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

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

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Saturday, January 31th, 2015

Dweck, H.K., Ebrahim, S.A., Farhan, A., Hansson, B.S. and Stensmyr, M.C. (2015). Olfactory proxy detection of dietary antioxidants in Drosophila. Curr Biol [Epub ahead of print]. PubMed ID: 25619769

Summary: Dietary antioxidants play an important role in preventing oxidative stress. Whether animals in search of food or brood sites are able to judge the antioxidant content, and if so actively seek out resources with enriched antioxidant content, remains unclear. This study shows that the vinegar fly Drosophila melanogaster detects the presence of hydroxycinnamic acids (HCAs)-potent dietary antioxidants abundant in fruit-via olfactory cues. Flies were unable to smell HCAs directly but were found to be equipped with dedicated olfactory sensory neurons detecting yeast-produced ethylphenols that are exclusively derived from HCAs. These neurons were housed on the maxillary palps, expressed the odorant receptor Or71a, and were necessary and sufficient for proxy detection of HCAs. Activation of these neurons in adult flies induced positive chemotaxis, oviposition, and increased feeding. Further, fly larvae also sought yeast enriched with HCAs and used the same ethylphenol cues as the adults but relied for detection upon a larval unique odorant receptor (Or94b), which was co-expressed with a receptor (Or94a) detecting a general yeast volatile. Also, the ethylphenols acted as reliable cues for the presence of dietary antioxidants, as these volatiles were produced-upon supplementation of HCAs-by a wide range of yeasts known to be consumed by flies. For flies, dietary antioxidants are presumably important to counteract acute oxidative stress induced by consumption or by infection by entomopathogenic microorganisms. The ethylphenol pathway described in this study adds another layer to the fly's defensive arsenal against toxic microbes.

Hu, Y., Han, Y., Shao, Y., Wang, X., Ma, Y., Ling, E. and Xue, L. (2015). Gr33a modulates Drosophila male courtship preference. Sci Rep 5: 7777. PubMed ID: 25586066

Summary: In any gamogenetic species, attraction between individuals of the opposite sex promotes reproductive success that guarantees their thriving. Consequently, mate determination between two sexes is effortless for an animal. However, choosing a spouse from numerous attractive partners of the opposite sex needs deliberation. In Drosophila melanogaster, both younger virgin females and older ones are equally liked options to males; nevertheless, when given options, males prefer younger females to older ones. Non-volatile cuticular hydrocarbons, considered as major pheromones in Drosophila, constitute females' sexual attraction that act through males' gustatory receptors (Grs) to elicit male courtship. To date, only a few putative Grs are known to play roles in male courtship. This study reports that loss of Gr33a function or abrogating the activity of Gr33a neurons does not disrupt male-female courtship, but eliminates males' preference for younger mates. Furthermore, ectopic expression of human amyloid precursor protein (APP; see Drosophila Appl ) in Gr33a neurons abolishes males' preference behavior. Such function of APP is mediated by the transcription factor Forkhead box O (dFoxO). These results not only provide mechanistic insights into Drosophila male courtship preference, but also establish a novel Drosophila model for Alzheimer's disease (AD).

Solanki, N., Wolf, R. and Heisenberg, M. (2015). Central complex and mushroom bodies mediate novelty choice behavior in Drosophila. J Neurogenet: 1-16. PubMed ID: 25585638

Summary: Novelty choice, a visual paired-comparison task for the fly Drosophila melanogaster is studied with severely restrained single animals in a flight simulator. The virtual environment simulates free flight for rotation in the horizontal plane. The behavior has three functional components: visual azimuth orientation, working memory and pattern discrimination (perception). This paper relates a study of novelty choice in relation to its neural substrate in the brain and shows that it requires the central complex and in particular the ring neurons of the ellipsoid body. Surprisingly, it also involves the mushroom bodies which are needed specifically in the comparison of patterns of different size.

