryo, requires both cell-cell and cell-ECM adhesions. However, whether the function of these two types of adhesion is coordinated during DC is not known. This study analyzed possible interdependence between cell-cell and cell-ECM adhesions during DC, and its effect on the actomyosin network. Loss of cell-ECM adhesion was found to result in aberrant distributions of cadherin-mediated adhesions and actin networks in the amnioserosa; and subsequent disruption of myosin recruitment and dynamics. Moreover, loss of cell-cell adhesion caused an upregulation of cell-ECM adhesion, leading to reduced cell deformation and force transmission across amnioserosa cells. These results show how interdependence between cell-cell and cell-ECM adhesions is important in regulating cell behaviours, force generation and force transmission critical for tissue morphogenesis.
Goto, H., Kimmey, S. C., Row, R. H., Matus, D. Q. and Martin, B. L. (2017). FGF and canonical Wnt signaling cooperate to induce paraxial mesoderm from tailbud neuromesodermal progenitors through regulation of a two-step EMT. Development [Epub ahead of print]. PubMed ID: 28242612
Evolutionary Homolog Study
Mesoderm induction begins during gastrulation. Recent evidence from several vertebrate species indicates mesoderm induction continues after gastrulation in neuromesodermal progenitor cells (NMPs) within the posterior-most embryonic structure called the tailbud. It is unclear to what extent the molecular mechanisms of mesoderm induction are conserved between gastrula and post-gastrula stages of development. Fibroblast growth factor (FGF) signaling is required for mesoderm induction during gastrulation through positive transcriptional regulation of the t-box transcription factor brachyury (ntla in zebrafish and Byn in Drosophila). This study found that FGF is continuously required for paraxial mesoderm (PM) induction in zebrafish post-gastrula NMPs, but has the opposite effect on brachyury expression. FGF signaling represses brachyury and the NMP marker sox2 (see Drosophila SoxNeuro) through regulation of tbx16 and msgn1, thereby committing cells to a PM fate. FGF mediated PM induction in NMPs functions in tight coordination with canonical Wnt signaling during the epithelial to mesenchymal transition from NMP to mesodermal progenitor. Wnt signaling initiates the EMT, while FGF signaling terminates this event. These results indicate that germ layer induction in the tailbud is not a simple continuation of gastrulation events.
Huang, Y. S., Ku, H. Y., Tsai, Y. C., Chang, C. H., Pao, S. H., Sun, Y. H. and Chiou, A. (2017). 5D imaging via light sheet microscopy reveals cell dynamics during the eye-antenna disc primordium formation in Drosophila. Sci Rep 7: 44945. PubMed ID: 28322328
Although the eye-antenna disc primordium primordium (EADP) is thought to be derived from the visual primordium, which is defined by so expression, ey and so expressions do not overlap. Consistently, loss of so does not affect ey and toy expressions and the formation of the EADP. Other genes in the retinal determination network, namely, dachshund (dac) and eyes absent (eya), are not expressed in the EADP. These observations strongly suggest that the EADP formation is independent of the retinal determination network genes so, dac and eya. Its origin and the course of formation need further clarification. 5D images of engrailed (en) and eye gone (eyg) gene expressions during the course of the (EADP) formation of Drosophila embryos from embryonic stages 13 through 16 were recorded via light sheet microscopy and analyzed to reveal the cell dynamics involved in the development of the EADP. Detailed analysis of the time-lapsed images revealed the process of EADP formation and its invagination trajectory, which involved an inversion of the EADP anterior-posterior axis relative to the body. Furthermore, analysis of the en-expression pattern in the EADP provided strong evidence that the EADP is derived from one of the en-expressing head segments.

Friday, April 28th

Afik, S., Bartok, O., Artyomov, M. N., Shishkin, A. A., Kadri, S., Hanan, M., Zhu, X., Garber, M. and Kadener, S. (2017). Defining the 5' and 3' landscape of the Drosophila transcriptome with Exo-seq and RNaseH-seq. Nucleic Acids Res [Epub ahead of print]. PubMed ID: 28335028
Cells regulate biological responses in part through changes in transcription start sites (TSS) or cleavage and polyadenylation sites (PAS). To fully understand gene regulatory networks, it is therefore critical to accurately annotate cell type-specific TSS and PAS. This study presents a simple and straightforward approach for genome-wide annotation of 5'- and 3'-RNA ends. The approach reliably discerns bona fide PAS from false PAS that arise due to internal poly(A) tracts, a common problem with current PAS annotation methods. This methodology was appled to study the impact of temperature on the Drosophila melanogaster head transcriptome. Hundreds of previously unidentified TSS and PAS were found, revealing two interesting phenomena: first, genes with multiple PASs tend to harbor a motif near the most proximal PAS, which likely represents a new cleavage and polyadenylation signal. Second, motif analysis of promoters of genes affected by temperature suggested that boundary element association factor of 32 kDa (BEAF-32) and DREF mediates a transcriptional program at warm temperatures, a result that was validated in a fly line where beaf-32 is downregulated. These results demonstrate the utility of a high-throughput platform for complete experimental and computational analysis of mRNA-ends to improve gene annotation.
Zhu, J. Y., Heidersbach, A., Kathiriya, I. S., Garay, B. I., Ivey, K. N., Srivastava, D., Han, Z. and King, I. N. (2017). The E3 ubiquitin ligase Nedd4/Nedd4L is directly regulated by microRNA 1. Development 144(5): 866-875. PubMed ID: 28246214
miR-1 is a small noncoding RNA molecule that modulates gene expression in heart and skeletal muscle. Loss of Drosophila miR-1 produces defects in somatic muscle and embryonic heart development, which have been partly attributed to miR-1 directly targeting Delta to decrease Notch signaling. This study shows that overexpression of miR-1 in the fly wing can paradoxically increase Notch activity independently of its effects on Delta. Analyses of potential miR-1 targets revealed that miR-1 directly regulates the 3'UTR of the E3 ubiquitin ligase Nedd4. Analysis of embryonic and adult fly heart revealed that the Nedd4 protein regulates heart development in Drosophila. Larval fly hearts overexpressing miR-1 have profound defects in actin filament organization that are partially rescued by concurrent overexpression of Nedd4. These results indicate that miR-1 and Nedd4 act together in the formation and actin-dependent patterning of the fly heart. Importantly, it was found that the biochemical and genetic relationship between miR-1 and the mammalian ortholog Nedd4-like (Nedd4l) is evolutionarily conserved in the mammalian heart, potentially indicating a role for Nedd4L in mammalian postnatal maturation. Thus, miR-1-mediated regulation of Nedd4/Nedd4L expression may serve to broadly modulate the trafficking or degradation of Nedd4/Nedd4L substrates in the heart.
Skrajna, A., Yang, X. C., Bucholc, K., Zhang, J., Hall, T. M., Dadlez, M., Marzluff, W. F. and Dominski, Z. (2017). U7 snRNP is recruited to histone pre-mRNA in a FLASH-dependent manner by two separate regions of the Stem-Loop Binding Protein. RNA [Epub ahead of print]. PubMed ID: 28289156
Cleavage of histone pre-mRNAs at the 3' end requires Stem-Loop Binding Protein (SLBP) and U7 snRNP that consists of U7 snRNA and a unique Sm ring containing two U7-specific proteins: Lsm10 and Lsm11. Lsm11 interacts with FLASH and together they bring a subset of polyadenylation factors to U7 snRNP, including the CPSF73 endonuclease that cleaves histone pre-mRNA. SLBP binds to a conserved stem-loop structure upstream of the cleavage site and acts by promoting an interaction between the U7 snRNP and a sequence element located downstream of the cleavage site. This study shows that both human and Drosophila SLBPs stabilize U7 snRNP on histone pre-mRNA via two regions that are not directly involved in recognizing the stem-loop structure: helix B of the RNA Binding Domain and the C-terminal region that follows the RNA Binding Domain. Stabilization of U7 snRNP binding to histone pre-mRNA by SLBP requires FLASH but not the polyadenylation factors. Thus, FLASH plays two roles in 3' end processing of histone pre-mRNAs: it interacts with Lsm11 to form a docking platform for the polyadenylation factors and it co-operates with SLBP to recruit U7 snRNP to histone pre-mRNA.
Foo, L. C., Song, S. and Cohen, S. M. (2017). miR-31 mutants reveal continuous glial homeostasis in the adult Drosophila brain. Embo J [Epub ahead of print]. PubMed ID: 28320737
The study of adult neural cell production has concentrated on neurogenesis. The mechanisms controlling adult gliogenesis are still poorly understood. This study provides evidence for a homeostatic process that maintains the population of glial cells in the Drosophila adult brain. Flies lacking microRNA miR-31a start adult life with a normal complement of glia, but transiently lose glia due to apoptosis. miR-31a expression identifies a subset of predominantly gliogenic adult neural progenitor cells. Failure to limit expression of the predicted E3 ubiquitin ligase, Rchy1, in these cells results in glial loss. After an initial decline in young adults, glial numbers recovered due to compensatory overproduction of new glia by adult progenitor cells, indicating an unexpected plasticity of the Drosophila nervous system. Experimentally induced ablation of glia was also followed by recovery of glia over time. These studies provide evidence for a homeostatic mechanism that maintains the number of glia in the adult fly brain.

Thursday, April 27th

Arenz, A., Drews, M. S., Richter, F. G., Ammer, G. and Borst, A. (2017). The temporal tuning of the Drosophila motion detectors is determined by the dynamics of their input elements. Curr Biol 27(7): 929-944. PubMed ID: 28343964
Detecting the direction of motion contained in the visual scene is crucial for many behaviors. However, because single photoreceptors only signal local luminance changes, motion detection requires a comparison of signals from neighboring photoreceptors across time in downstream neuronal circuits. For signals to coincide on readout neurons that thus become motion and direction selective, different input lines need to be delayed with respect to each other. Classical models of motion detection rely on non-linear interactions between two inputs after different temporal filtering. However, recent studies have suggested the requirement for at least three, not only two, input signals. This study comprehensively characterized the spatiotemporal response properties of all columnar input elements to the elementary motion detectors in the fruit fly, T4 and T5 cells, via two-photon calcium imaging. Between these input neurons, large differences were found in temporal dynamics. Based on this, computer simulations show that only a small subset of possible arrangements of these input elements maps onto a recently proposed algorithmic three-input model in a way that generates a highly direction-selective motion detector, suggesting plausible network architectures. Moreover, modulating the motion detection system by octopamine-receptor activation, the temporal tuning of T4 and T5 cells was found to be shifted toward higher frequencies, and this shift can be fully explained by the concomitant speeding of the input elements.
Foldi, I., Anthoney, N., Harrison, N., Gangloff, M., Verstak, B., Nallasivan, M. P., AlAhmed, S., Zhu, B., Phizacklea, M., Losada-Perez, M., Moreira, M., Gay, N. J. and Hidalgo, A. (2017). Three-tier regulation of cell number plasticity by neurotrophins and Tolls in Drosophila. J Cell Biol [Epub ahead of print]. PubMed ID: 28373203
Cell number plasticity is coupled to circuitry in the nervous system, adjusting cell mass to functional requirements. In mammals, this is achieved by neurotrophin (NT) ligands, which promote cell survival via their Trk and p75NTR receptors and cell death via p75NTR and Sortilin. Drosophila NTs (DNTs; see NT1) bind Toll receptors (see Toll-6 & Toll-7) instead to promote neuronal survival, but whether they can also regulate cell death is unknown. This study show that DNTs and Tolls can switch from promoting cell survival to death in the central nervous system (CNS) via a three-tier mechanism. First, DNT cleavage patterns result in alternative signaling outcomes. Second, different Tolls can preferentially promote cell survival or death. Third, distinct adaptors downstream of Tolls can drive either apoptosis or cell survival. Toll-6 promotes cell survival via MyD88-NF-κB and cell death via Wek-Sarm-JNK. The distribution of adaptors changes in space and time and may segregate to distinct neural circuits. This novel mechanism for CNS cell plasticity may operate in wider contexts.
Farca Luna, A. J., Perier, M. and Seugnet, L. (2017). Amyloid precursor protein in Drosophila glia regulates sleep and genes Involved in glutamate recycling. J Neurosci 37(16): 4289-4300. PubMed ID: 28314820
Amyloid precursor protein (App) plays a crucial role in Alzheimer's disease via the production and deposition of toxic β-amyloid peptides. App is heavily expressed in neurons, the focus of the vast majority of studies investigating its function. Meanwhile, almost nothing is known about App's function in glia, where it is also expressed, and can potentially participate in the regulation of neuronal physiology. This report investigated whether Appl, the Drosophila homolog of App, could influence sleep-wake regulation when its function is manipulated in glial cells. Appl inhibition in astrocyte-like and cortex glia resulted in higher sleep amounts and longer sleep bout duration during the night, while overexpression had the opposite effect. These sleep phenotypes were not the result of developmental defects, and were correlated with changes in expression in glutamine synthetase (GS) in astrocyte-like glia and in changes in the gap-junction component innexin2 in cortex glia. Downregulating both GS and innexin2, but not either one individually, resulted in higher sleep amounts, similarly to Appl inhibition. Consistent with these results, the expression of GS and innexin2 are increased following sleep deprivation, indicating that GS and innexin2 genes are dynamically linked to vigilance states. Interestingly, the reduction of GS expression and the sleep phenotype observed upon Appl inhibition could be rescued by increasing the expression of the glutamate transporter dEaat1. In contrast, reducing dEaat1 expression severely disrupted sleep. These results associate glutamate recycling, sleep, and a glial function for the App family proteins.
Dolan, M. J., Luan, H., Shropshire, W. C., Sutcliffe, B., Cocanougher, B., Scott, R. L., Frechter, S., Zlatic, M., Jefferis, G. S. and White, B. H. (2017). Facilitating neuron-specific genetic manipulations in Drosophila using a split GAL4 repressor. Genetics [Epub ahead of print]. PubMed ID: 28363977
Efforts to map neural circuits have been galvanized by the development of genetic technologies that permit the manipulation of targeted sets of neurons in the brains of freely behaving animals. The success of these efforts relies on the experimenter's ability to target arbitrarily small subsets of neurons for manipulation, but such specificity of targeting cannot routinely be achieved using existing methods. In Drosophila melanogaster, a widely used technique for refined cell-type specific manipulation is the Split GAL4 system, which augments the targeting specificity of the binary GAL4-UAS system by making GAL4 transcriptional activity contingent upon two enhancers, rather than one. To permit more refined targeting, this study introduces the "Killer Zipper" (KZip+), a suppressor that makes Split GAL4 targeting contingent upon a third enhancer. KZip+ acts by disrupting both the formation and activity of Split GAL4 heterodimers; this added layer of control can be used to selectively remove unwanted cells from a Split GAL4 expression pattern or to subtract neurons of interest from a pattern to determine their requirement in generating a given phenotype. To facilitate application of the KZip+ technology, a versatile set of LexAop-KZip+ fly lines were developed that can be used directly with the large number of LexA driver lines with known expression patterns. The Killer Zipper significantly sharpens the precision of neuronal genetic control available in Drosophila and may be extended to other organisms where Split GAL4-like systems are used.

Wednesday, April 26th

M'Angale, P. G. and Staveley, B. E. (2017). Bax-inhibitor-1 knockdown phenotypes are suppressed by Buffy and exacerbate degeneration in a Drosophila model of Parkinson disease. PeerJ 5: e2974. PubMed ID: 28243526
Bax inhibitor-1 (BI-1) is an evolutionarily conserved cytoprotective transmembrane protein that acts as a suppressor of Bax-induced apoptosis by regulation of endoplasmic reticulum stress-induced cell death. BI-1 was knocked down in the sensitive dopa decarboxylase (Ddc) expressing neurons of Drosophila to investigate its neuroprotective functions. BI-1-induced phenotypes were rescied by co-expression with the pro-survival Buffy, and the effect of BI-1 knockdown on the neurodegenerative alpha-synuclein-induced Parkinson disease (PD) model was determined. Knockdown of BI-1 was achieved under the direction of the Ddc-Gal4 transgene and resulted in shortened lifespan and precocious loss of locomotor ability. Co-expression of Buffy with BI-1-RNAi resulted in suppression of the reduced lifespan and impaired climbing ability. Expression of human alpha-synuclein in Drosophila dopaminergic neurons results in neuronal degeneration, accompanied by the age-dependent loss in climbing ability. It is concluded that knockdown of BI-1 in the dopaminergic neurons of Drosophila results in a shortened lifespan and premature loss in climbing ability, phenotypes that appear to be strongly associated with models of PD in Drosophila, and which are suppressed upon overexpression of Buffy and worsened by co-expression with alpha-synuclein. This suggests that BI-1 is neuroprotective and its knockdown can be counteracted by the overexpression of the pro-survival Bcl-2 homologue.
Demir, E. and Marcos, R. (2017). Assessing the genotoxic effects of two lipid peroxidation products (4-oxo-2-nonenal and 4-hydroxy-hexenal) in haemocytes and midgut cells of Drosophila melanogaster larvae. Food Chem Toxicol 105: 1-7. PubMed ID: 28343031
Lipid peroxidation products can induce tissue damage and are implicated in diverse pathological conditions, including aging, atherosclerosis, brain disorders, cancer, lung and various liver disorders. Since in vivo studies produce relevant information, Drosophila melanogaster was selected as a suitable in vivo model to characterise the potential risks associated to two lipid peroxidation products namely 4-oxo-2-nonenal (4-ONE) and 4-hydroxy-hexenal (4-HHE). Toxicity, intracellular reactive oxygen species production, and genotoxicity were the end-points evaluated. Haemocytes and midgut cells were the evaluated targets. Results showed that both compounds penetrate the intestine of the larvae, affecting midgut cells, and reaching haemocytes. Significant genotoxic effects, as determined by the comet assay, were observed in both selected cell targets in a concentration/time dependent manner. This study highlights the importance of D. melanogaster as a model organism in the study of the different biological effects caused by lipid peroxidation products entering via ingestion. This is the first study reporting genotoxicity data in haemocytes and midgut cells of D. melanogaster larvae for the two selected compounds.
O'Connor, et al. (2017). A Drosophila model of Fragile X syndrome exhibits defects in phagocytosis by innate immune cells. J Cell Biol 216(3): 595-605. PubMed ID: 28223318
Fragile X syndrome, the most common known monogenic cause of autism, results from the loss of FMR1, a conserved, ubiquitously expressed RNA-binding protein. Recent evidence suggests that Fragile X syndrome and other types of autism are associated with immune system defects. This study found that Drosophila melanogaster Fmr1 mutants exhibit increased sensitivity to bacterial infection and decreased phagocytosis of bacteria by systemic immune cells. Using tissue-specific RNAi-mediated knockdown, Fmr1 was shown to play a cell-autonomous role in the phagocytosis of bacteria. Fmr1 mutants also exhibit delays in two processes that require phagocytosis by glial cells, the immune cells in the brain: neuronal clearance after injury in adults and the development of the mushroom body, a brain structure required for learning and memory. Delayed neuronal clearance is associated with reduced recruitment of activated glia to the site of injury. These results suggest a previously unrecognized role for Fmr1 in regulating the activation of phagocytic immune cells both in the body and the brain.
Pan, C., Wang, W., Yuan, H., Yang, L., Chen, B., Li, D. and Chen, J. (2017). The immediate early protein WSV187 can influence viral replication via regulation of JAK/STAT pathway in Drosophila. Dev Comp Immunol 72: 89-96. PubMed ID: 28232015
The world production of shrimp is seriously affected by the white spot syndrome virus (WSSV). Viral immediate-early (IE) genes encode regulatory proteins critical for the viral lifecycle. In spite of their importance, only five out of the 21 identified WSSV IE genes are functionally characterized. This paper reports the use of Drosophila melanogaster as a model to explore the role of WSSV IE gene wsv187. In vivo expression of WSV187 in transgenic flies show WSV187 localized in the cytoplasm. Overexpression of wsv187 results wing defects consistent with phenotypes observed in JAK/STAT exacerbated flies. After artificial infection of the DCV virus, the flies expressing wsv187 showed a lower viral load, a higher survival rate and an up-regulated STAT92E expression. These data demonstrate wsv187 plays a role in the controlling of virus replication by activating host JAK/STAT pathway.

