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





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Wednesday, May 31st

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Zimmerman, J. E., Chan, M. T., Lenz, O. T., Keenan, B. T., Maislin, G. and Pack, A. I. (2017). Glutamate is a wake-active neurotransmitter in Drosophila melanogaster. Sleep 40(2) [Epub ahead of print]. PubMed ID: 28364503
Summary:
In mammals, there is evidence that glutamate has a role as a wake-active neurotransmitter. So using video-based analysis of Drosophila behavior, a study was undertaken to examine if glutamate, which has been previously shown to have an excitatory role in neuromuscular junctions in Drosophila, may have a conserved wake-active role in the adult brain. Using 6- to 9-day-old female flies, the effect was examined of perturbations of the glutamatergic signaling on total wakefulness and wake bout architecture. Neuronal activity of glutamatergic neurons in the brains of adult flies was increased or decreased using Upstream Activating Sequence (UAS) NaChBac (a voltage-gated bacterial Na+ channel) and UAS EKO ('electrical knockout channel'), respectively. Neurotransmission was blocked from glutamatergic neurons in adult flies using the UAS-driven temperature-sensitive dynamin mutation shibirets. The behavior of flies was examined with loss of function mutations of individual subunits of brain-specific ionotropic glutamate receptors. Increasing the activity of glutamatergic neurons in the adult brain led to a significant increase in wakefulness compared to the control groups both in the daytime and nighttime and decreasing the activity of these same neurons reduced wakefulness in the nighttime. Blocking neurotransmitter release in glutamatergic neurons significantly reduced wake in the nighttime. The ionotropic receptor mutants had significantly less wake in the nighttime than their respective genetic background controls. The results show the following: glutamate is indeed a wake-active neurotransmitter in Drosophila; there is a major time of day effect associated with loss of glutamatergic neurotransmission; and it is a major wake-active neurotransmitter in the nighttime.
Schultzhaus, J. N. and Carney, G. E. (2017). Dietary protein content alters both male and female contributions to Drosophila melanogaster female post-mating response traits. J Insect Physiol [Epub ahead of print]. PubMed ID: 28414060
Summary:
Males transfer sperm, proteins and other molecules to females during mating. In Drosophila melanogaster, these molecules contribute to the induction of egg maturation, ovulation, oviposition, sperm storage and changes in female receptivity. This suite of physiological and behavioral changes is referred to as the female post-mating response (PMR). Protein is a necessary macronutrient for both male and female reproduction, but imbalances in protein content can decrease reproductive potential. Dietary protein affects the production of proteins in the male ejaculate that are important for induction of the PMR, and female fecundity increases with dietary protein while lifetime mating rate decreases. The effects of dietary protein levels on other aspects of the female PMR and on male ability to induce the PMR are unknown. To investigate how protein content affects PMR, flies were raised on diets containing low, moderate or high levels of protein and mated females and males from each diet in a combinatorial manner. The mating duration for each pair, an indication of male reproductive investment, was measured, and then two aspects of the female PMR were evaluated, fecundity and female remating latency. Mating duration was negatively correlated with male dietary protein, and females that mated with high protein males laid fewer eggs. Female diet had no effect on mating duration, but females fed diets with higher protein content laid more eggs and remated sooner. Therefore, dietary protein levels can affect postcopulatory processes important for reproductive output in a sexually dimorphic manner.
Younus, F., Fraser, N. J., Coppin, C. W., Liu, J. W., Correy, G. J., Chertemps, T., Pandey, G., Maibeche, M., Jackson, C. J. and Oakeshott, J. G. (2017). Molecular basis for the behavioral effects of the odorant degrading enzyme Esterase 6 in Drosophila. Sci Rep 7: 46188. PubMed ID: 28393888
Summary:
Previous electrophysiological and behavioural studies implicate Esterase 6 in the processing of the pheromone cis-vaccenyl acetate and various food odorants that affect aggregation and reproductive behaviours. This study shows that Esterase 6 has relatively high activity against many of the short-mid chain food esters, but negligible activity against cis-vaccenyl acetate. The crystal structure of Esterase 6 confirms its substrate-binding site can accommodate many short-mid chain food esters but not cis-vaccenyl acetate. Immunohistochemical assays show Esterase 6 is expressed in non-neuronal cells in the third antennal segment that could be accessory or epidermal cells surrounding numerous olfactory sensilla, including basiconics involved in food odorant detection. Esterase 6 is also produced in trichoid sensilla, but not in the same cell types as the cis-vaccenyl acetate binding protein LUSH. The data support a model in which esterase 6 acts as a direct odorant degrading enzyme for many bioactive food esters, but not cis-vaccenyl acetate.
Roland, B., Deneux, T., Franks, K. M., Bathellier, B. and Fleischmann, A. (2017). Odor identity coding by distributed ensembles of neurons in the mouse olfactory cortex. Elife 6. PubMed ID: 28489003 Evolutionary Homolog Study:
Olfactory perception and behaviors critically depend on the ability to identify an odor across a wide range of concentrations. This study used calcium imaging to determine how odor identity is encoded in olfactory cortex. Despite considerable trial-to-trial variability, odor identity can accurately be decoded from ensembles of co-active neurons that are distributed across piriform cortex without any apparent spatial organization. However, piriform response patterns change substantially over a 100-fold change in odor concentration, apparently degrading the population representation of odor identity. This problem can be resolved by decoding odor identity from a subpopulation of concentration-invariant piriform neurons. These concentration-invariant neurons are overrepresented in piriform cortex but not in olfactory bulb mitral and tufted cells. It is therefore proposed that distinct perceptual features of odors are encoded in independent subnetworks of neurons in the olfactory cortex.

Tuesday, May 30

Syed, M. H., Mark, B. and Doe, C. Q. (2017). Steroid hormone induction of temporal gene expression in Drosophila brain neuroblasts generates neuronal and glial diversity. Elife 6 [Epub ahead of print]. PubMed ID: 28394252
Summary:
An important question in neuroscience is how stem cells generate neuronal diversity. During Drosophila embryonic development, neural stem cells (neuroblasts) sequentially express transcription factors that generate neuronal diversity; regulation of the embryonic temporal transcription factor cascade is lineage-intrinsic. In contrast, larval neuroblasts generate longer ~50 division lineages, and currently only one mid-larval molecular transition is known: Chinmo/Imp/Lin-28+ neuroblasts transition to Syncrip+ neuroblasts. This study shows that the hormone ecdysone is required to down-regulate Chinmo/Imp and activate Syncrip, plus two late neuroblast factors, Broad and E93. Seven-up triggers Chinmo/Imp to Syncrip/Broad/E93 transition by inducing expression of the Ecdysone receptor in mid-larval neuroblasts, rendering them competent to respond to the systemic hormone ecdysone. Importantly, late temporal gene expression is essential for proper neuronal and glial cell type specification. This is the first example of hormonal regulation of temporal factor expression in Drosophila embryonic or larval neural progenitors.
Subramanian, A., et al. (2017). Remodeling of peripheral nerve ensheathment during the larval-to-adult transition in Drosophila. Dev Neurobiol [Epub ahead of print]. PubMed ID: 28388016
Summary:
Over the course of a four-day period of metamorphosis, the Drosophila larval nervous system is remodeled. In peripheral nerves in the abdomen, five pairs of abdominal nerves (A4-A8) fuse to form the terminal nerve trunk. This reorganization is associated with selective remodeling of four layers that ensheath each peripheral nerve. The neural lamella (NL), is the first to dismantle; its breakdown is initiated by 6 hours after puparium formation, and is completely removed by the end of the first day. This layer begins to re-appear on the third day of metamorphosis. Perineurial Glial (PG) cells situated just underneath the NL, undergo significant proliferation on the first day of metamorphosis, and at that stage contribute to 95% of the glial cell population. Cells of the two inner layers, Sub-Perineurial Glia (SPG) and Wrapping Glia (WG) increase in number on the second half of metamorphosis. Induction of cell death in perineurial glia via the cell death gene reaper and the Diptheria toxin (DT-1) gene, results in abnormal bundling of the peripheral nerves, suggesting that perineurial glial cells play a role in the process. A significant number of animals fail to eclose in both reaper and DT-1 targeted animals, suggesting that disruption of PG also impacts eclosion behavior. These studies will help establish the groundwork for further work on cellular and molecular processes that underlie the co-ordinated remodeling of glia and the peripheral nerves they ensheath.
Strother, J. A., Wu, S. T., Wong, A. M., Nern, A., Rogers, E. M., Le, J. Q., Rubin, G. M. and Reiser, M. B. (2017). The emergence of directional selectivity in the visual motion pathway of Drosophila. Neuron 94(1): 168-182.e110. PubMed ID: 28384470
Summary:
The perception of visual motion is critical for animal navigation, and flies are a prominent model system for exploring this neural computation. In Drosophila, the T4 cells of the medulla are directionally selective and necessary for ON motion behavioral responses. To examine the emergence of directional selectivity, genetic driver lines were developed for the neuron types with the most synapses onto T4 cells. Using calcium imaging, it was found that these neuron types are not directionally selective and that selectivity arises in the T4 dendrites. By silencing each input neuron type, which neurons are necessary for T4 directional selectivity and ON motion behavioral responses were identified. Tthe sign of the connections between these neurons and T4 cells were determined using neuronal photoactivation. These results indicate a computational architecture for motion detection that is a hybrid of classic theoretical models.
Ueoka, Y., Hiroi, M., Abe, T. and Tabata, T. (2017). Suppression of a single pair of mushroom body output neurons in Drosophila triggers aversive associations. FEBS Open Bio 7(4): 562-576. PubMed ID: 28396840
Summary:
Memory includes the processes of acquisition, consolidation and retrieval. In the study of aversive olfactory memory in Drosophila melanogaster, flies are first exposed to an odor (conditioned stimulus, CS+) that is associated with an electric shock (unconditioned stimulus, US), then to another odor (CS-) without the US, before allowing the flies to choose to avoid one of the two odors. The center for memory formation is the mushroom body which consists of Kenyon cells (KCs), dopaminergic neurons (DANs) and mushroom body output neurons (MBONs). However, the roles of individual neurons are not fully understood. This study focused on the role of a single pair of GABAergic neurons (MBON-gamma1pedc) and found that it could inhibit the effects of DANs, resulting in the suppression of aversive memory acquisition during the CS- odor presentation, but not during the CS+ odor presentation. It is proposed that MBON-gamma1pedc suppresses the DAN-dependent effect that can convey the aversive US during the CS- odor presentation, and thereby prevents an insignificant stimulus from becoming an aversive US.

Monday, May 29th

Simoes, S., Oh, Y., Wang, M. F., Fernandez-Gonzalez, R. and Tepass, U. (2017). Myosin II promotes the anisotropic loss of the apical domain during Drosophila neuroblast ingression. J Cell Biol [Epub ahead of print]. PubMed ID: 28363972
Summary:
Epithelial-mesenchymal transitions play key roles in development and cancer and entail the loss of epithelial polarity and cell adhesion. This study used quantitative live imaging of ingressing neuroblasts (NBs) in Drosophila melanogaster embryos to assess apical domain loss and junctional disassembly. Ingression is independent of the Snail family of transcriptional repressors and down-regulation of Drosophila E-cadherin (DEcad) transcription. Instead, the posttranscriptionally regulated decrease in DEcad coincides with the reduction of cell contact length and depends on tension anisotropy between NBs and their neighbors. A major driver of apical constriction and junctional disassembly are periodic pulses of junctional and medial myosin II that result in progressively stronger cortical contractions during ingression. Effective contractions require the molecular coupling between myosin and junctions and apical relaxation of neighboring cells. Moreover, planar polarization of myosin leads to the loss of anterior-posterior junctions before the loss of dorsal-ventral junctions. It is concluded that planar-polarized dynamic actomyosin networks drive apical constriction and the anisotropic loss of cell contacts during NB ingression.
Eritano, A. S., Altamirano, A., Beyeler, S., Gaytan, N., Velasquez, M. and Riggs, B. (2017). The endoplasmic reticulum is partitioned asymmetrically during mitosis prior to cell fate selection in proneuronal cells in the early Drosophila embryo. Mol Biol Cell [Epub ahead of print]. PubMed ID: 28381427
Summary:
Asymmetric cell division is the primary mechanism to generate cellular diversity and relies on the correct partitioning of cell fate determinants. However, the mechanism by which these determinants are delivered and positioned is poorly understood and the upstream signal to initiate asymmetric cell division is currently unknown. This study reports that the Endoplasmic Reticulum (ER) is asymmetrically partitioned during mitosis in epithelial cells just prior to delamination and selection of a proneural cell fate in the early Drosophila embryo. At the start of gastrulation, the ER divides asymmetrically in a population of asynchronously dividing cells at the anterior end of the embryo. This asymmetric division of the ER is dependent on the highly conserved ER membrane protein Jagunal (Jagn). RNA inhibition of jagn, just prior to the start of gastrulation, disrupts this asymmetric division of the ER. In addition, jagn deficient embryos display defects in apical-basal spindle orientation in delaminated embryonic neuroblasts (NB). The results presented in this study describe a striking model in which an organelle is partitioned asymmetrically in an otherwise symmetrically dividing cell population just upstream of cell fate determination, and updates previous models of spindle-based selection of cell fate during mitosis.
Perez-Mockus, G., Roca, V., Mazouni, K. and Schweisguth, F. (2017). Neuralized regulates Crumbs endocytosis and epithelium morphogenesis via specific Stardust isoforms. J Cell Biol 216(5):1405-1420. PubMed ID: 28400441
Summary:
Crumbs (Crb) is a conserved determinant of apical membrane identity that regulates epithelial morphogenesis in many developmental contexts. This study identifoed the Crb complex protein Stardust (Sdt) as a target of the E3 ubiquitin ligase Neuralized (Neur) in Drosophila melanogaster. Neur interacts with and down-regulates specific Sdt isoforms containing a Neur binding motif (NBM). Using a CRISPR (clustered regularly interspaced short palindromic repeats)-induced deletion of the NBM-encoding exon, it was found that Sdt is a key Neur target and that Neur acts via Sdt to down-regulate Crb. It was further shown that Neur promotes the endocytosis of Crb via the NBM-containing isoforms of Sdt. Although the regulation of Crb by Neur is not strictly essential, it contributes to epithelium remodeling in the posterior midgut and thereby facilitates the trans-epithelial migration of the primordial germ cells in early embryos. Thus, this study uncovers a novel regulatory mechanism for the developmental control of Crb-mediated morphogenesis.
Corson, F., Couturier, L., Rouault, H., Mazouni, K. and Schweisguth, F. (2017). Self-organized Notch dynamics generate stereotyped sensory organ patterns in Drosophila. Science [Epub ahead of print]. PubMed ID: 28386027
Summary:
The emergence of spatial patterns in developing multicellular organisms relies on positional cues and cell-cell communication. Drosophila sensory organs have informed a paradigm where these operate in two distinct steps: prepattern factors drive localized proneural activity, then Notch-mediated lateral inhibition singles out neural precursors. This study shows that self-organization through Notch signaling also organizes the proneural stripes that resolve into rows of sensory bristles on the fly thorax. Patterning, initiated by a gradient of Delta ligand expression, progresses through inhibitory signaling between and within stripes. Thus Notch signaling can support self-organized tissue patterning as a prepattern is transduced by cell-cell interactions into a refined arrangement of cellular fates.

Sunday, May 28th

Sellin, J., et al. (2017). Characterization of Drosophila saposin-related mutants as a model for lysosomal sphingolipid storage diseases. Dis Model Mech [Epub ahead of print]. PubMed ID: 28389479
Summary:
Sphingolipidoses are inherited diseases belonging to the class of lysosomal storage diseases (LSDs), which are characterized by the accumulation of indigestible material in the lysosome caused by specific defects in the lysosomal degradation machinery. The digestion of intra-lumenal membranes within lysosomes is facilitated by lysosomal sphingolipid activator proteins (saposins), which are cleaved from a Prosaposin precursor. prosaposin mutations cause some of the severest forms of sphingolipidoses, and are associated with perinatal lethality in mice, hampering studies on disease progression.This study identified the Drosophila Prosaposin orthologue Saposin-related (Sap-r) as a key regulator of lysosomal lipid homeostasis in the fly. Its mutation leads to a typical spingolipidosis phenotype with enlarged endo-lysosomal compartment and sphingolipid accumulation as shown by mass spectrometry and thin layer chromatography. sap-r mutants show reduced viability with approximately 50% adult survivors, allowing study of progressive neurodegeneration and analysis thelipid profile in young and aged flies. Additionally, a defect was observed in sterol homeostasis with local sterol depletion at the plasma membrane. Furthermore, autophagy was found to be increased, resulting in the accumulation of mitochondria in lysosomes, concomitant with increased oxidative stress. Together, this study establishes Drosophila sap-r mutants as a lysosomal storage disease model suitable for studying the age-dependent progression of lysosomal dysfunction associated with lipid accumulation and the resulting pathological signaling events.
Singh, S. K., Srivastav, S., Yadav, A. K. and Srikrishna, S. (2017). Knockdown of APPL mimics transgenic Abeta induced neurodegenerative phenotypes in Drosophila. Neurosci Lett 648: 8-13. PubMed ID: 28336338
Summary:
A variety of Drosophila mutant lines have been established as potential disease-models to study various disease mechanisms including human neurodegenerative diseases like Alzheimer's disease (AD), Huntington's disease (HD) and Parkinson's disease (PD). The evolutionary conservation of APP (Amyloid Precursor Protein) and APPL (Amyloid Precursor Protein-Like) and the comparable detrimental effects caused by their metabolic products strongly implies the conservation of their normal physiological functions. In view of this milieu, a comparative analysis on the pattern of neurodegenerative phenotypes between Drosophila APPL-RNAi line and transgenic Drosophila line expressing eye tissue specific human Aβ (Amyloid β) was undertaken. The results clearly show that Drosophila APPL-RNAi largely mimics transgenic Abeta in various phenotypes which include eye degeneration, reduced longevity and motor neuron deficit functions, etc. The ultra-structural morphological pattern of eye degeneration was confirmed by scanning electron microscopy. Further, a comparative study on longevity and motor behaviour between Abeta expressing and APPL knockdown lines revealed similar kind of behavioural deficit and longevity phenotypes. Therefore, it is suggested that APPL-knockdown can be used as an alternative approach to study neurodegenerative diseases in the fly model. This is the first report showing comparable phenotypes between APPL and Abeta in AD model of Drosophila.
Zhang, X., Wang, W.A., Jiang, L.X., Liu, H.Y., Zhang, B.Z., Lim, N., Li, Q.Y. and Huang, F.D. (2017). Down-regulation of RBO-PI4KIIIα facilitates Aβ42 secretion and ameliorates neural deficits in Aβ42-expressing Drosophila. J Neurosci [Epub ahead of print]. PubMed ID: 28424219
Summary:
Phosphoinositides and their metabolizing enzymes are involved in Aβ42 metabolism and Alzheimer's disease (AD) pathogenesis. In yeast and mammals, Eighty-five requiring 3 (EFR3), whose Drosophila homolog is Rolling Blackout (RBO), forms a plasma membrane-localized protein complex with phosphatidylinositol-4-kinase type IIIα (PI4KIIIα) and a scaffold protein to tightly control the level of plasmalemmal phosphatidylinositol-4-phosphate (PI4P). This study reports that RBO binds to Drosophila PI4KIIIα, and that in an Aβ42-expressing Drosophila model, separate genetic reduction of PI4KIIIα and RBO, or pharmacological inhibition of PI4KIIIα ameliorates synaptic transmission deficit, climbing ability decline, and premature death, and reduces neuronal accumulation of Aβ42. Moreover, RBO-PI4KIIIa downregulation increases neuronal Aβ42 release, and PI4P facilitates the assembly or oligomerization of Aβ42 in/on liposomes. These results indicate that RBO-PI4KIIIa downregulation facilitates neuronal Aβ42 release and consequently reduces neuronal Aβ42 accumulation likely via decreasing Aβ42 assembly in/on plasma membrane. This study suggests the RBO-PI4KIIIα complex as a potential therapeutic target and PI4KIIIα inhibitors as drug candidates for AD treatment.

