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


Thursday, December 31st, 2015

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Mensah, L. B., Davison, C., Fan, S. J., Morris, J. F., Goberdhan, D. C. and Wilson, C. (2015). Fine-Tuning of PI3K/AKT signalling by the tumour suppressor PTEN is required for maintenance of flight muscle function and mitochondrial integrity in ageing adult Drosophila melanogaster. PLoS One 10: e0143818. PubMed ID: 26599788
Insulin/insulin-like growth factor signalling (IIS), acting primarily through the PI3-kinase (PI3K)/AKT kinase signalling cassette, plays key evolutionarily conserved regulatory roles in nutrient homeostasis, growth, ageing and longevity. This study identified a novel hypomorphic allele of PI3K's direct antagonist, Pten, in Drosophila. Adults carrying combinations of this allele, Pten5, combined with strong loss-of-function Pten mutations exhibit subtle or no increase in mass, but are highly susceptible to a wide range of stresses. They also exhibit dramatic upregulation of the oxidative stress response gene, GstD1, and a progressive loss of motor function that ultimately leads to defects in climbing and flight ability. The latter phenotype is associated with mitochondrial disruption in indirect flight muscles, although overall muscle structure appears to be maintained. The phenotype is partially rescued by muscle-specific expression of the Bcl-2 homologue Buffy, which in flies, maintains mitochondrial integrity, modulates energy homeostasis and suppresses cell death. The flightless phenotype is also suppressed by mutations in downstream IIS signalling components, including those in the mechanistic Target of Rapamycin Complex 1 (mTORC1) pathway, suggesting that elevated IIS is responsible for functional decline in flight muscle. These data demonstrate that IIS levels must be precisely regulated by Pten in adults to maintain the function of the highly metabolically active indirect flight muscles, offering a new system to study the in vivo roles of IIS in the maintenance of mitochondrial integrity and adult ageing.

Dewey, E. B., Sanchez, D. and Johnston, C. A. (2015). Warts phosphorylates Mud to promote Pins-mediated mitotic spindle orientation in Drosophila, independent of Yorkie. Curr Biol 25: 2751-2762. PubMed ID: 26592339
Multicellular animals have evolved conserved signaling pathways that translate cell polarity cues into mitotic spindle positioning to control the orientation of cell division within complex tissue structures. These oriented cell divisions are essential for the development of cell diversity and the maintenance of tissue homeostasis. Despite intense efforts, the molecular mechanisms that control spindle orientation remain incompletely defined. This study describes a role for the Hippo (Hpo) kinase complex in promoting Partner of Inscuteable (Pins)-mediated spindle orientation. Knockdown of Hpo, Salvador (Sav), or Warts (Wts) each result in a partial loss of spindle orientation, a phenotype previously described following loss of the Pins-binding protein Mushroom body defect (Mud). Similar to orthologs spanning yeast to mammals, Wts kinase localizes to mitotic spindle poles, a prominent site of Mud localization. Wts directly phosphorylates Mud in vitro within its C-terminal coiled-coil domain. This Mud coiled-coil domain directly binds the adjacent Pins-binding domain to dampen the Pins/Mud interaction, and Wts-mediated phosphorylation uncouples this intramolecular Mud interaction. Loss of Wts prevents cortical Pins/Mud association without affecting Mud accumulation at spindle poles, suggesting phosphorylation acts as a molecular switch to specifically activate cortical Mud function. Finally, loss of Wts in Drosophila imaginal disc epithelial cells results in diminished cortical Mud and defective planar spindle orientation. These results provide new insights into the molecular basis for dynamic regulation of the cortical Pins/Mud spindle positioning complex and highlight a novel link with an essential, evolutionarily conserved cell proliferation pathway.

Keder, A., Rives-Quinto, N., Aerne, B. L., Franco, M., Tapon, N. and Carmena, A. (2015). The Hippo Pathway Core Cassette Regulates Asymmetric Cell Division. Curr Biol 25: 2739-2750. PubMed ID: 26592338
Asymmetric cell division (ACD) is a crucial process during development, homeostasis, and cancer. Stem and progenitor cells divide asymmetrically, giving rise to two daughter cells, one of which retains the parent cell self-renewal capacity, while the other is committed to differentiation. Any imbalance in this process can induce overgrowth or even a cancer-like state. This study shows that core components of the Hippo signaling pathway, an evolutionarily conserved organ growth regulator, modulate ACD in Drosophila. Hippo pathway inactivation disrupts the asymmetric localization of ACD regulators, leading to aberrant mitotic spindle orientation and defects in the generation of unequal-sized daughter cells. The Hippo pathway downstream kinase Warts, LATS1-2 in mammals, associates with the ACD modulators Inscuteable and Bazooka in vivo and phosphorylates Canoe, the ortholog of Afadin/AF-6, in vitro. Moreover, phosphosite mutant Canoe protein fails to form apical crescents in dividing neuroblasts in vivo, and the lack of Canoe phosphorylation by Warts leads to failures of Discs Large apical localization in metaphase neuroblasts. Given the relevance of ACD in stem cells during tissue homeostasis, and the well-documented role of the Hippo pathway as a tumor suppressor, these results represent a potential route for perturbations in the Hippo signaling to induce tumorigenesis via aberrant stem cell divisions.

Siudeja, K., Nassari, S., Gervais, L., Skorski, P., Lameiras, S., Stolfa, D., Zande, M., Bernard, V., Rio Frio, T. and Bardin, A. J. (2015). Frequent somatic mutation in adult intestinal stem cells drives neoplasia and genetic mosaicism during aging. Cell Stem Cell 17: 663-674. PubMed ID: 26607382
Adult stem cells may acquire mutations that modify cellular behavior, leading to functional declines in homeostasis or providing a competitive advantage resulting in premalignancy. However, the frequency, phenotypic impact, and mechanisms underlying spontaneous mutagenesis during aging are unclear. This study reports two mechanisms of genome instability in adult Drosophila intestinal stem cells (ISCs) that cause phenotypic alterations in the aging intestine. First, frequent loss of heterozygosity was found arising from mitotic homologous recombination in ISCs that results in genetic mosaicism. Second, somatic deletion of DNA sequences and large structural rearrangements, resembling those described in cancers and congenital diseases, frequently result in gene inactivation. Such modifications induced somatic inactivation of the X-linked tumor suppressor Notch in ISCs, leading to spontaneous neoplasias in wild-type males. Together, these findings reveal frequent genomic modification in adult stem cells and show that somatic genetic mosaicism has important functional consequences on aging tissues.

Wednesday, December 30th

Tataroglu, O., Zhao, X., Busza, A., Ling, J., O'Neill, J. S. and Emery, P. (2015). Calcium and SOL protease mediate temperature resetting of circadian clocks. Cell 163: 1214-1224. PubMed ID: 26590423
Circadian clocks integrate light and temperature input to remain synchronized with the day/night cycle. Although light input to the clock is well studied, the molecular mechanisms by which circadian clocks respond to temperature remain poorly understood. This study found that temperature phase shifts Drosophila circadian clocks through degradation of the pacemaker protein Tim. This degradation is mechanistically distinct from photic Cry-dependent Tim degradation. Thermal Tim degradation is triggered by cytosolic calcium increase and Calmodulin binding to Tim and is mediated by the atypical calpain protease Sol. This thermal input pathway and Cry-dependent light input thus converge on Tim, providing a molecular mechanism for the integration of circadian light and temperature inputs. Mammals use body temperature cycles to keep peripheral clocks synchronized with their brain pacemaker. Interestingly, downregulating the mammalian Sol homolog SOLH blocks thermal mPER2 (see Drosophila Per) degradation and phase shifts. Thus, it is proposed that circadian thermosensation in insects and mammals share common principles.

Nikhil, K.L., Vaze, K.M., Ratna, K. and Sharma, V.K. (2015). Circadian clock properties of fruit flies Drosophila melanogaster exhibiting early and late emergence chronotypes. Chronobiol Int [Epub ahead of print]. PubMed ID: 26654995
The role of circadian clocks in timing daily behaviors is widely acknowledged, and while empirical evidence suggests that clock period is correlated with the preferred phase of a rhythmic behavior (chronotype), other clock properties have also been hypothesized to underlie chronotype variation. This study reports that fruit fly Drosophila melanogaster populations exhibiting evening emergence chronotype (late) are characterized by higher incidence of behavioral arrhythmicity in constant dim light, wider range of entrainment, reduced rates of re-entrainment to simulated jet-lag and higher amplitude of both entrained and free-running rhythms as compared to those exhibiting morning emergence chronotype (early). These results thus highlight the role of circadian clock properties such as zeitgeber sensitivity, amplitude and coupling in driving chronotype variation.

Nikhil, K. L., Vaze, K. M. and Sharma, V. K. (2015). Late emergence chronotypes of fruit flies Drosophila melanogaster exhibit higher accuracy of entrainment. Chronobiol Int 32: 1477-1485. PubMed ID: 26595175
Inter-individual variation in phase-of-entrainment (chronotype) is widely observed in many species. In light of considerable limitations of previous studies proposing that the late chronotypes exhibit weakly stable rhythms, outbred Drosophila populations exhibiting early and late emergence chronotypes were employed to re-visit such associations. Contrary to previous reports, this study observed that the late chronotypes consistently exhibit higher stability in emergence and activity-rest rhythms as compared to the early chronotypes, both under laboratory and semi-natural conditions. This stability is not associated with higher precision of circadian clocks, thus demonstrating the existence of genetic correlations between accuracy of entrainment and chronotype. The results highlight a possible complex interplay of clock period, phase response curve and accuracy in determining phase-of-entrainment.

Beatus, T., Guckenheimer, J. M. and Cohen, I. (2015). Controlling roll perturbations in fruit flies. J R Soc Interface 12 [Epub ahead of print]. PubMed ID: 25762650
Owing to aerodynamic instabilities, stable flapping flight requires ever-present fast corrective actions. This study investigated how flies control perturbations along their body roll angle, which is unstable and their most sensitive degree of freedom. A magnet was glued to each fly, and a short magnetic pulse was applied that rolls it in mid-air. Fast video shows flies correct perturbations up to 100 degrees within 30 +/- 7 ms by applying a stroke-amplitude asymmetry that is well described by a linear proportional-integral controller. For more aggressive perturbations, evidence is shown for nonlinear and hierarchical control mechanisms. Flies respond to roll perturbations within 5 ms, making this correction reflex one of the fastest in the animal kingdom.

Maesani, A., Ramdya, P., Cruchet, S., Gustafson, K., Benton, R. and Floreano, D. (2015). Fluctuation-driven neural dynamics reproduce Drosophila locomotor patterns. PLoS Comput Biol 11: e1004577. PubMed ID: 26600381
The neural mechanisms determining the timing of even simple actions, such as when to walk or rest, are largely mysterious. One intriguing, but untested, hypothesis posits a role for ongoing activity fluctuations in neurons of central action selection circuits that drive animal behavior from moment to moment. To examine how fluctuating activity can contribute to action timing, high-resolution measurements of freely walking Drosophila melanogaster were paired with data-driven neural network modeling and dynamical systems analysis. Dynamical models that best reproduced both Drosophila basal and odor-evoked locomotor patterns exhibited specific characteristics. First, ongoing fluctuations were required. In a stochastic resonance-like manner, these fluctuations allowed neural activity to escape stable equilibria and to exceed a threshold for locomotion. Second, odor-induced shifts of equilibria in these models caused a depression in locomotor frequency following olfactory stimulation. These models predict that activity fluctuations in action selection circuits cause behavioral output to more closely match sensory drive and may therefore enhance navigation in complex sensory environments. Together these data reveal how simple neural dynamics, when coupled with activity fluctuations, can give rise to complex patterns of animal behavior.

Davies, A., Louis, M. and Webb, B. (2015). A Model of Drosophila Larva Chemotaxis. PLoS Comput Biol 11: e1004606. PubMed ID: 26600460
Detailed observations of larval Drosophila chemotaxis have characterised the relationship between the odour gradient and the runs, head casts and turns made by the animal. This study used a computational model to test whether hypothesised sensorimotor control mechanisms are sufficient to account for larval behaviour. The model combines three mechanisms based on simple transformations of the recent history of odour intensity at the head location. The first is an increased probability of terminating runs in response to gradually decreasing concentration, the second an increased probability of terminating head casts in response to rapidly increasing concentration, and the third a biasing of run directions up concentration gradients through modulation of small head casts. This model can be tuned to produce behavioural statistics comparable to those reported for the larva, and this tuning results in similar chemotaxis performance to the larva. Each mechanism can be demonstrated to enable odour approach, but the combination of mechanisms is most effective. How these low-level control mechanisms relate to behavioural measures such as the preference indices was used to investigate larval learning behaviour in group assays.

Tuesday, December 29th

Dear, M. L., Dani, N., Parkinson, W., Zhou, S. and Broadie, K. (2015). Two matrix metalloproteinase classes reciprocally regulate synaptogenesis. Development [Epub ahead of print]. PubMed ID: 26603384
Synaptogenesis requires orchestrated intercellular communication between synaptic partners, with trans-synaptic signals necessarily traversing the extracellular synaptomatrix separating presynaptic and postsynaptic cells. Extracellular matrix metalloproteinases (Mmps) regulated by secreted tissue inhibitors of metalloproteinases (Timps), cleave secreted and membrane-associated targets to sculpt the extracellular environment and modulate intercellular signaling. This study tested Mmp roles at the neuromuscular junction (NMJ) model synapse in the reductionist Drosophila system, which contains just two Mmps (secreted Mmp1 and GPI-anchored Mmp2) and one secreted Timp. All three matrix metalloproteome components co-dependently localize in the synaptomatrix. Both Mmp1 and Mmp2 independently restrict synapse morphogenesis and functional differentiation. Surprisingly, either dual knockdown or simultaneous inhibition of the two Mmp classes together restores normal synapse development, identifying a novel reciprocal suppression mechanism. The two Mmp classes co-regulate a Wnt trans-synaptic signaling pathway modulating structural and functional synaptogenesis, including the GPI-anchored heparan sulfate proteoglycan (HSPG) Wnt co-receptor Dally-like Protein (Dlp), cognate receptor Frizzled-2 and Wingless ligand. Loss of either Mmp1 or Mmp2 reciprocally misregulates Dlp at the synapse, with normal signaling restored by co-removal of both Mmp classes. Correcting Wnt co-receptor Dlp levels in both mmp mutants prevents structural and functional synaptogenic defects. Taken together, these results identify a novel Mmp mechanism that fine-tunes HSPG co-receptor function to modulate Wnt signaling to coordinate synapse structural and functional development.

Sturgeon, M., Davis, D., Albers, A., Beatty, D., Austin, R., Ferguson, M., Tounsel, B. and Liebl, F. L. (2015). The Notch ligand E3 ligase, Mind Bomb1, regulates glutamate receptor localization in Drosophila. Mol Cell Neurosci 70: 11-21. PubMed ID: 26596173
The postsynaptic density (PSD) is a protein-rich network important for the localization of postsynaptic glutamate receptors (GluRs) and for signaling downstream of these receptors. Although hundreds of PSD proteins have been identified, many are functionally uncharacterized. A reverse genetic screen for mutations that affected GluR localization was conducted using Drosophila genes that encode homologs of mammalian PSD proteins. 42.8% of the mutants analyzed exhibited a significant change in GluR localization at the third instar larval neuromuscular junction (NMJ), a model synapse that expresses homologs of AMPA receptors. The E3 ubiquitin ligase, Mib1, which promotes Notch signaling, was identified as a regulator of synaptic GluR localization. Mib1 positively regulates the localization of the GluR subunits GluRIIA, GluRIIB, and GluRIIC. Mutations in mib1 and ubiquitous expression of Mib1 that lacks its ubiquitin ligase activity result in the loss of synaptic GluRIIA-containing receptors. In contrast, overexpression of Mib1 in all tissues increases postsynaptic levels of GluRIIA. Cellular levels of Mib1 are also important for the structure of the presynaptic motor neuron. While deficient Mib1 signaling leads to overgrowth of the NMJ, ubiquitous overexpression of Mib1 results in a reduction in the number of presynaptic motor neuron boutons and branches. These synaptic changes may be secondary to attenuated glutamate release from the presynaptic motor neuron in mib1 mutants as mib1 mutants exhibit significant reductions in the vesicle-associated protein cysteine string protein and in the frequency of spontaneous neurotransmission.

Cho, R. W., Buhl, L. K., Volfson, D., Tran, A., Li, F., Akbergenova, Y. and Littleton, J. T. (2015). Phosphorylation of Complexin by PKA regulates activity-dependent spontaneous neurotransmitter release and structural synaptic plasticity. Neuron 88: 749-761. PubMed ID: 26590346
Synaptic plasticity is a fundamental feature of the nervous system that allows adaptation to changing behavioral environments. Most studies of synaptic plasticity have examined the regulated trafficking of postsynaptic glutamate receptors that generates alterations in synaptic transmission. Whether and how changes in the presynaptic release machinery contribute to neuronal plasticity is less clear. The SNARE complex mediates neurotransmitter release in response to presynaptic Ca(2+) entry. This study shows that the SNARE fusion clamp Complexin undergoes activity-dependent phosphorylation that alters the basic properties of neurotransmission in Drosophila. Retrograde signaling following stimulation activates PKA-dependent phosphorylation of the Complexin C terminus that selectively and transiently enhances spontaneous release. Enhanced spontaneous release is required for activity-dependent synaptic growth. These data indicate that SNARE-dependent fusion mechanisms can be regulated in an activity-dependent manner and highlight the key role of spontaneous neurotransmitter release as a mediator of functional and structural plasticity.

Xu, Y. and Wang, T. (2015). CULD is required for rhodopsin and TRPL channel endocytic trafficking and survival of photoreceptor cells. J Cell Sci [Epub ahead of print]. PubMed ID: 26598556
Endocytosis of G-protein-coupled receptors (GPCRs) and associated channels contributes to desensitization and adaptation of a variety of signaling cascades. In Drosophila, the major light sensing rhodopsin, Rh1, and the downstream ion channel, Transient Receptor Potential Like (TRPL), are endocytosed in response to light, but the mechanism is unclear. Using an RNA-Sequencing approach, this study discovered CULD (CG17352), a photoreceptor-cell enriched CUB- and LDLa-domain transmembrane protein that is required for endocytic trafficking of Rh1 and TRPL. CULD localized to endocytic Rh1- or TRPL-positive vesicles. Mutations in culd resulted in the accumulation of Rh1 and TRPL within endocytic vesicles, and disrupted the regular turnover of endocytic Rh1 and TRPL. In addition, loss of CULD induced light- and age-dependent retinal degeneration, and reduced levels of Rh1 but not TRPL suppressed retinal degeneration in culd null mutant flies. These data demonstrate that CULD plays an important role in the endocytic turnover of Rh1 and TRPL, and suggest that CULD-dependent rhodopsin endocytic trafficking is required for maintaining photoreceptor integrity.

Monday, December 28th

Cohn, R., Morantte, I. and Ruta, V. (2015). Coordinated and compartmentalized neuromodulation shapes sensory processing in Drosophila. Cell 163: 1742-1755. PubMed ID: 26687359
Learned and adaptive behaviors rely on neural circuits that flexibly couple the same sensory input to alternative output pathways. This study shows that the Drosophila mushroom body functions like a switchboard in which neuromodulation reroutes the same odor signal to different behavioral circuits, depending on the state and experience of the fly. Using functional synaptic imaging and electrophysiology, it was shown that dopaminergic inputs to the mushroom body modulate synaptic transmission with exquisite spatial specificity, allowing individual neurons to differentially convey olfactory signals to each of their postsynaptic targets. Moreover, the dopaminergic neurons function as an interconnected network, encoding information about both an animal's external context and internal state to coordinate synaptic plasticity throughout the mushroom body. These data suggest a general circuit mechanism for behavioral flexibility in which neuromodulatory networks act with synaptic precision to transform a single sensory input into different patterns of output activity.

Zhang, F., Huang, Z. X., Bao, H., Cong, F., Wang, H., Chai, P. C., Xi, Y., Ge, W., Somers, W. G., Yang, Y., Cai, Y. and Yang, X. (2015). Phosphotyrosyl phosphatase activator facilitates Miranda localization through dephosphorylation in dividing neuroblasts. Development [Epub ahead of print]. PubMed ID: 26586222
The mechanism for the basal targeting of the Miranda (Mira) complex during the asymmetric division of Drosophila neuroblasts (NBs) is yet to be fully understood. This study has identified conserved Phosphotyrosyl Phosphatase Activator (PTPA) as a novel mediator for the basal localization of the Mira complex in larval brain NBs. In ptpa NBs, Mira remains cytoplasmic during early mitosis where its basal localization is delayed until anaphase. Detailed analyses indicate that PTPA acts independently of, and prior to, aPKC activity to localize Mira. Mechanistically, the data show that the phosphorylation status of the Thr591 (T591) residue determines the subcellular localization of Mira and that PTPA facilitates the dephosphorylation of T591. Furthermore, PTPA associates with the Protein Phosphatase 4 complex to mediate Mira localization. Based on these results, a two-step process for Mira basal localization during NB division is revealed where PTPA/PP4-mediated cortical association followed by apical aPKC-mediated basal restriction.

Farnsworth, D. R., Bayraktar, O. A. and Doe, C. Q. (2015). Aging neural progenitors lose competence to respond to mitogenic Notch signaling. Curr Biol 25: 3058-3068. PubMed ID: 26585279
Drosophila neural stem cells (neuroblasts) are a powerful model system for investigating stem cell self-renewal, specification of temporal identity, and progressive restriction in competence. Notch signaling is a conserved cue that is an important determinant of cell fate in many contexts across animal development; for example, mammalian T cell differentiation in the thymus and neuroblast specification in Drosophila are both regulated by Notch signaling. However, Notch also functions as a mitogen, and constitutive Notch signaling potentiates T cell leukemia as well as Drosophila neuroblast tumors. While the role of Notch signaling has been studied in these and other cell types, it remains unclear how stem cells and progenitors change competence to respond to Notch over time. Notch is required in type II neuroblasts for normal development of their transit amplifying progeny, intermediate neural progenitors (INPs). This study finds that aging INPs lose competence to respond to constitutively active Notch signaling. Moreover, reducing the levels of the old INP temporal transcription factor Eyeless/Pax6 allows Notch signaling to promote the de-differentiation of INP progeny into ectopic INPs, thereby creating a proliferative mass of ectopic progenitors in the brain. These findings provide a new system for studying progenitor competence and identify a novel role for the conserved transcription factor Eyeless/Pax6 in blocking Notch signaling during development.