Tuesday, April 25th

An, H., Ge, W., Xi, Y. and Yang, X. (2017). Inscuteable maintains type I neuroblast lineage identity via Numb/Notch signaling in the Drosophila larval brain. J Genet Genomics 44(3): 151-162. PubMed ID: 28325554
In the Drosophila larval brain, type I and type II neuroblasts (NBs) undergo a series of asymmetric divisions which give rise to distinct progeny lineages. The intermediate neural progenitors (INPs) exist only in type II NB lineages. This study reveals a novel function of Inscuteable (Insc) that acts to maintain type I NB lineage identity. In insc type I NB clones of mosaic analyses with a repressible cell marker (MARCM), the formation of extra Deadpan (Dpn)+ NB-like and GMC-like cells is observed. The lack of Insc leads to the defective localization and segregation of Numb during asymmetric cell division. By the end of cytokinesis, this results in insufficient Numb in ganglion mother cells (GMCs). The formation of extra Deadpan (Dpn)+ cells in insc clones is prevented by the attenuation of Notch activity. This suggests that Insc functions through the Numb/Notch signaling pathway. In the absence of Insc in type I NB lineages, the cellular identity of GMCs is altered where they adopt an INP-like cell fate as indicated by the initiation of Dpn expression accompanied by a transient presence of Earmuff (Erm). These INP-like cells have the capacity to divide multiple times. It is concluded that Insc is necessary for the maintenance of type I NB lineage identity. Genetic manipulations to eliminate most type I NBs with overproliferating type II NBs in the larval brain lead to altered circadian rhythms and defective phototaxis in adult flies. This indicates that the homeogenesis of NB lineages is important for the adult's brain function.
Zhang, Q., Zagozewski, J., Cheng, S., Dixit, R., Zhang, S., de Melo, J., Mu, X., Klein, W. H., Brown, N. L., Wigle, J. T., Schuurmans, C. and Eisenstat, D. D. (2017). Regulation of Brn3b by Dlx1 and Dlx2 is required for retinal ganglion cell differentiation in the vertebrate retina. Development. PubMed ID: 28356311
Evolutionary Homolog Study
Regulated retinal ganglion cell (RGC) differentiation and axonal guidance is required for a functional visual system. Homeodomain and basic helix loop helix transcription factors are required for retinogenesis, as well as patterning, differentiation and maintenance of specific retinal cell types. It was hypothesized that Dlx1/Dlx2 (see Drosophila Distalless) and Brn3b (see Drosophila Acj6) homeobox genes function in parallel intrinsic pathways to determine RGC fate, and Dlx1/Dlx2/Brn3b triple knockout mice were generated. A more severe retinal phenotype was found in the Dlx1/Dlx2/Brn3b null retinas than predicted by combining features of the Brn3b single and Dlx1/Dlx2 double knockout retinas, including near total RGC loss with a marked increase in amacrine cells in the ganglion cell layer. Furthermore, it was discovered that DLX1 and DLX2 function as direct transcriptional activators of Brn3b expression. Knockdown of Dlx2 expression in primary embryonic retinal cultures and Dlx2 gain-of-function in utero strongly support that DLX2 is both necessary and sufficient for Brn3b expression in vivo. It is suggested that Atoh7 (see Drosophila Atonal) specifies RGC committed progenitors and that Dlx1/Dlx2 functions both downstream of Atoh7 and in parallel but cooperative pathways involving regulation of Brn3b expression to determine RGC fate.
Xu, J., Hao, X., Yin, M. X., Lu, Y., Jin, Y., Xu, J., Ge, L., Wu, W., Ho, M., Yang, Y., Zhao, Y. and Zhang, L. (2017). Function of Nerfin-1 in preventing medulla neurons dedifferentiation requires its inhibition of Notch activity. Development [Epub ahead of print]. PubMed ID: 28242614
Drosophila larval central nervous system comprises the central brain, ventral nerve cord and optic lobe. In these regions, neuroblasts divide asymmetrically to self-renew and generate differentiated neurons or glia. To date, mechanisms of preventing neuron dedifferentiation are still unclear, especially in the optic lobe. This study shows that the zinc finger transcription factor Nerfin-1 is expressed in early stage of medulla neurons and essential for maintaining their differentiation. Loss of Nerfin-1 activates Notch signaling, which promotes neuron-to-NB reversion. Repressing Notch signaling largely rescues dedifferentiation in nerfin-1 mutant clones. Thus, it is concluded that Nerfin-1 represses Notch activity in medulla neurons and prevents them from dedifferentiation.
Cheung, S. K. and Scott, K. (2017). GABAA receptor-expressing neurons promote consumption in Drosophila melanogaster. PLoS One 12(3): e0175177. PubMed ID: 28362856
Feeding decisions are highly plastic and bidirectionally regulated by neurons that either promote or inhibit feeding. In Drosophila melanogaster, recent studies have identified four GABAergic interneurons that act as critical brakes to prevent incessant feeding. These GABAergic neurons may inhibit target neurons that drive consumption. This study tested this hypothesis by examining GABA receptors and neurons that promote consumption. Resistance to dieldrin (RDL), a GABAA type receptor, is required for proper control of ingestion. Knockdown of Rdl in a subset of neurons causes overconsumption of tastants. Acute activation of these neurons is sufficient to drive consumption of appetitive substances and non-appetitive substances and acute silencing of these neurons decreases consumption. Taken together, these studies identify GABAA receptor-expressing neurons that promote Drosophila ingestive behavior and provide insight into feeding regulation.

Monday, April 24th

Andreyeva, E. N., et al. (2017). Regulatory functions and chromatin loading dynamics of linker histone H1 during endoreplication in Drosophila. Genes Dev 31(6): 603-616. PubMed ID: 28404631
Eukaryotic DNA replicates asynchronously, with discrete genomic loci replicating during different stages of S phase. Drosophila larval tissues undergo endoreplication without cell division, and the latest replicating regions occasionally fail to complete endoreplication, resulting in underreplicated domains of polytene chromosomes. This study shows that linker histone H1 is required for the underreplication (UR) phenomenon in Drosophila salivary glands. H1 directly interacts with the Suppressor of UR (SUUR) protein and is required for SUUR binding to chromatin in vivo. These observations implicate H1 as a critical factor in the formation of underreplicated regions and an upstream effector of SUUR. It was also demonstrated that the localization of H1 in chromatin changes profoundly during the endocycle. At the onset of endocycle S (endo-S) phase, H1 is heavily and specifically loaded into late replicating genomic regions and is then redistributed during the course of endoreplication. The data suggest that cell cycle-dependent chromosome occupancy of H1 is governed by several independent processes. In addition to the ubiquitous replication-related disassembly and reassembly of chromatin, H1 is deposited into chromatin through a novel pathway that is replication-independent, rapid, and locus-specific. This cell cycle-directed dynamic localization of H1 in chromatin may play an important role in the regulation of DNA replication timing.
Grigorian, M., DeBruhl, H. and Lipsick, J. S. (2017). The role of variant histone H2AV in D. melanogaster larval hematopoiesis. Development [Epub ahead of print]. PubMed ID: 28242611
Replication-independent histone variants can replace the canonical replication-dependent histones. Vertebrates have multiple H2A variant histones, including H2AZ and H2AX that are present in most eukaryotes. H2AZ regulates transcriptional activation as well as maintenance of gene silencing, while H2AX is important in DNA damage repair. The fruit fly Drosophila melanogaster has only one histone H2A variant (H2AV), which is a chimera of H2AZ and H2AX. This study found that lack of H2AV led to the formation of black melanotic masses in the third instar larvae of Drosophila. The formation of these masses was found in conjunction with a loss of a majority of the primary lymph gland lobes. Interestingly, the cells of the posterior signaling center were preserved in these mutants. Reduction of H2AV levels by RNAi knockdown caused a milder phenotype that preserved the lymph gland structure, but that included precocious differentiation of the prohemocytes located within the medullary zone and secondary lobes of the lymph gland. Mutant rescue experiments suggest that the H2AZ-like rather than the H2AX-like function of H2AV is primarily required for normal hematopoiesis.
Erceg, J., Pakozdi, T., Marco-Ferreres, R., Ghavi-Helm, Y., Girardot, C., Bracken, A. P. and Furlong, E. E. (2017). Dual functionality of cis-regulatory elements as developmental enhancers and Polycomb response elements. Genes Dev 31(6): 590-602. PubMed ID: 28381411
Developmental gene expression is tightly regulated through enhancer elements, which initiate dynamic spatio-temporal expression, and Polycomb response elements (PREs), which maintain stable gene silencing. These two cis-regulatory functions are thought to operate through distinct dedicated elements. By examining the occupancy of the Drosophila pleiohomeotic repressive complex (PhoRC) during embryogenesis, extensive co-occupancy was revealed at developmental enhancers. Using an established in vivo assay for PRE activity, it was demonstrated that a subset of characterized developmental enhancers can function as PREs, silencing transcription in a Polycomb-dependent manner. Conversely, some classic Drosophila PREs can function as developmental enhancers in vivo, activating spatio-temporal expression. This study therefore uncovers elements with dual function: activating transcription in some cells (enhancers) while stably maintaining transcriptional silencing in others (PREs). Given that enhancers initiate spatio-temporal gene expression, reuse of the same elements by the Polycomb group (PcG) system may help fine-tune gene expression and ensure the timely maintenance of cell identities.
Fan, W., Lam, S. M., Xin, J., Yang, X., Liu, Z., Liu, Y., Wang, Y., Shui, G. and Huang, X. (2017). Drosophila TRF2 and TAF9 regulate lipid droplet size and phospholipid fatty acid composition. PLoS Genet 13(3): e1006664. PubMed ID: 28273089
The general transcription factor TBP (TATA-box binding protein) and its associated factors (TAFs) together form the TFIID complex, which directs transcription initiation. Through RNAi and mutant analysis, this study identified a specific TBP family protein, TRF2, and a set of TAFs that regulate lipid droplet (LD) size in the Drosophila larval fat body. Among the three Drosophila TBP genes, trf2, tbp and trf1, only loss of function of trf2 results in increased LD size. Moreover, TRF2 and TAF9 regulate fatty acid composition of several classes of phospholipids. Through RNA profiling, TRF2 and TAF9 were found to affect the transcription of a common set of genes, including peroxisomal fatty acid beta-oxidation-related genes that affect phospholipid fatty acid composition. Knockdown of several TRF2 and TAF9 target genes results in large LDs, a phenotype which is similar to that of trf2 mutants. Together, these findings provide new insights into the specific role of the general transcription machinery in lipid homeostasis.

Sunday, April 23rd

He, X., Yu, J., Wang, M., Cheng, Y., Han, Y., Yang, S., Shi, G., Sun, L., Fang, Y., Gong, S. T., Wang, Z., Fu, Y. X., Pan, L. and Tang, H. (2017). Bap180/Baf180 is required to maintain homeostasis of intestinal innate immune response in Drosophila and mice. Nat Microbiol 2: 17056. PubMed ID: 28418397
Immune homeostasis is a prerequisite to protective immunity against gastrointestinal infections. In Drosophila, immune deficiency (IMD) signalling (tumour necrosis factor receptor/interleukin-1 receptor, TNFR/IL-1R in mammals) is indispensable for intestinal immunity against invading bacteria. However, how this local antimicrobial immune response contributes to inflammatory regulation remains poorly defined. This study shows that flies lacking intestinal Bap180 (a subunit of the ]SWI/SNF complex) are susceptible to infection as a result of hyper-inflammation rather than bacterial overload. Detailed analysis shows that Bap180 is induced by the IMD-Relish response to both enteropathogenic and commensal bacteria. Upregulated Bap180 can feed back to restrain overreactive IMD signalling, as well as to repress the expression of the pro-inflammatory gene eiger (TNF), a critical step to prevent excessive tissue damage and elongate the lifespan of flies, under pathological and physiological conditions, respectively. Furthermore, intestinal targeting of Baf180 renders mice susceptible to a more aggressive infectious colitis caused by Citrobacter rodentium. Together, Bap180 and Baf180 serve as a conserved transcriptional repressor that is critical for the maintenance of innate immune homeostasis in the intestines.
Maki, K., Shibata, T. and Kawabata, S. I. (2017). Transglutaminase-catalyzed incorporation of polyamines masks the DNA-binding region of the transcription factor Relish. J Biol Chem [Epub ahead of print]. PubMed ID: 28258224
In Drosophila, the immune deficiency (IMD) pathway-dependent signal is finally transmitted through proteolytic conversion of the nuclear factor-κB-like transcription factor Relish to the active N-terminal fragment Relish-N to induce its translocation from the cytosol into the nucleus for the expression of IMD-controlled genes. Previous studies have demonstrated that transglutaminase (TG) suppresses the IMD pathway by polymerizing Relish-N to inhibit its nuclear translocation. A synthetic amine, such as monodansylcadaverine (DCA) or biotin-labeled pentylamine, ingested by flies is TG-dependently incorporated into Relish-N, causing the nuclear translocation of modified Relish-N in gut epithelial cells. DCA-incorporated Gln residues were located in the Rel homology domain, the DNA-binding region of Relish-N. TG-catalyzed DCA incorporation inhibits the binding of Relish-N to the Rel-responsive element of the κB sequence. TG localizes not only in the cytosol but also in the nucleus. Natural polyamines, including spermidine and spermine, competitively inhibited TG-dependent DCA incorporation into Relish-N. Relish-N is also modified by spermine, and the transcription of cecropin A1 and diptericin genes controlled by the IMD pathway is reduced. These findings suggest that intracellular TG regulates the transcriptional activity of Relish-N through the incorporation of polyamines into Relish-N as well as through protein-protein crosslinking of Relish-N.
Zhang, H., Dong, S., Chen, X., Stanley, D., Beerntsen, B., Feng, Q. and Song, Q. (2017). Relish2 mediates bursicon homodimer-induced prophylactic immunity in the mosquito Aedes aegypti. Sci Rep 7: 43163. PubMed ID: 28225068
Bursicon is a neuropeptide hormone consisting of two cystine-knot proteins (burs α and burs β), responsible for cuticle tanning and other developmental processes in insects. Recent studies show that each bursicon subunit forms homodimers that induce prophylactic immunity in Drosophila melanogaster. This study investigated the hypothesis that bursicon homodimers act in prophylactic immunity in insects, and possibly arthropods, generally, using the mosquito, Aedes aegypti. Burs α and burs β were found to be expressed in larvae, pupae and newly emerged adults. Treating newly emerged Ae. aegypti and D. melanogaster adults with recombinant bursicon (r-bursicon) heterodimer led to cuticle tanning in both species. Treating larvae and adults with r-bursicon homodimers led to up-regulation of five anti-microbial peptide (AMP) genes, noting the possibility that bursicon heterodimers also lead to up-regulation of these genes can not been excluded. The induced AMPs effectively suppressed the growth of bacteria in vitro. RNAi knock-down of the transcriptional factor Relish2 (see Drosophila Relish) abolished the influence of r-bursicon homodimers on AMP production. It is infered the bursicon homodimers induce expression of AMP genes via Relish2 in Ae. aegypti, as prophylactic immunity to protect mosquitoes during the vulnerable stages of each molt.
Chen, L., Paquette, N., Mamoor, S., Rus, F., Nandy, A., Leszyk, J., Shaffer, S. A. and Silverman, N. (2017). Innate immune signaling in Drosophila is regulated by TGFbeta-activated kinase (Tak1)-triggered ubiquitin editing. J Biol Chem [Epub ahead of print]. PubMed ID: 28377500
Coordinated regulation of innate immune responses is necessary in all metazoans. In Drosophila, the Imd pathway detects gram-negative bacterial infections through recognition of DAP-type peptidoglycan and activation of the NF-kappaB precursor Relish, which drives robust antimicrobial peptide (AMP) gene expression. Imd is a receptor-proximal adaptor protein homologous to mammalian RIP1 that is regulated by proteolytic cleavage and K63-polyubiquitination. However, the precise events and molecular mechanisms that control the post-translational modification of Imd remain unclear. This study demonstrates that Imd is rapidly K63-polyubiquitinated at lysine residues 137 and 153 by the sequential action of two E2 enzymes, Ubc5 (Effete) and Ubc13 (Bendless)-Uev1a, in conjunction with the E3 ligase Diap2. K63-ubiquitination activates the TGFβ-activated kinase (Tak1), which feeds back to phosphorylate Imd, triggering the removal of K63-chains and the addition of K48-polyubiquitin. This ubiquitin editing process results in the proteosomal degradation of Imd, which is proposed to function to restore homeostasis to the Drosophila immune response.

Saturday, April 22nd

Frenkel, L., Muraro, N. I., Beltran Gonzalez, A. N., Marcora, M. S., Bernabo, G., Hermann-Luibl, C., Romero, J. I., Helfrich-Forster, C., Castano, E. M., Marino-Busjle, C., Calvo, D. J. and Ceriani, M. F. (2017). Organization of circadian behavior relies on glycinergic transmission. Cell Rep 19(1): 72-85. PubMed ID: 28380364
The small ventral lateral neurons (sLNvs) constitute a central circadian pacemaker in the Drosophila brain. They organize daily locomotor activity, partly through the release of the neuropeptide pigment-dispersing factor (PDF), coordinating the action of the remaining clusters required for network synchronization. Despite extensive efforts, the basic principles underlying communication among circadian clusters remain obscure. This study identified classical neurotransmitters released by sLNvs through disruption of specific transporters. Adult-specific RNAi-mediated downregulation of the glycine transporter or impairment of glycine synthesis in LNv neurons increased period length by nearly an hour without affecting rhythmicity of locomotor activity. Electrophysiological recordings showed that glycine reduces spiking frequency in circadian neurons. Interestingly, downregulation of glycine receptor subunits in specific sLNv targets impaired rhythmicity, revealing involvement of glycine in information processing within the network. These data identify glycinergic inhibition of specific targets as a cue that contributes to the synchronization of the circadian network.
Denis, B., Claisse, G., Le Rouzic, A., Wicker-Thomas, C., Lepennetier, G. and Joly, D. (2017). Male accessory gland proteins affect differentially female sexual receptivity and remating in closely related Drosophila species. J Insect Physiol 99: 67-77. PubMed ID: 28342762
In sexual species, mating success depends on the male's capacity to find sexual partners and on female receptivity to mating. Mating is under evolutionary constraints to prevent interspecific mating and to maximize the reproductive success of both sexes. In Drosophila melanogaster, female receptivity to mating is mainly controlled by Sex peptide (SP, i.e. Acp70A) produced by the male accessory glands with other proteins (Acps). The transfer of SP during copulation dramatically reduces female receptivity to mating and prevents remating with other males. To date, female postmating responses are well-known in D. melanogaster but have been barely investigated in closely-related species or strains exhibiting different mating systems (monoandrous versus polyandrous). This study describes the diversity of mating systems in two strains of D. melanogaster and the three species of the yakuba complex. Remating delay and sexual receptivity were measured in cross-experiments following SP orthologs or Acp injections within females. Interestingly, strong differences were discovered between the two strains of D. melanogaster as well as among the three species of the yakuba complex. These results suggest that reproductive behavior is under the control of complex sexual interactions between the sexes and evolves rapidly, even among closely-related species.
Smith, D. T., Clarke, N. V., Boone, J. M., Fricke, C. and Chapman, T. (2017). Sexual conflict over remating interval is modulated by the sex peptide pathway. Proc Biol Sci 284(1850). PubMed ID: 28250180
Sexual conflict, in which the evolutionary interests of males and females diverge, shapes the evolution of reproductive systems across diverse taxa. This study used the fruit fly to study sexual conflict in natural, three-way interactions comprising a female, her current and previous mates. The potential for sexual conflict was manipulated by using sex peptide receptor (SPR) null females and by varying remating from 3 to 48 h, a period during which natural rematings frequently occur. SPR-lacking females do not respond to sex peptide (SP) transferred during mating and maintain virgin levels of high receptivity and low fecundity. In the absence of SPR, there was a convergence of fitness interests, with all individuals gaining highest productivity at 5 h remating. This suggests that the expression of sexual conflict was reduced. An unexpected second male-specific advantage to early remating was observed, resulting from an increase in the efficiency of second male sperm use. This early window of opportunity for exploitation by second males depended on the presence of SPR. The results suggest that the SP pathway can modulate the expression of sexual conflict in this system, and show how variation in the selective forces that shape conflict and cooperation can be maintained.
Retzke, T., Thoma, M., Hansson, B. S. and Knaden, M. (2017). Potencies of effector genes in silencing odor-guided behavior in Drosophila melanogaster. J Exp Biol [Epub ahead of print]. PubMed ID: 28235908
The genetic toolbox in Drosophila offers a multitude of different effector constructs to silence neurons and neuron populations. This study investigated the potencies of several effector genes - when expressed in olfactory sensory neurons (OSNs) - to abolish odor-guided behavior in three different bioassays. Two of the tested effectors (tetanus toxin and Kir2.1) are capable of mimicking the Orco mutant phenotype in all of tested behavioral paradigms. In both cases the effectiveness depended on effector expression levels as full suppression of odor-guided behavior was observed only in flies homozygous for both Gal4-driver and UAS-effector constructs. Interestingly, the impact of the effector genes differed between chemotactic assays (i.e. the fly has to follow an odor gradient to localize the odor source) and anemotactic assays (i.e. the fly has to walk upwind after detecting an attractive odorant). In conclusion, these results underline the importance of performing appropriate control experiments when exploiting the Drosophila genetic toolbox and demonstrate that some odor-guided behaviors are more resistant to genetic perturbations than others.
Kurz, C. L., Charroux, B., Chaduli, D., Viallat-Lieutaud, A. and Royet, J. (2017). Peptidoglycan sensing by octopaminergic neurons modulates Drosophila oviposition. Elife 6. PubMed ID: 28264763
As infectious diseases pose a threat to host integrity, eukaryotes have evolved mechanisms to eliminate pathogens. In addition to develop strategies reducing infection, animals can engage in behaviours that lower the impact of the infection. The molecular mechanisms by which microbes impact host behaviour are not well understood. This study demonstrated that bacterial infection of Drosophila females reduces oviposition and that bacterial cell wall peptidoglycan, the component that activates Drosophila antibacterial response, is also the elicitor of this behavioral change. Peptidoglycan regulates egg laying rate by activating PGRP-LC -> NF-κB (Relish) signaling pathway in octopaminergic neurons and that, a dedicated peptidoglycan degrading enzyme acts in these neurons to buffer this behavioural response. This study shows that a unique ligand and signaling cascade are used in immune cells to mount an immune response and in neurons to control fly behavior following infection. This may represent a case of behavioural immunity.
Aranha, M. M., Herrmann, D., Cachitas, H., Neto-Silva, R. M., Dias, S. and Vasconcelos, M. L. (2017). apterous brain neurons control receptivity to male courtship in Drosophila melanogaster females. Sci Rep 7: 46242. PubMed ID: 28401905
Courtship behaviours allow animals to interact and display their qualities before committing to reproduction. In fly courtship, the female decides whether or not to mate and is thought to display receptivity by slowing down to accept the male. Very little is known on the neuronal brain circuitry controlling female receptivity. This study used genetic manipulation and behavioural studies to identify a novel set of neurons in the brain that controls sexual receptivity in the female without triggering the postmating response. These neurons, defined by the expression of the transcription factor Apterous, affect the modulation of female walking speed during courtship. Interestingly, it was found that the Apterous neurons required for female receptivity are neither Doublesex nor Fruitless positive suggesting that Apterous neurons are not specified by the sex-determination cascade. Overall, these findings identify a neuronal substrate underlying female response to courtship and highlight the central role of walking speed in the receptivity behaviour.