Ng, C. H., Basil, A. H., Hang, L., Tan, R., Goh, K. L., O'Neill, S., Zhang, X., Yu, F. and Lim, K. L. (2017). Genetic or pharmacological activation of the Drosophila PGC-1alpha ortholog spargel rescues the disease phenotypes of genetic models of Parkinson's disease. Neurobiol Aging 55: 33-37. PubMed ID: 28407521
Summary:
Despite intensive research, the etiology of Parkinson's disease (PD) remains poorly understood and the disease remains incurable. However, compelling evidence gathered over decades of research strongly support a role for mitochondrial dysfunction in PD pathogenesis. Related to this, PGC-1&alpha, a key regulator of mitochondrial biogenesis, has recently been proposed to be an attractive target for intervention in PD. This study shows that silencing of expression of the Drosophila PGC-1α ortholog spargel results in PD-related phenotypes in flies and also seems to negate the effects of AMPK activation, which has been previously demonstrated to be neuroprotective; that is, AMPK-mediated neuroprotection appears to require PGC-1alpha. Importantly, this study further showed that genetic or pharmacological activation of the Drosophila PGC-1alpha ortholog spargel is sufficient to rescue the disease phenotypes of Parkin and LRRK2 genetic fly models of PD, thus supporting the proposed use of PGC-1alpha-related strategies for neuroprotection in PD.
Raj, K. and Sarkar, S. (2017). Transactivation domain of human c-Myc Is essential to alleviate poly(Q)-mediated neurotoxicity in Drosophila disease models. J Mol Neurosci 62(1):55-66. PubMed ID: 28316031
Evolutionary Homolog Study
Polyglutamine (poly(Q)) disorders, such as Huntington's disease (HD) and spinocerebellar ataxias, represent a group of neurological disorders which arise due to an atypically expanded poly(Q) tract in the coding region of the affected gene. Pathogenesis of these disorders inside the cells begins with the assembly of these mutant proteins in the form of insoluble inclusion bodies (IBs), which progressively sequester several vital cellular transcription factors and other essential proteins, and finally leads to neuronal dysfunction and apoptosis. Earlier studies have shown that targeted upregulation of Drosophila myc (dmyc) dominantly suppresses the poly(Q) toxicity in Drosophila. The present study examines the ability of the human c-myc proto-oncogene and also identifies the specific c-Myc isoform which drives the mitigation of poly(Q)-mediated neurotoxicity, so that it could be further substantiated as a potential drug target. This study reports that similar to dmyc, tissue-specific induced expression of human c-myc also suppresses poly(Q)-mediated neurotoxicity by an analogous mechanism. Among the three isoforms of c-Myc, the rescue potential was maximally manifested by the full-length c-Myc2 protein, followed by c-Myc1, but not by c-MycS which lacks the transactivation domain. This study suggests that strategies focussing on the transactivation domain of c-Myc could be a very useful approach to design novel drug molecules against poly(Q) disorders.
Wu, C. H., Giampetruzzi, A., Tran, H., Fallini, C., Gao, F. B. and Landers, J. E. (2017). A Drosophila model of ALS reveals a partial loss of function of causative human PFN1 mutants. Hum Mol Genet. PubMed ID: 28379367
Summary:
Mutations in the profilin 1 (PFN1) gene are causative for familial amyotrophic lateral sclerosis (fALS). However, it is still not fully understood how these mutations lead to neurodegeneration. To address this question, a novel Drosophila model was generated expressing human wild-type and ALS-causative PFN1 mutants. At larval neuromuscular junctions (NMJ), motor neuron expression of wild-type human PFN1 increases the number of ghost boutons, active zone density, F-actin content, and the formation of filopodia. In contrast, the expression of ALS-causative human PFN1 mutants causes a less pronounced phenotype, suggesting a loss of function of these mutants in promoting NMJ remodeling. Importantly, expression of human PFN1 in motor neurons results in progressive locomotion defects and shorter lifespan in adult flies, while ALS-causative PFN1 mutants display a less toxic effect. In summary, this study provides evidence that PFN1 is important in regulating NMJ morphology and influences survival and locomotion in Drosophila. Furthermore, the results suggest ALS-causative human PFN1 mutants display a partial loss-of-function relative to wild-type hPFN1 that may contribute to human disease pathogenesis.

Saturday, May 27th

Yu, Z., O'Farrell, P. H., Yakubovich, N. and DeLuca, S. Z. (2017). The Mitochondrial DNA Polymerase Promotes Elimination of Paternal Mitochondrial Genomes. Curr Biol 27(7): 1033-1039. PubMed ID: 28318978
Summary:
Mitochondrial DNA (mtDNA) is typically inherited from only one parent. In animals, this is usually the mother. Active programs enforce uniparental inheritance at two levels, eliminating paternal mitochondrial genomes or destroying mitochondria delivered to the zygote by the sperm. Both levels operate in Drosophila. As sperm formation begins, hundreds of doomed mitochondrial genomes are visualized within the two huge mitochondria of each spermatid. These genomes abruptly disappear during spermatogenesis. Genome elimination, which is not in the interests of the restricted genomes, is directed by nuclear genes. Mutation of EndoG, which encodes a mitochondria-targeted endonuclease, retarded elimination. This study shows that knockdown of the nuclear-encoded mtDNA polymerase (Pol gamma-alpha), Tamas, produces a more complete block of mtDNA elimination. Tamas is found in large particles that localize to mtDNA during genome elimination. A simple possible mechanism was discounted by showing that the 3'-exonuclease function of the polymerase is not needed. While DNA elimination is a surprising function for DNA polymerase, it could provide a robust nexus for nuclear control of mitochondrial genome copy number, since use of common interactions for elimination and replication might limit options for the mitochondrial genome to escape restriction. It is suggested that the DNA polymerase may play this role more widely and that inappropriate activation of its elimination ability might underlie association of DNA loss syndromes with mutations of the human mtDNA polymerase.
Sawyer, E. M., Brunner, E. C., Hwang, Y., Ivey, L. E., Brown, O., Bannon, M., Akrobetu, D., Sheaffer, K. E., Morgan, O., Field, C. O., Suresh, N., Gordon, M. G., Gunnell, E. T., Regruto, L. A., Wood, C. G., Fuller, M. T. and Hales, K. G. (2017). Testis-specific ATP synthase peripheral stalk subunits required for tissue-specific mitochondrial morphogenesis in Drosophila. BMC Cell Biol 18(1): 16. PubMed ID: 28335714
Summary:
In Drosophila early post-meiotic spermatids, mitochondria undergo dramatic shaping into the Nebenkern, a spherical body with complex internal structure that contains two interwrapped giant mitochondrial derivatives. The purpose of this study was to elucidate genetic and molecular mechanisms underlying the shaping of this structure. The knotted onions (knon) gene encodes an unconventionally large testis-specific paralog of ATP synthase subunit d and is required for internal structure of the Nebenkern as well as its subsequent disassembly and elongation. Knon localizes to spermatid mitochondria and, when exogenously expressed in flight muscle, alters the ratio of ATP synthase complex dimers to monomers. By RNAi knockdown mitochondrial shaping roles were uncovered for other testis-expressed ATP synthase subunits. This study demonstrates the first known instance of a tissue-specific ATP synthase subunit affecting tissue-specific mitochondrial morphogenesis. Since ATP synthase dimerization is known to affect the degree of inner mitochondrial membrane curvature in other systems, the effect of Knon and other testis-specific paralogs of ATP synthase subunits may be to mediate differential membrane curvature within the Nebenkern.
Qin, X., Park, B. O., Liu, J., Chen, B., Choesmel-Cadamuro, V., Belguise, K., Heo, W. D. and Wang, X. (2017). Cell-matrix adhesion and cell-cell adhesion differentially control basal myosin oscillation and Drosophila egg chamber elongation. Nat Commun 8: 14708. PubMed ID: 28406187
Summary:
Pulsatile actomyosin contractility, important in tissue morphogenesis, has been studied mainly in apical but less in basal domains. Basal myosin oscillation underlying egg chamber elongation is regulated by both cell-matrix and cell-cell adhesions. However, the mechanism by which these two adhesions govern basal myosin oscillation and tissue elongation is unknown. This study demonstrates that cell-matrix adhesion positively regulates basal junctional Rho1 activity and medio-basal ROCK and myosin activities, thus strongly controlling tissue elongation. Differently, cell-cell adhesion governs basal myosin oscillation through controlling medio-basal distributions of both ROCK and myosin signals, which are related to the spatial limitations of cell-matrix adhesion and stress fibres. Contrary to cell-matrix adhesion, cell-cell adhesion weakly affects tissue elongation. In vivo optogenetic protein inhibition spatiotemporally confirms the different effects of these two adhesions on basal myosin oscillation. This study highlights the activity and distribution controls of basal myosin contractility mediated by cell-matrix and cell-cell adhesions, respectively, during tissue morphogenesis.
Eun, S.H., Feng, L., Cedeno-Rosario, L., Gan, Q., Wei, G., Cui, K., Zhao, K. and Chen, X. (2017). Polycomb group gene E(z) is required for spermatogonial dedifferentiation in Drosophila adult testis. J Mol Biol [Epub ahead of print]. PubMed ID: 28434938
Summary:
Dedifferentiation is an important process to replenish lost stem cells during aging or regeneration after injury to maintain tissue homeostasis. This study reports that Enhancer of Zeste [E(z)], a component of the Polycomb Repression Complex 2 (PRC2), is required to maintain a stable pool of germline stem cells (GSCs) within the niche microenvironment. During aging, germ cells with reduced E(z) activity cannot meet that requirement, but the defect neither arises from increased GSC death nor premature differentiation. Instead, the decrease of GSCs upon inactivation of E(z) in the germline could be attributed to defective dedifferentiation. During recovery from genetically manipulated GSC depletion, E(z) mutant germ cells also fail to replenish lost GSCs. Taken together, these data suggest that E(z) acts intrinsically in germ cells to activate dedifferentiation and thus replenish lost GSCs during both aging and tissue regeneration.

Friday, May 26th

Mureli, S., Thanigaivelan, I., Schaffer, M. L. and Fox, J. L. (2017). Cross-modal influence of mechanosensory input on gaze responses to visual motion in Drosophila. J Exp Biol. PubMed ID: 28385799
Summary:
Animals typically combine inertial and visual information to stabilize their gaze against confounding self-generated visual motion, and to maintain a level gaze when the body is perturbed by external forces. In vertebrates, an inner ear vestibular system provides information about body rotations and accelerations, but gaze stabilization is less understood in insects, which lack a vestibular organ. In flies, the halteres, reduced hindwings imbued with hundreds of mechanosensory cells, sense inertial forces and provide input to neck motoneurons that control gaze. These neck motoneurons also receive input from the visual system. Head movement responses to visual motion and physical rotations of the body have been measured independently, but how inertial information might influence gaze responses to visual motion has not been fully explored. In this study, the head movement responses to visual motion were measured in intact and haltere-ablated tethered flies to explore the haltere's role in modulating visually-guided head movements in the absence of rotation. It is noted that visually-guided head movements occur only during flight. Although halteres are not necessary for head movements, the amplitude of the response is smaller in haltereless flies at higher speeds of visual motion. This modulation occurred in the absence of rotational body movements, demonstrating that the inertial forces associated with straight tethered flight are important for gaze-control behavior. The cross-modal influence of halteres on the fly's responses to fast visual motion indicates that the haltere's role in gaze stabilization extends beyond its canonical function as a sensor of angular rotations of the thorax.
Paisios, E., Rjosk, A., Pamir, E. and Schleyer, M. (2017). Common microbehavioral 'footprint' of two distinct classes of conditioned aversion. Learn Mem 24(5): 191-198. PubMed ID: 28416630
Summary:
Avoiding unfavorable situations is a vital skill and a constant task for any animal. Situations can be unfavorable because they feature something that the animal wants to escape from, or because they do not feature something that it seeks to obtain. This study investigated whether the microbehavioral mechanisms by which these two classes of aversion come about are shared or distinct. Larval Drosophila were found to avoid odors either previously associated with a punishment, or previously associated with the lack of a reward. These two classes of conditioned aversion are found to be strikingly alike at the microbehavioral level. In both cases larvae show more head casts when oriented toward the odor source than when oriented away, and direct fewer of their head casts toward the odor than away when oriented obliquely to it. Thus, conditioned aversion serving two qualitatively different functions-escape from a punishment or search for a reward-is implemented by the modulation of the same microbehavioral features. These features also underlie conditioned approach, albeit with opposite sign. That is, the larvae show conditioned approach toward odors previously associated with a reward, or with the lack of a punishment. In order to accomplish both these classes of conditioned approach the larvae show fewer head casts when oriented toward an odor, and direct more of their head casts toward it when they are headed obliquely. Given that the Drosophila larva is a genetically tractable model organism that is well suited to study simple circuits at the single-cell level, these analyses can guide future research into the neuronal circuits underlying conditioned approach and aversion, and the computational principles of conditioned search and escape.
Tang, X., Roessingh, S., Hayley, S. E., Chu, M. L., Tanaka, N. K., Wolfgang, W., Song, S., Stanewsky, R. and Hamada, F. N. (2017). The role of PDF neurons in setting preferred temperature before dawn in Drosophila. Elife 6. PubMed ID: 28463109
Summary:
Animals have sophisticated homeostatic controls. While mammalian body temperature fluctuates throughout the day, small ectotherms, such as Drosophila, achieve a body temperature rhythm (BTR) through their preference of environmental temperature. This study demonstrates that pigment dispersing factor (PDF) neurons play an important role in setting preferred temperature before dawn. Amall lateral ventral neurons (sLNvs), a subset of PDF neurons, activate the dorsal neurons 2 (DN2s), the main circadian clock cells that regulate temperature preference rhythm (TPR). The number of temporal contacts between sLNvs and DN2s peak before dawn. The data suggest that the thermosensory Anterior Cells (ACs) likely contact sLNvs via serotonin signaling. Together, the ACs-sLNs-DN2s neural circuit regulates the proper setting of temperature preference before dawn. Given that sLNvs are important for sleep and that BTR and sleep have a close temporal relationship, these data highlight a possible neuronal interaction between body temperature and sleep regulation.
Rombaut, A., Guilhot, R., Xuereb, A., Benoit, L., Chapuis, M. P., Gibert, P. and Fellous, S. (2017). Invasive Drosophila suzukii facilitates Drosophila melanogaster infestation and sour rot outbreaks in the vineyards. R Soc Open Sci 4(3): 170117. PubMed ID: 28405407
Summary:
How do invasive pests affect interactions between members of pre-existing agrosystems? The invasive pest Drosophila suzukii is suspected to be involved in the aetiology of sour rot, a grapevine disease that otherwise develops following Drosophila melanogaster infestation of wounded berries. This study combined field observations with laboratory assays to disentangle the relative roles of both Drosophila in disease development. The emergence was observed of numerous D. suzukii, but no D. melanogaster flies, from bunches that started showing mild sour rot symptoms days after field collection. However, bunches that already showed severe rot symptoms in the field mostly contained D. melanogaster. In the laboratory, oviposition by D. suzukii triggered sour rot development. An independent assay showed the disease increased grape attractiveness to ovipositing D. melanogaster females. These results suggest that in invaded vineyards, D. suzukii facilitates D. melanogaster infestation and, consequently, favours sour rot outbreaks. Rather than competing with close species, the invader subsequently permits their reproduction in otherwise non-accessible resources and may cause more frequent, or more extensive, disease outbreaks.

Thursday, May 25th

Morishita, K., Anh Suong, D. N., Yoshida, H. and Yamaguchi, M. (2017). The Drosophila DOCK family protein Sponge is required for development of the air sac primordium. Exp Cell Res [Epub ahead of print]. PubMed ID: 28341448
Summary:
Dedicator of cytokinesis (DOCK) family genes are known as DOCK1-DOCK11 in mammals. DOCK family proteins mainly regulate actin filament polymerization and/or depolymerization and are GEF proteins, which contribute to cellular signaling events by activating small G proteins. Sponge (Spg) is a Drosophila counterpart to mammalian DOCK3/DOCK4, and plays a role in embryonic central nervous system development, R7 photoreceptor cell differentiation, and adult thorax development. In order to conduct further functional analyses on Spg in vivo, its localization was examined in third instar larval wing imaginal discs. Immunostaining with purified anti-Spg IgG revealed that Spg mainly localized in the air sac primordium (ASP) in wing imaginal discs. Spg is therefore predicted to play an important role in the ASP. The specific knockdown of Spg by the breathless-GAL4 driver in tracheal cells induced lethality accompanied with a defect in ASP development and the induction of apoptosis. The monitoring of ERK signaling activity in wing imaginal discs by immunostaining with anti-diphospho-ERK IgG revealed reductions in the ERK signal cascade in Spg knockdown clones. Furthermore, the overexpression of D-raf suppressed defects in survival and the proliferation of cells in the ASP induced by the knockdown of Spg. Collectively, these results indicate that Spg plays a critical role in ASP development and tracheal cell viability that is mediated by the ERK signaling pathway.
Richard, M., Bauer, R., Tavosanis, G. and Hoch, M. (2017). The gap junction protein Innexin3 is required for eye disc growth in Drosophila. Dev Biol [Epub ahead of print]. PubMed ID: 28390801
Summary:
The Drosophila compound eye develops from a bilayered epithelial sac composed of an upper peripodial epithelium layer and a lower disc proper, the latter giving rise to the eye itself. The gap junction protein Innexin2 (Inx2) has been shown to be crucial for early larval eye disc growth. By analysing the contribution of other Innexins to eye size control, this study identified Innexin3 (Inx3) as an important growth regulator. Depleting inx3 during larval eye development reduces eye size, while elevating inx3 levels increases eye size, thus phenocopying the inx2 loss- and gain-of-function situation. As demonstrated previously for inx2, inx3 regulates disc cell proliferation and interacts genetically with the Dpp pathway, being required for the proper activation of the Dpp pathway transducer Mad at the furrow and the expression of Dpp receptor Punt in the eye disc. At the developmental timepoint corresponding to eye disc growth, Inx3 colocalises with Inx2 in disc proper and peripodial epithelium cell membranes. In addition, Inx3 protein levels were shown to critically depend on inx2 throughout eye development, and inx3 was shown to modulates Inx2 protein levels in the larval eye disc. Rescue experiments demonstrate that Inx3 and Inx2 cooperate functionally to enable eye disc growth in Drosophila. Finally, it was demonstrated that expression of Inx3 and Inx2 is not only needed in the disc proper but also in the peripodial epithelium to regulate growth of the eye disc. These data provide a functional demonstration that putative Inx2/Inx3 heteromeric channels regulate organ size.
Percival-Smith, A., Ponce, G. and Pelling, J. J. (2017). The non-cell autonomous requirement of Proboscipedia for growth and differentiation of the distal maxillary palp during metamorphosis of Drosophila melanogaster. Genet Res Int 2017: 2624170. PubMed ID: 28357140
Summary:
The Drosophila maxillary palpus that develops during metamorphosis is composed of two elements: the proximal maxillary socket and distal maxillary palp. The HOX protein, Proboscipedia (PB), was required for development of the proximal maxillary socket and distal maxillary palp. For growth and differentiation of the distal maxillary palp, PB was required in the cells of, or close to, the maxillary socket, as well as the cells of the distal maxillary palp. Therefore, PB is required in cells outside the distal maxillary palp for the expression, by some mechanism, of a growth factor or factors that promote the growth of the distal maxillary palp. Both wingless (wg) and hedgehog (hh) genes were expressed in cells outside the distal maxillary palp in the lancinia and maxillary socket, respectively. Both wg and hh were required for distal maxillary palp growth, and hh was required noncell autonomously for distal maxillary palp growth. However, expression of wg-GAL4 and hh-GAL4 during maxillary palp differentiation did not require PB, ruling out a direct role for PB in the regulation of transcription of these growth factors.
Hao, Y. and Jin, L. H. (2017). Dual role for Jumu in the control of hematopoietic progenitors in the Drosophila lymph gland. Elife 6. PubMed ID: 28350299
Summary:
The Drosophila lymph gland is a hematopoietic organ in which the maintenance of hematopoietic progenitor cell fate relies on intrinsic factors and extensive interaction with cells within a microenvironment. The posterior signaling center (PSC) is required for maintaining the balance between progenitors and their differentiation into mature hemocytes. Moreover, some factors from the progenitors cell-autonomously control blood cell differentiation. This study shos that Jumeau (Jumu), a member of the forkhead (Fkh) transcription factor family, controls hemocyte differentiation of lymph gland through multiple regulatory mechanisms. Jumu maintains the proper differentiation of prohemocytes by cell-autonomously regulating the expression of Col in medullary zone and by non-cell-autonomously preventing the generation of expanded PSC cells. Jumu can also cell-autonomously control the proliferation of PSC cells through positive regulation of dMyc expression. Deficiency of jumu throughout the lymph gland can induce the differentiation of lamellocytes via activating Toll signaling.

Wednesday, May 24th

Wang, Y., Zhang, H., Shi, M., Liou, Y.C., Lu, L. and Yu, F. (2017). Sec71 functions as a GEF for the small GTPase Arf1 to govern dendrite pruning of Drosophila sensory neurons. Development [Epub ahead of print]. PubMed ID: 28420712
Summary:
Pruning, whereby neurons eliminate their exuberant neurites, is central for the maturation of the nervous system. In Drosophila, sensory neurons, ddaCs, selectively prune their larval dendrites without affecting their axons during metamorphosis. However, it is unknown whether the secretory pathway plays a role in dendrite pruning. This study shows that the small GTPase Arf1, an important regulator of secretory pathway, is specifically required for dendrite pruning of ddaC/D/E sensory neurons but dispensable for apoptosis of ddaF neurons. Analyses of the GTP and GDP-locked forms of Arf1 indicate that the cycling of Arf1 between GDP-bound and GTP-bound forms is essential for dendrite pruning. Sec71 was identified as a guanine nucleotide exchange factor for Arf1 that preferentially interacts with its GDP-bound form. Like Arf1, Sec71 is also important for dendrite pruning, but not apoptosis, of sensory neurons. Arf1 and Sec71 are interdependent for their localizations on Golgi. Finally, Sec71/Arf1-mediated trafficking process is a prerequisite for Rab5-dependent endocytosis to facilitate endocytosis and degradation of the cell adhesion molecule Neuroglian
Cervantes-Sandoval, I., Phan, A., Chakraborty, M. and Davis, R. L. (2017). Reciprocal synapses between mushroom body and dopamine neurons form a positive feedback loop required for learning. Elife 6. PubMed ID: 28489528
Summary:
Current thought envisions dopamine neurons conveying the reinforcing effect of the unconditioned stimulus during associative learning to the axons of Drosophila mushroom body Kenyon cells for normal olfactory learning. This study shows, using functional GFP reconstitution experiments, that Kenyon cells and dopamine neurons form axoaxonic reciprocal synapses. The dopamine neurons receive cholinergic input via nicotinic acetylcholine receptors from the Kenyon cells; knocking down these receptors impairs olfactory learning revealing the importance of these receptors at the synapse. Blocking the synaptic output of Kenyon cells during olfactory conditioning reduces presynaptic calcium transients in dopamine neurons, a finding consistent with reciprocal communication. Moreover, silencing Kenyon cells decreases the normal chronic activity of the dopamine neurons. These results reveal a new and critical role for positive feedback onto dopamine neurons through reciprocal connections with Kenyon cells for normal olfactory learning (Cervantes-Sandoval, 2017).
Richlitzki, A., Latour, P. and Schwarzel, M. (2017). Null EPAC mutants reveal a sequential order of versatile cAMP effects during Drosophila aversive odor learning. Learn Mem 24(5): 210-215. PubMed ID: 28416632
Summary:
This study defines a role of the cAMP intermediate EPAC in Drosophila aversive odor learning by means of null epac mutants. Complementation analysis revealed that EPAC acts downstream from the rutabaga adenylyl cyclase and in parallel to protein kinase A. By means of targeted knockdown and genetic rescue, mushroom body Kenyon cells (KCs) were identified as a necessary and sufficient site of EPAC action. Mechanistic insights were provided by analyzing acquisition dynamics and using the "performance increment" as a means to access the trial-based sequential organization of odor learning. Thereby it was shown that versatile cAMP-dependent mechanisms are engaged within a sequential order that correlate to individual trials of the training session.
Gore, B.B., Miller, S.M., Jo, Y.S., Baird, M.A., Hoon, M., Sanford, C.A., Hunker, A., Lu, W., Wong, R.O. and Zweifel, L.S. (2017). Roundabout receptor 2 maintains inhibitory control of the adult midbrain. Elife 6. PubMed ID: 28394253
Evolutionary Homolog Study:
The maintenance of excitatory and inhibitory balance in the brain is essential for its function. This study found that the developmental axon guidance receptor Roundabout 2 (Robo2) (see Drosophila robo1) is critical for the maintenance of inhibitory synapses in the adult ventral tegmental area (VTA), a brain region important for the production of the neurotransmitter dopamine (see Drosophila brain and dopaminergic system). Following selective genetic inactivation of Robo2 in the adult VTA of mice, reduced inhibitory control results in altered neural activity patterns, enhanced phasic dopamine release, behavioral hyperactivity, associative learning deficits, and a paradoxical inversion of psychostimulant responses. These behavioral phenotypes can be phenocopied by selective inactivation of synaptic transmission from local GABAergic neurons of the VTA, demonstrating an important function for Robo2 in regulating the excitatory and inhibitory balance of the adult brain.