Vagnoni, A., Hoffmann, P. C. and Bullock, S. L. (2015). Reducing Lissencephaly-1 levels augments mitochondrial transport and has a protective effect in adult Drosophila neurons. J Cell Sci [Epub ahead of print]. PubMed ID: 26598558
Defective transport of mitochondria in axons is implicated in the pathogenesis of several age-associated neurodegenerative diseases. However, the regulation and function of axonal mitochondrial motility during normal ageing is poorly understood. This study used novel imaging procedures to characterise axonal transport of these organelles in the adult Drosophila wing nerve. During early adult life there is a boost and progressive decline in the proportion of mitochondria that are motile, which is not due to general changes in cargo transport. Experimental inhibition of mitochondrial transport specifically in adulthood accelerates the appearance of focal protein accumulations in ageing axons, suggestive of defects in protein homeostasis. Unexpectedly, lowering levels of Lissencephaly-1 (Lis1), a dynein motor co-factor, augments axonal mitochondrial transport in ageing wing neurons. Lis1 mutations suppress focal protein accumulations in ageing neurons, including those caused by interfering with the mitochondrial transport machinery. These data provide new insights into the dynamics of mitochondrial motility in adult neurons in vivo, identify Lis1 as a negative regulator of transport of these organelles and provide evidence of a link between mitochondrial movement and neuronal protein homeostasis.

Sunday, December 27th

Peng, F., Zhao, Y., Huang, X., Chen, C., Sun, L., Zhuang, L. and Xue, L. (2015). Loss of Polo ameliorates APP-induced Alzheimer's disease-like symptoms in Drosophila. Sci Rep 5: 16816. PubMed ID: 26597721
The amyloid precursor protein (APP) has been implicated in the pathogenesis of Alzheimer's disease (AD). Despite extensive studies, little is known about the regulation of APP's functions in vivo. This study report that expression of human APP in Drosophila, in the same temporal-spatial pattern as its homolog APPL, induced morphological defects in wings and larval NMJ, larva and adult locomotion dysfunctions, male choice disorder and lifespan shortening. To identify additional genes that modulate APP functions, a genetic screen was performed, and it was found that loss of Polo, a key regulator of cell cycle, partially suppressed APP-induced morphological and behavioral defects in larval and adult stages. Finally, eye-specific expression of APP induced retina degeneration and cell cycle re-entry; both phenotypes were mildly ameliorated by loss of Polo. These results suggest Polo is an important in vivo regulator of the pathological functions of APP, and provide insight into the role of cell cycle re-entry in AD pathogenesis.

Acevedo, S. F., Peru, Y. C. d. P. R. L., Gonzalez, D. A., Rodan, A. R. and Rothenfluh, A. (2015). S6 kinase reflects and regulates ethanol-induced sedation. J Neurosci 35: 15396-15402. PubMed ID: 26586826
Individuals at risk for Alcohol use disorders (AUDs) are sensitive to alcohol's rewarding effects and/or resistant to its aversive and sedating effects. The molecular basis for these traits is poorly understood. This study shows that p70 S6 kinase (S6k), acting downstream of the insulin receptor (InR) and the small GTPase Arf6, is a key mediator of ethanol-induced sedation in Drosophila. S6k signaling in the adult nervous system determines flies' sensitivity to sedation. Furthermore, S6k activity, measured via levels of phosphorylation (P-S6k), is a molecular marker for sedation and overall neuronal activity: P-S6k levels are decreased when neurons are silenced, as well as after acute ethanol sedation. Conversely, P-S6k levels rebound upon recovery from sedation and are increased when neuronal activity is enhanced. Reducing neural activity increases sensitivity to ethanol-induced sedation, whereas neuronal activation decreases ethanol sensitivity. These data suggest that ethanol has acute silencing effects on adult neuronal activity, which suppresses InR/Arf6/S6k signaling and results in behavioral sedation. In addition, activity of InR/Arf6/S6k signaling was shown to determine flies' behavioral sensitivity to ethanol-induced sedation, highlighting this pathway in acute responses to ethanol.

Lee, S., Bang, S.M., Hong, Y.K., Lee, J.H., Jeong, H., Park, S.H., Liu, Q.F., Lee, I.S. and Cho, K.S. (2015). The calcineurin inhibitor, Sarah/Nebula, exacerbates Aβ42 phenotypes in a Drosophila model of Alzheimer's disease. Dis Model Mech [Epub ahead of print]. PubMed ID: 26659252
Expression of the Down syndrome critical region 1 (DSCR1) protein, an inhibitor of the Ca2+-dependent phosphatase calcineurin, is elevated in the brains of patients with Down syndrome (DS) or Alzheimer's disease (AD). This study investigated the role of sarah (sra)/nebula, a Drosophila DSCR1 ortholog, in amyloid-β42 (Aβ42)-induced neurological phenotypes in Drosophila. sra expression was detected in the mushroom bodies, a center for learning and memory in flies. Moreover, similar to humans with AD, Aβ42-expressing flies show increased Sra levels in the brain. Interestingly, overexpression of sra using the UAS-GAL4 system exacerbates the rough eye phenotype, decreases survival rates, and increases neuronal cell death in Aβ42-expressing flies without modulating Aβ42 expression. Moreover, neuronal overexpression of sra in combination with Aβ42 dramatically reduces both locomotor activity and the adult lifespan of Aβ42-expressing flies, while flies with overexpression of sra alone show normal climbing ability albeit with a slightly reduced lifespan. Similarly, treatment with chemical inhibitors of calcineurin such as FK506 and cyclosporin A, or knockdown of calcineurin expression by RNAi, exacerbate the Aβ42-induced rough eye phenotype. Furthermore, sra-overexpressing flies display significantly decreased mitochondrial DNA and ATP levels, as well as increased susceptibility to oxidative stress compared to that of control flies. Taken together, these results demonstrating that sra overexpression augments Aβ42 cytotoxicity in Drosophila suggest that DSCR1 up-regulation or calcineurin down-regulation in the brain may exacerbate Aβ42-associated neuropathogenesis in AD or DS.

Gonzales, E. D., Tanenhaus, A. K., Zhang, J., Chaffee, R. P. and Yin, J. C. (2015). Early onset sleep defects in Drosophila models of Huntington's Disease reflect alterations of PKA/CREB Signaling. Hum Mol Genet [Epub ahead of print]. PubMed ID: 26604145
Huntington's Disease (HD) is a progressive neurological disorder whose non-motor symptoms include sleep disturbances. Whether sleep and activity abnormalities are primary molecular disruptions of mutant Huntingtin (mutHtt) expression or result from neurodegeneration is unclear. This study reports that Drosophila models of HD exhibit sleep and activity disruptions very early in adulthood, as soon as sleep patterns have developed. Pan-neuronal expression of full-length or N-terminally truncated mutHtt recapitulates sleep phenotypes of HD patients: impaired sleep initiation, fragmented and diminished sleep, and nighttime hyperactivity. Sleep deprivation of HD model flies results in exacerbated sleep deficits, indicating that homeostatic regulation of sleep is impaired. Elevated PKA/CREB activity in healthy flies produces patterns of sleep and activity similar to those in the HD models. It was asked whether aberrations in PKA/CREB signaling were responsible for these early onset sleep/activity phenotypes. Decreasing signaling through the cAMP/PKA pathway was shown to suppresses mutHtt-induced developmental lethality. Genetically reducing PKA abolishes sleep/activity deficits in HD model flies, restores the homeostatic response and extends median lifespan. In vivo reporters, however, show dCREB2 activity is unchanged, or decreased when sleep/activity patterns are abnormal, suggesting dissociation of PKA and dCREB2 occurs early in pathogenesis. Collectively, these data suggests that sleep defects may reflect a primary pathological process in HD, and that measurements of sleep and cAMP/PKA could be prodromal indicators of disease, and serve as therapeutic targets for intervention.

Saturday, December 26th

Rister, J., Razzaq, A., Boodram, P., Desai, N., Tsanis, C., Chen, H., Jukam, D. and Desplan, C. (2015). Single–base pair differences in a shared motif determine differential Rhodopsin expression. Science 350: 1258-1261. Science Magazine
The final identity and functional properties of a neuron are specified by terminal differentiation genes, which are controlled by specific motifs in compact regulatory regions. To determine how these sequences integrate inputs from transcription factors that specify cell types, this study compared the regulatory mechanism of Drosophila Rhodopsin genes (see NinaE/Rh1) that are expressed in subsets of photoreceptors to that of phototransduction genes that are expressed broadly, in all photoreceptors. Both sets of genes share an 11–base pair (bp) activator motif. Broadly expressed genes contain a palindromic version that mediates expression in all photoreceptors. In contrast, each Rhodopsin exhibits characteristic single-bp substitutions that break the symmetry of the palindrome and generate activator or repressor motifs critical for restricting expression to photoreceptor subsets. Sensory neuron subtypes can therefore evolve through single-bp changes in short regulatory motifs, allowing the discrimination of a wide spectrum of stimuli.

Philip, P., Boija, A., Vaid, R., Churcher, A. M., Meyers, D. J., Cole, P. A., Mannervik, M. and Stenberg, P. (2015). CBP binding outside of promoters and enhancers in Drosophila melanogaster. Epigenetics Chromatin 8: 48. PubMed ID: 26604986
CREB-binding protein (CBP, also known as nejire) is a transcriptional co-activator that is conserved in metazoans. CBP and the related p300 protein have been used to predict enhancers when they occur with monomethylation of histone H3 on lysine 4 (H3K4me1). This study shows that CBP is bound at genomic sites with a wide range of functions. As expected, CBP was bound at active promoters and enhancers. In addition, the strongest CBP sites in the genome were found at Polycomb response elements embedded in histone H3 lysine 27 trimethylated (H3K27me3) chromatin, where they correlate with binding of the Pho repressive complex. CBP also binds to most insulators in the genome. At a subset of these, CBP may regulate insulating activity, measured as the ability to prevent repressive H3K27 methylation from spreading into adjacent chromatin. It is concluded that CBP could be involved Polycomb repression and insulator activity. A CBP at all functional elements may be to regulate interactions between distant chromosomal regions, and it is speculated that CBP is controlling higher order chromatin organization.

Cannavò, E., Khoueiry, P., Garfield, D.A., Geeleher, P., Zichner, T., Gustafson, E.H., Ciglar, L., Korbel, J.O. and Furlong, E.E. (2015). Shadow enhancers are pervasive features of developmental regulatory networks. Curr Biol [Epub ahead of print]. PubMed ID: 26687625
Embryogenesis is remarkably robust to segregating mutations and environmental variation; under a range of conditions, embryos of a given species develop into stereotypically patterned organisms. Such robustness is thought to be conferred, in part, through elements within regulatory networks that perform similar, redundant tasks. Redundant enhancers (or "shadow" enhancers), for example, can confer precision and robustness to gene expression, at least at individual, well-studied loci. However, the extent to which enhancer redundancy exists and can thereby have a major impact on developmental robustness remains unknown. This study systematically assessed and identifies over 1,000 predicted shadow enhancers during Drosophila mesoderm development. The activity of 23 elements, associated with five genes, was examined in transgenic embryos, while natural structural variation among individuals was used to assess their ability to buffer against genetic variation. Data reveal three clear properties of enhancer redundancy within developmental systems. First, it is much more pervasive than previously anticipated, with 64% of loci examined having shadow enhancers. Their spatial redundancy is often partial in nature, while the non-overlapping function may explain why these enhancers are maintained within a population. Second, over 70% of loci do not follow the simple situation of having only two shadow enhancers-often there are three (rols), four (CadN and ade5), or five (Traf1), at least one of which can be deleted with no obvious phenotypic effects. Third, although shadow enhancers can buffer variation, patterns of segregating variation suggest that they play a more complex role in development than generally considered.

Stampfel, G., Kazmar, T., Frank, O., Wienerroither, S., Reiter, F. and Stark, A. (2015). Transcriptional regulators form diverse groups with context-dependent regulatory functions. Nature 528(7580):147-51. PubMed ID: 26550828
One of the most important questions in biology is how transcription factors (TFs) and cofactors control enhancer function and thus gene expression. Enhancer activation usually requires combinations of several TFs, indicating that TFs function synergistically and combinatorially. However, while TF binding has been extensively studied, little is known about how combinations of TFs and cofactors control enhancer function once they are bound. It is typically unclear which TFs participate in combinatorial enhancer activation, whether different TFs form functionally distinct groups, or if certain TFs might substitute for each other in defined enhancer contexts. This study assesses the potential regulatory contributions of TFs and cofactors to combinatorial enhancer control with enhancer complementation assays. GAL4-DNA-binding-domain fusions of 812 Drosophila TFs and cofactors were recruited to 24 enhancer contexts, and enhancer activities were measured by 82,752 luciferase assays in S2 cells. Most factors were functional in at least one context, yet their contributions differed between contexts and varied from repression to activation (up to 289-fold) for individual factors. Based on functional similarities across contexts, 15 groups of TFs were defined that differ in developmental functions and protein sequence features. Similar TFs can substitute for each other, enabling enhancer re-engineering by exchanging TF motifs, and TF-cofactor pairs cooperate during enhancer control and interact physically. Overall, this study shows that activators and repressors can have diverse regulatory functions that typically depend on the enhancer context. The systematic functional characterization of TFs and cofactors should further understanding of combinatorial enhancer control and gene regulation.

Friday, December 25th

Dembeck, L. M., Huang, W., Carbone, M. A. and Mackay, T. F. (2015). Genetic basis of natural variation in body pigmentation in Drosophila melanogaster. Fly (Austin): [Epub ahead of print]. PubMed ID: 26554300
Body pigmentation in insects and other organisms is typically variable within and between species and is often associated with fitness. Regulatory variants with large effects at bab1, t and e affect variation in abdominal pigmentation in several populations of Drosophila melanogaster. A genome wide association (GWA) analysis of variation in abdominal pigmentation was performed using the inbred, sequenced lines of the Drosophila Genetic Reference Panel (DGRP). The large effects of regulatory variants were confirmed in bab1, t and e. These analyses were, however, imperfect proxies for the effects of segregating variants. This study describes the results of an extreme quantitative trait locus (xQTL) GWA analysis of female body pigmentation in an outbred population derived from light and dark DGRP lines. The effects on pigmentation of 28 genes implicated by the DGRP GWA study were replicated, including bab1, t and e and seven genes previously validated by RNAi and/or mutant analyses. Many additional loci were identified. The genetic architecture of Drosophila pigmentation is complex, with a few major genes and many other loci with smaller effects.

Dembeck, L. M., Boroczky, K., Huang, W., Schal, C., Anholt, R. R. and Mackay, T. F. (2015). Genetic architecture of natural variation in cuticular hydrocarbon composition in Drosophila. Elife 4 [Epub ahead of print]. PubMed ID: 26568309
Insect cuticular hydrocarbons (CHCs) prevent desiccation and serve as chemical signals that mediate social interactions. Drosophila CHCs have been studied extensively, but the genetic basis for individual variation in CHC composition is largely unknown. This study quantified variation in CHC profiles in the D. melanogaster Genetic Reference Panel (DGRP) and identified novel CHCs. Principal component (PC) analysis was used to extract PCs that explain the majority of CHC variation and identified polymorphisms in or near 305 and 173 genes in females and males, respectively, associated with variation in these PCs. In addition, 17 DGRP lines contain the functional Desat2 allele characteristic of African and Caribbean D. melanogaster females (more 5,9-C27:2 and less 7,11-C27:2, female sex pheromone isomers). Disruption of expression of 24 candidate genes affected CHC composition in at least one sex. These genes are associated with fatty acid metabolism and represent mechanistic targets for individual variation in CHC composition.

Rahman, R., Chirn, G. W., Kanodia, A., Sytnikova, Y. A., Brembs, B., Bergman, C. M. and Lau, N. C. (2015). Unique transposon landscapes are pervasive across Drosophila melanogaster genomes. Nucleic Acids Res [Epub ahead of print]. PubMed ID: 26578579
To understand how transposon landscapes (TLs) vary across animal genomes, this study describes a new method called the Transposon Insertion and Depletion AnaLyzer (TIDAL) and a database of >300 TLs in Drosophila melanogaster (TIDAL-Fly). This analysis reveals pervasive TL diversity across cell lines and fly strains, even for identically named sub-strains from different laboratories such as the ISO1 strain used for the reference genome sequence. On average, >500 novel insertions exist in every lab strain, inbred strains of the Drosophila Genetic Reference Panel (DGRP), and fly isolates in the Drosophila Genome Nexus (DGN). A minority (<25%) of transposon families comprise the majority (>70%) of TL diversity across fly strains. A sharp contrast between insertion and depletion patterns indicates that many transposons are unique to the ISO1 reference genome sequence. Although TL diversity from fly strains reaches asymptotic limits with increasing sequencing depth, rampant TL diversity causes unsaturated detection of TLs in pools of flies. Finally, novel transposon insertions were shown to negatively correlate with Piwi-interacting RNA (piRNA) levels for most transposon families, except for the highly-abundant roo retrotransposon. This study provides a useful resource for Drosophila geneticists to understand how transposons create extensive genomic diversity in fly cell lines and strains.

Vedelek, B., Blastyak, A. and Boros, I. M. (2015). Cross-species interaction between rapidly evolving telomere-specific Drosophila proteins. PLoS One 10: e0142771. PubMed ID: 26566042
Telomere integrity in Drosophila melanogaster is maintained by a putative multisubunit complex called terminin that is believed to act in analogy to the mammalian shelterin complex in protecting chromosome ends from being recognized as sites of DNA damage. The five proteins supposed to form the terminin complex are HP1-ORC associated protein (HOAP), HP1-HOAP interacting protein (HipHop), Verrocchio, Drosophila Telomere Loss/Modigliani and Heterochromatic Protein 1. Four of these proteins evolve rapidly within the Drosophila genus. The accelerated evolution of terminin components may indicate the involvement of these proteins in the process by which new species arise, as the resulting divergence of terminin proteins might prevent hybrid formation, thus driving speciation. However, terminin is not an experimentally proven entity, and no biochemical studies have been performed to investigate its assembly and action in detail. Motivated by these facts in order to initiate biochemical studies on terminin function, attempts were made to reconstitute terminin by co-expressing its subunits in bacteria, and the possible role of the fast-evolving parts of terminin components in complex assembly was investigated. The results suggest formation of stable subcomplexes of terminin, but not of the whole complex in vitro. It was found that the accelerated evolution is restricted to definable regions of terminin components, and that the divergence of D. melanogaster Drosophila Telomere Loss and D. yakuba Verrocchio proteins does not preclude their stable interaction.

Ignatenko, O. M., Zakharenko, L. P., Dorogova, N. V. and Fedorova, S. A. (2015). P elements and the determinants of hybrid dysgenesis have different dynamics of propagation in Drosophila melanogaster populations. Genetica 143: 751-759. PubMed ID: 26530414
Intraspecific hybrid dysgenesis (HD) appears after some strains of D. melanogaster are crossed. The predominant idea is that the movement of transposable P elements causes HD. It is believed that P elements appeared in the D. melanogaster genome in the middle of the last century by horizontal transfer, simultaneously with the appearance of HD determinants. A subsequent simultaneous expansion of HD determinants and P elements occurred. This study analyzed the current distribution of HD determinants in natural populations of D. melanogaster and found no evidence of their further spread. However, full-sized P elements were identified in the genomes of all analyzed natural D. melanogaster strains independent of their cytotypes. Thus, the expansion of P elements does not correlate with the expansion of HD determinants. The ovaries of dysgenic females did not contain germ cells despite the equal number of primordial germ cells in early stages in dysgenic and non-dysgenic embryos. It is proposed that HD does not result from DNA damage caused by P element transposition, but it would be the disruption in the regulation of dysgenic ovarian formation that causes the dysgenic phenotypes.

Beck, E. A. and Llopart, A. (2015). Widespread positive selection drives differentiation of centromeric proteins in the Drosophila melanogaster subgroup. Sci Rep 5: 17197. PubMed ID: 26603658
Rapid evolution of centromeric satellite repeats is thought to cause compensatory amino acid evolution in interacting centromere-associated kinetochore proteins. Cid, a protein that mediates kinetochore/centromere interactions, displays particularly high amino acid turnover. Rapid evolution of both Cid and centromeric satellite repeats led to a hypothesis that the apparent compensatory evolution may extend to interacting partners in the Condensin I complex (i.e., SMC2, SMC4, Cap-H, Cap-D2, and Cap-G) and HP1s. Missense mutations in these proteins often result in improper centromere formation and aberrant chromosome segregation, thus selection for maintained function and coevolution among proteins of the complex is likely strong. This study reports evidence of rapid evolution and recurrent positive selection in seven centromere-associated proteins in species of the Drosophila melanogaster subgroup, and further postulate that positive selection on these proteins could be a result of centromere drive and compensatory changes, with kinetochore proteins competing for optimal spindle attachment.

Thursday, December 24th

Tan, L., Zhang, K.X., Pecot, M.Y., Nagarkar-Jaiswal, S., Lee, P.T., Takemura, S.Y., McEwen, J.M., Nern, A., Xu, S., Tadros, W., Chen, Z., Zinn, K., Bellen, H.J., Morey, M. and Zipursky, S.L. (2015). Ig superfamily ligand and receptor pairs expressed in synaptic partners in Drosophila. Cell 163: 1756-1769. PubMed ID: 26687360
Information processing relies on precise patterns of synapses between neurons. The cellular recognition mechanisms regulating this specificity are poorly understood. In the medulla of the Drosophila visual system, different neurons form synaptic connections in different layers. This study identifies candidate cell recognition molecules underlying this specificity. Using RNA sequencing (RNA-seq), it was shown that neurons with different synaptic specificities express unique combinations of mRNAs encoding hundreds of cell surface and secreted proteins. Using RNA-seq and protein tagging, it was demonstrated that 21 paralogs of the Dpr family, a subclass of immunoglobulin (Ig)-domain containing proteins, are expressed in unique combinations in homologous neurons with different layer-specific synaptic connections. Dpr interacting proteins (DIPs), comprising nine paralogs of another subclass of Ig-containing proteins, are expressed in a complementary layer-specific fashion in a subset of synaptic partners. The study proposes that pairs of Dpr/DIP paralogs contribute to layer-specific patterns of synaptic connectivity. 

Bahl, A., Serbe, E., Meier, M., Ammer, G. and Borst, A. (2015). Neural mechanisms for Drosophila contrast vision. Neuron [Epub ahead of print]. PubMed ID: 26673659
Spatial contrast, the difference in adjacent luminance values, provides information about objects, textures, and motion and supports diverse visual behaviors. Contrast computation is therefore an essential element of visual processing. The underlying mechanisms, however, are poorly understood. In human psychophysics, contrast illusions are means to explore such computations, but humans offer limited experimental access. Via behavioral experiments in Drosophila, this study shows that flies are also susceptible to contrast illusions. Using genetic silencing techniques, electrophysiology, and modeling, the mechanisms and neuronal correlates underlying the behavior were dissected. Results indicate that spatial contrast computation involves lateral inhibition within the same pathway that computes motion of luminance increments (ON pathway). Yet motion-blind flies, in which downstream motion-sensitive neurons needed for optomotor behavior were silenced, exhibit fully intact contrast responses. In conclusion, spatial contrast and motion cues are first computed by overlapping neuronal circuits which subsequently feed into parallel visual processing streams.

