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


Friday, September 30th, 2016

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Mickolajczyk, K. J., Deffenbaugh, N. C., Arroyo, J. O., Andrecka, J., Kukura, P. and Hancock, W. O. (2015). Kinetics of nucleotide-dependent structural transitions in the kinesin-1 hydrolysis cycle. Proc Natl Acad Sci U S A 112: E7186-7193. PubMed ID: 26676576
To dissect the kinetics of structural transitions underlying the stepping cycle of kinesin-1 at physiological ATP, interferometric scattering microscopy was used to track the position of gold nanoparticles attached to individual motor domains in processively stepping dimers. Labeled heads resided stably at positions 16.4 nm apart, corresponding to a microtubule-bound state, and at a previously unseen intermediate position, corresponding to a tethered state. The chemical transitions underlying these structural transitions were identified by varying nucleotide conditions and carrying out parallel stopped-flow kinetics assays. At saturating ATP, kinesin-1 spends half of each stepping cycle with one head bound, specifying a structural state for each of two rate-limiting transitions. Analysis of stepping kinetics in varying nucleotides shows that ATP binding is required to properly enter the one-head-bound state, and hydrolysis is necessary to exit it at a physiological rate. These transitions differ from the standard model in which ATP binding drives full docking of the flexible neck linker domain of the motor. Thus, this work defines a consensus sequence of mechanochemical transitions (see Full-microtubule interaction diagram for kinesin-1) that can be used to understand functional diversity across the kinesin superfamily.
Senaratne, T. N., Joyce, E. F., Nguyen, S. C. and Wu, C. T. (2016). Investigating the interplay between sister chromatid cohesion and homolog pairing in Drosophila nuclei. PLoS Genet 12: e1006169. PubMed ID: 27541002
Following DNA replication, sister chromatids must stay connected for the remainder of the cell cycle in order to ensure accurate segregation in the subsequent cell division. This important function involves an evolutionarily conserved protein complex known as cohesin; any loss of cohesin causes premature sister chromatid separation in mitosis. This study examined the role of cohesin in sister chromatid cohesion prior to mitosis, using fluorescence in situ hybridization (FISH) to assay the alignment of sister chromatids in interphase Drosophila cells. Surprisingly, it was found that sister chromatid cohesion can be maintained in G2 with little to no cohesin. This capacity to maintain cohesion is widespread in Drosophila, unlike in other systems where a reduced dependence on cohesin for sister chromatid segregation has been observed only at specific chromosomal regions, such as the rDNA locus in budding yeast. Additionally, it was shown that condensin II antagonizes the alignment of sister chromatids in interphase, supporting a model wherein cohesin and condensin II oppose each other's functions in the alignment of sister chromatids. Finally, because the maternal and paternal homologs are paired in the somatic cells of Drosophila, and because condensin II has been shown to antagonize this pairing, the possibility is considered that condensin II-regulated mechanisms for aligning homologous chromosomes may also contribute to sister chromatid cohesion.
Momen-Roknabadi, A., Di Talia, S. and Wieschaus, E. (2016). Transcriptional timers regulating mitosis in early Drosophila embryos. Cell Rep 16: 2793-2801. PubMed ID: 27626650
The development of an embryo requires precise spatiotemporal regulation of cellular processes. During Drosophila gastrulation, a precise temporal pattern of cell division is encoded through transcriptional regulation of cdc25string in 25 distinct mitotic domains. Using a genetic screen, it was demonstrated that the same transcription factors that regulate the spatial pattern of cdc25string transcription encode its temporal activation. buttonhead and empty spiracles were identified as the major activators of cdc25string expression in mitotic domain 2. The effect of these activators is balanced through repression by hairy, sloppy paired 1, and huckebein. Within the mitotic domain, temporal precision of mitosis is robust and unaffected by changing dosage of rate-limiting transcriptional factors. However, precision can be disrupted by altering the levels of the two activators or two repressors. It is proposed that the additive and balanced action of activators and repressors is a general strategy for precise temporal regulation of cellular transitions during development.
Meghini, F., Martins, T., Tait, X., Fujimitsu, K., Yamano, H., Glover, D. M. and Kimata, Y. (2016). Targeting of Fzr/Cdh1 for timely activation of the APC/C at the centrosome during mitotic exit. Nat Commun 7: 12607. PubMed ID: 27558644
A multi-subunit ubiquitin ligase, the anaphase-promoting complex/cyclosome (APC/C), regulates critical cellular processes including the cell cycle. To accomplish its diverse functions, APC/C activity must be precisely regulated in time and space. The interphase APC/C activator Fizzy-related (Fzr or Cdh1) is localized at centrosomes in animal cells. However, neither the mechanism of its localization nor its importance is clear. This study identified the centrosome component Spd2 as a major partner of Fzr in Drosophila. The localization of Fzr to the centriole during interphase depends on direct interaction with Spd2. By generating Spd2 mutants unable to bind Fzr, it was shown that centrosomal localization of Fzr is essential for optimal APC/C activation towards its centrosomal substrate Aurora A. Finally, it was shown that Spd2 is also a novel APC/C(Fzr) substrate. This study is the first to demonstrate the critical importance of distinct subcellular pools of APC/C activators in the spatiotemporal control of APC/C activity.

Thursday, September 29th

Zhang, Y. V., Hannan, S. B., Stapper, Z. A., Kern, J. V., Jahn, T. R. and Rasse, T. M. (2016). The Drosophila KIF1A homolog unc-104 is important for site-specific synapse maturation. Front Cell Neurosci 10: 207. PubMed ID: 27656128
Mutations in the kinesin-3 family member KIF1A have been associated with hereditary spastic paraplegia (HSP), hereditary and sensory autonomic neuropathy type 2 (HSAN2) and non-syndromic intellectual disability (ID). Loss of KIF1A or its homolog unc-104 causes early postnatal or embryonic lethality in mice and Drosophila, respectively. An hypomorphic allele of unc-104, unc-104bris), was used to investigate impact on synapse maturation at the Drosophila neuromuscular junction (NMJ). Unc-104bris) mutants exhibit structural defects where a subset of synapses at the NMJ lack all investigated active zone (AZ) proteins, suggesting a complete failure in the formation of the cytomatrix at the active zone (CAZ) at these sites. Modulating synaptic Bruchpilot (Brp) levels by overexpression or RNAi suggests that the loss of AZ components such as Ca(2+) channels and Liprin-α is caused by impaired kinesin-3 based transport rather than due to the absence of the key AZ organizer protein, Brp. In addition to defects in CAZ assembly, unc-104bris mutants display further defects such as depletion of dense core and synaptic vesicle (SV) markers from the NMJ. Notably, the level of Rab3, which is important for the allocation of AZ proteins to individual release sites, was severely reduced at unc-104bris mutant NMJs. Overexpression of Rab3 partially ameliorates synaptic phenotypes of unc-104bris larvae, suggesting that lack of presynaptic Rab3 contributes to defects in synapse maturation.
Huang, Y., Huang, S., Lam, S. M., Liu, Z., Shui, G. and Zhang, Y. Q. (2016). Acsl, the Drosophila ortholog of intellectual disability-related ACSL4, inhibits synaptic growth by altered lipids. J Cell Sci [Epub ahead of print]. PubMed ID: 27656110
Nervous system development and function are tightly regulated by metabolic processes, including the metabolism of lipids such as fatty acids (FAs). Mutations in long-chain acyl-CoA synthetase 4 (ACSL4) are associated with non-syndromic intellectual disabilities. A previous study reported that Acsl, the Drosophila ortholog of mammalian ACSL3 and ACSL4, inhibits neuromuscular synapse growth by suppressing transforming growth factor-beta/bone morphogenetic protein (BMP) signaling. This study reports that Acsl regulates the composition of FAs and membrane lipid, which in turn affect neuromuscular junction (NMJ) synapse development. Acsl mutant brains had decreased abundance of C16:1 fatty acyls; restoration of Acsl expression abrogated NMJ overgrowth and the increase in BMP signaling. A lipidomic analysis revealed that Acsl suppressed the levels of three lipid raft components in the brain, including mannosyl glucosylceramide (MacCer), phosphoethanolamine ceramide, and ergosterol. MacCer level was elevated in Acsl mutant NMJs and along with sterol promoted NMJ overgrowth but was not associated with the increase in BMP signaling in the mutants. These findings suggest that Acsl inhibits NMJ growth by stimulating C16:1 and concomitantly suppressing raft-associated lipid levels.
Morelli, E., Mastrodonato, V., Beznoussenko, G. V., Mironov, A. A., Tognon, E. and Vaccari, T. (2016). An essential step of kinetochore formation controlled by the SNARE protein Snap29. EMBO J [Epub ahead of print]. PubMed ID: 27647876
The kinetochore is an essential structure that mediates accurate chromosome segregation in mitosis and meiosis. While many of the kinetochore components have been identified, the mechanisms of kinetochore assembly remain elusive. This study identified a novel role for Snap29, an unconventional SNARE, in promoting kinetochore assembly during mitosis in Drosophila and human cells. Snap29 localizes to the outer kinetochore and prevents chromosome mis-segregation and the formation of cells with fragmented nuclei. Snap29 promotes accurate chromosome segregation by mediating the recruitment of Knl1 at the kinetochore and ensuring stable microtubule attachments. Correct Knl1 localization to kinetochore requires human or Drosophila Snap29, and is prevented by a Snap29 point mutant that blocks Snap29 release from SNARE fusion complexes. Such mutant causes ectopic Knl1 recruitment to trafficking compartments. It is proposed that part of the outer kinetochore is functionally similar to membrane fusion interfaces.
Pylypenko, O., et al. (2016). Coordinated recruitment of Spir actin nucleators and myosin V motors to Rab11 vesicle membranes. Elife 5 [Epub ahead of print]. PubMed ID: 27623148 Evolutionary Homolog Study
There is growing evidence for a coupling of actin assembly and myosin motor activity in cells. However, mechanisms for recruitment of actin nucleators and motors on specific membrane compartments remain unclear. This study reports how Spir actin nucleators (see Drosophila Spire) and myosin V (see Drosophila Didum) motors coordinate their specific membrane recruitment. The myosin V globular tail domain (MyoV-GTD) interacts directly with an evolutionarily conserved Spir sequence motif. Crystal structures of MyoVa-GTD bound either to the Spir-2 motif or to Rab11 (see Drosophila Rab11) was determined, and it was shown that a Spir-2:MyoVa:Rab11 complex can form. The ternary complex architecture explains how Rab11 vesicles support coordinated F-actin nucleation and myosin force generation for vesicle transport and tethering. New insights are also provided into how myosin activation can be coupled with the generation of actin tracks. Since MyoV binds several Rab GTPases, synchronized nucleator and motor targeting could provide a common mechanism to control force generation and motility in different cellular processes.

Wednesday, September 28th

Vinayagam, A., Kulkarni, M. M., Sopko, R., Sun, X., Hu, Y., Nand, A., Villalta, C., Moghimi, A., Yang, X., Mohr, S. E., Hong, P., Asara, J. M. and Perrimon, N. (2016). An integrative analysis of the InR/PI3K/Akt network identifies the dynamic response to insulin signaling. Cell Rep 16: 3062-3074. PubMed ID: 27626673
Insulin regulates an essential conserved signaling pathway affecting growth, proliferation, and metabolism. To expand understanding of the insulin pathway, biochemical, genetic, and computational approaches were applied to build a comprehensive Drosophila InR/PI3K/Akt network. First, the dynamic protein-protein interaction network surrounding the insulin core pathway was mapped using bait-prey interactions connecting 566 proteins. Combining RNAi screening and phospho-specific antibodies, it was found that 47% of interacting proteins affect pathway activity, and, using quantitative phosphoproteomics, it was demonstrates that approximately 10% of interacting proteins are regulated by insulin stimulation at the level of phosphorylation. Next, these orthogonal datasets were integrated to characterize the structure and dynamics of the insulin network at the level of protein complexes, and this method was validated by identifying regulatory roles for the Protein Phosphatase 2A (PP2A) and Reptin-Pontin chromatin-remodeling complexes as negative and positive regulators of ribosome biogenesis, respectively. Altogether, this study represents a comprehensive resource for the study of the evolutionary conserved insulin network.
Zhang, G., Hao, Y. and Jin, L. H. (2016). Overexpression of jumu induces melanotic nodules by activating Toll signaling in Drosophila. Insect Biochem Mol Biol 77: 31-38. PubMed ID: 27507244
Melanotic nodules are commonly assumed to be caused by an abnormal immune response. Several hematopoietic mutants and signaling pathways, including the Toll, JAK/STAT, Ras and JNK pathways, can cause melanotic nodules to develop when specifically activated in hemocytes. This study used the UAS-Gal4 system to overexpress jumeau (jumu) in the fly immune response system. Jumeau (Jumu) is a new member of the winged-helix/forkhead (WH/FKH) gene family of transcription factors, which plays an important role in the growth and morphogenesis of Drosophila and participates in the proliferation and differentiation of hemocytes. Overexpressing jumu in both hemocytes and the fat body generated many melanotic nodules in larvae and adult flies. The nodules observed in the fat body were surrounded by large numbers of blood cells through a process that appeared similar to foreign body encapsulation. This phenomenon is caused by Toll pathway activation and leads to blood cells deposited in the fat body. In addition, the dissociation of fat cells and the abnormal proliferation and differentiation of blood cells are also reported. These results suggest a Jumu-mediated crosstalk between hematopoiesis and the fat body, especially during the Toll-dependent formation of melanotic nodules.
Whitney, D. S., Peterson, F. C., Kittell, A. W., Egner, J. M., Prehoda, K. E. and Volkman, B. F. (2016). Binding of Crumbs to the Par-6 CRIB-PDZ module is regulated by Cdc42. Biochemistry 55: 1455-1461. PubMed ID: 26894406
Par-6 is a scaffold protein that organizes other proteins into a complex required to initiate and maintain cell polarity. Cdc42-GTP binds the CRIB module of Par-6 and alters the binding affinity of the adjoining PDZ domain. Allosteric regulation of the Par-6 PDZ domain was first demonstrated using a peptide identified in a screen of typical carboxyl-terminal ligands. Crumbs, a membrane protein that localizes a conserved polarity complex, was subsequently identified as a functional partner for Par-6 that likely interacts with the PDZ domain. This study shows by nuclear magnetic resonance that Par-6 binds a Crumbs carboxyl-terminal peptide and reports the crystal structure of the PDZ-peptide complex. The Crumbs peptide binds Par-6 more tightly than the previously studied carboxyl peptide ligand and interacts with the CRIB-PDZ module in a Cdc42-dependent manner. The Crumbs:Par-6 crystal structure reveals specific PDZ-peptide contacts that contribute to its higher affinity and Cdc42-enhanced binding. Comparisons with existing structures suggest that multiple C-terminal Par-6 ligands respond to a common conformational switch that transmits the allosteric effects of GTPase binding.
Sato, M., Yasugi, T., Minami, Y., Miura, T. and Nagayama, M. (2016). Notch-mediated lateral inhibition regulates proneural wave propagation when combined with EGF-mediated reaction diffusion. Proc Natl Acad Sci U S A 113: E5153-5162. PubMed ID: 27535937
Notch-mediated lateral inhibition regulates binary cell fate choice, resulting in salt and pepper patterns during various developmental processes. However, how Notch signaling behaves in combination with other signaling systems remains elusive. The wave of differentiation in the Drosophila visual center or "proneural wave" accompanies Notch activity that is propagated without the formation of a salt and pepper pattern, implying that Notch does not form a feedback loop of lateral inhibition during this process. However, mathematical modeling and genetic analysis clearly showed that Notch-mediated lateral inhibition is implemented within the proneural wave. Because partial reduction in EGF signaling causes the formation of the salt and pepper pattern, it is most likely that EGF diffusion cancels salt and pepper pattern formation in silico and in vivo. Moreover, the combination of Notch-mediated lateral inhibition and EGF-mediated reaction diffusion enables a function of Notch signaling that regulates propagation of the wave of differentiation.

Tuesday, September 27th

Grabe, V., Baschwitz, A., Dweck, H. K., Lavista-Llanos, S., Hansson, B. S. and Sachse, S. (2016). Elucidating the neuronal architecture of olfactory glomeruli in the Drosophila antennal lobe. Cell Rep 16: 3401-3413. PubMed ID: 27653699
Olfactory glomeruli are morphologically conserved spherical compartments of the olfactory system, distinguishable solely by their chemosensory repertoire, anatomical position, and volume. Little is known, however, about their numerical neuronal composition. This study therefore characterized their neuronal architecture and correlated these anatomical features with their functional properties in Drosophila melanogaster. All olfactory sensory neurons (OSNs) innervating each glomerulus were quantitatively mapped, including sexually dimorphic distributions. The data reveal the impact of OSN number on glomerular dimensions and demonstrate yet unknown sex-specific differences in several glomeruli. Moreover, uniglomerular projection neurons were quantified for each glomerulus, which unraveled a glomerulus-specific numerical innervation. Correlation between morphological features and functional specificity showed that glomeruli innervated by narrowly tuned OSNs seem to possess a larger number of projection neurons and are involved in less lateral processing than glomeruli targeted by broadly tuned OSNs. This study demonstrates that the neuronal architecture of each glomerulus encoding crucial odors is unique.
Turrel, O., Lampin-Saint-Amaux, A., Préat, T. and Goguel, V. (2016). Drosophila neprilysins are involved in middle-term and long-term memory. J Neurosci 36: 9535-9546. PubMed ID: 27629706
Neprilysins are type II metalloproteinases known to degrade and inactivate a number of small peptides. Neprilysins in particular are the major amyloid-β peptide-degrading enzymes. In mouse models of Alzheimer's disease, neprilysin overexpression improves learning and memory deficits, whereas neprilysin deficiency aggravates the behavioral phenotypes. However, whether these enzymes are involved in memory in nonpathological conditions is an open question. Drosophila melanogaster is a well suited model system with which to address this issue. Several memory phases have been characterized in this organism and the neuronal circuits involved are well described. The fly genome contains five neprilysin-encoding genes, four of which are expressed in the adult (see Neprilysin 4). Using conditional RNA interference, this study shows that all four neprilysins are involved in middle-term and long-term memory. Strikingly, all four are required in a single pair of neurons, the dorsal paired medial (DPM) neurons that broadly innervate the mushroom bodies (MBs), the center of olfactory memory. Neprilysins are also required in the MB, reflecting the functional relationship between the DPM neurons and the MB, a circuit believed to stabilize memories. Together, these data establish a role for neprilysins in two specific memory phases and further show that DPM neurons play a critical role in the proper targeting of neuropeptides involved in these processes.

Knecht, Z. A., Silbering, A. F., Ni, L., Klein, M., Budelli, G., Bell, R., Abuin, L., Ferrer, A. J., Samuel, A. D., Benton, R. and Garrity, P. A. (2016). Distinct combinations of variant ionotropic glutamate receptors mediate thermosensation and hygrosensation in Drosophila. Elife 5. PubMed ID: 27656904
Ionotropic Receptors (IRs) are a large subfamily of variant ionotropic glutamate receptors present across Protostomia. While these receptors are most extensively studied for their roles in chemosensory detection, recent work has implicated two family members, IR21a and IR25a, in thermosensation in Drosophila. This study characterized one of the most evolutionarily deeply conserved receptors, IR93a, and shows that it is co-expressed and functions with IR21a and IR25a to mediate physiological and behavioral responses to cool temperatures. IR93a is also co-expressed with IR25a and a distinct receptor, IR40a, in a discrete population of sensory neurons in the sacculus, a multi-chambered pocket within the antenna. This combination of receptors was demonstrated to be required for neuronal responses to dry air and behavioral discrimination of humidity differences. These results identify IR93a as a common component of molecularly and cellularly distinct IR pathways important for thermosensation and hygrosensation in insects.
Garrett, A.M., Tadenev, A.L., Hammond, Y.T., Fuerst, P.G. and Burgess, R.W. (2016). Replacing the PDZ-interacting C-termini of DSCAM and DSCAML1 with epitope tags causes different phenotypic severity in different cell populations. Elife 5. PubMed ID: 27637097
Evolutionary Homolog Study
Different types of neurons in the retina are organized vertically into layers and horizontally in a mosaic pattern that helps ensure proper neural network formation and information processing throughout the visual field. The vertebrate Dscams (DSCAM and DSCAML1) (see Drosophila Dscam4 and Dscam1, respectively) are cell adhesion molecules that support the development of this organization by promoting self-avoidance at the level of cell types, promoting normal developmental cell death, and directing vertical neurite stratification. To understand the molecular interactions required for these activities, this study tested the functional significance of the interaction between the C-terminus of the Dscams and multi-PDZ domain-containing scaffolding proteins in mouse. It was hypothesized that this PDZ-interacting domain would mediate a subset of the Dscams' functions. Instead, it was found that in the absence of these interactions, some cell types develop almost normally, while others resemble complete loss of function. Thus, there is a differential dependence on this domain for Dscams' functions in different cell types.

Monday, September 26th

Kim, M., Lee, H., Hur, J.H., Choe, J. and Lim, C. (2016). CRTC potentiates light-independent timeless transcription to sustain circadian rhythms in Drosophila. Sci Rep 6: 32113. PubMed ID: 27577611
Light is one of the strongest environmental time cues for entraining endogenous circadian rhythms. Emerging evidence indicates that CREB-regulated transcription co-activator 1 (CRTC1) is a key player in this pathway, stimulating light-induced Period1 (Per1) transcription in mammalian clocks. This study demonstrates a light-independent role of Drosophila CRTC in sustaining circadian behaviors. Genomic deletion of the crtc locus causes long but poor locomotor rhythms in constant darkness. Overexpression or RNA interference-mediated depletion of CRTC in circadian pacemaker neurons similarly impairs the free-running behavioral rhythms, implying that Drosophila clocks are sensitive to the dosage of CRTC. The crtc null mutation delays the overall phase of circadian gene expression yet it remarkably dampens light-independent oscillations of TIMELESS (TIM) proteins in the clock neurons. In fact, CRTC overexpression enhances CLOCK/CYCLE (CLK/CYC)-activated transcription from tim but not per promoter in clock-less S2 cells whereas CRTC depletion suppresses it. Consistently, TIM overexpression partially but significantly rescues the behavioral rhythms in crtc mutants. Taken together, these data suggest that CRTC is a novel co-activator for the CLK/CYC-activated tim transcription to coordinate molecular rhythms with circadian behaviors over a 24-hour time-scale. The study proposes that CRTC-dependent clock mechanisms have co-evolved with selective clock genes among different species.