Tuesday, May 23rd

Reilein, A., Melamed, D., Park, K. S., Berg, A., Cimetta, E., Tandon, N., Vunjak-Novakovic, G., Finkelstein, S. and Kalderon, D. (2017). Alternative direct stem cell derivatives defined by stem cell location and graded Wnt signalling. Nat Cell Biol 19(5):433-444. PubMed ID: 28414313
Summary:
Adult stem cells provide a renewable source of differentiated cells for a wide variety of tissues and generally give rise to multiple cell types. Basic principles of stem cell organization and regulation underlying this behaviour are emerging. Local niche signals maintain stem cells, while different sets of signals act outside the niche to diversify initially equivalent stem cell progeny. This study shows that Drosophila ovarian follicle stem cells (FSCs) produced two distinct cell types directly. This cell fate choice was determined by the anterior-posterior position of an FSC and by the magnitude of spatially graded Wnt pathway activity. These findings reveal a paradigm of immediate diversification of stem cell derivatives according to stem cell position within a larger population, guided by a graded niche signal. It was also found that FSCs strongly resemble mammalian intestinal stem cells in many aspects of their organization, including population asymmetry and dynamic heterogeneity.
Lucchetta, E.M. and Ohlstein, B. (2017). Amitosis of polyploid cells regenerates functional stem cells in the Drosophila intestine. Cell Stem Cell [Epub ahead of print]. PubMed ID: 28343984
Summary:
Organ fitness depends on appropriate maintenance of stem cell populations, and aberrations in functional stem cell numbers are associated with malignancies and aging. Symmetrical division is the best characterized mechanism of stem cell replacement, but other mechanisms could also be deployed, particularly in situations of high stress. This study shows that after severe depletion, intestinal stem cells (ISCs) in the Drosophila midgut are replaced by spindle-independent ploidy reduction of cells in the enterocyte lineage through a process known as amitosis. Amitosis is also induced by the functional loss of ISCs coupled with tissue demand and in aging flies, underscoring the generality of this mechanism. However, random homologous chromosome segregation during ploidy reduction can expose deleterious mutations through loss of heterozygosity. Together, these data highlight amitosis as an unappreciated mechanism for restoring stem cell homeostasis, but one with some associated risk in animals carrying mutations.

Li, Y., Pang, Z., Huang, H., Wang, C., Cai, T. and Xi, R. (2017). Transcription factor antagonism controls enteroendocrine cell specification from intestinal stem cells. Sci Rep 7: 988. PubMed ID: 28428611
Summary:
The balanced maintenance and differentiation of local stem cells is required for homeostatic renewal of tissues. In the Drosophila midgut, the transcription factor Escargot (Esg) maintains undifferentiated states in intestinal stem cells, whereas the transcription factors Scute (Sc) and Prospero (Pros) promote enteroendocrine cell specification. However, the mechanism through which Esg and Sc/Pros coordinately regulate stem cell differentiation is unknown. By combining chromatin immunoprecipitation analysis with genetic studies, this study shows that both Esg and Sc bind to a common promoter region of pros. Moreover, antagonistic activity between Esg and Sc controls the expression status of Pros in stem cells, thereby, specifying whether stem cells remain undifferentiated or commit to enteroendocrine cell differentiation. These data therefore reveal transcription factor antagonism between Esg and Sc as a novel mechanism that underlies fate specification from intestinal stem cells in Drosophila.

Lai, C. M., Lin, K. Y., Kao, S. H., Chen, Y. N., Huang, F. and Hsu, H. J. (2017). Hedgehog signaling establishes precursors for germline stem cell niches by regulating cell adhesion. J Cell Biol [Epub ahead of print]. PubMed ID: 28363970
Summary:
Stem cells require different types of supporting cells, or niches, to control stem cell maintenance and differentiation. However, little is known about how those niches are formed. This study reports that in the development of the Drosophila melanogaster ovary, the Hedgehog (Hh) gradient sets differential cell affinity for somatic gonadal precursors to specify stromal intermingled cells, which contributes to both germline stem cell maintenance and differentiation niches in the adult. Traffic Jam (an orthologue of a large Maf transcription factor in mammals) is a novel transcriptional target of Hh signaling to control cell-cell adhesion by negative regulation of E-cadherin expression. These results demonstrate the role of Hh signaling in niche establishment by segregating somatic cell lineages for differentiation.

Monday, May 22nd

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
Summary:
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 chromatin-remodelling switch/sucrose non-fermentable (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.

Meers, M. P., Henriques, T., Lavender, C. A., McKay, D. J., Strahl, B. D., Duronio, R. J., Adelman, K. and Matera, A. G. (2017). Histone gene replacement reveals a post-transcriptional role for H3K36 in maintaining metazoan transcriptome fidelity. Elife 6. PubMed ID: 28346137
Summary:
Histone H3 lysine 36 methylation (H3K36me) is thought to participate in a host of co-transcriptional regulatory events. To study the function of this residue independent from the enzymes that modify it, a 'histone replacement' system was used in Drosophila to generate a non-modifiable H3K36 lysine-to-arginine (H3K36R) mutant. Global dysregulation of mRNA levels was observed in H3K36R animals that correlates with the incidence of H3K36me3. Similar to previous studies, it was found that mutation of H3K36 also resulted in H4 hyperacetylation. However, neither cryptic transcription initiation, nor alternative pre-mRNA splicing, contributed to the observed changes in expression, in contrast with previously reported roles for H3K36me. Interestingly, knockdown of the RNA surveillance nuclease, Xrn1, and members of the CCR4-Not deadenylase complex, restored mRNA levels for a class of downregulated, H3K36me3-rich genes. A post-transcriptional role is proposed for modification of replication-dependent H3K36 in the control of metazoan gene expression.
Kreher, J., Kovac, K., Bouazoune, K., Macinkovic, I., Ernst, A. L., Engelen, E., Pahl, R., Finkernagel, F., Murawska, M., Ullah, I. and Brehm, A. (2017). EcR recruits dMi-2 and increases efficiency of dMi-2-mediated remodelling to constrain transcription of hormone-regulated genes. Nat Commun 8: 14806. PubMed ID: 28378812
Summary:
Gene regulation by steroid hormones plays important roles in health and disease. In Drosophila, the hormone ecdysone governs transitions between key developmental stages. Ecdysone-regulated genes are bound by a heterodimer of Ecdysone receptor (EcR) and Ultraspiracle. According to the bimodal switch model, steroid hormone receptors recruit corepressors in the absence of hormone and coactivators in its presence. This study shows that the nucleosome remodeller dMi-2 is recruited to ecdysone-regulated genes to limit transcription. Contrary to the prevalent model, recruitment of the dMi-2 corepressor increases upon hormone addition to constrain gene activation through chromatin remodelling. Furthermore, EcR and dMi-2 form a complex that is devoid of Ultraspiracle. Unexpectedly, EcR contacts the dMi-2 ATPase domain and increases the efficiency of dMi-2-mediated nucleosome remodelling. This study identifies a non-canonical EcR-corepressor complex with the potential for a direct regulation of ATP-dependent nucleosome remodelling by a nuclear hormone receptor.
Lev, I., Seroussi, U., Gingold, H., Bril, R., Anava, S. and Rechavi, O. (2017). MET-2-dependent H3K9 methylation suppresses transgenerational small RNA inheritance. Curr Biol 27(8): 1138-1147. PubMed ID: 28343968
Evolutionary Homolog Study
In C. elegans, alterations to chromatin produce transgenerational effects, such as inherited increase in lifespan and gradual loss of fertility. Inheritance of histone modifications can be induced by double-stranded RNA-derived heritable small RNAs. This study shows that the mortal germline phenotype, which is typical of met-2 mutants, defective in H3K9 methylation, depends on HRDE-1, an argonaute that carries small RNAs across generations, and is accompanied by accumulated transgenerational misexpression of heritable small RNAs. It was discovered that MET-2 inhibits small RNA inheritance, and, as a consequence, induction of RNAi in met-2 mutants leads to permanent RNAi responses that do not terminate even after more than 30 generations. Potentiation of heritable RNAi in met-2 animals results from global hyperactivation of the small RNA inheritance machinery. Thus, changes in histone modifications can give rise to drastic transgenerational epigenetic effects, by controlling the overall potency of small RNA inheritance.

Sunday, May 21st

Lee, J.H., Lee, C.W., Park, S.H. and Choe, K.M. (2017). Spatiotemporal regulation of cell fusion by JNK and JAK/STAT signaling during Drosophila wound healing. J Cell Sci [Epub ahead of print]. PubMed ID: 28424232
Summary:
Cell-cell fusion is widely observed during development and disease and imposes a dramatic change on participating cells. Cell fusion should be tightly controlled, but the underlying mechanism is poorly understood. This study found that the JAK/STAT pathway suppresses cell fusion during wound healing and delimits the event to the vicinity of the wound in the Drosophila larval epidermis. In the absence of JAK/STAT signaling, a large syncytium containing 3-fold the number of nuclei observed in wild-type tissue forms in wounded epidermis. upd2 and upd3 are transcriptionally induced by wounding and are required for suppressing excess cell fusion. JNK is activated in the wound vicinity and activity peaks at approximately 8 h after injury, whereas JAK/STAT signaling is activated in an adjoining concentric ring and activity peaks at a later stage. Cell fusion occurrs primarily in the wound vicinity, where JAK/STAT activation is suppressed by fusion-inducing JNK signaling. JAK/STAT signaling is both necessary and sufficient for the induction of βPS integrin expression, suggesting that the suppression of cell fusion is mediated at least in part by integrin protein.

Shimizu, H., Wilkin, M. B., Woodcock, S. A., Bonfini, A., Hung, Y., Mazaleyrat, S. and Baron, M. (2017). The Drosophila ZO-1 protein Polychaetoid suppresses Deltex-regulated Notch activity to modulate germline stem cell niche formation. Open Biol 7(4). PubMed ID: 28424321
Summary:
The developmental signalling protein Notch can be proteolytically activated following ligand-interaction at the cell surface, or can be activated independently of its ligands, following Deltex (Dx)-induced Notch endocytosis and trafficking to the lysosomal membrane. The means by which different pools of Notch are directed towards these alternative outcomes remains poorly understood. This study found that the Drosophila ZO-1 protein Polychaetoid (Pyd) suppresses specifically the Dx-induced form of Notch activation both in vivo and in cell culture assays. The physiological relevance and direction of the Pyd/Dx interaction was confirmed by showing that the expanded ovary stem cell niche phenotypes of pyd mutants require the presence of functional Dx and other components that are specific to the Dx-induced Notch activation mechanism. In S2 cells Pyd can form a complex with Dx and Notch at the cell surface and reduce Dx-induced Notch endocytosis. Similar to other known activities of ZO-1 family proteins, the action of Pyd on Dx-induced endocytosis and signalling was found to be cell density dependent. Thus, together, these results suggest an alternative means by which external cues can tune Notch signalling through Pyd regulation of Dx-induced Notch trafficking.
Roumengous, S., Rousset, R. and Noselli, S. (2017). Polycomb and Hox genes control JNK-induced remodeling of the segment boundary during Drosophila morphogenesis. Cell Rep 19(1): 60-71. PubMed ID: 28380363
Summary:
In segmented tissues, anterior and posterior compartments represent independent morphogenetic domains, which are made of distinct lineages separated by boundaries. During dorsal closure of the Drosophila embryo, specific 'mixer cells' (MCs) are reprogrammed in a JNK-dependent manner to express the posterior determinant engrailed (en) and cross the segment boundary. This study showed that JNK signaling induces de novo expression of en in the MCs through repression of Polycomb (Pc) and release of the en locus from the silencing PcG bodies. Whereas reprogramming occurs in MCs from all thoracic and abdominal segments, cell mixing is restricted to the central abdominal region. This spatial control of MC remodeling depends on the antagonist activity of the Hox genes abdominal-A and Abdominal-B. Together, these results reveal an essential JNK/en/Pc/Hox gene regulatory network important in controlling both the plasticity of segment boundaries and developmental reprogramming.
Zhang, X., Spiegelman, N.A., Nelson, O.D., Jing, H. and Lin, H. (2017). SIRT6 regulates Ras-related protein R-Ras2 by lysine defatty-acylation. Elife 6. PubMed ID: 28406396
Evolutionary Homolog Study:
The Ras family of GTPases are important in cell signaling and frequently mutated in human tumors. Understanding their regulation is thus important for studying biology and human diseases. This study reports that a novel posttranslational mechanism, reversible lysine fatty acylation, regulates R-Ras2 (see Drosophila Ras64B), a member of the Ras family. SIRT6 (see Drosophila Sirt6), a sirtuin with established tumor suppressor function, regulates the lysine fatty acylation of R-Ras2. In mouse embryonic fibroblasts (MEFs), Sirt6 knockout (KO) increases R-Ras2 lysine fatty acylation. Lysine fatty acylation promotes the plasma membrane localization of R-Ras2 and its interaction with phosphatidylinositol 3-kinase PI3K, leading to activated Akt (see Drosophila Akt1) and increased cell proliferation. These data establish lysine fatty acylation as a previously unknown mechanism that regulates the Ras family of GTPases and provides an important mechanism by which SIRT6 functions as a tumor suppressor.

Yu, P., et al. (2017). FGF-dependent metabolic control of vascular development. Nature 545(7653): 224-228. PubMed ID: 28467822 Evolutionary Homolog Study:
Blood and lymphatic vasculatures are intimately involved in tissue oxygenation and fluid homeostasis maintenance. Assembly of these vascular networks involves sprouting, migration and proliferation of endothelial cells. Recent studies have suggested that changes in cellular metabolism are important to these processes. Although much is known about vascular endothelial growth factor (VEGF)-dependent regulation of vascular development and metabolism, little is understood about the role of fibroblast growth factors (FGFs) in this context. This study identified FGF receptor (FGFR; see Drosophila Breathless) signalling as a critical regulator of vascular development. This is achieved by FGF-dependent control of c-MYC (MYC; see Drosophila Myc) expression that, in turn, regulates expression of the glycolytic enzyme hexokinase 2 (HK2; see Drosophila Hexokinase A). A decrease in HK2 levels in the absence of FGF signalling inputs results in decreased glycolysis, leading to impaired endothelial cell proliferation and migration. Pan-endothelial- and lymphatic-specific Hk2 knockouts phenocopy blood and/or lymphatic vascular defects seen in Fgfr1/Fgfr3 double mutant mice, while HK2 overexpression partly rescues the defects caused by suppression of FGF signalling. Thus, FGF-dependent regulation of endothelial glycolysis is a pivotal process in developmental and adult vascular growth and development.
Janda, C. Y., et al. (2017). Surrogate Wnt agonists that phenocopy canonical Wnt and beta-catenin signalling. Nature 545(7653): 234-237. PubMed ID: 28467818 Evolutionary Homolog Study:
Wnt proteins (see Drosophila Wingless) modulate cell proliferation and differentiation and the self-renewal of stem cells by inducing β-catenin-dependent signalling through the Wnt receptor frizzled (FZD; see Drosophila Frizzled) and the co-receptors LRP5 and LRP6 (see Drosophila Arrow) to regulate cell fate decisions and the growth and repair of several tissues. As a result of their acylation, Wnt proteins are very hydrophobic and require detergents for purification, which presents major obstacles to the preparation and application of recombinant Wnt proteins. This hydrophobicity has hindered the determination of the molecular mechanisms of Wnt signalling activation. This study develop surrogate Wnt agonists, water-soluble FZD-LRP5/LRP6 heterodimerizers, with FZD5/FZD8-specific and broadly FZD-reactive binding domains. These Wnt agonists elicit a characteristic β-catenin signalling response in a FZD-selective fashion and enhance the osteogenic lineage commitment of primary mouse and human mesenchymal stem cells. These surrogates demonstrate that canonical Wnt signalling can be activated by bi-specific ligands that induce receptor heterodimerization. Furthermore, these easily produced, non-lipidated Wnt surrogate agonists facilitate functional studies of Wnt signalling and the exploration of Wnt agonists for translational applications in regenerative medicine.

Saturday, May 20th

Mondal, T., Lavanya, A. V., Mallick, A., Dadmala, T. L., Kumbhare, R. M., Bhadra, U. and Bhadra, M. P. (2017). Novel Triazole linked 2-phenyl benzoxazole derivatives induce apoptosis by inhibiting miR-2, miR-13 and miR-14 function in Drosophila melanogaster. Apoptosis [Epub ahead of print]. PubMed ID: 28401354
Summary:
Apoptosis is an important phenomenon in multi cellular organisms for maintaining tissue homeostasis and embryonic development. Defect in apoptosis leads to a number of disorders like- autoimmune disorder, immunodeficiency and cancer. 21-22 nucleotides containing micro RNAs (miRNAs/miRs) function as a crucial regulator of apoptosis alike other cellular pathways. Recently, small molecules have been identified as a potent inducer of apoptosis. This study has identified novel Triazole linked 2-phenyl benzoxazole derivatives (13j and 13h) as a negative regulator of apoptosis inhibiting micro RNAs (miR-2, miR-13 and miR-14) in a well established in vivo model Drosophila melanogaster where the process of apoptosis is very similar to human apoptosis. These compounds inhibit miR-2, miR-13 and miR-14 activity at their target sites, which induce an increased caspase activity, and in turn influence the caspase dependent apoptotic pathway. These two compounds also increase the mitochondrial reactive oxygen species (ROS) level to trigger apoptotic cell death.
Nonaka, S., Ando, Y., Kanetani, T., Hoshi, C., Nakai, Y., Nainu, F., Nagaosa, K., Shiratsuchi, A. and Nakanishi, Y. (2017). Signaling pathway for phagocyte priming upon encounter with apoptotic cells. J Biol Chem. PubMed ID: 28325838
Summary:
The phagocytic elimination of cells undergoing apoptosis is an evolutionarily conserved innate immune mechanism for eliminating unnecessary cells. This study found that the pre-incubation of a Drosophila phagocyte cell line with the fragments of apoptotic cells enhanced the subsequent phagocytosis of apoptotic cells, accompanied by an augmented expression of the engulfment receptors Draper and integrin alphaPS3. The DNA-binding activity of the transcription repressor Tailless was transiently raised in those phagocytes, depending on two partially overlapping signal-transduction pathways for the induction of phagocytosis as well as the occurrence of engulfment. The RNAi knockdown of tailless in phagocytes abrogated the enhancement of both phagocytosis and engulfment receptor expression. Furthermore, the hemocyte-specific RNAi of tailless reduced apoptotic cell clearance in Drosophila embryos. It is proposed that two partially overlapping signal-transduction pathways for phagocytosis are initiated; transcription repressor Tailless is activated; expression of engulfment receptors is stimulated; and phagocytic activity is enhanced. This phenomenon most likely ensures the phagocytic elimination of apoptotic cells that stimulated phagocytes find thereafter and is thus considered as a mechanism to prime phagocytes in innate immunity.
Kang, Y., Marischuk, K., Castelvecchi, G.D. and Bashirullah, A. (2017). HDAC inhibitors disrupt programmed resistance to apoptosis during Drosophila development. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 28455414
Summary:
It has been previously shown that the ability to respond to apoptotic triggers is regulated during Drosophila development, effectively dividing the fly life cycle into stages that are either sensitive or resistant to apoptosis. This study shows that the developmentally programmed resistance to apoptosis involves transcriptional repression of critical pro-apoptotic genes by histone deacetylases (HDACs). Administration of HDAC inhibitors (HDACi), like Trichostatin A (TSA) or Suberoylanilide Hydroxamic Acid (SAHA), increases expression of pro-apoptotic genes and is sufficient to sensitize otherwise resistant stages. Conversely, reducing levels of pro-apoptotic genes confers resistance to otherwise sensitive stages. Given that resistance to apoptosis is a hallmark of cancer cells, and that HDACi have been recently added to the repertoire of FDA-approved agents for cancer therapy, these results provide new insights for how HDACi help kill malignant cells and also raise concerns for their potential unintended effects on healthy cells.