Friday, April 21st

Rousset, R., Carballes, F., Parassol, N., Schaub, S., Cerezo, D. and Noselli, S. (2017). Signalling crosstalk at the leading edge controls tissue closure dynamics in the Drosophila embryo. PLoS Genet 13(2): e1006640. PubMed ID: 28231245
During Dorsal closure (DC), JNK (JUN N-terminal Kinase) signalling controls leading edge (LE) differentiation generating local forces and cell shape changes essential for DC. The LE represents a key morphogenetic domain in which, in addition to JNK, a number of signalling pathways converges and interacts (anterior/posterior -AP- determination; segmentation genes, such as Wingless; Decapentaplegic). To better characterize properties of the LE morphogenetic domain, this study sought out new JNK target genes through a genomic approach: 25 were identified of which 8 are specifically expressed in the LE, similarly to decapentaplegic or puckered. Quantitative in situ gene profiling of this new set of LE genes reveals complex patterning of the LE along the AP axis, involving a three-way interplay between the JNK pathway, segmentation and HOX genes. Patterning of the LE into discrete domains appears essential for coordination of tissue sealing dynamics. Loss of anterior or posterior HOX gene function leads to strongly delayed and asymmetric DC, due to incorrect zipping in their respective functional domain. Therefore, in addition to significantly increasing the number of JNK target genes identified so far, the results reveal that the LE is a highly heterogeneous morphogenetic organizer, sculpted through crosstalk between JNK, segmental and AP signalling. This fine-tuning regulatory mechanism is essential to coordinate morphogenesis and dynamics of tissue sealing.
Werner, K., Donow, C. and Pandur, P. (2017). Chip/Ldb1 interacts with Tailup/islet1 to regulate cardiac gene expression in Drosophila. Genesis [Epub ahead of print]. PubMed ID: 28296185
The LIM-homeodomain transcription factor Tailup (Tup) is a component of the complex cardiac transcriptional network governing specification and differentiation of cardiac cells in Drosophila. LIM-domain containing factors are known to interact with the adaptor molecule Chip/Ldb1 to form higher order protein complexes to regulate gene expression thereby determining a cell's developmental fate. However, with respect to Drosophila heart development, it has not been investigated yet, whether Chip and Tup interact to regulate the generation of different cardiac cell types. This study shows that Chip is required for normal heart development and that it interacts with tup in this context. Particularly the number of Odd skipped-expressing pericardial cells depends on balanced amounts of Chip and Tup. Data from luciferase assays using Hand- and even-skipped reporter constructs in Drosophila S2 cells indicate that Chip and Tup act as a tetrameric complex on the regulatory regions of Hand and even-skipped. Finally five Tup binding sites were identified in the eve mesodermal enhancer, which adds Tup as novel factor to directly regulate eve expression. Taken together this study provides novel findings regarding cardiac gene expression regulation in Drosophila.
Wang, M. F., Hunter, M., Wang, G., McFaul, C., Yip, C. M. and Fernandez-Gonzalez, R. (2017). Automated cell tracking identifies mechanically-oriented cell divisions during Drosophila axis elongation. Development [Epub ahead of print]. PubMed ID: 28213553
Embryos extend their anterior-posterior (AP) axis in the conserved process of axis elongation. Drosophila axis elongation occurs in an epithelial monolayer, the germband, and is driven by cell intercalation, cell shape changes, and oriented cell divisions at the posterior germband. Anterior germband cells also divide during axis elongation. Image analysis and pattern recognition methods were developed to track dividing cells from confocal microscopy movies in a generally-applicable approach. Mesectoderm cells, forming the ventral midline, divided parallel to the AP axis, while lateral cells displayed a uniform distribution of division orientations. Mesectoderm cells did not intercalate and sustained increased AP strain before cell division. After division, mesectoderm cell density increased along the AP axis, thus relieving strain. Laser ablation was used to isolate mesectoderm cells from other tissues. Uncoupling the mesectoderm from intercalating cells did not affect cell division orientation. Conversely, separating the mesectoderm from the anterior and posterior poles of the embryo resulted in uniformly-oriented divisions. These data suggest that mesectoderm cells align their division angle to reduce strain caused by mechanical forces along the AP axis of the embryo.
Sauteur, L., Affolter, M. and Belting, H. G. (2017). Distinct and redundant functions of Esama and VE-cadherin during vascular morphogenesis. Development [Epub ahead of print]. PubMed ID: 28264837
Evolutionary Homolog Study
The cardiovascular system forms during early embryogenesis and adapts to embryonic growth by sprouting angiogenesis and vascular remodeling. These processes require fine-tuning of cell-cell adhesion to maintain and reestablish endothelial contacts, while allowing cell motility. This study compared the contribution of two endothelial cell specific adhesion proteins - VE-cadherin (VE-cad/Cdh5; see Drosophila Shotgun) and Esama (Endothelial cell-selective adhesion molecule a) - during angiogenic sprouting and blood vessel fusion (anastomosis) in the zebrafish embryo by genetic analyses. Different combinations of mutant alleles can be placed into a phenotypic series with increasing defects in filopodial contact formation. Contact formation in esama mutants appear wild-type like, while esama-/-; ve-cad+/- and ve-cad single mutants exhibit intermediate phenotypes. The lack of both proteins interrupts filopodial interaction completely. Furthermore, double mutants do not form a stable endothelial monolayer, display intrajunctional gaps, dislocalization of Zo-1 (see Drosophila Polychaetoid) and defects in apical-basal polarization. In summary, VE-cadherin and Esama have distinct and redundant functions during blood vessel morphogenesis and both adhesion proteins are central to endothelial cell recognition during anastomosis.

Thursday, April 20th

Monedero Cobeta, I., Salmani, B. Y. and Thor, S. (2017). Anterior-posterior gradient in neural stem and daughter cell proliferation governed by spatial and temporal Hox control. Curr Biol [Epub ahead of print]. PubMed ID: 28392108
A readily evident feature of animal central nervous systems (CNSs), apparent in all vertebrates and many invertebrates alike, is its "wedge-like" appearance, with more cells generated in anterior than posterior regions. This wedge could conceivably be established by an antero-posterior (A-P) gradient in the number of neural progenitor cells, their proliferation behaviors, and/or programmed cell death (PCD). However, the contribution of each of these mechanisms, and the underlying genetic programs, are not well understood. Building upon recent progress in the Drosophila melanogaster (Drosophila) ventral nerve cord (VNC), this study addressed these issues in a comprehensive manner. Although PCD plays a role in controlling cell numbers along the A-P axis, the main driver of the wedge is a gradient of daughter proliferation, with divisions directly generating neurons (type 0) being more prevalent posteriorly and dividing daughters (type I) more prevalent anteriorly. In addition, neural progenitor (NB) cell-cycle exit occurs earlier posteriorly. The gradient of type I > 0 daughter proliferation switch and NB exit combine to generate radically different average lineage sizes along the A-P axis, differing by more than 3-fold in cell number. The Hox homeotic genes, expressed in overlapping A-P gradients and with a late temporal onset in NBs, trigger the type I > 0 daughter proliferation switch and NB exit. Given the highly evolutionarily conserved expression of overlapping Hox homeotic genes in the CNS, these results point to a common mechanism for generating the CNS wedge.
Hirono, K., Kohwi, M., Clark, M. Q., Heckscher, E. S. and Doe, C. Q. (2017). Hirono, K., Kohwi, M., Clark, M. Q., Heckscher, E. S. and Doe, C. Q. (2017). The Hunchback temporal transcription factor establishes, but is not required to maintain, early-born neuronal identity. Neural Dev 12(1): 1. PubMed ID: 28137283
Drosophila and mammalian neural progenitors typically generate a diverse family of neurons in a stereotyped order. Neuronal diversity can be generated by the sequential expression of temporal transcription factors. In Drosophila, neural progenitors (neuroblasts) sequentially express the temporal transcription factors Hunchback (Hb), Kruppel, Pdm, and Castor. Hb is necessary and sufficient to specify early-born neuronal identity in multiple lineages, and is maintained in the post-mitotic neurons produced during each neuroblast expression window. Surprisingly, nothing is currently known about whether Hb acts in neuroblasts or post-mitotic neurons (or both) to specify first-born neuronal identity. This study selectively removed Hb from post-mitotic neurons, and assayed the well-characterized NB7-1 and NB1-1 lineages for defects in neuronal identity and function. Loss of Hb from embryonic and larval post-mitotic neurons did not affect neuronal identity. Furthermore, removing Hb from post-mitotic neurons throughout the entire CNS has no effect on larval locomotor velocity, a sensitive assay for motor neuron and pre-motor neuron function. It is concluded that Hb functions in progenitors (neuroblasts/GMCs) to establish heritable neuronal identity that is maintained by a Hb-independent mechanism. It is suggested that Hb acts in neuroblasts to establish an epigenetic state that is permanently maintained in early-born neurons.
Santiago, C. and Bashaw, G.J. (2017). Islet coordinately regulates motor axon guidance and dendrite targeting through the Frazzled/DCC receptor. Cell Rep 18: 1646-1659. PubMed ID: 28199838
Motor neuron axon targeting in the periphery is correlated with the positions of motor neuron inputs in the CNS, but how these processes are coordinated to form a myotopic map remains poorly understood. This study shows that the LIM homeodomain factor Islet (Isl) controls targeting of both axons and dendrites in Drosophila motor neurons through regulation of the Frazzled (Fra)/DCC receptor. Isl is required for fra expression in ventrally projecting motor neurons, and isl and fra mutants have similar axon guidance defects. Single-cell labeling indicates that isl and fra are also required for dendrite targeting in a subset of motor neurons. Finally, overexpression of Fra rescues axon and dendrite targeting defects in isl mutants. These results indicate that Fra acts downstream of Isl in both the periphery and the CNS, demonstrating how a single regulatory relationship is used in multiple cellular compartments to coordinate neural circuit wiring.

Schwabe, T., Li, X. and Gaul, U. (2017). Dynamic analysis of the mesenchymal-epithelial transition of blood-brain barrier forming glia in Drosophila. Biol Open 6(2):232-243. PubMed ID: 28108476
During development, many epithelia are formed by a mesenchymal-epithelial transition (MET). This study examined the major stages and underlying mechanisms of MET during blood-brain barrier formation in Drosophila. Contact with the basal lamina was shown to be essential for the growth of the barrier-forming subperineurial glia (SPG). Septate junctions (SJs), which provide insulation of the paracellular space, are not required for MET, but are necessary for the establishment of polarized SPG membrane compartments. In vivo time-lapse imaging reveals that the Moody GPCR signalling pathway regulates SPG cell growth and shape, with different levels of signalling causing distinct phenotypes. Timely, well-coordinated SPG growth is essential for the uniform insertion of SJs and thus the insulating function of the barrier. This is the first dynamic in vivo analysis of all stages in the formation of a secondary epithelium and of the key role trimeric G protein signalling plays in this important morphogenetic process.

Wednesday, April 19th

Kezos, J. N., Cabral, L. G., Wong, B. D., Khou, B. K., Oh, A., Harb, J. F., Chiem, D., Bradley, T. J., Mueller, L. D. and Rose, M. R. (2017). Starvation but not locomotion enhances heart robustness in Drosophila. J Insect Physiol [Epub ahead of print]. PubMed ID: 28285040
Insects and vertebrates have multiple major physiological systems, each species having a circulatory system, a metabolic system, and a respiratory system that enable locomotion and survival in stressful environments, among other functions. Broadening understanding of the physiology of Drosophila melanogaster requires the parsing of interrelationships among such major component physiological systems. By combining electrical pacing and flight exhaustion assays with manipulative conditioning, this study started to unpack the interrelationships between cardiac function, locomotor performance, and other functional characters such as starvation and desiccation resistance. Manipulative sequences incorporating these four physiological characters were applied to five D. melanogaster lab populations that share a common origin from the wild and a common history of experimental evolution. While exposure to starvation or desiccation significantly reduced flight duration, exhaustion due to flight only affected subsequent desiccation resistance. A strong association was found between flight duration and desiccation resistance, providing additional support for the hypothesis that these traits depend on glycogen and water content. However, there was negligible impact on rate of cardiac arrests from exhaustion by flight or exposure to desiccant. Brief periods of starvation significantly lowered the rate of cardiac arrest. These results provide suggestive support for the adverse impact of lipids on Drosophila heart robustness, a parallel result to those of many comparable studies in human cardiology. Overall, this study underscores clear distinctions among the connections between specific physiological responses to stress and specific types of physiological performance.
Uchizono, S., Tabuki, Y., Kawaguchi, N., Tanimura, T. and Itoh, T. Q. (2017). Mated Drosophila melanogaster females consume more amino acids during the dark phase. PLoS One 12(2): e0172886. PubMed ID: 28241073
To maintain homeostasis, animals must ingest appropriate quantities, determined by their internal nutritional state, of suitable nutrients. In the fruit fly Drosophila melanogaster, an amino acid deficit induces a specific appetite for amino acids and thus results in their increased consumption. Although multiple processes of physiology, metabolism, and behavior are under circadian control in many organisms, it is unclear whether the circadian clock also modulates such motivated behavior driven by an internal need. Differences in levels of amino acid consumption by flies between the light and dark phases of the day:night cycle were examined using a capillary feeder assay following amino acid deprivation. Female flies exhibited increased consumption of amino acids during the dark phase compared with the light phase. Investigation of mutants lacking a functional period gene (per0), a well-characterized clock gene in Drosophila, found no difference between the light and dark phases in amino acid consumption by per0 flies. Furthermore, increased consumption of amino acids during the dark phase was observed in mated but not in virgin females, which strongly suggested that mating is involved in the rhythmic modulation of amino acid intake. Egg production, which is induced by mating, did not affect the rhythmic change in amino acid consumption, although egg-laying behavior showed a per0-dependent change in rhythm. Elevated consumption of amino acids during the dark phase was partly induced by the action of a seminal protein, sex peptide (SP), on the sex peptide receptor (SPR) in females. Moreover, the increased consumption of amino acids during the dark phase is induced in mated females independently of their internal level of amino acids. These results suggest that a post-mating SP/SPR signal elevates amino acid consumption during the dark phase via the circadian clock.
Gibert, J. M., Mouchel-Vielh, E. and Peronnet, F. (2017). Modulation of yellow expression contributes to thermal plasticity of female abdominal pigmentation in Drosophila melanogaster. Sci Rep 7: 43370. PubMed ID: 28230190
Phenotypic plasticity describes the ability of a given genotype to produce distinct phenotypes in different environments. This study used the temperature sensitivity of abdominal pigmentation in Drosophila melanogaster females as a model to analyse the effect of the environment on development. Previous work has shown that thermal plasticity of abdominal pigmentation in females involves the pigmentation gene tan (t). However, the expression of the pigmentation gene yellow (y) was also modulated by temperature in the abdominal epidermis of pharate females. This study investigate the contribution of y to female abdominal pigmentation plasticity. First, it was shown that y is required for the production of black Dopamine-melanin. Then, using in situ hybridization, it was shown that the expression of y is strongly modulated by temperature in the abdominal epidermis of pharate females but not in bristles. Interestingly, these two expression patterns are known to be controlled by distinct enhancers. However, the activity of the y-wing-body epidermal enhancer only partially mediates the effect of temperature suggesting that additional regulatory sequences are involved. In addition, it was shown that y and t co-expression is needed to induce strong black pigmentation indicating that y contributes to female abdominal pigmentation plasticity.
Megha and Hasan, G. (2017). IP3R mediated Ca2+ release regulates protein metabolism in Drosophila neuroendocrine cells: implications for development under nutrient stress. Development [Epub ahead of print]. PubMed ID: 28289132
Successful completion of animal development is fundamentally reliant on nutritional cues. Adaptations for surviving nutritional loss are coordinated in part by neural circuits. As neuropeptides secreted by neuroendocrine (NE) cells (see Mapping peptidergic cells in Drosophila: where DIMM fits in) critically modulate neural circuits, this study investigated NE cell function during development under nutrient stress. Starved Drosophila larvae exhibited reduced pupariation, if either insulin signaling or IP3/Ca2+ signaling, were down-regulated in NE cells. Moreover, an IP3R (Inositol 1,4,5-trisphosphate receptor) loss-of-function mutant displayed reduced protein synthesis, which was rescued by over-expression of either InR (insulin receptor) or IP3R in NE cells of the mutant, suggesting that the two signaling pathways may be functionally compensatory. Furthermore, cultured IP3R mutant NE cells, but not neurons, exhibited reduced protein translation. Thus cell-specific regulation of protein synthesis by IP3R in NE cells influences protein metabolism. It is proposed that this regulation helps developing animals survive poor nutritional conditions.

Tuesday, April 18th

Theofel, I., Bartkuhn, M., Boettger, T., Gartner, S. M., Kreher, J., Brehm, A. and Rathke, C. (2017). tBRD-1 and tBRD-2 regulate expression of genes necessary for spermatid differentiation. Biol Open [Epub ahead of print]. PubMed ID: 28235844
Male germ cell differentiation proceeds to a large extent in the absence of active gene transcription. In Drosophila, hundreds of genes whose proteins are required during post-meiotic spermatid differentiation (spermiogenesis) are transcribed in primary spermatocytes. Transcription of these genes depends on the sequential action of the testis meiotic arrest complex (tMAC), Mediator complex, and testis-specific TFIID (tTFIID) complex. How the action of these protein complexes is coordinated and which other factors are involved in the regulation of transcription in spermatocytes is not well understood. This study shows that the bromodomain proteins tBRD-1 and tBRD-2 regulate gene expression in primary spermatocytes and share a subset of target genes. The function of tBRD-1 was essential for the sub-cellular localization of endogenous tBRD-2 but dispensable for its protein stability. Comparison of different microarray data sets showed that in primary spermatocytes, the expression of a defined number of genes depend on the function of the bromodomain proteins tBRD-1 and tBRD-2, the tMAC component Aly, the Mediator component Med22, and the tTAF Sa.
Mensah, L. B., Goberdhan, D. C. and Wilson, C. (2017). mTORC1 signalling mediates PI3K-dependent large lipid droplet accumulation in Drosophila ovarian nurse cells. Biol Open [Epub ahead of print]. PubMed ID: 28302666
Insulin and insulin-like growth factor signalling (IIS), which is primarily mediated by the PI3-kinase (PI3K)/PTEN/Akt kinase signalling cassette, is a highly evolutionary conserved pathway involved in co-ordinating growth, development, ageing and nutrient homeostasis with dietary intake. It controls transcriptional regulators, in addition to promoting signalling by mechanistic Target of Rapamycin (mTOR) Complex 1 (mTORC1; see Tor), which stimulates biosynthesis of proteins and other macromolecules, and drives organismal growth. Previous studies in nutrient-storing germline nurse cells of the Drosophila ovary showed that a cytoplasmic pool of activated phosphorylated Akt (pAkt) controlled by Pten, an antagonist of IIS, cell-autonomously regulates accumulation of large lipid droplets in these cells at late stages of oogenesis. This study shows that the large lipid droplet phenotype induced by Pten mutation is strongly suppressed when mTor function is removed. Furthermore, nurse cells lacking either Tsc1 or Tsc2, which negatively regulate mTORC1 activity, also accumulate large lipid droplets via a mechanism involving Rheb, the downstream G-protein target of TSC2, which positively regulates mTORC1. It is concluded that elevated IIS/mTORC1 signalling is both necessary and sufficient to induce large lipid droplet formation in late-stage nurse cells, suggesting roles for this pathway in aspects of lipid droplet biogenesis, in addition to control of lipid metabolism.
Lin, Y. T., Barske, L., DeFalco, T. and Capel, B. (2017). Numb regulates somatic cell lineage commitment during early gonadogenesis in mice. Development. PubMed ID: 28360133
Evolutionary Homolog Study
During early gonadogenesis, proliferating cells in the coelomic epithelium (CE) give rise to most somatic cells in both XX and XY gonads. Previous dye-labeling experiments showed that a single CE cell could give rise to additional CE cells and to both supporting and interstitial cell lineages, implying that cells in the CE domain are multipotent progenitors, and suggesting that an asymmetric division is involved in the acquisition of gonadal cell fates. This study found that NUMB (see Drosophila Numb) is asymmetrically localized in CE cells, suggesting that it might be involved. To test this hypothesis, Numb was conditionally deleted on a Numb-like mutant background just prior to gonadogenesis. Mutant gonads showed a loss of cell polarity in the surface epithelial layers, large interior cell patches expressing the undifferentiated marker LHX9, and loss of differentiated cells in somatic cell lineages. These results indicate that NUMB is necessary for establishing polarity in CE cells, and that asymmetric divisions resulting from CE polarity are required for commitment to differentiated somatic cell fates. Surprisingly, germ cells, which do not arise from the CE, were also affected in mutants, which may be a direct or indirect effect of loss of Numb.
Yang, Z., Sun, J., Hu, Y., Wang, F., Wang, X., Qiao, H. H., Xu, J., Mao, D., Ren, X., Pan, L. X., Xu, R. G., Xu, B. W., Zhang, Y., Li, H., Miao, W., Hu, Y., Chang, Z., Wang, D., Li, H., Chang, Z., Liu, L. P., Liu, Q. and Ni, J. Q. (2017). Histone H1 defect in escort cells triggers germline tumor in Drosophila ovary. Dev Biol 424(1): 40-49. PubMed ID: 28232075
Drosophila ovary is recognized as one of the best model systems to study stem cell biology in vivo. An autonomous role of the histone H1 has been identfied in germline stem cell (GSC) maintenance. This study found that histone H1 depletion in escort cells (ECs) resulted in an increase of spectrosome-containing cells (SCCs), an ovary tumor-like phenotype. Further analysis showed that the Dpp pathway is excessively activated in these SCC cells, while the expression of bam is attenuated. In the H1-depleted ECs, both transposon activity and DNA damage had increased dramatically, followed by EC apoptosis, which is consistent with the role of H1 in other somatic cells. Surprisingly, H1-depleted ECs acquired cap cell characteristics including dpp expression, and the resulting abnormal Dpp level inhibits SCC further differentiation. Most interestingly, double knockdown of H1 and dpp in ECs can reduce the number of SCCs to the normal level, indicating that the additional Dpp secreted by ECs contributes to the germline tumor. Taken together, these findings indicate that histone H1 is an important epigenetic factor in controlling EC characteristics and a key suppressor of germline tumor.