Nieto, P. S., Revelli, J. A., Garbarino-Pico, E., Condat, C. A., Guido, M. E. and Tamarit, F. A. (2015). Effects of different per translational kinetics on the dynamics of a core circadian clock model. PLoS One 10: e0115067. PubMed ID: 25607544

Summary: Living beings display self-sustained daily rhythms in multiple biological processes, which persist in the absence of external cues since they are generated by endogenous circadian clocks. The period (per) gene is a central player within the core molecular mechanism for keeping circadian time in most animals. Recently, the modulation of PER translation has been reported, both in mammals and flies, suggesting that translational regulation of clock components is important for the proper clock gene expression and molecular clock performance. Because translational regulation ultimately implies changes in the kinetics of translation and, therefore, in the circadian clock dynamics, how and to what extent the molecular clock dynamics is affected by the kinetics of PER translation was studied. With this objective, a minimal mathematical model of the molecular circadian clock was used to qualitatively characterize the dynamical changes derived from kinetically different PER translational mechanisms. Emergence of self-sustained oscillations with characteristic period, amplitude, and phase lag (time delays) between per mRNA and protein expression was found to depend on the kinetic parameters related to PER translation. Interestingly, under certain conditions, a PER translation mechanism with saturable kinetics introduces longer time delays than a mechanism ruled by a first-order kinetics. In addition, the kinetic laws of PER translation significantly changed the sensitivity of the model to parameters related to the synthesis and degradation of per mRNA and PER degradation. Lastly, a set of parameters, with realistic values, was found for which the model reproduces some experimental results reported recently for Drosophila melanogaster, and some predictions derived from this analysis are reported.

Friday, January 30th

Pert, M., Gan, M., Saint, R. and Murray, M.J. (2015). Netrins and Frazzled/DCC promote the migration and mesenchymal to epithelial transition of Drosophila midgut cells. Biol Open [Epub ahead of print]. PubMed ID: 25617422

Summary: Mesenchymal-epithelial transitions (METs) are important in both development and the growth of secondary tumours. Although the molecular basis for epithelial polarity is well studied, less is known about the cues that induce MET. This study shows that Netrins, well known as chemotropic guidance factors, provide a basal polarising cue during the Drosophila midgut MET. Both netrinA and netrinB were expressed in the visceral mesoderm, the substrate upon which midgut cells migrate, while their receptor frazzled (fra) was expressed in midgut cells. Netrins were required to polarise Fra to the basal surface, and Netrins and Fra underwent mutually-dependent endocytosis, with Fra subsequently trafficking to late endosomes. Mutations to fra and netrins affected both migration and MET but to different degrees. Loss of fra strongly delayed migration, midgut cells failed to extend protrusions, and apico-basal polarisation of proteins and epithelium formation was inhibited. In netrin mutants, the migration phenotype was weaker and cells still extended protrusions. However, apico-basal polarisation of proteins, including Fra, and F-Actin was greatly disrupted and a monolayer failed to form. Delocalised accumulations of F-Actin were prevalent in netrin mutants but not fra mutants suggesting delocalised Fra may disrupt the MET. βPS localisation was also affected in netrin mutants in that a basal gradient was reduced while localisation to the midgut/VM interface was increased. Since a similar effect was seen when endocytosis was inhibited, Netrin and Fra may regulate Integrin turnover. The results suggest Netrin-dependent basal polarisation of Fra is critical for the formation of an epithelium.

Kumar, R.P., Dobi, K.C., Baylies, M.K. and Abmayr, S.M. (2015). Muscle cell fate choice requires the T-Box transcription factor Midline in Drosophila. Genetics [Epub ahead of print]. PubMed ID: 25614583