Poulton, J.S., Cuningham, J.C. and Peifer, M. (2017). Centrosome and spindle assembly checkpoint loss leads to neural apoptosis and reduced brain size. J Cell Biol 216: 1255-1265. PubMed ID: 28351851
Summary:
Accurate mitotic spindle assembly is critical for mitotic fidelity and organismal development. Multiple processes coordinate spindle assembly and chromosome segregation. Two key components are centrosomes and the spindle assembly checkpoint (SAC), and mutations affecting either can cause human microcephaly. In vivo studies in Drosophila melanogaster have found that loss of either component alone is well tolerated in the developing brain, in contrast to epithelial tissues of the imaginal discs. This study reveals that one reason for that tolerance is the compensatory relationship between centrosomes and the SAC. In the absence of both centrosomes and the SAC, brain cells, including neural stem cells, experience massive errors in mitosis, leading to increased cell death, which reduces the neural progenitor pool and severely disrupts brain development. However, data also demonstrate that neural cells are much more tolerant of aneuploidy than epithelial cells. These data provide novel insights into the mechanisms by which different tissues manage genome stability and parallels with human microcephaly.

Friday, May 19th

Paiardi, C., Mirzoyan, Z., Zola, S., Parisi, F., Vingiani, A., Pasini, M.E. and Bellosta, P. (2017). The Stearoyl-CoA Desaturase-1 (Desat1) in Drosophila cooperated with Myc to induce autophagy and growth, a potential new link to tumor survival. Genes (Basel) 8. PubMed ID: 28452935
Summary:
Lipids are an important energy supply in our cells and can be stored or used to produce macromolecules during lipogenesis when cells experience nutrient starvation. Proteomic analysis reveals that the Drosophila homologue of human Stearoyl-CoA desaturase-1 (Desat1) is an indirect target of Myc in fat cells. Stearoyl-CoA desaturases are key enzymes in the synthesis of monounsaturated fatty acids critical for the formation of complex lipids such as triglycerides and phospholipids. Their function is fundamental for cellular physiology, however in tumors, overexpression of SCD-1 and SCD-5 has been found frequently associated with a poor prognosis. Another gene that is often upregulated in tumors is the proto-oncogene c-myc, where its overexpression or increased protein stability, favor cellular growth. This study reports a potential link between Myc and Desat1 to control autophagy and growth. Using Drosophila, it was found that expression of Desat1, in metabolic tissues like the fat body, in the gut and in epithelial cells, is necessary for Myc function to induce autophagy a cell eating mechanism important for energy production. In addition, reduction of Desat1 affects Myc ability to induce growth in epithelial cells. These data also identify, in pancreatic tumor cells, a significant correlation between the expression of Myc and SCD-1 proteins, suggesting the existence of a potential functional relationship between the activities of these proteins in sustaining tumor progression.

Tower, J., Landis, G.N., Shen, J., Choi, R., Fan, Y., Lee, D. and Song, J. (2017). Mifepristone/RU486 acts in Drosophila melanogaster females to counteract the life span-shortening and pro-inflammatory effects of male Sex Peptide. Biogerontology [Epub ahead of print]. PubMed ID: 28451923
Summary:
Males with null mutation of Sex Peptide (SP) gene were compared to wild-type males for the ability to cause physiological changes in females that could be reversed by mifepristone. Males from wild-type strains decrease median female lifespan by average -51%. Feeding mifepristone increases life span of these females by average +106%. In contrast, SP-null males do not decrease female life span, and mifepristone increases median life span of these females by average +14%, which is equivalent to the effect of mifepristone in virgin females (average +16%). Expression of innate immune response transgenic reporter (Drosocin-GFP) is increased in females mated to wild-type males, and this expression is reduced by mifepristone. In contrast, SP-null males do not increase Drosocin-GFP reporter expression in the female. Similarly, mating increases endogenous microbial load, and this effect is reduced or absent in females fed mifepristone and in females mated to SP-null males; no loss of intestinal barrier integrity is detected using dye-leakage assay. Reduction of microbial load by treating adult flies with doxycycline reduces the effects of both mating and mifepristone on lifespan. Finally, mifepristone blocks the negative effect on life span caused by transgenic expression of SP in virgin females. The data support the conclusion that the majority of the life span-shortening, immune-suppressive and pro-inflammatory effects of mating are due to male SP, and demonstrate that mifepristone acts in females to counteract these effects of male SP.

Ng, Y. S., Sorvina, A., Bader, C. A., Weiland, F., Lopez, A. F., Hoffmann, P., Shandala, T. and Brooks, D. A. (2017).. Proteome analysis of Drosophila mutants identifies a regulatory role for 14-3-3epsilon in metabolic pathways. J Proteome Res. PubMed ID: 28365999
Summary:
The loss of Drosophila 14-3-3epsilon resulted in reduced survival of mutants during larval-to-adult transition, which is known to depend on an energy supply coming from the histolysis of fat body tissue. This study reports a differential proteomic analysis of larval fat body tissue at the onset of larval-to-adult transition, with the loss of 14-3-3epsilon resulting in the altered abundance of 16 proteins. These included proteins linked to protein biosynthesis, glycolysis, tricarboxylic acid cycle, and lipid metabolic pathways. The ecdysone receptor (EcR), which is responsible for initiating the larval-to-adult transition, colocalized with 14-3-3epsilon in wild-type fat body tissues. The altered protein abundance in 14-3-3epsilon mutant fat body tissue was associated with transcriptional deregulation of alcohol dehydrogenase, fat body protein 1, and lamin genes, which are known targets of the EcR. This study indicates that 14-3-3epsilon has a critical role in cellular metabolism involving either molecular crosstalk with the EcR or direct interaction with metabolic proteins.
Moraru, A., Cakan-Akdogan, G., Strassburger, K., Males, M., Mueller, S., Jabs, M., Muelleder, M., Frejno, M., Braeckman, B. P., Ralser, M. and Teleman, A. A. (2017). THADA regulates the organismal balance between energy storage and heat production. Dev Cell 41(1): 72-81.e76. PubMed ID: 28399403
Summary:
Human susceptibility to obesity is mainly genetic, yet the underlying evolutionary drivers causing variation from person to person are not clear. One theory rationalizes that populations that have adapted to warmer climates have reduced their metabolic rates, thereby increasing their propensity to store energy. This study uncovered the function of a gene that supports this theory. THADA is one of the genes most strongly selected during evolution as humans settled in different climates. THADA knockout flies are obese, hyperphagic, have reduced energy production, and are sensitive to the cold. THADA binds the sarco/ER Ca2+ ATPase (SERCA) and acts on it as an uncoupler. Reducing SERCA activity in THADA mutant flies rescues their obesity, pinpointing SERCA as a key effector of THADA function. In sum, this identifies THADA as a regulator of the balance between energy consumption and energy storage, which was selected during human evolution.

Thursday May 19th

Ryazansky, S., Radion, E., Mironova, A., Akulenko, N., Abramov, Y., Morgunova, V., Kordyukova, M.Y., Olovnikov, I. and Kalmykova, A. (2017). Natural variation of piRNA expression affects immunity to transposable elements. PLoS Genet 13: e1006731. PubMed ID: 28448516
Summary:
In the Drosophila germline, transposable elements (TEs) are silenced by PIWI-interacting RNA (piRNA) that originate from distinct genomic regions termed piRNA clusters and are processed by PIWI-subfamily Argonaute proteins. This study explores the variation in the ability to restrain an alien TE in different Drosophila strains. The I-element is a retrotransposon involved in the phenomenon of I-R hybrid dysgenesis in Drosophila melanogaster. Genomes of R strains do not contain active I-elements, but harbour remnants of ancestral I-related elements. The permissivity to I-element activity of R females, called reactivity, varies considerably in natural R populations, indicating the existence of a strong natural polymorphism in defense systems targeting transposons. To reveal the nature of such polymorphisms, ovarian small RNAs between R strains with low and high reactivity were compared. It was shown that reactivity negatively correlates with the ancestral I-element-specific piRNA content. Analysis of piRNA clusters containing remnants of I-elements shows increased expression of the piRNA precursors and enrichment by the Heterochromatin Protein 1 homolog, Rhino, in weak R strains, which is in accordance with stronger piRNA expression by these regions. To explore the nature of the differences in piRNA production, weak and strong strains were analyzed and it was shown that the efficiency of maternal inheritance of piRNAs as well as the I-element copy number are very similar in both strains. At the same time, germline and somatic uni-strand piRNA clusters generate more piRNAs in strains with low reactivity, suggesting the relationship between the efficiency of primary piRNA production and variable response to TE invasions. The strength of adaptive genome defense is likely driven by naturally occurring polymorphisms in the rapidly evolving piRNA pathway proteins. The study hypothesizes that hyper-efficient piRNA production is contributing to elimination of a telomeric retrotransposon HeT-A, which was observed in one particular transposon-resistant R strain.

Harrington, A.W., McKain, M.R., Michalski, D., Bauer, K.M., Daugherty, J.M. and Steiniger, M. (2017). Drosophila melanogaster retrotransposon and inverted repeat-derived endogenous siRNAs are differentially processed in distinct cellular locations. BMC Genomics 18: 304. PubMed ID: 28415970
Summary:
Endogenous small interfering (esi)RNAs repress mRNA levels and retrotransposon mobility in Drosophila somatic cells by poorly understood mechanisms. 21 nucleotide esiRNAs are primarily generated from retrotransposons and two inverted repeat (hairpin) loci in Drosophila culture cells in a Dicer2 dependent manner. Additionally, proteins involved in 3' end processing, such as Symplekin, CPSF73 and CPSR100, have been recently implicated in the esiRNA pathway.
This study presents evidence of overlap between two essential RNA metabolic pathways: esiRNA biogenesis and mRNA 3' end processing. A nucleus-specific interaction between the essential esiRNA cleavage enzyme Dicer2 (Dcr2) and Symplekin, a component of the core cleavage complex (CCC) required for 3' end processing of all eukaryotic mRNAs, was identified. This interaction is mediated by the N-terminal 271 amino acids of Symplekin; CCC factors CPSF73 and CPSF100 do not contact Dcr2. While Dcr2 binds the CCC, Dcr2 knockdown does not affect mRNA 3' end formation. RNAi-depletion of CCC components Symplekin and CPSF73 causes perturbations in esiRNA abundance that correlate with fluctuations in retrotransposon and hairpin esiRNA precursor levels. esiRNAs generated from retrotransposons and hairpins have distinct physical characteristics including a higher predominance of 22 nucleotide hairpin-derived esiRNAs and differences in 3' and 5' base preference. Additionally, retrotransposon precursors and derived esiRNAs are highly enriched in the nucleus while hairpins and hairpin derived esiRNAs are predominantly cytoplasmic similar to canonical mRNAs. RNAi-depletion of either CPSF73 or Symplekin results in nuclear retention of both hairpin and retrotransposon precursors suggesting that polyadenylation indirectly affects cellular localization of Dcr2 substrates. Together, these observations support a novel mechanism in which differences in localization of esiRNA precursors impacts esiRNA biogenesis. Hairpin-derived esiRNAs are generated in the cytoplasm independent of Dcr2-Symplekin interactions, while retrotransposons are processed in the nucleus.

Pritykin, Y., Brito, T., Schupbach, T., Singh, M. and Pane, A. (2017). Integrative analysis unveils new functions for the Drosophila Cutoff protein in non-coding RNA biogenesis and gene regulation. RNA [Epub ahead of print]. PubMed ID: 28420675
Summary:
Piwi-Interacting RNAs (piRNAs) are central components of the piRNA pathway, which directs transposon silencing and guarantees genome integrity in the germ cells of several metazoans. In Drosophila, piRNAs are produced from discrete regions of the genome termed piRNA clusters, whose expression relies on the RDC complex comprised of the core proteins Rhino, Deadlock and Cutoff. To date, the RDC complex has been exclusively implicated in the regulation of the piRNA loci. This study further elucidates the function of Cutoff and the RDC complex by performing genome-wide ChIP-seq and RNA-seq assays in the Drosophila germline and analyzing these data together with other publicly available data sets. In agreement with previous studies, it was confirmed that Cutoff is involved in the transcriptional regulation of piRNA clusters and in the repression of transposable elements in germ cells. Surprisingly, however, it was found that Cutoff is enriched at and affects the expression of other non-coding RNAs, including spliceosomal RNAs (snRNAs) and small nucleolar RNAs (snoRNAs). At least in some instances, Cutoff appears to act at a transcriptional level in concert with Rhino and perhaps Deadlock. Finally, mutations in Cutoff result in the deregulation of hundreds of protein-coding genes in germ cells.

Zang, K.E., Ho, E. and Ringstad, N. (2017). Inhibitory peptidergic modulation of C. elegans serotonin neurons is gated by T-type calcium channels. Elife 6. PubMed ID: 28165324
Evolutionary Homolog Study:
Serotonin is an evolutionarily ancient molecule that functions in generating and modulating many behavioral states. Although much is known about how serotonin acts on its cellular targets, how serotonin release is regulated in vivo remains poorly understood. In the nematode C. elegans, serotonin neurons (see Drosophila serotonergic system) that drive female reproductive behavior are directly modulated by inhibitory neuropeptides. This study reports the isolation of mutants in which inhibitory neuropeptides fail to properly modulate serotonin neurons and the behavior they mediate. The corresponding mutations affect the T-type calcium channel CCA-1 (see Drosophila Ca-α1T) and symmetrically re-tune its voltage-dependencies of activation and inactivation towards more hyperpolarized potentials. This shift in voltage dependency strongly and specifically bypasses the behavioral and cell physiological effects of peptidergic inhibition on serotonin neurons. These results indicate that T-type calcium channels are critical regulators of a C. elegans serotonergic circuit and demonstrate a mechanism in which T-type channels functionally gate inhibitory modulation in vivo.

Wednesday, May 17th

Zhang, Y.V., Hannan, S.B., Kern, J.V., Stanchev, D.T., KoƧ, 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
Summary:
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. Disease associated KIF1A mutations have been associated with motor and sensory dysfunctions as well as non-syndromic intellectual disability in humans. 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, there is a marked loss of postsynaptic scaffolding proteins and reduced complexity of the sub-synaptic reticulum, which can 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.

Sugie, A., Mohl, C., Hakeda-Suzuki, S., Matsui, H., Suzuki, T. and Tavosanis, G. (2017). Analyzing synaptic modulation of Drosophila melanogaster photoreceptors after exposure to prolonged light. J Vis Exp(120) [Epub ahead of print]. PubMed ID: 28287587
Summary:
The nervous system has the remarkable ability to adapt and respond to various stimuli. This neural adjustment is largely achieved through plasticity at the synaptic level. The Active Zone (AZ) is the region at the presynaptic membrane that mediates neurotransmitter release and is composed of a dense collection of scaffold proteins. AZs of Drosophila photoreceptors undergo molecular remodeling after prolonged exposure to natural ambient light. Thus the level of neuronal activity can rearrange the molecular composition of the AZ and contribute to the regulation of the functional output. Starting from the light exposure set-up preparation to the immunohistochemistry, this protocol details how to quantify the number, the spatial distribution, and the delocalization level of synaptic molecules at AZs in Drosophila photoreceptors. Using image analysis software, clusters of the GFP-fused AZ component Bruchpilot were identified for each R8 photoreceptor (R8) axon terminal. Detected Bruchpilot spots were automatically assigned to individual R8 axons. To calculate the distribution of spot frequency along the axon, a customized software plugin was used. Each axon's start-point and end-point were manually defined and the position of each Bruchpilot spot was projected onto the connecting line between start and end-point. Besides the number of Bruchpilot clusters, the delocalization level of Bruchpilot-GFP within the clusters was also quantified. These measurements reflect in detail the spatially resolved synaptic dynamics in a single neuron under different environmental conditions to stimuli.
Messeant, J., et al. (2017). Wnts contribute to neuromuscular junction formation through distinct signaling pathways. Development. PubMed ID: 28348167
Evolutionary Homolog Study
Understanding the developmental steps shaping the formation of the neuromuscular junction (NMJ) connecting motoneurons to skeletal muscle fibers, is critical. Wnt morphogens are key players in the formation of this specialized peripheral synapse. This study demonstrates through Wnt4 and Wnt11 gain of function studies in culture or in mice that Wnts enhance acetylcholine receptor (AChR) clustering and motor axon outgrowth. In contrast, loss of Wnt11 or Wnt-dependent signaling in vivo decreases AChR clustering and motor nerve terminal branching. Both Wnt4 and Wnt11 stimulate AChR clustering and mRNA downstream activation of the beta-catenin pathway. Strikingly, Wnt4 and Wnt11 co-immunoprecipitate with Vangl2 (see Drosophila Van Gogh), a core component of the Planar Cell Polarity (PCP) pathway, which accumulates at embryonic NMJ. Moreover, mice bearing a Vangl2 loss of function mutation (looptail) exhibit a decreased number of AChR clusters and overgrowth of motor axons bypassing AChR clusters. Taken together, these results provide genetic and biochemical evidences that Wnt4 and Wnt11 cooperatively contribute to mammalian NMJ formation through activation of both the canonical and Vangl2-dependent core PCP pathways.
Lee, J. Y., Lee, L. J., Fan, C. C., Chang, H. C., Shih, H. A., Min, M. Y. and Chang, M. S. (2017). Important roles of Vilse in dendritic architecture and synaptic plasticity.. Sci Rep 7: 45646. PubMed ID: 28368047
Evolutionary Homolog Study
Vilse/Arhgap39 is a Rho GTPase activating protein (RhoGAP) and utilizes its WW domain to regulate Rac/Cdc42-dependent morphogenesis in Drosophila and murine hippocampal neurons. However, the function of Vilse in mammalian dendrite architecture and synaptic plasticity remained unclear. This study aimed to explore the possible role of Vilse in dendritic structure and synaptic function in the brain. Homozygous knockout of Vilse resulted in premature embryonic lethality in mice. Changes in dendritic complexity and spine density were noticed in hippocampal neurons of Camk2a-Cre mediated forebrain-specific Vilse knockout (VilseDelta/Delta) mice. VilseDelta/Delta mice displayed impaired spatial memory in water maze and Y-maze tests. Electrical stimulation in hippocampal CA1 region revealed that the synaptic transmission and plasticity were defected in VilseDelta/Delta mice. Collectively, these results demonstrate that Vilse is essential for embryonic development and required for spatial memory.
Liu, M., Feng, Z., Ke, H., Liu, Y., Sun, T., Dai, J., Cui, W. and Pastor-Pareja, J. C. (2017). Tango1 spatially organizes ER exit sites to control ER export. J Cell Biol. PubMed ID: 28280122
Summary:
Exit of secretory cargo from the endoplasmic reticulum (ER) takes place at specialized domains called ER exit sites (ERESs). In mammals, loss of TANGO1 and other MIA/cTAGE (melanoma inhibitory activity/cutaneous T cell lymphoma-associated antigen) family proteins prevents ER exit of large cargoes such as collagen. This study shows that Drosophila melanogaster Tango1, the only MIA/cTAGE family member in fruit flies, is a critical organizer of the ERES-Golgi interface. Tango1 rings hold COPII (coat protein II; Sec23) carriers and Golgi in close proximity at their center. Loss of Tango1, present at ERESs in all tissues, reduces ERES size and causes ERES-Golgi uncoupling, which impairs secretion of not only collagen, but also all other cargoes examined. Further supporting an organizing role of Tango1, its overexpression creates more and larger ERESs. These results suggest that spatial coordination of ERES, carrier, and Golgi elements through Tango1's multiple interactions increases secretory capacity in Drosophila and allows secretion of large cargo.
Meng, J., Ma, X., Tao, H., Jin, X., Witvliet, D., Mitchell, J., Zhu, M., Dong, M.Q., Zhen, M., Jin, Y. and Qi, Y.B. (2017). Myrf ER-Bound Transcription Factors Drive C. elegans Synaptic Plasticity via Cleavage-Dependent Nuclear Translocation. Dev Cell 41: 180-194. PubMed ID: 28441531
Evolutionary Homolog Study:
Synaptic refinement is a critical step in nervous system maturation, requiring a carefully timed reorganization and refinement of neuronal connections. This study identified myrf-1 and myrf-2 (see Drosophila CG3328), two C. elegans homologs of Myrf family transcription factors, as key regulators of synaptic rewiring. MYRF-1 and its paralog MYRF-2 are functionally redundant specifically in synaptic rewiring. They co-exist in the same protein complex and act cooperatively to regulate synaptic rewiring. MYRF proteins localize to the ER membrane and are cleaved into active N-terminal fragments, which then translocate into the nucleus to drive synaptic rewiring. Overexpression of active forms of MYRF is sufficient to accelerate synaptic rewiring. MYRF-1 and MYRF-2 are the first genes identified to be indispensable for promoting synaptic rewiring in C. elegans. These findings reveal a molecular mechanism underlying synaptic rewiring and developmental circuit plasticity.