Monday, April 17th

Goolam, M. and Zernicka-Goetz, M. (2017). The chromatin modifier Satb1 regulates cell fate through Fgf signalling in the early mouse embryo. Development [Epub ahead of print]. PubMed ID: 28289135
Evolutionary Homolog Study
The separation of embryonic from extra-embryonic tissues within the inner-cell-mass (ICM) to generate the epiblast (EPI), that will form the new organism, from the primitive endoderm (PE), that will form the yolk sac, is a crucial developmental decision. This study identified a chromatin modifier, Satb1, with a distinct role in this decision. Satb1 is differentially expressed within 16-cell-stage embryos with higher expression levels in the ICM progenitor cells. Depleting Satb1 increases the number of EPI cells at the expense of PE. This phenotype can be rescued by simultaneous depletion of both Satb1 and Satb2, due to their antagonistic effect on the pluripotency regulator Nanog. Consequently, increasing Satb1 expression leads to differentiation into PE and a decrease in EPI, due to the modulation of expression of several pluripotency- and differentiation-related genes by Satb1. Finally, Satb1 was shown to be a downstream target of the Fgf signalling pathway, linking chromatin modification and Fgf signalling. Together, these results identify a role for Satb1 in the lineage choice between pluripotency and differentiation and further understanding of early embryonic lineage segregation.
Rong, X., Zhou, Y., Liu, Y., Zhao, B., Wang, B., Wang, C., Gong, X., Tang, P., Lu, L., Li, Y., Zhao, C. and Zhou, J. (2017). Glutathione peroxidase 4 inhibits Wnt/beta-catenin signaling and regulates dorsal organizer formation in zebrafish embryos. Development. PubMed ID: 28302747
Evolutionary Homolog Study
The Wnt/β-catenin signaling pathway plays pivotal roles in axis formation during embryogenesis and in adult tissue homeostasis. Glutathione peroxidase 4 (GPx4) is a selenoenzyme and participates in the reduction of peroxides. Its synthesis depends on the availability of the element selenium. However, the roles of GPx4 in vertebrate embryonic development and underlying mechanisms are largely unknown. This study shows that maternal loss of zebrafish gpx4b promotes embryonic dorsal organizer formation, whereas overexpression of GPx4b inhibits the development of the dorsal organizer. Depletion of GPx4/GPx4b increases, while GPx4/GPx4b overexpression decreases, Wnt/beta-catenin signaling in vivo and in vitro. Functional and epistatic studies showed that GPx4 functions at the Tcf/Lef (see Drosophila Pangolin) level, independently of selenocysteine activation. Mechanistically, GPx4 interacts with Tcf/Lefs and inhibits Wnt activity by preventing the binding of Tcf/Lefs to the promoters of Wnt target genes, resulting in inhibitory action in the presence of Wnt/β-catenin signaling. These findings unravel GPx4 as a suppressor of Wnt/beta-catenin signals, suggesting a possible relationship between the Wnt/β-catenin pathway and selenium via the association of Tcf/Lef family proteins with GPx4.
Winfree, L. M., Speese, S. D. and Logan, M. A. (2017). Protein phosphatase 4 coordinates glial membrane recruitment and phagocytic clearance of degenerating axons in Drosophila. Cell Death Dis 8(2): e2623. PubMed ID: 28230857
Neuronal damage induced by injury, stroke, or neurodegenerative disease elicits swift immune responses from glial cells, including altered gene expression, directed migration to injury sites, and glial clearance of damaged neurons through phagocytic engulfment. Collectively, these responses hinder further cellular damage, but the mechanisms that underlie these important protective glial reactions are still unclear. This study shows that the evolutionarily conserved trimeric protein phosphatase 4 (PP4) serine/threonine phosphatase complex is a novel set of factors required for proper glial responses to nerve injury in the adult Drosophila brain. Glial-specific knockdown of PP4 results in reduced recruitment of glia to severed axons and delayed glial clearance of degenerating axonal debris. This study shows that PP4 functions downstream of the the glial engulfment receptor Draper to drive glial morphogenesis through the guanine nucleotide exchange factor SOS and the Rho GTPase Rac1, revealing that PP4 molecularly couples Draper to Rac1-mediated cytoskeletal remodeling to ensure glial infiltration of injury sites and timely removal of damaged neurons from the CNS.
Sanial, M., Becam, I., Hofmann, L., Behague, J., Arguelles, C., Gourhand, V., Bruzzone, L., Holmgren, R. A. and Plessis, A. (2017). Dose dependent transduction of Hedgehog relies on phosphorylation-based feedback between the GPCR Smoothened and the kinase Fused. Development [Epub ahead of print]. PubMed ID: 28360132
Smoothened (SMO) is a GPCR-related protein required for the transduction of Hedgehog (HH). The HH gradient leads to graded phosphorylation of SMO, mainly by the PKA and CKI kinases. How thresholds in HH morphogen regulate SMO to promote switch-like transcriptional responses is a central unsolved issue. Using the wing imaginal disc model in Drosophila, this study identified novel SMO phosphosites that enhance the effects of the PKA/CKI kinases on SMO accumulation, its localization at the plasma membrane and its activity. Surprisingly, phosphorylation at these sites is induced by the kinase Fused (FU), a known downstream effector of SMO. In turn activation of SMO induces FU to act on its downstream targets. Together these data provide evidence for a SMO/FU positive regulatory loop nested within a multi-kinase phosphorylation cascade. It is proposed that this complex interplay amplifies signaling above a threshold that allows high HH signaling.
Zhou, J., Edgar, B. A. and Boutros, M. (2017). ATF3 acts as a rheostat to control JNK signalling during intestinal regeneration. Nat Commun 8: 14289. PubMed ID: 28272390
Epithelial barrier function is maintained by coordination of cell proliferation and cell loss, whereas barrier dysfunction can lead to disease and organismal death. JNK signalling is a conserved stress signalling pathway activated by bacterial infection and tissue damage, often leading to apoptotic cell death and compensatory cell proliferation. This study shows that the stress inducible transcription factor ATF3 restricts JNK activity in the Drosophila midgut. ATF3 regulates JNK-dependent apoptosis and regeneration through the transcriptional regulation of the JNK antagonist, Raw. Enterocyte-specific ATF3 inactivation increases JNK activity and sensitivity to infection, a phenotype that can be rescued by Raw overexpression or JNK suppression. ATF3 depletion enhances intestinal regeneration triggered by infection, but does not compensate for the loss of enterocytes and ATF3-depleted flies succumb to infection due to intestinal barrier dysfunction. In sum, this study has provided a mechanism to explain how an ATF3-Raw module controls JNK signalling to maintain normal intestinal barrier function during acute infection.
Xiao, X., Yang, L., Pang, X., Zhang, R., Zhu, Y., Wang, P., Gao, G. and Cheng, G. (2017). A Mesh-Duox pathway regulates homeostasis in the insect gut. Nat Microbiol 2: 17020. PubMed ID: 28248301
The metazoan gut harbours complex communities of commensal and symbiotic bacterial microorganisms. The quantity and quality of these microorganisms fluctuate dynamically in response to physiological changes. The mechanisms that hosts have developed to respond to and manage such dynamic changes and maintain homeostasis remain largely unknown. This study identified a dual oxidase (Duox)-regulating pathway that contributes to maintaining homeostasis in the gut of both Aedes aegypti and Drosophila melanogaster. A gut-membrane-associated protein, named Mesh, plays an important role in controlling the proliferation of gut bacteria by regulating Duox expression through an Arrestin-mediated MAPK JNK/ERK phosphorylation cascade. Expression of both Mesh and Duox is correlated with the gut bacterial microbiome, which, in mosquitoes, increases dramatically soon after a blood meal. Ablation of Mesh abolishes Duox induction, leading to an increase of the gut microbiome load. This study reveals that the Mesh-mediated signalling pathway is a central homeostatic mechanism of the insect gut.

Sunday, April 16th

Matsuoka, S., Armstrong, A., Sampson, L. L., Laws, K. M. and Drummond-Barbosa, D. (2017). Adipocyte metabolic pathways regulated by diet control the female germline stem cell lineage in Drosophila. Genetics [Epub ahead of print]. PubMed ID: 28396508
Nutrients affect adult stem cells through complex mechanisms involving multiple organs. Adipocytes are highly sensitive to diet and have key metabolic roles, and obesity increases the risk for many cancers. How diet-regulated adipocyte metabolic pathways influence normal stem cell lineages, however, remains unclear. Drosophila melanogaster has highly conserved adipocyte metabolism and a well-characterized female germline stem cell (GSC) lineage response to diet. This study conducted an isobaric tags for relative and absolute quantification (iTRAQ) proteomic analysis to identify diet-regulated adipocyte metabolic pathways that control the female GSC lineage. On a rich (relative to poor) diet, adipocyte Hexokinase-C and metabolic enzymes involved in pyruvate/acetyl-coA production are upregulated, promoting a shift of glucose metabolism towards macromolecule biosynthesis. Adipocyte-specific knockdown shows that these enzymes support early GSC progeny survival. Further, enzymes catalyzing fatty acid oxidation and phosphatidylethanolamine synthesis in adipocytes promote GSC maintenance, whereas lipid and iron transport from adipocytes controls vitellogenesis and GSC number, respectively. These results show a functional relationship between specific metabolic pathways in adipocytes and distinct processes in the GSC lineage, suggesting the adipocyte metabolism-stem cell link as an important area of investigation in other stem cell systems.
Matsui, T., Nieto-Estevez, V., Kyrychenko, S., Schneider, J. W. and Hsieh, J. (2017). RB controls growth, survival, and neuronal migration in human cerebral organoids. Development [Epub ahead of print]. PubMed ID: 28087635
Evolutionary Homolog Study
Retinoblastoma (RB; see Drosophila Rb) is a tumor suppressor gene which regulates cell cycle entry to S phase via E2F transcription factors (see Drosophila E2F). Using knockout (KO) mice, it has been described that Rb plays a role in cell migration and differentiation in developing and adult brain as well as apoptosis. In addition, the RB family is required for the self-renewal and survival of human embryonic stem cells (ESCs). However, little is known about the role of this gene in human brain development. This study investigated the role of RB in cerebral organoids from human ESCs deficient for RB. RB was shown to be expressed abundantly in neural stem/progenitor cells in organoids at 15 and 28 days in culture. The results revealed that the loss of RB promotes S phase entry of DCX+ cells and increases apoptosis of Sox2+ neural stem/progenitor cells, Doublecortin+ and Tuj1+ (Neuron-specific class III β-tubulin) neurons, which was associated with the upregulation of the CYCLIN A2 and of the apoptosis-regulating BAX genes. Moreover, aberrant Tuj1+ neuronal migration was observed in RB-KO organoids, and upregulation of the VLDLR gene, a receptor important in Reelin signaling. Interestingly, ectopically localized Tuj1+ cells were also found in teratomas from RB-KO human ESCs. These results suggest that RB gene has critical roles in human brain development.
Tian, A., Wang, B. and Jiang, J. (2017). Injury-stimulated and self-restrained BMP signaling dynamically regulates stem cell pool size during Drosophila midgut regeneration. Proc Natl Acad Sci U S A 114(13): E2699-E2708. PubMed ID: 28289209
Many adult organs rely on resident stem cells to maintain homeostasis. Upon injury, stem cells increase proliferation, followed by lineage differentiation to replenish damaged cells. Whether stem cells also change division mode to transiently increase their population size as part of a regenerative program and, if so, what the underlying mechanism is have remained largely unexplored. This study showed that injury stimulates the production of two bone morphogenetic protein (BMP) ligands, Dpp and Gbb, which drive an expansion of intestinal stem cells (ISCs) by promoting their symmetric self-renewing division in Drosophila adult midgut. BMP production in enterocytes is inhibited by BMP signaling itself, and BMP autoinhibition is required for resetting ISC pool size to the homeostatic level after tissue repair. This study suggests that dynamic BMP signaling controls ISC population size during midgut regeneration and reveals mechanisms that precisely control stem cell number in response to tissue needs.
Monkkonen, T., Landua, J. D., Visbal, A. P. and Lewis, M. T. (2017). Epithelial and non-epithelial Ptch1 play opposing roles to regulate proliferation and morphogenesis of the mouse mammary gland. Development 144(7): 1317-1327. PubMed ID: 28275010
Evolutionary Homolog Study
Patched 1 (Ptch1; see Drosophila Patched) has epithelial, stromal and systemic roles in murine mammary gland organogenesis, yet specific functions remain undefined. Cre-recombinase-mediated Ptch1 ablation in mammary epithelium increased proliferation and branching, but did not phenocopy transgenic expression of activated smoothened (SmoM2; see Drosophila Smoothened). The epithelium showed no evidence of canonical hedgehog signaling, and hyperproliferation was not blocked by smoothened (SMO) inhibition, suggesting a non-canonical function of PTCH1. Consistent with this possibility, nuclear localization of cyclin B1 was increased. In non-epithelial cells, heterozygous Fsp-Cre-mediated Ptch1 ablation increased proliferation and branching, with dysplastic terminal end buds (TEB) and ducts. By contrast, homozygous Ptch1 ablation decreased proliferation and branching, producing stunted ducts filled with luminal cells showing altered ovarian hormone receptor expression. Ducts of Fsp-Cre;Ptch1fl/fl mice were similar to Fsp-Cre;SmoM2 ducts, but Fsp-Cre;SmoM2 outgrowths were not stunted, suggesting that the histology might be mediated by Smo in the local stroma, with systemic Ptch1 required for ductal outgrowth and proper hormone receptor expression in the mammary epithelium.
Nalapareddy, K., Nattamai, K. J., Kumar, R. S., Karns, R., Wikenheiser-Brokamp, K. A., Sampson, L. L., Mahe, M. M., Sundaram, N., Yacyshyn, M. B., Yacyshyn, B., Helmrath, M. A., Zheng, Y. and Geiger, H. (2017). Canonical Wnt signaling ameliorates aging of intestinal stem cells. Cell Rep 18(11): 2608-2621. PubMed ID: 28297666
Evolutionary Homolog Study
Although intestinal homeostasis is maintained by intestinal stem cells (ISCs), regeneration is impaired upon aging. This study first uncover changes in intestinal architecture, cell number, and cell composition upon aging. Second, a decline was identified in the regenerative capacity of ISCs upon aging because of a decline in canonical Wnt signaling (see Drosophila Wingless) in ISCs. Changes in expression of Wnts are found in stem cells themselves and in their niche, including Paneth cells and mesenchyme. Third, reactivating canonical Wnt signaling enhances the function of both murine and human ISCs and, thus, ameliorates aging-associated phenotypes of ISCs in an organoid assay. These data demonstrate a role for impaired Wnt signaling in physiological aging of ISCs and further identify potential therapeutic avenues to improve ISC regenerative potential upon aging.
Balasooriya, G., Goschorska, M., Piddini, E. and Rawlins, E. L. (2017). FGFR2 is required for airway basal cell self-renewal and terminal differentiation. Development [Epub ahead of print]. PubMed ID: 28348168
Evolutionary Homolog Study
Airway stem cells slowly self-renew and produce differentiated progeny to maintain homeostasis throughout the life-span of an individual. Mutations in the molecular regulators of these processes may drive cancer or degenerative disease, but are also potential therapeutic targets. Conditionally deleting one copy of FGF Receptor 2 (see Drosophila Breathless) in adult mouse airway basal cells results in self-renewal and differentiation phenotypes. This study shows that FGFR2 signalling correlates with maintenance of expression of a key transcription factor for basal cell self-renewal and differentiation, SOX2 (see Drosophila Sox Neuro). This heterozygous phenotype illustrates that subtle changes in Receptor Tyrosine Kinase signalling can have significant effects, perhaps providing an explanation for the numerous changes seen in cancer.

Saturday, April 15th

Khadilkar, R. J., Ray, A., Chetan, D. R., Sinha, A. R., Magadi, S. S., Kulkarni, V. and Inamdar, M. S. (2017). Differential modulation of the cellular and humoral immune responses in Drosophila is mediated by the endosomal ARF1-Asrij axis. Sci Rep 7(1): 118. PubMed ID: 28273919
How multicellular organisms maintain immune homeostasis across various organs and cell types is an outstanding question in immune biology and cell signaling. In Drosophila, blood cells (hemocytes) respond to local and systemic cues to mount an immune response. While endosomal regulation of Drosophila hematopoiesis is reported, the role of endosomal proteins in cellular and humoral immunity is not well-studied. This study demonstrated a functional role for endosomal proteins in immune homeostasis. The ubiquitous trafficking protein ADP Ribosylation Factor 1 (ARF1) and the hemocyte-specific endosomal regulator Asrij differentially regulate humoral immunity. Asrij and ARF1 play an important role in regulating the cellular immune response by controlling the crystal cell melanization and phenoloxidase activity. ARF1 and Asrij mutants show reduced survival and lifespan upon infection, indicating perturbed immune homeostasis. The ARF1-Asrij axis suppresses the Toll pathway anti-microbial peptides (AMPs) by regulating ubiquitination of the inhibitor Cactus. The Imd pathway is inversely regulated- while ARF1 suppresses AMPs, Asrij is essential for AMP production. Several immune mutants have reduced Asrij expression, suggesting that Asrij co-ordinates with these pathways to regulate the immune response. This study highlights the role of endosomal proteins in modulating the immune response by maintaining the balance of AMP production. Similar mechanisms can now be tested in mammalian hematopoiesis and immunity.
White, P. M., Serbus, L. R., Debec, A., Codina, A., Bray, W., Guichet, A., Lokey, R. S. and Sullivan, W. (2017). Reliance of Wolbachia on high rates of host proteolysis revealed by a genome-wide RNAi screen of Drosophila cells. Genetics [Epub ahead of print]. PubMed ID: 28159754
Wolbachia are gram-negative, obligate, intracellular bacteria carried by a majority of insect species worldwide. This study identified 36 candidate genes that dramatically reduced Wolbachia titer and 41 that increased Wolbachia titer. Host gene knockdowns that reduced Wolbachia titer spanned a broad array of biological pathways including genes that influenced mitochondrial function and lipid metabolism. In addition, knockdown of 7 genes in the host ubiquitin and proteolysis pathways significantly reduced Wolbachia titer. To test the in vivo relevance of these results, this study found that drug and mutant inhibition of proteolysis reduced levels of Wolbachia in the Drosophila oocyte. The presence of Wolbachia in either cell lines or oocytes dramatically alters the distribution and abundance of ubiquinated proteins. Functional studies revealed that maintenance of Wolbachia titer relies on an intact host Endoplasmic-Reticulum-associated protein degradation pathway (ERAD). Accordingly, electron microscopy studies demonstrated that Wolbachia is intimately associated with the host Endoplasmic-Reticulum and dramatically alters the morphology of this organelle. Given Wolbachia lack essential amino acid biosynthetic pathways, the reliance of Wolbachia on high rates of host proteolysis via ubiquitination and the ERAD pathways may be a key mechanism for provisioning Wolbachia with amino acids. In addition, the reliance of Wolbachia on the ERAD pathway and disruption of ER morphology suggests a previously unsuspected mechanism for Wolbachia's potent ability to prevent RNA virus replication.
Kenmoku, H., Hori, A., Kuraishi, T. and Kurata, S. (2017). A novel mode of induction of the humoral innate immune response in Drosophila larvae. Dis Model Mech 10(3): 271-281. PubMed ID: 28250052
Drosophila adults have been utilized as a genetically tractable model organism to decipher the molecular mechanisms of humoral innate immune responses. In an effort to promote the utility of Drosophila larvae as an additional model system, this study describes a novel aspect of an induction mechanism for innate immunity in these larvae. By using a fine tungsten needle created for manipulating semi-conductor devices, larvae were subjected to septic injury. However, although Toll pathway mutants were susceptible to infection with Gram-positive bacteria as had been shown for Drosophila adults, microbe clearance was not affected in the mutants. In addition, Drosophila larvae were found to be sensitive to mechanical stimuli with respect to the activation of a sterile humoral response. In particular, pinching with forceps to a degree that might cause minor damage to larval tissues could induce the expression of the antifungal peptide gene Drosomycin; notably, this induction was partially independent of the Toll and immune deficiency pathways.
Chen, C. F., Ruiz-Vega, R., Vasudeva, P., Espitia, F., Krasieva, T. B., de Feraudy, S., Tromberg, B. J., Huang, S., Garner, C. P., Wu, J., Hoon, D. S. and Ganesan, A. K. (2017). ATR mutations promote the growth of melanoma tumors by modulating the immune microenvironment. Cell Rep 18(10): 2331-2342. PubMed ID: 28273450
Evolutionary Homolog Study
Melanomas accumulate a high burden of mutations that could potentially generate neoantigens, yet somehow suppress the immune response to facilitate continued growth. This study identified a subset of human melanomas that have loss-of-function mutations in ATR (see Drosophila Meiotic 41), a kinase that recognizes and repairs UV-induced DNA damage and is required for cellular proliferation. ATR mutant tumors exhibit both the accumulation of multiple mutations and the altered expression of inflammatory genes, resulting in decreased T cell recruitment and increased recruitment of macrophages known to spur tumor invasion. Taken together, these studies identify a mechanism by which melanoma cells modulate the immune microenvironment to promote continued growth.