Carrillo, R.A., Özkan, E., Menon, K.P., Nagarkar-Jaiswal, S., Lee, P.T., Jeon, M., Birnbaum, M.E., Bellen, H.J., Garcia, K.C. and Zinn, K. (2015). Control of synaptic connectivity by a network of Drosophila IgSF cell surface proteins. Cell 163: 1770-1782. PubMed ID: 26687361
This study defined a network of interacting Drosophila cell surface proteins in which a 21-member IgSF subfamily, the Dprs, binds to a nine-member subfamily, the DIPs. The structural basis of the Dpr-DIP interaction code appears to be dictated by shape complementarity within the Dpr-DIP binding interface. Each of the six dpr and DIP genes examined is expressed by a unique subset of larval and pupal neurons. In the neuromuscular system, interactions between Dpr11 and DIP-γ affect presynaptic terminal development, trophic factor responses, and neurotransmission. In the visual system, dpr11 is selectively expressed by R7 photoreceptors that use Rh4 opsin (yR7s). Their primary synaptic targets, Dm8 amacrine neurons, express DIP-γ. In dpr11 or DIP-γ mutants, yR7 terminals extend beyond their normal termination zones in layer M6 of the medulla. DIP-γ is also required for Dm8 survival or differentiation. These findings suggest that Dpr-DIP interactions are important determinants of synaptic connectivity.

Jeanne, J. M. and Wilson, R. I. (2015). Convergence, divergence, and reconvergence in a feedforward network improves neural speed and accuracy. Neuron 88: 1014-1026. PubMed ID: 26586183
One of the proposed canonical circuit motifs employed by the brain is a feedforward network where parallel signals converge, diverge, and reconverge. This study investigated a network with this architecture in the Drosophila olfactory system. Focus was placed on a glomerulus whose receptor neurons converge in an all-to-all manner onto six projection neurons that then reconverge onto higher-order neurons. Foth convergence and reconvergence were found to improve the ability of a decoder to detect a stimulus based on a single neuron's spike train. The first transformation implements averaging, and it improves peak detection accuracy but not speed; the second transformation implements coincidence detection, and it improves speed but not peak accuracy. In each case, the integration time and threshold of the postsynaptic cell are matched to the statistics of convergent spike trains.

Wednesday, December 23

Reimels, T. A. and Pfleger, C. M. (2015). Drosophila Rabex-5 restricts Notch activity in hematopoietic cells and maintains hematopoietic homeostasis. J Cell Sci [Epub ahead of print]. PubMed ID: 26567216
Hematopoietic homeostasis requires the maintenance of a reservoir of undifferentiated blood cell progenitors and the ability to replace or expand differentiated blood cell lineages when necessary. Multiple signaling pathways function in these processes, but how their spatiotemporal control is established and their activity is coordinated in the context of the entire hematopoietic network are still poorly understood. This study reports that loss of the gene Rabex-5 in Drosophila causes several hematopoietic abnormalities including blood cell (hemocyte) overproliferation, increased size of the hematopoietic organ (the lymph gland), lamellocyte differentiation, and melanotic mass formation. Hemocyte-specific Rabex-5 knockdown was sufficient to increase hemocyte populations, increase lymph gland size, and induce melanotic masses. Rabex-5 negatively regulates Ras, and Ras activity was shown to be responsible for specific Rabex-5 hematopoietic phenotypes. Surprisingly, Ras-independent Notch protein accumulation and transcriptional activity in the lymph gland underlie multiple distinct hematopoietic phenotypes of Rabex-5 loss. Thus, Rabex-5 plays an important role in Drosophila hematopoiesis and may serve as an axis coordinating Ras and Notch signaling in the lymph gland.

Rudolf, K., Umetsu, D., Aliee, M., Sui, L., Julicher, F. and Dahmann, C. (2015). A local difference in Hedgehog signal transduction increases mechanical cell bond tension and biases cell intercalations along the Drosophila anteroposterior compartment boundary. Development 142: 3845-3858. PubMed ID: 26577205
In the developing Drosophila wing disc, maintenance of the straight anteroposterior (AP) compartment boundary involves a local increase in mechanical tension at cell bonds along the boundary. This study shows that a local difference in Hedgehog signal transduction activity between anterior and posterior cells is necessary and sufficient to increase mechanical tension along the AP boundary. This difference in Hedgehog signal transduction is also required to bias cell rearrangements during cell intercalations to keep the characteristic straight shape of the AP boundary. Moreover, severing cell bonds along the AP boundary does not reduce tension at neighboring bonds, implying that active mechanical tension is upregulated, cell bond by cell bond. Finally, differences in the expression of the homeodomain-containing protein Engrailed also contribute to the straight shape of the AP boundary, independently of Hedgehog signal transduction and without modulating cell bond tension. These data reveal a novel link between local differences in Hedgehog signal transduction and a local increase in active mechanical tension of cell bonds that biases junctional rearrangements. The large-scale shape of the AP boundary thus emerges from biochemical signals inducing patterns of active tension on cell bonds.

Huang, J. and Xue, L. (2015). Loss of flfl triggers JNK-dependent cell death in Drosophila. Biomed Res Int 2015: 623573. PubMed ID: 26583122
falafel (flfl) encodes a Drosophila homolog of human SMEK whose in vivo functions remain elusive. Gain-of-function and loss-of-function analysis was performed in in Drosophila and flfl was identified as a negative regulator of JNK pathway-mediated cell death. While ectopic expression of flfl suppresses TNF-triggered JNK-dependent cell death, loss of flfl promotes JNK activation and cell death in the developing eye and wing. These data report for the first time an essential physiological function of flfl in maintaining tissue homeostasis and organ development. As the JNK signaling pathway has been evolutionary conserved from fly to human, a similar role of PP4R3 in JNK-mediated physiological process is speculated.

Bornstein, B., et al. (2015). Developmental axon pruning requires destabilization of cell adhesion by JNK signaling. Neuron 88: 926-940. PubMed ID: 26586184
Developmental axon pruning is essential for normal brain wiring in vertebrates and invertebrates. How axon pruning occurs in vivo is not well understood. In a mosaic loss-of-function screen, this study found that Bsk, the Drosophila JNK, is required for axon pruning of mushroom body γ neurons, but not their dendrites. By combining in vivo genetics, biochemistry, and high-resolution microscopy, this study demonstrated that the mechanism by which Bsk is required for pruning is through reducing the membrane levels of the adhesion molecule Fasciclin II (FasII), the NCAM ortholog. Conversely, overexpression of FasII is sufficient to inhibit axon pruning. Finally, this study showed that overexpressing other cell adhesion molecules, together with weak attenuation of JNK signaling, strongly inhibits pruning. Taken together, this study uncovered a novel and unexpected interaction between the JNK pathway and cell adhesion and found that destabilization of cell adhesion is necessary for efficient pruning.

Tuesday, December 22nd

Lu, T., Wang, S., Gao, Y., Mao, Y., Yang, Z., Liu, L., Song, X., Ni, J. and Xie, T. (2015). COP9-Hedgehog axis regulates the function of the germline stem cell progeny differentiation niche in the Drosophila ovary. Development 142: 4242-4252. PubMed ID: 26672093
It has been proposed that escort cells (ECs) form a differentiation niche to control germline stem cells (GSC) lineage specification extrinsically in the Drosophila ovary. However, it remains poorly understood how the maintenance and function of the differentiation niche are regulated at the molecular level. This study reveals a new role of COP9 in the differentiation niche to modulate autocrine Hedgehog (Hh) signaling, thereby promoting GSC lineage differentiation. COP9, which is a highly conserved protein complex composed of eight CSN subunits, catalyzes the removal of Nedd8 protein modification from target proteins. Genetic results demonstrate that all the COP9 components and the hh pathway components, including hh itself, are required in ECs to promote GSC progeny differentiation. Interestingly, COP9 is required in ECs to maintain Hh signaling activity, and activating Hh signaling in ECs can partially bypass the requirement for COP9 in GSC progeny differentiation. Finally, both COP9 and Hh signaling in ECs promote GSC progeny differentiation partly by preventing BMP signaling and maintaining cellular processes. Therefore, this study demonstrates that the COP9-Hh signaling axis operates in the differentiation niche to promote GSC progeny differentiation partly by maintaining EC cellular processes and preventing BMP signaling. This provides new insight into how the function of the differentiation niche is regulated at the molecular level.

Suzuki, T., Takayama, R. and Sato, M. (2015). eyeless/Pax6 controls the production of glial cells in the visual center of Drosophila melanogaster. Dev Biol [Epub ahead of print]. PubMed ID: 26670857
Pax6 is known as a neurogenic factor in the development of the central nervous system and regulates proliferation of neuronal progenitor cells and promotes neuronal differentiation. In addition to neurogenesis, Pax6 is also involved in the specification and maturation of glial cells. This study shows that Eyeless (Ey), Drosophila homolog of Pax6, regulates the production of glial cells in the brain. In the developing fly visual center, the production of neurons and glial cells are controlled by the temporal transcription factors that are sequentially expressed in neuroblasts (NBs). Among them, NBs of the last temporal window produce astrocyte-like glial cells. Ey is strongly expressed in the middle aged NBs, whose temporal window is earlier compared with glia producing older NBs. Weak Ey expression is also detected in the glia producing NBs. The results suggest that Ey expression in the middle aged NBs indirectly control gliogenesis from the oldest NBs by regulating other temporal transcription factors. Additionally, weak Ey expression in the NBs of last temporal window may directly control gliogenesis. Ey is also expressed in neurons produced from the NBs of Ey-positive temporal window. Interestingly, neuron-specific overexpression of Ey causes significant increase in glial cells suggesting that neuronal expression of Ey may also contribute to gliogenesis. Thus, Pax6-dependent regulation of astrocyte-like glial development is conserved throughout the animal kingdom.

Jin, Y., Ha, N., Fores, M., Xiang, J., Glasser, C., Maldera, J., Jimenez, G. and Edgar, B. A. (2015). EGFR/Ras signaling controls Drosophila intestinal stem cell proliferation via Capicua-regulated genes. PLoS Genet 11: e1005634. PubMed ID: 26683696
Epithelial renewal in the Drosophila intestine is orchestrated by Intestinal Stem Cells (ISCs). Following damage or stress the intestinal epithelium produces ligands that activate the epidermal growth factor receptor (EGFR) in ISCs. This promotes their growth and division and, thereby, epithelial regeneration. This study demonstrates that the HMG-box transcriptional repressor, Capicua (Cic), mediates these functions of EGFR signaling. Depleting Cic in ISCs activated them for division, whereas overexpressed Cic inhibited ISC proliferation and midgut regeneration. Epistasis tests showed that Cic acted as an essential downstream effector of EGFR/Ras signaling, and immunofluorescence showed that Cic's nuclear localization was regulated by EGFR signaling. ISC-specific mRNA expression profiling and DNA binding mapping using DamID indicated that Cic represses cell proliferation via direct targets including string (Cdc25), Cyclin E, and the ETS domain transcription factors Ets21C and Pointed (pnt). pnt was required for ISC over-proliferation following Cic depletion, and ectopic pnt restored ISC proliferation even in the presence of overexpressed dominant-active Cic. These studies identify Cic, Pnt, and Ets21C as critical downstream effectors of EGFR signaling in Drosophila ISCs.

Sanchez, C. G., Teixeira, F. K., Czech, B., Preall, J. B., Zamparini, A. L., Seifert, J. R., Malone, C. D., Hannon, G. J. and Lehmann, R. (2015). Regulation of ribosome biogenesis and protein synthesis controls germline stem cell differentiation. Cell Stem Cell [Epub ahead of print]. PubMed ID: 26669894
Complex regulatory networks regulate stem cell behavior and contributions to tissue growth, repair, and homeostasis. A full understanding of the networks controlling stem cell self-renewal and differentiation, however, has not yet been realized. To systematically dissect these networks and identify their components, this study performed an unbiased, transcriptome-wide in vivo RNAi screen in female Drosophila germline stem cells (GSCs). Based on characterized cellular defects, 646 identified genes were classified into phenotypic and functional groups, and a comprehensive set was unveiled of networks regulating GSC maintenance, survival, and differentiation. This analysis revealed an unexpected role for ribosomal assembly factors in controlling stem cell cytokinesis. Moreover, the data show that the transition from self-renewal to differentiation relies on enhanced ribosome biogenesis accompanied by increased protein synthesis. Collectively, these results detail the extensive genetic networks that control stem cell homeostasis and highlight the intricate regulation of protein synthesis during differentiation.

Monday, December 21st

Sun, J., Wei, H. M., Xu, J., Chang, J. F., Yang, Z., Ren, X., Lv, W. W., Liu, L. P., Pan, L. X., Wang, X., Qiao, H. H., Zhu, B., Ji, J. Y., Yan, D., Xie, T., Sun, F. L. and Ni, J. Q. (2015). Histone H1-mediated epigenetic regulation controls germline stem cell self-renewal by modulating H4K16 acetylation. Nat Commun 6: 8856. PubMed ID: 26581759
Epigenetics plays critical roles in controlling stem cell self-renewal and differentiation. Histone H1 is one of the most critical chromatin regulators, but its role in adult stem cell regulation remains unclear. This study reports that H1 is intrinsically required in the regulation of germline stem cells (GSCs) in the Drosophila ovary. The loss of H1 from GSCs causes their premature differentiation through activation of the key GSC differentiation factor Bam. Interestingly, the acetylated H4 lysine 16 (H4K16ac) is selectively augmented in the H1-depleted GSCs. Furthermore, overexpression of mof reduces H1 association on chromatin. In contrast, the knocking down of mof significantly rescues the GSC loss phenotype. Taken together, these results suggest that H1 functions intrinsically to promote GSC self-renewal by antagonizing MOF function. Since H1 and H4K16 acetylation are highly conserved from fly to human, the findings from this study might be applicable to stem cells in other systems.

Doyen, C. M., Chalkley, G. E., Voets, O., Bezstarosti, K., Demmers, J. A., Moshkin, Y. M. and Verrijzer, C. P. (2015). A testis-specific chaperone and the chromatin remodeler ISWI mediate repackaging of the paternal genome. Cell Rep 13: 1310-1318. PubMed ID: 26549447
During spermatogenesis, the paternal genome is repackaged into a non-nucleosomal, highly compacted chromatin structure. Bioinformatic analysis revealed that Drosophila sperm chromatin proteins are characterized by a motif related to the high-mobility group (HMG) box, which is termed male-specific transcript (MST)-HMG box. MST77F is a MST-HMG-box protein that forms an essential component of sperm chromatin. The deposition of MST77F onto the paternal genome requires the chaperone function of tNAP (CG5017, termed milkah), a testis-specific NAP protein. MST77F, in turn, enables the stable incorporation of the protamines MST35Ba and MST35Bb into sperm chromatin. Following MST-HMG-box protein deposition, the ATP-dependent chromatin remodeler ISWI mediates the appropriate organization of sperm chromatin. Conversely, at fertilization, maternal ISWI targets the paternal genome and drives its repackaging into de-condensed nucleosomal chromatin. Failure of this transition in ISWI mutant embryos is followed by mitotic defects, aneuploidy, and haploid embryonic divisions. Thus, ISWI enables bi-directional transitions between two fundamentally different forms of chromatin.

Ellis, K., Friedman, C. and Yedvobnick, B. (2015). Drosophila domino exhibits genetic interactions with a wide spectrum of chromatin protein-encoding loci. PLoS One 10: e0142635. PubMed ID: 26555684
The Drosophila domino gene encodes protein of the SWI2/SNF2 family that has widespread roles in transcription, replication, recombination and DNA repair. This study investigated the potential relationship of Domino protein to other chromatin-associated proteins through a genetic interaction analysis. Genetic modification of a domino wing margin phenotype was scored for through coexpression of RNAi directed against a set of previously characterized and more newly characterized chromatin-encoding loci. A set of other SWI2/SNF2 loci were also assayed for interaction with domino. The results show that the majority of tested loci exhibit synergistic enhancement or suppression of the domino wing phenotype. Therefore, depression in domino function sensitizes the wing margin to alterations in the activity of numerous chromatin components. In several cases the genetic interactions are associated with changes in the level of cell death measured across the dorsal-ventral margin of the wing imaginal disc. These results highlight the broad realms of action of many chromatin proteins and suggest significant overlap with Domino function in fundamental cell processes, including cell proliferation, cell death and cell signaling.

Nakagawa, T., Ikehara, T., Doiguchi, M., Imamura, Y., Higashi, M., Yoneda, M. and Ito, T. (2015).. Enhancer of acetyltransferase Chameau (EAChm) is a novel transcriptional co-activator. PLoS One 10: e0142305. PubMed ID: 26555228
Acetylation of nucleosomal histones by diverse histone acetyltransferases (HAT) plays pivotal roles in many cellular events. Discoveries of novel HATs and HAT related factors have provided new insights to understand the roles and mechanisms of histone acetylation. This study identified prominent Histone H3 acetylation activity in vitro and purified its activity, showing that it is composed of the MYST acetyltransferase Chameau and Enhancer of the Acetyltransferase Chameau (EAChm; CG13463) family. EAChm is a negatively charged acidic protein retaining aspartate and glutamate. Furthermore, Chameau and EAChm stimulate transcription in vitro together with purified general transcription factors. In addition, RNA-seq analysis of Chameau KD and EAChm KD S2 cells suggest that Chameau and EAChm regulate transcription of common genes in vivo. These results suggest that EAChm regulates gene transcription in Drosophila embryos by enhancing Acetyltransferase Chameau activity.

Sunday, December 20th

Seeds, A.M., Tsui, M.M., Sunu, C., Spana, E.P. and York, J.D. (2015). Inositol phosphate kinase 2 is required for imaginal disc development in Drosophila. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 26647185
Inositol phosphate kinase 2 (Ipk2), also known as IP multikinase IPMK, is an evolutionarily conserved protein that initiates production of inositol phosphate intracellular messengers (IPs), which are critical for regulating nuclear and cytoplasmic processes. This study reports that Ipk2 kinase activity is required for the development of the adult fruit fly epidermis. Ipk2 mutants show impaired development of their imaginal discs. Loss of Ipk2 activity results in increased apoptosis and impairment of proliferation during larval and pupal development. The proliferation defect is in part attributed to a reduction in JAK/STAT signaling, possibly by controlling production or secretion of the pathway's activating ligand, Unpaired. Constitutive activation of the JAK/STAT pathway downstream of Unpaired partially rescues the disk growth defects in Ipk2 mutants. These results demonstrate an essential role for Ipk2 in producing inositide messengers required for imaginal disc tissue maturation and subsequent formation of adult body structures and provides molecular insights to signaling pathways involved in tissue growth and stability during development.

Goto, T., Sato, K., Sone, H., Koganezawa, M., Ito, H. and Yamamoto, D. (2015). Zeste tunes the timing of ecdysone actions in triggering programmed tissue degeneration in Drosophila. J Neurogenet: 1-5. PubMed ID: 26577029
In the pupal stage, the fly body undergoes extensive metamorphic remodeling, in which programmed cell death plays a critical role. Two of the constituent processes in this remodeling were studied, salivary gland degeneration and breakdown of the eclosion muscle, which are triggered by an increase and a decrease in the circulating steroid hormone ecdysone at the start and end of metamorphosis, respectively. Knockdown of zeste (z), a gene encoding a sequence-specific DNA-binding protein implicated in transvection, in salivary gland cells advances the initiation of their degeneration, whereas z knockdown in neurons delays muscle breakdown. Knockdown of an ecdysone-inducible gene, E74, retards salivary gland degeneration with little effect on eclosion muscle breakdown. It is proposed that Zeste tunes the sensitivity of ecdysone targets to this hormone in order to ensure a high safety margin so that the cell death program will be activated when the ecdysone titer is at a sufficiently high level that is reached only at a defined stage during metamorphosis.

Pelaez, N., Gavalda-Miralles, A., Wang, B., Navarro, H. T., Gudjonson, H., Rebay, I., Dinner, A. R., Katsaggelos, A. K., Amaral, L. A. and Carthew, R. W. (2015). Dynamics and heterogeneity of a fate determinant during transition towards cell differentiation. Elife 4 [Epub ahead of print]. PubMed ID: 26583752
Yan is an ETS-domain transcription factor responsible for maintaining Drosophila eye cells in a multipotent state. Using a fluorescent reporter for Yan expression, this study observed a biphasic distribution of Yan in multipotent cells. Transitions to various differentiated states occurred over the course of this dynamic process, suggesting that Yan expression level does not strongly determine cell potential. Consistent with this conclusion, perturbing Yan expression by varying gene dosage had no effect on cell fate transitions. However, it was observed that as cells transited to differentiation, Yan expression became highly heterogeneous and this heterogeneity was transient. Signals received via the EGF Receptor were necessary for the transience in Yan noise since genetic loss caused sustained noise. Since these signals are essential for eye cells to differentiate, it is suggested that dynamic heterogeneity of Yan is a necessary element of the transition process, and cell states are stabilized through noise reduction.

Hurd, T. R., Liang, F. X. and Lehmann, R. (2015). Curly encodes Dual Oxidase, which acts with Heme Peroxidase Curly Su to shape the adult Drosophila wing. PLoS Genet 11: e1005625. PubMed ID: 26587980
Curly, described almost a century ago, is one of the most frequently used markers in Drosophila genetics. Despite this the molecular identity of Curly has remained obscure. This study shows that Curly mutations arise in the gene dual oxidase (duox), which encodes a reactive oxygen species (ROS) generating NADPH oxidase. Using Curly mutations and RNA interference (RNAi), this study demonstrated that Duox autonomously stabilizes the wing on the last day of pupal development. Through genetic suppression studies, this study identified a novel heme peroxidase, Curly Su (Cysu; CG5873) that acts with Duox to form the wing. Ultrastructural analysis suggests that Duox and Cysu are required in the wing to bond and adhere the dorsal and ventral cuticle surfaces during its maturation. In Drosophila, Duox is best known for its role in the killing of pathogens by generating bactericidal ROS. This work adds to a growing number of studies suggesting that Duox's primary function is more structural, helping to form extracellular and cuticle structures in conjunction with peroxidases.