Garbe, D. S., Vigderman, A. S., Moscato, E., Dove, A. E., Vecsey, C. G., Kayser, M. S. and Sehgal, A. (2016). Changes in female Drosophila sleep following mating are mediated by SPSN-SAG neurons. J Biol Rhythms [Epub ahead of print]. PubMed ID: 27658900
Female Drosophila melanogaster, like many other organisms, exhibit different behavioral repertoires after mating with a male. These postmating responses (PMRs) include increased egg production and laying, increased rejection behavior (avoiding further male advances), decreased longevity, altered gustation and decreased sleep. Sex Peptide (SP), a protein transferred from the male during copulation, is largely responsible for many of these behavioral responses, and acts through a specific circuit to induce rejection behavior and alter dietary preference. However, less is known about the mechanisms and neurons that influence sleep in mated females. This study investigated postmating changes in female sleep across strains and ages and on different media and reports that these changes are robust and relatively consistent under a variety of conditions. Female sleep is reduced by male-derived SP acting through the canonical sex peptide receptor (SPR) within the same neurons responsible for altering other PMRs. This circuit includes the SPSN-SAG neurons, whose silencing by a chemogenetic silencer (DREADD) induces postmating behaviors including sleep. These data are consistent with the idea that mating status is communicated to the central brain through a common circuit that diverges in higher brain centers to modify a collection of postmating sensorimotor processes.
Apostolopoulou, A. A., Kohn, S., Stehle, B., Lutz, M., Wust, A., Mazija, L., Rist, A., Galizia, C. G., Ludke, A. and Thum, A. S. (2016). Caffeine taste signaling in Drosophila larvae. Front Cell Neurosci 10: 193. PubMed ID: 27555807
The Drosophila larva has a simple peripheral nervous system with a comparably small number of sensory neurons located externally at the head or internally along the pharynx to assess its chemical environment. It is assumed that larval taste coding occurs mainly via external organs (the dorsal, terminal, and ventral organ). However, the contribution of the internal pharyngeal sensory organs has not been explored. This study finds that larvae require a single pharyngeal gustatory receptor neuron pair called D1, which is located in the dorsal pharyngeal sensilla, in order to avoid caffeine and to associate an odor with caffeine punishment. In contrast, caffeine-driven reduction in feeding in non-choice situations does not require D1. Hence, this work provides data on taste coding via different receptor neurons, depending on the behavioral context. Furthermore, the larval pharyngeal system is shown to be involved in bitter tasting. Using ectopic expressions, the caffeine receptor in neuron D1 was shown to require the function of at least four receptor genes: the putative co-receptors Gr33a, Gr66a, the putative caffeine-specific receptor Gr93a, and yet unknown additional molecular component(s). This suggests that larval taste perception is more complex than previously assumed already at the sensory level. Taste information from different sensory organs located outside at the head or inside along the pharynx of the larva is assembled to trigger taste guided behaviors.
Keesey, I. W., Koerte, S., Retzke, T., Haverkamp, A., Hansson, B. S. and Knaden, M. (2016). Adult frass provides a pheromone signature for Drosophila feeding and aggregation. J Chem Ecol [Epub ahead of print]. PubMed ID: 27539589
Adult Drosophila melanogaster locate food resources by using distinct olfactory cues that often are associated with the fermentation of fruit. However, in addition to being an odorous food source and providing a possible site for oviposition, fermenting fruit also provides a physical substrate upon which flies can attract and court a potential mate. This study demonstrates that Drosophila adults are able to recruit additional flies to a food source by covering the exposed surface area with fecal spots, and that this recruitment is mediated via olfactory receptors (Ors). Analyses of the deposited frass material demonstrates that frass contains several previously studied pheromone components, such as methyl laurate (ML), methyl myristate (MM), methyl palmitate (MP), and 11-cis-vaccenyl acetate (cVA), in addition to several cuticular hydrocarbons (CHCs) that are known to be behaviorally active. Moreover, this study also demonstrates that adult feeding is increased in the presence of frass, although it appears that Ors are less likely to mediate this phenomenon. In summary, the frass deposited by the fly onto the fruit provides both pheromone and CHC cues that lead to increased feeding and aggregation in Drosophila. This research is the first step in examining Drosophila frass as an important chemical signature that provides information about both the sex and the species of the fly that generated the fecal spots.

Sunday, September 25th

Sanchez-Martinez, A., Beavan, M., Gegg, M. E., Chau, K. Y., Whitworth, A. J. and Schapira, A. H. (2016). Parkinson disease-linked GBA mutation effects reversed by molecular chaperones in human cell and fly models. Sci Rep 6: 31380. PubMed ID: 27539639
GBA gene mutations are the greatest cause of Parkinson disease (PD). GBA encodes the lysosomal enzyme glucocerebrosidase (GCase) but the mechanisms by which loss of GCase contributes to PD remain unclear. Inhibition of autophagy and the generation of endoplasmic reticulum (ER) stress are both implicated. Mutant GCase can unfold in the ER and be degraded via the unfolded protein response, activating ER stress and reducing lysosomal GCase. Small molecule chaperones that cross the blood brain barrier help mutant GCase refold and traffic correctly to lysosomes are putative treatments for PD. This study treated fibroblast cells from PD patients with heterozygous GBA mutations and Drosophila expressing human wild-type, N370S and L444P GBA with the molecular chaperones ambroxol and isofagomine. Both chaperones increased GCase levels and activity, but also GBA mRNA, in control and mutant GBA fibroblasts. Expression of mutated GBA in Drosophila resulted in dopaminergic neuronal loss, a progressive locomotor defect, abnormal aggregates in the ER and increased levels of the ER stress reporter Xbp1-EGFP. Treatment with both chaperones lowered ER stress and prevented the loss of motor function, providing proof of principle that small molecule chaperones can reverse mutant GBA-mediated ER stress in vivo and might prove effective for treating PD.
Padash Barmchi, M., Gilbert, M., Thomas, M., Banks, L., Zhang, B. and Auld, V. J. (2016). A Drosophila model of HPV E6-induced malignancy reveals essential roles for Magi and the Insulin Receptor. PLoS Pathog 12: e1005789. PubMed ID: 27537218
The causative agents of cervical cancers, high-risk human papillomaviruses (HPVs), cause cancer through the action of two oncoproteins, E6 and E7. The E6 oncoprotein cooperates with an E3 ubiquitin ligase (UBE3A; see Drosophila Ube3a) to target the p53 tumour suppressor and important polarity and junctional PDZ proteins for proteasomal degradation. However, the causative link between degradation of PDZ proteins and E6-mediated malignancy is largely unknown. An in vivo model of HPV E6-mediated cellular transformation was developed using Drosophila as model. Co-expression of E6 and human UBE3A in wing and eye epithelia results in severe morphological abnormalities. Furthermore, E6, via its PDZ-binding motif and in cooperation with UBE3A, targets a suite of PDZ proteins, including Magi, Dlg and Scribble. Similar to human epithelia, Drosophila Magi is a major degradation target. Magi overexpression rescues the cellular abnormalities caused by E6+UBE3A coexpression and this activity of Magi is PDZ domain-dependent. Tumorigenesis occurred when E6+UBE3A are expressed in conjunction with activated/oncogenic forms of Ras or Notch. This study identified the insulin receptor signaling pathway as being required for E6+UBE3A induced hyperplasia. These results suggest a highly conserved mechanism of HPV E6 mediated cellular transformation.
Levinson, S. and Cagan, R. L. (2016). Drosophila cancer models identify functional differences between Ret fusions. Cell Rep 16: 3052-3061. PubMed ID: 27626672
Drosophila models of RET fusions CCDC6-RET and NCOA4-RET were generated and compared. Both RET fusions directed cells to migrate, delaminate, and undergo EMT, and both resulted in lethality when broadly expressed. In all phenotypes examined, NCOA4-RET was more severe than CCDC6-RET, mirroring their effects on patients. A functional screen against the Drosophila kinome and a library of cancer drugs found that CCDC6-RET and NCOA4-RET acted through different signaling networks and displayed distinct drug sensitivities. Combining data from the kinome and drug screens identified the WEE1 inhibitor AZD1775 plus the multi-kinase inhibitor sorafenib as a synergistic drug combination that is specific for NCOA4-RET. This work emphasizes the importance of identifying and tailoring a patient's treatment to their specific RET fusion isoform and identifies a multi-targeted therapy that may prove effective against tumors containing the NCOA4-RET fusion.
Dhondt, I., Petyuk, V. A., Cai, H., Vandemeulebroucke, L., Vierstraete, A., Smith, R. D., Depuydt, G. and Braeckman, B. P. (2016). FOXO/DAF-16 activation slows down turnover of the majority of proteins in C. elegans. Cell Rep 16: 3028-3040. PubMed ID: 27626670
Evolutionary Homolog Study
Most aging hypotheses assume the accumulation of damage, resulting in gradual physiological decline and, ultimately, death. Avoiding protein damage accumulation by enhanced turnover should slow down the aging process and extend the lifespan. However, lowering translational efficiency extends rather than shortens the lifespan in C. elegans. This study examined turnover of individual proteins were studied in the long-lived insulin receptor/daf-2 mutant. Intriguingly, the majority of proteins displayed prolonged half-lives in daf-2, whereas others remained unchanged, signifying that longevity is not supported by high protein turnover. This slowdown was most prominent for translation-related and mitochondrial proteins. The slowdown of protein dynamics and decreased abundance of the translational machinery may point to the importance of anabolic attenuation in lifespan extension, as suggested by the hyperfunction theory.

Saturday, September 24th

Elyashiv, E., Sattath, S., Hu, T. T., Strutsovsky, A., McVicker, G., Andolfatto, P., Coop, G. and Sella, G. (2016). A genomic map of the effects of linked selection in Drosophila. PLoS Genet 12: e1006130. PubMed ID: 27536991
Natural selection at one site shapes patterns of genetic variation at linked sites. Quantifying the effects of 'linked selection' on levels of genetic diversity is key to making reliable inference about demography, building a null model in scans for targets of adaptation, and learning about the dynamics of natural selection. This study introduced the first method that jointly infers parameters of distinct modes of linked selection, notably background selection and selective sweeps, from genome-wide diversity data, functional annotations and genetic maps. The central idea is to calculate the probability that a neutral site is polymorphic given local annotations, substitution patterns, and recombination rates. Information is then combined across sites and samples using composite likelihood in order to estimate genome-wide parameters of distinct modes of selection. In addition to parameter estimation, this approach yields a map of the expected neutral diversity levels along the genome. To illustrate the utility of this approach, it was applied to genome-wide resequencing data from 125 lines in Drosophila melanogaster and diversity levels was reliably predicted at the 1Mb scale. The results corroborate estimates of a high fraction of beneficial substitutions in proteins and untranslated regions (UTR). They allow distinguishing between the contribution of sweeps and other modes of selection around amino acid substitutions and uncovered evidence for pervasive sweeps in untranslated regions (UTRs). This inference further suggests a substantial effect of other modes of linked selection and of adaptation in particular. More generally, it was demonstrated that linked selection has had a larger effect in reducing diversity levels and increasing their variance in D. melanogaster than previously appreciated.
Yassin, A., Delaney, E. K., Reddiex, A. J., Seher, T. D., Bastide, H., Appleton, N. C., Lack, J. B., David, J. R., Chenoweth, S. F., Pool, J. E. and Kopp, A. (2016). The pdm3 locus is a hotspot for recurrent evolution of female-limited color dimorphism in Drosophila. Curr Biol. PubMed ID: 27546577
Sex-limited polymorphisms are an intriguing form of sexual dimorphism that offer unique opportunities to reconstruct the evolutionary changes that decouple male and female traits encoded by a shared genome. This study investigated the genetic basis of a Mendelian female-limited color dimorphism (FLCD) that segregates in natural populations of more than 20 species of the Drosophila montium subgroup. In these species, females have alternative abdominal color morphs, light and dark, whereas males have only one color morph in each species. A comprehensive molecular phylogeny of the montium subgroup supports multiple origins of FLCD. Despite this, FLCD mapped to the same locus in four distantly related species-the transcription factor POU domain motif 3 (pdm3), which acts as a repressor of abdominal pigmentation in D. melanogaster. In D. serrata, FLCD maps to a structural variant in the first intron of pdm3; however, this variant is not found in the three other species-D. kikkawai, D. leontia, and D. burlai-and sequence analysis strongly suggests the pdm3 alleles responsible for FLCD originated independently at least three times. It is proposed that cis-regulatory changes in pdm3 form sexually dimorphic and monomorphic alleles that segregate within species and are preserved, at least in one species, by structural variation. Surprisingly, pdm3 has not been implicated in the evolution of sex-specific pigmentation outside the montium subgroup, suggesting that the genetic paths to sexual dimorphism may be constrained within a clade but variable across clades.
Librado, P. and Rozas, J. (2016). Weak polygenic selection drives the rapid adaptation of the chemosensory system: lessons from the upstream regions of the major gene families. Genome Biol Evol [Epub ahead of print]. PubMed ID: 27503297
The animal chemosensory system is involved in essential biological processes, most of them mediated by proteins encoded in multigene families. These multigene families have been fundamental for the adaptation to new environments, significantly contributing to phenotypic variation. This adaptive potential contrasts, however, with the lack of studies at their upstream regions, especially taking into account the evidence linking their transcriptional changes to certain phenotypic effects. This study explicitly characterised the contribution of the upstream sequences of the major chemosensory gene families to rapid adaptive processes. For that, the genome sequences of 158 lines were analyzed from a population of Drosophila melanogaster that recently colonised North America, and functional and transcriptional data available for this species were integrated. Both, strong negative and strong positive selection were found to shape transcriptional evolution at the genome-wide level. The chemosensory upstream regions, however, exhibit a distinctive adaptive landscape, including multiple mutations of small beneficial effect and a reduced number of cis-regulatory elements. Together, these results suggest that the promiscuous and partially redundant transcription and function of the chemosensory genes provide evolutionarily opportunities for rapid adaptive episodes through weak polygenic selection.
Lewis, S. H., Webster, C. L., Salmela, H. and Obbard, D. J. (2016). Repeated duplication of Argonaute2 is associated with strong selection and testis specialization in Drosophila. Genetics [Epub ahead of print]. PubMed ID: 27535930
Argonaute2 (Ago2) is a rapidly evolving nuclease in the Drosophila melanogaster RNA interference (RNAi) pathway that targets viruses and transposable elements in somatic tissues. This study reconstruct the history of Ago2 duplications across the Drosophila obscura group, and patterns of gene expression were used to infer new functional specialization. Some duplications were shown to be old, shared by the entire species group, and losses may be common, including previously undetected losses in the lineage leading to D. pseudoobscura. While the original (syntenic) gene copy has generally retained the ancestral ubiquitous expression pattern, most of the novel Ago2 paralogues have independently specialized to testis-specific expression. Using population genetic analyses, it was shown that most testis-specific paralogues have significantly lower genetic diversity than the genome-wide average. This suggests recent positive selection in three different species, and model-based analyses provide strong evidence of recent hard selective sweeps in or near four of the six D. pseudoobscura Ago2 paralogues. It is speculated that the repeated evolution of testis-specificity in obscura group Ago2 genes, combined with their dynamic turnover and strong signatures of adaptive evolution, may be associated with highly derived roles in the suppression of transposable elements or meiotic drive. This study highlights the lability of RNAi pathways, even within well-studied groups such as Drosophila, and suggests that strong selection may act quickly after duplication in RNAi pathways, potentially giving rise to new and unknown RNAi functions in non-model species.

Signor, S.A., Liu, Y., Rebeiz, M. and Kopp, A. (2016). Genetic convergence in the evolution of male-specific color patterns in Drosophila. Curr Biol [Epub ahead of print]. PubMed ID: 27546578
Convergent evolution provides a type of natural replication that can be exploited to understand the roles of contingency and constraint in the evolution of phenotypes and the gene networks that control their development. For sex-specific traits, convergence offers the additional opportunity for testing whether the same gene networks follow different evolutionary trends in males versus females. Thus study used an unbiased, systematic mapping approach to compare the genetic basis of evolutionary changes in male-limited pigmentation in several pairs of Drosophila species that represent independent evolutionary transitions. A strong evidence for repeated recruitment of the same genes to specify similar pigmentation in different species was found. At one of these genes, ebony, convergent evolution of sexually dimorphic and monomorphic expression through cis-regulatory changes was observed. However, this functional convergence has a different molecular basis in different species, reflecting both parallel fixation of ancestral alleles and independent origin of distinct mutations with similar functional consequences. These results show that a strong evolutionary constraint at the gene level is compatible with a dominant role of chance at the molecular level.

Lack, J. B., Yassin, A., Sprengelmeyer, Q. D., Johanning, E. J., David, J. R. and Pool, J. E. (2016). Life history evolution and cellular mechanisms associated with increased size in high-altitude Drosophila. Ecol Evol 6: 5893-5906. PubMed ID: 27547363
Understanding the physiological and genetic basis of growth and body size variation has wide-ranging implications, from cancer and metabolic disease to the genetics of complex traits. This study examined the evolution of body and wing size in high-altitude Drosophila melanogaster from Ethiopia, flies with larger size than any previously known population. Specifically, attempts were made to identify life history characteristics and cellular mechanisms that may have facilitated size evolution. The large-bodied Ethiopian flies laid significantly fewer but larger eggs relative to lowland, smaller-bodied Zambian flies. The highland flies were found to achieve larger size in a similar developmental period, potentially aided by a reproductive strategy favoring greater provisioning of fewer offspring. At the cellular level, cell proliferation was a strong contributor to wing size evolution, but both thorax and wing size increases involved important changes in cell size. Nuclear size measurements were consistent with elevated somatic ploidy as an important mechanism of body size evolution. The significance of these results for the genetic basis of evolutionary changes in body and wing size in Ethiopian D. melanogaster is discussed.