Tuesday, May 16th

Lee, T. V., Pandey, A. and Jafar-Nejad, H. (2017). Xylosylation of the Notch receptor preserves the balance between its activation by trans-Delta and inhibition by cis-ligands in Drosophila. PLoS Genet 13(4): e1006723. PubMed ID: 28394891
Summary:
The Drosophila glucoside xylosyltransferase Shams xylosylates Notch and inhibits Notch signaling in specific contexts including wing vein development. However, the molecular mechanisms underlying context-specificity of the shams phenotype is not known. It is hypothesized that Shams might affect Delta-mediated Notch signaling. This study found that altering the gene dosage of Delta affects the wing vein and head bristle phenotypes caused by loss of Shams or by mutations in the Notch xylosylation sites. Clonal analysis suggests that loss of shams promotes Delta-mediated Notch activation. Further, Notch trans-activation by ectopically overexpressed Delta shows a dramatic increase upon loss of shams. In vivo, cell aggregation and ligand-receptor binding assays show that shams knock-down in Notch-expressing cells enhances the binding between Notch and trans-Delta without affecting the binding between Notch and trans-Serrate and cell surface levels of Notch. Removing one copy of endogenous ligands mimics the effects of loss shams on Notch trans-activation by ectopic Delta. This favors the notion that trans-activation of Notch by Delta overcomes the cis-inhibition of Notch by endogenous ligands upon loss of shams. Taken together, these data suggest that xylosylation selectively impedes the binding of Notch with trans-Delta without affecting its binding with cis-ligands and thereby assists in determining the balance of Notch receptor's response to cis-ligands vs. trans-Delta during Drosophila development.
Liu, K., Shen, D., Shen, J., Gao, S. M., Li, B., Wong, C., Feng, W. and Song, Y. (2017). The super elongation complex drives neural stem cell fate commitment. Dev Cell 40(6): 537-551.e536. PubMed ID: 28350987
Summary:
Asymmetric stem cell division establishes an initial difference between a stem cell and its differentiating sibling, critical for maintaining homeostasis and preventing carcinogenesis. Yet the mechanisms that consolidate and lock in such initial fate bias remain obscure. This study used Drosophila neuroblasts to demonstrate that the super elongation complex (SEC) acts as an intrinsic amplifier to drive cell fate commitment. SEC is highly expressed in neuroblasts, where it promotes self-renewal by physically associating with Notch transcription activation complex and enhancing HES (hairy and E(spl)) transcription. HES in turn upregulates SEC activity, forming an unexpected self-reinforcing feedback loop with SEC. SEC inactivation leads to neuroblast loss, whereas its forced activation results in neural progenitor dedifferentiation and tumorigenesis. These studies unveil an SEC-mediated intracellular amplifier mechanism in ensuring robustness and precision in stem cell fate commitment and provide mechanistic explanation for the highly frequent association of SEC overactivation with human cancers.
Pimmett, V.L., Deng, H., Haskins, J.A., Mercier, R.J., LaPointe, P. and Simmonds, A.J. (2017). The activity of the Drosophila Vestigial protein is modified by Scalloped-dependent phosphorylation. Dev Biol [Epub ahead of print]. PubMed ID: 28322734
Summary:
The Drosophila vestigial gene is required for proliferation and differentiation of the adult wing and for differentiation of larval and adult muscle identity. Vestigial is part of a multi-protein transcription factor complex, which includes Scalloped, a TEAD-class DNA binding protein. Binding Scalloped is necessary for translocation of Vestigial into the nucleus. This study shows that Vestigial is extensively post-translationally modified and at least one of these modifications is required for proper function during development. There is p38-dependent phosphorylation of Serine 215 in the carboxyl-terminal region of Vestigial. Phosphorylation of Serine 215 occurs in the nucleus and requires the presence of Scalloped. Comparison of a phosphomimetic and non-phosphorylatable mutant forms of Vestigial shows differences in the ability to rescue the wing and muscle phenotypes associated with a null vestigial allele.
Thomas, J.T., Eric Dollins, D., Andrykovich, K.R., Chu, T., Stultz, B.G., Hursh, D.A. and Moos, M. (2017). SMOC can act as both an antagonist and an expander of BMP signaling. Elife 6. PubMed ID: 28323621
Summary:
The matricellular protein SMOC (Secreted Modular Calcium binding protein) is conserved phylogenetically from vertebrates to arthropods. It has been previously shown that SMOC inhibits bone morphogenetic protein (BMP) signaling downstream of its receptor via activation of mitogen-activated protein kinase (MAPK) signaling. In contrast, the most prominent effect of the Drosophila orthologue, pentagone (pent), is expanding the range of BMP signaling during wing patterning. Using SMOC deletion constructs this study found that SMOC-∆EC, lacking the extracellular calcium binding (EC) domain, inhibits BMP2 signaling, whereas SMOC-EC (EC domain only) enhances BMP2 signaling. The SMOC-EC domain binds HSPGs with a similar affinity to BMP2 and can expand the range of BMP signaling in an in vitro assay by competition for HSPG-binding. Together with data from studies in vivo the study proposes a model to explain how these two activities contribute to the function of Pent in Drosophila wing development and SMOC in mammalian joint formation.

Monday, May 15th

Shen, H.C., Chu, S.Y., Hsu, T.C., Wang, C.H., Lin, I.Y. and Yu, H.H. (2017). Semaphorin-1a prevents Drosophila olfactory projection neuron dendrites from mis-targeting into select antennal lobe regions. PLoS Genet [Epub ahead of print]. PubMed ID: 28448523
Summary:
Elucidating how appropriate neurite patterns are generated in neurons of the olfactory system is crucial for comprehending the construction of the olfactory map. In the Drosophila olfactory system, projection neurons (PNs), primarily derived from four neural stem cells (called neuroblasts), populate their cell bodies surrounding to and distribute their dendrites in distinct but overlapping patterns within the primary olfactory center of the brain, the antennal lobe (AL). However, it remains unclear whether the same molecular mechanisms are employed to generate the appropriate dendritic patterns in discrete AL glomeruli among PNs produced from different neuroblasts. By examining a previously explored transmembrane protein Semaphorin-1a (Sema-1a) which was proposed to globally control initial PN dendritic targeting along the dorsolateral-to-ventromedial axis of the AL, this study discovered a new role for Sema-1a in preventing dendrites of both uni-glomerular and poly-glomerular PNs from aberrant invasion into select AL regions and, intriguingly, this Sema-1a-deficient dendritic mis-targeting phenotype seems to associate with the origins of PNs from which they are derived. Further, ectopic expression of Sema-1a results in PN dendritic mis-projection from a select AL region into adjacent glomeruli, strengthening the idea that Sema-1a plays an essential role in preventing abnormal dendritic accumulation in select AL regions. Taken together, these results demonstrate that Sema-1a repulsion keeps dendrites of different types of PNs away from each other, enabling the same types of PN dendrites to be sorted into destined AL glomeruli and permitting for functional assembly of olfactory circuitry.

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
Summary:
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 has 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.
Liu, L., Tian, Y., Zhang, X. Y., Zhang, X., Li, T., Xie, W. and Han, J. (2017). Neurexin restricts axonal branching in columns by promoting Ephrin clustering. Dev Cell 41(1): 94-106. PubMed ID: 28366281
Summary:
Columnar restriction of neurites is critical for forming nonoverlapping receptive fields and preserving spatial sensory information from the periphery in both vertebrate and invertebrate nervous systems, but the underlying molecular mechanisms remain largely unknown. This study demonstrates that Drosophila homolog of α-neurexin (DNrx) plays an essential role in columnar restriction during L4 axon branching. Depletion of DNrx from L4 neurons resulted in misprojection of L4 axonal branches into neighboring columns due to impaired Ephrin clustering. The proper Ephrin clustering requires its interaction with the intracellular region of DNrx. Furthermore, it was found that Drosophila neuroligin 4 (DNlg4) in Tm2 neurons binds to DNrx and initiates DNrx clustering in L4 neurons, which subsequently induces Ephrin clustering. This study demonstrates that DNrx promotes ephrin clustering and reveals that ephrin/Eph signaling from adjacent L4 neurons restricts axonal branches of L4 neurons in columns.
Murakami, S., Minami-Ohtsubo, M., Nakato, R., Shirahige, K. and Tabata, T. (2017). Two components of aversive memory in Drosophila, anesthesia-sensitive and anesthesia-resistant memory, require distinct domains within the Rgk1 small GTPase. J Neurosci [Epub ahead of print]. PubMed ID: 28416593
Summary:
For aversive olfactory memory in Drosophila, multiple components have been identified that exhibit different stabilities. Intermediate-term memory generated after single cycle conditioning is divided into anesthesia-sensitive memory (ASM) and anesthesia-resistant memory (ARM), with the latter being more stable. This study determined that the ASM and ARM pathways converged on the Rgk1 small GTPase and that the N-terminal domain-deleted Rgk1 was sufficient for ASM formation, whereas the full-length form was required for ARM formation. Rgk1 is specifically accumulated at the synaptic site of the Kenyon cells (KCs), the intrinsic neurons of the mushroom bodies (MBs), which play a pivotal role in olfactory memory formation. A higher than normal Rgk1 level enhanced memory retention, which is consistent with the result that Rgk1 suppressed Rac-dependent memory decay; these findings suggest that rgk1 bolsters ASM via the suppression of forgetting. It is proposed that Rgk1 plays a pivotal role in the regulation of memory stabilization by serving as a molecular node that resides at KC synapses, where the ASM and ARM pathway may interact.

Sunday, May 14th

Felsenberg, J., Barnstedt, O., Cognigni, P., Lin, S. and Waddell, S. (2017). Re-evaluation of learned information in Drosophila. Nature 544(7649): 240-244. PubMed ID: 28379939
Summary:
Animals constantly assess the reliability of learned information to optimize their behaviour. On retrieval, consolidated long-term memory can be neutralized by extinction if the learned prediction was inaccurate. Alternatively, retrieved memory can be maintained, following a period of reconsolidation during which it is labile. Although extinction and reconsolidation provide opportunities to alleviate problematic human memories, a detailed mechanistic understanding of memory updating is lacking. This study identified neural operations underpinning the re-evaluation of memory in Drosophila. Reactivation of reward-reinforced olfactory memory can lead to either extinction or reconsolidation, depending on prediction accuracy. Each process recruits activity in specific parts of the mushroom body output network and distinct subsets of reinforcing dopaminergic neurons. Memory extinction requires output neurons with dendrites in the α and α' lobes of the mushroom body, which drive negatively reinforcing dopaminergic neurons that innervate neighbouring zones. The aversive valence of these new extinction memories neutralizes previously learned odour preference. Memory reconsolidation requires the γ2α'1 mushroom body output neurons. This pathway recruits negatively reinforcing dopaminergic neurons innervating the same compartment and re-engages positively reinforcing dopaminergic neurons to reconsolidate the original reward memory. These data establish that recurrent and hierarchical connectivity between mushroom body output neurons and dopaminergic neurons enables memory re-evaluation driven by reward-prediction error.
Schnell, B., Ros, I. G. and Dickinson, M. H. (2017). A descending neuron correlated with the rapid steering maneuvers of flying Drosophila. Curr Biol 27(8): 1200-1205. PubMed ID: 28392112
Summary:
To navigate through the world, animals must stabilize their path against disturbances and change direction to avoid obstacles and to search for resources. Locomotion is thus guided by sensory cues but also depends on intrinsic processes, such as motivation and physiological state. Flies, for example, turn with the direction of large-field rotatory motion, an optomotor reflex that is thought to help them fly straight. Occasionally, however, they execute fast turns, called body saccades, either spontaneously or in response to patterns of visual motion such as expansion. These turns can be measured in tethered flying Drosophila, which facilitates the study of underlying neural mechanisms. Whereas there is evidence for an efference copy input to visual interneurons during saccades, the circuits that control spontaneous and visually elicited saccades are not well known. Using two-photon calcium imaging and electrophysiological recordings in tethered flying Drosophila, this study identified a descending neuron whose activity is correlated with both spontaneous and visually elicited turns during tethered flight. The cell's activity in open- and closed-loop experiments suggests that it does not underlie slower compensatory responses to horizontal motion but rather controls rapid changes in flight path. The activity of this neuron can explain some of the behavioral variability observed in response to visual motion and appears sufficient for eliciting turns when artificially activated. This work provides an entry point into studying the circuits underlying the control of rapid steering maneuvers in the fly brain.
Mohorianu, I.I., Bretman, A., Smith, D.T., Fowler, E., Dalmay, T. and Chapman, T. (2017). Genomic responses to socio-sexual environment in male Drosophila melanogaster exposed to conspecific rivals. RNA [Epub ahead of print]. PubMed ID: 28428330
Summary:
Socio-sexual environments have profound effects on fitness. Local sex ratios can alter the threat of sexual competition, to which males respond via plasticity in reproductive behaviours and ejaculate composition. In Drosophila melanogaster, males detect the presence of conspecific mating rivals prior to mating using multiple, redundant sensory cues. Males that respond to rivals gain significant fitness benefits by altering mating duration and ejaculate composition. This study investigated the underlying genome-wide changes involved. RNA-seq was used to analyse male transcriptomic responses 2, 26 and 50h after exposure to rivals, a time period that has previously been identified as encompassing the major facets of male responses to rivals. The results show a strong early activation of multiple sensory genes in the head-thorax (HT), prior to the expression of any phenotypic differences. This gene expression response is reduced by 26h, at the time of maximum phenotypic change, and shut off by 50h. In the abdomen (A) fewer genes change in expression and gene expression responses appear to increase over time. The results also suggest that different sets of functionally equivalent genes might be activated in different replicates. This could represent a mechanism by which robustness is conferred upon highly plastic traits. Overall, these data reveal that mRNA-seq can identify subtle genomic signatures characteristic of flexible behavioural phenotypes.
Leitão-Gonçalves, R., Carvalho-Santos, Z., Francisco, A.P., Fioreze, G.T., Anjos, M., Baltazar, C., Elias, A.P., Itskov, P.M., Piper, M.D.W. and Ribeiro, C. (2017). Commensal bacteria and essential amino acids control food choice behavior and reproduction. PLoS Biol 15: e2000862. PubMed ID: 28441450
Summary:
Choosing the right nutrients to consume is essential to health and wellbeing across species. However, the factors that influence these decisions are poorly understood. This is particularly true for dietary proteins, which are important determinants of lifespan and reproduction. This study shows that in Drosophila melanogaster, essential amino acids (eAAs) and the concerted action of the commensal bacteria Acetobacter pomorum and Lactobacilli are critical modulators of food choice. Using a chemically defined diet, it was shown that the absence of any single eAA from the diet is sufficient to elicit specific appetites for amino acid (AA)-rich food. Furthermore, commensal bacteria buffer the animal from the lack of dietary eAAs: both increased yeast appetite and decreased reproduction induced by eAA deprivation are rescued by the presence of commensals. Surprisingly, these effects do not seem to be due to changes in AA titers, suggesting that gut bacteria act through a different mechanism to change behavior and reproduction. Thus, eAAs and commensal bacteria are potent modulators of feeding decisions and reproductive output. This demonstrates how the interaction of specific nutrients with the microbiome can shape behavioral decisions and life history traits.

Saturday, May 13th

Martinez, A., Lectez, B., Ramirez, J., Popp, O., Sutherland, J. D., Urbe, S., Dittmar, G., Clague, M. J. and Mayor, U. (2017). Quantitative proteomic analysis of Parkin substrates in Drosophila neurons. Mol Neurodegener 12(1): 29. PubMed ID: 28399880
Summary:
Parkin (PARK2; see Drosophila Parkin) is an E3 ubiquitin ligase that is commonly mutated in Familial Parkinson's Disease (PD). In cell culture models, Parkin is recruited to acutely depolarised mitochondria by PINK1 (see Drosophila Pink1). PINK1 activates Parkin activity leading to ubiquitination of multiple proteins, which in turn promotes clearance of mitochondria by mitophagy. Many substrates have been identified using cell culture models in combination with depolarising drugs or proteasome inhibitors, but not in more physiological settings. This study utilized the recently introduced BioUb strategy to isolate ubiquitinated proteins in flies. Following Parkin Wild-Type (WT) and Parkin Ligase dead (LD) expression, mass spectrometry and stringent bioinformatics analysis identified those proteins differentially ubiquitinated, providing the first survey of steady state Parkin substrates using an in vivo model. An in vivo ubiquitination assay was used to validate one of those substrates in SH-SY5Y cells. This study identified 35 proteins that are more prominently ubiquitinated following Parkin over-expression. These include several mitochondrial proteins and a number of endosomal trafficking regulators such as v-ATPase sub-units, Syx5/STX5, ALiX/PDCD6IP and Vps4. The retromer component, Vps35, another PD-associated gene that has recently been shown to interact genetically with parkin, was also identified. Importantly, Parkin-dependent ubiquitination of VPS35 was validated in human neuroblastoma cells. Collectively these results provide new leads to the possible physiological functions of Parkin activity that are not overtly biased by acute mitochondrial depolarisation.
Lo Piccolo, L. and Yamaguchi, M. (2017). RNAi of arcRNA hsromega affects sub-cellular localization of Drosophila FUS to drive neurodiseases. Exp Neurol 292: 125-134. PubMed ID: 28342748
Summary:
A conspicuous feature of some neurodegenerative diseases is the loss of nuclear activities of RNA-binding proteins (RBPs) like Fused in sarcoma (FUS) and eventually, their accumulation in cytoplasmic proteinaceous inclusions. A subset of Long non-coding RNAs (lncRNAs) is the core of nuclear bodies (NBs), which are the sites of RNA processing and sequestration of specific ribonucleoproteins (RNPs) complexes. In Drosophila melanogaster the lncRNA hsromega is the architectural RNA (arcRNA) of the NB omega speckles (omega-speckles). This study shows that the neuron-specific and motor neuron-specific knockdown of hsromega impairs locomotion in larval and adult flies and induces anatomical defects in presynaptic terminals of motor neurons, suggesting a novel role of arcRNA hsromega in development of neuromuscular junctions. Since RBPs are recognized as important regulators of neuronal activities, to examine the molecular mechanism of such neurodegeneration, interaction was examined between hsromega and Drosophila orthologue of human FUS (dFUS; Cabeza). Strictly, it was found that dFUS genetically and physically interacts with the arcRNA hsromega. Moreover, a fine regulation of gene expression occurs between hsromega and dFUS and surprisingly, depletion of hsromega was found to affect the sub-cellular compartmentalization of dFUS thus, enhancing its cytoplasmic localization and inducing its loss of nuclear function. The model that is proposed shows the role of arcRNA in diseases affecting the nervous system and in particular it elucidates the molecular mechanism underlying the loss of dFUS nuclear function in the absence of its mutations. These new findings could provide new insights into the pathogenesis of neurodegenerative disease dependent on mis-function or mis-localization of aggregation prone RNA binding proteins like FUS in Amyotrophic Lateral Sclerosis.
Feuillette, S., Delarue, M., Riou, G., Gaffuri, A.L., Wu, J., Lenkei, Z., Boyer, O., Frébourg, T., Campion, D. and Lecourtois, M. (2017). Neuron-to-Neuron Transfer of FUS in Drosophila primary neuronal culture Is enhanced by ALS-associated mutations. J Mol Neurosci [Epub ahead of print]. PubMed ID: 28429234
Summary:
The DNA- and RNA-binding protein fused in sarcoma (FUS; see Drosophila Cabeza) has been pathologically and genetically linked to amyotrophic lateral sclerosis (ALS) or frontotemporal lobar degeneration (FTLD). Cytoplasmic FUS-positive inclusions have been identified in the brain and spinal cord of a subset of patients suffering with ALS/FTLD. An increasing number of reports suggest that FUS protein can behave in a prion-like manner. However, no neuropathological studies or experimental data are available regarding cell-to-cell spread of these pathological protein assemblies. This study investigated the ability of wild-type and mutant forms of FUS to transfer between neuronal cells. The study combined the use of Drosophila models for FUS proteinopathies with that of the primary neuronal cultures to address neuron-to-neuron transfer of FUS proteins. Using conditional co-culture models and an optimized flow cytometry-based methodology, it was demonstrated that ALS-mutant forms of FUS proteins can transfer between well-differentiated mature Drosophila neurons. These new observations support that a propagating mechanism could be applicable to FUS, leading to the sequential dissemination of pathological proteins over years.

Anelli, V., Villefranc, J.A., Chhangawala, S., Martinez-McFaline, R., Riva, E., Nguyen, A., Verma, A., Bareja, R., Chen, Z., Scognamiglio, T., Elemento, O. and Houvras, Y. (2017). Oncogenic BRAF disrupts thyroid morphogenesis and function via twist expression. Elife 6. PubMed ID: 28350298
Evolutionary Homolog Study:
Thyroid cancer is common, yet the sequence of alterations that promote tumor formation are incompletely understood. This study describes a novel model of thyroid carcinoma in zebrafish that reveals temporal changes due to BRAFV600E (see Drosophila Raf). Through the use of real-time in vivo imaging, disruption in thyroid follicle structure was observed to occur early in thyroid development. Combinatorial treatment using BRAF and MEK inhibitors reverses the developmental effects induced by BRAFV600E. Adult zebrafish expressing BRAFV600E in thyrocytes develop invasive carcinoma. A gene expression signature from zebrafish thyroid cancer was identified and found to be predictive of disease-free survival in patients with papillary thyroid cancer. Gene expression studies nominate TWIST2 (see Drosophila twist) as a key effector downstream of BRAF. Using CRISPR/Cas9 to genetically inactivate a TWIST2 orthologue, the effects of BRAFV600E were suppressed and thyroid morphology and hormone synthesis were restored. These data suggest that expression of TWIST2 plays a role in an early step of BRAFV600E-mediated transformation.