Saturday, December 19th

Okumura, M., Kato, T., Miura, M. and Chihara, T. (2015). Hierarchical axon targeting of Drosophila olfactory receptor neurons specified by the proneural transcription factors Atonal and Amos. Genes Cells [Epub ahead of print]. PubMed ID: 26663477
Sensory information is spatially represented in the brain to form a neural map. It has been suggested that axon-axon interactions are important for neural map formation; however, the underlying mechanisms are not fully understood. This study used the Drosophila antennal lobe, the first olfactory center in the brain, as a model for studying neural map formation. Olfactory receptor neurons (ORNs) expressing the same odorant receptor target their axons to a single glomerulus out of approximately 50 glomeruli in the antennal lobe. Previous studies have shown that the axons of Atonal ORNs, specified by Atonal, a basic helix-loop-helix (bHLH) transcription factor, pioneer antennal lobe formation; however, the details remain to be elucidated. This study shows that genetic ablation of Atonal ORNs affects antennal lobe structure and axon targeting of Amos ORNs, another type of ORN specified by the bHLH transcription factor Amos. During development, Atonal ORNs reach the antennal lobe and form the axon commissure before Amos ORNs. It was also found that N-cadherin knockdown specifically in Atonal ORNs disrupts the glomerular boundary in the whole antennal lobe. These results suggest that Atonal ORNs function as pioneer axons. Thus, correct axon targeting of Atonal ORNs is essential for formation of the whole antennal lobe.

Im, S. H., Takle, K., Jo, J., Babcock, D. T., Ma, Z., Xiang, Y. and Galko, M. J. (2015). Tachykinin acts upstream of autocrine Hedgehog signaling during nociceptive sensitization in Drosophila. Elife 4 [Epub ahead of print]. PubMed ID: 26575288
Pain signaling in vertebrates is modulated by neuropeptides like Substance P (SP). To determine whether such modulation is conserved and potentially uncover novel interactions between nociceptive signaling pathways, SP/Tachykinin signaling was analyzed in a Drosophila model of tissue damage-induced nociceptive hypersensitivity. Tissue-specific knockdowns and genetic mutant analyses revealed that both Tachykinin and Tachykinin-like receptor (DTKR99D) are required for damage-induced thermal nociceptive sensitization. Electrophysiological recording showed that DTKR99D is required in nociceptive sensory neurons for temperature-dependent increases in firing frequency upon tissue damage. DTKR overexpression caused both behavioral and electrophysiological thermal nociceptive hypersensitivity. Hedgehog, another key regulator of nociceptive sensitization, was produced by nociceptive sensory neurons following tissue damage. Surprisingly, genetic epistasis analysis revealed that DTKR function was upstream of Hedgehog-dependent sensitization in nociceptive sensory neurons. These results highlight a conserved role for Tachykinin signaling in regulating nociception and the power of Drosophila for genetic dissection of nociception.

Nikhil, K.L., Vaze, K.M., Ratna, K. and Sharma, V.K. (2015). Circadian clock properties of fruit flies Drosophila melanogaster exhibiting early and late emergence chronotypes. Chronobiol Int [Epub ahead of print]. PubMed ID: 26654995
The role of circadian clocks in timing daily behaviors is widely acknowledged, and while empirical evidence suggests that clock period is correlated with the preferred phase of a rhythmic behavior (chronotype), other clock properties have also been hypothesized to underlie chronotype variation. This study reports that fruit fly Drosophila melanogaster populations exhibiting evening emergence chronotype (late) are characterized by higher incidence of behavioral arrhythmicity in constant dim light, wider range of entrainment, reduced rates of re-entrainment to simulated jet-lag and higher amplitude of both entrained and free-running rhythms as compared to those exhibiting morning emergence chronotype (early). These results thus highlight the role of circadian clock properties such as zeitgeber sensitivity, amplitude and coupling in driving chronotype variation.

Ichinose, T., Aso, Y., Yamagata, N., Abe, A., Rubin, G. M. and Tanimoto, H. (2015). Reward signal in a recurrent circuit drives appetitive long-term memory formation. Elife 4 [Epub ahead of print]. PubMed ID: 26573957
Dopamine signals reward in animal brains. A single presentation of a sugar reward to Drosophila activates distinct subsets of dopamine neurons that independently induce short- and long-term olfactory memories (STM and LTM, respectively). This study shows that a recurrent reward circuit underlies the formation and consolidation of LTM. This feedback circuit is composed of a single class of reward-signaling dopamine neurons (PAM-alpha1) projecting to a restricted region of the mushroom body (MB), and a specific MB output cell type, MBON-α1, whose dendrites arborize that same MB compartment. Both MBON-α1 and PAM-α1 neurons are required during the acquisition and consolidation of appetitive LTM. MBON-α1 additionally mediates the retrieval of LTM, which is dependent on the dopamine receptor signaling in the MB αβ neurons. These results suggest that a reward signal transforms a nascent memory trace into a stable LTM using a feedback circuit at the cost of memory specificity.

Friday, December 18th

Zhao, X., Bergland, A. O., Behrman, E. L., Gregory, B. D., Petrov, D. A. and Schmidt, P. S. (2015). Global transcriptional profiling of diapause and climatic adaptation in Drosophila melanogaster. Mol Biol Evol [Epub ahead of print]. PubMed ID: 26568616
Wild populations of Drosophila experience highly heterogeneous environments over broad geographical ranges as well as over seasonal and annual timescales. Diapause is a primary adaptation to environmental heterogeneity, and in D. melanogaster the propensity to enter diapause varies predictably with latitude and season. This study performed global transcriptomic profiling of naturally occurring variation in diapause expression elicited by short day photoperiod and moderately low temperature in two tissue types associated with neuroendocrine and endocrine signaling, heads and ovaries. Diapause in D. melanogaster was shown to be an actively regulated phenotype at the transcriptional level, suggesting that diapause is not a simple physiological or reproductive quiescence. Differentially expressed genes and pathways are highly distinct in heads and ovaries, demonstrating that the diapause response is not uniform throughout the soma and suggesting that it may be comprised of functional modules associated with specific tissues. Genes down-regulated in heads of diapausing flies are significantly enriched for clinally varying SNPs and seasonally oscillating SNPs, consistent with the hypothesis that diapause is a driving phenotype of climatic adaptation. Chromosome location-based co-regulation of gene expression is present in the transcriptional regulation of diapause. Taken together, these results demonstrate that diapause is a complex phenotype actively regulated in multiple tissues, and support the hypothesis that natural variation in diapause propensity underlies adaptation to spatially and temporally varying selective pressures.

Morozova, T. V., Huang, W., Pray, V. A., Whitham, T., Anholt, R. R. and Mackay, T. F. (2015). Polymorphisms in early neurodevelopmental genes affect natural variation in alcohol sensitivity in adult Drosophila. BMC Genomics 16: 865. PubMed ID: 26503115
Alcohol abuse and alcoholism are significant public health problems, but the genetic basis for individual variation in alcohol sensitivity remains poorly understood. Genome wide association analyses was performed for alcohol sensitivity using the sequenced, inbred lines of the D. melanogaster Genetic Reference Panel (DGRP) together with extreme QTL mapping in an advanced intercross population derived from sensitive and resistant DGRP lines. The DGRP was shown to harbor substantial genetic variation for alcohol sensitivity and tolerance. 247 candidate genes affecting alcohol sensitivity were identified in the DGRP or the DGRP-derived advanced intercross population, some of which met a Bonferroni-corrected significance threshold, while others occurred among the top candidate genes associated with variation in alcohol sensitivity in multiple analyses. Among these were candidate genes associated with development and function of the nervous system, including several genes in the Dopamine decarboxylase (Ddc) cluster involved in catecholamine synthesis. 58 of these genes formed a genetic interaction network. Candidate genes were verified using mutational analysis, targeted gene disruption through RNAi knock-down and transcriptional profiling. Two-thirds of the candidate genes have been implicated in previous Drosophila, mouse and human studies of alcohol-related phenotypes. It is concluded that individual variation in alcohol sensitivity in Drosophila is highly polygenic and in part determined by variation in evolutionarily conserved signaling pathways that are associated with catecholamine neurotransmitter biosynthesis and early development of the nervous system.

Li, Q. and Gong, Z. (2015). Cold-sensing regulates Drosophila growth through insulin-producing cells. Nat Commun 6: 10083. PubMed ID: 26648410
Across phyla, body size is linked to climate. For example, rearing fruit flies at lower temperatures results in bigger body sizes than those observed at higher temperatures. The underlying molecular basis of this effect is poorly understood. This study provides evidence that the temperature-dependent regulation of Drosophila body size depends on a group of cold-sensing neurons and insulin-producing cells (IPCs). Electrically silencing IPCs completely abolishes the body size increase induced by cold temperature. IPCs are directly innervated by cold-sensing neurons. Stimulation of these cold-sensing neurons activates IPCs, promotes synthesis and secretion of Drosophila insulin-like peptides and induces a larger body size, mimicking the effects of rearing the flies in cold temperature. Taken together, these findings reveal a neuronal circuit that mediates the effects of low temperature on fly growth. 

Hirabayashi, S. and Cagan, R. L. (2015). Salt-inducible kinases mediate nutrient-sensing to link dietary sugar and tumorigenesis in Drosophila. Elife 4 [Epub ahead of print]. PubMed ID: 26573956
How cancer cells sense and promote growth in the nutrient favorable conditions remain incompletely understood. Epidemiological studies have indicated that obesity is a risk factor for various types of cancers. Feeding Drosophila a high dietary sugar not only directs metabolic defects including obesity and organismal insulin resistance, but also transform Ras/Src-activated cells into aggressive tumors. This study demonstrates that Ras/Src-activated cells are sensitive to perturbations in the Hippo signaling pathway. Evidence is provided that nutritional cues activate Salt-inducible kinase, leading to Hippo pathway downregulation in Ras/Src-activated cells. The result is Yorkie-dependent increase in Wingless signaling, a key mediator that promotes diet-enhanced Ras/Src-tumorigenesis in an otherwise insulin-resistant environment. Through this mechanism, Ras/Src-activated cells are positioned to efficiently respond to nutritional signals and ensure tumor growth upon nutrient rich condition including obesity.

Chaston, J. M., Dobson, A. J., Newell, P. D. and Douglas, A. E. (2015). Host genetic control of the microbiota mediates Drosophila nutritional phenotype. Appl Environ Microbiol [Epub ahead of print]. PubMed ID: 26567306
A wealth of studies has demonstrated that resident microorganisms (microbiota) influence the pattern of nutrient allocation to animal protein and energy stores. This study demonstrates that members of the gut microbiota in Drosophila mediate the effect of certain animal genetic determinants on an important nutritional trait, triglyceride (lipid) content. Parallel analysis of the taxonomic composition of the associated bacterial community and host nutritional indices (glucose, glycogen, triglyceride, and protein contents) in multiple Drosophila genotypes revealed significant associations between the abundance of certain microbial taxa and host nutritional phenotype. By a genome-wide association study of Drosophila lines colonized with a defined microbiota, multiple host genes were statistically associated with the abundance of one bacterium, Acetobacter tropicalis. Experiments using mutant Drosophila validated the genetic association evidence and reveal that host genetic control of microbiota abundance affects the nutritional status of the flies. These data indicate that the abundance of the resident microbiota is influenced by host genotype, with consequent effects on nutrient allocation patterns.

Qin, S., Yin, H., Yang, C., Dou, Y., Liu, Z., Zhang, P., Yu, H., Huang, Y., Feng, J., Hao, J., Hao, J., Deng, L., Yan, X., Dong, X., Zhao, Z., Jiang, T., Wang, H. W., Luo, S. J. and Xie, C. (2015). A magnetic protein biocompass. Nat Mater [Epub ahead of print]. PubMed ID: 26569474
The notion that animals can detect the Earth's magnetic field was once ridiculed, but is now well established. Yet the biological nature of such magnetosensing phenomenon remains unknown. This study reports a putative magnetic receptor (Drosophila CG8198, here named MagR) and a multimeric magnetosensing rod-like protein complex, identified by theoretical postulation and genome-wide screening, and validated with cellular, biochemical, structural and biophysical methods. The magnetosensing complex consists of the identified putative magnetoreceptor and known magnetoreception-related photoreceptor cryptochromes (Cry), has the attributes of both Cry- and iron-based systems, and exhibits spontaneous alignment in magnetic fields, including that of the Earth. Such a protein complex may form the basis of magnetoreception in animals, and may lead to applications across multiple fields.

Thorat, L., Mani, K. P., Thangaraj, P., Chatterjee, S. and Nath, B. B. (2015). Downregulation of dTps1 in Drosophila melanogaster larvae confirms involvement of trehalose in redox regulation following desiccation. Cell Stress Chaperones [Epub ahead of print]. PubMed ID: 26577464
As a survival strategy to environmental water deficits, desiccation-tolerant organisms are commonly known for their ability to recruit stress-protective biomolecules such as trehalose. Trehalose plays a pivotal role in larval desiccation tolerance in Drosophila. Trehalose has emerged as a versatile molecule, serving mainly as energy source in insects and also being a stress protectant. While several recent reports have revealed the unconventional role of trehalose in scavenging reactive oxygen species in yeast and plants, this aspect has not received much attention in animals. This study examined the status of desiccation-induced generation of reactive oxygen species in D. melanogaster larvae and the possible involvement of trehalose in ameliorating the harmful consequences thereof. Insect trehalose synthesis is governed by the enzyme trehalose 6-phosphate synthase 1 (TPS1). Using the ubiquitous da-GAL4-driven expression of the dTps1-RNAi transgene, dTps1-downregulated Drosophila larvae were generated possessing depleted levels of dTps1 transcripts. This resulted in the inability of the larvae for trehalose synthesis, thereby allowing elucidation of the significance of trehalose in the regulation of desiccation-responsive redox homeostasis. Furthermore, the results from molecular genetics studies, biochemical assays, electron spin resonance analyses and a simple, non-invasive method of whole larval live imaging suggested that trehalose in collaboration with superoxide dismutase (SOD) is involved in the maintenance of redox state in D. melanogaster.

Jha, A. R., Zhou, D., Brown, C. D., Kreitman, M., Haddad, G. G. and White, K. P. (2015). Shared genetic signals of hypoxia adaptation in Drosophila and in high-altitude human populations. Mol Biol Evol [Epub ahead of print]. PubMed ID: 26576852
The ability to withstand low oxygen (hypoxia tolerance) is a polygenic and mechanistically conserved trait that has important implications for both human health and evolution. However, little is known about the diversity of genetic mechanisms involved in hypoxia adaptation in evolving populations. This study used experimental evolution and whole-genome sequencing in Drosophila melanogaster to investigate the role of natural variation in adaptation to hypoxia. Using a generalized linear mixed model, significant allele frequency differences were identified between three independently evolved hypoxia-tolerant populations and normoxic control populations for approximately 3,800 single nucleotide polymorphisms. Around 50% of these variants are clustered in 66 distinct genomic regions. These regions contain genes that are differentially expressed between hypoxia-tolerant and normoxic populations and several of the differentially expressed genes are associated with metabolic processes. Additional genes associated with respiratory and open tracheal system development also show evidence of directional selection. RNAi-mediated knockdown of several candidate genes' expression significantly enhanced survival in severe hypoxia. Using genomewide single nucleotide polymorphism data from four high-altitude human populations-Sherpas, Tibetans, Ethiopians, and Andeans, several human orthologs of the genes under selection in flies were found to be also likely under positive selection in all four high-altitude human populations. Thus, these results indicate that selection for hypoxia tolerance can act on standing genetic variation in similar genes and pathways present in organisms diverged by hundreds of millions of years.

Thursday, December 17th

Del Castillo, U., Winding, M., Lu, W. and Gelfand, V.I. (2015). Interplay between kinesin-1 and cortical dynein during axonal outgrowth and microtubule organization in Drosophila neurons. Elife 4 [Epub ahead of print]. PubMed ID: 26615019
This study investigates how microtubule motors organize microtubules in Drosophila neurons. It was shown that, during the initial stages of axon outgrowth, microtubules display mixed polarity and minus-end-out microtubules push the tip of the axon, consistent with kinesin-1 driving outgrowth by sliding antiparallel microtubules. At later stages, the microtubule orientation in the axon switches from mixed to uniform polarity with plus-end-out. Dynein knockdown prevents this rearrangement and results in microtubules of mixed orientation in axons and accumulation of microtubule minus-ends at axon tips. Microtubule reorganization requires recruitment of dynein to the actin cortex, as actin depolymerization phenocopies dynein depletion, and direct recruitment of dynein to the membrane bypasses the actin requirement. These results show that cortical dynein slides 'minus-end-out' microtubules from the axon, generating uniform microtubule arrays. The study speculates that differences in microtubule orientation between axons and dendrites could be dictated by differential activity of cortical dynein.

Rousso, T., Schejter, E.D. and Shilo, B.Z. (2015). Orchestrated content release from Drosophila glue-protein vesicles by a contractile actomyosin network. Nat Cell Biol [Epub ahead of print]. PubMed ID: 26641716
Releasing content from large vesicles measuring several micrometres in diameter poses exceptional challenges to the secretory system. An actomyosin network commonly coats these vesicles, and is thought to provide the necessary force mediating efficient cargo release. This study describes the spatial and temporal dynamics of the formation of this actomyosin coat around large vesicles and the resulting vesicle collapse, in live Drosophila melanogaster salivary glands. The Formin family protein Diaphanous (Dia) was identified as the main actin nucleator involved in generating this structure, and Rho was uncovered as an integrator of actin assembly and contractile machinery activation comprising this actomyosin network. High-resolution imaging reveals a unique cage-like organization of myosin II on the actin coat. This myosin arrangement requires branched-actin polymerization, and is critical for exerting a non-isotropic force, mediating efficient vesicle contraction.

Plevock, K.M., Galletta, B.J., Slep, K.C. and Rusan, N.M. (2015). Newly characterized region of CP190 associates with microtubules and mediates proper spindle morphology in Drosophila stem cells. PLoS One 10: e0144174. PubMed ID: 26649574
CP190 is a large, multi-domain protein, first identified as a centrosome protein with oscillatory localization over the course of the cell cycle. During interphase it has a well-established role within the nucleus as a chromatin insulator. Upon nuclear envelope breakdown, there is a striking redistribution of CP190 to centrosomes and the mitotic spindle, in addition to the population at chromosomes. This study investigates CP190 in detail by performing domain analysis in cultured Drosophila S2 cells combined with protein structure determination by X-ray crystallography, in vitro biochemical characterization, and in vivo fixed and live imaging of cp190 mutant flies. A novel N-terminal centrosome and microtubule (MT) targeting region, sufficient for spindle localization, was identified. This region consists of a highly conserved BTB domain and a linker region that serves as the MT binding domain. The 2.5 Å resolution structure of the CP190 N-terminal 126 amino acids exhibits a canonical BTB domain fold and exists as a stable dimer in solution. The ability of the linker region to robustly localize to MTs requires BTB domain-mediated dimerization. Deletion of the linker region using CRISPR significantly alters spindle morphology and leads to DNA segregation errors in the developing Drosophila brain neuroblasts. Collectively, the study highlights a multivalent MT-binding architecture in CP190, which confers distinct subcellular cytoskeletal localization and function during mitosis.

Melkov, A., Simchoni, Y., Alcalay, Y. and Abdu, U. (2015). Dynamic microtubule organization and mitochondrial transport are regulated by distinct Kinesin-1 pathways. Biol Open [Epub ahead of print]. PubMed ID: 26581590
The microtubule (MT) plus-end motor kinesin heavy chain (Khc) is well known for its role in long distance cargo transport. Recent evidence showed that Khc is also required for the organization of the cellular MT network by mediating MT sliding. This study found that mutations in Khc and the gene of its adaptor protein, kinesin light chain (Klc) resulted in identical bristle morphology defects, with the upper part of the bristle being thinner and flatter than normal and failing to taper towards the bristle tip. Bristle mitochondria transport was shown to require Khc but not Klc as a competing force to dynein heavy chain (Dhc). Surprisingly, Dhc was demonstrated to be the primary motor for both anterograde and retrograde fast mitochondria transport. The upper part of Khc and Klc mutant bristles lacked stable MTs. When following dynamic MT polymerization via the use of GFP-tagged end-binding protein 1 (EB1), it was noted that at Khc and Klc mutant bristle tips, dynamic MTs significantly deviated from the bristle parallel growth axis, relative to wild-type bristles. GFP-EB1 failed to concentrate as a focus at the tip of Khc and Klc mutant bristles. It is proposed that the failure of bristle tapering is due to defects in directing dynamic MTs at the growing tip. Thus, this study revealed a new function for Khc and Klc in directing dynamic MTs during polarized cell growth. Moreover, this study has demonstrated a novel mode of coordination in mitochondrial transport between Khc and Dhc.

Wednesday, December 16th

Vichas, A., Laurie, M.T. and Zallen, J.A. (2015). The Ski2-family helicase Obelus regulates Crumbs alternative splicing and cell polarity. J Cell Biol 211: 1011-1024. PubMed ID: 26644515
Alternative splicing can have profound consequences for protein activity, but the functions of most alternative splicing regulators are not known. This study shows that Obelus, a conserved Ski2-family helicase, is required for cell polarity and adherens junction organization in the Drosophila melanogaster embryo. In obelus mutants, epithelial cells display an expanded apical domain, aggregation of adherens junctions at the cell membrane, and microtubule-dependent defects in centrosome positioning. Through whole-genome transcriptome analysis, it was found that Obelus is required for the alternative splicing of a small number of transcripts in the early embryo, including the pre-mRNA that encodes the apical polarity protein Crumbs. In obelus mutants, inclusion of an alternative exon results in increased expression of a Crumbs isoform that contains an additional epidermal growth factor-like repeat in the extracellular domain. Overexpression of this alternative Crumbs isoform recapitulates the junctional aggregation and centrosome positioning defects of obelus mutants. These results indicate that regulation of Crumbs alternative splicing by the Obelus helicase modulates epithelial polarity during development. 

Lee, D. M., Rodrigues, F. F., Yu, C. G., Swan, M. and Harris, T. J. (2015). PH Domain-Arf G protein interactions localize the Arf-GEF Steppke for cleavage furrow regulation in Drosophila. PLoS One 10: e0142562. PubMed ID: 26556630
The recruitment of GDP/GTP exchange factors (GEFs) to specific subcellular sites dictates where they activate small G proteins for the regulation of various cellular processes. Cytohesins are a conserved family of plasma membrane GEFs for Arf small G proteins that regulate endocytosis. This paper reports how the pleckstrin homology (PH) domain of the Drosophila cytohesin Steppke affects its localization and activity at cleavage furrows of the early embryo. The PH domain is necessary for Steppke furrow localization, and for it to regulate furrow structure. However, the PH domain was not sufficient for the localization. The Steppke PH domain preferentially binds PIP3 in vitro through a conserved mechanism. However, disruption of residues for PIP3 binding had no apparent effect on GFP-Steppke localization and effects. Rather, residues for binding to GTP-bound Arf G proteins made major contributions to this Steppke localization and activity. Arf1-GFP, Arf6-GFP and Arl4-GFP localized to furrows. However, probably due to redundancies it was difficult to assess how individual Arf small G proteins affect Steppke. Nonetheless, these data show that the Steppke PH domain and its conserved residues for binding to GTP-bound Arf G proteins have substantial effects on Steppke localization and activity in early Drosophila embryos.