Friday, September 23rd

Ganguly, A., Manahan, C. C., Top, D., Yee, E. F., Lin, C., Young, M. W., Thiel, W. and Crane, B. R. (2016). Changes in active site histidine hydrogen bonding trigger cryptochrome activation. Proc Natl Acad Sci U S A 113: 10073-10078. PubMed ID: 27551082
Cryptochrome (CRY) is the principal light sensor of the insect circadian clock. Photoreduction of the Drosophila CRY (dCRY) flavin cofactor to the anionic semiquinone (ASQ) restructures a C-terminal tail helix (CTT) that otherwise inhibits interactions with targets that include the clock protein Timeless (TIM). All-atom molecular dynamics (MD) simulations indicate that flavin reduction destabilizes the CTT, which undergoes large-scale conformational changes (the CTT release) on short (25 ns) timescales. The CTT release correlates with the conformation and protonation state of conserved His378, which resides between the CTT and the flavin cofactor. Poisson-Boltzmann calculations indicate that flavin reduction substantially increases the His378 pKa Consistent with coupling between ASQ formation and His378 protonation, dCRY displays reduced photoreduction rates with increasing pH; however, His378Asn/Arg variants show no such pH dependence. Replica-exchange MD simulations also support CTT release mediated by changes in His378 hydrogen bonding and verify other responsive regions of the protein previously identified by proteolytic sensitivity assays. His378 dCRY variants show varying abilities to light-activate TIM and undergo self-degradation in cellular assays. Surprisingly, His378Arg/Lys variants do not degrade in light despite maintaining reactivity toward TIM, thereby implicating different conformational responses in these two functions. Thus, the dCRY photosensory mechanism involves flavin photoreduction coupled to protonation of His378, whose perturbed hydrogen-bonding pattern alters the CTT and surrounding regions.
Vo, U., Vajpai, N., Flavell, L., Bobby, R., Breeze, A. L., Embrey, K. J. and Golovanov, A. P. (2016). Monitoring Ras interactions with the nucleotide exchange factor Son of Sevenless (Sos) using site-specific NMR reporter signals and intrinsic fluorescence. J Biol Chem 291: 1703-1718. PubMed ID: 26565026
The activity of Ras is controlled by the interconversion between GTP- and GDP-bound forms partly regulated by the binding of the guanine nucleotide exchange factor Son of Sevenless (Sos). The details of Sos binding, leading to nucleotide exchange and subsequent dissociation of the complex, are not completely understood. This study used uniformly (15)N-labeled Ras as well as labeled Sos for observing site-specific details of Ras-Sos interactions in solution. Binding of various forms of Ras (loaded with GDP and mimics of GTP or nucleotide-free) at the allosteric and catalytic sites of Sos was comprehensively characterized by monitoring signal perturbations in the NMR spectra. The overall affinity of binding between these protein variants as well as their selected functional mutants was also investigated using intrinsic fluorescence. The data support a positive feedback activation of Sos by Ras.GTP with Ras.GTP binding as a substrate for the catalytic site of activated Sos more weakly than Ras.GDP, suggesting that Sos should actively promote unidirectional GDP --> GTP exchange on Ras in preference of passive homonucleotide exchange. Ras.GDP weakly binds to the catalytic but not to the allosteric site of Sos. This confirms that Ras.GDP cannot properly activate Sos at the allosteric site. The novel site-specific assay described may be useful for design of drugs aimed at perturbing Ras-Sos interactions.
Kim, G. W., Won, J. H., Lee, O. K., Lee, S. S., Han, J. H., Tsogtbaatar, O., Nam, S., Kim, Y. and Cho, K. O. (2016). Sol narae (Sona) is a Drosophila ADAMTS involved in Wg signaling. Sci Rep 6: 31863. PubMed ID: 27535473
ADAMTS (a disintegrin and metalloproteases with thrombospondin motif) family consists of secreted proteases, and is shown to cleave extracellular matrix proteins. Their malfunctions result in cancers and disorders in connective tissues. This paper reports that a Drosophila ADAMTS named Sol narae (Sona; CG9850) promotes Wnt/Wingless (Wg) signaling. sona loss-of-function mutants are lethal and rare escapers had malformed appendages, indicating that sona is essential for fly development and survival. sona exhibited positive genetic interaction with wntless (wls) that encodes a cargo protein for Wg. Loss of sona decreased the level of extracellular Wg, and also reduced the expression level of Wg effector proteins such as Senseless (Sens), Distalless (Dll) and Vestigial (Vg). Sona and Wg colocalized in Golgi and endosomal vesicles, and were in the same protein complex. Furthermore, co-expression of Wg and Sona generated ectopic wing margin bristles. This study suggests that Sona is involved in Wg signaling by regulating the level of extracellular Wg.
Mason, F. M., Xie, S., Vasquez, C. G., Tworoger, M. and Martin, A. C. (2016). RhoA GTPase inhibition organizes contraction during epithelial morphogenesis. J Cell Biol 214: 603-617. PubMed ID: 27551058
During morphogenesis, contraction of the actomyosin cytoskeleton within individual cells drives cell shape changes that fold tissues. Coordination of cytoskeletal contractility is mediated by regulating RhoA GTPase activity. Guanine nucleotide exchange factors (GEFs) activate and GTPase-activating proteins (GAPs) inhibit RhoA activity. Most studies of tissue folding, including apical constriction, have focused on how RhoA is activated by GEFs to promote cell contractility, with little investigation as to how GAPs may be important. This study identified a critical role for a RhoA GAP, Cumberland GAP (C-GAP), which coordinates with a RhoA GEF, RhoGEF2, to organize spatiotemporal contractility during Drosophila melanogaster apical constriction. C-GAP spatially restricts RhoA pathway activity to a central position in the apical cortex. RhoGEF2 pulses precede myosin, and C-GAP is required for pulsation, suggesting that contractile pulses result from RhoA activity cycling. Finally, C-GAP expression level influences the transition from reversible to irreversible cell shape change, which defines the onset of tissue shape change. These data demonstrate that RhoA activity cycling and modulating the ratio of RhoGEF2 to C-GAP are required for tissue folding.
Liu, M., Li, Y., Liu, A., Li, R., Su, Y., Du, J., Li, C. and Zhu, A. J. (2016). The exon junction complex regulates the splicing of cell polarity gene dlg1 to control Wingless signaling in development. Elife 5. PubMed ID: 27536874
Wingless (Wg)/Wnt signaling is conserved in all metazoan animals and plays critical roles in development. The Wg/Wnt morphogen reception is essential for signal activation, whose activity is mediated through the receptor complex and a scaffold protein Dishevelled (Dsh). This study reports that the exon junction complex (EJC) activity is indispensable for Wg signaling by maintaining an appropriate level of Dsh protein for Wg ligand reception in Drosophila. Transcriptome analyses in Drosophila wing imaginal discs indicate that the EJC controls the splicing of the cell polarity gene discs large 1 (dlg1), whose coding protein directly interacts with Dsh. Genetic and biochemical experiments demonstrate that Dlg1 protein acts independently from its role in cell polarity to protect Dsh protein from lysosomal degradation. More importantly, human orthologous Dlg protein is sufficient to promote Dvl protein stabilization and Wnt signaling activity, thus revealing a conserved regulatory mechanism of Wg/Wnt signaling by Dlg and EJC.
Restrepo, S. and Basler, K. (2016). Drosophila wing imaginal discs respond to mechanical injury via slow InsP3R-mediated intercellular calcium waves. Nat Commun 7: 12450. PubMed ID: 27503836
Calcium signalling is a highly versatile cellular communication system that modulates basic functions such as cell contractility, essential steps of animal development such as fertilization and higher-order processes such as memory. This study probed the function of calcium signalling in Drosophila wing imaginal discs through a combination of ex vivo and in vivo imaging and genetic analysis. Wing discs were found display slow, long-range intercellular calcium waves (ICWs) when mechanically stressed in vivo or cultured ex vivo. These slow imaginal disc intercellular calcium waves (SIDICs) are mediated by the inositol-3-phosphate receptor, the endoplasmic reticulum (ER) calcium pump SERCA and the key gap junction component Inx2. The knockdown of genes required for SIDIC formation and propagation negatively affects wing disc recovery after mechanical injury. These results reveal a role for ICWs in wing disc homoeostasis and highlight the utility of the wing disc as a model for calcium signalling studies.

Thursday, September 22nd

Lin, C., Chang, Y. C., Cheng, Y. C., Lai, P. J., Yeh, C. H., Hsieh, W. H., Hu, K., Wu, J. T., Lee, H. H., Lo, M. T. and Ho, Y. L. (2016). Probing the fractal pattern of heartbeats in Drosophila pupae by visible optical recording system. Sci Rep 6: 31950. PubMed ID: 27535299
Judiciously tuning heart rates is critical for regular cardiovascular function. The fractal pattern of heartbeats - a multiscale regulation in instantaneous fluctuations - is well known for vertebrates. The most primitive heart system of the Drosophila provides a useful model to understand the evolutional origin of such a fractal pattern as well as the alterations of fractal pattern during diseased statuses. A non-invasive visible optical heart rate recording system especially suitable for long-term recording was developed by using principal component analysis (PCA) instead of fluorescence recording system to avoid the confounding effect from intense light irradiation. To deplete intracellular Ca(2+) levels, the expression of sarco-endoplasmic reticulum Ca(2+)-ATPase (SERCA) was tissue-specifically knocked down. The SERCA group shows longer heart beat intervals as compared to the control group. The multiscale correlation of SERCA group, on the other hand, is weaker than that of the control Drosophila. It is concluded that fractal correlations were presented in control group but were disrupted by the heart specific SERCA depletion.
Wang, L. Y., Hung, C. L., Chen, Y. R., Yang, J. C., Wang, J., Campbell, M., Izumiya, Y., Chen, H. W., Wang, W. C., Ann, D. K. and Kung, H. J. (2016). KDM4A Coactivates E2F1 to Regulate the PDK-Dependent Metabolic Switch between Mitochondrial Oxidation and Glycolysis. Cell Rep 16: 3016-3027. PubMed ID: 27626669
Evolutionary Homolog Study:
The histone lysine demethylase KDM4A/JMJD2A (see Drosophila Jumonji) has been implicated in prostate carcinogenesis through its role in transcriptional regulation. This study describes KDM4A as a E2F1 (see Drosophila E2F1) coactivator and demonstrate a functional role for the E2F1-KDM4A complex in the control of tumor metabolism. KDM4A associates with E2F1 on target gene promoters and enhances E2F1 chromatin binding and transcriptional activity, thereby modulating the transcriptional profile essential for cancer cell proliferation and survival. The pyruvate dehydrogenase kinases (PDKs; see Drosophila Pdk) PDK1 and PDK3 are direct targets of KDM4A and E2F1 and modulate the switch between glycolytic metabolism and mitochondrial oxidation. Downregulation of KDM4A leads to elevated activity of pyruvate dehydrogenase and mitochondrial oxidation, resulting in excessive accumulation of reactive oxygen species. The altered metabolic phenotypes can be partially rescued by ectopic expression of PDK1 and PDK3, indicating a KDM4A-dependent tumor metabolic regulation via PDK. These results suggest that KDM4A is a key regulator of tumor metabolism and a potential therapeutic target for prostate cancer.
Hateley, S., Hosamani, R., Bhardwaj, S.R., Pachter, L. and Bhattacharya, S. (2016). Transcriptomic response of Drosophila melanogaster pupae developed in hypergravity. Genomics [Epub ahead of print]. PubMed ID: 27621057
Altered gravity can perturb normal development and induce corresponding changes in gene expression. Understanding this relationship between the physical environment and a biological response is important for NASA's space travel goals. This study used RNA-Seq and qRT-PCR techniques to profile changes in early Drosophila melanogaster pupae exposed to chronic hypergravity (3g, or three times Earth's gravity). During the pupal stage, D. melanogaster rely upon gravitational cues for proper development. Assessing gene expression changes in the pupae under altered gravity conditions helps highlight gravity-dependent genetic pathways. A robust transcriptional response was observed in hypergravity-treated pupae compared to controls, with 1513 genes showing a significant (q<0.05) difference in gene expression. Five major biological processes were affected: ion transport, redox homeostasis, immune response, proteolysis, and cuticle development. This outlines the underlying molecular and biological changes occurring in Drosophila pupae in response to hypergravity; gravity is important for many biological processes on Earth.

Saras, A. and Tanouye, M. A. (2016). Seizure suppression by high temperature via cAMP modulation in Drosophila. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 27558668
Bang Sensitive (BS) Drosophila mutants display characteristic seizure like activity (SLA) and paralysis after mechanical shock. After high frequency electrical stimulation (HFS) of the brain, they generate robust seizures at very low threshold voltage. This paper reports an important phenomenon, which effectively suppresses SLA in BS mutants. High temperature causes seizure suppression in all BS mutants (parabss1, eas, sda) examined in this study. This effect is fully reversible and flies show complete recovery from BS paralysis once the temperature effect is nullified. High temperature induces an increase in seizure threshold after a brief pulse of heat shock (HS). By genetic screening, the involvement of cAMP was identified in the suppression of seizures by high temperature. It is proposed that HS induces adenylyl cyclase which in turn increases cAMP concentration which eventually suppresses seizures in mutant flies. In summary, this study describes an unusual phenomenon, where high temperature can suppress SLA in flies by modulating cAMP concentration.

Wednesday, September 21th

Kelpsch, D. J., Groen, C. M., Fagan, T. N., Sudhir, S. and Tootle, T. L. (2016). Fascin regulates nuclear actin during Drosophila oogenesis. Mol Biol Cell [Epub ahead of print]. PubMed ID: 27535426
Drosophila oogenesis provides a developmental system to study nuclear actin. During Stages 5-9, nuclear actin levels are high in the oocyte and exhibit variation within the nurse cells. Cofilin and Profilin, which regulate the nuclear import and export of actin, also localize to the nuclei. Expression of GFP-tagged Actin results in nuclear actin rod formation. These findings indicate that nuclear actin must be tightly regulated during oogenesis. One factor mediating this regulation is Fascin. Overexpression of Fascin enhances nuclear GFP-Actin rod formation, and Fascin colocalizes with the rods. Loss of Fascin reduces, while overexpression of Fascin increases, the frequency of nurse cells with high levels of nuclear actin; but neither alters the overall nuclear level of actin within the ovary. These data suggest that Fascin regulates the ability of specific cells to accumulate nuclear actin. Evidence indicates Fascin positively regulates nuclear actin through Cofilin. Loss of Fascin results in decreased nuclear Cofilin. Additionally, Fascin and Cofilin genetically interact, as double heterozygotes exhibit a reduction in the number of nurse cells with high nuclear actin levels. These findings are likely applicable beyond Drosophila follicle development, as the localization and functions of Fascin, and the mechanisms regulating nuclear actin, are widely conserved.
Wen, K., Yang, L., Xiong, T., Di, C., Ma, D., Wu, M., Xue, Z., Zhang, X., Long, L., Zhang, W., Zhang, J., Bi, X., Dai, J., Zhang, Q., Lu, Z. J. and Gao, G. (2016). Critical roles of long noncoding RNAs in Drosophila spermatogenesis. Genome Res 26: 1233-1244. PubMed ID: 27516619
Long noncoding RNAs (lncRNAs), a recently discovered class of cellular RNAs, play important roles in the regulation of many cellular developmental processes. Although lncRNAs have been systematically identified in various systems, most of them have not been functionally characterized in vivo in animal models. This study identified 128 testis-specific Drosophila lncRNAs and knocked out 105 of them using an optimized three-component CRISPR/Cas9 system. Among the lncRNA knockouts, 33 (31%) exhibited a partial or complete loss of male fertility, accompanied by visual developmental defects in late spermatogenesis. In addition, six knockouts were fully or partially rescued by transgenes in a trans configuration, indicating that those lncRNAs primarily work in trans Furthermore, gene expression profiles for five lncRNA mutants revealed that testis-specific lncRNAs regulate global gene expression, orchestrating late male germ cell differentiation. Compared with coding genes, the testis-specific lncRNAs evolved much faster. Moreover, lncRNAs of greater functional importance exhibited higher sequence conservation, suggesting that they are under constant evolutionary selection. Collectively, these results reveal critical functions of rapidly evolving testis-specific lncRNAs in late Drosophila spermatogenesis.
Klein, J.D., Qu, C., Yang, X., Fan, Y., Tang, C. and Peng, J.C. (2016). c-Fos repression by Piwi regulates Drosophila ovarian germline formation and tissue morphogenesis. PLoS Genet 12: e1006281. PubMed ID: 27622269
Drosophila melanogaster Piwi functions within the germline stem cells (GSCs) and the somatic niche to regulate GSC self-renewal and differentiation. How Piwi influences GSCs is largely unknown. This study uncovered a genetic interaction between Piwi and c-Fos in the somatic niche that influences GSCs. c-Fos is a proto-oncogene that influences many cell and developmental processes. In wild-type ovarian cells, c-Fos is post-transcriptionally repressed by Piwi, which destabilizes the c-Fos mRNA by promoting the processing of its 3' untranslated region (UTR) into Piwi-interacting RNAs (piRNAs). The c-Fos 3' UTR is sufficient to trigger Piwi-dependent destabilization of a GFP reporter. Piwi represses c-Fos in the somatic niche to regulate GSC maintenance and differentiation and in the somatic follicle cells to affect somatic cell disorganization, tissue dysmorphogenesis, oocyte maturation arrest, and infertility.
Dubey, P., Shirolikar, S. and Ray, K. (2016). Localized, reactive F-actin dynamics prevents abnormal somatic cell penetration by mature spermatids. Dev Cell [Epub ahead of print]. PubMed ID: 27546008
Spermatogenesis occurs inside a somatic cell enclosure. Sperm release, the most important final step and a target for contraceptives, has been extensively studied in fixed tissue preparations. This study provides a time-lapse description of the release process in Drosophila testis ex vivo. The spermatid tails exit the somatic enclosure and enter the testicular duct first, followed by the spermatid heads. Prior to this, individual spermatid heads attempt to invade the head cyst cell, and on each occasion they are repelled by a rapid and local F-actin polymerization response from the head cyst cell. The F-actin assembly involves N-WASp, D-WIP, and Arp2/3 complex and dissipates once the spermatid head retreats back into the fold. These findings revise the existing spermiation model in Drosophila and suggest that somatic cells can actively oppose mechanical cell invasion attempts using calibrated F-actin dynamics in situ.

Tuesday, September 20th

Sakuma, C., Saito, Y., Umehara, T., Kamimura, K., Maeda, N., Mosca, T. J., Miura, M. and Chihara, T. (2016). The Strip-Hippo pathway regulates synaptic terminal formation by modulating actin organization at the Drosophila neuromuscular synapses. Cell Rep 16: 2289-2297. PubMed ID: 27545887
Synapse formation requires the precise coordination of axon elongation, cytoskeletal stability, and diverse modes of cell signaling. The underlying mechanisms of this interplay, however, remain unclear. This study demonstrates that Strip, a component of the striatin-interacting phosphatase and kinase (STRIPAK) complex that regulates these processes, is required to ensure the proper development of synaptic boutons at the Drosophila neuromuscular junction. In doing so, Strip negatively regulates the activity of the Hippo (Hpo) pathway, an evolutionarily conserved regulator of organ size whose role in synapse formation is currently unappreciated. Strip functions genetically with Enabled, an actin assembly/elongation factor and the presumptive downstream target of Hpo signaling, to modulate local actin organization at synaptic termini. This regulation occurs independently of the transcriptional co-activator Yorkie, the canonical downstream target of the Hpo pathway. This study identifies a previously unanticipated role of the Strip-Hippo pathway in synaptic development, linking cell signaling to actin organization.
Bohme, M. A., Beis, C., Reddy-Alla, S., Reynolds, E., Mampell, M. M., Grasskamp, A. T., Lutzkendorf, J., Bergeron, D. D., Driller, J. H., Babikir, H., Gottfert, F., Robinson, I. M., O'Kane, C. J., Hell, S. W., Wahl, M. C., Stelzl, U., Loll, B., Walter, A. M. and Sigrist, S. J. (2016). Active zone scaffolds differentially accumulate Unc13 isoforms to tune Ca2+ channel-vesicle coupling. Nat Neurosci [Epub ahead of print]. PubMed ID: 27526206
Brain function relies on fast and precisely timed synaptic vesicle (SV) release at active zones (AZs). Efficacy of SV release depends on distance from SV to Ca2+ channel, but molecular mechanisms controlling this are unknown. This study found that distances can be defined by targeting two unc-13 (Unc13) isoforms to presynaptic AZ subdomains. Super-resolution and intravital imaging of developing Drosophila melanogaster glutamatergic synapses revealed that the Unc13B isoform was recruited to nascent AZs by the scaffolding proteins Syd-1 and Liprin-alpha, and Unc13A was positioned by Bruchpilot and Rim-binding protein complexes at maturing AZs. Unc13B localized 120 nm away from Ca2+ channels, whereas Unc13A localized only 70 nm away and was responsible for docking SVs at this distance. Unc13Anull mutants suffered from inefficient, delayed and EGTA-supersensitive release. Mathematical modeling suggested that synapses normally operate via two independent release pathways differentially positioned by either isoform. Isoform-specific Unc13-AZ scaffold interactions were identified, regulating SV-Ca2+-channel topology whose developmental tightening optimizes synaptic transmission.
Wang, T., Jones, R. T., Whippen, J. M. and Davis, G. W. (2016). α2δ-3 is required for rapid transsynaptic homeostatic signaling. Cell Rep 16: 2875-2888. PubMed ID: 27626659
The homeostatic modulation of neurotransmitter release, termed presynaptic homeostatic potentiation (PHP), is a fundamental type of neuromodulation, conserved from Drosophila to humans, that stabilizes information transfer at synaptic connections throughout the nervous system. This study demonstrates that α2δ-3 (straitjacket), an auxiliary subunit of the presynaptic calcium channel, is required for PHP. The α2δ gene family has been linked to chronic pain, epilepsy, autism, and the action of two psychiatric drugs: gabapentin and pregabalin. Loss of α2δ-3 blocks both the rapid induction and sustained expression of PHP due to a failure to potentiate presynaptic calcium influx and the RIM-dependent readily releasable vesicle pool. These deficits are independent of α2δ-3-mediated regulation of baseline calcium influx and presynaptic action potential waveform. α2δ proteins reside at the extracellular face of presynaptic release sites throughout the nervous system, a site ideal for mediating rapid, transsynaptic homeostatic signaling in health and disease.
Sheng, N., Shi, Y. S., Lomash, R. M., Roche, K. W. and Nicoll, R. A. (2015). Neto auxiliary proteins control both the trafficking and biophysical properties of the kainate receptor GluK1. Elife 4. PubMed ID: 26720915
Evolutionary Homolog Study
Kainate receptors (KARs) are a subfamily of glutamate receptors mediating excitatory synaptic transmission and Neto proteins (see Drosophila Neto) are recently identified auxiliary subunits for KARs. However, the roles of Neto proteins in the synaptic trafficking of KAR GluK1 are poorly understood. Using the hippocampal CA1 pyramidal neuron as a null background system this study found that surface expression of GluK1 receptor itself is very limited and is not targeted to excitatory synapses. Both Neto1 and Neto2 profoundly increase GluK1 surface expression and also drive GluK1 to synapses. However, the regulation GluK1 synaptic targeting by Neto proteins is independent of their role in promoting surface trafficking. Interestingly, GluK1 is excluded from synapses expressing AMPA receptors and is selectively incorporated into silent synapses. Neto2, but not Neto1, slows GluK1 deactivation, whereas Neto1 speeds GluK1 desensitization and Neto2 slows desensitization. These results establish critical roles for Neto auxiliary subunits controlling KARs properties and synaptic incorporation.

Mahoney, R. E., Azpurua, J. and Eaton, B. A. (2016). Insulin signaling controls neurotransmission via the 4eBP-dependent modification of the exocytotic machinery. Elife 5. PubMed ID: 27525480
Altered insulin signaling has been linked to widespread nervous system dysfunction including cognitive dysfunction, neuropathy and susceptibility to neurodegenerative disease. However, knowledge of the cellular mechanisms underlying the effects of insulin on neuronal function is incomplete. This study shows that cell autonomous insulin signaling within the Drosophila CM9 motor neuron regulates the release of neurotransmitter via alteration of the synaptic vesicle fusion machinery. This effect of insulin utilizes the FOXO-dependent regulation of the thor gene, which encodes the Drosophila homologue of the eif-4e binding protein (4eBP). A critical target of this regulatory mechanism is Complexin, a synaptic protein known to regulate synaptic vesicle exocytosis. The amounts of Complexin protein observed at the synapse was found to be regulated by insulin, and genetic manipulations of Complexin levels support the model that increased synaptic Complexin reduces neurotransmission in response to insulin signaling.
Miki, T., Malagon, G., Pulido, C., Llano, I., Neher, E. and Marty, A. (2016). Actin- and myosin-dependent vesicle loading of presynaptic docking sites prior to exocytosis. Neuron 91: 808-823. PubMed ID: 27537485
Evolutionary Homolog Study
Variance analysis of postsynaptic current amplitudes suggests the presence of distinct docking sites (also called release sites) where vesicles pause before exocytosis. Docked vesicles participate in the readily releasable pool (RRP), but the relation between docking site number and RRP size remains unclear. It is also unclear whether all vesicles of the RRP are equally release competent, and what cellular mechanisms underlie RRP renewal. This study addressed these questions at single glutamatergic synapses, counting released vesicles using deconvolution. A remarkably low variance of cumulative vesicle counts during action potential trains. This, combined with Monte Carlo simulations, indicates that vesicles transit through two successive states before exocytosis, so that the RRP is up to 2-fold higher than the docking site number. The transition to the second state has a very rapid rate constant, and is specifically inhibited by latrunculin B and blebbistatin, suggesting the involvement of actin and myosin.