Friday, May 12th

Mojica-Vazquez, L. H., Benetah, M. H., Baanannou, A., Bernat-Fabre, S., Deplancke, B., Cribbs, D. L., Bourbon, H. M. and Boube, M. (2017). Tissue-specific enhancer repression through molecular integration of cell signaling inputs. PLoS Genet 13(4): e1006718. PubMed ID: 28394894
Summary:
The bric-a-brac2 (bab2) gene is required for distal leg segmentation. Previous work has shown that the Distal-less (Dll) homeodomain and Rotund (Rn) zinc-finger activating transcription factors control limb-specific bab2 expression by binding directly a single critical leg/antennal enhancer (LAE) within the bric-a-brac locus. This study shows that the EGFR-responsive C15 homeodomain and the Notch-regulated Bowl zinc-finger transcription factors also interact directly with the LAE enhancer as a repressive duo. The appendage patterning gene bab2 is the first identified direct target of the Bowl repressor, an Odd-skipped/Osr family member. Moreover, C15 was shown to act on LAE activity independently of its regular partner, the Aristaless homeoprotein. Instead, C15 interacts physically with the Dll activator through contacts between their homeodomain and binds competitively with Dll to adjacent cognate sites on LAE, adding potential new layers of regulation by C15. Lastly, C15 and Bowl activities were shown to regulate also rn expression. These findings shed light on how the concerted action of two transcriptional repressors, in response to cell signaling inputs, shapes and refines gene expression along the limb proximo-distal axis in a timely manner.
Mendoza-Garcia, P., Hugosson, F., Fallah, M., Higgins, M. L., Iwasaki, Y., Pfeifer, K., Wolfstetter, G., Varshney, G., Popichenko, D., Gergen, J. P., Hens, K., Deplancke, B. and Palmer, R. H. (2017). The Zic family homologue Odd-paired regulates Alk expression in Drosophila. PLoS Genet 13(4): e1006617. PubMed ID: 28369060
Summary:
The Anaplastic Lymphoma Kinase (Alk) receptor tyrosine kinase (RTK) plays a critical role in the specification of founder cells (FCs) in the Drosophila visceral mesoderm (VM) during embryogenesis. Reporter gene and CRISPR/Cas9 deletion analysis reveals enhancer regions in and upstream of the Alk locus that influence tissue-specific expression in the amnioserosa (AS), the VM and the epidermis. By performing high throughput yeast one-hybrid screens (Y1H) with a library of Drosophila transcription factors (TFs) this study identified Odd-paired (Opa), the Drosophila homologue of the vertebrate Zic family of TFs, as a novel regulator of embryonic Alk expression. Further characterization identifies evolutionarily conserved Opa-binding cis-regulatory motifs in one of the Alk associated enhancer elements. Employing Alk reporter lines as well as CRISPR/Cas9-mediated removal of regulatory elements in the Alk locus, modulation of Alk expression by Opa was shown in the embryonic AS, epidermis and VM. In addition, enhancer elements were identified that integrate input from additional TFs, such as Binou (Bin) and Bagpipe (Bap), to regulate VM expression of Alk in a combinatorial manner. Taken together, these data show that the Opa zinc finger TF is a novel regulator of embryonic Alk expression.
Corrales-Berjano, M., Rosado Diez, A., Cortini, R., van Arensbergen, J., van Steensel, B. and Filion, G. J. (2017). Clustering of Drosophila housekeeping promoters facilitates their expression. Genome Res [Epub ahead of print]. PubMed ID: 28420691
Summary:
Housekeeping genes of animal genomes cluster in the same chromosomal regions. It has long been suggested that this organization contributes to their steady expression across all the tissues of the organism. This study shows that the activity of Drosophila housekeeping gene promoters depends on the expression of their neighbours. By measuring the expression of ~ 85,000 reporters integrated in Kc167 cells, the best predictors of expression were identified as chromosomal contacts with the promoters and terminators of active genes. Surprisingly, the chromatin composition at the insertion site and the contacts with enhancers were less informative. These results are substantiated by the existence of genomic 'paradoxical' domains, rich in euchromatic features and enhancers, but where the reporters are expressed at low level, concomitant with a deficit of interactions with promoters and terminators. This indicates that the proper function of housekeeping genes relies not on contacts with long distance enhancers but on spatial clustering. Overall these results suggest that spatial proximity between genes increases their expression and that the linear architecture of the Drosophila genome contributes to this effect.
Qiu, Y. and Gilmour, D. S. (2017). Identification of regions in the Spt5 subunit of DSIF that are involved in promoter proximal pausing. J Biol Chem [Epub ahead of print]. PubMed ID: 28213523
Summary:
DRB-sensitivity inducing factor (DSIF2, or Spt4/5) is a conserved transcription elongation factor that both inhibits and stimulates transcription elongation in metazoans. In Drosophila and vertebrates, DSIF together with negative elongation factor (NELF) associates with RNA polymerase II (Pol II) during early elongation and causes Pol II to pause in the promoter proximal region of genes. The mechanism of how DSIF establishes pausing is not known. This study constructed Spt5 mutant forms of DSIF and tested their capacity to restore promoter proximal pausing to DSIF-depleted Drosophila nuclear extracts. The C-terminal repeats (CTR) region of Spt5, which has been implicated in both inhibition and stimulation of elongation, is dispensable for promoter proximal pausing. A region encompassing KOW4 and KOW5 of Spt5 is essential for pausing, and mutations in KOW5 specifically shift the location of the pause. RNA crosslinking analysis reveals that KOW5 directly contacts the nascent transcript and deletion of KOW5 disrupts this interaction. These results suggest that KOW5 is involved in promoter proximal pausing through contact with the nascent RNA.

Thursday, May 11th

Zhang, H. and Blumenthal, E. M. (2017). Identification of multiple functional receptors for tyramine on an insect secretory epithelium. Sci Rep 7(1): 168. PubMed ID: 28279025
Summary:
The biogenic amine tyramine (TA) regulates many aspects of invertebrate physiology and development. Although three TA receptor subtypes have been identified (TAR1-3), specific receptors have not been linked to physiological responses in native tissue. In the Malpighian (renal) tubule of Drosophila melanogaster, TA activates a transepithelial chloride conductance, resulting in diuresis and depolarization of the transepithelial potential. In the current work, mutation or RNAi-mediated knockdown in the stellate cells of the tubule of TAR2 (tyrR, CG7431) resulted in a dramatic reduction, but not elimination, of the TA-mediated depolarization. Mutation or knockdown of TAR3 (tyrRII, CG16766) had no effect. However, deletion of both genes, or knockdown of TAR3 on a TAR2 mutant background, eliminated the TA responses. Thus while TAR2 is responsible for the majority of the TA sensitivity of the tubule, TAR3 also contributes to the response. Knockdown or mutation of TAR2 also eliminated the response of tubules to the related amine octopamine (OA), indicating that OA can activate TAR2. This finding contrasts to reports that heterologously expressed TAR2 is highly selective for TA over OA. This is the first report of TA receptor function in a native tissue and indicates unexpected complexity in the physiology of the Malpighian tubule.
Dutta, D., Paul, M. S., Singh, A., Mutsuddi, M. and Mukherjee, A. (2017). Regulation of Notch signaling by the Heterogeneous Nuclear Ribonucleoprotein Hrp48 and Deltex in Drosophila melanogaster. Genetics [Epub ahead of print]. PubMed ID: 28396507
Summary:
Notch signaling is an evolutionarily conserved pathway that is found to be involved in a number of cellular events throughout development. A protein-protein interaction screen identified Hrp48, a heterogeneous nuclear ribonucleoprotein (hnRNP) in Drosophila as a novel interacting partner of Deltex (Dx), a cytoplasmic modulator of Notch signaling. Immunocytochemical analysis revealed that Dx and Hrp48 colocalize in cytoplasmic vesicles. dx mutant also showed strong genetic interactions with hrp48 mutant alleles. The coexpression of Dx and Hrp48 resulted in the depletion of cytoplasmic Notch in larval wing imaginal discs and downregulation of Notch targets, cut and wingless. Earlier it has been shown that Sex-lethal (Sxl), on binding with Notch mRNA, negatively regulates Notch signaling. The overexpression of Hrp48 was found to inhibit Sxl expression and consequently rescued Notch signaling activity. In the present study, it was observed that Dx together with Hrp48 can regulate Notch signaling in Sxl-independent manner. In addition, Dx and Hrp48 displayed synergistic effect on caspase-mediated cell death. These results suggest that Dx and Hrp48 together negatively regulate Notch signaling in Drosophila.
Franz, A., Shlyueva, D., Brunner, E., Stark, A. and Basler, K. (2017). Probing the canonicity of the Wnt/Wingless signaling pathway. PLoS Genet 13(4): e1006700. PubMed ID: 28369070
Summary:
The hallmark of canonical Wnt signaling is the transcriptional induction of Wnt target genes by the β-catenin/TCF complex. Several studies have proposed alternative interaction partners for β-catenin or TCF, but the relevance of potential bifurcations in the distal Wnt pathway remains unclear. This study examined, on a genome-wide scale, the requirement for Armadillo (Arm, Drosophila β-catenin) and Pangolin (Pan, Drosophila TCF) in the Wnt/Wingless(Wg)-induced transcriptional response of Drosophila Kc cells. Using somatic genetics, it was demonstrated that both Arm and Pan are absolutely required for mediating activation and repression of target genes. Furthermore, by means of STARR-sequencing Wnt/Wg-responsive enhancer elements were identified and it was found that all responsive enhancers depend on Pan. Together, these results confirm the dogma of canonical Wnt/Wg signaling and argue against the existence of distal pathway branches in this system.
Lee, J. H., Lee, C. W., Park, S. H. and Choe, K. M. (2017). Spatiotemporal regulation of cell fusion by JNK and JAK/STAT signaling during Drosophila wound healing. J Cell Sci [Epub ahead of print]. PubMed ID: 28424232
Summary:
Cell-cell fusion should be tightly controlled, but the underlying mechanism is poorly understood. This study found that the JAK/STAT pathway suppressed cell fusion during wound healing and delimited the event to the vicinity of the wound in the Drosophila larval epidermis. In the absence of JAK/STAT signaling, a large syncytium containing 3-fold the number of nuclei observed in wild-type tissue formed in wounded epidermis. upd2 and upd3 were transcriptionally induced by wounding and were required for suppressing excess cell fusion. JNK was activated in the wound vicinity and activity peaked at approximately 8 h after injury, whereas JAK/STAT signaling was activated in an adjoining concentric ring and activity peaked at a later stage. Cell fusion occurred primarily in the wound vicinity, where JAK/STAT activation was suppressed by fusion-inducing JNK signaling. JAK/STAT signaling was both necessary and sufficient for the induction of βPS integrin expression, suggesting that the suppression of cell fusion was mediated at least in part by integrin protein.

Wednesday, May 10th

Kandasamy, S. K., Zhu, L. and Fukunaga, R. (2017). The C-terminal dsRNA-binding domain of Drosophila Dicer-2 is crucial for efficient and high-fidelity production of siRNA and loading of siRNA to Argonaute2. RNA [Epub ahead of print]. PubMed ID: 28416567
Summary:
Drosophila Dicer-2 efficiently and precisely produces 21-nt siRNAs from long double-stranded RNA (dsRNA) substrates and loads these siRNAs onto the effector protein Argonaute2 for RNA silencing. The functional roles of each domain of the multi-domain Dicer-2 enzyme in the production and loading of siRNAs are not fully understood. This suty characterized Dicer-2 mutants lacking either the N-terminal helicase domain or C-terminal dsRNA-binding domain (CdsRBD) (ΔHelicase and ΔCdsRBD, respectively) in vivo and in vitro. ΔCdsRBD Dicer-2 was found to produce siRNAs with lowered efficiency and length-fidelity, producing a smaller ratio of 21 nt siRNAs and higher ratios of 20 nt and 22 nt siRNAs in vivo and in vitro. It was also found that ΔCdsRBD Dicer-2 cannot load siRNA duplexes to Argonaute2 in vitro. Consistent with these findings, DeltaCdsRBD Dicer-2 causes partial loss of RNA silencing activity in vivo. Thus, Dicer-2 CdsRBD is crucial for the efficiency and length fidelity in siRNA production and for siRNA loading. Together with previous findings, it is proposed that CdsRBD binds the proximal body region of a long dsRNA substrate whose 5'-monophosphate end is anchored by the phosphate-binding pocket in the PAZ domain. CdsRBD aligns the RNA to the RNA cleavage active site in the RNaseIII domain for efficient and high-fidelity siRNA production. This study reveals multi functions of Dicer-2 CdsRBD and sheds light on the molecular mechanism by which Dicer-2 produces 21 nt siRNAs with a high efficiency and fidelity for efficient RNA silencing.
Harrington, A. W., McKain, M. R., Michalski, D., Bauer, K. M., Daugherty, J. M. and Steiniger, M. (2017). Drosophila melanogaster retrotransposon and inverted repeat-derived endogenous siRNAs are differentially processed in distinct cellular locations. BMC Genomics 18(1): 304. PubMed ID: 28415970
Summary:
Endogenous small interfering (esi)RNAs repress mRNA levels and retrotransposon mobility in Drosophila somatic cells. esiRNAs are primarily generated from retrotransposons and two inverted repeat (hairpin) loci in a Dicer2 dependent manner. Additionally, proteins involved in 3' end processing, such as Symplekin, CPSF73 and CPSF100, have been implicated in the esiRNA pathway. This study presents evidence of overlap between two essential RNA metabolic pathways: esiRNA biogenesis and mRNA 3' end processing. A nucleus-specific interaction was identified between the essential esiRNA cleavage enzyme Dicer2 (Dcr2) and Symplekin, a component of the core cleavage complex (CCC) required for 3' end processing. This interaction is mediated by the N-terminal 271 amino acids of Symplekin; CCC factors CPSF73 and CPSF100 do not contact Dcr2. While Dcr2 binds the CCC, Dcr2 knockdown does not affect mRNA 3' end formation. RNAi-depletion of CCC components Symplekin and CPSF73 causes perturbations in esiRNA abundance that correlate with fluctuations in retrotransposon and hairpin esiRNA precursor levels. RNAi-depletion of either CPSF73 or Symplekin results in nuclear retention of both hairpin and retrotransposon precursors suggesting that polyadenylation indirectly affects cellular localization of Dcr2 substrates. Together, these observations support a novel mechanism in which differences in localization of esiRNA precursors impacts esiRNA biogenesis. Hairpin-derived esiRNAs are generated in the cytoplasm independent of Dcr2-Symplekin interactions, while retrotransposons are processed in the nucleus.
Tay, M. L. and Pek, J. W. (2017). Maternally inherited stable intronic sequence RNA triggers a self-reinforcing feedback loop during development. Curr Biol 27(7): 1062-1067. PubMed ID: 28343963
Summary:
Maternally inherited noncoding RNAs (ncRNAs) can regulate zygotic gene expression across generations. Recently, many stable intronic sequence RNAs (sisRNAs), which are byproducts of pre-mRNA splicing, were found to be maternally deposited and persist till zygotic transcription in Xenopus and Drosophila. In various organisms, sisRNAs can be in linear or circular conformations, and they have been suggested to regulate host gene expression. It is unknown whether maternally deposited sisRNAs can regulate zygotic gene expression in the embryos. This study shows that a maternally inherited sisRNA (sisR-4) from the deadpan locus is important for embryonic development in Drosophila. Mothers, but not fathers, mutant for sisR-4 produce embryos that fail to hatch. During embryogenesis, sisR-4 promotes transcription of its host gene (deadpan), which is essential for development. Interestingly, sisR-4 functions by activating an enhancer present in the intron where sisR-4 is encoded. It is proposed that a maternal sisRNA triggers expression of its host gene via a positive feedback loop during embryogenesis.
Lee, J., Yoo, E., Lee, H., Park, K., Hur, J. H. and Lim, C. (2017). LSM12 and ME31B/DDX6 define distinct modes of posttranscriptional regulation by ATAXIN-2 protein complex in Drosophila circadian pacemaker neurons. Mol Cell 66(1): 129-140.e127. PubMed ID: 28388438
Summary:
ATAXIN-2 (ATX2) has been implicated in human neurodegenerative diseases, yet it remains elusive how ATX2 assembles specific protein complexes to execute its physiological roles. This study employed the posttranscriptional co-activator function of Drosophila ATX2 to demonstrate that LSM12 and ME31B/DDX6 are two ATX2-associating factors crucial for sustaining circadian rhythms. LSM12 acts as a molecular adaptor for the recruitment of TWENTY-FOUR (TYF) to ATX2. The ATX2-LSM12-TYF complex thereby stimulates TYF-dependent translation of the rate-limiting clock gene period (per) to maintain 24 hr periodicity in circadian behaviors. In contrast, ATX2 contributes to NOT1-mediated gene silencing and associates with NOT1 in a ME31B/DDX6-dependent manner. The ME31B/DDX6-NOT1 complex does not affect PER translation but supports high-amplitude behavioral rhythms along with ATX2, indicating a PER-independent clock function of ATX2. Taken together, these data suggest that the ATX2 complex may switch distinct modes of posttranscriptional regulation through its associating factors to control circadian clocks and ATX2-related physiology.

Tuesday, May 9th

Jeon, Y. M., Lee, S., Kim, S., Kwon, Y., Kim, K., Chung, C. G., Lee, S., Lee, S. B. and Kim, H. J. (2017). Neuroprotective effects of Protein tyrosine phosphatase 1B inhibition against ER stress-induced toxicity. Mol Cells [Epub ahead of print]. PubMed ID: 28359145
Summary:
Several lines of evidence suggest that endoplasmic reticulum (ER) stress plays a critical role in the pathogenesis of many neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Protein tyrosine phosphatase 1B (PTP1B) is known to regulate the ER stress signaling pathway, but its role in neuronal systems in terms of ER stress remains largely unknown. This study showed that rotenone-induced toxicity in human neuroblastoma cell lines and mouse primary cortical neurons was ameliorated by PTP1B inhibition. Moreover, the increase in the level of ER stress markers (eIF2alpha phosphorylation and PERK phosphorylation) induced by rotenone treatment was obviously suppressed by concomitant PTP1B inhibition. However, the rotenone-induced production of reactive oxygen species (ROS) was not affected by PTP1B inhibition, suggesting that the neuroprotective effect of the PTP1B inhibitor is not associated with ROS production. Moreover, it was found that MG132-induced toxicity involving proteasome inhibition was also ameliorated by PTP1B inhibition in a human neuroblastoma cell line and mouse primary cortical neurons. Consistently, downregulation of the PTP1B homologue gene in Drosophila mitigated rotenone- and MG132-induced toxicity. Taken together, these findings indicate that PTP1B inhibition may represent a novel therapeutic approach for ER stress-mediated neurodegenerative diseases.
Khalil, B., Cabirol-Pol, M. J., Miguel, L., Whitworth, A. J., Lecourtois, M. and Lievens, J. C. (2017). Enhancing Mitofusin/Marf ameliorates neuromuscular dysfunction in Drosophila models of TDP-43 proteinopathies. Neurobiol Aging 54: 71-83. PubMed ID: 28324764
Summary:
Transactive response DNA-binding protein 43 kDa (TDP-43) is considered a major pathological protein in amyotrophic lateral sclerosis and frontotemporal lobar degeneration. The precise mechanisms by which TDP-43 dysregulation leads to toxicity in neurons are not fully understood. Using TDP-43-expressing Drosophila, this study examined whether mitochondrial dysfunction is a central determinant in TDP-43 pathogenesis. Expression of human wild-type TDP-43 in Drosophila neurons results in abnormally small mitochondria. The mitochondrial fragmentation is correlated with a specific decrease in the mRNA and protein levels of the Drosophila profusion gene mitofusin/marf. Importantly, overexpression of Marf ameliorates defects in spontaneous walking activity and startle-induced climbing response of TDP-43-expressing flies. Partial inactivation of the mitochondrial profission factor, dynamin-related protein 1, also mitigates TDP-43-induced locomotor deficits. Expression of TDP-43 impairs neuromuscular junction transmission upon repetitive stimulation of the giant fiber circuit that controls flight muscles, which is also ameliorated by Marf overexpression. Enhancing the profusion gene mitofusin/marf is shown to be beneficial in an in vivo model of TDP-43 proteinopathies, serving as a potential therapeutic target.
Franco, L. M., Okray, Z., Linneweber, G. A., Hassan, B. A. and Yaksi, E. (2017). Reduced lateral inhibition impairs olfactory computations and behaviors in a Drosophila model of Fragile X syndrome. Curr Biol 27(8): 1111-1123. PubMed ID: 28366741
Summary:
Fragile X syndrome (FXS) patients present neuronal alterations that lead to severe intellectual disability, but the underlying neuronal circuit mechanisms are poorly understood. An emerging hypothesis postulates that reduced GABAergic inhibition of excitatory neurons is a key component in the pathophysiology of FXS. This idea was directly tested in a FXS Drosophila model. FXS flies were shown to exhibit strongly impaired olfactory behaviors. In line with this, olfactory representations are less odor specific due to broader response tuning of excitatory projection neurons. Impaired inhibitory interactions were found to underlie reduced specificity in olfactory computations. Finally, defective lateral inhibition across projection neurons was shown to be caused by weaker inhibition from GABAergic interneurons. Direct evidence is provided that deficient inhibition impairs sensory computations and behavior in an in vivo model of FXS. Together with evidence of impaired inhibition in autism and Rett syndrome, these findings suggest a potentially general mechanism for intellectual disability.
Klassen, M. P., Peters, C. J., Zhou, S., Williams, H. H., Jan, L. Y. and Jan, Y. N. (2017). Age-dependent diastolic heart failure in an in vivo Drosophila model. Elife 6 [Epub ahead of print]. PubMed ID: 28328397
Summary:
While the signals and complexes that coordinate the heartbeat are well established, how the heart maintains its electromechanical rhythm over a lifetime remains an open question with significant implications to human health. Reasoning that this homeostatic challenge confronts all pulsatile organs, this study developed a high resolution imaging and analysis toolset for measuring cardiac function in intact, unanesthetized Drosophila melanogaster. As in humans, normal aging primarily manifests as defects in relaxation (diastole) while preserving contractile performance. Using this approach, it was discovered that a pair of two-pore potassium channel (K2P) subunits (FlyBase gene: sandman), largely dispensable early in life, are necessary for terminating contraction (systole) in aged animals, where their loss culminates in fibrillatory cardiac arrest. As the pumping function of its heart is acutely dispensable for survival, Drosophila represents a uniquely accessible model for understanding the signaling networks maintaining cardiac performance during normal aging.