Friday, April 14th

Mohr, C., Kleiner, S., Blanchette, M., Pyrowolakis, G. and Hartmann, B. (2017). Sex-specific transcript diversity in the fly head Is established during pupal stages and adulthood and is largely independent of the mating process and the germline. Sex Dev [Epub ahead of print]. PubMed ID: 28273663
Alternative splicing (AS), the process which generates multiple RNA and protein isoforms from a single pre-mRNA, greatly contributes to transcript diversity and compensates for the fact that the gene number does not scale with organismal complexity. A number of genomic approaches have established that the extent of AS is much higher than previously expected, raising questions on its spatio-temporal regulation and function. The present study addresses AS in the context of sex-specific neuronal development in the model Drosophila melanogaster. At least 47 genes display sex-specific AS in the adult fly head. Unlike targets of the classical Sex lethal-dependent sex determination cascade, sex-specific isoforms of the vast majority of these genes are not present during larval development but start accumulating during metamorphosis or later, indicating the existence of novel mechanisms in the induction of sex-specific AS. It was also established that sex-specific AS in the adult fly head is largely independent of the germline or the mating process. Finally, the role of sex-specific AS of the sulfotransferase Tango13 pre-mRNA was investigated and first evidence is provided that differential expression of certain isoforms of this protein significantly affects courtship and mating behavior in male flies.
Niinuma, S. and Tomari, Y. (2017). ATP is dispensable for both miRNA- and Smaug-mediated deadenylation reactions. RNA [Epub ahead of print]. PubMed ID: 28250202
microRNAs (miRNAs) as well as the RNA-binding protein Smaug recruit the CCR4-NOT deadenylase complex for shortening of the poly(A) tail. It has been believed that ATP is required for deadenylation induced by miRNAs or Smaug, based on the fact that the deadenylation reaction is blocked by ATP depletion. However, when isolated, neither of the two deadenylases in the CCR4-NOT complex requires ATP by themselves. Thus, it remains unknown why ATP is required for deadenylation by ribonucleoprotein complexes like miRNAs and Smaug. This study found that, in the absence of the ATP-regenerating system, ATP is rapidly consumed into AMP, a strong deadenylase inhibitor, in Drosophila cell lysate. Importantly, hydrolysis of AMP was sufficient to reactivate deadenylation by miRNAs or Smaug, suggesting that AMP accumulation, rather than ATP depletion, caused the inhibition of the deadenylation reaction. These results indicate that ATP is dispensable for deadenylation induced by miRNAs or Smaug and emphasize caution in the use of ATP depletion methods.
Rojas-Benitez, D., Eggers, C. and Glavic, A. (2017). Modulation of the proteostasis machinery to overcome stress caused by diminished levels of t6A-modified tRNAs in Drosophila. Biomolecules 7(1). PubMed ID: 28272317
Transfer RNAs (tRNAs) harbor a subset of post-transcriptional modifications required for structural stability or decoding function. N6-threonylcarbamoyladenosine (t6A) is a universally conserved modification found at position 37 in tRNA that pair A-starting codons (ANN) and is required for proper translation initiation and to prevent frame shift during elongation. In its absence, the synthesis of aberrant proteins is likely, evidenced by the formation of protein aggregates. The aim of this work was to study the relationship between t6A-modified tRNAs and protein synthesis homeostasis machinery using Drosophila melanogaster. The Gal4/UAS system was used to knockdown genes required for t6A synthesis in a tissue and time specific manner and in vivo reporters of unfolded protein response (UPR) activation. The results suggest that t6A-modified tRNAs, synthetized by the threonyl-carbamoyl transferase complex (TCTC), are required for organismal growth and imaginal cell survival, and is most likely to support proper protein synthesis.
Chen, X. and Rosbash, M. (2017). MicroRNA-92a is a circadian modulator of neuronal excitability in Drosophila. Nat Commun 8: 14707. PubMed ID: 28276426
Many biological and behavioural processes of animals are governed by an endogenous circadian clock, which is dependent on transcriptional regulation. This study addresses post-transcriptional regulation and the role of miRNAs in Drosophila circadian rhythms. At least six miRNAs show cycling expression levels within the pigment dispersing factor (PDF) cell-pacemaker neurons; only mir-92a peaks during the night. In vivo calcium monitoring, dynamics of PDF projections, ArcLight, GCaMP6 imaging and sleep assays indicate that mir-92a suppresses neuronal excitability. In addition, mir-92a levels within PDF cells respond to light pulses and also affect the phase shift response. Translating ribosome affinity purification (TRAP) and in vitro luciferase reporter assay indicate that mir-92a suppresses expression of sirt2, which is homologous to human sir2 and sirt3. sirt2 RNAi also phenocopies mir-92a overexpression. These experiments indicate that sirt2 is a functional mir-92a target and that mir-92a modulates PDF neuronal excitability via suppressing SIRT2 levels in a rhythmic manner.

Thursday, April 13th

Domsch, K., Acs, A., Obermeier, C., Nguyen, H. T. and Reim, I. (2017). Identification of the essential protein domains for Mib2 function during the development of the Drosophila larval musculature and adult flight muscles. PLoS One 12(3): e0173733. PubMed ID: 28282454
The proper differentiation and maintenance of myofibers is fundamental to a functional musculature. Disruption of numerous mostly structural factors leads to perturbations of these processes. Among the limited number of known regulatory factors for these processes is Mind bomb2 (Mib2), a muscle-associated E3 ubiquitin ligase, which was previously established to be required for maintaining the integrity of larval muscles. This study has examined the mechanistic aspects of Mib2 function by performing a detailed functional dissection of the Mib2 protein. The ankyrin repeats, in its entirety, and the hitherto uncharacterized Mib-specific domains (MIB), are shown to be important for the major function of Mib2 in skeletal and visceral muscles in the Drosophila embryo. Furthermore, novel mib2 alleles were identified that have arisen from a forward genetic screen aimed at identifying regulators of myogenesis. Two of these alleles are viable, but flightless hypomorphic mib2 mutants, and harbor missense mutations in the MIB domain and RING finger, respectively. Functional analysis of these new alleles, including in vivo imaging, demonstrates that Mib2 plays an additional important role in the development of adult thorax muscles, particularly in maintaining the larval templates for the dorsal longitudinal indirect flight muscles during metamorphosis.
Lammers, K., Abeln, B., Husken, M., Lehmacher, C., Psathaki, O. E., Alcorta, E., Meyer, H. and Paululat, A. (2017).. Formation and function of intracardiac valve cells in the Drosophila heart. J Exp Biol [Epub ahead of print]. PubMed ID: 28254880
Drosophila harbors a simple tubular heart that ensures hemolymph circulation within the body. The heart is built by a few different cell types, including cardiomyocytes that define the luminal heart channel and ostia cells that constitute openings in the heart wall allowing hemolymph to enter the heart chamber. Regulation of flow directionality within a tube, such as blood flow in arteries or insect hemolymph within the heart lumen, requires a dedicated gate, valve, or flap-like structure that prevents backflow of fluids. In the Drosophila heart, intracardiac valves provide this directionality of hemolymph streaming, with one valve being present in larvae and three valves in the adult fly. Each valve is built by two specialized cardiomyocytes that exhibit a unique histology. The capacity to open and close the heart lumen was found to rely on a unique myofibrillar setting as well as on the presence of large membranous vesicles. These vesicles are of endocytic origin and probably represent unique organelles of valve cells. Moreover, the working mode of the cells was characterised in real time. Valve cells exhibit a highly flexible shape and during each heartbeat, oscillating shape changes result in closing and opening of the heart channel. Finally, a set of novel valve cell markers useful for future in-depth analyses of cell differentiation in wildtype and mutant animals were identified.
Nakaoka, T., Iga, M., Yamada, T., Koujima, I., Takeshima, M., Zhou, X., Suzuki, Y., Ogihara, M. H. and Kataoka, H. (2017). Deep sequencing of the prothoracic gland transcriptome reveals new players in insect ecdysteroidogenesis. PLoS One 12(3): e0172951. PubMed ID: 28257485
Ecdysteroids are steroid hormones that induce molting and determine developmental timing in arthropods. In insect larva, the prothoracic gland (PG) is a major organ for ecdysone synthesis and release. Released ecdysone is converted into the active form, 20-hydroxyecdysone (20E) in the peripheral tissues. All processes from ecdysone synthesis and release from the PG to its conversion to 20E are called ecdysteroidogenesis and are under the regulation of numerous factors expressed in the PG and peripheral tissues. Classical genetic approaches and recent transcriptomic screening in the PG identified several genes responsible for ecdysone synthesis and release, whereas the regulatory mechanism remains largely unknown. This study analyzed RNA-seq data of the silkworm Bombyx mori PG and employed the fruit fly Drosophila melanogaster GAL4/UAS binary RNAi system to comprehensively screen for genes involved in ecdysone synthesis and/or release. It was found that the genes encoding delta-aminolevulinic acid synthase (CG3017/Aminolevulinate synthase/Alas) and putative NAD kinase (CG33156) were highly expressed in the PG of both B. mori and D. melanogaster. Neither alas nor CG33156 RNAi-induced larvae could enter into the pupal stage, and they had a lower abundance of the active form ecdysteroids in their prolonged larval stage. These results demonstrated that alas and CG33156 are indispensable for ecdysteroidogenesis.
Armstrong, B. E., Henner, A., Stewart, S. and Stankunas, K. (2017). Shh promotes direct interactions between epidermal cells and osteoblast progenitors to shape regenerated zebrafish bone. Development 144(7): 1165-1176. PubMed ID: 28351866
Evolutionary Homolog Study
Zebrafish innately regenerate amputated fins by mechanisms that expand and precisely position injury-induced progenitor cells to re-form tissue of the original size and pattern. For example, cell signaling networks direct osteoblast progenitors (pObs) to rebuild thin cylindrical bony rays with a stereotypical branched morphology. Hedgehog/Smoothened (Hh/Smo) signaling has been variably proposed to stimulate overall fin regenerative outgrowth or promote ray branching. Using a photoconvertible patched2 (see Drosophila Patched) reporter, active Hh/Smo output to a narrow distal regenerate zone comprising pObs and adjacent motile basal epidermal cells was identified. This Hh/Smo activity is driven by epidermal Sonic hedgehog a (Shha) rather than Ob-derived Indian hedgehog a (Ihha), which nevertheless functions atypically to support bone maturation. Using BMS-833923, a uniquely effective Smo inhibitor, and high-resolution imaging, it was shown that Shha/Smo is functionally dedicated to ray branching during fin regeneration. Hh/Smo activation enables transiently divided clusters of Shha-expressing epidermis to escort pObs into similarly split groups. This co-movement likely depends on epidermal cellular protrusions that directly contact pObs only where an otherwise occluding basement membrane remains incompletely assembled. Progressively separated pObs pools then continue regenerating independently to collectively re-form a now branched skeletal structure.
Vollmer, J., Fried, P., Aguilar-Hidalgo, D., Sanchez-Aragon, M., Iannini, A., Casares, F. and Iber, D. (2017). Growth control in the Drosophila eye disc by the cytokine Unpaired. Development 144(5): 837-843. PubMed ID: 28246213
A fundamental question in developmental biology is how organ size is controlled. Previous studies have shown that the area growth rate in the Drosophila eye primordium declines inversely proportionally to the increase in its area. How the observed reduction in the growth rate is achieved is unknown. This study explored the dilution of the cytokine Unpaired (Upd) as a possible candidate mechanism. In the developing eye, upd expression is transient, ceasing at the time when the morphogenetic furrow first emerges. It was confirmed experimentally that the diffusion and stability of the JAK/STAT ligand Upd are sufficient to control eye disc growth via a dilution mechanism. It was further shown that sequestration of Upd by ectopic expression of an inactive form of the receptor Domeless (Dome) results in a substantially lower growth rate, but the area growth rate still declines inversely proportionally to the area increase. This growth rate-to-area relationship is no longer observed when Upd dilution is prevented by the continuous, ectopic expression of Upd. It is concluded that a mechanism based on the dilution of the growth modulator Upd can explain how growth termination is controlled in the eye disc.
Montes, A. J. and Morata, G. (2017). Homeostatic response to blocking cell division in Drosophila imaginal discs: Role of the Fat/Dachsous (Ft/Ds) pathway. Dev Biol 424(2):113-123. PubMed ID: 28300568
One major problem in developmental biology is the identification of the mechanisms that control the final size of tissues and organs. This issue was identified in the imaginal discs of Drosophila by analysing the response to blocking cell division in large domains in the wing and leg discs. The affected domains may be zones of restricted lineage like compartments, or zones of open lineage that may integrate cells from the surrounding territory. The results reveal the existence of a powerful homeostatic mechanism that can compensate for gross differences in growth rates and builds structures of normal size. This mechanism functions at the level of whole discs, inducing additional cell proliferation to generate the cells that populate the cell division-arrested territory and generating an active recruitment process to integrate those cells. The activation of this response mechanism is mediated by alterations in the normal activity of PCP genes of the Fat/Ds system: in discs mutant for dachs, ds or four jointed the response mechanism is not activated.

Wednesday, April 12th

Li, D., Liu, Y., Pei, C., Zhang, P., Pan, L., Xiao, J., Meng, S., Yuan, Z. and Bi, X. (2017). miR-285-Yki/Mask double-negative feedback loop mediates blood-brain barrier integrity in Drosophila. Proc Natl Acad Sci U S A 114(12):E2365-E2374. PubMed ID: 28265104
The blood-brain barrier (BBB) physiologically isolates the brain from circulating blood or the hemolymph system, and its integrity is strictly maintained to perform sophisticated neuronal functions. The underlying mechanisms of subperineurial glia (SPG) growth and BBB maintenance during development are not clear. This study reports an miR-285-Yorkie (Yki)/Multiple Ankyrin repeats Single KH domain (Mask) double-negative feedback loop that regulates SPG growth and BBB integrity. Flies with a loss of miR-285 have a defective BBB with increased SPG ploidy and disruptive septate junctions. Mechanistically, miR-285 directly targets the Yki cofactor Mask to suppress Yki activity and down-regulates the expression of its downstream target cyclin E, a key regulator of cell cycle. Disturbance of cyclin E expression in SPG causes abnormal endoreplication, which leads to aberrant DNA ploidy and defective septate junctions. Moreover, the expression of miR-285 is increased by knockdown of yki or mask and is decreased with yki overexpression, thus forming a double-negative feedback loop. This regulatory loop is crucial for sustaining an appropriate Yki/Mask activity and cyclin E level to maintain SPG ploidy and BBB integrity. Perturbation of this signaling loop, either by dysregulated miR-285 expression or Yki activity, causes irregular SPG ploidy and BBB disruption. Furthermore, ectopic expression of miR-285 promotes canonical Hippo pathway-mediated apoptosis independent of the p53 or JNK pathway. Collectively, these results reveal an exquisite regulatory mechanism for BBB maintenance through an miR-285-Yki/Mask regulatory circuit.
LaFever, K. S., Wang, X., Page-McCaw, P., Bhave, G. and Page-McCaw, A. (2017). Both Drosophila matrix metalloproteinases have released and membrane-tethered forms but have different substrates. Sci Rep 7: 44560. PubMed ID: 28300207
Matrix metalloproteinases (MMPs) are extracellular proteases that can cleave extracellular matrix and alter signaling pathways. They have been implicated in many disease states, but it has been difficult to understand the contribution of individual MMPs, as there are over 20 MMPs in vertebrates. The vertebrate MMPs have overlapping substrates, they exhibit genetic redundancy and compensation, and pharmacological inhibitors are non-specific. In contrast, there are only two MMP genes in Drosophila, DmMmp1 and DmMmp2, which makes Drosophila an attractive system to analyze the basis of MMP specificity. Previously, Drosophila MMPs have been categorized by their pericellular localization, as Mmp1 appeared to be secreted and Mmp2 appeared to be membrane-anchored, suggesting that protein localization was the critical distinction in this small MMP family. This study reports that products of both genes are found at the cell surface and released into media. Additionally, it was shown that products of both genes contain GPI-anchors, and unexpectedly, that GPI-anchored MMPs promote cell adhesion when they are rendered inactive. Finally, by using new reagents and assays, it was shown that the two MMPs cleave different substrates, suggesting that this is the important distinction within this smallest MMP family.
Kayashima, Y., Katayanagi, Y., Tanaka, K., Fukutomi, R., Hiramoto, S. and Imai, S. (2017). Alkylresorcinols activate SIRT1 and delay ageing in Drosophila melanogaster. Sci Rep 7: 43679. PubMed ID: 28252007
Sirtuins are enzymes that catalyze NAD+ dependent protein deacetylation. The natural polyphenolic compound resveratrol received renewed interest when recent findings implicated resveratrol as a potent SIRT1 activator capable of mimicking the effects of calorie restriction. However, resveratrol directly interacts with fluorophore-containing peptide substrates. It was demonstrated that the SIRT1 activation of resveratrol is affected by the amino acid composition of the substrate. Resveratrol did increase the enzyme activity in cases in which hydrophobic amino acids are at the +1 position to the acetylated lysine in the substrate. Alkylresorcinols (ARs) are compounds that belong to the family of phenolic lipids, and they are found in numerous biological species. This study shows that the natural activators ARs increased the Vmax of recombinant SIRT1 for NAD+ and peptide substrate, and that ARs decreased acetylated histone in human monocyte cells by stimulating SIRT1-dependent deacetylation of substrates. ARs also extended the lifespan of Drosophila melanogaster, which was shown to be dependent on functional Sir2. These results demonstrated that ARs are natural catalytic activators for sirtuin.
Tavares, L., Correia, A., Santos, M. A., Relvas, J. B. and Pereira, P. S. (2017). dMyc is required in retinal progenitors to prevent JNK-mediated retinal glial activation. PLoS Genet 13(3): e1006647. PubMed ID: 28267791
In the nervous system, glial cells provide crucial insulation and trophic support to neurons and are important for neuronal survival. In reaction to a wide variety of insults, glial cells respond with changes in cell morphology and metabolism to allow repair. Additionally, these cells can acquire migratory and proliferative potential. In particular, after axonal damage or pruning the clearance of axonal debris by glial cells is key for a healthy nervous system. Thus, bidirectional neuron-glial interactions are crucial in development, but little is known about the cellular sensors and signalling pathways involved. This study shows that decreased cellular fitness in retinal progenitors caused by reduced Drosophila Myc expression triggers non cell-autonomous activation of retinal glia proliferation and overmigration. Glia migration occurs beyond its normal limit near the boundary between differentiated photoreceptors and precursor cells, extending into the progenitor domain and is stimulated by JNK activation (and the function of its target Mmp1), while proliferative responses are mediated by Dpp/TGF-beta signalling activation.
van Tienen, L. M., Mieszczanek, J., Fiedler, M., Rutherford, T. J. and Bienz, M. (2017). Constitutive scaffolding of multiple Wnt enhanceosome components by Legless/BCL9. Elife 6. PubMed ID: 28296634
Wnt/beta-catenin signaling elicits context-dependent transcription switches that determine normal development and oncogenesis. These are mediated by the Wnt enhanceosome, a multiprotein complex binding to the Pygo chromatin reader and acting through TCF/LEF-responsive enhancers. Pygo renders this complex Wnt-responsive, by capturing β-catenin via the Legless/BCL9 adaptor. This study used CRISPR/Cas9 genome engineering of Drosophila legless (lgs) and human BCL9 and B9L to show that the C-terminus downstream of their adaptor elements is crucial for Wnt responses. BioID proximity labeling revealed that BCL9 and B9L, like PYGO2, are constitutive components of the Wnt enhanceosome. Wnt-dependent docking of & beta-catenin to the enhanceosome apparently causes a rearrangement that apposes the BCL9/B9L C-terminus to TCF. This C-terminus binds to the Groucho/TLE co-repressor, and also to the Chip/LDB1-SSDP enhanceosome core complex via an evolutionary conserved element. An unexpected link between BCL9/B9L, PYGO2 and nuclear co-receptor complexes suggests that these β-catenin co-factors may coordinate Wnt and nuclear hormone responses.
Fores, M., Simon-Carrasco, L., Ajuria, L., Samper, N., Gonzalez-Crespo, S., Drosten, M., Barbacid, M. and Jimenez, G. (2017). A new mode of DNA binding distinguishes Capicua from other HMG-box factors and explains its mutation patterns in cancer. PLoS Genet 13(3): e1006622. PubMed ID: 28278156
HMG-box proteins, including Sox/SRY (Sox) and TCF/LEF1 (TCF) family members, bind DNA via their HMG-box. This study reports that Capicua (CIC), an HMG-box transcriptional repressor involved in Ras/MAPK signaling and cancer progression, employs an additional distinct mode of DNA binding that enables selective recognition of its targets. Contrary to previous assumptions, the HMG-box of CIC does not bind DNA alone but instead requires a distant motif (referred to as C1) present at the C-terminus of all CIC proteins. The HMG-box and C1 domains are both necessary for binding specific TGAATGAA-like sites, do not function via dimerization, and are active in the absence of cofactors, suggesting that they form a bipartite structure for sequence-specific binding to DNA. This binding mechanism operates throughout Drosophila development and in human cells, ensuring specific regulation of multiple CIC targets. It thus appears that HMG-box proteins generally depend on auxiliary DNA binding mechanisms for regulating their appropriate genomic targets, but that each sub-family has evolved unique strategies for this purpose. Finally, the key role of C1 in DNA binding also explains the fact that this domain is a hotspot for inactivating mutations in oligodendroglioma and other tumors.
Lomaev, D., Mikhailova, A., Erokhin, M., Shaposhnikov, A. V., Moresco, J. J., Blokhina, T., Wolle, D., Aoki, T., Ryabykh, V., Yates, J. R., Shidlovskii, Y. V., Georgiev, P., Schedl, P. and Chetverina, D. (2017). The GAGA factor regulatory network: Identification of GAGA factor associated proteins. PLoS One 12(3): e0173602. PubMed ID: 28296955
The Drosophila GAGA factor (GAF) has an extraordinarily diverse set of functions that include the activation and silencing of gene expression, nucleosome organization and remodeling, higher order chromosome architecture and mitosis. One hypothesis that could account for these diverse activities is that GAF is able to interact with partners that have specific and dedicated functions. To test this possibility affinity purification coupled with high throughput mass spectrometry were used to identify GAF associated partners. Consistent with this hypothesis the GAF interacting network includes a large collection of factors and complexes that have been implicated in many different aspects of gene activity, chromosome structure and function. Moreover, GAF interactions with a small subset of partners was shown to be direct; however for many others the interactions could be indirect, and depend upon intermediates that serve to diversify the functional capabilities of the GAF protein.
Anderson, C. M., Hu, J., Thomas, R., Gainous, T. B., Celona, B., Sinha, T., Dickel, D. E., Heidt, A. B., Xu, S. M., Bruneau, B. G., Pollard, K. S., Pennacchio, L. A. and Black, B. L. (2017). Cooperative activation of cardiac transcription through myocardin bridging of paired MEF2 sites. Development 144(7): 1235-1241. PubMed ID: 28351867
Evolutionary Homolog Study
Enhancers frequently contain multiple binding sites for the same transcription factor. These homotypic binding sites often exhibit synergy, whereby the transcriptional output from two or more binding sites is greater than the sum of the contributions of the individual binding sites alone. Although this phenomenon is frequently observed, the mechanistic basis for homotypic binding site synergy is poorly understood. This study identified a bona fide cardiac-specific Prkaa2 enhancer that is synergistically activated by homotypic MEF2 (see Drosophila Mef2) binding sites. Two MEF2 sites in the enhancer function cooperatively due to bridging of the MEF2C-bound sites by the SAP domain-containing co-activator protein myocardin, and paired sites were shown to buffer the enhancer from integration site-dependent effects on transcription in vivo Paired MEF2 sites are prevalent in cardiac enhancers, suggesting that this might be a common mechanism underlying synergy in the control of cardiac gene expression in vivo.