Monday, September 19th

Fairchild, M.J., Yang, L., Goodwin, K. and Tanentzapf, G. (2016). Occluding junctions maintain stem cell niche homeostasis in the fly testes. Curr Biol [Epub ahead of print]. PubMed ID: 27546574
Stem cells can be controlled by their local microenvironment, known as the stem cell niche. The Drosophila testes contain a morphologically distinct niche called the hub, composed of a cluster of between 8 and 20 cells known as hub cells, which contact and regulate germline stem cells (GSCs) and somatic cyst stem cells (CySCs). Both hub cells and CySCs originate from somatic gonadal precursor cells during embryogenesis, but whereas hub cells, once specified, cease all mitotic activity, CySCs remain mitotic into adulthood. Cyst cells, derived from the CySCs, first encapsulate the germline and then, using occluding junctions, form an isolating permeability barrier. This barrier promotes germline differentiation by excluding niche-derived stem cell maintenance factors. This study shows that the somatic permeability barrier is also required to regulate stem cell niche homeostasis. Loss of occluding junction components in the somatic cells results in hub overgrowth. Enlarged hubs are active and recruit more GSCs and CySCs to the niche. Surprisingly, hub growth results from depletion of occluding junction components in cyst cells, not from depletion in the hub cells themselves. Moreover, hub growth is caused by incorporation of cells that previously express markers for cyst cells and not by hub cell proliferation. Importantly, depletion of occluding junctions disrupts Notch and mitogen-activated protein kinase (MAPK) signaling, and hub overgrowth defects are partially rescued by modulation of either signaling pathway. Overall, these data show that occluding junctions shape the signaling environment between the soma and the germline in order to maintain niche homeostasis.

Wigby, S., Perry, J. C., Kim, Y. H. and Sirot, L. K. (2016). Developmental environment mediates male seminal protein investment in Drosophila melanogaster. Funct Ecol 30: 410-419. PubMed ID: 27546947
Males of many species fine-tune their ejaculates in response to sperm competition risk. This study manipulated the developmental environment of Drosophila by rearing flies at low and high density, resulting in large and small adult phenotypes, respectively. Large males produced more of two key seminal proteins, sex peptide (SP) and ovulin, and were more successful at obtaining matings with both virgin and previously mated females. However, there was only a weak and non-significant trend for large males to transfer more absolute quantities of SP at mating, and thus, small males ejaculated proportionally more of their stored accessory gland SP resources. Males transferred more receptivity-inhibiting SP to large females. Despite this, large females remated more quickly than small females and thus responded to their developmental environment over and above the quantity of SP they received. The results are consistent with two non-mutually exclusive hypotheses. First, flies might respond to condition-dependent reproductive opportunities, with (1) small males investing heavily in ejaculates when mating opportunities arise and large males strategically partitioning SP resources and (2) small females remating at reduced rates because they have higher mating costs or need to replenish sperm less often. Second, flies may be primed by their larval environment to deal with similar adult population densities, with (1) males perceiving high density as signalling increased competition, leading small males to invest proportionally more SP resources at mating and (2) females perceiving high density as signalling abundant potential mates, leading to a higher sexual receptivity threshold. Thus, by influencing the mating frequencies of both sexes, as well as the quantity of seminal proteins produced by males and received by females, the developmental environment is likely to have far-reaching and sex-specific consequences for sexual selection and sexual conflict.
Fregoso Lomas, M., De Vito, S., Boisclair Lachance, J.F., Houde, J. and Nilson, L.A. (2016). Determination of EGFR signaling output by opposing gradients of BMP and JAK/STAT activity. Curr Biol [Epub ahead of print]. PubMed ID: 27593379
A relatively small number of signaling pathways drive a wide range of developmental decisions, but how this versatility in signaling outcome is generated is not clear. In the Drosophila follicular epithelium, localized epidermal growth factor receptor (EGFR) activation induces distinct cell fates depending on its location. Posterior follicle cells respond to EGFR activity by expressing the T-box transcription factors Midline and H15, while anterior cells respond by expressing the homeodomain transcription factor Mirror. This study shows that the choice between these alternative outputs of EGFR signaling is regulated by antiparallel gradients of JAK/STAT and BMP pathway activity and that mutual repression between Midline/H15 and Mirror generates a bistable switch that toggles between alternative EGFR signaling outcomes. JAK/STAT and BMP pathway input is integrated through their joint and opposing regulation of both sides of this switch. By converting this positional information into a binary decision between EGFR signaling outcomes, this regulatory network ultimately allows the same ligand-receptor pair to establish both the anterior-posterior (AP) and dorsal-ventral (DV) axes of the issue.

Zhang, T., Oatley, J., Bardwell, V.J. and Zarkower, D. (2016). DMRT1 is required for mouse spermatogonial stem cell maintenance and replenishment. PLoS Genet 12: e1006293. PubMed ID: 27583450
Evolutionary Homolog Study
Male mammals produce sperm for most of postnatal life and therefore require a robust germ line stem cell system (see Drosophila spermatogenesis), with precise balance between self-renewal and differentiation. Prior work has established doublesex- and mab-3-related transcription factor 1 (Dmrt1) (see Drosophila dsx) as a conserved transcriptional regulator of male sexual differentiation. This study investigated the role of Dmrt1 in mouse spermatogonial stem cell (SSC) homeostasis. It was found that Dmrt1 maintains SSCs during steady state spermatogenesis, where it regulates expression of Plzf (see Drosophila CG4424), another transcription factor required for SSC maintenance. Dmrt1 is required for recovery of spermatogenesis after germ cell depletion. Committed progenitor cells expressing Ngn3 (see Drosophila tap) normally do not contribute to SSCs marked by the Id4-Gfp (see Drosophila emc) transgene, but do so when spermatogonia are chemically depleted using busulfan. Removal of Dmrt1 from Ngn3-positive germ cells blocks the replenishment of Id4-GFP-positive SSCs and recovery of spermatogenesis after busulfan treatment. These data therefore reveal that Dmrt1 supports SSC maintenance in two ways: allowing SSCs to remain in the stem cell pool under normal conditions; and enabling progenitor cells to help restore the stem cell pool after germ cell depletion.

Sunday, September 18th

Stepanik, V., Dunipace, L., Bae, Y.K., Macabenta, F., Sun, J., Trisnadi, N. and Stathopoulos, A. (2016). The migrations of Drosophila muscle founders and primordial germ cells are interdependent. Development 143: 3206-3215. PubMed ID: 27578182
Caudal visceral mesoderm (CVM) cells migrate from posterior to anterior of the Drosophila embryo as two bilateral streams of cells to support the specification of longitudinal muscles along the midgut. To accomplish this long-distance migration, CVM cells receive input from their environment, but little is known about how this collective cell migration is regulated. In a screen, it was found that wunen mutants exhibit CVM cell migration defects. Wunens are lipid phosphate phosphatases known to regulate the directional migration of primordial germ cells (PGCs). PGC and CVM cell types interact while PGCs are en route to the somatic gonadal mesoderm, and previous studies have shown that CVM impacts PGC migration. In turn, it was found that CVM cells exhibit an affinity for PGCs, localizing to the position of PGCs whether mislocalized or trapped in the endoderm. In the absence of PGCs, CVM cells exhibit subtle changes, including more cohesive movement of the migrating collective, and an increased number of longitudinal muscles is found at anterior sections of the larval midgut. These data demonstrate that PGC and CVM cell migrations are interdependent and suggest that distinct migrating cell types can coordinately influence each other to promote effective cell migration during development. 

Hanlon, C.D. and Andrew, D.J. (2016). Drosophila FoxL1 non-autonomously coordinates organ placement during embryonic development. Dev Biol [Epub ahead of print]. PubMed ID: 27618755
Determining how organs attain precise positioning within an organism is a crucial facet of developmental biology. The Fox family winged-helix transcription factors are known to play key roles in development of multiple organs. Drosophila FoxL1 (aka Fd64A) is dynamically expressed in embryos but its function is completely uncharacterized. FoxL1 is expressed in a single group of body wall - muscles in the 2nd and 3rd thoracic segments, in homologous abdominal muscles at earlier stages, and in the hindgut mesoderm from early through late embryogenesis. This study shows that FoxL1 expression in T2 and T3 is in VIS5, which is not a single muscle spanning the entire thorax, as previously published, but is, instead, three individual muscles, each spanning a single thoracic segment. foxL1 mutations were generated and it was found that, surprisingly, none of the tissues that express FoxL1 are affected by its loss. Instead, loss of foxL1 results in defects in salivary gland positioning and morphology, as well as defects in the migration of hemocytes, germ cells and Malpighian tubules. Also, FoxL1-dependent expression of secreted Sema2a in T3 VIS5 is required for normal salivary gland positioning. Altogether, these findings suggest that Drosophila FoxL1 functions like its mammalian counterpart in non-autonomously orchestrating the behaviors of surrounding tissues.

Clark, E. and Akam, M. (2016). Odd-paired controls frequency doubling in Drosophila segmentation by altering the pair-rule gene regulatory network. Elife [Epub ahead of print]. PubMed ID: 27525481
The Drosophila embryo transiently exhibits a double segment periodicity, defined by the expression of seven "pair-rule" genes, each in a pattern of seven stripes. At gastrulation, interactions between the pair-rule genes lead to frequency doubling and the patterning of fourteen parasegment boundaries. In contrast to earlier stages of Drosophila anteroposterior patterning, this transition is not well understood. By carefully analysing the spatiotemporal dynamics of pair-rule gene expression, this study demonstrates that frequency-doubling is precipitated by multiple coordinated changes to the network of regulatory interactions between the pair-rule genes. The broadly expressed but temporally patterned transcription factor, Odd-paired (Opa/Zic), was identified to be the cause of these changes. The patterning of the even-numbered parasegment boundaries relies on Opa-dependent regulatory interactions. These findings indicate that the pair-rule gene regulatory network has a temporally-modulated topology, permitting the pair-rule genes to play stage-specific patterning roles.

Nakamura, T., Gehrke, A. R., Lemberg, J., Szymaszek, J. and Shubin, N. H. (2016). Digits and fin rays share common developmental histories. Nature 537: 225-228. PubMed ID: 27533041
Evolutionary Homolog Study:
Understanding the evolutionary transformation of fish fins into tetrapod limbs is a fundamental problem in biology. The search for antecedents of tetrapod digits in fish has remained controversial because the distal skeletons of limbs and fins differ structurally, developmentally, and histologically. Moreover, comparisons of fins with limbs have been limited by a relative paucity of data on the cellular and molecular processes underlying the development of the fin skeleton. This study provides a functional analysis, using CRISPR/Cas9 and fate mapping, of 5' hox genes and enhancers in zebrafish that are indispensable for the development of the wrists and digits of tetrapods. Cells marked by the activity of an autopodial hoxa13 (see Drosophila Abd-B) enhancer exclusively form elements of the fin fold, including the osteoblasts of the dermal rays. In hox13 knockout fish, a marked reduction and loss of fin rays was found to be associated with an increased number of endochondral distal radials. These discoveries reveal a cellular and genetic connection between the fin rays of fish and the digits of tetrapods and suggest that digits originated via the transition of distal cellular fates.

Saturday, September 17th

Börner, K. and Becker, P.B. (2016). Splice variants of the SWR1-type nucleosome remodeling factor Domino have distinct functions during Drosophila melanogaster oogenesis. Development 143: 3154-3167. PubMed ID: 27578180
SWR1-type nucleosome remodeling factors replace histone H2A by variants to endow chromatin locally with specialized functionality. In Drosophila melanogaster a single H2A variant, H2A.V, combines functions of mammalian H2A.Z and H2A.X in transcription regulation and the DNA damage response. A major role in H2A.V incorporation for the only SWR1-like enzyme in flies, Domino, is assumed but not well documented in vivo. It is also unclear whether the two alternatively spliced isoforms, DOM-A and DOM-B, have redundant or specialized functions. Loss of both DOM isoforms compromises oogenesis, causing female sterility. This study systematically explored roles of the two DOM isoforms during oogenesis using a cell type-specific knockdown approach. Despite their ubiquitous expression, DOM-A and DOM-B have non-redundant functions in germline and soma for egg formation. It was shown that chromatin incorporation of H2A.V in germline and somatic cells depends on DOM-B, whereas global incorporation in endoreplicating germline nurse cells appears to be independent of DOM. By contrast, DOM-A promotes the removal of H2A.V from stage 5 nurse cells. Remarkably, therefore, the two DOM isoforms have distinct functions in cell type-specific development and H2A.V exchange. 

Seelk, S., Adrian-Kalchhauser, I., Hargitai, B., Hajduskova, M., Gutnik, S., Tursun, B. and Ciosk, R. (2016). Increasing Notch signaling antagonizes PRC2-mediated silencing to promote reprogramming of germ cells into neurons. Elife [Epub ahead of print]. PubMed ID: 27602485
Evolutionary Homolog Study
Cell-fate reprogramming is at the heart of development, yet very little is known about the molecular mechanisms promoting or inhibiting reprogramming in intact organisms. In the C. elegans germline, reprogramming germ cells into somatic cells requires chromatin perturbation. This study shows that such reprogramming is facilitated by GLP-1/Notch (see Drosophila Notch) signaling pathway. This is surprising, since this pathway is best known for maintaining undifferentiated germline stem cells/progenitors (see Drosophila germline). Through a combination of genetics, tissue-specific transcriptome analysis, and functional studies of candidate genes, a possible explanation for this unexpected role of GLP-1/Notch was uncovered. The study proposes that GLP-1/Notch promotes reprogramming by activating specific genes, silenced by the Polycomb repressive complex 2 (PRC2) (see Drosophila E(z)), and identifies the conserved histone demethylase UTX-1 (see Drosophila Utx) as a crucial GLP-1/Notch target facilitating reprogramming. These findings have wide implications, ranging from development to diseases associated with abnormal Notch signaling.

Lee, H., Cho, D.Y., Whitworth, C., Eisman, R., Phelps, M., Roote, J., Kaufman, T., Cook, K., Russell, S., Przytycka, T. and Oliver, B. (2016). Effects of gene dose, chromatin, and network topology on expression in Drosophila melanogaster. PLoS Genet 12: e1006295. PubMed ID: 27599372
Deletions, commonly referred to as deficiencies by Drosophila geneticists, are valuable tools for mapping genes and for genetic pathway discovery via dose-dependent suppressor and enhancer screens. More recently, it has become clear that deviations from normal gene dosage are associated with multiple disorders in a range of species including humans. While some of the transcriptional effects brought about by gene dosage changes and the chromosome rearrangement breakpoints associated with them are beginning to be understood, much of this work relies on isolated examples. This study systematically examined deficiencies of the left arm of chromosome 2 and characterized gene-by-gene dosage responses that vary from collapsed expression through modest partial dosage compensation to full or even over compensation. Negligible long-range effects of creating novel chromosome domains at deletion breakpoints were found, suggesting that cases of gene regulation due to altered nuclear architecture are rare. These rare cases include trans de-repression when deficiencies delete chromatin characterized as repressive in other studies. Generally, effects of breakpoints on expression are promoter proximal (~100bp) or in the gene body. Effects of deficiencies genome-wide are in genes with regulatory relationships to genes within the deleted segments, highlighting the subtle expression network defects in these sensitized genetic backgrounds.

Alvi, Z. A., Chu, T. C., Schawaroch, V. and Klaus, A. V. (2015). Genomic and expression analysis of transition proteins in Drosophila. Spermatogenesis 5: e1178518. PubMed ID: 27512614
This study analyzed putative protein sequences of the transition protein-like proteins in 12 Drosophila species based on the reference sequences of transition protein-like protein (Tpl94D) expressed in Drosophila melanogaster sperm nuclei. Transition proteins aid in transforming chromatin from a histone-based nucleosome structure to a protamine-based structure during spermiogenesis - the post-meiotic stage of spermatogenesis. Sequences were obtained from NCBI Ref-Seq database using NCBI ORF-Finder (PSI-BLAST). Sequence alignments and analysis of the amino acid content indicate that orthologs for Tpl94D are present in the melanogaster species subgroup (D. simulans, D. sechellia, D. erecta, and D. yakuba), D. ananassae, and D. pseudoobscura, but absent in D. persmilis, D. willistoni, D. mojavensis, D. virilis, and D. grimshawi. Transcriptome next generation sequence (RNA-Seq) data for testes and ovaries was used to conduct differential gene expression analysis for Tpl94D in D. melanogaster, D. simulans, D. yakuba, D. ananassae, and D. pseudoobscura. The identified Tpl94D orthologs show high expression in the testes as compared to the ovaries. Additionally, 2 isoforms of Tpl94D were detected in D. melanogaster with isoform A being much more highly expressed than isoform B. Functional analyses of the conserved region revealed that the same high mobility group (HMG) box/DNA binding region is conserved for both Drosophila Tpl94D and Drosophila protamine-like proteins (MST35Ba and MST35Bb). Based on the rigorous bioinformatic approach and the conservation of the HMG box reported in this work, it is suggested that the Drosophila Tpl94D orthologs should be classified as their own transition protein group.

Friday, September 16th

Ren, Q., Awasaki, T., Huang, Y.F., Liu, Z. and Lee, T. (2016). Cell class-lineage analysis reveals sexually dimorphic lineage compositions in the Drosophila brain. Curr Biol [Epub ahead of print]. PubMed ID: 27618265
The morphology and physiology of neurons are directed by developmental decisions made within their lines of descent from single stem cells. Distinct stem cells may produce neurons having shared properties that define their cell class, such as the type of secreted neurotransmitter. This study developed the transgenic cell class-lineage intersection (CLIn) system to assign cells of a particular class to specific lineages within the Drosophila brain. CLIn also enables birth-order analysis and genetic manipulation of particular cell classes arising from particular lineages. The power of CLIn was demonstrated in the context of the eight central brain type II lineages, which produce highly diverse progeny through intermediate neural progenitors. 18 dopaminergic neurons from three distinct clusters were mapped to six type II lineages that show lineage-characteristic neurite trajectories. In addition, morphologically distinct dopaminergic neurons are produced within a given lineage, and they arise in an invariant sequence. Type II lineages that produce doublesex- and fruitless-expressing neurons were identified, and whether female-specific apoptosis in these lineages accounts for the lower number of these neurons in the female brain was examined. Blocking apoptosis in these lineages results in more cells in both sexes with males still carrying more cells than females. This argues that sex-specific stem cell fate together with differential progeny apoptosis contribute to the final sexual dimorphism.
Thompson-Peer, K. L., DeVault, L., Li, T., Jan, L. Y. and Jan, Y. N. (2016). In vivo dendrite regeneration after injury is different from dendrite development. Genes Dev 30: 1776-1789. PubMed ID: 27542831
Neurons receive information along dendrites and send signals along axons to synaptic contacts. The factors that control axon regeneration have been examined in many systems, but dendrite regeneration has been largely unexplored. This study reports that, in intact Drosophila larvae, a discrete injury that removes all dendrites induces robust dendritic growth that recreates many features of uninjured dendrites, including the number of dendrite branches that regenerate and responsiveness to sensory stimuli. However, the growth and patterning of injury-induced dendrites is significantly different from uninjured dendrites. Regenerated arbors cover much less territory than uninjured neurons, fail to avoid crossing over other branches from the same neuron, respond less strongly to mechanical stimuli, and are pruned precociously. Finally, silencing the electrical activity of the neurons specifically blocks injury-induced, but not developmental, dendrite growth. By elucidating the essential features of dendrites grown in response to acute injury, this work builds a framework for exploring dendrite regeneration in physiological and pathological conditions.
Fitzgerald, J. E. and Clark, D. A. (2015). Nonlinear circuits for naturalistic visual motion estimation. Elife 4: e09123. PubMed ID: 26499494
Many animals use visual signals to estimate motion. Canonical models suppose that animals estimate motion by cross-correlating pairs of spatiotemporally separated visual signals, but recent experiments indicate that humans and flies perceive motion from higher-order correlations that signify motion in natural environments. This study shows how biologically plausible processing motifs in neural circuits could be tuned to extract this information. Known aspects of Drosophila's visual circuitry can embody this tuning and predict fly behavior. Segregating motion signals into ON/OFF channels can enhance estimation accuracy by accounting for natural light/dark asymmetries. Furthermore, a diversity of inputs to motion detecting neurons can provide access to more complex higher-order correlations. Collectively, these results illustrate how non-canonical computations improve motion estimation with naturalistic inputs. This argues that the complexity of the fly's motion computations, implemented in its elaborate circuits, represents a valuable feature of its visual motion estimator.
Hückesfeld, S., Peters, M. and Pankratz, M.J. (2016). Central relay of bitter taste to the protocerebrum by peptidergic interneurons in the Drosophila brain. Nat Commun 7: 12796. PubMed ID: 27619503
Bitter is a taste modality associated with toxic substances evoking aversive behaviour in most animals, and the valence of different taste modalities is conserved between mammals and Drosophila. Despite knowledge gathered in the past on the peripheral perception of taste, little is known about the identity of taste interneurons in the brain. This study shows that hugin neuropeptide-containing neurons in the Drosophila larval brain are necessary for avoidance behaviour to caffeine, and when activated, result in cessation of feeding and mediates a bitter taste signal within the brain. Hugin neuropeptide-containing neurons project to the neurosecretory region of the protocerebrum and functional imaging demonstrates that these neurons are activated by bitter stimuli and by activation of bitter sensory receptor neurons. The study proposes that hugin neurons projecting to the protocerebrum act as gustatory interneurons relaying bitter taste information to higher brain centres in Drosophila larvae.