Lye, C. M., Blanchard, G. B., Naylor, H. W., Muresan, L., Huisken, J., Adams, R. J. and Sanson, B. (2015). Mechanical coupling between endoderm invagination and axis extension in Drosophila. PLoS Biol 13: e1002292. PubMed ID: 26544693
This study addressed the role of tissue-scale physical forces during axis extension, using Drosophila germband extension (GBE) as a model. Previous studies have shown that cells elongate in the anteroposterior (AP) axis in the extending germband, suggesting that an extrinsic tensile force contributed to body axis extension. This study further characterized the AP cell elongation patterns during GBE, by tracking cells and quantifying their apical cell deformation over time. AP cell elongation forms a gradient culminating at the posterior of the embryo, consistent with an AP-oriented tensile force propagating from there. To identify the morphogenetic movements that could be the source of this extrinsic force, gastrulation movements were mapped temporally using light sheet microscopy to image whole Drosophila embryos. Both mesoderm and endoderm invaginations were found to be synchronous with the onset of GBE. The AP cell elongation gradient remains when mesoderm invagination is blocked but is abolished in the absence of endoderm invagination. This suggested that endoderm invagination is the source of the tensile force. Evidence of this force was sought in a simplified system without polarized cell intercalation, in acellular embryos. Posteriorwards Myosin II flows were identified towards the presumptive posterior endoderm, which still undergoes apical constriction in acellular embryos as in wildtype. Tension was shown to be increased in the AP orientation, compared to dorsoventral orientation or to either orientations more anteriorly in the embryo. It is proposeed that apical constriction leading to endoderm invagination is the source of the extrinsic force contributing to germband extension. This highlights the importance of physical interactions between tissues during morphogenesis.

Giachello, C. N. and Baines, R. A. (2015). Inappropriate neural activity during a sensitive period in embryogenesis results in persistent seizure-like behavior. Curr Biol 25: 2964-2968. PubMed ID: 26549258
Maturation of neural circuits requires activity-dependent processes that underpin the emergence of appropriate behavior in the adult. It has been proposed that disruption of these events, during specific critical periods when they exert maximal influence, may lead to neurodevelopmental diseases, including epilepsy. However, complexity of neurocircuitry, coupled with the lack of information on network formation in mammals, makes it difficult to directly investigate this hypothesis. Alternative models, including the fruit fly Drosophila melanogaster, show remarkable similarities between experimental seizure-like activity and clinical phenotypes. In particular, a group of flies, termed bang-sensitive (bs) mutants have been extensively used to investigate the pathophysiological mechanisms underlying seizure. Seizure phenotype can be measured in larval stages using an electroshock assay, and this behavior in bs mutants is dramatically reduced following ingestion of typical anti-epileptic drugs (AEDs). This study describes a critical period of embryonic development in Drosophila during which manipulation of neural activity is sufficient to significantly influence seizure behavior at postembryonic stages. Inhibition of elevated activity, characteristic of bs seizure models, during the critical period is sufficient to suppress seizure. By contrast, increasing neuronal excitation during the same period in wild-type (WT) is sufficient to permanently induce a seizure behavior. Further, this study shows that induction of seizure in WT correlates with functional alteration of motoneuron inputs that is a characteristic of bs mutants. Induction of seizure is rescued by prior administration of AEDs, opening a new perspective for early drug intervention in the treatment of genetic epilepsy.

Tuesday, December 15th

Khan, M.R., Li, L., Pérez-Sánchez, C., Saraf, A., Florens, L., Slaughter, B.D., Unruh, J.R. and Si, K. (2015). Amyloidogenic oligomerization transforms Drosophila Orb2 from a translation repressor to an activator. Cell 163: 1468-1483. PubMed ID: 26638074
Memories are thought to be formed in response to transient experiences, in part through changes in local protein synthesis at synapses. In Drosophila, the amyloidogenic (prion-like) state of the RNA binding protein Orb2 has been implicated in long-term memory, but how conformational conversion of Orb2 promotes memory formation is unclear. Combining in vitro and in vivo studies, this study finds that the monomeric form of Orb2 represses translation and removes mRNA poly(A) tails, while the oligomeric form enhances translation and elongates the poly(A) tails and imparts its translational state to the monomer. The CG13928 protein, which binds only to monomeric Orb2, promotes deadenylation, whereas the putative poly(A) binding protein CG4612 promotes oligomeric Orb2-dependent translation. These data support a model in which monomeric Orb2 keeps target mRNA in a translationally dormant state and experience-dependent conversion to the amyloidogenic state activates translation, resulting in persistent alteration of synaptic activity and stabilization of memory.

Lin, T., et al. (2015). Spindle-F is the central mediator of Ik2 kinase-dependent dendrite pruning in Drosophila sensory neurons. PLoS Genet 11: e1005642. PubMed ID: 26540204
During development, certain Drosophila sensory neurons undergo dendrite pruning that selectively eliminates their dendrites but leaves the axons intact. How these neurons regulate pruning activity in the dendrites remains unknown. This study identifies a coiled-coil protein Spindle-F (Spn-F) that is required for dendrite pruning in Drosophila sensory neurons. Spn-F acts downstream of IKK-related kinase Ik2 in the same pathway for dendrite pruning. Spn-F exhibits a punctate pattern in larval neurons, whereas these Spn-F puncta become redistributed in pupal neurons, a step that is essential for dendrite pruning. The redistribution of Spn-F from puncta in pupal neurons requires the phosphorylation of Spn-F by Ik2 kinase to decrease Spn-F self-association, and depends on the function of microtubule motor dynein complex. Spn-F is a key component to link Ik2 kinase to dynein motor complex, and the formation of Ik2/Spn-F/dynein complex is critical for Spn-F redistribution and for dendrite pruning. These findings reveal a novel regulatory mechanism for dendrite pruning achieved by temporal activation of Ik2 kinase and dynein-mediated redistribution of Ik2/Spn-F complex in neurons.

Cattenoz, P. B., Popkova, A., Southall, T., Aiello, G., Brand, A. and Giangrande, A. (2015). . Functional conservation of the Glide/Gcm regulatory network controlling glia, hemocyte and tendon cell differentiation in Drosophila. Genetics [Epub ahead of print] . PubMed ID: 26567182
This study shows the results and the validation of a DamID genome-wide screen that identifies the direct targets of Gcm, a potent transcription factor that controls glia, hemocyte and tendon cell differentiation in Drosophila. The screen highlights three major signaling pathways interacting with Gcm: Notch, Hedgehog and JAK/STAT, which all involve feedback loops. Furthermore, the screen identifies effector molecules that are necessary for cell-cell interactions during late developmental processes and/or in ontogeny. Typically, Immunoglobulin domain-containing proteins control cell adhesion and axonal navigation. This shows that early and transiently expressed fate determinants not only control other transcription factors that in turn implement a specific developmental program but also directly affect late developmental events and cell function. This study also provides the first evidence for the conservation of Gcm direct targets in humans.

Sitaraman, D., Aso, Y., Rubin, G.M. and Nitabach, M.N. (2015). Control of sleep by dopaminergic inputs to the Drosophila mushroom body. Front Neural Circuits 9: 73. PubMed ID: 26617493
The Drosophila mushroom body (MB) is an associative learning network that is important for the control of sleep. Particular intrinsic MB Kenyon cell (KC) classes have been identified that regulate sleep through synaptic activation of particular MB output neurons (MBONs) whose axons convey sleep control signals out of the MB to downstream target regions. Specifically, it was found that sleep-promoting KCs increase sleep by preferentially activating cholinergic sleep-promoting MBONs, while wake-promoting KCs decrease sleep by preferentially activating glutamatergic wake-promoting MBONs. By using a combination of genetic and physiological approaches to identify wake-promoting dopaminergic neurons (DANs) that innervate the MB, it was shown that they activate wake-promoting MBONs. These studies reveal a dopaminergic sleep control mechanism that likely operates by modulation of KC-MBON microcircuits.

Monday, December 14th

Liu, C., Haynes, P. R., Donelson, N. C., Aharon, S. and Griffith, L. C. (2015). Sleep in populations of Drosophila melanogaster. eNeuro 2 [Epub ahead of print]. PubMed ID: 26465005
The fruit fly Drosophila melanogaster is a diurnal insect active during the day with consolidated sleep at night. Social interactions between pairs of flies have been shown to affect locomotor activity patterns, but effects on locomotion and sleep patterns have not been assessed for larger populations. This study used a commercially available locomotor activity monitor (LAM25H) system to record and analyze sleep behavior. Surprisingly, it was found that same-sex populations of flies synchronize their sleep/wake activity, resulting in a population sleep pattern, which is similar but not identical to that of isolated individuals. Like individual flies, groups of flies show circadian and homeostatic regulation of sleep, as well as sexual dimorphism in sleep pattern and sensitivity to starvation and a known sleep-disrupting mutation (amnesiac). Populations of flies, however, exhibit distinct sleep characteristics from individuals. Differences in sleep appear to be due to olfaction-dependent social interactions and change with population size and sex ratio. These data support the idea that it is possible to investigate neural mechanisms underlying the effects of population behaviors on sleep by directly looking at a large number of animals in laboratory conditions.

Chen, C., Buhl, E., Xu, M., Croset, V., Rees, J. S., Lilley, K. S., Benton, R., Hodge, J. J. and Stanewsky, R. (2015). Drosophila Ionotropic Receptor 25a mediates circadian clock resetting by temperature. Nature 527: 516-520. PubMed ID: 26580016
Circadian clocks are endogenous timers adjusting behaviour and physiology with the solar day. Visual and non-visual photoreceptors are responsible for synchronizing circadian clocks to light, but clock-resetting is also achieved by alternating day and night temperatures with only 2-4 degrees C difference. This study shows that Drosophila Ionotropic Receptor 25a (IR25a) is required for behavioural synchronization to low-amplitude temperature cycles. This channel is expressed in sensory neurons of internal stretch receptors previously implicated in temperature synchronization of the circadian clock. IR25a is required for temperature-synchronized clock protein oscillations in subsets of central clock neurons. Extracellular leg nerve recordings reveal temperature- and IR25a-dependent sensory responses, and IR25a misexpression confers temperature-dependent firing of heterologous neurons. It is proposed that IR25a is part of an input pathway to the circadian clock that detects small temperature differences. This pathway operates in the absence of known 'hot' and 'cold' sensors in the Drosophila antenna, revealing the existence of novel periphery-to-brain temperature signalling channels.

Shim, J., Lee, Y., Jeong, Y. T., Kim, Y., Lee, M. G., Montell, C. and Moon, S. J. (2015). The full repertoire of Drosophila gustatory receptors for detecting an aversive compound. Nat Commun 6: 8867. PubMed ID: 26568264
The ability to detect toxic compounds in foods is essential for animal survival. However, the minimal subunit composition of gustatory receptors required for sensing aversive chemicals in Drosophila is unknown. This study reports that three gustatory receptors, GR8a, GR66a and GR98b function together in the detection of L-canavanine, a plant-derived insecticide. Ectopic co-expression of Gr8a and Gr98b in Gr66a-expressing, bitter-sensing gustatory receptor neurons (GRNs) confers responsiveness to L-canavanine. Furthermore, misexpression of all three Grs enables salt- or sweet-sensing GRNs to respond to L-canavanine. Introduction of these Grs in sweet-sensing GRNs switches L-canavanine from an aversive to an attractive compound. Co-expression of GR8a, GR66a and GR98b in Drosophila S2 cells induces an L-canavanine-activated nonselective cation conductance. It is concluded that three GRs collaborate to produce a functional L-canavanine receptor. Thus, these results clarify the full set of GRs underlying the detection of a toxic tastant that drives avoidance behaviour in an insect.

Kallman, B. R., Kim, H. and Scott, K. (2015). Excitation and inhibition onto central courtship neurons biases mate choice. Elife 4 [Epub ahead of print]. PubMed ID: 26568316
The ability to distinguish males from females is essential for productive mate selection and species propagation. Recent studies in Drosophila have identified different classes of contact chemosensory neurons that detect female or male pheromones and influence courtship decisions. This study examined central neural pathways in the male brain that process female and male pheromones using anatomical, calcium imaging, optogenetic, and behavioral studies. Sensory neurons were found that detect female pheromones, but not male pheromones, activate a novel class of neurons in the ventral nerve cord to cause activation of P1 neurons, male-specific command neurons that trigger courtship. In addition, sensory neurons that detect male pheromones, as well as those that detect female pheromones, activate central mAL neurons to inhibit P1. These studies demonstrate that the balance of excitatory and inhibitory drives onto central courtship-promoting neurons controls mating decisions.

Kidd, P. B., Young, M. W. and Siggia, E. D. (2015). Temperature compensation and temperature sensation in the circadian clock. Proc Natl Acad Sci U S A 112: E6284-6292. PubMed ID: 26578788
All known circadian clocks have an endogenous period that is remarkably insensitive to temperature, a property known as temperature compensation, while at the same time being readily entrained by a diurnal temperature oscillation. Although temperature compensation and entrainment are defining features of circadian clocks, their mechanisms remain poorly understood. Most models presume that multiple steps in the circadian cycle are temperature-dependent, thus facilitating temperature entrainment, but then insist that the effect of changes around the cycle sums to zero to enforce temperature compensation. An alternative theory proposes that the circadian oscillator evolved from an adaptive temperature sensor: a gene circuit that responds only to temperature changes. This theory implies that temperature changes should linearly rescale the amplitudes of clock component oscillations but leave phase relationships and shapes unchanged. This study shows using timeless luciferase reporter measurements and Western blots against Timeless protein that this prediction is satisfied by the Drosophila circadian clock. Evidence is reviewed for pathways that couple temperature to the circadian clock; previously unidentified evidence is shown for coupling between the Drosophila clock and the heat-shock pathway.

Gardner, B., Strus, E., Meng, Q. C., Coradetti, T., Naidoo, N. N., Kelz, M. B. and Williams, J. A. (2015). Sleep homeostasis and general anesthesia: Are fruit flies well rested after emergence from Propofol?. Anesthesiology [Epub ahead of print]. PubMed ID: 26556728
Shared neurophysiologic features between sleep and anesthetic-induced hypnosis indicate a potential overlap in neuronal circuitry underlying both states. The authors explored the hypothesis that propofol anesthesia also dispels sleep pressure in the fruit fly. Propofol was administered by transferring flies onto food containing various doses of propofol. High-performance liquid chromatography was used to measure the tissue concentrations of ingested propofol. To determine whether propofol anesthesia substitutes for natural sleep, the flies were subjected to 10-h sleep deprivation (SD), followed by 6-h propofol exposure, and monitored for subsequent sleep. Oral propofol treatment was shown to cause anesthesia in flies as indicated by a dose-dependent reduction in locomotor activity and increased arousal threshold. Recovery sleep in flies fed propofol after SD was delayed until after flies had emerged from anesthesia. SD was also associated with a significant increase in mortality in propofol-fed flies. Together, these data indicate that fruit flies are effectively anesthetized by ingestion of propofol and suggest that homologous molecular and neuronal targets of propofol are conserved in Drosophila. However, behavioral measurements indicate that propofol anesthesia does not satisfy the homeostatic need for sleep and may compromise the restorative properties of sleep.

Sunday, December 13th

Costechareyre, D., Capo, F., Fabre, A., Chaduli, D., Kellenberger, C., Roussel, A., Charroux, B. and Royet, J. (2015). Tissue-specific regulation of Drosophila NF-κB pathway activation by peptidoglycan recognition protein SC. J Innate Immun [Epub ahead of print]. PubMed ID: 26513145
In Drosophila, peptidoglycan (PGN) is detected by PGN recognition proteins (PGRPs) that act as pattern recognition receptors. Some PGRPs such as PGRP-LB or PGRP-SCs are able to cleave PGN, therefore reducing the amount of immune elicitors and dampening immune deficiency (IMD) pathway activation. By generating PGRP-SC-specific mutants, this study reevaluated the roles of PGRP-LB, PGRP-SC1 and PGRP-SC2 during immune responses. These genes were shown to be expressed in different gut domains, and they follow distinct transcriptional regulation. Loss-of-function mutant analysis indicates that PGRP-LB is playing a major role in IMD pathway activation and bacterial load regulation in the gut, although PGRP-SCs are expressed at high levels in this organ. PGRP-SC2 is the main negative regulator of IMD pathway activation in the fat body. Accordingly, mutants for either PGRP-LB or PGRP-SC2 displayed a distinct susceptibility to bacteria depending on the infection route. Lastly, PGRP-SC1 and PGRP-SC2 are required in vivo for full Toll pathway activation by Gram-positive bacteria.

Sansone, C. L., Cohen, J., Yasunaga, A., Xu, J., Osborn, G., Subramanian, H., Gold, B., Buchon, N. and Cherry, S. (2015). Microbiota-dependent priming of antiviral intestinal immunity in Drosophila. Cell Host Microbe 18: 571-581. PubMed ID: 26567510
Enteric pathogens must overcome intestinal defenses to establish infection. In Drosophila, the ERK signaling pathway inhibits enteric virus infection. The intestinal microflora also impacts immunity but its role in enteric viral infection is unknown. This study shows that two signals are required to activate antiviral ERK signaling in the intestinal epithelium. One signal depends on recognition of peptidoglycan from the microbiota, particularly from the commensal Acetobacter pomorum, which primes the NF-κB-dependent induction of a secreted factor, Pvf2. However, the microbiota is not sufficient to induce this pathway; a second virus-initiated signaling event involving release of transcriptional paused genes mediated by the kinase Cdk9 is also required for Pvf2 production. Pvf2 stimulates antiviral immunity by binding to the receptor tyrosine kinase PVR, which is necessary and sufficient for intestinal ERK responses. These findings demonstrate that sensing of specific commensals primes inflammatory signaling required for epithelial responses that restrict enteric viral infections.

Helenius, I. T., Haake, R. J., Kwon, Y. J., Hu, J. A., Krupinski, T., Casalino-Matsuda, S. M., Sporn, P. H., Sznajder, J. I. and Beitel, G. J. (2015). Identification of Drosophila Zfh2 as a mediator of hypercapnic immune regulation by a Genome-Wide RNA interference screen. J Immunol. PubMed ID: 26643480

Hypercapnia, elevated partial pressure of CO2 in blood and tissue, develops in many patients with chronic severe obstructive pulmonary disease and other advanced lung disorders. Patients with advanced disease frequently develop bacterial lung infections. Hypercapnia has been shown to suppress induction of NF-κB-regulated innate immune response genes required for host defense, and it increases mortality from bacterial infections. However, the molecular mediators of hypercapnic immune suppression are undefined. This study reports a genome-wide RNA interference screen in Drosophila S2* cells stimulated with bacterial peptidoglycan. The screen identified 16 genes with human orthologs whose knockdown reduced hypercapnic suppression of the gene encoding the antimicrobial peptide Diptericin (Dipt), but did not increase Dipt mRNA levels in air. In vivo tests of one of the strongest screen hits, zinc finger homeodomain 2 (Zfh2; mammalian orthologs ZFHX3/ATBF1 and ZFHX4), demonstrate that reducing zfh2 function improves survival of flies exposed to elevated CO2 and infected with Staphylococcus aureus. Tissue-specific knockdown of zfh2 in the fat body mitigates hypercapnia-induced reductions in Dipt and improves resistance of CO2-exposed flies to infection. Zfh2 mutations also partially rescue hypercapnia-induced delays in egg hatching, suggesting that Zfh2's role in mediating responses to hypercapnia extends beyond the immune system. Taken together these results identify Zfh2 as the first in vivo mediator of hypercapnic immune suppression.

Gutzwiller, F., Carmo, C. R., Miller, D. E., Rice, D. W., Newton, I. L., Hawley, R. S., Teixeira, L. and Bergman, C. M. (2015). Dynamics of Wolbachia pipientis gene expression across the Drosophila melanogaster life cycle. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 26497146
Symbiotic interactions between microbes and their multicellular hosts have manifold biological consequences. To better understand how bacteria maintain symbiotic associations with animal hosts, this study analyzed genome-wide gene expression for the endosymbiotic alpha-proteobacteria Wolbachia pipientis across the entire life cycle of Drosophila. The majority of Wolbachia genes are expressed stably across the D. melanogaster life cycle, but 7.8% of Wolbachia genes exhibit robust stage- or sex-specific expression differences when studied in the whole-organism context. Differentially-expressed Wolbachia genes are typically up-regulated after Drosophila embryogenesis and include many bacterial membrane, secretion system, and ankyrin-repeat containing proteins. Sex-biased genes are often organized as small operons of uncharacterized genes and are mainly up-regulated in adult Drosophila males in an age-dependent manner. Expression levels of previously reported candidate genes thought to be involved in host-microbe interaction were systematically investigate, including those in the WO-A and WO-B prophages and in the Octomom region that has been implicated in regulating bacterial titre and pathogenicity. This work provides comprehensive insight into the developmental dynamics of gene expression for a widespread endosymbiont in its natural host context, and shows that public gene expression data harbour rich resources to probe the functional basis of the Wolbachia-Drosophila symbiosis and annotate the transcriptional outputs of the Wolbachia genome.

Saturday, December 12th

Bozicevic, V., Hutter, S., Stephan, W. and Wollstein, A. (2015). Population genetic evidence for cold adaptation in European Drosophila melanogaster populations. Mol Ecol [Epub ahead of print]. PubMed ID: 26558479
Drosophila melanogaster populations from Europe (the Netherlands and France) and Africa (Rwanda and Zambia) were studied to uncover genetic evidence of adaptation to cold. This study presents four lines of evidence for genes involved in cold adaptation from four perspectives: (1) the frequency of SNPs at genes previously known to be associated with chill-coma recovery time (CCRT), startle reflex (SR), and resistance to starvation stress (RSS) vary along environmental gradients and therefore among populations; (2) SNPs of genes that correlate significantly with latitude and altitude in African and European populations overlap with SNPs that correlate with a latitudinal cline from North America; (3) at the genome-wide level, the top candidate genes are enriched in gene ontology (GO) terms that are related to cold tolerance; (4) GO enriched terms from North American clinal genes overlap significantly with those from Africa and Europe. Each SNP was tested in 10 independent runs of Bayenv2, using the median Bayes factors to ascertain candidate genes. None of the candidate genes were found close to the breakpoints of cosmopolitan inversions, and only four candidate genes were linked to QTLs related to CCRT. To overcome the limitation that only four populations were used to test correlations with environmental gradients, simulations were performed to estimate the power of this approach for detecting selection. Based on the results a novel network of genes is proposed that is involved in cold adaptation.