Monday, April 10th

Zhang, Y. V., Ormerod, K. G. and Littleton, J. T. (2017). Astrocyte Ca2+ Influx Negatively Regulates Neuronal Activity. eNeuro 4(2). PubMed ID: 28303263
Maintenance of neural circuit activity requires appropriate regulation of excitatory and inhibitory synaptic transmission. Recently, glia have emerged as key partners in the modulation of neuronal excitability; however, the mechanisms by which glia regulate neuronal signaling are still being elucidated. This study describes an analysis of how Ca2+ signals within Drosophila astrocyte-like glia regulate excitability in the nervous system. Drosophila astrocytes exhibit robust Ca2+ oscillatory activity manifested by fast, recurrent microdomain Ca2+ fluctuations within processes that infiltrate the synaptic neuropil. Unlike the enhanced neuronal activity and behavioral seizures that were previously observed during manipulations that trigger Ca2+ influx into Drosophila cortex glia, this study found that acute induction of astrocyte Ca2+ influx leads to a rapid onset of behavioral paralysis and a suppression of neuronal activity. It was observed that Ca2+ influx triggers rapid endocytosis of the GABA transporter (GAT) from astrocyte plasma membranes, suggesting that increased synaptic GABA levels contribute to the neuronal silencing and paralysis. Rab11 was identfied as a novel regulator of GAT trafficking that is required for this form of activity regulation. Suppression of Rab11 function strongly offsets the reduction of neuronal activity caused by acute astrocyte Ca2+ influx, likely by inhibiting GAT endocytosis. These data provide new insights into astrocyte Ca2+ signaling and indicate that distinct glial subtypes in the Drosophila brain can mediate opposing effects on neuronal excitability.
Cope, A. J., Sabo, C., Vasilaki, E., Barron, A. B. and Marshall, J. A. (2017). A computational model of the integration of landmarks and motion in the insect central complex. PLoS One 12(2): e0172325. PubMed ID: 28241061
The insect central complex (CX) has been implicated in a wide range of behaviours. Recent experimental evidence from Drosophila and the cockroach (Blaberus discoidalis) has demonstrated the existence of neural activity corresponding to the animal's orientation within a virtual arena (a neural 'compass'), and this provides an insight into one component of the CX structure. There are two key features of the compass activity: an offset between the angle represented by the compass and the true angular position of visual features in the arena, and the remapping of the 270 degrees visual arena onto an entire circle of neurons in the compass. This study presents a computational model which can reproduce this experimental evidence in detail, and predicts the computational mechanisms that underlie the data. It is predicted that both the offset and remapping of the fly's orientation onto the neural compass can be explained by plasticity in the synaptic weights between segments of the visual field and the neurons representing orientation. Furthermore, it is predicted that this learning is reliant on the existence of neural pathways that detect rotational motion across the whole visual field and uses this rotation signal to drive the rotation of activity in a neural ring attractor. This model also reproduces the 'transitioning' between visual landmarks seen when rotationally symmetric landmarks are presented. This model can provide the basis for further investigation into the role of the central complex, which promises to be a key structure for understanding insect behaviour, as well as suggesting approaches towards creating fully autonomous robotic agents.
Daniele, J. R., Baqri, R. M. and Kunes, S. (2017). Analysis of axonal trafficking via a novel live imaging technique reveals distinct Hedgehog transport kinetics. Biol Open [Epub ahead of print]. PubMed ID: 28298319
The Drosophila eye is an ideal model to study development, intracellular signaling, behavior, and neurodegenerative disease.Using axonal transport of the morphogen Hedgehog (Hh), which is integral to eye-brain development and implicated in stem cell maintenance and neoplastic disease, this study demonstrated the ability to quantify and characterize its trafficking in various neuron types and a neurodegeneration model in live early 3rd instar larval Drosophila. Neuronal Hh was found to favor fast anterograde transport and varies in speed and flux with respect to axonal position. This suggests distinct trafficking pathways along the axon. Lastly, abnormal transport is rorported of Hh in an accepted model of photoreceptor neurodegeneration. As a technical complement to existing eye-specific disease models, the ability to directly visualize transport in real time was demonstrated in intact and live animals, and secreted cargoes were tracked from the axon to their release points. Particle dynamics can now be precisely calculated and it is posited that this method could be conveniently applied to characterizing disease pathogenesis and genetic screening in other established models of neurodegeneration.
Delventhal, R., Menuz, K., Joseph, R., Park, J., Sun, J. S. and Carlson, J. R. (2017). The taste response to ammonia in Drosophila. Sci Rep 7: 43754. PubMed ID: 28262698
Ammonia is both a building block and a breakdown product of amino acids and is found widely in the environment. The odor of ammonia is attractive to many insects, including insect vectors of disease. The olfactory response of Drosophila to ammonia has been studied in some detail, but the taste response has received remarkably little attention. This study shows that ammonia is a taste cue for Drosophila. Nearly all sensilla of the major taste organ of the Drosophila head house a neuron that responds to neutral solutions of ammonia. Ammonia is toxic at high levels to many organisms, and it was found to have a negative valence in two paradigms of taste behavior, one operating over hours and the other over seconds. Physiological and behavioral responses to ammonia depend at least in part on Gr66a+ bitter-sensing taste neurons, which activate a circuit that deters feeding. The Amt transporter, a critical component of olfactory responses to ammonia, is widely expressed in taste neurons but is not required for taste responses. This work establishes ammonia as an ecologically important taste cue in Drosophila, and shows that it can activate circuits that promote opposite behavioral outcomes via different sensory systems.
Daniele, J. R., Chu, T. and Kunes, S. (2017). A novel proteolytic event controls Hedgehog intracellular sorting and distribution to receptive fields. Biol Open [Epub ahead of print]. PubMed ID: 28298318
The patterning activity of a morphogen depends on secretion and dispersal mechanisms that shape its distribution to the cells of a receptive field. In the case of the protein Hedgehog (Hh), these mechanisms of secretion and transmission remain unclear. In the developing Drosophila visual system, Hedgehog is partitioned for release at opposite poles of photoreceptor neurons. Release into the retina regulates the progression of eye development; axon transport and release at axon termini trigger the development of postsynaptic neurons in the brain. This study shows that this binary targeting decision is controlled by a C-terminal proteolysis. Hh with an intact C-terminus undergoes axonal transport, whereas a C-terminal proteolysis enables Hedgehog to remain in the retina, creating a balance between eye and brain development. Thus, a novel mechanism is defined for the apical/basal targeting of this developmentally important protein ,and it is posited that similar post-translational regulation could underlie the polarity of related ligands.
Litwin-Kumar, A., Harris, K. D., Axel, R., Sompolinsky, H. and Abbott, L. F. (2017). Optimal degrees of synaptic connectivity. Neuron 93(5): 1153-1164. PubMed ID: 28215558
Synaptic connectivity varies widely across neuronal types. Cerebellar granule cells receive five orders of magnitude fewer inputs than the Purkinje cells they innervate, and cerebellum-like circuits, including the insect mushroom body, also exhibit large divergences in connectivity. In contrast, the number of inputs per neuron in cerebral cortex is more uniform and large. This study investigated how the dimension of a representation formed by a population of neurons depends on how many inputs each neuron receives and what this implies for learning associations. This theory predicts that the dimensions of the cerebellar granule-cell and Drosophila Kenyon-cell representations are maximized at degrees of synaptic connectivity that match those observed anatomically, showing that sparse connectivity is sometimes superior to dense connectivity. When input synapses are subject to supervised plasticity, however, dense wiring becomes advantageous, suggesting that the type of plasticity exhibited by a set of synapses is a major determinant of connection density.

Sunday, April 9th

Kamber Kaya, H.E., Ditzel, M., Meier, P. and Bergmann, A. (2017). An inhibitory mono-ubiquitylation of the Drosophila initiator caspase Dronc functions in both apoptotic and non-apoptotic pathways. PLoS Genet 13: e1006438. PubMed ID: 28207763
Apoptosis is an evolutionary conserved cell death mechanism, which requires activation of initiator and effector caspases. The Drosophila initiator caspase Dronc, the ortholog of mammalian Caspase-2 and Caspase-9, has an N-terminal CARD domain that recruits Dronc into the apoptosome for activation. In addition to its role in apoptosis, Dronc also has non-apoptotic functions such as compensatory proliferation. One mechanism to control the activation of Dronc is ubiquitylation. However, the mechanistic details of ubiquitylation of Dronc are less clear. For example, monomeric inactive Dronc is subject to non-degradative ubiquitylation in living cells, while ubiquitylation of active apoptosome-bound Dronc triggers its proteolytic degradation in apoptotic cells. This study examined the role of non-degradative ubiquitylation of Dronc in living cells in vivo, i.e. in the context of a multi-cellular organism. In vivo data suggest that in living cells Dronc is mono-ubiquitylated on Lys78 (K78) in its CARD domain. This ubiquitylation prevents activation of Dronc in the apoptosome and protects cells from apoptosis. Furthermore, K78 ubiquitylation plays an inhibitory role for non-apoptotic functions of Dronc. Further, not all of the non-apoptotic functions of Dronc require its catalytic activity. In conclusion, data demonstrate a mechanism whereby Dronc's apoptotic and non-apoptotic activities can be kept silenced in a non-degradative manner through a single ubiquitylation event in living cells.

Duncan, D. M., Kiefel, P. and Duncan, I. (2017). Mutants for Drosophila Isocitrate dehydrogenase 3b are defective in mitochondrial function and larval cell death. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 28104670
The death of larval salivary gland cells during metamorphosis in Drosophila melanogaster has been a key system for studying steroid controlled programmed cell death. This death is induced by a pulse of the steroid hormone ecdysone that takes place at the end of the prepupal period. For many years, it has been thought that the ecdysone direct response gene Eip93F (E93) plays a critical role in initiating salivary gland cell death. This conclusion was based largely on the finding that the three "type" alleles of E93 cause a near-complete block in salivary gland cell death. This study shows that these three mutations are in fact allelic to Idh3b, a nearby gene that encodes the beta subunit of isocitrate dehydrogenase 3, a mitochondrial enzyme of the tricarboxylic acid (TCA) cycle. The strongest of the Idh3b alleles appears to cause a near-complete block in oxidative phosphorylation, as mitochondria are depolarized in mutant larvae, and development arrests early during cleavage in embryos from homozygous-mutant germ line mothers. Idh3b-mutant larval salivary gland cells fail to undergo mitochondrial fragmentation, which normally precedes the death of these cells, and do not initiate autophagy, an early step in the cell death program. These observations suggest a close relationship between the TCA cycle and the initiation of larval cell death. In normal development, tagged Idh3b is released from salivary gland mitochondria during their fragmentation, suggesting that Idh3b may be an apoptogenic factor that functions much like released cytochrome c in mammalian cells.
Katheder, N. S., Khezri, R., O'Farrell, F., Schultz, S. W., Jain, A., Rahman, M. M., Schink, K. O., Theodossiou, T. A., Johansen, T., Juhasz, G., Bilder, D., Brech, A., Stenmark, H. and Rusten, T. E. (2017). Microenvironmental autophagy promotes tumour growth. Nature 541(7637):417-420. PubMed ID: 28077876
As malignant tumours develop, they interact intimately with their microenvironment and can activate autophagy, a catabolic process which provides nutrients during starvation. How tumours regulate autophagy in vivo and whether autophagy affects tumour growth is controversial. This study demonstrates, using RasV12scrib−/− tumour cells, a well characterized Drosophila melanogaster malignant tumour model, that non-cell-autonomous autophagy is induced both in the tumour microenvironment and systemically in distant tissues. Tumour growth can be pharmacologically restrained using autophagy inhibitors, and early-stage tumour growth and invasion are genetically dependent on autophagy within the local tumour microenvironment. Induction of autophagy is mediated by Drosophila tumour necrosis factor (Eiger) and interleukin-6-like signalling (Unpaired) from metabolically stressed tumour cells, whereas tumour growth depends on active amino acid transport. Dormant growth-impaired tumours from autophagy-deficient animals reactivate tumorous growth when transplanted into autophagy-proficient hosts. It is concluded that transformed cells engage surrounding normal cells as active and essential microenvironmental contributors to early tumour growth through nutrient-generating autophagy.
Loudhaief, R., Brun-Barale, A., Benguettat, O., Nawrot-Esposito, M. P., Pauron, D., Amichot, M. and Gallet, A. (2017). Apoptosis restores cellular density by eliminating a physiologically or genetically induced excess of enterocytes in the Drosophila midgut. Development 144(5): 808-819. PubMed ID: 28246211
Using pathogens or high levels of opportunistic bacteria to damage the gut, studies in Drosophila have identified many signaling pathways involved in gut regeneration. Dying cells emit signaling molecules that accelerate intestinal stem cell proliferation and progenitor differentiation to replace the dying cells quickly. This process has been named 'regenerative cell death'. This study, mimicking environmental conditions, showed that the ingestion of low levels of opportunistic bacteria was sufficient to launch an accelerated cellular renewal program despite the brief passage of bacteria in the gut and the absence of cell death and this is is due to the moderate induction of the JNK pathway that stimulates stem cell proliferation. Consequently, the addition of new differentiated cells to the gut epithelium, without preceding cell loss, leads to enterocyte overcrowding. Finally, it was shown that a couple of days later, the correct density of enterocytes is promptly restored by means of a wave of apoptosis involving Hippo signaling and preferential removal of old enterocytes.

Saturday, April 8th

Menegazzi, P., Dalla Benetta, E., Beauchamp, M., Schlichting, M., Steffan-Dewenter, I. and Helfrich-Förster, C. (2017). Adaptation of circadian neuronal network to photoperiod in high-latitude European Drosophilids. Curr Biol 27: 833-839. PubMed ID: 28262491
The genus Drosophila contains over 2,000 species that, stemming from a common ancestor in the Old World Tropics, populate today very different environments. This study found significant differences in the activity pattern of Drosophila species belonging to the holarctic virilis group, i.e., D. ezoana and D. littoralis, collected in Northern Europe, compared to that of the cosmopolitan D. melanogaster, collected close to the equator. These behavioral differences might have been of adaptive significance for colonizing high-latitude habitats and hence adjust to long photoperiods. Most interestingly, the flies' locomotor activity correlates with the neurochemistry of their circadian clock network, which differs between low and high latitude for the expression pattern of the blue light photopigment cryptochrome (CRY) and the neuropeptide Pigment-dispersing factor (PDF). In D. melanogaster, CRY and PDF are known to modulate the timing of activity and to maintain robust rhythmicity under constant conditions. The rhythmic behavior of the high-latitude virilis group species could be partially stimulated by mimicking their CRY/PDF expression patterns in a laboratory strain of D. melanogaster. Data suggest that these alterations in the CRY/PDF clock neurochemistry might have allowed the virilis group species to colonize high-latitude environments.

Karageorgi, M., Bracker, L. B., Lebreton, S., Minervino, C., Cavey, M., Siju, K. P., Grunwald Kadow, I. C., Gompel, N. and Prud'homme, B. (2017). Evolution of multiple sensory systems drives novel egg-laying behavior in the fruit pest Drosophila suzukii. Curr Biol [Epub ahead of print]. PubMed ID: 28285999
The rise of a pest species represents a unique opportunity to address how species evolve new behaviors and adapt to novel ecological niches. This question was addressed by studying the egg-laying behavior of Drosophila suzukii, an invasive agricultural pest species that has spread from Southeast Asia to Europe and North America in the last decade. While most closely related Drosophila species lay their eggs on decaying plant substrates, D. suzukii oviposits on ripening fruit, thereby causing substantial economic losses to the fruit industry. D. suzukii has evolved an enlarged, serrated ovipositor that presumably plays a key role by enabling females to pierce the skin of ripe fruit. This study explored how D. suzukii selects oviposition sites, and how this behavior differs from that of closely related species. Behavioral experiments were combined in multiple species with neurogenetics and mutant analysis in D. suzukii to show that this species has evolved a specific preference for oviposition on ripe fruit. The results also establish that changes in mechanosensation, olfaction, and presumably gustation have contributed to this ecological shift. These observations support a model in which the emergence of D. suzukii as an agricultural pest is the consequence of the progressive modification of several sensory systems, which collectively underlie a radical change in oviposition behavior.
Cogni, R., Kuczynski, K., Koury, S., Lavington, E., Behrman, E. L., O'Brien, K. R., Schmidt, P. S. and Eanes, W. F. (2017). On the long-term stability of clines in some metabolic genes in Drosophila melanogaster. Sci Rep 7: 42766. PubMed ID: 28220806
Very little information exists for long-term changes in genetic variation in natural populations. This study took the unique opportunity to compare a set of data for SNPs in 15 metabolic genes from eastern US collections of Drosophila melanogaster that span a large latitudinal range and represent two collections separated by 12 to 13 years. This was expanded to a 22-year interval for the Adh gene and approximately 30 years for the G6pd and Pgd genes. During these intervals, five genes showed a statistically significant change in average SNP allele frequency corrected for latitude. While much remains unchanged, five genes were seen that wx latitudinal clines have been lost or gained and two where the slope significantly changes. The long-term frequency shift towards a southern favored Adh S allele reported in Australia populations is not observed in the eastern US over a period of 21 years. There is no general pattern of southern-favored or northern-favored alleles increasing in frequency across the genes. This observation points to the fluid nature of some allelic variation over this time period and the action of selective responses or migration that may be more regional than uniformly imposed across the cline.
Rajpurohit, S., Richardson, R., Dean, J., Vazquez, R., Wong, G. and Schmidt, P. S. (2016). Pigmentation and fitness trade-offs through the lens of artificial selection. Biol Lett 12(10). PubMed ID: 28120808
Pigmentation is a classic phenotype that varies widely and adaptively in nature both within and among taxa. Genes underlying pigmentation phenotype are highly pleiotropic, creating the potential for functional trade-offs. However, the basic tenets of this trade-off hypothesis with respect to life-history traits have not been directly addressed. In natural populations of Drosophila melanogaster, the degree of melanin pigmentation covaries with fecundity and several other fitness traits. To examine correlations and potential trade-offs associated with variation in pigmentation, replicate outbred populations were selected for extreme pigmentation phenotypes. Replicate populations responded rapidly to the selection regime and after 100 generations of artificial selection were phenotyped for pigmentation as well as the two basic fitness parameters of fecundity and longevity. The data demonstrate that selection on pigmentation resulted in a significant shift in both fecundity and longevity profiles. Selection for dark pigmentation resulted in greater fecundity and no pronounced change in longevity, whereas selection for light pigmentation decreased longevity but did not affect fecundity. These results indicate the pleiotropic nature of alleles underlying pigmentation phenotype and elucidate possible trade-offs between pigmentation and fitness traits that may shape patterns of phenotypic variation in natural populations.