Reichert, M. C., Brown, H. E. and Evans, T. A. (2016). In vivo functional analysis of Drosophila Robo1 immunoglobulin-like domains. Neural Dev 11: 15. PubMed ID: 27539083
In animals with bilateral symmetry, midline crossing of axons in the developing central nervous system is regulated by Slit ligands and their neuronal Roundabout (Robo) receptors. Multiple structural domains are present in an evolutionarily conserved arrangement in Robo family proteins, but understanding of the functional importance of individual domains for midline repulsive signaling is limited. This study has examined the functional importance of each of the five conserved immunoglobulin-like (Ig) domains within the Drosophila Robo1 receptor. A series of Robo1 variants were generated, each lacking one of the five Ig domains (Ig1-5), and each was tested for its ability to bind Slit when expressed in cultured Drosophila cells. A transgenic approach was used to express each variant in robo1's normal expression pattern in wild-type and robo1 mutant embryos. Individual deletion of Ig domains 2-5 does not interfere with Robo1's ability to bind Slit, while deletion of Ig1 strongly disrupts Slit binding. None of the five Ig domains (Ig1-5) are individually required for proper expression of Robo1 in embryonic neurons, for exclusion from commissural axon segments in wild-type embryos, or for downregulation by Commissureless (Comm), a negative regulator of Slit-Robo repulsion in Drosophila. Each of the Robo1 Ig deletion variants (with the exception of Robo1Ig1) were able to restore midline crossing in robo1 mutant embryos to nearly the same extent as full-length Robo1, indicating that Ig domains 2-5 are individually dispensable for midline repulsive signaling in vivo. These findings indicate that four of the five Ig domains within Drosophila Robo1 are dispensable for its role in midline repulsion, despite their strong evolutionary conservation, and highlight a unique requirement for the Slit-binding Ig1 domain in the regulation of midline crossing.
Alvarez-Rivero, J., Moris-Sanz, M., Estacio-Gomez, A., Montoliu-Nerin, M., Diaz-Benjumea, F. J. and Herrero, P. (2016). Variability in the number of abdominal leucokinergic neurons in adult Drosophila melanogaster. J Comp Neurol [Epub ahead of print]. PubMed ID: 27506156
Developmental plasticity allows individuals with the same genotype to show different phenotypes in response to environmental changes. An example of this is how neuronal diversity is protected at the expense of neuronal number under sustained undernourishment during the development of the Drosophila optic lobe. In the development of the Drosophila central nervous system, neuroblasts go through two phases of neurogenesis separated by a period of mitotic quiescence. Although during embryonic development much evidence indicates that both cell number and the cell fates generated by each neuroblast are very precisely controlled in a cell autonomous manner, after quiescence extrinsic factors control the reactivation of neuroblast proliferation in a poorly understood manner. Moreover, there is very little information about whether environmental changes affect lineage progression during postembryonic neurogenesis. Using as a model system the pattern of abdominal leucokinergic neurons (ABLKs), this study analysed how changes in a set of environmental factors affect the number of ABLKs generated during postembryonic neurogenesis. The variability in ABLK number between individuals and between hemiganglia of the same individual is described and, by genetic analysis, the Bithorax-Complex genes and the Ecdysone hormone were identified as critical factors in these differences. The possible adaptive roles involved in this process were explored.

Thursday, September 15th

Luo, H., Li, X., Claycomb, J.M. and Lipshitz, H.D. (2016). The Smaug RNA-binding protein is essential for microRNA synthesis during the Drosophila maternal-to-zygotic transition. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 27591754
Metazoan embryos undergo a maternal-to-zygotic transition (MZT) during which maternal gene products are eliminated and the zygotic genome becomes transcriptionally active. During this process RNA-binding proteins (RBPs) and the microRNA-induced silencing complex (miRISC) target maternal mRNAs for degradation. In Drosophila, the Smaug (SMG), Brain tumor (BRAT) and Pumilio (PUM) RBPs bind to and direct the degradation of largely distinct subsets of maternal mRNAs. SMG has also been shown to be required for zygotic synthesis of mRNAs and several members of the miR-309 family of microRNAs (miRNAs) during the MZT. This study carried out global analysis of small RNAs both in wild type and in smg mutants. It was found that 85% all miRNA species encoded by the genome are present during the MZT. Whereas loss of SMG has no detectable effect on Piwi-interacting RNAs (piRNAs) or small interfering RNAs (siRNAs), zygotic production of more than 70 species of miRNAs fails or is delayed in smg mutants. SMG is also required for the synthesis and stability of a key miRISC component, Argonaute 1 (AGO1), but plays no role in accumulation of the Argonaute-family proteins associated with piRNAs or siRNAs. In smg mutants, maternal mRNAs that are predicted targets of the SMG-dependent zygotic miRNAs fail to be cleared. BRAT and PUM share target mRNAs with these miRNAs but not with SMG itself. The study hypothesizes that SMG controls the MZT, not only through direct targeting of a subset of maternal mRNAs for degradation but, indirectly, through production and function of miRNAs and miRISC, which act together with BRAT and/or PUM to control clearance of a distinct subset of maternal mRNAs.

Guida, V., Cernilogar, F. M., Filograna, A., De Gregorio, R., Ishizu, H., Siomi, M. C., Schotta, G., Bellenchi, G. C. and Andrenacci, D. (2016). Production of small non-coding RNAs from the flamenco locus is regulated by the gypsy retrotransposon of Drosophila melanogaster. Genetics [Epub ahead of print]. PubMed ID: 27558137
Protective mechanisms based on RNA silencing directed against the propagation of transposable elements are highly conserved in eukaryotes. The control of transposable elements is mediated by small non-coding RNAs, which derive from transposon-rich heterochromatic regions that function as small RNA-generating loci. These clusters are transcribed and the precursor transcripts are processed to generate piRNAs and endo-siRNAs, which silence transposable elements in gonads and somatic tissues. The flamenco locus is a Drosophila melanogaster small RNA cluster that controls gypsy and other transposable elements, which has played an important role in understanding how small non-coding RNAs repress transposable elements. This study describe a cosuppression mechanism triggered by new euchromatic gypsy insertions in genetic backgrounds carrying flamenco alleles defective in gypsy suppression. The silencing of gypsy was found to be accompanied by the silencing of other transposons regulated by flamenco, and of specific flamenco sequences from which small RNAs against gypsy originate. This cosuppression mechanism seems to depend on a post-transcriptional regulation that involves both endo-siRNA and piRNA pathways and is associated with the occurrence of developmental defects. In conclusion, it is proposed that new gypsy euchromatic insertions trigger a post-transcriptional silencing of gypsy sense and antisense sequences, which modifies the flamenco activity. This cosuppression mechanism interferes with some developmental processes presumably by influencing the expression of specific genes.
Murphy, D., Cieply, B., Carstens, R., Ramamurthy, V. and Stoilov, P. (2016). The Musashi 1 controls the splicing of photoreceptor-specific exons in the vertebrate retina. PLoS Genet 12: e1006256. PubMed ID: 27541351
Evolutionary Homolog Study
Alternative pre-mRNA splicing expands the coding capacity of eukaryotic genomes, potentially enabling a limited number of genes to govern the development of complex anatomical structures. Alternative splicing is particularly prevalent in the vertebrate nervous system, where it is required for neuronal development and function. This study shows that photoreceptor cells (see photoreceptors in Drosophila), a type of sensory neuron, express a characteristic splicing program that affects a broad set of transcripts and is initiated prior to the development of the light sensing outer segments. Surprisingly, photoreceptors lack prototypical neuronal splicing factors and their splicing profile is driven to a significant degree by the Musashi 1 (MSI1) (see Drosophila Rbp6) protein. A striking feature of the photoreceptor splicing program are exons that display a "switch-like" pattern of high inclusion levels in photoreceptors and near complete exclusion outside of the retina. Several ubiquitously expressed genes that are involved in the biogenesis and function of primary cilia produce highly photoreceptor specific isoforms through use of such "switch-like" exons. These results suggest a potential role for alternative splicing in the development of photoreceptors and the conversion of their primary cilia to the light sensing outer segments.

Broyer, R., Monfort, E. and Wilhelm, J. E. (2016). Cup regulates oskar mRNA stability during oogenesis. Dev Biol [Epub ahead of print]. PubMed ID: 27554167
The proper regulation of the localization, translation, and stability of maternally deposited transcripts is essential for embryonic development in many organisms. These different forms of regulation are mediated by the various protein subunits of the ribonucleoprotein (RNP) complexes that assemble on maternal mRNAs. However, while many of the subunits that regulate the localization and translation of maternal transcripts have been identified, relatively little is known about how maternal mRNAs are stockpiled and stored in a stable form to support early development. One of the best characterized regulators of maternal transcripts is Cup - a broadly conserved component of the maternal RNP complex that in Drosophila acts as a translational repressor of the localized message oskar. This study found that loss of cup disrupts the localization of both the oskar mRNA and its associated proteins to the posterior pole of the developing oocyte. This defect is not due to a failure to specify the oocyte or to disruption of RNP transport. Rather, the localization defects are due to a drop in oskar mRNA levels in cup mutant egg chambers. Thus, in addition to its role in regulating oskar mRNA translation, Cup also plays a critical role in controlling the stability of the oskar transcript. This suggests that Cup is ideally positioned to coordinate the translational control function of the maternal RNP complex with its role in storing maternal transcripts in a stable form.

Wednesday, September 14th

Urrutia, H., Aleman, A. and Eivers, E. (2016). Drosophila Dullard functions as a Mad phosphatase to terminate BMP signaling. Sci Rep 6: 32269. PubMed ID: 27578171
Bone morphogenetic proteins (BMPs) are growth factors that provide essential signals for normal embryonic development and adult tissue homeostasis. A key step in initiating BMP signaling is ligand induced phosphorylation of receptor Smads (R-Smads) by type I receptor kinases, while linker phosphorylation of R-Smads has been shown to cause BMP signal termination. This study demonstrates that the phosphatase Dullard is involved in dephosphorylating the Drosophila R-Smad, Mad, and is integral in controlling BMP signal duration. A hypomorphic Dullard allele or Dullard knockdown leads to increased Mad phosphorylation levels, while Dullard overexpression results in reduced Mad phosphorylations. Co-immunoprecipitation binding assays demonstrate phosphorylated Mad and Dullard physically interact, while mutation of Dullard's phosphatase domain still allows Mad-Dullard interactions but abolishes its ability to regulate Mad phosphorylations. Finally, linker and C-terminally phosphorylated Mad can be regulated by one of two terminating mechanisms, degradation by proteasomes or dephosphorylation by the phosphatase Dullard.

Yu, Y., Huang, R., Ye, J., Zhang, V., Wu, C., Cheng, G., Jia, J. and Wang, L. (2016). Regulation of starvation-induced hyperactivity by insulin and glucagon signaling in adult Drosophila. Elife [Epub ahead of print]. PubMed ID: 27612383
Starvation induces sustained increase in locomotion, which facilitates food localization and acquisition and hence composes an important aspect of food-seeking behavior. This study investigated how nutritional states modulate starvation-induced hyperactivity in adult Drosophila. The receptor of adipokinetic hormone (AKHR), the insect analog of glucagon, is required for starvation-induced hyperactivity. AKHR is expressed in a small group of octopaminergic neurons in the brain. Silencing AKHR+ neurons and blocking octopamine signaling in these neurons eliminates starvation-induced hyperactivity, whereas activation of these neurons accelerates the onset of hyperactivity upon starvation. Neither AKHR nor AKHR+ neurons are involved in increased food consumption upon starvation, suggesting that starvation-induced hyperactivity and food consumption are independently regulated. Single cell analysis of AKHR+ neurons identified the co-expression of Drosophila insulin-like receptor (dInR), which imposes suppressive effect on starvation-induced hyperactivity. Therefore, insulin and glucagon signaling exert opposite effects on starvation-induced hyperactivity via a common neural target in Drosophila.

Galletta, B. J., Fagerstrom, C. J., Schoborg, T. A., McLamarrah, T. A., Ryniawec, J. M., Buster, D. W., Slep, K. C., Rogers, G. C. and Rusan, N. M. (2016). A centrosome interactome provides insight into organelle assembly and reveals a non-duplication role for Plk4. Nat Commun 7: 12476. PubMed ID: 27558293
The centrosome is the major microtubule-organizing centre of many cells, best known for its role in mitotic spindle organization. How the proteins of the centrosome are accurately assembled to carry out its many functions remains poorly understood. The non-membrane-bound nature of the centrosome dictates that protein-protein interactions drive its assembly and functions. To investigate this massive macromolecular organelle, a 'domain-level' centrosome interactome was generated using direct protein-protein interaction data from a focused yeast two-hybrid screen. Biochemistry, cell biology and the model organism Drosophila was then used to provide insight into the protein organization and kinase regulatory machinery required for centrosome assembly. Finally, a novel role for Plk4, the master regulator of centriole duplication, was identified. Plk4 phosphorylates Cep135 to properly position the essential centriole component Asterless. This interaction landscape affords a critical framework for research of normal and aberrant centrosomes.
Huang, P., Nedelcu, D., Watanabe, M., Jao, C., Kim, Y., Liu, J. and Salic, A. (2016). Cellular Cholesterol Directly Activates Smoothened in Hedgehog Signaling. Cell 166: 1176-1187 e1114. PubMed ID: 27545348
Evolutionary Homolog Study:
In vertebrates, sterols are necessary for Hedgehog signaling, a pathway critical in embryogenesis and cancer. Sterols activate the membrane protein Smoothened by binding its extracellular, cysteine-rich domain (CRD). Major unanswered questions concern the nature of the endogenous, activating sterol and the mechanism by which it regulates Smoothened. This study reports crystal structures of CRD complexed with sterols and alone, revealing that sterols induce a dramatic conformational change of the binding site, which is sufficient for Smoothened activation and is unique among CRD-containing receptors. Hedgehog signaling was shown to require sterol binding to Smoothened, and key residues for sterol recognition and activity were defined. Cholesterol itself was shown to bind and activate Smoothened. Furthermore, the effect of oxysterols is abolished in Smoothened mutants that retain activation by cholesterol and Hedgehog. It is proposed that the endogenous Smoothened activator is cholesterol, not oxysterols, and that vertebrate Hedgehog signaling controls Smoothened by regulating its access to cholesterol.

Tuesday, September 13th

Kahn, T.G., Dorafshan, E., Schultheis, D., Zare, A., Stenberg, P., Reim, I., Pirrotta, V. and Schwartz, Y.B. (2016). Interdependence of PRC1 and PRC2 for recruitment to Polycomb Response Elements. Nucleic Acids Res [Epub ahead of print]. PubMed ID: 27557709
Polycomb Group (PcG) proteins are epigenetic repressors essential for control of development and cell differentiation. They form multiple complexes of which PRC1 and PRC2 are evolutionary conserved and obligatory for repression. The targeting of PRC1 and PRC2 is poorly understood and has been proposed to be hierarchical and involve tri-methylation of histone H3 (H3K27me3) and/or monoubiquitylation of histone H2A (H2AK118ub). This study tested this hypothesis using the Drosophila model. It was discovered that neither H3K27me3 nor H2AK118ub is required for targeting PRC complexes to Polycomb Response Elements (PREs). PRC1 can bind PREs in the absence of PRC2 but at many PREs PRC2 requires PRC1 to be targeted. It was shown that one role of H3K27me3 is to allow PcG complexes anchored at PREs to interact with surrounding chromatin. In contrast, the bulk of H2AK118ub is unrelated to PcG repression. These findings radically change the view of how PcG repression is targeted and suggest that PRC1 and PRC2 can communicate independently of histone modifications.

Penke, T. J., McKay, D. J., Strahl, B. D., Matera, A. G. and Duronio, R. J. (2016). Direct interrogation of the role of H3K9 in metazoan heterochromatin function. Genes Dev [Epub ahead of print]. PubMed ID: 27566777
A defining feature of heterochromatin is methylation of Lys9 of histone H3 (H3K9me), a binding site for heterochromatin protein 1 (HP1). Although H3K9 methyltransferases and HP1 are necessary for proper heterochromatin structure, the specific contribution of H3K9 to heterochromatin function and animal development is unknown. Using a recently developed platform to engineer histone genes in Drosophila, H3K9R mutant flies were generated, separating the functions of H3K9 and nonhistone substrates of H3K9 methyltransferases. Nucleosome occupancy and HP1a binding at pericentromeric heterochromatin are markedly decreased in H3K9R mutants. Despite these changes in chromosome architecture, a small percentage of H3K9R mutants complete development. Consistent with this result, expression of most protein-coding genes, including those within heterochromatin, is similar between H3K9R and controls. In contrast, H3K9R mutants exhibit increased open chromatin and transcription from piRNA clusters and transposons, resulting in transposon mobilization. Hence, transposon silencing is a major developmental function of H3K9.
Li, X., Yang, F., Chen, H., Deng, B., Li, X. and Xi, R. (2016). Control of germline stem cell differentiation by polycomb and trithorax group genes in the niche microenvironment. Development [Epub ahead of print]. PubMed ID: 27510973
Polycomb and Trithorax group (PcG and TrxG) genes function to regulate gene transcription by maintaining the repressive or active chromatin state, respectively. This antagonistic activity is important for body patterning during embryonic development, but whether this function module has a role in adult tissues is unclear. This study reports that in the Drosophila oogenesis, disruption of the Polycomb responsive complex 1 (PRC1) specifically in the supporting escort cells causes blockage of cystoblast differentiation and germline stem cell- like tumor formation. The tumor is caused by derepression of decapentaplegic (dpp) which prevents cystoblast differentiation. Interestingly, activation of dpp in escort cells requires the function of TrxG gene brahma (brm), suggesting that loss of PRC1 in escort cells causes Brm-dependent dpp expression. This study suggests a requirement for balanced activity between PcG and TrxG in an adult stem cell niche, and disruption of this balance could lead to the loss of tissue homeostasis and tumorigenesis.
Navarro-Costa, P., McCarthy, A., Prudencio, P., Greer, C., Guilgur, L. G., Becker, J. D., Secombe, J., Rangan, P. and Martinho, R. G. (2016). Early programming of the oocyte epigenome temporally controls late prophase I transcription and chromatin remodelling. Nat Commun 7: 12331. PubMed ID: 27507044
Oocytes are arrested for long periods of time in the prophase of the first meiotic division (prophase I). As chromosome condensation poses significant constraints to gene expression, the mechanisms regulating transcriptional activity in the prophase I-arrested oocyte are still not entirely understood. It was hypothesized that gene expression during the prophase I arrest is primarily epigenetically regulated. This study comprehensively defines the Drosophila female germ line epigenome throughout oogenesis and shows that the oocyte has a unique, dynamic and remarkably diversified epigenome characterized by the presence of both euchromatic and heterochromatic marks. The perturbation of the oocyte's epigenome in early oogenesis, through depletion of the dKDM5 histone demethylase, results in the temporal deregulation of meiotic transcription and affects female fertility. Taken together, these results indicate that the early programming of the oocyte epigenome primes meiotic chromatin for subsequent functions in late prophase I.

Monday, September 12th

Mukherjee, A., Patel, B., Koga, H., Cuervo, A.M. and Jenny, A. (2016). Selective endosomal microautophagy is starvation-inducible in Drosophila. Autophagy [Epub ahead of print]. PubMed ID: 27487474
Autophagy delivers cytosolic components to lysosomes for degradation and is thus essential for cellular homeostasis and to cope with different stressors. As such, autophagy counteracts various human diseases and its reduction leads to aging-like phenotypes. Macroautophagy (MA) can selectively degrade organelles or aggregated proteins, whereas selective degradation of single proteins has only been described for chaperone-mediated autophagy (CMA) and endosomal microautophagy (eMI). These 2 autophagic pathways, are specific for proteins containing KFERQ-related targeting motifs. Using a KFERQ-tagged fluorescent biosensor, this study identified an eMI-like pathway in Drosophila melanogaster. It was found that this biosensor localizes to late endosomes and lysosomes upon prolonged starvation in a KFERQ- and Hsc70-4- dependent manner. Furthermore, fly eMI requires endosomal multivesicular body formation mediated by ESCRT complex components. Importantly, induction of Drosophila eMI requires longer starvation than the induction of MA and is independent of the critical MA genes atg5, atg7, and atg12. Furthermore, inhibition of Tor signaling induces eMI in flies under nutrient rich conditions, and, as eMI in Drosophila also requires atg1 and atg13, these data suggest that these genes may have a novel, additional role in regulating eMI in flies. Overall, this study provides evidence for a novel, starvation-inducible catabolic process resembling endosomal microautophagy in the Drosophila fat body.

Xu, D., Shan, B., Sun, H., Xiao, J., Zhu, K., Xie, X., Li, X., Liang, W., Lu, X., Qian, L. and Yuan, J. (2016). USP14 regulates autophagy by suppressing K63 ubiquitination of Beclin 1. Genes Dev 30: 1718-1730. PubMed ID: 27542828
Evolutionary Homolog Study
The ubiquitin-proteasome system (UPS) and autophagy are two major intracellular degradative mechanisms that mediate the turnover of complementary repertoires of intracellular proteomes. Simultaneously activating both UPS and autophagy might provide a powerful strategy for the clearance of misfolded proteins. However, it is not clear whether UPS and autophagy can be controlled by a common regulatory mechanism. K48 deubiquitination by USP14 (see Drosophila Usp14) is known to inhibit UPS. This study shows that USP14 regulates autophagy by negatively controlling K63 ubiquitination of Beclin 1 (see Drosophila Atg6). Furthermore, activation of USP14 by Akt (see Drosophila Akt1)-mediated phosphorylation provides a mechanism for Akt to negatively regulate autophagy by promoting K63 deubiquitination. Data suggest that Akt-regulated USP14 activity modulates both proteasomal degradation and autophagy through controlling K48 and K63 ubiquitination, respectively. Therefore, regulation of USP14 provides a mechanism for Akt to control both proteasomal and autophagic degradation. The study proposes that inhibition of USP14 may provide a strategy to promote both UPS and autophagy for developing novel therapeutics targeting neurodegenerative diseases. 