Summary: Drosophila Midline (Mid) is an ortholog of vertebrate Tbx20, which plays roles in the developing heart, migrating cranial motor neurons and endothelial cells. Mid functions in cell fate specification and differentiation of tissues that include the ectoderm, cardioblasts, neuroblasts, and egg chambers; however, a role in the somatic musculature has not been described. This study identified mid in genetic and molecular screens for factors contributing to somatic muscle morphogenesis. Mid was expressed in founder cells (FCs) for several muscle fibers, and functioned cooperatively with the T-box protein H15 in lateral oblique muscle 1 and the segment border muscle. Mid was particularly important for the specification and development of the lateral transverse (LT) muscles LT3 and LT4, which arise by asymmetric division of a single muscle progenitor. Mid was expressed in this progenitor and its two sibling FCs, but was maintained only in the LT4 FC. Both muscles were frequently missing in mid mutant embryos, and LT4-associated expression of the transcription factor Krüppel (Kr) was lost. When present, LT4 adopted an LT3-like morphology. Coordinately, mid misexpression caused LT3 to adopt an LT4-like morphology and was associated with ectopic Kr expression. From these data, mid functions first in the progenitor to direct development of LT3 and LT4, and later in the FCs to influence which of these differentiation profiles is selected. Mid is the first T-box factor shown to influence LT3 and LT4 muscle identity and, along with the T-box protein Optomotor-blind-related-gene-1 (Org-1) is representative of a new class of transcription factors in muscle specification.

Matsuda, R., Hosono, C., Saigo, K. and Samakovlis, C. (2015). The intersection of the extrinsic Hedgehog and WNT/Wingless signals with the intrinsic Hox code underpins branching pattern and tube shape diversity in the Drosophila airways. PLoS Genet 11: e1004929. PubMed ID: 25615601

Summary: The tubular networks of the Drosophila respiratory system and vertebrate vasculature show distinct branching patterns and tube shapes in different body regions. These local variations are crucial for organ function and organismal fitness. Organotypic patterns and tube geometries in branched networks are typically controlled by variations of extrinsic signaling but the impact of intrinsic factors on branch patterns and shapes is not well explored. This study shows that the intersection of extrinsic hedgehog(hh) and WNT/wingless (wg) signaling with the tube-intrinsic Hox code of distinct segments specifies the tube pattern and shape of the Drosophila airways. In the cephalic part of the airways, hh signaling induces expression of the transcription factor (TF) knirps (kni) in the anterior dorsal trunk (DTa1). Kni represses the expression of another TF spalt major (salm), making DTa1 a narrow and long tube. In DTa branches of more posterior metameres, Bithorax Complex (BX-C) Hox genes autonomously divert hh signaling from inducing kni, thereby allowing DTa branches to develop as salm-dependent thick and short tubes. Moreover, the differential expression of BX-C genes is partly responsible for the anterior-to-posterior gradual increase of the DT tube diameter through regulating the expression level of Salm, a transcriptional target of WNT/wg signaling. Thus, these results highlight how tube intrinsic differential competence can diversify tube morphology without changing availabilities of extrinsic factors.

Froldi, F., Szuperak, M., Weng, C. F., Shi, W., Papenfuss, A. T. and Cheng, L. Y. (2015). The transcription factor Nerfin-1 prevents reversion of neurons into neural stem cells. Genes Dev 29: 129-143. PubMed ID: 25593306

Summary: Cellular dedifferentiation is the regression of a cell from a specialized state to a more multipotent state and is implicated in cancer. However, the transcriptional network that prevents differentiated cells from reacquiring stem cell fate is so far unclear. Neuroblasts (NBs), the Drosophila neural stem cells, are a model for the regulation of stem cell self-renewal and differentiation. This study shows that the Drosophila zinc finger transcription factor Nervous fingers 1 (Nerfin-1) locks neurons into differentiation, preventing their reversion into NBs. Following Prospero-dependent neuronal specification in the ganglion mother cell (GMC), a Nerfin-1-specific transcriptional program maintains differentiation in the post-mitotic neurons. The loss of Nerfin-1 causes reversion to multipotency and results in tumors in several neural lineages. Both the onset and rate of neuronal dedifferentiation in nerfin-1 mutant lineages are dependent on Myc- and Target of rapamycin (Tor)-mediated cellular growth. In addition, Nerfin-1 is required for NB differentiation at the end of neurogenesis. RNA sequencing (RNA-seq) and chromatin immunoprecipitation (ChIP) analysis show that Nerfin-1 administers its function by repression of self-renewing-specific and activation of differentiation-specific genes. These findings support the model of bidirectional interconvertibility between neural stem cells and their post-mitotic progeny and highlight the importance of the Nerfin-1-regulated transcriptional program in neuronal maintenance.