Friday, April 7th

Giardina, T. J., Clark, A. G. and Fiumera, A. C. (2017). Estimating mating rates in wild Drosophila melanogaster females by decay rates of male reproductive proteins in their reproductive tracts. Mol Ecol Resour [Epub ahead of print]. PubMed ID: 28213940
Female Drosophila melanogaster frequently mate with multiple males in nature as shown through parentage analysis. Although polyandry is well documented, little is known about the timing between mating events in wild Drosophila populations due to the challenge of following behaviors of individual females. This study used the presence of a male reproductive protein that is transferred to the female during mating (Sex Peptide, SP) to determine whether she had recently mated. Females were sampled throughout the day, control matings were conducted to determine the decay rate of SP within the female reproductive tract and computer simulations were performed to fit the observed proportion of mated females to a non-homogenous Poisson process that defined the expected time between successive matings for a given female. In control matings, 100% of mated females tested positive for SP 0.5 hrs after the start of mating (ASM), but only 24% tested positive 24 hrs ASM. Overall, 35% of wild-caught females tested positive for the presence of SP. Fitting the observed data to a simple non-homogenous Poisson model provided the inference that females are mating, on average, approximately every 27 hrs (with 95% credibility interval 23-31 hrs). Thus it appears that females are mating a bit less frequently that once per day in this natural population and that mating events tend to occur either early in the morning or late in the afternoon.
Boutros, C. L., Miner, L. E., Mazor, O. and Zhang, S. X. (2017). Measuring and altering mating drive in male Drosophila melanogaster. J Vis Exp(120). PubMed ID: 28287580
Despite decades of investigation, the neuronal and molecular bases of motivational states remain mysterious. A novel, reductionist, and scalable system for in-depth investigation of motivation has been developed using the mating drive of male Drosophila melanogaster, the methods for which are detailed in this study. The behavioral paradigm centers on the finding that male mating drive decreases alongside fertility over the course of repeated copulations and recovers over ~3 d. In this system, the powerful neurogenetic tools available in the fly converge with the genetic accessibility and putative wiring diagram available for sexual behavior. This convergence allows rapid isolation and interrogation of small neuronal populations with specific motivational functions. This paper details the design and execution of the satiety assay that is used to measure and alter courtship motivation in the male fly. Using this assay, it was demonstrated that low male mating drive can be overcome by stimulating dopaminergic neurons. The satiety assay is simple, affordable, and robust to influences of genetic background. This satiety assay should generate many new insights into the neurobiology of motivational states.
Ferguson, L., Petty, A., Rohrscheib, C., Troup, M., Kirszenblat, L., Eyles, D. W. and van Swinderen, B. (2017). Transient dysregulation of dopamine signaling in a developing Drosophila arousal circuit permanently impairs behavioral responsiveness in adults. Front Psychiatry 8: 22. PubMed ID: 28243212
The dopamine ontogeny hypothesis for schizophrenia proposes that transient dysregulation of the dopaminergic system during brain development increases the likelihood of this disorder in adulthood. To test this hypothesis in a high-throughput animal model, this study transiently manipulated dopamine signaling in the developing fruit fly Drosophila melanogaster and examined behavioral responsiveness in adult flies. Either a transient increase of dopamine neuron activity or a transient decrease of dopamine receptor expression during fly brain development permanently impairs behavioral responsiveness in adults. A screen for impaired responsiveness revealed sleep-promoting neurons in the central brain as likely postsynaptic dopamine targets modulating these behavioral effects. Transient dopamine receptor knockdown during development in a restricted set of ~20 sleep-promoting neurons recapitulated the dopamine ontogeny phenotype, by permanently reducing responsiveness in adult animals. This suggests that disorders involving impaired behavioral responsiveness might result from defective ontogeny of sleep/wake circuits.
Sugime, Y., Watanabe, D., Yasuno, Y., Shinada, T., Miura, T. and Tanaka, N. K. (2017). Upregulation of juvenile hormone titers in female Drosophila melanogaster through mating experiences and host food occupied by eggs and larvae. Zoolog Sci 34(1): 52-57. PubMed ID: 28148219
Juvenile hormone (JH) plays a crucial role in the determination of developmental timing in insects. In Drosophila melanogaster, reports indicate that JH titers are the highest immediately following eclosion and that the mating experience increases the titers in females. However, the titers have not been successively measured for an extended period of time after eclosion. This study reveals that JH titers are increased after eclosion in virgin females when supplied with food that is occupied by eggs and larvae as well as in mated females. With the presence of eggs and larvae, food induced the virgin females to lay unfertilized eggs. When combined with previous work indicating that females are attracted to such food where they prefer to lay eggs, these results suggest that flies can prepare themselves to lay eggs by changing the titers of JH under the presence of growing larvae, ensuring that the food is an appropriate place to oviposit.

Thursday, March 6th

Krug, L., Chatterjee, N., Borges-Monroy, R., Hearn, S., Liao, W. W., Morrill, K., Prazak, L., Rozhkov, N., Theodorou, D., Hammell, M. and Dubnau, J. (2017). Retrotransposon activation contributes to neurodegeneration in a Drosophila TDP-43 model of ALS. PLoS Genet 13(3): e1006635. PubMed ID: 28301478
Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are two incurable neurodegenerative disorders that exist on a symptomological spectrum and share both genetic underpinnings and pathophysiological hallmarks. Functional abnormality of TAR DNA-binding protein 43 (TDP-43; see Drosophila TBPH), an aggregation-prone RNA and DNA binding protein, is observed in the vast majority of both familial and sporadic ALS cases and in ~40% of FTLD cases, but the cascade of events leading to cell death are not understood. This study expressed human TDP-43 (hTDP-43) in Drosophila neurons and glia, a model that recapitulates many of the characteristics of TDP-43-linked human disease including protein aggregation pathology, locomotor impairment, and premature death. Such expression of hTDP-43 impairs small interfering RNA (siRNA) silencing, which is the major post-transcriptional mechanism of retrotransposable element (RTE) control in somatic tissue. This is accompanied by de-repression of a panel of both LINE and LTR families of RTEs, with somewhat different elements being active in response to hTDP-43 expression in glia versus neurons. hTDP-43 expression in glia causes an early and severe loss of control of a specific RTE, the endogenous retrovirus (ERV) gypsy. Gypsy causes the degenerative phenotypes in these flies because it was possilble to rescue the toxicity of glial hTDP-43 either by genetically blocking expression of this RTE or by pharmacologically inhibiting RTE reverse transcriptase activity. Moreover, evidence is provided that activation of DNA damage-mediated programmed cell death underlies both neuronal and glial hTDP-43 toxicity, consistent with RTE-mediated effects in both cell types. These findings suggest a novel mechanism in which RTE activity contributes to neurodegeneration in TDP-43-mediated diseases such as ALS and FTLD.
Suggs, J. A., Melkani, G. C., Glasheen, B. M., Detor, M. M., Melkani, A., Marsan, N. P., Swank, D. M. and Bernstein, S. I. (2017). A Drosophila model of dominant inclusion body myopathy 3 shows diminished myosin kinetics that reduce muscle power and yield myofibrillar defects. Dis Model Mech [Epub ahead of print]. PubMed ID: 28258125
Inclusion body myopathy type 3 (IBM-3) patients display congenital joint contractures with early-onset muscle weakness that becomes more severe in adults. The disease arises from an autosomal dominant point mutation causing an E706K substitution in myosin heavy chain type IIa. The corresponding myosin mutation (E701K) in Drosophila Myosin was expressed in homozygous Drosophila indirect flight muscles and the myofibrillar degeneration and inclusion bodies observed in the human disease was recapitulated. Purified E701K myosin has dramatically reduced actin-sliding velocity and ATPase levels. Since IBM-3 is a dominant condition, the disease state was examined in heterozygote Drosophila in order to gain a mechanistic understanding of E701K pathogenicity. Myosin ATPase activities in heterozygotes suggest that approximately equimolar levels of myosin accumulate from each allele. In vitro actin sliding velocity rates for myosin isolated from the heterozygotes were lower than the control, but higher than for the pure mutant isoform. Although sarcomeric ultrastructure was nearly wild-type in young adults, mechanical analysis of skinned indirect flight muscle fibers revealed an 85% decrease in maximum oscillatory power generation and an approximately 6-fold reduction in the frequency at which maximum power was produced. Rate constant analyses suggest a decrease in the rate of myosin attachment to actin, with myosin spending decreased time in the strongly bound state. These mechanical alterations result in a one third decrease in wing beat frequency and marginal flight ability. With aging, muscle ultrastructure and function progressively declined. Aged myofibrils showed Z-line streaming, consistent with the human heterozygote phenotype. Based upon the mechanical studies, it is hypothesize that the mutation decreases the probability of the power stroke occurring and/or alters the degree of movement of the myosin lever arm, resulting in decreased in vitro motility, reduced muscle power output and focal myofibrillar disorganization similar to that seen in human IBM-3 patients.
Kayashima, Y., Katayanagi, Y., Tanaka, K., Fukutomi, R., Hiramoto, S. and Imai, S. (2017). Alkylresorcinols activate SIRT1 and delay ageing in Drosophila melanogaster. Sci Rep 7: 43679. PubMed ID: 28252007
Sirtuins are enzymes that catalyze NAD+ dependent protein deacetylation. The natural polyphenolic compound resveratrol received renewed interest when recent findings implicated resveratrol as a potent SIRT1 activator capable of mimicking the effects of calorie restriction. However, resveratrol directly interacts with fluorophore-containing peptide substrates. It has been demonstrated that the SIRT1 activation of resveratrol is affected by the amino acid composition of the substrate. Resveratrol does increase the enzyme activity in cases in which hydrophobic amino acids are at the +1 position to the acetylated lysine in the substrate. Alkylresorcinols (ARs) are compounds that belong to the family of phenolic lipids, and they are found in numerous biological species. This study shows that the natural activators ARs increase the Vmax of recombinant SIRT1 for NAD+ and peptide substrate, and that ARs decrease acetylated histone in human monocyte cells by stimulating SIRT1-dependent deacetylation of substrates. ARs also extend the lifespan of Drosophila melanogaster, that was shown to be dependent on functional Sir2. These results demonstrate that ARs are natural catalytic activators for sirtuin.

Kawasaki, H., Suzuki, T., Ito, K., Takahara, T., Goto-Inoue, N., Setou, M., Sakata, K. and Ishida, N. (2017). Minos-insertion mutant of the Drosophila GBA gene homologue showed abnormal phenotypes of climbing ability, sleep and life span with accumulation of hydroxy-glucocerebroside. Gene [Epub ahead of print]. PubMed ID: 28286087
Gaucher's disease in humans is considered a deficiency of glucocerebrosidase (GlcCerase) that results in the accumulation of its substrate, glucocerebroside (GlcCer). Although mouse models of Gaucher's disease have been reported from several laboratories, these models are limited due to the perinatal lethality of GlcCerase gene. This study examined phenotypes of Drosophila melanogaster homologues genes of the human Gaucher's disease gene by using Minos insertion. One of two Minos insertion mutants to unknown function gene (CG31414; Glucocerebrosidase 1b) accumulates the hydroxy-GlcCer in whole body of Drosophila melanogaster. This mutant showed abnormal phenotypes of climbing ability and sleep, and short lifespan. These abnormal phenotypes are very similar to that of Gaucher's disease in human. In contrast, another Minos insertion mutant (CG31148; Glucocerebrosidase 1a) and its RNAi line did not show such severe phenotype as observed in CG31414 gene mutation. The data suggests that Drosophila CG31414 gene mutation might be useful for unraveling the molecular mechanism of Gaucher's disease.

Wednesday, April 5th

Barber, K.R., Tanquary, J., Bush, K., Shaw, A., Woodson, M., Sherman, M. and Wairkar, Y.P. (2017). Active zone proteins are transported via distinct mechanisms regulated by Par-1 kinase. PLoS Genet 13: e1006621. PubMed ID: 28222093
Disruption of synapses underlies a plethora of neurodevelopmental and neurodegenerative disease. Presynaptic specialization called the active zone plays a critical role in the communication with postsynaptic neuron. While the role of many proteins at the active zones in synaptic communication is relatively well studied, very little is known about how these proteins are transported to the synapses. For example, are there distinct mechanisms for the transport of active zone components or are they all transported in the same transport vesicle? Is active zone protein transport regulated? This study shows that overexpression of Par-1/MARK kinase, a protein whose misregulation has been implicated in Autism spectrum disorders (ASDs) and neurodegenerative disorders, lead to a specific block in the transport of an active zone protein component- Bruchpilot at Drosophila neuromuscular junctions. Consistent with a block in axonal transport, there is a decrease in number of active zones and reduced neurotransmission in flies overexpressing Par-1 kinase. Interestingly, Par-1 was found to act independently of Tau-one of the most well studied substrates of Par-1, revealing a presynaptic function for Par-1 that is independent of Tau. Thus, this study strongly suggests that there are distinct mechanisms that transport components of active zones and that they are tightly regulated.
Hegle, A. P., Frank, C. A., Berndt, A., Klose, M., Allan, D. W. and Accili, E. A. (2017). The Ih channel gene promotes synaptic transmission and coordinated movement in Drosophila melanogaster. Front Mol Neurosci 10: 41. PubMed ID: 28286469
Hyperpolarization-activated cyclic nucleotide-gated "HCN" channels, which underlie the hyperpolarization-activated current (Ih), have been proposed to play diverse roles in neurons. The presynaptic HCN channel is thought to both promote and inhibit neurotransmitter release from synapses, depending upon its interactions with other presynaptic ion channels. In larvae of Drosophila melanogaster, inhibition of the presynaptic HCN channel by the drug ZD7288 reduces the enhancement of neurotransmitter release at motor terminals by serotonin but this drug has no effect on basal neurotransmitter release, implying that the channel does not contribute to firing under basal conditions. This study shows that genetic disruption of the sole HCN gene (Ih) reduces the amplitude of the evoked response at the neuromuscular junction (NMJ) of third instar larvae by decreasing the number of released vesicles. The anatomy of the (NMJ) is not notably affected by disruption of the Ih gene. It is proposed that the presynaptic HCN channel is active under basal conditions and promotes neurotransmission at larval motor terminals. Finally, it was demonstrated that Ih partial loss-of-function mutant adult flies have impaired locomotion, and, thus, it is hypothesized that the presynaptic HCN channel at the (NMJ) may contribute to coordinated movement.
Devergne, O., Sun, G. H. and Schupbach, T. (2017). Stratum, a homolog of the human GEF Mss4, partnered with Rab8, controls the basal restriction of basement membrane proteins in epithelial cells. Cell Rep 18(8): 1831-1839. PubMed ID: 28228250
The basement membrane (BM), a sheet of extracellular matrix lining the basal side of epithelia, is essential for epithelial cell function and integrity, yet the mechanisms that control the basal restriction of BM proteins are poorly understood. In epithelial cells, a specialized pathway is dedicated to restrict the deposition of BM proteins basally. This study reports the identification of a factor in this pathway, a homolog of the mammalian guanine nucleotide exchange factor (GEF) Mss4, which is named Stratum (CG7787). The loss of Stratum leads to the missecretion of BM proteins at the apical side of the cells, forming aberrant layers in close contact with the plasma membrane. This study found that Rab8 GTPase acts downstream of Stratum in this process. Altogether, these results uncover the importance of this GEF/Rab complex in specifically coordinating the basal restriction of BM proteins, a critical process for the establishment and maintenance of epithelial cell polarity.
Kuintzle, R. C., Chow, E. S., Westby, T. N., Gvakharia, B. O., Giebultowicz, J. M. and Hendrix, D. A. (2017). Circadian deep sequencing reveals stress-response genes that adopt robust rhythmic expression during aging. Nat Commun 8: 14529. PubMed ID: 28221375
Disruption of the circadian clock, which directs rhythmic expression of numerous output genes, accelerates aging. To enquire how the circadian system protects aging organisms, compare circadian transcriptomes in heads of young and old Drosophila melanogaster were compared. The core clock and most output genes remained robustly rhythmic in old flies, while others lost rhythmicity with age, resulting in constitutive over- or under-expression. Unexpectedly, a subset of genes was identified that adopted increased or de novo rhythmicity during aging, enriched for stress-response functions. These genes, termed late-life cyclers, were also rhythmically induced in young flies by constant exposure to exogenous oxidative stress, and this upregulation is CLOCK-dependent. Age-onset rhythmicity was identified in several putative primary piRNA transcripts overlapping antisense transposons. These results suggest that, as organisms age, the circadian system shifts greater regulatory priority to the mitigation of accumulating cellular stress.

Tuesday, April 4th

Zhang, Y. V., Hannan, S. B., Kern, J. V., Stanchev, D. T., Koc, B., Jahn, T. R. and Rasse, T. M. (2017). The KIF1A homolog Unc-104 is important for spontaneous release, postsynaptic density maturation and perisynaptic scaffold organization. Sci Rep 7: 38172. PubMed ID: 28344334
The kinesin-3 family member KIF1A has been shown to be important for experience dependent neuroplasticity. In Drosophila, amorphic mutations in the KIF1A homolog unc-104 disrupt the formation of mature boutons. A hypomorphic mutation in the forkhead-associated domain of Unc-104, unc-104bris, impairs active zone maturation resulting in an increased fraction of post-synaptic glutamate receptor fields that lack the active zone scaffolding protein Bruchpilot. This study shows that the unc-104bris mutation causes defects in synaptic transmission as manifested by reduced amplitude of both evoked and miniature excitatory junctional potentials. Structural defects observed in the postsynaptic compartment of mutant NMJs include reduced glutamate receptor field size, and altered glutamate receptor composition. In addition, a marked loss was observed of postsynaptic scaffolding proteins and reduced complexity of the sub-synaptic reticulum, which could be rescued by pre- but not postsynaptic expression of unc-104. These results highlight the importance of kinesin-3 based axonal transport in synaptic transmission and provide novel insights into the role of Unc-104 in synapse maturation.
Kim, E. Z., Vienne, J., Rosbash, M. and Griffith, L. C. (2017). Non-reciprocal homeostatic compensation in Drosophila potassium channel mutants. J Neurophysiol: jn.00002.02017. PubMed ID: 28298298
Homeostatic control of intrinsic excitability is important for long-term regulation of neuronal activity. In conjunction with many other forms of plasticity, intrinsic homeostasis helps neurons maintain stable activity regimes in the face of external input variability and destabilizing genetic mutations. This study reports a mechanism by which Drosophila melanogaster larval motor neurons stabilize hyperactivity induced by the loss of the delayed rectifying K+ channel ShakerCognate B (Shab) , by upregulating the Ca2+-dependent K+ channel encoded by the slowpoke (slo) gene. Loss of SLO does not trigger a reciprocal compensatory upregulation of SHAB, implying that homeostatic signaling pathways utilize compensatory pathways unique to the channel that was mutated. SLO upregulation due to loss of SHAB involves nuclear Ca2+ signaling and dCREB, suggesting that the slowpoke homeostatic response is transcriptionally mediated. Examination of the changes in gene expression induced by these mutations suggests that there is not a generic transcriptional response to increased excitability in motor neurons, but that homeostatic compensations are influenced by the identity of the lost conductance.
Soukup, S. F. and Verstreken, P. (2017). EndoA/Endophilin-A creates docking stations for autophagic proteins at synapses. Autophagy: 1-2. PubMed ID: 28282269
Synapses are very specialized compartments with high metabolic demand to maintain neurotransmission, an essential step for basic brain function. Neurons are post-mitotic and synapses need to stay functional over time-sometimes over decades. Given that synapses are often at a long distance from the cell body, they must use local mechanisms to regulate protein quality control. This study shows that macroautophagy/autophagy is one of these local processes and found that it is under strict control of the synapse-enriched protein EndoA/Endophilin-A, previously only implicated in endocytosis. Metabolic and neuronal stimulation induce synaptic autophagy and phosphorylation of EndoA by the Parkinson disease kinase Lrrk/LRRK2 is essential to promote the process. EndoA induces membrane curvature in vitro, and, mechanistically, phosphorylated EndoA creates curved membrane-protein docking sites that are capable of recruiting Atg3. This work reveals a synapse-enriched branch of autophagy under the control of EndoA that may be deregulated in Parkinson disease.
Gramlich, M. W. and Klyachko, V. A. (2017). Actin/Myosin-V- and activity-dependent inter-synaptic vesicle exchange in central neurons. Cell Rep 18(9): 2096-2104. PubMed ID: 28249156
Evolutionary Homology Study:
Vesicle sharing between synaptic boutons is an important component of the recycling process that synapses employ to maintain vesicle pools. However, the mechanisms supporting and regulating vesicle transport during the inter-synaptic exchange remain poorly understood. Using nanometer-resolution tracking of individual synaptic vesicles and advanced computational algorithms, this study found that long-distance axonal transport of synaptic vesicles between hippocampal boutons is partially mediated by the actin network, with myosin V (see Drosophila Didum) as the primary actin-dependent motor that drives this vesicle transport. Furthermore, it was found that vesicle exit from the synapse to the axon and long-distance vesicle transport are both rapidly and dynamically regulated by activity. These findings were corroborated with two complementary modeling approaches of vesicle exit, which closely reproduced experimental observations. These findings uncover the roles of actin and myosin V in supporting the inter-synaptic vesicle exchange and reveal that this process is dynamically modulated in an activity-dependent manner.
Glebov, O. O., Jackson, R. E., Winterflood, C. M., Owen, D. M., Barker, E. A., Doherty, P., Ewers, H. and Burrone, J. (2017). Nanoscale Structural Plasticity of the Active Zone Matrix Modulates Presynaptic Function. Cell Rep 18(11): 2715-2728. PubMed ID: 28297674
Evolutionary Homology Study:
The active zone (AZ) matrix of presynaptic terminals coordinates the recruitment of voltage-gated calcium channels (VGCCs) and synaptic vesicles to orchestrate neurotransmitter release. However, the spatial organization of the AZ and how it controls vesicle fusion remain poorly understood. This study employed super-resolution microscopy and ratiometric imaging of hippocampal neurons to visualize the AZ structure on the nanoscale, revealing segregation between the AZ matrix, VGCCs, and putative release sites. Long-term blockade of neuronal activity leads to reversible AZ matrix unclustering and presynaptic actin depolymerization, allowing for enrichment of AZ machinery. Conversely, patterned optogenetic stimulation of postsynaptic neurons retrogradely enhanced AZ clustering. In individual synapses, AZ clustering was inversely correlated with local VGCC recruitment and vesicle cycling. Acute actin depolymerization led to rapid (5 min) nanoscale AZ matrix unclustering. A model whereby neuronal activity modulates presynaptic function in a homeostatic manner by altering the clustering state of the AZ matrix.
Molumby, M. J., Anderson, R. M., Newbold, D. J., Koblesky, N. K., Garrett, A. M., Schreiner, D., Radley, J. J. and Weiner, J. A. (2017). gamma-Protocadherins Interact with Neuroligin-1 and Negatively Regulate Dendritic Spine Morphogenesis. Cell Rep 18(11): 2702-2714. PubMed ID: 28297673
Evolutionary Homology Study:
The 22 γ-Protocadherin (γ-Pcdh) cell adhesion molecules are critical for the elaboration of complex dendritic arbors in the cerebral cortex. This study provides evidence that the γ-Pcdhs negatively regulate synapse development by inhibiting the postsynaptic cell adhesion molecule, neuroligin-1 (Nlg1; see Drosophila Neuroligin). Mice lacking all γ-Pcdhs in the forebrain exhibit significantly increased dendritic spine density in vivo, while spine density is significantly decreased in mice overexpressing one of the 22 γ-Pcdh isoforms. Co-expression of γ-Pcdhs inhibits the ability of Nlg1 to increase spine density and to induce presynaptic differentiation in hippocampal neurons in vitro. The γ-Pcdhs physically interact in cis with Nlg1 both in vitro and in vivo, and evidence is presented that this disrupts Nlg1 binding to its presynaptic partner neurexin1β (see Drosophila Neurexin-1). Together with prior work, these data identify a mechanism through which γ-Pcdhs could coordinate dendrite arbor growth and complexity with spine maturation in the developing brain.