Hegedus, K., Takats, S., Boda, A., Jipa, A., Nagy, P., Varga, K., Kovacs, A. L. and Juhasz, G. (2016). The Ccz1-Mon1-Rab7 module and Rab5 control distinct steps of autophagy. Mol Biol Cell [Epub ahead of print]. PubMed ID: 27559127
The small GTPase Rab5 promotes recruitment of the Ccz1-Mon1 guanosine exchange complex to endosomes to activate Rab7, which facilitates endosome maturation and fusion with lysosomes. How these factors function during autophagy is incompletely understood. This study shows that autophagosomes accumulate due to impaired fusion with lysosomes upon loss of the Ccz1-Mon1-Rab7 module in starved Drosophila fat cells. In contrast, autophagosomes generated in Rab5 null mutant cells normally fuse with lysosomes during the starvation response. Consistent with that, Rab5 is dispensable for the Ccz1-Mon1-dependent recruitment of Rab7 to PI3P-positive autophagosomes, which are generated by the action of the Atg14-containing Vps34 PI3 kinase complex. Finally, Rab5 was found to be required for proper lysosomal function. Thus, the Ccz1-Mon1-Rab7 module is required for autophagosome-lysosome fusion, whereas Rab5 loss interferes with a later step of autophagy: the breakdown of autophagic cargo within lysosomes.
Bader, C. A., et al. (2016). A molecular probe for the detection of polar lipids in live cells. PLoS One 11: e0161557. PubMed ID: 27551717
This study describes the potential for ReZolve-L1 to localise to intracellular compartments containing polar lipids, such as for example sphingomyelin and phosphatidylethanolamine. In live Drosophila fat body tissue from third instar larvae, ReZolve-L1 interacted mainly with lipid droplets, including the core region of these organelles. The presence of polar lipids in the core of these lipid droplets was confirmed by Raman mapping and while this was consistent with the distribution of ReZolve-L1 it did not exclude that the molecular probe might be detecting other lipid species. In response to complete starvation conditions, ReZolve-L1 was detected mainly in Atg8-GFP autophagic compartments, and showed reduced staining in the lipid droplets of fat body cells. The induction of autophagy by Tor inhibition also increased ReZolve-L1 detection in autophagic compartments, whereas Atg9 knock down impaired autophagosome formation and altered the distribution of ReZolve-L1. Finally, during Drosophila metamorphosis fat body tissues showed increased ReZolve-L1 staining in autophagic compartments at two hours post puparium formation, when compared to earlier developmental time points. It is concluded that ReZolve-L1 is a new live cell imaging tool, which can be used as an imaging reagent for the detection of polar lipids in different intracellular compartments.

Sunday, September 11th

Lee, E., Cho, E., Kang, D. H., Jeong, E. H., Chen, Z., Yoo, S. H. and Kim, E. Y. (2016). Pacemaker-neuron-dependent disturbance of the molecular clockwork by a Drosophila CLOCK mutant homologous to the mouse Clock mutation. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 27489346
Circadian clocks are composed of transcriptional/translational feedback loops (TTFLs) at the cellular level. In Drosophila TTFLs, the transcription factor Clock (Clk)/Cycle (Cyc) activates clock target gene expression, which is repressed by the physical interaction with Period (Per). This study shows that amino acids (AA) 657-707 of Clk, a region that is homologous to the mouse Clock exon 19-encoded region, is crucial for Per binding and E-box-dependent transactivation in S2 cells. Consistently, in transgenic flies expressing Clk with an AA657-707 deletion in the Clock (Clkout) genetic background (p{Clk-Δ};Clkout), oscillation of core clock genes' mRNAs displayed diminished amplitude compared with control flies, and the highly abundant dCLK&Delta657-707 showed significantly decreased binding to Per. Behaviorally, the p{dClk-Δ};Clkout flies exhibited arrhythmic locomotor behavior in the photic entrainment condition but showed anticipatory activities of temperature transition and improved free-running rhythms in the temperature entrainment condition. Surprisingly, p{dClk-Δ};Clkout flies showed pacemaker-neuron-dependent alterations in molecular rhythms; the abundance of dCLK target clock proteins was reduced in ventral lateral neurons (LNvs) but not in dorsal neurons (DNs) in both entrainment conditions. In p{dClk-Delta};Clkout flies, however, strong but delayed molecular oscillations in temperature cycle-sensitive pacemaker neurons, such as DN1s and DN2s, were correlated with delayed anticipatory activities of temperature transition. Taken together, this study reveals that the LNv molecular clockwork is more sensitive than the clockwork of DNs to dysregulation of dCLK by AA657-707 deletion. Therefore, it is proposed that the dCLK/CYC-controlled TTFL operates differently in subsets of pacemaker neurons, which may contribute to their specific functions.
Leong, J. C., Esch, J. J., Poole, B., Ganguli, S. and Clandinin, T. R. (2016). Direction selectivity in Drosophila emerges from preferred-direction enhancement and null-direction suppression. J Neurosci 36: 8078-8092. PubMed ID: 27488629
Across animal phyla, motion vision relies on neurons that respond preferentially to stimuli moving in one, preferred direction over the opposite, null direction. In the elementary motion detector of Drosophila, direction selectivity emerges in two neuron types, T4 and T5, but the computational algorithm underlying this selectivity remains unknown. This study found that the receptive fields of both T4 and T5 exhibit spatiotemporally offset light-preferring and dark-preferring subfields, each obliquely oriented in spacetime. In a linear-nonlinear modeling framework, the spatiotemporal organization of the T5 receptive field predicts the activity of T5 in response to motion stimuli. These findings demonstrate that direction selectivity emerges from the enhancement of responses to motion in the preferred direction, as well as the suppression of responses to motion in the null direction. Thus, remarkably, T5 incorporates the essential algorithmic strategies used by the Hassenstein-Reichardt correlator and the Barlow-Levick detector. The model developed in this paper for T5 also provides an algorithmic explanation for the selectivity of T5 for moving dark edges: the model captures all two- and three-point spacetime correlations relevant to motion in this stimulus class. More broadly, the findings reveal the contribution of input pathway visual processing, specifically center-surround, temporally biphasic receptive fields, to the generation of direction selectivity in T5. As the spatiotemporal receptive field of T5 in Drosophila is common to the simple cell in vertebrate visual cortex, this stimulus-response model of T5 will inform efforts in an experimentally tractable context to identify more detailed, mechanistic models of a prevalent computation.
Schlichting, M., Menegazzi, P. and Helfrich-Forster, C. (2015). Normal vision can compensate for the loss of the circadian clock. Proc Biol Sci 282 [Epub ahead of print]. PubMed ID: 26378222
Circadian clocks are thought to be essential for timing the daily activity of animals, and consequently increase fitness. This view was recently challenged for clock-less fruit flies and mice that exhibited astonishingly normal activity rhythms under outdoor conditions. Compensatory mechanisms appear to enable even clock mutants to live a normal life in nature. This study showed that gradual daily increases/decreases of light in the laboratory suffice to provoke normally timed sharp morning (M) and evening (E) activity peaks in clock-less flies. It was also shown that the compound eyes, but not Cryptochrome (Cry), mediate the precise timing of M and E peaks under natural-like conditions, as Cry-less flies do and eyeless flies do not show these sharp peaks independently of a functional clock. Nevertheless, the circadian clock appears critical for anticipating dusk, as well as for inhibiting sharp activity peaks during midnight. Clock-less flies only increase E activity after dusk and not before the beginning of dusk, and respond strongly to twilight exposure in the middle of the night. Furthermore, the circadian clock responds to natural-like light cycles, by slightly broadening Timeless (Tim) abundance in the clock neurons, and this effect is mediated by Cry.
Shorter, J. R., et al. (2016). Obp56h modulates mating behavior in Drosophila melanogaster. G3 (Bethesda) 6(10):3335-3342. PubMed ID: 27558663
Social interactions in insects are driven by conspecific chemical signals that are detected via olfactory and gustatory neurons. Odorant binding proteins (Obps) transport volatile odorants to chemosensory receptors, but their effects on behaviors remain poorly characterized. This study reports that RNAi knockdown of Obp56h gene expression in Drosophila melanogaster enhances mating behavior by reducing courtship latency. The change in mating behavior that results from inhibition of Obp56h expression is accompanied by significant alterations in cuticular hydrocarbon (CHC) composition, including reduction in 5-tricosene (5-T), an inhibitory sex pheromone produced by males that increases copulation latency during courtship. Whole genome RNA sequencing confirms that expression of Obp56h is virtually abolished in Drosophila heads. Inhibition of Obp56h expression also affects expression of other chemoreception genes, including upregulation of lush in both sexes and Obp83ef in females, and reduction in expression of Obp19b and Or19b in males. In addition, several genes associated with lipid metabolism, which underlies the production of cuticular hydrocarbons, show altered transcript abundances. These data show that modulation of mating behavior through reduction of Obp56h is accompanied by altered cuticular hydrocarbon profiles and implicate 5-T as a possible ligand for Obp56h.

Saturday, September 10th

Duarte, F. M., Fuda, N. J., Mahat, D. B., Core, L. J., Guertin, M. J. and Lis, J. T. (2016). Transcription factors GAF and HSF act at distinct regulatory steps to modulate stress-induced gene activation. Genes Dev 30: 1731-1746. PubMed ID: 27492368
The coordinated regulation of gene expression at the transcriptional level is fundamental to development and homeostasis. Inducible systems are invaluable when studying transcription because the regulatory process can be triggered instantaneously, allowing the tracking of ordered mechanistic events. This study used precision run-on sequencing (PRO-seq) to examine the genome-wide heat shock (HS) response in Drosophila and the function of two key transcription factors on the immediate transcription activation or repression of all genes regulated by HS. The primary HS response genes and the rate-limiting steps in the transcription cycle were identified that are regulated by GAGA-associated factor (GAF) and HS factor (HSF). GAF acts upstream of promoter-proximally paused RNA polymerase II (Pol II) formation (likely at the step of chromatin opening), and GAF-facilitated Pol II pausing is critical for HS activation. In contrast, HSF is dispensable for establishing or maintaining Pol II pausing but is critical for the release of paused Pol II into the gene body at a subset of highly activated genes. Additionally, HSF has no detectable role in the rapid HS repression of thousands of genes.
Wang, H., Becuwe, M., Housden, B.E., Chitraju, C., Porras, A.J., Graham, M.M., Liu, X.N., Thiam, A.R., Savage, D.B., Agarwal, A.K., Garg, A., Olarte, M.J., Lin, Q., Frõhlich, F., Hannibal-Bach, H.K., Upadhyayula, S., Perrimon, N., Kirchhausen, T., Ejsing, C.S., Walther, T.C. and Farese, R.V. (2016). Seipin is required for converting nascent to mature lipid droplets. Elife [Epub ahead of print]. PubMed ID: 27564575
How proteins control the biogenesis of cellular lipid droplets (LDs) is poorly understood. Using Drosophila and human cells, this study shows that seipin, an ER protein implicated in LD biology, mediates a discrete step in LD formation-the conversion of small, nascent LDs to larger, mature LDs. Seipin forms discrete and dynamic foci in the ER that interact with nascent LDs to enable their growth. In the absence of seipin, numerous small, nascent LDs accumulate near the ER and most often fail to grow. Those that do grow prematurely acquire lipid synthesis enzymes and undergo expansion, eventually leading to the giant LDs characteristic of seipin deficiency. These observations identify a discrete step of LD formation, namely the conversion of nascent LDs to mature LDs, and define a molecular role for seipin in this process, most likely by acting at ER-LD contact sites to enable lipid transfer to nascent LDs.

Koštál, V., Korbelová, J., Štětina, T., Poupardin, R., Colinet, H., Zahradníčková, H., Opekarová, I., Moos, M. and ŠimekŠ, P. (2016). Physiological basis for low-temperature survival and storage of quiescent larvae of the fruit fly Drosophila melanogaster. Sci Rep 6: 32346. PubMed ID: 27573891
The cryopreservation techniques proposed for embryos of the fruit fly Drosophila melanogaster are not yet ready for practical use. Alternative methods for long-term storage of D. melanogaster strains, although urgently needed, do not exist. This study describes a narrow interval of low temperatures under which the larvae of D. melanogaster can be stored in quiescence for up to two months. The development of larvae was arrested at the pre-wandering stage under fluctuating thermal regime (FTR), which simultaneously results in diminishing the accumulation of indirect chill injuries. Physiological, metabolomic, and transcriptomic analyses revealed that compared to larvae stored at constant low temperatures, the larvae stored under FTR conditions are able to decrease the rates of depletion of energy substrates, exploit brief warm episodes of FTR for homeostatic control of metabolite levels, and more efficiently exert protection against oxidative damage. 

Sarup, P., Petersen, S. M., Nielsen, N. C., Loeschcke, V. and Malmendal, A. (2016). Mild heat treatments induce long-term changes in metabolites associated with energy metabolism in Drosophila melanogaster. Biogerontology [Epub ahead of print]. PubMed ID: 27511372
Heat-induced hormesis, the beneficial effect of mild heat-induced stress, increases the average lifespan of many organisms. Yet little is known about the mechanisms underlying this effect. This study used nuclear magnetic resonance spectroscopy to investigate the long-term effects of repeated mild heat treatments on the metabolome of male Drosophila melanogaster. 10 days after the heat treatment, metabolic aging appears to be slowed down, and a treatment response with 40 % higher levels of alanine and lactate and lower levels of aspartate and glutamate were measured. All treatment effects had disappeared 16 days later. Metabolic reprogramming has been associated with the life extending effects of dietary restriction. The metabolite changes induced by the hormetic treatment suggest that the positive effects might not be limited to the repair pathways induced, but that there also is a change in energy metabolism. A possible direct link between changes in energy metabolism and heat induced increase in Hsp70 expression is discussed.

Friday, September 9th

Yang, D.S., Roh, S. and Jeong, S. (2016). The axon guidance function of Rap1 small GTPase is independent of PlexA RasGAP activity in Drosophila. Dev Biol [Epub ahead of print]. PubMed ID: 27565025
Plexins (Plexs) comprise a large family of cell surface receptors for semaphorins (Semas) that function as evolutionarily conserved guidance molecules. GTPase activating protein (GAP) activity for Ras family small GTPases has been implicated in plexin signaling cascades through its RasGAP domain. However, little is known about how Ras family GTPases are controlled in vivo by plexin signaling. This study found that Drosophila Rap1, a member of the Ras family of GTPases, plays an important role controlling intersegmental nerve b motor axon guidance during neural development. Gain-of-function studies using dominant-negative and constitutively active forms of Rap1 indicate that Rap1 contributes to axonal growth and guidance. Genetic interaction analyses demonstrate that the Sema-1a/PlexA-mediated repulsive guidance function is regulated positively by Rap1. Furthermore, neuronal expression of mutant PlexA robustly restores defasciculation defects in PlexA null mutants when the catalytic arginine fingers of the PlexA RasGAP domain critical for GAP activity are disrupted. However, deleting the RasGAP domain abolishes the ability of PlexA to rescue the PlexA guidance phenotypes. These findings suggest that PlexA-mediated motor axon guidance is dependent on the presence of the PlexA RasGAP domain, but not on its GAP activity toward Ras family small GTPases.

Mossman, J.A., Tross, J.G., Li, N., Wu, Z. and Rand, D.M. (2016). Mitochondrial-nuclear interactions mediate sex-specific transcriptional profiles in Drosophila. Genetics [Epub ahead of print]. PubMed ID: 27558138
The assembly and function of mitochondria require coordinated expression from two distinct genomes, the mitochondrial DNA (mtDNA) and nuclear DNA (nDNA). This study tested how the transcriptome responds to mtDNA and nDNA variation, along with mitonuclear interactions (mtDNA x nDNA) in Drosophila. Two mtDNA haplotypes that differ in a substantial number of single nucleotide polymorphisms, with >100 amino acid differences, were used. Each haplotype was placed on each of two D. melanogaster nuclear backgrounds and was tested for transcription differences in both sexes. Large numbers of transcripts were found to be differentially expressed between nuclear backgrounds, and mtDNA type altered the expression of nDNA genes, suggesting a retrograde, trans-effect of mitochondrial genotype. Females are generally more sensitive to genetic perturbation than males, and males demonstrate an asymmetrical effect of mtDNA in each nuclear background; mtDNA effects are nuclear background-specific. MtDNA sensitive genes are not enriched in male- or female-limited expression space in either sex. The responses to mitonuclear covariation were shown to be substantially different between the sexes, yet the mtDNA genes are consistently differentially expressed across nuclear backgrounds and sexes. These results provide evidence that mtDNA main effects can be consistent across nuclear backgrounds, but the interactions between mtDNA and nDNA can lead to sex-specific global transcript responses.

Jaszczak, J. S., Wolpe, J. B., Bhandari, R., Jaszczak, R. G. and Halme, A. (2016). Growth coordination during Drosophila melanogaster imaginal disc regeneration is mediated by signaling through the Relaxin receptor Lgr3 in the prothoracic gland. Genetics [Epub ahead of print]. PubMed ID: 27558136
Damage to Drosophila melanogaster imaginal discs activates a regeneration checkpoint that 1) extends larval development and 2) coordinates the regeneration of the damaged disc with the growth of undamaged discs. These two systemic responses to damage are both mediated by Dilp8, a member of the insulin/IGF/relaxin family of peptide hormones, which is released by regenerating imaginal discs. Growth coordination between regenerating and undamaged imaginal discs is dependent on Dilp8 activation of NOS in the prothoracic gland (PG), which slows the growth of undamaged discs by limiting ecdysone synthesis. This study demonstrates that the Drosophila relaxin receptor homologue Lgr3, a leucine-rich repeat-containing G-protein coupled receptor, is required for Dilp8-dependent growth coordination and developmental delay during the regeneration checkpoint. Lgr3 regulates these responses to damage via distinct mechanisms in different tissues. Using tissue-specific RNAi disruption of Lgr3 expression, Lgr3 was shown to function in the PG upstream of nitric oxide synthase (NOS), and is necessary for NOS activation and growth coordination during the regeneration checkpoint. When Lgr3 is depleted from neurons, imaginal disc damage no longer produces either developmental delay or growth inhibition. To reconcile these discrete tissue requirements for Lgr3 during regenerative growth coordination, it was demonstrated that Lgr3 activity in the both the CNS and PG is necessary for NOS activation in the PG following damage. Together, these results identify new roles for a relaxin receptor in mediating damage signaling to regulate growth and developmental timing.
Ahmed, Y. A., Yates, E. A., Moss, D. J., Loeven, M. A., Hussain, S. A., Hohenester, E., Turnbull, J. E. and Powell, A. K. (2016). Panels of chemically-modified heparin polysaccharides and natural heparan sulfate saccharides both exhibit differences in binding to Slit and Robo, as well as variation between protein binding and cellular activity. Mol Biosyst [Epub ahead of print]. PubMed ID: 27502551
Heparin/heparan sulfate (HS) glycosaminoglycans are required for Slit-Robo cellular responses. Evidence exists for interactions between each combination of Slit, Robo and heparin/HS and for formation of a ternary complex. Heparin/HS are complex mixtures displaying extensive structural diversity. The relevance of this diversity has been studied to a limited extent using a few select chemically-modified heparins as models of HS diversity. This study extended these studies by parallel screening of structurally diverse panels of eight chemically-modified heparin polysaccharides and numerous natural HS oligosaccharide chromatographic fractions for binding to both Drosophila Slit and Robo N-terminal domains and for activation of a chick retina axon response to the Slit fragment. Both the polysaccharides and oligosaccharide fractions displayed variability in binding and cellular activity that could not be attributed solely to increasing sulfation, extending evidence for the importance of structural diversity to natural HS as well as model modified heparins. They also displayed differences in their interactions with Slit compared to Robo, with Robo preferring compounds with higher sulfation. Furthermore, the patterns of cellular activity across compounds were different to those for binding to each protein, suggesting that biological outcomes are selectively determined in a subtle manner that does not simply reflect the sum of the separate interactions of heparin/HS with Slit and Robo.
Garcia-Caceres, C., et al. (2016). Astrocytic insulin signaling couples brain glucose uptake with nutrient availability. Cell 166: 867-880. PubMed ID: 27518562
Evolutionary Homolog Study:
Astrocytic insulin signaling co-regulates hypothalamic glucose sensing and systemic glucose metabolism. Postnatal ablation of insulin receptors (IRs; see Drosophila Insulin-like receptor) in glial fibrillary acidic protein (GFAP)-expressing cells affects hypothalamic astrocyte morphology, mitochondrial function, and circuit connectivity. Accordingly, astrocytic IR ablation reduces glucose-induced activation of hypothalamic pro-opio-melanocortin (POMC) neurons and impairs physiological responses to changes in glucose availability. Hypothalamus-specific knockout of astrocytic IRs, as well as postnatal ablation by targeting glutamate aspartate transporter (GLAST)-expressing cells, replicates such alterations. A normal response to altering directly CNS glucose levels in mice lacking astrocytic IRs indicates a role in glucose transport across the blood-brain barrier (BBB). This was confirmed in vivo in GFAP-IR KO mice by using positron emission tomography and glucose monitoring in cerebral spinal fluid. It is concluded that insulin signaling in hypothalamic astrocytes co-controls CNS glucose sensing and systemic glucose metabolism via regulation of glucose uptake across the BBB.
Thomsen, A. R., et al. (2016). GPCR-G protein-β-Arrestin super-complex mediates sustained G protein signaling. Cell 166: 907-919. PubMed ID: 27499021
Evolutionary Homolog Study:
Classically, G protein-coupled receptor (GPCR) stimulation promotes G protein signaling at the plasma membrane, followed by rapid β-arrestin-mediated desensitization and receptor internalization into endosomes. However, it has been demonstrated that some GPCRs activate G proteins from within internalized cellular compartments, resulting in sustained signaling. This study used a variety of biochemical, biophysical, and cell-based methods to demonstrate the existence, functionality, and architecture of internalized receptor complexes composed of a single GPCR, β-arrestin (see Drosophila Kurtz), and G protein. These super-complexes or "megaplexes" more readily form at receptors that interact strongly with β-arrestins via a C-terminal tail containing clusters of serine/threonine phosphorylation sites. Single-particle electron microscopy analysis of negative-stained purified megaplexes reveals that a single receptor simultaneously binds through its core region with G protein and through its phosphorylated C-terminal tail with β-arrestin. The formation of such megaplexes provides a potential physical basis for the newly appreciated sustained G protein signaling from internalized GPCRs.