Thursday, January 29th

Gao, M., Thomson, T.C., Creed, T.M., Tu, S., Loganathan, S.N., Jackson, C.A., McCluskey, P., Lin, Y., Collier, S.E., Weng, Z., Lasko, P., Ohi, M.D. and Arkov, A.L. (2015).Glycolytic enzymes localize to ribonucleoprotein granules in Drosophila germ cells, bind Tudor and protect from transposable elements. EMBO Rep. [Epub ahead of print]. PubMed ID: 25600116

Summary: Germ cells give rise to all cell lineages in the next-generation and are responsible for the continuity of life. In a variety of organisms, germ cells and stem cells contain large ribonucleoprotein granules. Although these particles were discovered more than 100 years ago, their assembly and functions are not well understood. This study reports that glycolytic enzymes are components of these granules in Drosophila germ cells and both their mRNAs and the enzymes themselves are enriched in germ cells. These enzymes were specifically required for germ cell development and they protected their genomes from transposable elements, providing the first link between metabolism and transposon silencing. In the granules, glycolytic enzymes associated with the evolutionarily conserved Tudor protein. Biochemical and single-particle EM structural analyses of purified Tudor showed a flexible molecule and suggested a mechanism for the recruitment of glycolytic enzymes to the granules. This data indicates that germ cells, similarly to stem cells and tumor cells, might prefer to produce energy through the glycolytic pathway, thus linking a particular metabolism to pluripotency.

Ables, E.T., Bois, K.E., Garcia, C.A. and Drummond-Barbosa, D. (2015). Ecdysone response gene E78 controls ovarian germline stem cell niche formation and follicle survival in Drosophila. Dev Biol [Epub ahead of print]. PubMed ID: 25624267

Summary: Nuclear hormone receptors have emerged as important regulators of mammalian and Drosophila adult physiology, affecting such seemingly diverse processes as adipogenesis, carbohydrate metabolism, circadian rhythm, stem cell function, and gamete production. Although nuclear hormone receptors Ecdysone Receptor (EcR) and Ultraspiracle (Usp) have multiple known roles in Drosophila development and regulate key processes during oogenesis, the adult function of the majority of nuclear hormone receptors remains largely undescribed. Ecdysone-induced protein 78C (E78), a nuclear hormone receptor closely related to Drosophila E75 and to mammalian Rev-Erb and Peroxisome Proliferator Activated Receptors, was originally identified as an early ecdysone target; however, it has remained unclear whether E78 significantly contributes to adult physiology or reproductive function. To further explore the biological function of E78 in oogenesis, this study used available E78 reporters and created a new E78 loss-of-function allele. E78 was found to be expressed throughout the germline during oogenesis, and was important for proper egg production and for the maternal control of early embryogenesis. E78 was required during development to establish the somatic germline stem cell (GSC) niche, and that E78 function in the germline promoted the survival of developing follicles. Consistent with its initial discovery as an ecdysone-induced target, there were significant genetic interactions between E78 and components of the ecdysone signaling pathway. Taken together with the previously described roles of EcR, Usp, and E75, these results suggest that nuclear hormone receptors are critical for the broad transcriptional control of a wide variety of cellular processes during oogenesis.