Monday, April 3rd

Verd, B., Crombach, A. and Jaeger, J. (2017). Dynamic maternal gradients control timing and shift-rates for Drosophila gap gene expression. PLoS Comput Biol 13(2): e1005285. PubMed ID: 28158178
This study simulated dynamic morphogen interpretation by the gap gene network in Drosophila. Gap genes are activated by maternal morphogen gradients encoded by bicoid (bcd) and caudal (cad). These gradients decay at the same time-scale as the establishment of the antero-posterior gap gene pattern. This study used a reverse-engineering approach, based on data-driven regulatory models called gene circuits, to isolate and characterise the explicitly time-dependent effects of changing morphogen concentrations on gap gene regulation. To achieve this, the system was simulate in the presence and absence of dynamic gradient decay. Comparison between these simulations reveals that maternal morphogen decay controls the timing and limits the rate of gap gene expression. In the anterior of the embyro, it affects peak expression and leads to the establishment of smooth spatial boundaries between gap domains. In the posterior of the embryo, it causes a progressive slow-down in the rate of gap domain shifts, which is necessary to correctly position domain boundaries and to stabilise the spatial gap gene expression pattern. A newly developed method was used for the analysis of transient dynamics in non-autonomous (time-variable) systems to understand the regulatory causes of these effects. By providing a rigorous mechanistic explanation for the role of maternal gradient decay in gap gene regulation, this study demonstrates that such analyses are feasible and reveal important aspects of dynamic gene regulation which would have been missed by a traditional steady-state approach. More generally, it highlights the importance of transient dynamics for understanding complex regulatory processes in development.
Liu, Y., Sepich, D.S. and Solnica-Krezel, L. (2017). Stat3/Cdc25a-dependent cell proliferation promotes embryonic axis extension during zebrafish gastrulation. PLoS Genet 13: e1006564. PubMed ID: 28222105
Evolutionary Homolog Study:
Cell proliferation has generally been considered dispensable for anteroposterior extension of embryonic axis during vertebrate gastrulation. Signal transducer and activator of transcription 3 (Stat3) (see Drosophila Stat92E), a conserved controller of cell proliferation, survival and regeneration, is associated with human scoliosis, cancer and Hyper IgE Syndrome. Zebrafish Stat3 has been proposed to govern convergence and extension gastrulation movements in part by promoting Wnt/Planar Cell Polarity (PCP) signaling (see Drosophila wg), a conserved regulator of mediolaterally polarized cell behaviors. Using zebrafish stat3 null mutants and pharmacological tools, this study demonstrates that cell proliferation contributes to anteroposterior embryonic axis extension. Zebrafish embryos lacking maternal and zygotic Stat3 expression exhibit normal convergence movements and planar cell polarity signaling, but transient axis elongation defect due to insufficient number of cells resulting largely from reduced cell proliferation and increased apoptosis. Pharmacologic inhibition of cell proliferation during gastrulation phenocopies axis elongation defects. Stat3 regulates cell proliferation and axis extension in part via upregulation of Cdc25a (see Drosophila stg) expression during oogenesis. Accordingly, restoring Cdc25a expression in stat3 mutants partially suppresses cell proliferation and gastrulation defects. During later development, stat3 mutant zebrafish exhibit stunted growth, scoliosis, excessive inflammation, and fail to thrive, affording a genetic tool to study Stat3 function in vertebrate development, regeneration, and disease.
Combs, P. A. and Eisen, M. B. (2017) Genome-wide measurement of spatial expression in patterning mutants of Drosophila melanogaster. . F1000Res 6: 41. PubMed ID: 28299188
Patterning in the Drosophila melanogaster embryo is affected by multiple maternal factors, but the effect of these factors on spatial gene expression has not been systematically analyzed. This study characterized the effect of the maternal factors Zelda, Hunchback and Bicoid by cryosectioning wildtype and mutant blastoderm stage embryos and sequencing mRNA from each slice. The resulting atlas of spatial gene expression highlights the intersecting roles of these factors in regulating spatial patterns, and serves as a resource for researchers studying spatial patterning in the early embryo. A large number of genes was identified with both expected and unexpected patterning changes, and through integrated analysis of transcription factor binding data common themes were identified in genes with complex dependence on these transcription factors.
Chen, Y.J., Huang, J., Huang, L., Austin, E. and Hong, Y. (2017). Phosphorylation potential of Drosophila E-Cadherin intracellular domain is essential for development and regulating adherens junction biosynthetic dynamics. Development [Epub ahead of print]. PubMed ID: 28219985
E-Cadherin intracellular domain contains a highly conserved serine cluster whose phosphorylations are essential for binding to β-Catenin. phosphorylation of E-Cadherin regulates adherens junction (AJ) formation and dynamics. An extensive array of Drosophila E-Cadherin (DE-Cad) endogenous knock-in alleles were generated that carry mutations targeting this highly conserved serine cluster. Mutant analyses suggest that the overall phosphorylation potential of the serine cluster enhance the recruitment of β-Catenin by DE-Cad in vivo. Moreover, phosphorylation potential of the serine cluster only moderately increases β-Catenin in AJ and is in fact dispensable for AJ formation in vivo. Nonetheless, phosphorylation-dependent recruitment of β-Catenin is essential for development, likely by enhancing the interactions between DE-Cad and α-Catenin. Specific phospho-mutants also dramatically affect the biosynthetic turn-over of mutant DE-Cad during apical-basal polarization and specifically rescued the polarity defects in embryonic epithelia lacking polarity proteins Stardust and Crumbs.

Sunday, April 2nd

El-Sharnouby, S., Fischer, B., Magbanua, J. P., Umans, B., Flower, R., Choo, S. W., Russell, S. and White, R. (2017). Regions of very low H3K27me3 partition the Drosophila genome into topological domains. PLoS One 12(3): e0172725. PubMed ID: 28282436
It is now well established that eukaryote genomes have a common architectural organization into topologically associated domains (TADs) and evidence is accumulating that this organization plays an important role in gene regulation. However, the mechanisms that partition the genome into TADs and the nature of domain boundaries are still poorly understood. This study investigated boundary regions in the Drosophila genome and found that they can be identified as domains of very low H3K27me3. The genome-wide H3K27me3 profile partitions into two states; very low H3K27me3 identifies Depleted (D) domains that contain housekeeping genes and their regulators such as the histone acetyltransferase-containing nonspecific lethal (NSL) complex, whereas domains containing moderate-to-high levels of H3K27me3 (Enriched or E domains) are associated with regulated genes, irrespective of whether they are active or inactive. The D domains correlate with the boundaries of TADs and are enriched in a subset of architectural proteins, particularly Chromator, BEAF-32, and Z4/Putzig. However, rather than being clustered at the borders of these domains, these proteins bind throughout the H3K27me3-depleted regions and are much more strongly associated with the transcription start sites of housekeeping genes than with the H3K27me3 domain boundaries. While this study has not demonstrated causality, it is suggested that the D domain chromatin state, characterised by very low or absent H3K27me3 and established by housekeeping gene regulators, acts to separate topological domains thereby setting up the domain architecture of the genome.
Lo Piccolo, L., Attardi, A., Bonaccorso, R., Li Greci, L., Giurato, G., Ingrassia, A. M. and Onorati, M. C. (2017). ISWI ATP-dependent remodeling of nucleoplasmic omega-speckles in the brain of Drosophila melanogaster. J Genet Genomics 44(2): 85-94. PubMed ID: 28209301
Heterogeneous nuclear ribonucleoproteins (hnRNPs) belong to the RNA-binding proteins family. They are involved in processing heterogeneous nuclear RNAs (hnRNAs) into mature mRNAs. These proteins participate in every step of mRNA cycle, such as mRNA export, localization, translation, stability and alternative splicing. At least 14 major hnRNPs, which have structural and functional homologues in mammals, are expressed in Drosophila melanogaster. Until now, six of these hnRNPs are known to be nucleus-localized and associated with the long non-coding RNA (lncRNA) heat shock responsive omega (hsromega) in the omega speckle compartments (omega-speckles). The chromatin remodeler ISWI is the catalytic subunit of several ATP-dependent chromatin-remodeling complexes, and it is an essential factor for organization of omega-speckles. Indeed, in ISWI null mutant, severe defects in omega-speckles structure are detectable. This study clarifies the role of ISWI in the hnRNPs-hsromega interaction. Moreover, this study describes how ISWI by its remodeling activity, controls hsromega and hnRNPs engagement in omega-speckles. Finally, it was demonstrated that the sequestration of hnRNPs in omega-speckles nuclear compartment is a fundamental event in gene expression control and represents a key step in the regulation of several pathways.
Janssens, D. H., Hamm, D. C., Anhezini, L., Xiao, Q., Siller, K. H., Siegrist, S. E., Harrison, M. M. and Lee, C. Y. (2017). An Hdac1/Rpd3-poised circuit balances continual self-renewal and rapid restriction of developmental potential during asymmetric stem cell division. Dev Cell 40(4): 367-380.e367. PubMed ID: 28245922
earmuff (erm) uniquely functions to restrict the developmental potential of intermediate neural progenitors (INPs) generated by asymmetrically dividing neural stem cells (neuroblasts). This study demonstrates that the histone deacetylase Hdac1/Rpd3 functions together with self-renewal transcriptional repressors to maintain the erm immature INP enhancer in an inactive but poised state in neuroblasts. Within 2 hr of immature INP birth, downregulation of repressor activities alleviates Rpd3-mediated repression on the erm enhancer, enabling acetylation of multiple histone proteins and activating Erm expression. Erm restricts the developmental potential in immature INPs by repressing genes encoding neuroblast transcriptional activators. It. is proposed that poising the fast-activating enhancers of master regulators of differentiation through continual histone deacetylation in stem cells enables self-renewal and rapid restriction of developmental potential following asymmetric division.
Coleman, R. T. and Struhl, G. (2017). Causal role for inheritance of H3K27me3 in maintaining the OFF state of a Drosophila HOX gene. JScience [Epub ahead of print]. PubMed ID: 28302795
Many eukaryotic cells can respond to transient environmental or developmental stimuli with heritable changes in gene expression that are associated with nucleosome modifications. However, it remains uncertain whether modified nucleosomes play a causal role in transmitting such epigenetic memories, as opposed to controlling or merely reflecting transcriptional states inherited by other means. This study provides in vivo evidence that H3K27 trimethylated nucleosomes, once established at a repressed Drosophila HOX gene, remain heritably associated with that gene and can carry the memory of the silenced state through multiple rounds of replication, even when the capacity to copy the H3K27me3 mark to newly incorporated nucleosomes is diminished or abolished. Hence, in this context, the inheritance of H3K27 trimethylation conveys epigenetic memory.
Sen, P., Luo, J., Hada, A., Hailu, S. G., Dechassa, M. L., Persinger, J., Brahma, S., Paul, S., Ranish, J. and Bartholomew, B. (2017). Loss of Snf5 induces formation of an aberrant SWI/SNF complex. Cell Rep 18(9): 2135-2147. PubMed ID: 28249160
Evolutionary Homolog Study
The SWI/SNF chromatin remodeling complex is highly conserved from yeast to human, and aberrant SWI/SNF complexes contribute to human disease. The Snf5/SMARCB1/INI1 subunit of SWI/SNF is a tumor suppressor frequently lost in pediatric rhabdoid cancers. This study examined the effects of Snf5 (see Drosophila Snf5-related 1) loss on the composition, nucleosome binding, recruitment, and remodeling activities of yeast SWI/SNF. The Snf5 subunit is shown by crosslinking-mass spectrometry (CX-MS) and subunit deletion analysis to interact with the ATPase domain of Snf2 (see Drosophila Brahma) and to form a submodule consisting of Snf5, Swp82, and Taf14. Snf5 promotes binding of the Snf2 ATPase domain to nucleosomal DNA and enhances the catalytic and nucleosome remodeling activities of SWI/SNF. Snf5 is also required for SWI/SNF recruitment by acidic transcription factors. RNA-seq analysis suggests that both the recruitment and remodeling functions of Snf5 are required in vivo for SWI/SNF regulation of gene expression. Thus, loss of SNF5 alters the structure and function of SWI/SNF.
Dutta, A., Sardiu, M., Gogol, M., Gilmore, J., Zhang, D., Florens, L., Abmayr, S. M., Washburn, M. P. and Workman, J. L. (2017).. Composition and function of mutant Swi/Snf complexes. Cell Rep 18(9): 2124-2134. PubMed ID: 28249159
Evolutionary Homolog Study
The 12-subunit Swi/Snf chromatin remodeling complex is conserved from yeast to humans. It functions to alter nucleosome positions by either sliding nucleosomes on DNA or evicting histones. Interestingly, 20% of all human cancers carry mutations in subunits of the Swi/Snf complex. Many of these mutations cause protein instability and loss, resulting in partial Swi/Snf complexes. Although several studies have shown that histone acetylation and activator-dependent recruitment of Swi/Snf regulate its function, it is less well understood how subunits regulate stability and function of the complex. Using functional proteomic and genomic approaches, this study has assembled the network architecture of yeast Swi/Snf. In addition, it was found that subunits of the Swi/Snf complex regulate occupancy of the catalytic subunit Snf2 (see Drosophila Brahma), thereby modulating gene transcription. These findings have direct bearing on how cancer-causing mutations in orthologous subunits of human Swi/Snf may lead to aberrant regulation of gene expression by this complex.

Saturday, April 1st

Misra, S., Pandey, A. K., Gupta, S., Kumar, A., Khanna, P., Shankar, J. and Ravi Ram, K. (2017). Estrogen related receptor is required for the testicular development and for the normal sperm axoneme/mitochondrial derivatives in Drosophila males. Sci Rep 7: 40372. PubMed ID: 28094344
Estrogen related receptors (ERRs), categorized as orphan nuclear receptors, are critical for energy homeostasis and somatic development. However, significance of ERRs in the development of reproductive organs/organelles/cells remain poorly understood, albeit their homology to estrogen receptors. In this context, this study shows that knockdown of ERR in the testes leads to improperly developed testes with mis-regulation of genes (aly, mia, bruce, bam, bgcn, fzo and eya) involved in spermatogenesis, resulting in reduced male fertility. The observed testicular deformity is consistent with the down-regulation of SOX-E group of gene (SOX100B) in Drosophila. Dispersion/disintegration of fusomes (microtubule based structures associated with endoplasmic reticulum derived vesicle, interconnecting spermatocytes) was demonstrated in ERR knockdown testes. A few ERR knockdown testes go through spermatogenesis but have significantly fewer sperm. Moreover, flagella of these sperm are defective with abnormal axoneme and severely reduced mitochondrial derivatives, suggesting a possible role for ERR in mitochondrial biogenesis, analogous to mammalian ERRalpha. Interestingly, similar knockdown of remaining seventeen nuclear receptors did not yield a detectable reproductive or developmental defect in Drosophila. These findings add newer dimensions to the functions envisaged for ERR and provide the foundation for deciphering the relevance of orphan nuclear receptors in ciliopathies and testicular dysgenesis.
Shen, W. and Sun, J. (2017). Dynamic Notch signaling specifies each cell fate in Drosophila spermathecal lineage. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 28258114
Spermathecae are glandular organs in insect female reproductive tract and play essential roles for insect reproduction; however, the molecular mechanism involved in their development is largely unknown. Drosophila spermathecae consist of class-III secretory units, in which each secretory cell discharges its products to the central lumen through an end-apparatus and a canal. Secretory unit formation in Drosophila spermathecae utilizes a fixed cell lineage, in which each secretory unit precursor (SUP) divides to produce one pIIb cell and one pIIa cell. The former differentiates into an apical cell (AC), whereas the latter divides again to produce a secretory cell (SC) and a basal cell (BC). It is unclear how each cell acquires its identity and contributes to secretory unit formation. This study demonstrates that Notch signaling is required and sufficient for the specification of lumen epithelial precursors (LEPs; vs. SUPs), pIIb (vs. pIIa), and SCs (vs. BCs) sequentially. Notch activation in LEPs and SCs apparently utilizes different ligand mechanism. In addition, Notch signaling both suppresses and activates transcription factors Hindsight (Hnt) and Cut during spermathecal lineage specification, supporting the notion that Notch signaling can have opposite biological outcomes in different cellular environment. Furthermore, LEP-derived epithelial cells (ECs) and ACs show distinct cellular morphology and are essential for securing secretory units to the epithelial lumen. These data demonstrate for the first time the dynamic role of Notch signaling in binary cell fate determination in Drosophila spermathecae and the role of ECs and ACs in secretory unit formation.

Deshpande, G., Barr, J., Gerlitz, O., Lebedeva, L., Shidlovskii, Y. and Schedl, P. (2017). Cells on the move: Modulation of guidance cues during germ cell migration. Fly (Austin): [Epub ahead of print] PubMed ID: 28300473
In Drosophila melanogaster the progenitors of the germ-line stem cells, the primordial germ cells (PGCs) are formed on the outside surface of the early embryo, while the somatic gonadal precursor cells (SGPs) are specified during mid-embryogenesis. To form the primitive embryonic gonad, the PGCs travel from outside of the embryo, across the mid-gut and then migrate through the mesoderm to the SGPs. The migratory path of PGCs is dictated by a series of attractive and repulsive cues. Studies have shown that one of the key chemoattractants is the Hedgehog (Hh) ligand. Although, Hh is expressed in other cell types, the long-distance transmission of this ligand is specifically potentiated in the SGPs by the hmgcr isoprenoid biosynthetic pathway. The distant transmission of the Hh ligand is gated by restricting expression of hmgcr to the SGPs. This is particularly relevant in light of the recent findings that an ABC transporter, mdr49 also acts in a mesoderm specific manner to release the germ cell attractant. These studies have demonstrated that mdr49 functions in hh signaling likely via its role in the transport of cholesterol. Given the importance of cholesterol in the processing and long distance transmission of the Hh ligand, this observation has opened up an exciting avenue concerning the possible role of components of the sterol transport machinery in PGC migration.
Liu, T., Wang, Q., Li, W., Mao, F., Yue, S., Liu, S., Liu, X., Xiao, S. and Xia, L. (2017). Gcn5 determines the fate of Drosophila germline stem cells through degradation of Cyclin A. FASEB J [Epub ahead of print]. PubMed ID: 28188175
The fluctuating CDK-CYCLIN complex plays a general role in cell-cycle control. Many types of stem cells use unique features of the cell cycle to facilitate asymmetric division. However, the manner in which these features are established remains poorly understood. The cell cycle of Drosophila female germline stem cells (GSCs) is characterized by short G1 and very long G2 phases, making it an excellent model for the study of cell cycle control in stem cell fate determination. Using a Drosophila female GSCs model, this study found Gcn5, the first discovered histone acetyltransferase, to maintain germline stem cells in Drosophila ovaries. Gcn5 is dispensable for the transcriptional silencing of bam, but interacts with Cyclin A to facilitate proper turnover in GSCs. Gcn5 promotes Cyclin A ubiquitination, which is dependent on its acetylating activity. Finally, knockdown of Cyclin A rescues the GSC-loss phenotype caused by lack of Gcn5. Collectively, these findings support the conclusion that Gcn5 acts through acetylation to facilitate Cyclin A ubiquitination and proper turnover, thereby determining the fate of GSCs.
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