Thursday, September 8th

Voelzmann, A., Okenve-Ramos, P., Qu, Y., Chojnowska-Monga, M., Del Caño-Espinel, M., Prokop, A. and Sanchez-Soriano, N. (2016). Tau and spectraplakins promote synapse formation and maintenance through Jun kinase and neuronal trafficking. Elife 5. PubMed ID: 27501441
The mechanisms regulating synapse numbers during development and aging are essential for normal brain function and closely linked to brain disorders including dementias. Using Drosophila, this study demonstrates roles of the microtubule-associated protein Tau in regulating synapse numbers, thus unravelling an important cellular requirement of normal Tau. In this context, it was found that Tau displays a strong functional overlap with microtubule-binding spectraplakins, establishing new links between two different neurodegenerative factors. Tau and the spectraplakin Short Stop act upstream of a three-step regulatory cascade ensuring adequate delivery of synaptic proteins. This cascade involves microtubule stability as the initial trigger, JNK signalling as the central mediator, and kinesin-3 mediated axonal transport as the key effector. This cascade acts during development (synapse formation) and aging (synapse maintenance) alike. Therefore, these findings suggest novel explanations for intellectual disability in Tau deficient individuals, as well as early synapse loss in dementias including Alzheimer's disease

Stavoe, A.K., Hill, S.E., Hall, D.H. and Colón-Ramos, D.A. (2016). KIF1A/UNC-104 transports ATG-9 to regulate neurodevelopment and autophagy at synapses. Dev Cell 38: 171-185. PubMed ID: 27396362
Evolutionary Homolog Study
Autophagy is a cellular degradation process important for neuronal development and survival. Neurons are highly polarized cells in which autophagosome biogenesis is spatially compartmentalized. The mechanisms and physiological importance of this spatial compartmentalization of autophagy in the neuronal development of living animals are not well understood. This study determines that, in Caenorhabditis elegans neurons, autophagosomes form near synapses and are required for neurodevelopment. It was shown through unbiased genetic screens and systematic genetic analyses that autophagy (see Drosophila autophagy) is required cell autonomously for presynaptic assembly and for axon outgrowth dynamics in specific neurons. Autophagosome biogenesis in the axon near synapses was observed, and this localization was found to depend on the synaptic vesicle kinesin, KIF1A/UNC-104 (see Drosophila Unc-104). KIF1A/UNC-104 coordinates localized autophagosome formation by regulating the transport of the integral membrane autophagy protein ATG-9 (see Drosophila Atg9). These findings indicate that autophagy is spatially regulated in neurons through the transport of ATG-9 by KIF1A/UNC-104 to regulate neurodevelopment.

Grant, P., Maga, T., Loshakov, A., Singhal, R., Wali, A., Nwankwo, J., Baron, K. and Johnson, D. (2016). An eye on trafficking genes: Identification of four eye color mutations in Drosophila. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 27558665
Genes that code for proteins involved in organelle biogenesis and intracellular trafficking produce products that are critical in normal cell function. Conserved orthologs of these are present in most or all eukaryotes including Drosophila melanogaster. Some of these genes were originally identified as eye color mutants with decreases in both types of pigments found in the fly eye. Using these criteria, this study molecularly mapped and evaluated the genome sequences of four eye color mutations: chocolate, maroon, mahogany, and red Malpighian tubules. Mapping was performed using deletion analysis and complementation tests. chocolate is an allele of the VhaAC39-1 gene, which is an ortholog of the Vacuolar H+ ATPase AC39 subunit 1. maroon corresponds to the Vps16A gene and its product is part of the HOPS complex, which participates in transport and in organelle fusion. red Malpighian tubule is the CG12207 gene, which encodes a protein of unknown function that includes a LysM domain. mahogany is the CG13646 gene, which is predicted to be an amino acid transporter. The strategy of identifying eye color genes based on perturbations in quantities of both types of eye color pigments has proven useful in identifying proteins involved in trafficking and biogenesis of lysosome related organelles. Mutants of these genes can provide valuable in vivo models to understand these processes.

Romani, P., Papi, A., Ignesti, M., Soccolini, G., Hsu, T., Gargiulo, G., Spisni, E. and Cavaliere, V. (2016). Dynamin controls extracellular level of Awd/Nme1 metastasis suppressor protein. Naunyn Schmiedebergs Arch Pharmacol. PubMed ID: 27449069
Dynamin GTPase (Dyn) plays a critical role in membrane-remodelling events underlying endocytosis. Studies in Drosophila identified a functional interaction between the Dyn homologue, encoded by the shibire (shi) gene, and Abnormal wing discs (Awd), a nucleoside diphosphate kinase (NDPK) that is the homologue of group I Nme human genes. These Drosophila studies showed that awd mutations enhance mutant shi phenotype and thus indicated the existence of a highly specific interaction between these genes. Furthermore, in human cells, it has been shown that Nme proteins promote Dyn activity in different membrane compartments through spatially controlled supply of GTP. Interestingly, Awd and Nme proteins have been detected in the extracellular environment. While no role has been inferred to extracellular Awd, presence of Nme1 in cancer patient serum is an unfavourable prognostic marker. The present work used Drosophila and human cell line models to investigate the shuttling Awd/Nme1 proteins between intracellular and extracellular spaces. By using classic and reverse genetic approaches, downregulation of Shi/Dyn1 activity was shown to enhance extracellular Awd/Nme1 in both Drosophila and human colon cell lines. This analyses was extended to colon cancer cell lines and knocking down Dyn1, besides to raising Nme1 extracellular amount, was shown to downregulates expression of molecular components that play key roles in tumour invasion. Interestingly, in vivo analyses of Drosophila larval adipocytes show that the conditional block of Shi activity greatly reduces intracellular amount of Awd confirming that Shi plays a key role in controlling the balance between intracellular and extracellular Awd.

Wednesday, September 7th

Xie, Y., Li, X., Deng, X., Hou, Y., O'Hara, K., Urso, A., Peng, Y., Chen, L. and Zhu, S. (2016). The Ets protein pointed prevents both premature differentiation and dedifferentiation of Drosophila intermediate neural progenitors. Development [Epub ahead of print]. PubMed ID: 27510969
Intermediate neural progenitor cells (INPs) need to avoid both dedifferentiation and differentiation during neurogenesis, but the mechanisms are not well understood. In Drosophila, the Ets protein Pointed P1 (PntP1) is required to generate INPs from type II neuroblasts. This study investigated how PntP1 promotes INP generation. By generating pntP1-specific mutants and using RNAi knockdown, the loss of PntP1 was shown to lead to both an increase in the type II neuroblast number and the elimination of INPs. The elimination of INPs results from premature differentiation of INPs due to the ectopic Prospero expression in newly generated immature INPs (imINP), whereas the increase in the type II neuroblast number results from the dedifferentiation of imINPs due to a loss of Earmuff at later stages of imINP development. Furthermore, reducing Buttonhead enhances the loss of INPs in pntP1 mutants, suggesting that PntP1 and Buttonhead act cooperatively to prevent premature INP differentiation. These results demonstrate that PntP1 prevents both the premature differentiation and dedifferentiation of INPs by regulating the expression of distinct target genes at different stages of imINP development.
Narushima, M., Uchigashima, M., Yagasaki, Y., Harada, T., Nagumo, Y., Uesaka, N., Hashimoto, K., Aiba, A., Watanabe, M., Miyata, M. and Kano, M. (2016). The metabotropic glutamate receptor subtype 1 mediates experience-dependent maintenance of mature synaptic connectivity in the visual thalamus. Neuron [Epub ahead of print]. PubMed ID: 27545713
Evolutionary Homolog Study:
Neural circuits formed during postnatal development have to be maintained stably thereafter, but their mechanisms remain largely unknown. This study reports that the metabotropic glutamate receptor subtype 1 (mGluR1; see Drosophila metabotropic Glutamate receptor) is essential for the maintenance of mature synaptic connectivity in the dorsal lateral geniculate nucleus (dLGN). In mGluR1 knockout (mGluR1-KO) mice, strengthening and elimination at retinogeniculate synapses occurred normally until around postnatal day 20 (P20). However, during the subsequent visual-experience-dependent maintenance phase, weak retinogeniculate synapses were newly recruited. These changes were similar to those of wild-type (WT) mice that underwent visual deprivation or inactivation of mGluR1 in the dLGN from P21. Importantly, visual deprivation was ineffective in mGluR1-KO mice, and the changes induced by visual deprivation in WT mice were rescued by pharmacological activation of mGluR1 in the dLGN. These results demonstrate that mGluR1 is crucial for the visual-experience-dependent maintenance of mature synaptic connectivity in the dLGN.
Fu, J., Murphy, K.A., Zhou, M., Li, Y.H., Lam, V.H., Tabuloc, C.A., Chiu, J.C. and Liu, Y. (2016). Codon usage affects the structure and function of the Drosophila circadian clock protein PERIOD. Genes Dev 30: 1761-1775. PubMed ID: 27542830
Codon usage bias is a universal feature of all genomes, but its in vivo biological functions in animal systems are not clear. To investigate the in vivo role of codon usage in animals, this study took advantage of the sensitivity and robustness of the Drosophila circadian system. By codon-optimizing parts of Drosophila period (per), a core clock gene that encodes a critical component of the circadian oscillator, per codon usage was shown to be important for circadian clock function. Codon optimization of per results in conformational changes of the PER protein, altered PER phosphorylation profile and stability, and impaired PER function in the circadian negative feedback loop, which manifests into changes in molecular rhythmicity and abnormal circadian behavioral output. The study provides an in vivo example that demonstrates the role of codon usage in determining protein structure and function in an animal system. These results suggest a universal mechanism in eukaryotes that uses a codon usage "code" within genetic codons to regulate cotranslational protein folding.

Drago, I. and Davis, R.L. (2016). Inhibiting the mitochondrial calcium uniporter during development impairs memory in adult Drosophila. Cell Rep [Epub ahead of print]. PubMed ID: 27568554
The uptake of cytoplasmic calcium into mitochondria is critical for a variety of physiological processes, including calcium buffering, metabolism, and cell survival. This study demonstrates that inhibiting the mitochondrial calcium uniporter in the Drosophila mushroom body neurons (MBn)-a brain region critical for olfactory memory formation-causes memory impairment without altering the capacity to learn. Inhibiting uniporter activity only during pupation impairs adult memory, whereas the same inhibition during adulthood is without effect. The behavioral impairment is associated with structural defects in MBn, including a decrease in synaptic vesicles and an increased length in the axons of the αβ MBn. These results reveal an in vivo developmental role for the mitochondrial uniporter complex in establishing the necessary structural and functional neuronal substrates for normal memory formation in the adult organism.

Tuesday, September 6th

Di Cara, F. and King-Jones, K. (2016). The Circadian clock is a key driver of steroid hormone production in Drosophila. Curr Biol [Epub ahead of print]. PubMed ID: 27546572
Biological clocks allow organisms to anticipate daily environmental changes such as temperature fluctuations, abundance of daylight, and nutrient availability. Many circadian-controlled physiological states are coordinated by the release of systemically acting hormones, including steroids and insulin. Thus, hormones relay circadian outputs to target tissues, and disrupting these endocrine rhythms impairs human health by affecting sleep patterns, energy homeostasis, and immune functions. It is largely unclear, however, whether circadian circuits control hormone levels indirectly via central timekeeping neurons or whether peripheral endocrine clocks can modulate hormone synthesis directly. This study shows that perturbing the circadian clock, specifically in the major steroid hormone-producing gland of Drosophila, the prothoracic gland (PG), unexpectedly blocks larval development due to an inability to produce sufficient steroids. This is surprising, because classic circadian null mutants are viable and result in arrhythmic adults. Timeless and Period, both core components of the insect clock, are required for transcriptional upregulation of steroid hormone-producing enzymes. Timeless couples the circadian machinery directly to the two canonical pathways that regulate steroid synthesis in insects, insulin and PTTH signaling, respectively. Activating insulin signaling directly modulates Timeless function, suggesting that the local clock in the PG is normally synced with systemic insulin cues. Because both PTTH and systemic insulin signaling are themselves under circadian control, it is concluded that de-synchronization of a local endocrine clock with external circadian cues is the primary cause for steroid production to fail.
Zhou, F., Qiang, K. M. and Beckingham, K. M. (2016). Failure to burrow and tunnel reveals roles for jim lovell in the growth and endoreplication of the Drosophila larval tracheae. PLoS One 11: e0160233. PubMed ID: 27494251
The Drosophila protein Jim Lovell (Lov) is a putative transcription factor of the BTB/POZ (Bric- a-Brac/Tramtrack/Broad/ Pox virus and Zinc finger) domain class that is expressed in many elements of the developing larval nervous system. It has roles in innate behaviors such as larval locomotion and adult courtship. In performing tissue-specific knockdown with the Gal4-UAS system this study identified a new behavioral phenotype for lov: larvae failed to burrow into their food during their growth phase and then failed to tunnel into an agarose substratum during their wandering phase. These phenotypes originate in a previously unrecognized role for lov in the tracheae. By using tracheal-specific Gal4 lines, Lov immunolocalization and a lov enhancer trap line, lov was stablished to be normally expressed in the tracheae from late in embryogenesis through larval life. Using an assay that monitors food burrowing, substrate tunneling and death lov tracheal knockdown was shown to result in tracheal fluid-filling, producing hypoxia that activates the aberrant behaviors and inhibits development. The role of lov in the tracheae that initiates this sequence of events was investigated. When lov levels are reduced, the tracheal cells are smaller, more numerous and show lower levels of endopolyploidization. Together these findings indicate that Lov is necessary for tracheal endoreplicative growth and that its loss in this tissue causes loss of tracheal integrity resulting in chronic hypoxia and abnormal burrowing and tunneling behavior.
Segal, D., Dhanyasi, N., Schejter, E. D. and Shilo, B. Z. (2016). Adhesion and fusion of muscle cells are promoted by filopodia. Dev Cell 38: 291-304. PubMed ID: 27505416
Indirect flight muscles (IFMs) in Drosophila are generated during pupariation by fusion of hundreds of myoblasts with larval muscle templates (myotubes). Live observation of these muscles during the fusion process revealed multiple long actin-based protrusions that emanate from the myotube surface and require Enabled and IRSp53 for their generation and maintenance. Fusion is blocked when formation of these filopodia is compromised. While filopodia are not required for the signaling process underlying critical myoblast cell-fate changes prior to fusion, myotube-myoblast adhesion appears to be filopodia dependent. Without filopodia, close apposition between the cell membranes is not achieved, the cell-adhesion molecule Duf is not recruited to the myotube surface, and adhesion-dependent actin foci do not form. It is therefore proposed that the filopodia are necessary to prime the heterotypic adhesion process between the two cell types, possibly by recruiting the cell-adhesion molecule Sns to discrete patches on the myoblast cell surface.
Wu, Z., Guo, W., Xie, Y. and Zhou, S. (2016). Juvenile hormone activates the transcription of Cell-division-cycle 6 (Cdc6) for polyploidy-dependent Insect vitellogenesis and oogenesis. J Biol Chem 291: 5418-5427. PubMed ID: 26728459
Although juvenile hormone (JH) is known to prevent insect larval metamorphosis and stimulate adult reproduction, the molecular mechanisms of JH action in insect reproduction remain largely unknown. The JH-receptor complex, composed of methoprene-tolerant and steroid receptor co-activator, acts on mini-chromosome maintenance (Mcm) genes Mcm4 and Mcm7 to promote DNA replication and polyploidy for the massive vitellogenin (Vg) synthesis required for egg production in the migratory locust. This study has investigated the involvement of cell-division-cycle 6 (Cdc6) in JH-dependent vitellogenesis and oogenesis, as Cdc6 is essential for the formation of prereplication complex. Cdc6 was shown to be expressed in response to JH and methoprene-tolerant, and Cdc6 transcription is directly regulated by the JH-receptor complex. Knockdown of Cdc6 inhibits polyploidization of fat body and follicle cells, resulting in the substantial reduction of Vg expression in the fat body as well as severely impaired oocyte maturation and ovarian growth. These data indicate the involvement of Cdc6 in JH pathway and a pivotal role of Cdc6 in JH-mediated polyploidization, vitellogenesis, and oogenesis.

Monday, September 5th

Ramat, A., Audibert, A., Louvet-Vallée, S., Simon, F., Fichelson, P. and Gho, M. (2016). Escargot and Scratch regulate neural commitment by antagonizing Notch-activity in Drosophila sensory organs. Development [Epub ahead of print]. PubMed ID: 27471258
During Notch (N)-mediated binary cell fate decisions, cells adopt two different fates according to the levels of N-pathway activation: an Noff-dependent or an Non-dependent fate. How cells maintain these N-activity levels over time remains largely unknown. This study addresses this question in the cell lineage that gives rise to the Drosophila mechanosensory organs. In this lineage a primary precursor cell undergoes a stereotyped sequence of oriented asymmetric cell divisions and transits through two different neural precursor states before acquiring a neuron identity. Using a combination of genetic and cell biology strategies, it was shown that Escargot and Scratch, two transcription factors belonging to the Snail superfamily, maintain an Noff neural commitment by blocking directly the transcription of N-gene targets. The study proposes that Snail factors act by displacing proneural transcription activators from DNA binding sites. As such, Snail factors maintain the Noff state in neural precursor cells by buffering any ectopic variation in the level of N-activity. Since Escargot and Scratch orthologs are present in other precursor cells, these findings are essential for the understanding of precursor cell fate acquisition in other systems.

Hasegawa, E., Truman, J. W. and Nose, A. (2016). Identification of excitatory premotor interneurons which regulate local muscle contraction during Drosophila larval locomotion. Sci Rep 6: 30806. PubMed ID: 27470675
Drosophila larval locomotion was used as a model to elucidate the working principles of motor circuits. Larval locomotion is generated by rhythmic and sequential contractions of body-wall muscles from the posterior to anterior segments, which in turn are regulated by motor neurons present in the corresponding neuromeres. Motor neurons are known to receive both excitatory and inhibitory inputs, combined action of which likely regulates patterned motor activity during locomotion. Although recent studies identified candidate inhibitory premotor interneurons, the identity of premotor interneurons that provide excitatory drive to motor neurons during locomotion remains unknown. This study searched for and identified two putative excitatory premotor interneurons in this system, termed CLI1 and CLI2 (cholinergic lateral interneuron 1 and 2). These neurons were segmentally arrayed and activated sequentially from the posterior to anterior segments during peristalsis. Consistent with their being excitatory premotor interneurons, the CLIs formed GRASP- and ChAT-positive putative synapses with motoneurons and were active just prior to motoneuronal firing in each segment. Moreover, local activation of CLI1s induced contraction of muscles in the corresponding body segments. Taken together, these results suggest that the CLIs directly activate motoneurons sequentially along the segments during larval locomotion.
Johnson, S. A., Zitserman, D. and Roegiers, F. (2016). Numb regulates the balance between Notch recycling and late endosome targeting in Drosophila neural progenitor cells. Mol Biol Cell [Epub ahead of print]. PubMed ID: 27466320
The Notch signaling pathway plays essential roles in both animal development and human disease. Regulation of Notch receptor levels in membrane compartments has been shown to impact signaling in a variety of contexts. This study used steady state and pulse labeling techniques to follow Notch receptors in sensory organ precursor cells (SOP) in Drosophila. The endosomal adaptor protein Numb was found to regulate levels of Notch receptor trafficking to Rab7-labeled late endosomes, but not early endosomes. Using an assay that labels different pools of Notch receptors as they move through the endocytic system, Numb was found to specifically suppress a recycled Notch receptor subpopulation, and excess Notch signaling in numb mutants were shown to require the recycling endosome GTPase Rab11 activity. These data therefore suggest that Numb controls the balance between Notch receptor recycling and receptor targeting to late endosomes to regulate signaling output following asymmetric cell division in Drosophila neural progenitors.
Hanley, O., Zewdu, R., Cohen, L. J., Jung, H., Lacombe, J., Philippidou, P., Lee, D. H., Selleri, L. and Dasen, J. S. (2016). Parallel Pbx-dependent pathways govern the coalescence and fate of motor columns. Neuron [Epub ahead of print]. PubMed ID: 27568519
Evolutionary Homolog Study:
The clustering of neurons sharing similar functional properties and connectivity is a common organizational feature of vertebrate nervous systems. Within motor networks, spinal motor neurons (MNs) segregate into longitudinally arrayed subtypes, establishing a central somatotopic map of peripheral target innervation. MN organization and connectivity relies on Hox transcription factors expressed along the rostrocaudal axis; however, the developmental mechanisms governing the orderly arrangement of MNs are largely unknown. This study shows that Pbx genes (see Drosophila Extradenticle), which encode Hox cofactors, are essential for the segregation and clustering of neurons within motor columns. In the absence of Pbx1 and Pbx3 function, Hox-dependent programs are lost and the remaining MN subtypes are unclustered and disordered. Identification of Pbx gene targets revealed an unexpected and apparently Hox-independent role in defining molecular features of dorsally projecting medial motor column (MMC) neurons. These results indicate Pbx genes act in parallel genetic pathways to orchestrate neuronal subtype differentiation, connectivity, and organization.