Taniguchi, K., Kokuryo, A., Imano, T., Minami, R., Nakagoshi, H. and Adachi-Yamada, T. (2014). Isoform-specific functions of Mud/NuMA mediate binucleation of Drosophila male accessory gland cells. BMC Dev Biol 14: 46. PubMed ID: 25527079

Summary: In standard cell division, the cells undergo karyokinesis and then cytokinesis. Some cells, however, such as cardiomyocytes and hepatocytes, can produce binucleate cells by going through mitosis without cytokinesis. This cytokinesis skipping is thought to be due to the inhibition of cytokinesis machinery such as the central spindle or the contractile ring, but the mechanisms regulating it are unclear. This study investigated them by characterizing the binucleation event during development of the Drosophila male accessory gland, in which all cells are binucleate. The accessory gland cells arrested the cell cycle at 50 hours after puparium formation (APF) and in the middle of the pupal stage stopped proliferating for 5 hours. They then restarted the cell cycle and at 55 hours APF entered the M-phase synchronously. At this stage, accessory gland cells binucleated by mitosis without cytokinesis. Binucleating cells displayed the standard karyokinesis progression but also showed unusual features such as a non-round shape, spindle orientation along the apico-basal axis, and poor assembly of the central spindle. Mud, a Drosophila homolog of NuMA, regulated the processes responsible for these three features, the classical isoform MudPBD and the two newly characterized isoforms MudL and MudS regulated them differently: MudL repressed cell rounding, MudPBD and MudS oriented the spindle along the apico-basal axis, and MudS and MudL repressed central spindle assembly. Importantly, overexpression of MudS induced binucleation even in standard proliferating cells such as those in imaginal discs. This study has characterized the binucleation in the Drosophila male accessory gland and examined mechanisms that regulated unusual morphologies of binucleating cells. Mud, a microtubule binding protein regulating spindle orientation, was shown to be involved in this binucleation. It is suggested that atypical functions exerted by three structurally different isoforms of Mud regulate cell rounding, spindle orientation and central spindle assembly in binucleation. It is also proposed that MudS is a key regulator triggering cytokinesis skipping in binucleation processes.

Mukai, M., Hira, S., Nakamura, K., Nakamura, S., Kimura, H., Sato, M. and Kobayashi, S. (2015). H3K36 trimethylation-mediated epigenetic regulation is activated by Bam and promotes germ cell differentiation during early oogenesis in Drosophila. Biol Open [Epub ahead of print]. PubMed ID: 25572421

Summary: Epigenetic silencing is critical for maintaining germline stem cells in Drosophila ovaries. However, it remains unclear how the differentiation factor, Bag-of-marbles (Bam), counteracts transcriptional silencing. This study found that the trimethylation of lysine 36 on histone H3 (H3K36me3), a modification that is associated with gene activation, is enhanced in Bam-expressing cells. H3K36me3 levels were reduced in flies deficient in Bam. Inactivation of the Set2 methyltransferase, which confers the H3K36me3 modification, in germline cells markedly reduced H3K36me3 and impaired differentiation. Genetic analyses revealed that Set2 acts downstream of Bam. Furthermore, orb expression, which is required for germ cell differentiation, was activated by Set2, probably through direct H3K36me3 modification of the orb locus. These data indicate that H3K36me3-mediated epigenetic regulation is activated by bam, and that this modification facilitates germ cell differentiation, probably through transcriptional activation. This work provides a novel link between Bam and epigenetic transcriptional control.

Wednesday, January 28th

Woodcock, K.J., Kierdorf, K., Pouchelon, C.A., Vivancos, V., Dionne, M.S. and Geissmann, F. (2014). Macrophage-derived Upd3 cytokine causes impaired glucose homeostasis and reduced lifespan in Drosophila fed a lipid-rich diet. Immunity. [Epub ahead of print]. Pubmed ID: 25601202