Bergland, A. O., Tobler, R., Gonzalez, J., Schmidt, P. and Petrov, D. (2015). Secondary contact and local adaptation contribute to genome-wide patterns of clinal variation in Drosophila melanogaster. Mol Ecol [Epub ahead of print]. PubMed ID: 26547394
Populations arrayed along broad latitudinal gradients often show patterns of clinal variation in phenotype and genotype. Such population differentiation can be generated and maintained by both historical demographic events and local adaptation. These evolutionary forces are not mutually exclusive and can in some cases produce nearly identical patterns of genetic differentiation among populations. This study investigated the evolutionary forces that generated and maintain clinal variation genome-wide among populations of Drosophila melanogaster sampled in North America and Australia. Patterns of clinal variation in these continents were contrasted with patterns of differentiation among ancestral European and African populations. Using established and novel methods derive in this study, it was shown that recently derived North America and Australia populations were likely founded by both European and African lineages and that this hybridization event likely contributed to genome-wide patterns of parallel clinal variation between continents. The pervasive effects of admixture means that differentiation at only several hundred loci can be attributed to the operation of spatially varying selection using an FST outlier approach. These results provide novel insight into the well-studied system of clinal differentiation in D. melanogaster and provide a context for future studies seeking to identify loci contributing to local adaptation in a wide variety of organisms, including other invasive species as well as temperate endemics.

Poyet, M., Le Roux, V., Gibert, P., Meirland, A., Prevost, G., Eslin, P. and Chabrerie, O. (2015). The wide potential trophic niche of the asiatic fruit fly Drosophila suzukii: The key of its invasion success in temperate Europe?. PLoS One 10: e0142785. PubMed ID: 26581101
The Asiatic fruit fly Drosophila suzukii has recently invaded Europe and North and South America, causing severe damage to fruit production systems. Although agronomic host plants of that fly are now well documented, little is known about the suitability of wild and ornamental hosts in its exotic area. In order to study the potential trophic niche of D. suzukii with relation to fruit characteristics, fleshy fruits from 67 plant species were sampled in natural and anthropic ecosystems (forests, hedgerows, grasslands, coastal areas, gardens and urban areas) of the north of France and submitted to experimental infestations. A set of fruit traits (structure, colour, shape, skin texture, diameter and weight, phenology) potentially interacting with oviposition choices and development success of D. suzukii was measured. Almost half of the tested plant species belonging to 17 plant families allowed the full development of D. suzukii. This suggests that the extreme polyphagy of the fly and the very large reservoir of hosts producing fruits all year round ensure temporal continuity in resource availability and contribute to the persistence and the exceptional invasion success of D. suzukii in natural habitats and neighbouring cultivated systems. Nevertheless, this very plastic trophic niche is not systematically beneficial to the fly. Some of the tested plants attractive to D. suzukii gravid females stimulate oviposition but do not allow full larval development. Planted near sensitive crops, these "trap plants" may attract and lure D. suzukii, therefore contributing to the control of the invasive fly.

Kain, J. S., Zhang, S., Akhund-Zade, J., Samuel, A. D., Klein, M. and de Bivort, B. L. (2015). Variability in thermal and phototactic preferences in Drosophila may reflect an adaptive bet-hedging strategy. Evolution [Epub ahead of print]. PubMed ID: 26531165
Organisms use various strategies to cope with fluctuating environmental conditions. In diversified bet-hedging, a single genotype exhibits phenotypic heterogeneity with the expectation that some individuals will survive transient selective pressures. To date, empirical evidence for bet-hedging is scarce. This study observed that individual Drosophila melanogaster flies exhibit striking variation in light- and temperature-preference behaviors. With a modeling approach that combines real world weather and climate data to simulate temperature preference-dependent survival and reproduction, this study found that a bet-hedging strategy may underlie the observed inter-individual behavioral diversity. Specifically, bet-hedging outcompetes strategies in which individual thermal preferences are heritable. Animals employing bet-hedging refrain from adapting to the coolness of spring with increased warm-seeking that inevitably becomes counterproductive in the hot summer. This strategy is particularly valuable when mean seasonal temperatures are typical, or when there is considerable fluctuation in temperature within the season. The model predicts, and and this study experimentally verified, that the behaviors of individual flies are not heritable. Finally, the effects of historical weather data, climate change, and geographic seasonal variation on the optimal strategies underlying behavioral variation between individuals was modeled, characterizing the regimes in which bet-hedging is advantageous.

Giraldo-Perez, P., Herrera, P., Campbell, A., Taylor, M. L., Skeats, A., Aggio, R., Wedell, N. and Price, T. A. (2015). Winter is coming: hibernation reverses the outcome of sperm competition in a fly. J Evol Biol [Epub ahead of print]. PubMed ID: 26565889
Sperm commonly compete within females to fertilise ova, but research has focused on short term sperm storage: sperm that are maintained in a female for only a few days or weeks before use. In nature, females of many species store sperm for months or years, often during periods of environmental stress, such as cold winters. This study examined the outcome of sperm competition in the fruit fly Drosophila pseudoobscura, simulating the conditions in which females survive winter. Females were mated to two males, and then the female was stored for up to 120 days at 4 degrees C. It was found that the outcome of sperm competition was consistent when sperm from two males was stored for 0, 1 or 30 days, with the last male to mate fathering most of the offspring. However, when females were stored in the cold for 120 days, the last male to mate fathered less than 5% of the offspring. Moreover, when sperm were stored long term the first male fathered almost all offspring even when he carried a meiotic driving sex chromosome that drastically reduces sperm competitive success under short term storage conditions. This suggests that long-term sperm storage can radically alter the outcome of sperm competition.

Yassin, A. and David, J. R. (2015). Within species reproductive costs affect the asymmetry of satyrisation in Drosophila. J Evol Biol [Epub ahead of print]. PubMed ID: 26538290
Understanding how species interactions influence their distribution and evolution is a fundamental question in evolutionary biology. Theory suggests that asymmetric reproductive interference, in which one species induces higher reproductive costs on another species, may be more important in delimiting species boundaries than interspecific competition over resources. However, the underlying mechanisms of such asymmetry remains unclear. This study tested whether differences in within species reproductive costs determine the between species asymmetry of costs using three allopatric Drosophila species belonging to the melanogaster subgroup. The results support this hypothesis, especially in a pair of insular species. Males of one species that induce costs to their conspecific females led to a 5-fold increase of heterospecific females mortality with dead flies bearing spectacular large melanised wounds on their genitalia. Males of the other species were harmful neither to their conspecific nor heterospecific females. Comparative studies of within species reproductive costs may therefore be a valuable tool for predicting between species interactions and community structures.

Friday, December 11th

Spellberg, M. J. and Marr, M. T. (2015). FOXO regulates RNA interference in Drosophila and protects from RNA virus infection. Proc Natl Acad Sci U S A 112: 14587-14592. PubMed ID: 26553999
Small RNA pathways are important players in posttranscriptional regulation of gene expression. These pathways play important roles in all aspects of cellular physiology from development to fertility to innate immunity. However, almost nothing is known about the regulation of the central genes in these pathways. The forkhead box O (FOXO) family of transcription factors is a conserved family of DNA-binding proteins that responds to a diverse set of cellular signals. FOXOs are crucial regulators of cellular homeostasis that have a conserved role in modulating organismal aging and fitness. This study shows that Drosophila FOXO (dFOXO) regulates the expression of core small RNA pathway genes. In addition, increased dFOXO activity results in an increase in RNA interference (RNAi) efficacy, establishing a direct link between cellular physiology and RNAi. Consistent with these findings, dFOXO activity is stimulated by viral infection and is required for effective innate immune response to RNA virus infection. This study reveals an unanticipated connection among dFOXO, stress responses, and the efficacy of small RNA-mediated gene silencing and suggests that organisms can tune their gene silencing in response to environmental and metabolic conditions.

Brewer-Jensen, P., Wilson, C. B., Abernethy, J., Mollison, L., Card, S. and Searles, L. L. (2015). Suppressor of sable [Su(s)] and Wdr82 down-regulate RNA from heat-shock-inducible repetitive elements by a mechanism that involves transcription termination. RNA [Epub ahead of print]. PubMed ID: 26577379
Although RNA polymerase II (Pol II) productively transcribes very long genes in vivo, transcription through extragenic sequences often terminates in the promoter-proximal region and the nascent RNA is degraded. Mechanisms that induce early termination and RNA degradation are not well understood in multicellular organisms. This study presents evidence that the suppressor of sable [su(s)] regulatory pathway of Drosophila plays a role in this process. Previous studies have shown that Su(s) promotes exosome-mediated degradation of transcripts from endogenous repeated elements at an Hsp70 locus (Hsp70-αβ elements). This report identifies Wdr82 as a component of this process and shows that it works with Su(s) to inhibit Pol II elongation through Hsp70-αβ elements. Furthermore, the unstable transcripts produced during this process are shown to be polyadenylated at heterogeneous sites that lack canonical polyadenylation signals. Two distinct regions were defined that mediate this regulation. These results indicate that the Su(s) pathway promotes RNA degradation and transcription termination through a novel mechanism.

Xie, X. and Dubrovsky, E. B. (2015). Knockout of Drosophila RNase ZL impairs mitochondrial transcript processing, respiration and cell cycle progression. Nucleic Acids Res [Epub ahead of print]. PubMed ID: 26553808
RNase ZL is a highly conserved tRNA 3'-end processing endoribonuclease. Similar to its mammalian counterpart, Drosophila RNase ZL (dRNaseZ) has a mitochondria targeting signal (MTS) flanked by two methionines at the N-terminus. Alternative translation initiation yields two protein forms: the long one is mitochondrial, and the short one may localize in the nucleus or cytosol. This study has generated a mitochondria specific knockout of the dRNaseZ gene. In this in vivo model, cells deprived of dRNaseZ activity display impaired mitochondrial polycistronic transcript processing, increased reactive oxygen species (ROS) and a switch to aerobic glycolysis compensating for cellular ATP. Damaged mitochondria impose a cell cycle delay at the G2 phase disrupting cell proliferation without affecting cell viability. Antioxidants attenuate genotoxic stress and rescue cell proliferation, implying a critical role for ROS. It is suggested that under a low-stress condition, ROS activate tumor suppressor p53, which modulates cell cycle progression and promotes cell survival. Transcriptional profiling of p53 targets confirms upregulation of antioxidant and cycB-Cdk1 inhibitor genes without induction of apoptotic genes. This study implicates Drosophila RNase ZL in a novel retrograde signaling pathway initiated by the damage in mitochondria and manifested in a cell cycle delay before the mitotic entry.

Novak, S. M., Joardar, A., Gregorio, C. C. and Zarnescu, D. C. (2015). Regulation of heart rate in Drosophila via Fragile X mental retardation protein. PLoS One 10: e0142836. PubMed ID: 26571124
RNA binding proteins play a pivotal role in post-transcriptional gene expression regulation, however little is understood about their role in cardiac function. Alterations in the levels of Fragile X Related 1 protein, FXR1, the predominant FraX member expressed in vertebrate striated muscle, have been linked to structural and functional defects in mice and zebrafish models. FraX proteins are established regulators of translation and are known to regulate specific targets in different tissues. To decipher the direct role of FraX proteins in the heart in vivo, Drosophila, which harbors a sole, functionally conserved and ubiquitously expressed FraX protein, dFmr1, was investigated. Using classical loss of function alleles as well as muscle specific RNAi knockdown, dFmr1 was shown to be required for proper heart rate during development. Functional analyses in the context of cardiac-specific dFmr1 knockdown by RNAi demonstrate that dFmr1 is required cell autonomously in cardiac cells for regulating heart rate. Interestingly, these functional defects are not accompanied by any obvious structural abnormalities, suggesting that dFmr1 may regulate a different repertoire of targets in Drosophila than in vertebrates. Taken together, these findings support the hypothesis that dFmr1 protein is essential for proper cardiac function and establish the fly as a new model for studying the role(s) of FraX proteins in the heart.

Thursday, December 10th

Yamanaka, N., Marques, G. and O'Connor, M. B. (2015). Vesicle-mediated steroid hormone secretion in Drosophila melanogaster. Cell 163: 907-919. PubMed ID: 26544939
Steroid hormones are a large family of cholesterol derivatives regulating development and physiology in both the animal and plant kingdoms, but little is known concerning mechanisms of their secretion from steroidogenic tissues. This study presents evidence that in Drosophila, endocrine release of the steroid hormone ecdysone is mediated through a regulated vesicular trafficking mechanism. Inhibition of calcium signaling in the steroidogenic prothoracic gland results in the accumulation of unreleased ecdysone, and the knockdown of calcium-mediated vesicle exocytosis components in the gland caused developmental defects due to deficiency of ecdysone. Accumulation of synaptotagmin-labeled vesicles in the gland is observed when calcium signaling is disrupted, and these vesicles contain an ABC transporter that functions as an ecdysone pump to fill vesicles. It is proposed that trafficking of steroid hormones out of endocrine cells is not always through a simple diffusion mechanism as presently thought, but instead can involve a regulated vesicle-mediated release process.

Winther, A. M., Vorontsova, O., Rees, K. A., Nareoja, T., Sopova, E., Jiao, W. and Shupliakov, O. (2015). An endocytic scaffolding protein together with Synapsin regulates synaptic vesicle clustering in the Drosophila neuromuscular junction. J Neurosci 35: 14756-14770. PubMed ID: 26538647
Many endocytic proteins accumulate in the reserve pool of synaptic vesicles (SVs) in synapses and relocalize to the endocytic periactive zone during neurotransmitter release. Currently little is known about their functions outside the periactive zone. This study shows that in the Drosophila neuromuscular junction (NMJ), the endocytic scaffolding protein Dap160 colocalizes during the SV cycle and forms a functional complex with the SV-associated phosphoprotein Synapsin, previously implicated in SV clustering. This direct interaction is essential for proper localization of synapsin at NMJs. In a dap160 rescue mutant lacking the interaction between Dap160 and synapsin, perturbed reclustering of SVs during synaptic activity is observed. The data indicate that in addition to the function in endocytosis, Dap160 is a component of a network of protein-protein interactions that serves for clustering of SVs in conjunction with synapsin. During the SV cycle, Dap160 interacts with synapsin dispersed from SVs and helps direct synapsin back to vesicles.

Ukken, F. P., Bruckner, J. J., Weir, K. L., Hope, S. J., Sison, S. L., Birschbach, R. M., Hicks, L., Taylor, K. L., Dent, E. W., Gonsalvez, G. B. and O'Connor-Giles, K. M. (2015). BAR-SH3 Sorting nexins are conserved Nervous wreck interactors that organize synapses and promote neurotransmission. J Cell Sci [Epub ahead of print]. PubMed ID: 26567222
Nervous wreck (Nwk) is a conserved F-BAR protein that attenuates synaptic growth and promotes synaptic function in Drosophila. In an effort to understand how Nwk carries out its dual roles, this study isolated interacting proteins through mass spectrometry. A conserved interaction is reported between Nwk proteins and BAR-SH3 Sorting nexins, a family of membrane-binding proteins implicated in diverse intracellular trafficking processes. In mammalian cells, BAR-SH3 Sorting nexins induce plasma membrane tubules that colocalize Nwk2, consistent with a possible functional interaction during early stages of endocytic trafficking. To study the role of BAR-SH3 Sorting nexins in vivo, advantage was taken of the lack of genetic redundancy in Drosophila, and CRISPR-based genome engineering was employed to generate null and endogenously tagged alleles of SH3PX1. SH3PX1 localizes to neuromuscular junctions where it regulates synaptic ultrastructure, but not synapse number. Consistently, neurotransmitter release is significantly diminished in SH3PX1 mutants. Double mutant and tissue-specific rescue experiments indicate that SH3PX1 promotes neurotransmitter release presynaptically, at least in part through functional interactions with Nwk, and may act to distinguish Nwk's roles in regulating synaptic growth and function.

Gireud, M., Sirisaengtaksin, N., Tsunoda, S. and Bean, A. J. (2015). Cell-free reconstitution of multivesicular body (MVB) cargo sorting. Journal-Methods Mol Biol 1270: 115-124. PubMed ID: 25702113
The signaling activity of cell surface localized membrane proteins occurs primarily while these proteins are located on the plasma membrane but is, in some cases, not terminated until the proteins are degraded. Following internalization and movement through the endocytic pathway en route to lysosomes, membrane proteins transit a late endosomal organelle called the multivesicular body (MVB). MVBs are formed by invagination of the limiting membrane of endosomes, resulting in an organelle possessing a limiting membrane and containing internal vesicles. The molecular machinery that regulates the separation of membrane proteins destined for degradation from those resulting in surface expression is not well understood. This study reconstituted an endosomal sorting event under cell-free conditions. Advantage was taken of the itinerary of a prototypical membrane protein, the Epidermal growth factor receptor (EGFR) and a biochemical monitor was designed for cargo movement into internal MVB vesicles that is generally modifiable for other membrane proteins. Since is it not known how internal vesicle formation is related to cargo sorting, morphological examination using transmission electron microscopy (TEM) allows separate monitoring of vesicle formation. This study determined that MVB sorting is dependent on cytosolic components, adenosine triphosphate (ATP), time, temperature, and an intact proton gradient. This assay reconstitutes the maturation of late endosomes and allows the morphological and biochemical examination of vesicle formation and membrane protein sorting.

Wednesday December 9th

Harmansa, S., Hamaratoglu, F., Affolter, M. and Caussinus, E. (2015). Dpp spreading is required for medial but not for lateral wing disc growth. Nature 527: 317-322. PubMed ID: 26550827
Drosophila Decapentaplegic has served as a paradigm to study morphogen-dependent growth control. However, the role of a Dpp gradient in tissue growth remains highly controversial. Two fundamentally different models have been proposed: the 'temporal rule' model suggests that all cells of the wing imaginal disc divide upon a 50% increase in Dpp signalling, whereas the 'growth equalization model' suggests that Dpp is only essential for proliferation control of the central cells. To discriminate between these two models, morphotrap, a membrane-tethered anti-green fluorescent protein (GFP) nanobody was generated and used, that enables immobilization of enhanced (e)GFP::Dpp on the cell surface, thereby abolishing Dpp gradient formation. In the absence of Dpp spreading, wing disc patterning is lost; however, lateral cells still divide at normal rates. These data are consistent with the growth equalization model, but do not fit a global temporal rule model in the wing imaginal disc.

Okamoto, N. and Nishimura, T. (2015). Signaling from glia and cholinergic neurons controls nutrient-dependent production of an insulin-like peptide for Drosophila body growth. Dev Cell 35: 295-310. PubMed ID: 26555050
The insulin-like peptide (ILP) family plays key biological roles in the control of body growth. Although the functions of ILPs are well understood, the mechanisms by which organisms sense their nutrient status and thereby control ILP production remain largely unknown. This study shows that signaling relay and feedback mechanisms control the nutrient-dependent expression of Drosophila ILP5 (Dilp5). The expression of dilp5 in brain insulin-producing cells (IPCs) is negatively regulated by the transcription factor FoxO. Glia-derived Dilp6 remotely regulates the FoxO activity in IPCs, primarily through Jeb secreted by cholinergic neurons. Dilp6 production by surface glia is amplified by cellular response to circulating Dilps derived from IPCs, in concert with amino acid signals. The induction of dilp5 is critical for sustaining body growth under restricted food conditions. These results provide a molecular framework that explains how the production of an endocrine hormone in a specific tissue is coordinated with environmental conditions.

Akiyama, T. and Gibson, M. C. (2015). Decapentaplegic and growth control in the developing Drosophila wing. Nature 527: 375-378. PubMed ID: 26550824
As a central model for morphogen action during animal development, the bone morphogenetic protein 2/4 (BMP2/4)-like ligand Decapentaplegic is proposed to form a long-range signalling gradient that directs both growth and pattern formation during Drosophila wing disc development. While the patterning role of Dpp secreted from a stripe of cells along the anterior-posterior compartmental boundary is well established, the mechanism by which a Dpp gradient directs uniform cell proliferation remains controversial and poorly understood. To determine the precise spatiotemporal requirements for Dpp during wing disc development, this study used CRISPR-Cas9-mediated genome editing to generate a flippase recognition target (FRT)-dependent conditional null allele. By genetically removing Dpp from its endogenous stripe domain, the requirement was confirmed of Dpp for the activation of a downstream phospho-Mothers against dpp gradient and the regulation of the patterning targets spalt, optomotor blind and brinker. Surprisingly, however, third-instar wing blade primordia devoid of compartmental dpp expression maintain relatively normal rates of cell proliferation and exhibit only mild defects in growth. These results indicate that during the latter half of larval development, the Dpp morphogen gradient emanating from the anterior-posterior compartment boundary is not directly required for wing disc growth.

Pahi, Z., Kiss, Z., Komonyi, O., Borsos, B. N., Tora, L., Boros, I. M. and Pankotai, T. (2015). dTAF10- and dTAF10b-containing complexes are required for ecdysone-driven larval-pupal morphogenesis in Drosophila melanogaster. PLoS One 10: e0142226. PubMed ID: 26556600
In eukaryotes the TFIID complex is required for preinitiation complex assembly which positions RNA polymerase II around transcription start sites. Histone acetyltransferase complexes including SAGA and ATAC, modulate transcription at several steps through modification of specific core histone residues. This study investigated the function of Drosophila proteins TAF10 and TAF10b, which are subunits of dTFIID and dSAGA, respectively. The simultaneous deletion of both dTaf10 genes impaired the recruitment of the dTFIID subunit dTAF5 to polytene chromosomes, while binding of other TFIID subunits, RNAPII was not affected. The lack of both dTAF10 proteins resulted in failures in the larval-pupal transition during metamorphosis and in transcriptional reprogramming at this developmental stage. Importantly, the phenotype resulting from dTaf10+dTaf10b mutation could be rescued by ectopically added ecdysone, suggesting that dTAF10- and/or dTAF10b-containing complexes are involved in the expression of ecdysone biosynthetic genes. These data support the idea that the presence of dTAF10 proteins in dTFIID and/or dSAGA is required only at specific developmental steps. It is proposed that distinct forms of dTFIID and/or dSAGA exist during Drosophila metamorphosis, wherein different TAF compositions serve to target RNAPII at different developmental stages and tissues.

Tuesday, December 8th

Bhadra, U., Mondal, T., Bag, I., Mukhopadhyay, D., Das, P., Parida, B. B., Mainkar, P. S., Reddy, C. R. and Bhadra, M. P. (2015). HDAC inhibitor misprocesses bantam oncomiRNA, but stimulates hid induced apoptotic pathway. Sci Rep 5: 14747. PubMed ID: 26442596
Apoptosis or programmed cell death is critical for embryogenesis and tissue homeostasis. Uncontrolled apoptosis leads to different human disorders including immunodeficiency, autoimmune disorder and cancer. Several small molecules that control apoptosis have been identified. This study has shown the functional role of triazole derivative (DCPTN-PT) that acts as a potent HDAC inhibitor (reducing the level of Rpd3/HDAC1 in Drosophila) and leads to the misexpression of proto onco microRNA (miRNA) bantam. To further understanding the mechanism of action of the molecule in the apoptotic pathway, a series of experiments were also performed in Drosophila, a well known model organism in which the nature of human apoptosis is very analogous. DCPTN-PT mis processes bantam microRNA and alters its down regulatory target hid function and cleavage of Caspase-3 which in turn influence components of the mitochondrial apoptotic pathway in Drosophila. However regulatory microRNAs in other pro-apoptotic genes are not altered. Simultaneously, treatment of same molecule also affects the mitochondrial regulatory pathway in human tumour cell lines suggesting its conservative nature between fly and human. It is reasonable to propose that triazole derivative (DCPTN-PT) controls bantam oncomiRNA and increases hid induced apoptosis and is also able to influence mitochondrial apoptotic pathway.