Monday, May 8th

Ren, Q., Yang, C. P., Liu, Z., Sugino, K., Mok, K., He, Y., Ito, M., Nern, A., Otsuna, H. and Lee, T. (2017). Stem cell-intrinsic, Seven-up-triggered temporal factor gradients diversify intermediate neural progenitors. Curr Biol [Epub ahead of print]. PubMed ID: 28434858
Summary:
Building a sizable, complex brain requires both cellular expansion and diversification. One mechanism to achieve these goals is production of multiple transiently amplifying intermediate neural progenitors (INPs) from a single neural stem cell. Like mammalian neural stem cells, Drosophila type II neuroblasts utilize INPs to produce neurons and glia. Within a given lineage, the consecutively born INPs produce morphologically distinct progeny, presumably due to differential inheritance of temporal factors. To uncover the underlying temporal fating mechanisms, type II neuroblasts' transcriptome was profiled across time. The results reveal opposing temporal gradients of Imp and Syp RNA-binding proteins (descending and ascending, respectively). Maintaining high Imp throughout serial INP production expands the number of neurons and glia with early temporal fate at the expense of cells with late fate. Conversely, precocious upregulation of Syp reduces the number of cells with early fate. Furthermore, this study reveals that the transcription factor Seven-up initiates progression of the Imp/Syp gradients. Interestingly, neuroblasts that maintain initial Imp/Syp levels can still yield progeny with a small range of early fates. It is therefore proposed that the Seven-up-initiated Imp/Syp gradients create coarse temporal windows within type II neuroblasts to pattern INPs, which subsequently undergo fine-tuned subtemporal patterning.
Omoto, J. J., Keles, M. F., Nguyen, B. M., Bolanos, C., Lovick, J. K., Frye, M. A. and Hartenstein, V. (2017). Visual input to the Drosophila central complex by developmentally and functionally distinct neuronal populations. Curr Biol 27(8): 1098-1110. PubMed ID: 28366740
Summary:
The Drosophila central brain consists of developmental-structural units of macrocircuitry formed by the sibling neurons of single neuroblasts. Lineage guides the connectivity and function of neurons, providing input to the central complex, a collection of neuropil compartments important for visually guided behaviors. The ellipsoid body (EB) is formed largely by the axons of ring (R) neurons, all of which are generated by a single lineage, DALv2. Two further lineages, DALcl1 and DALcl2, produce neurons that connect the anterior optic tubercle, a central brain visual center, with R neurons. Finally, DALcl1/2 receive input from visual projection neurons of the optic lobe medulla, completing a three-legged circuit that is called the anterior visual pathway (AVP). The AVP bears a fundamental resemblance to the sky-compass pathway, a visual navigation circuit described in other insects. DALcl1 and DALcl2 form two parallel channels, establishing connections with R neurons located in the peripheral and central domains of the EB, respectively. Although neurons of both lineages preferentially respond to bright objects, DALcl1 neurons have small ipsilateral, retinotopically ordered receptive fields, whereas DALcl2 neurons share a large excitatory receptive field in the contralateral hemifield. DALcl2 neurons become inhibited when the object enters the ipsilateral hemifield and display an additional excitation after the object leaves the field of view. Thus, the spatial position of a bright feature, such as a celestial body, may be encoded within this pathway.
Joseph, R. M., Sun, J. S., Tam, E. and Carlson, J. R. (2017). A receptor and neuron that activate a circuit limiting sucrose consumption. Elife 6. PubMed ID: 28332980
Summary:
The neural control of sugar consumption is critical for normal metabolism. In contrast to sugar-sensing taste neurons that promote consumption, this study identified a taste neuron that limits sucrose consumption in Drosophila. Silencing of the neuron increases sucrose feeding; optogenetic activation decreases it. The feeding inhibition depends on the IR60b receptor, as shown by behavioral analysis and Ca2+ imaging of an IR60b mutant. The IR60b phenotype shows a high degree of chemical specificity when tested with a broad panel of tastants. An automated analysis of feeding behavior in freely moving flies shows that IR60b limits the duration of individual feeding bouts. This receptor and neuron provide the molecular and cellular underpinnings of a new element in the circuit logic of feeding regulation. A dynamic model is proposed in which sucrose acts via IR60b to activate a circuit that inhibits feeding and prevents overconsumption.
Kim, D. H., Shin, M., Jung, S. H., Kim, Y. J. and Jones, W. D. (2017). A fat-derived metabolite regulates a peptidergic feeding circuit in Drosophila. PLoS Biol 15(3): e2000532. PubMed ID: 28350856
Summary:
This study shows that the enzymatic cofactor tetrahydrobiopterin (BH4) inhibits feeding in Drosophila. BH4 biosynthesis requires the sequential action of the conserved enzymes Punch, Purple, and Sepiapterin Reductase (Sptr). Although increased feeding is observed upon loss of Punch and Purple in the adult fat body, loss of Sptr must occur in the brain. Sptr expression is required in four adult neurons that express neuropeptide F (NPF), the fly homologue of the vertebrate appetite regulator neuropeptide Y (NPY). As expected, feeding flies BH4 rescues the loss of Punch and Purple in the fat body and the loss of Sptr in NPF neurons. Mechanistically, it was found BH4 deficiency reduces NPF staining, likely by promoting its release, while excess BH4 increases NPF accumulation without altering its expression. This study thus shows that, because of its physically distributed biosynthesis, BH4 acts as a fat-derived signal that induces satiety by inhibiting the activity of the NPF neurons.

Sunday, May 7th

Fricke, C. and Chapman, T. (2017). Variation in the post-mating fitness landscape in fruitflies. J Evol Biol [Epub ahead of print]. PubMed ID: 28391616
Summary:
Sperm competition is pervasive and fundamental to determining a male's overall fitness. Sperm traits and seminal fluid proteins (Sfps) are key factors. However, studies of sperm competition may often exclude females that fail to remate during a defined period. Hence, the resulting datasets contain fewer data from the potentially fittest males that have most success in preventing female remating. It is also important to consider a male's reproductive success before entering sperm competition, which is a major contributor to fitness. The exclusion of these data can both hinder understanding of the complete fitness landscapes of competing males and lessen the ability to assess the contribution of different determinants of reproductive success to male fitness. This is addressed using the Drosophila melanogaster model system, by (i) capturing a comprehensive range of intermating intervals that define the fitness of interacting wild type males, and (ii) analysing outcomes of sperm competition using selection analyses. Additional tests were conducted using males lacking the sex peptide (SP) ejaculate component versus genetically matched (SP+ ) controls. This allowed assessment of the comprehensive fitness effects of this important Sfp on sperm competition. The results showed a signature of positive, linear selection in wild type and SP+ control males on the length of the intermating interval and on male sperm competition defense. However, the fitness surface for males lacking SP was distinct, with local fitness peaks depending on contrasting combinations of remating intervals and offspring numbers. The results suggest that there are alternative routes to success in sperm competition and provide an explanation for the maintenance of variation in sperm competition traits.
Branstetter, M. G., Danforth, B. N., Pitts, J. P., Faircloth, B. C., Ward, P. S., Buffington, M. L., Gates, M. W., Kula, R. R. and Brady, S. G. (2017). Phylogenomic Insights into the Evolution of Stinging Wasps and the Origins of Ants and Bees. Curr Biol 27(7): 1019-1025. PubMed ID: 28376325
Summary:
The stinging wasps (Hymenoptera: Aculeata) are an extremely diverse lineage of hymenopteran insects, encompassing over 70,000 described species and a diversity of life history traits, including ectoparasitism, cleptoparasitism, predation, pollen feeding (bees [Anthophila] and Masarinae), and eusociality (social vespid wasps, ants, and some bees). The most well-studied lineages of Aculeata are the ants, which are ecologically dominant in most terrestrial ecosystems, and the bees, the most important lineage of angiosperm-pollinating insects. Establishing the phylogenetic affinities of ants and bees helps in understanding and reconstruction of patterns of social evolution as well as leading to full appreciation of the biological implications of the switch from carnivory to pollen feeding (pollenivory). Despite recent advancements in aculeate phylogeny, considerable uncertainty remains regarding higher-level relationships within Aculeata, including the phylogenetic affinities of ants and bees. Ultraconserved element (UCE) phylogenomics was used to resolve relationships among stinging-wasp families, gathering sequence data from >800 UCE loci and 187 samples, including 30 out of 31 aculeate families. The 187-taxon dataset was analyzed using multiple analytical approaches, and several alternative taxon sets were analyzed. Alternative hypotheses for the phylogenetic positions of ants and bees were tested. The results present a highly supported phylogeny of the stinging wasps. Most importantly, it was found unequivocal evidence that ants are the sister group to bees+apoid wasps (Apoidea) and that bees are nested within a paraphyletic Crabronidae. It was also demonstrated that taxon choice can fundamentally impact tree topology and clade support in phylogenomic inference.
Peters, R. S., et al. (2017). Evolutionary History of the Hymenoptera. Curr Biol 27(7): 1013-1018. PubMed ID: 28343967
Summary:
Hymenoptera (sawflies, wasps, ants, and bees) are one of four mega-diverse insect orders, comprising more than 153,000 described and possibly up to one million undescribed extant species. As parasitoids, predators, and pollinators, Hymenoptera play a fundamental role in virtually all terrestrial ecosystems and are of substantial economic importance. To understand the diversification and key evolutionary transitions of Hymenoptera, most notably from phytophagy to parasitoidism and predation (and vice versa) and from solitary to eusocial life, this study inferred the phylogeny and divergence times of all major lineages of Hymenoptera by analyzing 3,256 protein-coding genes in 173 insect species. These analyses suggest that extant Hymenoptera started to diversify around 281 million years ago (mya). The primarily ectophytophagous sawflies are found to be monophyletic. The species-rich lineages of parasitoid wasps constitute a monophyletic group as well. The little-known, species-poor Trigonaloidea are identified as the sister group of the stinging wasps (Aculeata). Finally, the evolutionary root of bees were located within the apoid wasp family "Crabronidae." These results reveal that the extant sawfly diversity is largely the result of a previously unrecognized major radiation of phytophagous Hymenoptera that did not lead to wood-dwelling and parasitoidism. They also confirm that all primarily parasitoid wasps are descendants of a single endophytic parasitoid ancestor that lived around 247 mya. These findings provide the basis for a natural classification of Hymenoptera and allow for future comparative analyses of Hymenoptera, including their genomes, morphology, venoms, and parasitoid and eusocial life styles.
Khost, D. E., Eickbush, D. G. and Larracuente, A. M. (2017). Single-molecule sequencing resolves the detailed structure of complex satellite DNA loci in Drosophila melanogaster. Genome Res [Epub ahead of print]. PubMed ID: 28373483
Summary:
Highly repetitive satellite DNA (satDNA) repeats are found in most eukaryotic genomes. SatDNAs are rapidly evolving and have roles in genome stability and chromosome segregation. Their repetitive nature poses a challenge for genome assembly and makes progress on the detailed study of satDNA structure difficult. This study used single-molecule sequencing long reads from Pacific Biosciences (PacBio) to determine the detailed structure of all major autosomal complex satDNA loci in Drosophila melanogaster, with a particular focus on the 260-bp and Responder satellites. The optimal de novo assembly methods and parameter combinations were determined that were required to produce a high-quality assembly of these previously unassembled satDNA loci and validate this assembly using molecular and computational approaches. It was determined that the computationally intensive PBcR-BLASR assembly pipeline yielded better assemblies than the faster and more efficient pipelines based on the MHAP hashing algorithm, and it is essential to validate assemblies of repetitive loci. The assemblies reveal that satDNA repeats are organized into large arrays interrupted by transposable elements. The repeats in the center of the array tend to be homogenized in sequence, suggesting that gene conversion and unequal crossovers lead to repeat homogenization through concerted evolution, although the degree of unequal crossing over may differ among complex satellite loci. Evidence was found for higher-order structure within satDNA arrays that suggest recent structural rearrangements. These assemblies provide a platform for the evolutionary and functional genomics of satDNAs in pericentric heterochromatin.

Saturday, May 6th

Galikova, M., Klepsatel, P., Munch, J. and Kuhnlein, R. P. (2017). Spastic paraplegia-linked phospholipase PAPLA1 is necessary for development, reproduction, and energy metabolism in Drosophila. Sci Rep 7: 46516. PubMed ID: 28422159
Summary:
The human PAPLA1 phospholipase family is associated with hereditary spastic paraplegia (HSP), a neurodegenerative syndrome characterized by progressive spasticity and weakness of the lower limbs. Taking advantage of a new Drosophila PAPLA1 mutant, this study describes novel functions of this phospholipase family in fly development, reproduction, and energy metabolism. Loss of Drosophila PAPLA1 reduces egg hatchability, pre-adult viability, developmental speed, and impairs reproductive functions of both males and females. In addition, this work describes novel metabolic roles of PAPLA1, manifested as decreased food intake, lower energy expenditure, and reduced ATP levels of the mutants. Moreover, PAPLA1 has an important role in the glycogen metabolism, being required for expression of several regulators of carbohydrate metabolism and for glycogen storage. In contrast, global loss of PAPLA1 does not affect fat reserves in adult flies. Interestingly, several of the PAPLA1 phenotypes in fly are reminiscent of symptoms described in some HSP patients, suggesting evolutionary conserved functions of PAPLA1 family in the affected processes. Altogether, this work reveals novel physiological functions of PAPLA1, which are likely evolutionary conserved from flies to humans.
Franco, L. M., Okray, Z., Linneweber, G. A., Hassan, B. A. and Yaksi, E. (2017). Reduced lateral inhibition impairs olfactory computations and behaviors in a Drosophila model of Fragile X syndrome. Curr Biol [Epub ahead of print]. PubMed ID: 28366741
Summary:
Fragile X syndrome (FXS) patients present neuronal alterations that lead to severe intellectual disability, but the underlying neuronal circuit mechanisms are poorly understood. An emerging hypothesis postulates that reduced GABAergic inhibition of excitatory neurons is a key component in the pathophysiology of FXS. This study directly tested this idea in a FXS Drosophila model. FXS flies were shown to exhibit strongly impaired olfactory behaviors. In line with this, olfactory representations are less odor specific due to broader response tuning of excitatory projection neurons. Impaired inhibitory interactions were shown to underlie reduced specificity in olfactory computations. Finally, this study showed that defective lateral inhibition across projection neurons is caused by weaker inhibition from GABAergic interneurons. This study provides direct evidence that deficient inhibition impairs sensory computations and behavior in an in vivo model of FXS. Together with evidence of impaired inhibition in autism and Rett syndrome, these findings suggest a potentially general mechanism for intellectual disability.
Gamberi, C., Hipfner, D. R., Trudel, M. and Lubell, W. D. (2017). Bicaudal C mutation causes myc and TOR pathway up-regulation and polycystic kidney disease-like phenotypes in Drosophila. PLoS Genet 13(4): e1006694. PubMed ID: 28406902
Summary:
Progressive cystic kidney degeneration underlies diverse renal diseases, including the most common cause of kidney failure, autosomal dominant Polycystic Kidney Disease (PKD). Genetic analyses of patients and animal models have identified several key drivers of this disease. The precise molecular and cellular changes underlying cystogenesis remain, however, elusive. Drosophila mutants lacking the translational regulator Bicaudal C (BicC, the fly ortholog of vertebrate BICC1 implicated in renal cystogenesis) exhibited progressive cystic degeneration of the renal tubules (so called Malpighian tubules) and reduced renal function. The BicC protein was shown to bind to Drosophila myc mRNA in tubules. Elevation of Myc protein levels was a cause of tubular degeneration in BicC mutants. Activation of the Target of Rapamycin (TOR) kinase pathway, another common feature of PKD, was found in BicC mutant flies. Rapamycin administration substantially reduced the cystic phenotype in flies. This study presents new mechanistic insight on BicC function and propose that Drosophila may serve as a genetically tractable model for dissecting the evolutionarily-conserved molecular mechanisms of renal cystogenesis.
Ishiguro, T., et al. (2017). Regulatory role of RNA chaperone TDP-43 for RNA misfolding and repeat-associated translation in SCA31. Neuron 94(1): 108-124.e107. PubMed ID: 28343865
Summary:
Microsatellite expansion disorders are pathologically characterized by RNA foci formation and repeat-associated non-AUG (RAN) translation. However, their underlying pathomechanisms and regulation of RAN translation remain unknown. This study reports that expression of expanded UGGAA (UGGAAexp) repeats, responsible for spinocerebellar ataxia type 31 (SCA31) in Drosophila, causes neurodegeneration accompanied by accumulation of UGGAAexp RNA foci and translation of repeat-associated pentapeptide repeat (PPR) proteins, consistent with observations in SCA31 patient brains. Motor-neuron disease (MND)-linked RNA-binding proteins (RBPs), TDP-43, FUS, and hnRNPA2B1, bind to and induce structural alteration of UGGAAexp. These RBPs suppress UGGAAexp-mediated toxicity in Drosophila by functioning as RNA chaperones for proper UGGAAexp folding and regulation of PPR translation. Furthermore, nontoxic short UGGAA repeat RNA suppressed mutated RBP aggregation and toxicity in MND Drosophila models. Thus, functional crosstalk of the RNA/RBP network regulates their own quality and balance, suggesting convergence of pathomechanisms in microsatellite expansion disorders and RBP proteinopathies.

Friday, May 5th

Pinheiro, D., Hannezo, E., Herszterg, S., Bosveld, F., Gaugue, I., Balakireva, M., Wang, Z., Cristo, I., Rigaud, S. U., Markova, O. and Bellaiche, Y. (2017). Transmission of cytokinesis forces via E-cadherin dilution and actomyosin flows. Nature [Epub ahead of print]. PubMed ID: 28296858
Summary:
During epithelial cytokinesis, the remodelling of adhesive cell-cell contacts between the dividing cell and its neighbours has profound roles in the integrity, arrangement and morphogenesis of proliferative tissues. In both vertebrates and invertebrates, this remodelling requires the activity of non-muscle myosin II (MyoII) in the interphasic cells neighbouring the dividing cell. However, the mechanisms coordinating cytokinesis and MyoII activity in the neighbours are unknown. This study found that in the Drosophila notum epithelium, each cell division is associated with a mechano-sensing and transmission event controlling MyoII dynamics in the neighbours. The ring pulling forces promote local junction elongation, resulting in local E-cadherin (E-Cad) dilution at the ingressing adherens junction (AJ). In turn, the reduction of E-Cad concentration and the contractility of the neighbouring cells promote self-organized actomyosin flows, ultimately leading to MyoII accumulation at the base of the ingressing AJ. While force transduction has been extensively studied in the context of AJ reinforcement to stabilize adhesive cell-cell contacts, an alternative mechano-sensing mechanism able to coordinate actomyosin dynamics between epithelial cells and to sustain AJ remodelling in response to mechanical forces is proposed.
Rehain-Bell, K., Love, A., Werner, M. E., MacLeod, I., Yates, J. R. and Maddox, A. S. (2017). A sterile 20 family kinase and its co-factor CCM-3 regulate contractile ring proteins on germline intercellular bridges. Curr Biol [Epub ahead of print]. PubMed ID: 28285996
Evolutionary Homolog Study
Germ cells in most animals are connected by intercellular bridges, actin-based rings that form stable cytoplasmic connections between cells promoting communication and coordination. Intercellular bridges are proposed to arise from stabilization of the cytokinetic ring during incomplete cytokinesis. Paradoxically, proteins that promote closure of cytokinetic rings are enriched on stably open intercellular bridges. Given this inconsistency, the mechanism of intercellular bridge stabilization is unclear. This study used the C. elegans germline as a model for identifying molecular mechanisms regulating intercellular bridges. It is reported that bridges are actually highly dynamic, changing size at precise times during germ cell development. Focused was placed on the regulation of bridge stability by anillins (see Drosophila Scrapes), key regulators of cytokinetic rings and cytoplasmic bridges. GCK-1, a conserved serine/threonine kinase, was identifed as a putative novel anillin interactor. GCK-1 works together with CCM-3, a known binding partner, to promote intercellular bridge stability and limit localization of both canonical anillin and non-muscle myosin II (NMM-II) to intercellular bridges. Additionally, it was found that a shorter anillin, known to stabilize bridges, also regulates NMM-II levels at bridges. Consistent with these results, negative regulators of NMM-II stabilize intercellular bridges in the Drosophila egg chamber. Together with these findings, this suggests that tuning of myosin levels is a conserved mechanism for the stabilization of intercellular bridges that can occur by diverse molecular mechanisms.
Kobb, A.B., Zulueta-Coarasa, T. and Fernandez-Gonzalez, R. (2017). Tension regulates myosin dynamics during Drosophila embryonic wound repair. J Cell Sci 130: 689-696. PubMed ID: 28202603
Summary:
Embryos repair epithelial wounds rapidly in a process driven by collective cell movements. Upon wounding, actin and the molecular motor non-muscle myosin II are redistributed in the cells adjacent to the wound, forming a supracellular purse string around the lesion. Purse string contraction coordinates cell movements and drives rapid wound closure. By using fluorescence recovery after photobleaching in Drosophila embryos, this study found that myosin turns over as the purse string contracts. Myosin turnover at the purse string is slower than in other actomyosin networks that have a lower level of contractility. Mathematical modelling suggested that myosin assembly and disassembly rates are both reduced by tension at the wound edge. Laser ablation was used to show that tension at the purse string increases as wound closure progresses, and that the increase in tension is associated with reduced myosin turnover. Reducing purse string tension by laser-mediated severing results in increased turnover and loss of myosin. Finally, myosin motor activity is necessary for its stabilization around the wound and for rapid wound closure. These results indicate that mechanical forces regulate myosin dynamics during embryonic wound repair.

Silva, M., Morsci, N., Nguyen, K. C., Rizvi, A., Rongo, C., Hall, D. H. and Barr, M. M. (2017). Cell-specific alpha-tubulin isotype regulates ciliary microtubule ultrastructure, Intraflagellar transport, and extracellular vesicle biology. Curr Biol 27(7): 968-980. PubMed ID: 28318980
Evolutionary Homolog Study
Cilia are found on most non-dividing cells in the human body and, when faulty, cause a wide range of pathologies called ciliopathies. Ciliary specialization in form and function is observed throughout the animal kingdom, yet mechanisms generating ciliary diversity are poorly understood. The "tubulin code"-a combination of tubulin isotypes and tubulin post-translational modifications-can generate microtubule diversity. Using C. elegans, alpha-tubulin isotype TBA-6 was shown to sculpt 18 A- and B-tubule singlets from nine ciliary A-B doublet microtubules in cephalic male (CEM) neurons. In CEM cilia, tba-6 regulates velocities and cargoes of intraflagellar transport (IFT) kinesin-2 motors kinesin-II and OSM-3/KIF17 without affecting kinesin-3 KLP-6 motility. In addition to their unique ultrastructure and accessory kinesin-3 motor, CEM cilia are specialized to produce extracellular vesicles. tba-6 also influences several aspects of extracellular vesicle biology, including cargo sorting, release, and bioactivity. It is concluded that this cell-specific alpha-tubulin isotype dictates the hallmarks of CEM cilia specialization. These findings provide insight into mechanisms generating ciliary diversity and lay a foundation for further understanding the tubulin code.