Sunday, September 4th

Tsai, S. Y., Chang, Y. L., Swamy, K. B., Chiang, R. L. and Huang, D. H. (2016). GAGA factor, a positive regulator of global gene expression, modulates transcriptional pausing and organization of upstream nucleosomes. Epigenetics Chromatin 9: 32. PubMed ID: 27468311
Promoter-proximal pausing is believed to represent a critical step in transcriptional regulation. GAGA sequence motifs have frequently been found in the upstream region of paused genes in Drosophila, implicating a prevalent binding factor, GAF, in transcriptional pausing. Using newly isolated mutants that retain only ~3 % normal GAF level, this study analyzed its impacts on transcriptional regulation in whole animals. The abundance of three major isoforms of RNA-Pol on Hsp70 was examined during heat shock. Paused RNA-Pol of Hsp70 was shown to be substantially reduced in mutants. Conversely, a global increase in paused RNA-Pol is observed when GAF is over-expressed. Coupled analyses of transcriptome and GAF genomic distribution show that 269 genes enriched for upstream GAF binding are down-regulated in mutants. Interestingly, ~15 % of them encode transcriptional factors, which might control ~2000 additional genes down-regulated in mutants. A positive correlation exists between promoter-proximal RNA-Pol density and GAF occupancy in WT, but not in mutants. Nucleosome occupancy is preferentially attenuated by GAF in the upstream region, thus strongly favoring nucleosome assembly. Significant genetic interactions were detected between GAF and the nucleosome remodeler NURF (see Iswi), the pausing factor NELF (see Nelf-A and Nelf-E), and BAB1 whose binding sites are enriched specifically in genes displaying GAF-dependent pausing. These results provide direct evidence to support a critical role of GAF in global gene expression, transcriptional pausing and upstream nucleosome organization of a group of genes.
Westermark, P. O. (2016). Linking core promoter classes to circadian transcription. PLoS Genet 12: e1006231. PubMed ID: 27504829
Circadian rhythms in transcription are generated by rhythmic abundances and DNA binding activities of transcription factors. Propagation of rhythms to transcriptional initiation involves the core promoter, its chromatin state, and the basal transcription machinery. This study characterize core promoters and chromatin states of genes transcribed in a circadian manner in mouse liver and in Drosophila. The core promoter was shown to be a critical determinant of circadian mRNA expression in both species. A distinct core promoter class, strong circadian promoters (SCPs), is identified in mouse liver but not Drosophila. There was no apparent SCP-like subpopulation of promoters in Drosophila with high amounts of paused Pol II and low nucleosome occupancy, at the same time also driving transcriptional rhythms with both high amplitudes and mean levels. SCPs are defined by specific core promoter features, and are shown to drive circadian transcriptional activities with both high averages and high amplitudes. Data analysis and mathematical modeling further provided evidence for rhythmic regulation of both polymerase II recruitment and pause release at SCPs. The analysis provides a comprehensive and systematic view of core promoters and their link to circadian mRNA expression in mouse and Drosophila, and thus reveals a crucial role for the core promoter in regulated, dynamic transcription.
Miller, A., Ralser, M., Kloet, S. L., Loos, R., Nishinakamura, R., Bertone, P., Vermeulen, M. and Hendrich, B. (2016). Sall4 controls differentiation of pluripotent cells independently of the Nucleosome Remodelling and Deacetylation (NuRD) complex. Development [Epub ahead of print]. PubMed ID: 27471257
Evolutionary Homolog Study:
Sall4 (See Drosophila Spalt) is an essential transcription factor for early mammalian development and is frequently overexpressed in cancer. Though it is reported to play an important role in embryonic stem cell self-renewal, whether it is an essential pluripotency factor has been disputed. This study shows that Sall4 is dispensable for ES cell pluripotency. Sall4 is an enhancer-binding protein that prevents precocious activation of the neural gene expression program in ES cells but is not required for maintenance of the pluripotency gene regulatory network. While a proportion of Sall4 protein physically associates with the Nucleosome Remodeling and Deacetylase (NuRD) complex, Sall4 neither recruits NuRD to chromatin nor influences transcription via NuRD; rather free Sall4 protein regulates transcription independently of NuRD. A model is proposed whereby enhancer binding by Sall4 and other pluripotency-associated transcription factors is responsible for maintaining the balance between transcriptional programs in pluripotent cells.
Dass, R.A., Sarshad, A.A., Carson, B.B., Feenstra, J.M., Kaur, A., Obrdlik, A., Parks, M.M., Prakash, V., Love, D.K., Pietras, K., Serra, R., Blanchard, S.C., Percipalle, P., Brown, A.M. and Vincent, C.T. (2016). Wnt5a signals through DVL1 to repress ribosomal DNA transcription by RNA polymerase I. PLoS Genet 12: e1006217. PubMed ID: 27500936
Evolutionary Homolog Study
Ribosome biogenesis is essential for cell growth and proliferation and is commonly elevated in cancer. Accordingly, numerous oncogene and tumor suppressor signaling pathways target rRNA synthesis. In breast cancer, non-canonical Wnt signaling by Wnt5a has been reported to antagonize tumor growth. This study shows that Wnt5a (see Drosophila Wnt5) rapidly represses rDNA gene transcription in breast cancer cells and generates a chromatin state with reduced transcription of rDNA by RNA polymerase I (Pol I). These effects are specifically dependent on Dishevelled1 (DVL1; see Drosophila Dsh), which accumulates in nucleolar organizer regions (NORs) and binds to rDNA regions of the chromosome. Upon DVL1 binding, the Pol I transcription activator and deacetylase Sirtuin 7 (SIRT7) (see Drosophila Sirt7) releases from rDNA loci, concomitant with disassembly of Pol I transcription machinery at the rDNA promoter. These findings reveal that Wnt5a signals through DVL1 to suppress rRNA transcription. This provides a novel mechanism for how Wnt5a exerts tumor suppressive effects and why disruption of Wnt5a signaling enhances mammary tumor growth in vivo.

Saturday, September 3rd

Viswanathan, M. C., Blice-Baum, A. C., Sang, T. K. and Cammarato, A. (2016). Cardiac-restricted expression of VCP/TER94 RNAi or disease alleles perturbs Drosophila heart structure and impairs function. J Cardiovasc Dev Dis 3. PubMed ID: 27500162
Valosin-containing protein (VCP) is a highly conserved mechanoenzyme that helps maintain protein homeostasis in all cells and serves specialized functions in distinct cell types. In skeletal muscle, it is critical for myofibrillogenesis and atrophy. However, little is known about VCP's role(s) in the heart. Its functional diversity is determined by differential binding of distinct cofactors/adapters, which is likely disrupted during disease. VCP mutations cause multisystem proteinopathy (MSP), a pleiotropic degenerative disorder that involves inclusion body myopathy. MSP patients display progressive muscle weakness. They also exhibit cardiomyopathy and die from cardiac and respiratory failure, which are consistent with critical myocardial roles for the enzyme. Nonetheless, efficient models to interrogate VCP in cardiac muscle remain underdeveloped and poorly studied. This study investigated the significance of VCP and mutant VCP in the Drosophila heart. Cardiac-restricted RNAi-mediated knockdown of TER94, the Drosophila VCP homolog, severely perturbed myofibrillar organization and heart function in adult flies. Furthermore, expression of MSP disease-causing alleles engendered cardiomyopathy in adults and structural defects in embryonic hearts. Drosophila may therefore serve as a valuable model for examining role(s) of VCP in cardiogenesis and for identifying novel heart-specific VCP interactions, which when disrupted via mutation, contribute to or elicit cardiac pathology.
Alexopoulou, Z., Lang, J., Perrett, R. M., Elschami, M., Hurry, M. E., Kim, H. T., Mazaraki, D., Szabo, A., Kessler, B. M., Goldberg, A. L., Ansorge, O., Fulga, T. A. and Tofaris, G. K. (2016). Deubiquitinase Usp8 regulates alpha-synuclein clearance and modifies its toxicity in Lewy body disease. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 27444016
In Parkinson disease, misfolded α-synuclein accumulates, often in a ubiquitinated form, in neuronal inclusions termed Lewy bodies. An important outstanding question is whether ubiquitination in Lewy bodies is directly relevant to alpha-synuclein trafficking or turnover and Parkinson's pathogenesis. By comparative analysis in human postmortem brains, it was found that ubiquitin immunoreactivity in Lewy bodies is largely due to K63-linked ubiquitin chains and markedly reduced in the substantia nigra compared with the neocortex. The ubiquitin staining in cells with Lewy bodies inversely correlated with the content and pathological localization of the deubiquitinase Usp8. Usp8 interacted and partly colocalized with alpha-synuclein in endosomal membranes and, both in cells and after purification, it deubiquitinated K63-linked chains on alpha-synuclein. Knockdown of Usp8 in the Drosophila eye reduced alpha-synuclein levels and α-synuclein-induced eye toxicity. Accordingly, in human cells, Usp8 knockdown increased the lysosomal degradation of α-synuclein. In the dopaminergic neurons of the Drosophila model, unlike knockdown of other deubiquitinases, Usp8 protected from α-synuclein-induced locomotor deficits and cell loss. These findings strongly suggest that removal of K63-linked ubiquitin chains on α-synuclein by Usp8 is a critical mechanism that reduces its lysosomal degradation in dopaminergic neurons and may contribute to α-synuclein accumulation in Lewy body disease.
Aditi, K., Shakarad, M. N. and Agrawal, N. (2016). . Altered lipid metabolism in Drosophila model of Huntington's disease. Sci Rep 6: 31411. PubMed ID: 27506601
Huntington's disease (HD) is late-onset, progressive neurodegenerative disorder caused by expansion of polyglutamine (polyQ) repeat within Huntingtin (Htt) protein. In HD patients, energy-related manifestations such as modulation of weight during entire course of disease with energy deficit at terminal stage have been reported, however, underlying reason remains elusive. Lipids, carbohydrate and protein constitute a predominant fraction of body's energy reservoir and perturbation in their homeostasis may influence weight. To discern role of these energy molecules in weight alteration, they were quantified in an in vivo transgenic Drosophila model of HD. Diseased flies were shown to exhibit change in weight due to an altered lipid metabolism, as evident from considerably high lipid levels at the time of disease onset followed by a pathologic decline at end-stage. An alteration in intracellular lipid droplet size suggested altered cellular lipid turnover. Furthermore, diseased flies displayed substantial changes in carbohydrate and protein content. Interestingly, alteration in weight and lipid levels are independent of the feeding pattern in diseased condition and exhibit weak correlation with insulin-like peptide or adipokinetic hormone producing cells. The results support the idea that lipid metabolism remains centrally affected in HD, leading to altered body weight and subsequently a prevalent energy deficient background.
Niccoli, T., Cabecinha, M., Tillmann, A., Kerr, F., Wong, C.T., Cardenes, D., Vincent, A.J., Bettedi, L., Li, L., Grönke, S. Dols, J. and Partridge, L. (2016). Increased glucose transport into neurons rescues Aβ toxicity in Drosophila. Curr Biol [Epub ahead of print]. PubMed ID: 27524482
Glucose hypometabolism is a prominent feature of the brains of patients with Alzheimer's disease (AD). Disease progression is associated with a reduction in glucose transporters in both neurons and endothelial cells of the blood-brain barrier. However, whether increasing glucose transport into either of these cell types offers therapeutic potential remains unknown. Using an adult-onset Drosophila model of Aβ (amyloid beta) toxicity, this study shows that genetic overexpression of a glucose transporter specifically in neurons, rescues lifespan, behavioral phenotypes, and neuronal morphology. This amelioration of Aβ toxicity is associated with a reduction in the protein levels of the unfolded protein response (UPR) negative master regulator Grp78 and an increase in the UPR. Genetic downregulation of Grp78 activity also protects against Aβ toxicity, confirming a causal effect of its alteration on AD-related pathology. Metformin, a drug that stimulates glucose uptake in cells, mimics these effects, with a concomitant reduction in Grp78 levels and rescue of the shortened lifespan and climbing defects of Aβ-expressing flies. These findings demonstrate a protective effect of increased neuronal uptake of glucose against Aβ toxicity and highlight Grp78 as a novel therapeutic target for the treatment of AD.

Friday, September 2nd

Yadav, R. and Sarkar, S. (2016). Drosophila glob1 is required for the maintenance of cytoskeletal integrity during oogenesis. Dev Dyn [Epub ahead of print]. PubMed ID: 27503269
Hemoglobins (Hbs) are evolutionarily conserved heme-containing metallo-proteins of the "Globin" protein family which harbour the characteristic "globin fold". Hemoglobins have been functionally diversified during evolution and its usual property of oxygen transport is rather a recent adaptation. Drosophila genome possesses three globin genes (glob1, glob2 and glob3). and earlier work has reported that adequate expression of glob1 is required for the various aspects of development and also to regulate the cellular level of reactive oxygen species (ROS). The present study illustrates the explicit role of Drosophila globin1 in progression of oogenesis. A dynamic expression pattern is reported of glob1 in somatic and germ cell derivatives of developing egg chambers during various stages of oogenesis which largely confines around the F-actin rich cellular components. Reduced expression of glob1 leads to various types of abnormalities during oogenesis which were primarily mediated by the inappropriately formed F-actin based cytoskeleton. Subsequent analysis in the somatic and germ line clones shows cell autonomous role of glob1 in the maintenance of the integrity of F-actin based cytoskeleton components in the somatic and germ cell derivatives. This study establishes a novel role of glob1 in maintenance of F-actin based cytoskeleton during progression of oogenesis in Drosophila.
McLaughlin, C. N., Nechipurenko, I. V., Liu, N. and Broihier, H. T. (2016). A Toll receptor-FoxO pathway represses Pavarotti/MKLP1 to promote microtubule dynamics in motoneurons. J Cell Biol 214: 459-474. PubMed ID: 27502486
FoxO proteins are evolutionarily conserved regulators of neuronal structure and function, yet the neuron-specific pathways within which they act are poorly understood. To elucidate neuronal FoxO function in Drosophila melanogaster, a screen was performed for FoxO's upstream regulators and downstream effectors. On the upstream side, genetic and molecular pathway analyses is presented indicating that the Toll-6 receptor, the Toll/interleukin-1 receptor domain adaptor dSARM, and FoxO function in a linear pathway. On the downstream side, it was found that Toll-6-FoxO signaling represses the mitotic kinesin Pavarotti/MKLP1 (Pav-KLP), which itself attenuates microtubule (MT) dynamics. In vivo functions were probed for this novel pathway, and it was found to be essential for axon transport and structural plasticity in motoneurons. Elevated expression of Pav-KLP underlies transport and plasticity phenotypes in pathway mutants, indicating that Toll-6-FoxO signaling promotes MT dynamics by limiting Pav-KLP expression. In addition to uncovering a novel molecular pathway, this work reveals an unexpected function for dynamic MTs in enabling rapid activity-dependent structural plasticity.
Yoo, S. K., Pascoe, H. G., Pereira, T., Kondo, S., Jacinto, A., Zhang, X. and Hariharan, I. K. (2016). Plexins function in epithelial repair in both Drosophila and zebrafish. Nat Commun 7: 12282. PubMed ID: 27452696
In most multicellular organisms, homeostasis is contingent upon maintaining epithelial integrity. When unanticipated insults breach epithelial barriers, dormant programmes of tissue repair are immediately activated. However, many of the mechanisms that repair damaged epithelia remain poorly characterized. This paper describe a role for Plexin A (PlexA), a protein with particularly well-characterized roles in axonal pathfinding, in the healing of damaged epithelia in Drosophila. Semaphorins, which are PlexA ligands, also regulate tissue repair. Drosophila PlexA was shown to have GAP activity for the Rap1 GTPase, which is known to regulate the stability of adherens junctions. The observations suggest that the inhibition of Rap1 activity by PlexA in damaged Drosophila epithelia allows epithelial remodelling, thus facilitating wound repair. A role was also demonstrate for Plexin A1, a zebrafish orthologue of Drosophila PlexA, in epithelial repair in zebrafish tail fins. Thus, plexins function in epithelial wound healing in diverse taxa.
Jayo, A., Malboubi, M., Antoku, S., Chang, W., Ortiz-Zapater, E., Groen, C., Pfisterer, K., Tootle, T., Charras, G., Gundersen, G. G. and Parsons, M. (2016). Fascin regulates nuclear movement and deformation in migrating cells. Dev Cell 38: 371-383. PubMed ID: 27554857
Evolutionary Homolog Study
Fascin is an F-actin-bundling protein shown to stabilize filopodia and regulate adhesion dynamics in migrating cells, and its expression is correlated with poor prognosis and increased metastatic potential in a number of cancers. This study identified the nuclear envelope protein nesprin-2 (see Drosophila Nesprin) as a binding partner for fascin in a range of cell types in vitro and in vivo. Nesprin-2 interacts with fascin through a direct, F-actin-independent interaction, and this binding is distinct and separable from a role for fascin within filopodia at the cell periphery. Moreover, disrupting the interaction between fascin and nesprin-2 C-terminal domain leads to specific defects in F-actin coupling to the nuclear envelope, nuclear movement, and the ability of cells to deform their nucleus to invade through confined spaces. Together, these results uncover a role for fascin that operates independently of filopodia assembly to promote efficient cell migration and invasion.

Thursday, September 1st

Deneke, V.E., Melbinger, A., Vergassola, M. and Di Talia, S. (2016). Waves of Cdk1 activity in S phase synchronize the cell cycle in Drosophila embryos. Dev Cell 38: 399-412. PubMed ID: 27554859
Embryos of most metazoans undergo rapid and synchronous cell cycles following fertilization. Using biosensors of Cdk1 and Chk1 activities, this study dissected the regulation of Cdk1 waves in the Drosophila syncytial blastoderm. Cdk1 waves were shown not to be controlled by the mitotic switch but by a double-negative feedback between Cdk1 and Chk1. S phase Cdk1 waves were shown to be fundamentally distinct and propagate as active trigger waves in an excitable medium, while mitotic Cdk1 waves propagate as passive phase waves. These findings show that in Drosophila embryos, Cdk1 positive feedback serves primarily to ensure the rapid onset of mitosis, while wave propagation is regulated by S phase events. 

Kim, M., O'Rourke, B. P., Soni, R. K., Jallepalli, P. V., Hendrickson, R. C. and Tsou, M. B. (2016). Promotion and suppression of centriole duplication are catalytically coupled through PLK4 to ensure centriole homeostasis. Cell Rep. PubMed ID: 27425613
Evolutionary Homolog Study:
PLK4 (see Drosophila Sak kinase) is the major kinase driving centriole duplication. Duplication occurs only once per cell cycle, forming one new (or daughter) centriole that is tightly engaged to the preexisting (or mother) centriole. Centriole engagement is known to block the reduplication of mother centrioles, but the molecular identity responsible for the block remains unclear. This study shows, using mammalian retinal pigment epithelial cell lines, that the centriolar cartwheel, the geometric scaffold for centriole assembly, forms the identity of daughter centrioles essential for the block, ceasing further duplication of the mother centriole to which it is engaged. To ensure a steady block, the cartwheel was shown to require constant maintenance by PLK4 through phosphorylation of the same substrate that drives centriole assembly. These results support a model that the cartwheel-bound PLK4 directly suppresses centriole reduplication.
Vijayraghavan, S., Tsai, F.L. and Schwacha, A. (2016). A checkpoint-related function of the MCM replicative helicase is required to avert accumulation of RNA:DNA hybrids during S-phase and ensuing DSBs during G2/M. PLoS Genet 12: e1006277. PubMed ID: 27556397
Evolutionary Homolog Study
The Mcm2-7 complex is the catalytic core of the eukaryotic replicative helicase. This study identifies a new role for this complex in maintaining genome integrity. Using both genetic and cytological approaches, it was found that a specific mcm (see Drosophila Mcm2) allele (mcm2DENQ) causes elevated genome instability that correlates with the appearance of numerous DNA-damage associated foci of γH2AX (see Drosophila His2Av) and Rad52 (see Drosophila spn-A). Further, the triggering events for this genome instability were found to be elevated levels of RNA:DNA hybrids and an altered DNA topological state, as over-expression of either RNaseH (an enzyme specific for degradation of RNA in RNA:DNA hybrids) or Topoisomerase 1 (an enzyme that relieves DNA supercoiling) can suppress the mcm2DENQ DNA-damage phenotype. Moreover, the observed DNA damage has several additional unusual properties, in that DNA damage foci appear only after S-phase (see cell cycle in Drosophila), in G2/M, and are dependent upon progression into metaphase. In addition, the resultant DNA damage is not due to spontaneous S-phase fork collapse. In total, these unusual mcm2DENQ phenotypes are markedly similar to those of a special previously-studied allele of the checkpoint sensor kinase ATR/MEC1 (see Drosophila mei-41), suggesting a possible regulatory interplay between Mcm2-7 and ATR during unchallenged growth. As RNA:DNA hybrids primarily result from transcription perturbations, the study suggests that surveillance-mediated modulation of the Mcm2-7 activity plays an important role in preventing catastrophic conflicts between replication forks and transcription complexes. Possible relationships among these effects and the recently discovered role of Mcm2-7 in the DNA replication checkpoint induced by HU treatment are discussed.

Shaikh, M. N., Gutierrez-Avino, F., Colonques, J., Ceron, J., Hammerle, B. and Tejedor, F. J. (2016). Minibrain drives the Dacapo dependent cell cycle exit of neurons in the Drosophila brain by promoting asense and prospero expression. Development [Epub ahead of print]. PubMed ID: 27510975
A key issue in neurodevelopment is to understand how precursor cells decide to stop dividing and commence their terminal differentiation at the correct time and place. This study shows that minibrain (mnb), the Drosophila ortholog of the Down syndrome candidate gene MNB/DYRK1A, is transiently expressed in newborn neuronal precursors known as ganglion cells (GCs). Mnb promotes the cell cycle exit of GCs through a dual mechanism that regulates the expression of the cyclin-dependent kinase inhibitor Dacapo, the homolog of vertebrate p27kip1. On the one hand, Mnb upregulates the expression of the proneural transcription factor (TF) Asense, which promotes Dacapo expression. On the other, Mnb induces the expression of Prospero, a homeodomain TF that in turn inhibits the expression of Deadpan, a pan-neural TF that represses dacapo. In addition to its effects on Asense and Prospero, Mnb also promotes the expression of the neuronal-specific RNA regulator Elav, strongly suggesting that Mnb facilitates neuronal differentiation. These actions of Mnb ensure the precise timing of neuronal birth, coupling the mechanisms that regulate neurogenesis, cell cycle control and terminal differentiation of neurons.
Zhaunova, L., Ohkura, H. and Breuer, M. (2016). Kdm5/Lid regulates chromosome architecture in meiotic prophase I independently of its histone demethylase activity. PLoS Genet 12: e1006241. PubMed ID: 27494704
During prophase of the first meiotic division (prophase I), chromatin dynamically reorganises to recombine and prepare for chromosome segregation. Histone modifying enzymes are major regulators of chromatin structure, but knowledge of their roles in prophase I is still limited. This study reports on crucial roles of Kdm5/Lid, one of two histone demethylases in Drosophila that remove one of the trimethyl groups at Lys4 of Histone 3 (H3K4me3). In the absence of Kdm5/Lid, the synaptonemal complex was only partially formed and failed to be maintained along chromosome arms, while localisation of its components at centromeres was unaffected. Kdm5/Lid was also required for karyosome formation and homologous centromere pairing in prophase I. Although loss of Kdm5/Lid dramatically increased the level of H3K4me3 in oocytes, catalytically inactive Kdm5/Lid can rescue the above cytological defects. Therefore Kdm5/Lid controls chromatin architecture in meiotic prophase I oocytes independently of its demethylase activity.

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