Wu, Y., Lindblad, J. L., Garnett, J., Kamber Kaya, H. E., Xu, D., Zhao, Y., Flores, E. R., Hardy, J. and Bergmann, A. (2015). Genetic characterization of two gain-of-function alleles of the effector caspase DrICE in Drosophila. Cell Death Differ . PubMed ID: 26542461
Caspases are the executioners of apoptosis. Although much is known about their physiological roles and structures, detailed analyses of missense mutations of caspases are lacking. As mutations within caspases are identified in various human diseases, the study of caspase mutants will help to elucidate how caspases interact with other components of the apoptosis pathway and how they may contribute to disease. DrICE is the major effector caspase in Drosophila required for developmental and stress-induced cell death. This study reports the isolation and characterization of six de novo drICE mutants, all of which carry point mutations affecting amino acids conserved among caspases in various species. These six mutants behave as recessive loss-of-function mutants in a homozygous condition. Surprisingly, however, two of the newly isolated drICE alleles are gain-of-function mutants in a heterozygous condition, although they are loss-of-function mutants homozygously. Interestingly, they only behave as gain-of-function mutants in the presence of an apoptotic signal. These two alleles carry missense mutations affecting conserved amino acids in close proximity to the catalytic cysteine residue. This result provides a significant exception to the expectation that mutations of conserved amino acids always abolish the pro-apoptotic activity of caspases.

Jin, A., Neufeld, T. P. and Choe, J. (2015). Kibra and aPKC regulate starvation-induced autophagy in Drosophila.Biochem Biophys Res Commun 468: 1-7. PubMed ID: 26551466
Autophagy is a bulk degradation system that functions in response to cellular stresses such as metabolic stress, endoplasmic reticulum stress, oxidative stress, and developmental processes. During autophagy, cytoplasmic components are captured in double-membrane vesicles called autophagosomes. The autophagosome fuses with the lysosome, producing a vacuole known as an autolysosome. The cellular components are degraded by lysosomal proteases and recycled. Autophagy is important for maintaining cellular homeostasis, and the process is evolutionarily conserved. Kibra is an upstream regulator of the hippo signaling pathway, which controls organ size by affecting cell growth, proliferation, and apoptosis. Kibra is mainly localized in the apical membrane domain of epithelial cells and acts as a scaffold protein. This study found that Kibra is required for autophagy to function properly. The absence of Kibra caused defects in the formation of autophagic vesicles and autophagic degradation. It was also found that the well-known cell polarity protein aPKC interacts with Kibra, and its activity affects autophagy upstream of Kibra. Constitutively active aPKC decreased autophagic vesicle formation and autophagic degradation. The interaction between aPKC and Kibra was confirmed in S2 cells and Drosophila larva. Taken together, these data suggest that Kibra and aPKC are essential for regulating starvation-induced autophagy.

Joffre, C., et al. (2015). The pro-apoptotic STK38 kinase is a new Beclin1 partner positively regulating autophagy. Curr Biol 25: 2479-2492. PubMed ID: 26387716
Autophagy plays key roles in development, oncogenesis, cardiovascular, metabolic, and neurodegenerative diseases. This study describes the STK38 protein kinase (also termed NDR1 and Tricornered in Drosophila) as a conserved regulator of autophagy. STK38 was discovered as a novel binding partner of Beclin1 (Atg6; see Drosophila Atg6), a key regulator of autophagy. STK38 promotes autophagosome formation in human cells and in Drosophila. Upon autophagy induction, STK38-depleted cells display impaired LC3B-II conversion; reduced ATG14L, ATG12, and WIPI-1 puncta formation; and significantly decreased Vps34 (Pi3K59F in Drosophila) activity, as judged by PI3P formation. Furthermore, it was observed that STK38 supports the interaction of the exocyst component Exo84 with Beclin1 and RalB, which is required to initiate autophagosome formation. Upon studying the activation of STK38 during autophagy induction, STK38 was found to be stimulated in a MOB1- and exocyst-dependent manner. In contrast, RalB depletion triggers hyperactivation of STK38, resulting in STK38-dependent apoptosis under prolonged autophagy conditions. Together, these data establish STK38 as a conserved regulator of autophagy in human cells and flies. Evidence is also provided demonstrating that STK38 and RalB assist the coordination between autophagic and apoptotic events upon autophagy induction, hence further proposing a role for STK38 in determining cellular fate in response to autophagic conditions.

Monday, December 7th

Russo, J., Harrington, A. W. and Steiniger, M. (2015). Antisense transcription of retrotransposons in Drosophila: The origin of endogenous small interfering RNA precursors. Genetics [Epub ahead of print]. PubMed ID: 26534950
To repress transposons and combat genomic instability, eukaryotes have evolved several small RNA mediated defense mechanisms. Specifically, in Drosophila somatic cells, endogenous small interfering (esi)RNAs suppress retrotransposon mobility. EsiRNAs are produced by Dicer-2 processing of double-stranded RNA precursors, yet the origins of these precursors are unknown. This study shows that most transposon families are transcribed in both the sense and antisense direction. LTR retrotransposons are generated from intra element transcription start sites with canonical RNA polymerase II promoters. Retrotransposon antisense transcripts were shown to be less polyadenylated than sense transcripts, which may promote nuclear retention of antisense transcripts and the double-stranded RNAs they form. Dicer-2 RNAi-depletion causes a decrease in the number of esiRNAs mapping to retrotransposons. These data support a model in which double-stranded RNA precursors are derived from convergent transcription and processed by Dicer-2 into esiRNAs that silence both sense and antisense retrotransposon transcripts. Reduction of sense retrotransposon transcripts potentially lowers element specific protein levels to prevent transposition. This mechanism preserves genomic integrity and is especially important for Drosophila fitness because mobile genetic elements are highly active.

Loedige, I., Jakob, L., Treiber, T., Ray, D., Stotz, M., Treiber, N., Hennig, J., Cook, K. B., Morris, Q., Hughes, T. R., Engelmann, J. C., Krahn, M. P. and Meister, G. (2015). The crystal structure of the NHL domain in complex with RNA reveals the molecular basis of Drosophila Brain-tumor-mediated gene regulation. Cell Rep 13: 1206-1220. PubMed ID: 26527002
TRIM-NHL proteins are conserved among metazoans and control cell fate decisions in various stem cell linages. The Drosophila TRIM-NHL protein Brain tumor (Brat) directs differentiation of neuronal stem cells by suppressing self-renewal factors. Brat is an RNA-binding protein and functions as a translational repressor. However, it is unknown which RNAs Brat regulates and how RNA-binding specificity is achieved. Using RNA immunoprecipitation and RNAcompete, this study identified Brat-bound mRNAs in Drosophila embryos and defined consensus binding motifs for Brat as well as a number of additional TRIM-NHL proteins, indicating that TRIM-NHL proteins are conserved, sequence-specific RNA-binding proteins. Brat-mediated repression and direct RNA-binding depend on the identified motif and show that binding of the localization factor Miranda to the Brat-NHL domain inhibits Brat activity. Finally, to unravel the sequence specificity of the NHL domain, the Brat-NHL domain in complex was crystallize with RNA, and a high-resolution protein-RNA structure of this fold is presented.

Prabu, J. R., Muller, M., Thomae, A. W., Schussler, S., Bonneau, F., Becker, P. B. and Conti, E. (2015). Structure of the RNA helicase MLE reveals the molecular mechanisms for uridine specificity and RNA-ATP coupling. Mol Cell 60: 487-499. PubMed ID: 26545078
The MLE helicase remodels the roX lncRNAs, enabling the lncRNA-mediated assembly of the Drosophila dosage compensation complex. This study identified a stable MLE core comprising the DExH helicase module and two auxiliary domains: a dsRBD and an OB-like fold. MLEcore is an unusual DExH helicase that can unwind blunt-ended RNA duplexes and has specificity for uridine nucleotides.The 2.1 A resolution structure of MLEcore was determined bound to a U10 RNA and ADP-AlF4. The OB-like and dsRBD folds bind the DExH module and contribute to form the entrance of the helicase channel. Four uridine nucleotides engage in base-specific interactions, rationalizing the conservation of uridine-rich sequences in critical roX substrates. roX2 binding is orchestrated by MLE's auxiliary domains, which is prerequisite for MLE localization to the male X chromosome. The structure visualizes a transition-state mimic of the reaction and suggests how eukaryotic DEAH/RHA helicases couple ATP hydrolysis to RNA translocation.

Yue, Y., Yang, Y., Dai, L., Cao, G., Chen, R., Hong, W., Liu, B., Shi, Y., Meng, Y., Shi, F., Xiao, M. and Jin, Y. (2015). Long-range RNA pairings contribute to mutually exclusive splicing. RNA [Epub ahead of print]. PubMed ID: 26554032
Mutually exclusive splicing is an important means of increasing the protein repertoire, by which the Down's syndrome cell adhesion molecule (Dscam) gene potentially generates 38,016 different isoforms in Drosophila melanogaster. However, the regulatory mechanisms remain obscure due to the complexity of the Dscam exon cluster. This study reveal a molecular model for the regulation of the mutually exclusive splicing of the serpent pre-mRNA based on competition between upstream and downstream RNA pairings. Such dual RNA pairings confer fine tuning of the inclusion of alternative exons. Moreover, the splicing outcome of alternative exons is mediated in relative pairing strength-correlated mode. Combined comparative genomics analysis and experimental evidence revealed similar bidirectional structural architectures in exon clusters 4 and 9 of the Dscam gene. These findings provide a novel mechanistic framework for the regulation of mutually exclusive splicing and may offer potentially applicable insights into long-range RNA-RNA interactions in gene regulatory networks.

Sunday, December 6th

Schoborg, T., Zajac, A.L., Fagerstrom, C.J., Guillen, R.X. and Rusan, N.M. (2015). An Asp-CaM complex is required for centrosome-pole cohesion and centrosome inheritance in neural stem cells. J Cell Biol [Epub ahead of print]. PubMed ID: 26620907
The interaction between centrosomes and mitotic spindle poles is important for efficient spindle formation, orientation, and cell polarity. However, our understanding of the dynamics of this relationship and implications for tissue homeostasis remains poorly understood. This study reports that Drosophila melanogaster calmodulin (CaM) regulates the ability of the microcephaly-associated protein, abnormal spindle (Asp), to cross-link spindle microtubules. Both proteins colocalize on spindles and move toward spindle poles, suggesting that they form a complex. Binding and structure-function analysis support this hypothesis. Disruption of the Asp-CaM interaction alone leads to unfocused spindle poles and centrosome detachment. This behavior leads to randomly inherited centrosomes after neuroblast division. It was further shown that spindle polarity is maintained in neuroblasts despite centrosome detachment, with the poles remaining stably associated with the cell cortex. Finally, CaM is required for Asp's spindle function; however, it is completely dispensable for Asp's role in microcephaly suppression.

Hall, E. T. and Verheyen, E. M. (2015). Ras-activated Dsor1 promotes Wnt signaling in Drosophila development. J Cell Sci. [Epub ahead of print]. PubMed ID: 26542023
Wnt/Wingless (Wg) and Ras/MAPK signaling both play fundamental roles in growth, cell-fate determination, and when dysregulated, can lead to tumorigenesis. Several conflicting modes of interaction between Ras/MAPK and Wnt signaling have been identified in specific cellular contexts, causing synergistic or antagonistic effects on target genes. This study found novel evidence that the dual specificity kinase Downstream of Raf1 (Dsor1), also known as MEK. is required for Wnt signaling. Knockdown of Dsor1 results in loss of Wingless target gene expression, as well as reductions in stabilized Armadillo (Arm; Drosophila beta-catenin). A close physical interaction was found between Dsor1 and Arm; catalytically inactive Dsor1 causes a reduction inactive Arm. These results suggest that Dsor1 normally counteracts the Axin-mediated destruction of Arm. Ras-Dsor1 activity is independent of upstream activation by EGFR, rather it appears to be activated by the insulin-like growth factor receptor to promote Wg signaling. Together our results suggest novel crosstalk between Insulin and Wg signaling via Dsor1.

Zhou, Y., Chang, R., Ji, W., Wang, N., Qi, M., Xu, Y., Guo, J. and Zhan, L. (2015). Loss of Scribble promotes Snail translation through translocation of HuR and enhances cancer drug resistance. J Biol Chem [Epub ahead of print]. PubMed ID: 26527679
Drug resistance of cancer cells to various therapeutic agents and molecular targets is a major problem facing current cancer research. The tumor suppressor gene Scribble encodes a polarity protein that is conserved between Drosophila and mammals; loss of the locus disrupts cell polarity, inhibits apoptosis, and mediates cancer process. However, the role of Scribble in drug resistance remains unknown. This study shows that knockdown of Scribble enhances drug resistance by permitting accumulation of Snail, which functions as a transcription factor during the epithelial-mesenchymal transition. Then, loss of Scribble activates the mRNA binding protein HuR (ELAV in Drosophila) by facilitating translocation of HuR from the nucleus to the cytoplasm. Furthermore, HuR can recognize AU-rich elements (AREs) of the Snail-encoding mRNA, thereby regulating Snail translation. Moreover, Loss of Scribble induced HuR translocation mediates the accumulation of Snail via activation of the p38 MAPK pathway. Thus, this work clarifies the role of polarity protein Scribble, which is directly implicated in the regulation of developmental transcription factor Snail, and suggesting a mechanism for Scribble mediating cancer drug resistance.

Lin, Y. H., Currinn, H., Pocha, S. M., Rothnie, A., Wassmer, T. and Knust, E. (2015). AP-2 complex-mediated endocytosis of Drosophila Crumbs regulates polarity via antagonizing Stardust. J Cell Sci [Epub ahead of print]. PubMed ID: 26527400
Maintenance of epithelial polarity depends on the correct localization and levels of polarity determinants. The evolutionarily conserved transmembrane protein Crumbs is crucial for the size and identity of the apical membrane, yet little is known about the molecular mechanisms controlling the amount of Crumbs at the surface. This study shows that Crumbs levels on the apical membrane depend on a well-balanced state of endocytosis and stabilization. The Adaptor Protein 2 (AP-2) complex binds to a motif in the cytoplasmic tail of Crumbs that overlaps with the binding site of Stardust, a protein known to stabilize Crumbs on the surface. Preventing endocytosis by mutations in AP-2 causes expansion of the Crumbs-positive plasma membrane and polarity defects, which can be partially rescued by removing one copy of crumbs. Strikingly, knocking-down both AP-2 and Stardust retains Crumbs on the membrane. This study provides evidence for a molecular mechanism, based on stabilization and endocytosis, to adjust surface levels of Crumbs, which are essential for maintaining epithelial polarity.

Saturday, December 5th

Talsma, A. D., Chaves, J. F., LaMonaca, A., Wieczorek, E. D. and Palladino, M. J. (2014).. Genome-wide screen for modifiers of Na+/K+ ATPase alleles identifies critical genetic loci. Mol Brain 7: 89. PubMed ID: 25476251
Mutations affecting the Na+/ K+ ATPase (a.k.a. the sodium-potassium pump) genes cause conditional locomotor phenotypes in flies and three distinct complex neurological diseases in humans. More than 50 mutations have been identified affecting the human ATP1A2 and ATP1A3 genes that are known to cause rapid-onset Dystonia Parkinsonism, familial hemiplegic migraine, alternating hemiplegia of childhood, and variants of familial hemiplegic migraine with neurological complications including seizures and various mood disorders. In flies, mutations affecting the Na pump α subunit gene have dramatic phenotypes including altered longevity, neural dysfunction, neurodegeneration, myodegeneration, and striking locomotor impairment. Locomotor defects can manifest as conditional bang-sensitive (BS) or temperature-sensitive (TS) paralysis: phenotypes well-suited for genetic screening. This study performed a genome-wide deficiency screen using three distinct missense alleles of ATPα and conditional locomotor function assays to identify novel modifier loci. A secondary screen confirmed allele-specificity of the interactions and many of the interactions were mapped to single genes and subsequently validated. Sixty-four modifier loci were identified, and classical mutations and RNAi were used to confirm 50 single gene interactions. The genes identified include those with known function, several with unknown function or that were otherwise uncharacterized, and many loci with no described association with locomotor or Na+/K+ ATPase function. In conclusion, this study has identified many critical regions and narrowed several of these to single genes. These data demonstrate there are many loci capable of modifying ATPα dysfunction, which may provide the basis for modifying migraine, locomotor and seizure dysfunction in animals.

Wu, Y., Gause, M., Xu, D., Misulovin, Z., Schaaf, C. A., Mosarla, R. C., Mannino, E., Shannon, M., Jones, E., Shi, M., Chen, W. F., Katz, O. L., Sehgal, A., Jongens, T. A., Krantz, I. D. and Dorsett, D. (2015). Drosophila Nipped-B mutants model Cornelia de Lange Syndrome in growth and behavior. PLoS Genet 11: e1005655. PubMed ID: 26544867
Individuals with Cornelia de Lange Syndrome (CdLS) display diverse developmental deficits, including slow growth, multiple limb and organ abnormalities, and intellectual disabilities. Severely-affected individuals most often have dominant loss-of-function mutations in the Nipped-B-Like (NIPBL) gene, and milder cases often have missense or in-frame deletion mutations in genes encoding subunits of the cohesin complex. Cohesin mediates sister chromatid cohesion to facilitate accurate chromosome segregation, and NIPBL is required for cohesin to bind to chromosomes. Individuals with CdLS, however, do not display overt cohesion or segregation defects. Rather, studies in human cells and model organisms indicate that modest decreases in NIPBL and cohesin activity alter the transcription of many genes that regulate growth and development. Sister chromatid cohesion factors, including the Nipped-B ortholog of human NIPBL, are also critical for gene expression and development in Drosophila melanogaster. This study describes how a modest reduction in Nipped-B activity alters growth and neurological function in Drosophila. These studies reveal that Nipped-B heterozygous mutant Drosophila show reduced growth, learning, and memory, and altered circadian rhythms. Importantly, the growth deficits are not caused by changes in systemic growth controls, but reductions in cell number and size attributable in part to reduced expression of myc (diminutive) and other growth control genes. The learning, memory and circadian deficits are accompanied by morphological abnormalities in brain structure. These studies confirm that Drosophila Nipped-B mutants provide a useful model for understanding CdLS, and provide new insights into the origins of birth defects.

Ruan, K., Zhu, Y., Li, C., Brazill, J.M. and Zhai, R.G. (2015). Alternative splicing of Drosophila Nmnat functions as a switch to enhance neuroprotection under stress. Nat Commun 6: 10057. PubMed ID: 26616331
Nicotinamide mononucleotide adenylyltransferase (NMNAT) is a conserved enzyme in the NAD synthetic pathway. It has also been identified as an effective and versatile neuroprotective factor. However, it remains unclear how healthy neurons regulate the dual functions of NMNAT and achieve self-protection under stress. This study shows that Drosophila Nmnat (DmNmnat) is alternatively spliced into two mRNA variants, RA and RB, which translate to protein isoforms with divergent neuroprotective capacities against spinocerebellar ataxia 1-induced neurodegeneration. Isoform PA/PC translated from RA is nuclear-localized with minimal neuroprotective ability, and isoform PB/PD translated from RB is cytoplasmic and has robust neuroprotective capacity. Under stress, RB is preferably spliced in neurons to produce the neuroprotective PB/PD isoforms. These results indicate that alternative splicing functions as a switch that regulates the expression of functionally distinct DmNmnat variants. Neurons respond to stress by driving the splicing switch to produce the neuroprotective variant and therefore achieve self-protection. 

Wang, X., Perumalsamy, H., Kwon, H. W., Na, Y. E. and Ahn, Y. J. (2015). Effects and possible mechanisms of action of acacetin on the behavior and eye morphology of Drosophila models of Alzheimer's disease. Sci Rep 5: 16127. PubMed ID: 26530776
The human beta-amyloid (Aβ; see Drosophila Appl) cleaving enzyme (BACE-1) is a target for Alzheimer's disease (AD) treatments. This study was conducted to determine if acacetin extracted from the whole Agastache rugosa plant had anti-BACE-1 and behavioral activities in Drosophila AD models and to determine acacetin's mechanism of action. Acacetin rescued APP/BACE1-expressing flies and kept them from developing both eye morphology and behavioral defects. The rtPCR analysis revealed that acacetin reduced both the human APP and BACE-1 mRNA levels in the transgenic flies, suggesting that it plays an important role in the transcriptional regulation of human BACE-1 and APP. Western blot analysis revealed that acacetin reduced Aβ production by interfering with BACE-1 activity and APP synthesis, resulting in a decrease in the levels of the APP carboxy-terminal fragments and the APP intracellular domain. Therefore, the protective effect of acacetin on Aβ production is mediated by transcriptional regulation of BACE-1 and APP, resulting in decreased APP protein expression and BACE-1 activity. Acacetin also inhibited APP synthesis, resulting in a decrease in the number of amyloid plaques.

Chakraborty, M., Selma-Soriano, E., Magny, E., Couso, J. P., Perez-Alonso, M., Charlet-Berguerand, N., Artero, R. and Llamusi, B. (2015). Pentamidine rescues contractility and rhythmicity in a Drosophila model of myotonic dystrophy heart dysfunction. Dis Model Mech. PubMed ID: 26515653
Up to 80% of myotonic dystrophy type 1 (DM1) patients will develop cardiac abnormalities at some point during the progression of their disease. Despite its importance, very few animal model studies have focused on the heart dysfunction in DM1. This study describes the characterization of the heart phenotype in a Drosophila model expressing pure expanded CUG repeats under the control of the cardiomyocyte-specific driver GMH5-Gal4. Morphologically, expression of 250 CUG repeats caused abnormalities in the parallel alignment of the spiral myofibrils in dissected fly hearts revealed by phalloidin staining. Moreover, combined immunofluorescence and in situ hybridization of splice factor Muscleblind and CUG repeats, respectively, confirmed detectable ribonuclear foci and Muscleblind sequestration, characteristic features of DM1, exclusively in flies expressing the expanded CTG repeats. Similarly to what has been reported in human DM1 patients, heart-specific expression of toxic RNA resulted in reduced survival, increased arrhythmia, altered diastolic and systolic function and reduced heart tube diameters and contractility in the model flies. As a proof of concept that the fly heart model can be used for in vivo testing of promising therapeutic compounds, flies were fed with pentamidine, a compound previously described to improve DM1 phenotypes. Pentamidine not only released Muscleblind and reduced ribonuclear formation in the Drosophila heart but rescued heart arrhythmicity and contractility, and improved fly survival in animals expressing 250 CUG repeats.