Thursday, May 4th

Vishal, K., Brooks, D. S., Bawa, S., Gameros, S., Stetsiv, M. and Geisbrecht, E. R. (2017). Adult muscle formation requires Drosophila Moleskin for proliferation of wing disc-associated muscle precursors. Genetics [Epub ahead of print]. PubMed ID: 28249984
Summary:
Adult muscle precursor (AMP) cells located in the notum of the larval wing disc undergo rapid amplification and eventual fusion to generate the Drosophila melanogaster indirect flight muscles (IFMs). This study finds that loss of Moleskin (Msk) function in these wing disc-associated myoblasts reduces the overall AMP pool size, resulting in the absence of IFM formation. This myoblast loss is due to a decrease in the AMP proliferative capacity and is independent of cell death. In contrast, disruption of Msk during pupal myoblast proliferation does not alter the AMP number, suggesting that Msk is specifically required for larval AMP proliferation. It has been previously shown that Wingless (Wg) signaling maintains expression of the Vestigal (Vg) transcription factor in proliferating myoblasts. However, other factors that influence Wg-mediated myoblast proliferation are largely unknown. This study examined the interactions between Msk and the Wg pathway in regulation of the AMP pool size. A myoblast-specific reduction of Msk was shown to result in the absence of Vg expression and a complete loss of the Wg pathway readout β-catenin/Armadillo (Arm). Moreover, msk RNAi knockdown abolishes expression of the Wg target Ladybird (Lbe) in leg disc myoblasts. Collectively, these results provide strong evidence that Msk acts through the Wg signaling pathway to control myoblast pool size and muscle formation by regulating Arm stability or nuclear transport.
Hevia, C. F., Lopez-Varea, A., Esteban, N. and de Celis, J. F. (2017). A search for genes mediating the growth promoting function of TGFβ in the Drosophila melanogaster wing disc. Genetics [Epub ahead of print]. PubMed ID: 28315837
Summary:
TGFβ signalling has a complex influence in cell proliferation, acting to stop cell division in differentiating cells, but also promoting cell division in immature cells. The activity of the pathway in Drosophila is mostly required to stimulate the proliferation of neural and epithelial tissues. Most interestingly, this function is not absolutely required for cell division, but it is needed for these tissues to reach their correct size. It is not known how TGFβ signalling promotes cell division in imaginal discs, or what are the interactions between TGFβ activity and other signalling pathways regulating cell proliferation. This work explored the disc autonomous function of TGFβ, via identification of Smad2 mediators of Drosophila wing imaginal disc growth. The genetic interactions were studied between TGFβ signalling and other pathways regulating wing disc growth, such as the Insulin and Hippo/Salvador/Warts pathways as well as cell cycle regulators. Using expression profiles a collection of TGFβ candidate target genes was identrified affecting imaginal growth. These candidates correspond to genes participating in the regulation of a variety of biochemical processes, including different aspects of cell metabolism, suggesting that TGFβ could affect cell proliferation by regulating the metabolic fitness of imaginal cells.
Wang, D., Li, J., Liu, S., Zhou, H., Zhang, L., Shi, W. and Shen, J. (2017). spalt is functionally conserved in Locusta and Drosophila to promote wing growth. Sci Rep 7: 44393. PubMed ID: 28300136
Summary:
Locusta has strong fly wings to ensure its long distance migration, but the molecular mechanism that regulates the Locusta wing development is poorly understood. To address the developmental mechanism of the Locusta flying wing, the Dpp target gene spalt (sal; see Drosophila Spalt) was cloned and its function was analyzed in wing growth in the Locusta. The Locusta wing size is apparently reduced with vein defects when sal is interfered by injection of dsRNA, indicating that sal is required for locust wing growth and vein formation. This function is conserved during the Drosophila wing development. To better understand sal's function in wing growth, the Drosophila wing disc as a model for further study. It was found that sal promotes cell proliferation in the whole wing disc via positive regulation of a microRNA bantam. These results unravel sal function in the Locusta wing growth and confirm a highly conserved function of sal in Locusta and Drosophila.
Harmansa, S., Alborelli, I., Bieli, D., Caussinus, E. and Affolter, M. (2017). A nanobody-based toolset to investigate the role of protein localization and dispersal in Drosophila. Elife 6 [Epub ahead of print]. PubMed ID: 28395731
Summary:
The role of protein localization along the apical-basal axis of polarized cells is difficult to investigate in vivo, partially due to lack of suitable tools. This study presents the GrabFP system, a collection of four nanobody-based GFP-traps that localize to defined positions along the apical-basal axis. The localization preference of the GrabFP traps can impose a novel localization on GFP-tagged target proteins and results in their controlled mislocalization. These new tools were used to mislocalize transmembrane and cytoplasmic GFP fusion proteins in the Drosophila wing disc epithelium and to investigate the effect of protein mislocalization. Furthermore, the GrabFP system was used as a tool to study the extracellular dispersal of the Decapentaplegic (Dpp) protein and showed that the Dpp gradient forming in the lateral plane of the Drosophila wing disc epithelium is essential for patterning of the wing imaginal disc.

Wednesday, May 3rd

Ibar, C. and Glavic, A. (2017). Drosophila p115 is required for Cdk1 activation and G2/M cell cycle transition. Mech Dev [Epub ahead of print]. PubMed ID: 28396045
Summary:
Golgi complex inheritance and its relationship with the cell cycle are central in cell biology. Golgi matrix proteins, known as golgins, are one of the components that underlie the shape and functionality of this organelle. In mammalian cells, golgins are phosphorylated during mitosis to allow fragmentation of the Golgi ribbon and they also participate in spindle dynamics; both processes are required for cell cycle progression. Little is known about the function of golgins during mitosis in metazoans in vivo. This is particularly significant in Drosophila, in which the Golgi architecture is distributed in numerous units scattered throughout the cytoplasm, in contrast with mammalian cells. This study examined the function of the ER/cis-Golgi golgin p115 during the proliferative phase of the Drosophila wing imaginal disc. Knockdown of p115 decreased tissue size. This phenotype was not caused by programmed cell death or cell size reductions, but by a reduction in the final cell number due to an accumulation of cells at the G2/M transition. This phenomenon frequently allows mitotic bypass and re-replication of DNA. These outcomes are similar to those observed following the partial loss of function of positive regulators of Cdk1 in Drosophila. In agreement with this, Cdk1 activation was reduced upon p115 knockdown. Interestingly, these phenotypes were fully rescued by Cdk1 overexpression and partially rescued by Myt1 depletion, but not by String (also known as Cdc25) overexpression. Additionally, the physical interaction between p115 and Cdk1 was confirmed, suggesting that the formation of a complex where both proteins are present is essential for the full activation of Cdk1 and thus the correct progression of mitosis in proliferating tissues.
Wei, K. H., Reddy, H. M., Rathnam, C., Lee, J., Lin, D., Ji, S., Mason, J. M., Clark, A. G. and Barbash, D. A. (2017). A Pooled Sequencing Approach Identifies a Candidate Meiotic Driver in Drosophila. Genetics [Epub ahead of print]. PubMed ID: 28258181
Summary:
Meiotic drive occurs when a selfish element increases its transmission frequency above the Mendelian ratio by hijacking the asymmetric divisions of female meiosis. New methods to reliably detect meiotic drive are therefore needed, particularly for discovering moderate-strength drivers that are likely to be more prevalent in natural populations than strong drivers. This study reports an efficient method that uses sequencing of large pools of backcross (BC1) progeny to test for deviations from Mendelian segregation genome-wide of single-nucleotide polymorphisms (SNPs) that distinguish the parental strains. Meiotic drive can be detected by a characteristic pattern of decay in distortion of SNP frequencies, caused by recombination unlinking the driver from distal loci. Control crosses allow allele-frequency distortion caused by meiotic drive to be distinguished from distortion resulting from developmental effects. This approach was used to test whether chromosomes with extreme telomere-length differences segregate at Mendelian ratios, as telomeric regions are a potential hotspot for meiotic drive due to their roles in meiotic segregation and multiple observations of high rates of telomere sequence evolution. Using four different pairings of long and short telomere strains, this study found no evidence that extreme telomere-length variation causes meiotic drive in Drosophila. However, one candidate meiotic driver was identified in a centromere-linked region that shows an ~8% increase in transmission frequency, corresponding to a ~54:46 segregation ratio. These results show that candidate meiotic drivers of moderate strength can be readily detected and localized in pools of F1 progeny.
Choi, S. H., Park, J. H., Nguyen, T. T., Shim, H. J. and Song, Y. H. (2017). Initiation of Drosophila chorion gene amplification requires Claspin and mus101, whereas Claspin, but not mus101, plays a major role during elongation. Dev Dyn [Epub ahead of print]. PubMed ID: 28294450
Summary:
Claspin and TopBP1 are checkpoint mediators that are required for the phosphorylation of Chk1 by ATR to maintain genomic stability. This study investigated the functions of Drosophila Claspin and mus101 (TopBP1 ortholog) during chorion(eggshell component) gene amplification, which occurs in follicle cells. Unlike Drosophila mei-41 (ATR ortholog) mutant embryos, Claspin and mus101 mutant embryos showed severe eggshell defects resulting from defects in chorion gene amplification. EdU incorporation assay during initiation and elongation stages revealed that Claspin and mus101 were required for initiation, while only Claspin had a major role in the efficient progression of the replication forks. Claspin proteins were enriched in the amplification foci both in the initiation and elongation stage-follicle cell nuclei in a mei-41-independent manner. It is concluded that Drosophila Claspin plays a major role in the initiation and elongation stages of chorion gene amplification by localizing to the amplification foci in a mei-41-independent manner. Drosophila mus101 is also involved in chorion gene amplification, mostly functioning in initiation, rather than elongation.
Brose, L., Crest, J., Tao, L. and Sullivan, W. (2017). Polo kinase mediates the phosphorylation and cellular localization of Nuf/FIP3, a Rab11 effector. Mol Biol Cell [Epub ahead of print]. PubMed ID: 28381422
Summary:
Animal cytokinesis involves both actin-myosin based contraction and vesicle-mediated membrane addition. In many cell types, including early Drosophila embryos, Nuf/FIP3, a Rab11 effector, mediates recycling endosome (RE)-based vesicle delivery to the cytokinesis furrow. Nuf exhibits a cell cycle-regulated concentration at the centrosome that is accompanied by dramatic changes in its phosphorylation state. This study demonstrates maximal phosphorylation of Nuf occurs at prophase, when centrosome-associated Nuf disperses throughout the cytoplasm. Accordingly, ectopic Cdk1 activation results in immediate Nuf dispersal from the centrosome. Screening of candidate kinases reveals a specific, dosage-sensitive interaction between Nuf and Polo with respect to Nuf-mediated furrow formation. Inhibiting Polo activity results in Nuf under-phosphorylation and prolonged centrosome association. In vitro, Polo directly binds and is required for Nuf phosphorylation at Ser225 and Thr227, matching previous in vivo mapped phosphorylation sites. These results demonstrate a role for Polo kinase in directly mediating Nuf cell cycle-dependent localization.

Tuesday, May 2nd

Saint-Leandre, B., Clavereau, I., Hua-Van, A. and Capy, P. (2017). Transcriptional polymorphism of piRNA regulatory genes underlies the mariner activity in D. simulans testes. Mol Ecol [Epub ahead of print]. PubMed ID: 28401606
Summary:
During colonization of new areas, natural populations have to deal with changing environments, and transposable elements (TEs) can be useful "tools" in the adaptation process since they are major contributor to the structural and functional evolution of genomes. In this general context, the activity (copy number, transcriptional and excision rate) of the mariner mos1 element was estimated in 19 natural populations of D. simulans. It is shown (1) that mos1 expression is always higher and more variable in testes than in ovaries; (2) that mos1 activity is higher in colonizing populations compared to the sub-Saharan African ones (ancestral populations); (3) that mos1 variations in transcript levels and copy number are negatively correlated to transcriptional variations of piRNA genes, aubergine and argonaute3. Furthermore, mos1 levels of expression in testes highly contrast with the low expression patterns of ago3. These results strongly suggest that the expression polymorphism of piRNA genes could be responsible for the mos1 variations, first between male and female germlines and second, according to the status of natural populations (colonizing or not). These results provide new perspectives about TEs and piRNA genes co-evolution in Drosophila germlines.
Kursel, L. E. and Malik, H. S. (2017). Recurrent gene duplication leads to diverse repertoires of centromeric histones in Drosophila species. Mol Biol Evol [Epub ahead of print]. PubMed ID: 28333217
Summary:
Despite their essential role in the process of chromosome segregation in most eukaryotes, centromeric histones show remarkable evolutionary lability. Not only have they been lost in multiple insect lineages, but they have also undergone gene duplication in multiple plant lineages. Based on detailed study of a handful of model organisms including Drosophila melanogaster, centromeric histone duplication is considered to be rare in animals. Using a detailed phylogenomic study, this study found that Cid, the centromeric histone gene, has undergone at least four independent gene duplications during Drosophila evolution. Duplicate Cid genes were found in D. eugracilis (Cid2), in the montium species subgroup (Cid3, Cid4) and in the entire Drosophila subgenus (Cid5). Cid3, Cid4, Cid5 all localize to centromeres in their respective species. Some Cid duplicates are primarily expressed in the male germline. With rare exceptions, Cid duplicates have been strictly retained after birth, suggesting that they perform non-redundant centromeric functions, independent from the ancestral Cid. Indeed, each duplicate encodes a distinct N-terminal tail, which may provide the basis for distinct protein-protein interactions. Finally, it was shown some Cid duplicates evolve under positive selection whereas others do not. Taken together, these results support the hypothesis that Drosophila Cid duplicates have subfunctionalized. Thus, these gene duplications provide an unprecedented opportunity to dissect the multiple roles of centromeric histones.
Pischedda, A. and Chippindale, A. K. (2017). Direct benefits of choosing a high fitness mate can offset the indirect costs associated with intralocus sexual conflict. J Evolution [Epub ahead of print]. PubMed ID: 28369895
Summary:
Intralocus sexual conflict generates a cost to mate choice: high fitness partners transmit genetic variation that confers lower fitness to offspring of the opposite sex. Earlier work in the fruit fly, Drosophila melanogaster, revealed that these indirect genetic costs were sufficient to reverse potential "good genes" benefits of sexual selection. However, mate choice can also confer direct fitness benefits by inducing larger numbers of progeny. This study considers whether direct benefits through enhanced fertility could offset the costs associated with intralocus sexual conflict in D. melanogaster. Using hemiclonal analysis, it was found that females mated to high fitness males produced 11% more offspring compared to those mated to low fitness males, and high fitness females produced 37% more offspring than low fitness females. These direct benefits more than offset the reduction in offspring fitness caused by intralocus sexual conflict, creating a net fitness benefit for each sex to pairing with a high fitness partner. These findings highlight the need to consider both direct and indirect effects when investigating the fitness impacts of mate choice. Direct fitness benefits may shelter sexually antagonistic alleles from selection, suggesting a novel mechanism for the maintenance of fitness variation.
Weinberger, S., Topping, M. P., Yan, J., Claeys, A., De Geest, N., Ozbay, D., Hassan, T., He, X., Albert, J. T., Hassan, B. A. and Ramaekers, A. (2017). Evolutionary changes in transcription factor coding sequence quantitatively alter sensory organ development and function. Elife 6. PubMed ID: 28406397
Summary:
'Toolkit' genes are highly conserved developmental regulators. While changes in their regulatory elements contribute to morphological evolution, the role of coding sequence (CDS) evolution remains unresolved. This study used CDS-specific knock-ins of the proneural transcription factor Atonal homologs (ATHs) to address this question. Drosophila Atonal CDS was endogenously replaced with that of distant ATHs at key phylogenetic positions, non-ATH proneural genes, and the closest CDS to ancestral proneural genes. ATHs and the ancestral-like gene rescued sensory organ fate in atonal mutants, in contrast to non-ATHs. Surprisingly, different ATHs displayed a gradient of quantitative variation in proneural activity and the number and functionality of sense organs. This proneural potency gradient correlated directly with ATH protein stability, including in response to Notch signaling, independently of mRNA levels or codon usage. This establishes a distinct and ancient function for ATHs and demonstrates that CDS evolution can underlie quantitative variation in sensory development and function.

Monday, May 1st

Fromental-Ramain, C., Ramain, P. and Hamiche, A. (2017). The Drosophila DAXX like protein (DLP) cooperates with ASF1 for H3.3 deposition and heterochromatin formation. Mol Cell Biol [Epub ahead of print]. PubMed ID: 28320872
Summary:
Histone variants are non-allelic isoforms of canonical histones and they are deposited, in contrast to canonical histones, in a replication-independent (RI) manner. RI deposition of H3.3, a histone variant from the H3.3 family, is mediated in mammals by distinct pathways involving either the histone regulator A (HIRA) complex or the death-associated protein (DAXX)/alpha-thalassemia X-linked mental retardation protein (ATRX) complex. This study investigated the function of Drosophila DAXX Like Protein (DLP) by using both fly genetics approaches and protein biochemistry. DLP specifically interacts with H3.3 and shows a prominent localization on the base of the X chromosome, where it appears to act in concert with XNP, the Drosophila homolog of ATRX, in heterochromatin assembly and maintenance. The functional association between DLP and XNP is further supported by a series of experiments, which illustrate genetic interactions and DLP-XNP-dependent localization of specific chromosomal proteins. In addition, DLP both participates in RI deposition of H3.3 and associates with the anti-silencing factor-1 (ASF1). It is suggested, in agreement with a recently proposed model, that DLP and ASF1 are part of a pre-deposition complex, which is recruited by XNP and is necessary to prevent DNA exposure in the nucleus.
Bellendir, S. P., Rognstad, D. J., Morris, L. P., Zapotoczny, G., Walton, W. G., Redinbo, M. R., Ramsden, D. A., Sekelsky, J. and Erie, D. A. (2017). Substrate preference of Gen endonucleases highlights the importance of branched structures as DNA damage repair intermediates. Nucleic Acids Res [Epub ahead of print]. PubMed ID: 28369583
Summary:
Human GEN1 and yeast Yen1 are endonucleases with the ability to cleave Holliday junctions (HJs), which are proposed intermediates in recombination. In vivo, GEN1 and Yen1 function secondarily to Mus81, which has weak activity on intact HJs. This study shows that the genetic relationship is reversed in Drosophila, with Gen mutants having more severe defects than mus81 mutants. In vitro, DmGen, like HsGEN1, efficiently cleaves HJs, 5 flaps, splayed arms, and replication fork structures. This study found that the cleavage rates for 5 flaps are significantly higher than those for HJs for both DmGen and HsGEN1, even in vast excess of enzyme over substrate. Kinetic studies suggest that the difference in cleavage rates results from a slow, rate-limiting conformational change prior to HJ cleavage: formation of a productive dimer on the HJ. Despite the stark difference in vivo that Drosophila uses Gen over Mus81 and humans use MUS81 over GEN1, in vitro activities of DmGen and HsGEN1 were found to be strikingly similar. These findings suggest that simpler branched structures may be more important substrates for Gen orthologs in vivo, and highlight the utility of using the Drosophila model system to further understand these enzymes.
Batie, M., Druker, J., D'Ignazio, L. and Rocha, S. (2017). KDM2 family members are regulated by HIF-1 in hypoxia. Cells 6(1) [Epub ahead of print]. PubMed ID: 28304334
Summary:
Hypoxia is not only a developmental cue but also a stress and pathological stimulus in many human diseases. The response to hypoxia at the cellular level relies on the activity of the transcription factor family, hypoxia inducible factor (HIF). HIF-1 is responsible for the acute response and transactivates a variety of genes involved in cellular metabolism, cell death, and cell growth. This study shows that hypoxia results in increased mRNA levels for human lysine (K)-specific demethylase 2 (KDM2) family members, KDM2A and KDM2B, and also for Drosophila melanogaster KDM2, a histone and protein demethylase. In human cells, KDM2 family member's mRNA levels are regulated by HIF-1 but not HIF-2 in hypoxia. Interestingly, only KDM2A protein levels are significantly induced in a HIF-1-dependent manner, while KDM2B protein changes in a cell type-dependent manner. Importantly, it was demonstrated that in human cells, KDM2A regulation by hypoxia and HIF-1 occurs at the level of promoter, with HIF-1 binding to the KDM2A promoter being required for RNA polymerase II recruitment. Taken together, these results demonstrate that KDM2 is a novel HIF target that can help coordinate the cellular response to hypoxia. In addition, these results might explain why KDM2 levels are often deregulated in human cancers.
Hug, C. B., Grimaldi, A. G., Kruse, K. and Vaquerizas, J. M. (2017). Chromatin architecture emerges during zygotic genome activation independent of transcription. Cell 169(2): 216-228.e219. PubMed ID: 28388407
Summary:
Chromatin architecture is fundamental in regulating gene expression. To investigate when spatial genome organization is first established during development, this study examined chromatin conformation during Drosophila embryogenesis and observed the emergence of chromatin architecture within a tight time window that coincides with the onset of transcription activation in the zygote. Prior to zygotic genome activation, the genome is mostly unstructured. Early expressed genes serve as nucleation sites for topologically associating domain (TAD) boundaries. Activation of gene expression coincides with the establishment of TADs throughout the genome and co-localization of housekeeping gene clusters, which remain stable in subsequent stages of development. However, the appearance of TAD boundaries is independent of transcription and requires the transcription factor Zelda for locus-specific TAD boundary insulation. These results offer insight into when spatial organization of the genome emerges and identify a key factor that helps trigger this architecture.
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