Landry, G. M., Hirata, T., Anderson, J. B., Cabrero, P., Gallo, C. J., Dow, J. A. and Romero, M. F. (2015). Sulfate and thiosulfate inhibit oxalate transport via a dPrestin(mSlc26a6)-dependent mechanism in an insect model of calcium oxalate nephrolithiasis. Am J Physiol Renal Physiol: ajprenal 00406 02015. PubMed ID: 26538444
Nephrolithiasis is one of the most common urinary tract disorders with the majority of kidney stones composed of calcium oxalate (CaOx). Given its prevalence (US occurrence 10%), it is still poorly understood, lacking progress in identifying new therapies because of its complex etiology. Drosophila is a recently developed model of CaOx nephrolithiasis. Effects of sulfate and thiosulfate on crystal formation were investigated using the Drosophila model, as well as electrophysiological effects on both Drosophila (Slc26a5/6; dprestin) and mouse (mSlc26a6) oxalate transporters utilizing the Xenopus oocyte heterologous expression system. Results indicate that both transport thiosulfate with a much higher affinity than sulfate. Additionally, both compounds were effective at decreasing CaOx crystallization when added to the diet. However, these results were not observed when compounds were applied to MTs ex vivo. Neither compound affected CaOx crystallization in dPrestin knock down animals indicating a role for principal cell-specific dPrestin in luminal oxalate transport. Furthermore,thiosulfate has a higher affinity for dPrestin and mSlc26a6 compared to oxalate These data indicate that thiosulfate's ability to act as a competitive inhibitor of oxalate via dPrestin, can explain the decrease in CaOx crystallization seen in the presence of thiosulfate, but not sulfate. Overall, these findings predict that thiosulfate or oxalate-mimics may be effective as therapeutic competitive inhibitors of CaOx crystallization.

Friday, December 4th

Ulianov, S. V., et al. (2015). Active chromatin and transcription play a key role in chromosome partitioning into topologically associating domains. Genome Res [Epub ahead of print]. PubMed ID: 26518482
Recent advances enabled by the Hi-C technique have unraveled many principles of chromosomal folding that were subsequently linked to disease and gene regulation. In particular, Hi-C revealed that chromosomes of animals are organized into topologically associating domains (TADs), evolutionary conserved compact chromatin domains that influence gene expression. Mechanisms that underlie partitioning of the genome into TADs remain poorly understood. To explore principles of TAD folding in Drosophila melanogaster, Hi-C and poly(A)+ RNA-seq were performed in four cell lines of various origins (S2, Kc167, DmBG3-c2, and OSC). Contrary to previous studies, regions between TADs (i.e., the inter-TADs and TAD boundaries) in Drosophila were found to be only weakly enriched with the insulator protein dCTCF, while another insulator protein Su(Hw) was found to be preferentially present within TADs. However, Drosophila inter-TADs harbor active chromatin and constitutively transcribed (housekeeping) genes. Accordingly, binding of insulator proteins dCTCF and Su(Hw) was found to predict TAD boundaries much worse than active chromatin marks do. Interestingly, inter-TADs correspond to decompacted inter-bands of polytene chromosomes, whereas TADs mostly correspond to densely packed bands. Collectively, these results suggest that TADs are condensed chromatin domains depleted in active chromatin marks, separated by regions of active chromatin. The mechanism of TAD self-assembly is proposed based on the ability of nucleosomes from inactive chromatin to aggregate, and on the lack of this ability in acetylated nucleosomal arrays. Finally, this hypothesis was tested by polymer simulations and it was found that TAD partitioning may be explained by different modes of inter-nucleosomal interactions for active and inactive chromatin.

Zielke, T., Glotov, A. and Saumweber, H. (2015). High-resolution in situ hybridization analysis on the chromosomal interval 61C7-61C8 of Drosophila melanogaster reveals interbands as open chromatin domains. Chromosoma [Epub ahead of print]. PubMed ID: 26520107
Eukaryotic chromatin is organized in contiguous domains that differ in protein binding, histone modifications, transcriptional activity, and in their degree of compaction. Genome-wide comparisons suggest that, overall, the chromatin organization is similar in different cells within an organism. This study compared the structure and activity of the 61C7-61C8 interval in polytene and diploid cells of Drosophila. By in situ hybridization on polytene chromosomes combined with high-resolution microscopy, the boundaries were mapped of the 61C7-8 interband and of the 61C7 and C8 band regions, respectively. The results demonstrate that the 61C7-8 interband is significantly larger than estimated previously. This interband extends over 20 kbp and is in the range of the flanking band domains. It contains several active genes and therefore can be considered as an open chromatin domain. Comparing the 61C7-8 structure of Drosophila S2 cells and polytene salivary gland cells by ChIP for chromatin protein binding and histone modifications, a highly consistent domain structure was observed for the proximal 13 kbp of the domain in both cell types. However, the distal 7 kbp of the open domain differs in protein binding and histone modification between both tissues. The domain contains four protein-coding genes in the proximal part and two noncoding transcripts in the distal part. The differential transcriptional activity of one of the noncoding transcripts correlates with the observed differences in the chromatin structure between both tissues.

Eagen, K. P., Hartl, T. A. and Kornberg, R. D. (2015). Stable Chromosome Condensation Revealed by Chromosome Conformation Capture. Cell 163: 934-946. PubMed ID: 26544940
Chemical cross-linking and DNA sequencing have revealed regions of intra-chromosomal interaction, referred to as topologically associating domains (TADs), interspersed with regions of little or no interaction, in interphase nuclei. TADs and the regions between them were found to correspond with the bands and interbands of polytene chromosomes of Drosophila. Further, the conservation of TADs between polytene and diploid cells of Drosophila was established. From direct measurements on light micrographs of polytene chromosomes, the states of chromatin folding in the diploid cell nucleus was deduced. Two states of folding, fully extended fibers containing regulatory regions and promoters, and fibers condensed up to 10-fold containing coding regions of active genes, constitute the euchromatin of the nuclear interior. Chromatin fibers condensed up to 30-fold, containing coding regions of inactive genes, represent the heterochromatin of the nuclear periphery. A convergence of molecular analysis with direct observation thus reveals the architecture of interphase chromosomes.

Panikar, C. S., Rajpathak, S. N., Abhyankar, V., Deshmukh, S. and Deobagkar, D. D. (2015). Presence of DNA methyltransferase activity and CpC methylation in Drosophila melanogaster. Mol Biol Rep 42: 1615-1621. PubMed ID: 26547851
Flies lack DNMT1/DNMT3 based methylation machinery. Despite recent reports confirming the presence of low DNA methylation in Drosophila; little is known about the methyltransferase. This study investigated the possible functioning of DNA methyltransferase in Drosophila. The 14 K oligo microarray slide was incubated with native cell extract from adult Drosophila to check the presence of the methyltransferase activity. The methylated oligo sequences were then identified by the binding of anti 5-methylcytosine monoclonal antibody. Methylation sensitive restriction enzyme mediated PCR was used to assess the methylation at a few selected loci identified on the array. A few of the total oligos were seen to be methylated under the assay conditions. Evidence is provided for the presence of de novo methyltransferase activity and identification of its sequence specificity. Presence of CpC methylation was detected in the selected genomic regions. This study provides an innovative approach to investigate methylation specificity of a native methyltransferase.

Thursday, December 3rd

Jiang, T., McKinley, R. F., McGill, M. A., Angers, S. and Harris, T. J. (2015). A Par-1-Par-3-centrosome cell polarity pathway and its tuning for isotropic cell adhesion. Curr Biol 25: 2701-2708. PubMed ID: 26455305
To form regulated barriers between body compartments, epithelial cells polarize into apical and basolateral domains and assemble adherens junctions (AJs). Despite close links with polarity networks that generate single polarized domains, AJs distribute isotropically around the cell circumference for adhesion with all neighboring cells. How AJs avoid the influence of polarity networks to maintain their isotropy has been unclear. In established epithelia, trans cadherin interactions could maintain AJ isotropy, but AJs are dynamic during epithelial development and remodeling, and thus specific mechanisms may control their isotropy. In Drosophila, aPKC prevents hyper-polarization of junctions as epithelia develop from cellularization to gastrulation. This study shows that aPKC does so by inhibiting a positive feedback loop between Bazooka (Baz)/Par-3, a junctional organizer, and centrosomes. Without aPKC, Baz and centrosomes lose their isotropic distributions and recruit each other to single plasma membrane (PM) domains. Surprisingly, loss- and gain-of-function analyses show that the Baz-centrosome positive feedback loop is driven by Par-1, a kinase known to phosphorylate Baz and inhibit its basolateral localization. This study found that Par-1 promotes the positive feedback loop through both centrosome microtubule effects and Baz phosphorylation. Normally, aPKC attenuates the circuit by expelling Par-1 from the apical domain at gastrulation. The combination of local activation and global inhibition is a common polarization strategy. Par-1 seems to couple both effects for a potent Baz polarization mechanism that is regulated for the isotropy of Baz and AJs around the cell circumference.

Tiwari, P., Kumar, A., Das, R. N., Malhotra, V. and VijayRaghavan, K. (2015). A tendon cell specific RNAi screen reveals novel candidates essential for muscle tendon interaction. PLoS One 10: e0140976. PubMed ID: 26488612
Tendons are fibrous connective tissue which connect muscles to the skeletal elements thus acting as passive transmitters of force during locomotion and provide appropriate body posture. Tendon-derived cues, albeit poorly understood, are necessary for proper muscle guidance and attachment during development. This study used dorsal longitudinal muscles of Drosophila and their tendon attachment sites to unravel the molecular nature of interactions between muscles and tendons. A genetic screen using RNAi-mediated knockdown in tendon cells was performed to find out molecular players involved in the formation and maintenance of myotendinous junction; 21 candidates were found out of 2507 RNAi lines screened. Of these, 19 were novel molecules in context of myotendinous system. Integrin-βPS and Talin, picked as candidates in this screen, are known to play important role in the cell-cell interaction and myotendinous junction formation validating the screen. Candidates were found with enzymatic function, transcription activity, cell adhesion, protein folding and intracellular transport function. Tango1, an ER exit protein involved in collagen secretion was identified as a candidate molecule involved in the formation of myotendinous junction. Tango1 knockdown was found to affect development of muscle attachment sites and formation of myotendinous junction. Tango1 was also found to be involved in secretion of Viking (Collagen type IV) and BM-40 from hemocytes and fat cells.

Hosono, C., Matsuda, R., Adryan, B. and Samakovlis, C. (2015). Transient junction anisotropies orient annular cell polarization in the Drosophila airway tubes. Nat Cell Biol 17: 1569-1576. PubMed ID: 26551273
Tubular organs exhibit a striking orientation of landmarks according to the physical anisotropy of the 3D shape, in addition to planar cell polarization. However, the influence of 3D tissue topography on the constituting cells remains underexplored. This study identified a regulatory network polarizing cellular biochemistry according to the physical anisotropy of the 3D tube geometry (tube cell polarization) by a genome-wide, tissue-specific RNAi screen. During Drosophila airway remodelling, each apical cellular junction is equipotent to establish perpendicular actomyosin cables, irrespective of the longitudinal or transverse tube axis. A dynamic transverse enrichment of atypical protein kinase C (aPKC) shifts the balance and transiently targets activated small GTPase RhoA, myosin phosphorylation and Rab11 vesicle trafficking to longitudinal junctions. It is proposed that the PAR complex translates tube physical anisotropy into longitudinal junctional anisotropy, where cell-cell communication aligns the contractile cytoskeleton of neighbouring cells.

Flores-Benitez, D. and Knust, E. (2015). Crumbs is an essential regulator of cytoskeletal dynamics and cell-cell adhesion during dorsal closure in Drosophila. Elife 4 [Epub ahead of print]. PubMed ID: 26544546
The evolutionarily conserved Crumbs protein is required for epithelial polarity and morphogenesis. This study identified a novel role of Crumbs as a negative regulator of actomyosin dynamics during dorsal closure in the Drosophila embryo. Embryos carrying a mutation in the FERM (protein 4.1/ezrin/radixin/moesin) domain-binding motif of Crumbs die due to an overactive actomyosin network associated with disrupted adherens junctions. This phenotype is restricted to the amnioserosa and does not affect other embryonic epithelia. This function of Crumbs requires DMoesin, the Rho1-GTPase, class-I p21-activated kinases and the Arp2/3 complex. Data presented here point to a critical role of Crumbs in regulating actomyosin dynamics, cell junctions and morphogenesis.

Wednesday, December 2nd

Nie, Y., Li, Q., Amcheslavsky, A., Duhart, J. C., Veraksa, A., Stocker, H., Raftery, L. A. and Ip, Y. T. (2015). Bunched and Madm function downstream of Tuberous sclerosis complex to regulate the growth of intestinal stem cells in Drosophila. Stem Cell Rev. PubMed ID: 26323255
The Drosophila adult midgut contains intestinal stem cells that support homeostasis and repair. This study shows that the leucine zipper protein Bunched and the adaptor protein Madm are novel regulators of intestinal stem cells. MARCM mutant clonal analysis and cell type specific RNAi revealed that Bunched and Madm were required within intestinal stem cells for proliferation. Transgenic expression of a tagged Bunched showed a cytoplasmic localization in midgut precursors, and the addition of a nuclear localization signal to Bunched reduced its function to cooperate with Madm to increase intestinal stem cell proliferation. Furthermore, the elevated cell growth and 4EBP phosphorylation phenotypes induced by loss of Tuberous Sclerosis Complex or overexpression of Rheb were suppressed by the loss of Bunched or Madm. Therefore, while the mammalian homolog of Bunched, TSC-22, is able to regulate transcription and suppress cancer cell proliferation, these data suggest the model that Bunched and Madm functionally interact with the TOR pathway in the cytoplasm to regulate the growth and subsequent division of intestinal stem cells.

Bailey, A. P., Koster, G., Guillermier, C., Hirst, E. M., MacRae, J. I., Lechene, C. P., Postle, A. D. and Gould, A. P. (2015). Antioxidant Role for lipid droplets in a stem cell niche of Drosophila. Cell 163: 340-353. PubMed ID: 26451484
Stem cells reside in specialized microenvironments known as niches. During Drosophila development, glial cells provide a niche that sustains the proliferation of neural stem cells (neuroblasts) during starvation. This study finds that the glial cell niche also preserves neuroblast proliferation under conditions of hypoxia and oxidative stress. Lipid droplets that form in niche glia during oxidative stress limit the levels of reactive oxygen species (ROS) and inhibit the oxidation of polyunsaturated fatty acids (PUFAs). These droplets protect glia and also neuroblasts from peroxidation chain reactions that can damage many types of macromolecules. The underlying antioxidant mechanism involves diverting PUFAs, including diet-derived linoleic acid, away from membranes to the core of lipid droplets, where they are less vulnerable to peroxidation. This study reveals an antioxidant role for lipid droplets that could be relevant in many different biological contexts.

Liu, Z., Zhong, G., Chai, P. C., Luo, L., Liu, S., Yang, Y., Baeg, G. H. and Cai, Y. (2015). Coordinated niche-associated signals promote germline homeostasis in the Drosophila ovary. J Cell Biol 211: 469-484. PubMed ID: 26504174
Stem cell niches provide localized signaling molecules to promote stem cell fate and to suppress differentiation. The Drosophila melanogaster ovarian niche is established by several types of stromal cells, including terminal filament cells, cap cells, and escort cells (ECs). This study shows that, in addition to its well-known function as a niche factor expressed in cap cells, the Drosophila transforming growth factor β molecule Decapentaplegic (Dpp) is expressed at a low level in ECs to maintain a pool of partially differentiated germline cells that may dedifferentiate to replenish germline stem cells upon their depletion under normal and stress conditions. This study further reveals that the Dpp level in ECs is modulated by Hedgehog (Hh) ligands, which originate from both cap cells and ECs. Hh signaling exerts its function by suppressing Janus kinase/signal transducer activity, which promotes Dpp expression in ECs. Collectively, these data suggest a complex interplay of niche-associated signals that controls the development of a stem cell lineage.

Fu, Z., Geng, C., Wang, H., Yang, Z., Weng, C., Li, H., Deng, L., Liu, L., Liu, N., Ni, J. and Xie, T. (2015). Twin promotes the maintenance and differentiation of germline stem cell lineage through modulation of multiple pathways. Cell Rep 13: 1366-1379. PubMed ID: 26549449
The central question in stem cell regulation is how the balance between self-renewal and differentiation is controlled at the molecular level. This study uses germline stem cells (GSCs) in the Drosophila ovary to demonstrate that the Drosophila CCR4 homolog Twin is required intrinsically to promote both GSC self-renewal and progeny differentiation. Twin/CCR4 is one of the two catalytic subunits in the highly conserved CCR4-NOT mRNA deadenylase complex. Twin works within the CCR4-NOT complex to intrinsically maintain GSC self-renewal, at least partly by sustaining E-cadherin-mediated GSC-niche interaction and preventing transposable element-induced DNA damage. It promotes GSC progeny differentiation by forming protein complexes with differentiation factors Bam and Bgcn independently of other CCR4-NOT components. Interestingly, Bam can competitively inhibit the association of Twin with Pop2 in the CCR4-NOT complex. Therefore, this study demonstrates that Twin has important intrinsic roles in promoting GSC self-renewal and progeny differentiation by functioning in different protein complexes.

Tuesday, December 1st

Seidner, G., Robinson, J. E., Wu, M., Worden, K., Masek, P., Roberts, S. W., Keene, A. C. and Joiner, W. J. (2015). Identification of neurons with a privileged role in sleep homeostasis in Drosophila melanogaster. Curr Biol 25: 2928-2938. PubMed ID: 26526372
Sleep is thought to be controlled by two main processes: a circadian clock that primarily regulates sleep timing and a homeostatic mechanism that detects and responds to sleep need. Whereas abundant experimental evidence suggests that sleep need increases with time spent awake, the contributions of different brain arousal systems have not been assessed independently of each other to determine whether certain neural circuits, rather than waking per se, selectively contribute to sleep homeostasis. This study found that flies sustained thermogenetic activation of three independent neurotransmitter systems promoted nighttime wakefulness. However, only sleep deprivation resulting from activation of cholinergic neurons was sufficient to elicit subsequent homeostatic recovery sleep, as assessed by multiple behavioral criteria. In contrast, sleep deprivation resulting from activation of octopaminergic neurons suppressed homeostatic recovery sleep, indicating that wakefulness can be dissociated from accrual of sleep need. Neurons that promote sleep homeostasis were found to innervate the central brain and motor control regions of the thoracic ganglion. Blocking activity of these neurons suppressed recovery sleep but did not alter baseline sleep, further differentiating between neural control of sleep homeostasis and daily fluctuations in the sleep/wake cycle. Importantly, selective activation of wake-promoting neurons without engaging the sleep homeostat impaired subsequent short-term memory, thus providing evidence that neural circuits that regulate sleep homeostasis are important for behavioral plasticity. Together, these data suggest a neural circuit model involving distinct populations of wake-promoting neurons, some of which are involved in homeostatic control of sleep and cognition.

Takemura, S. Y., et al. (2015). Synaptic circuits and their variations within different columns in the visual system of Drosophila. Journal-Proc Natl Acad Sci U S A 112: 13711-13716. PubMed ID: 26483464
This study reconstructed the synaptic circuits of seven columns in the second neuropil or medulla behind the fly's compound eye. These neurons embody some of the most stereotyped circuits in one of the most miniaturized of animal brains. The reconstructions allow study of variations between circuits in the medulla's neighboring columns. This variation in the number of synapses and the types of their synaptic partners has previously been little addressed because methods that visualize multiple circuits have not resolved detailed connections, and existing connectomic studies, which can see such connections, have not so far examined multiple reconstructions of the same circuit. This study addresses the omission by comparing the circuits common to all seven columns to assess variation in their connection strengths and the resultant rates of several different and distinct types of connection error. Error rates reveal that, overall, :lt;1% of contacts are not part of a consensus circuit, and those contacts that supplement (E+) or are missing from it (E-) were classified. Autapses, in which the same cell is both presynaptic and postsynaptic at the same synapse, are occasionally seen; two cells in particular, Dm9 and Mi1, form >/=20-fold more autapses than do other neurons. These results delimit the accuracy of developmental events that establish and normally maintain synaptic circuits with such precision, and thereby address the operation of such circuits. They also establish a precedent for error rates that will be required in the new science of connectomics.

Stevens, C. F. (2015). What the fly's nose tells the fly's brain. Proc Natl Acad Sci U S A 112: 9460-9465. PubMed ID: 26150492
The fly olfactory system has a three-layer architecture: The fly's olfactory receptor neurons send odor information to the first layer (the encoder) where this information is formatted as combinatorial odor code, one which is maximally informative, with the most informative neurons firing fastest. This first layer then sends the encoded odor information to the second layer (decoder), which consists of about 2,000 neurons that receive the odor information and "break" the code. For each odor, the amplitude of the synaptic odor input to the 2,000 second-layer neurons is approximately normally distributed across the population, which means that only a very small fraction of neurons receive a large input. Each odor, however, activates its own population of large-input neurons and so a small subset of the 2,000 neurons serves as a unique tag for the odor. Strong inhibition prevents most of the second-stage neurons from firing spikes, and therefore spikes from only the small population of large-input neurons is relayed to the third stage. This selected population provides the third stage (the user) with an odor label that can be used to direct behavior based on what odor is present (Stevens, 2015).

Kim, H., Choi, M. S., Kang, K. and Kwon, J. Y. (2015). Behavioral analysis of bitter taste perception in Drosophila larvae. Chem Senses [Epub ahead of print]. PubMed ID: 26512069
Insect larvae, which recognize food sources through chemosensory cues, are a major source of global agricultural loss. Gustation is an important factor that determines feeding behavior, and the gustatory receptors (Grs) act as molecular receptors that recognize diverse chemicals in gustatory receptor neurons (GRNs). The behavior of Drosophila larvae is relatively simpler than the adult fly, and a gustatory receptor-to-neuron map was established in a previous study of the major external larval head sensory organs. This study extensively examined The bitter taste responses of larvae using 2-choice behavioral assays. First, a panel of 23 candidate bitter compounds was tested to compare the behavioral responses of larvae and adults. Nine bitter compounds were tested, which elicit aversive behavior in a dose-dependent manner. A functional map of the larval GRNs was constructed with the use of Gr-GAL4 lines that drive expression of UAS-tetanus toxin and UAS-VR1 in specific gustatory neurons to identify bitter tastants-GRN combinations by suppressing and activating discrete subsets of taste neurons, respectively. The results suggest that many gustatory neurons act cooperatively in larval bitter sensing, and that these neurons have different degrees of responsiveness to different bitter compounds.

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