Summary:
Long-term consumption of fatty foods is associated with obesity, macrophage activation and inflammation, metabolic imbalance, and a reduced lifespan. This study took advantage of Drosophila genetics to investigate the role of macrophages and the pathway(s) that govern their response to dietary stress. Flies fed a lipid-rich diet presented with increased fat storage, systemic activation of JAK-STAT signaling, reduced insulin sensitivity, hyperglycemia, and a shorter lifespan. Drosophila macrophages produced the JAK-STAT-activating cytokine upd3, in a scavenger-receptor (crq) and JNK-dependent manner. Genetic depletion of macrophages or macrophage-specific silencing of upd3 decreased JAK-STAT activation and rescued insulin sensitivity and the lifespan of Drosophila, but did not decrease fat storage. NF-κB signaling made no contribution to the phenotype observed. These results identify an evolutionarily conserved "scavenger receptor-JNK-type 1 cytokine" cassette in macrophages, which controls glucose metabolism and reduces lifespan in Drosophila maintained on a lipid-rich diet via activation of the JAK-STAT pathway.

Landis, G. N., Salomon, M. P., Keroles, D., Brookes, N., Sekimura, T. and Tower, J. (2015). The progesterone antagonist mifepristone/RU486 blocks the negative effect on life span caused by mating in female Drosophila. Aging (Albany NY). PubMed ID: 25614682

Summary: Mating causes decreased life span in female Drosophila. This study reports that mifepristone blocked this effect, yielding life span increases up to +68%. Drug was fed to females after mating, in the absence of males, demonstrating function in females. Mifepristone did not increase life span of virgin females or males. Mifepristone reduced progeny production but did not reduce food intake. High-throughput RNA sequencing was used to identify genes up-regulated or down-regulated upon mating, and where the change was reduced by mifepristone. Five candidate positive regulators of life span were identified, including dosage compensation regulator Unr and three X-linked genes: multi sex combs (PcG gene), Dopamine 2-like receptor and CG14215. The 37 candidate negative genes included neuropeptide CNMamide and several involved in protein mobilization and immune response. The results inform the interpretation of experiments involving mifepristone, and implicate steroid hormone signaling in regulating the trade-off between reproduction and life span.

Min, B., Kwon, Y. C., Choe, K. M. and Chung, K. C. (2014). PINK1 phosphorylates transglutaminase 2 and blocks its proteasomal degradation. J Neurosci Res [Epub ahead of print]. PubMed ID: 25557247

Summary: Parkinson's disease (PD) is characterized by progressive dopaminergic neuronal loss and the formation of abnormal protein aggregates, referred to as Lewy bodies (LBs). PINK1 is a serine/threonine protein kinase that protects cells from stress-induced mitochondrial dysfunction. PINK1 gene mutations cause one form of autosomal recessive early-onset PD. Transglutaminase 2 (TG2) is an intracellular protein cross-linking enzyme that has an important role in LB formation during PD pathogenesis. This study identifies PINK1 as a novel TG2 binding partner and shows that PINK1 stabilizes the half-life of TG2 via inhibition of TG2 ubiquitination and subsequent proteasomal degradation. PINK1 affects TG2 stability in a kinase-dependent manner. In addition, PINK1 directly phosphorylates TG2 in carbonyl cyanide m-chlorophenyl hydrazine-induced mitochondrial damaged states, thereby enhancing TG2 accumulation and intracellular protein cross-linking products. This study further confirms the functional link between upstream PINK1 and downstream TG2 in Drosophila melanogaster. These data suggest that PINK1 positively regulates TG2 activity, which may be closely associated with aggresome formation in neuronal cells.

Gao, F., Chen, D., Si, J., Hu, Q., Qin, Z., Fang, M. and Wang, G. (2015). The mitochondrial protein BNIP3L is the substrate of PARK2 and mediates mitophagy in PINK1/PARK2 pathway. Hum Mol Genet [Epub ahead of print]. PubMed ID: 25612572

Summary: Mitochondrial dysfunction plays important roles in Parkinson's disease (PD) and the degradation of the damaged mitochondria by the mitochondria quality control system is important for dopaminergic (DA) neuronal survival. BNIP3L/Nix is a mitochondrial outer membrane protein that is required for the selective clearance of mitochondria. This study found that the mitochondrial protein BNIP3L acts downstream of the PINK1/PARK2 pathway to induce mitophagy. BNIP3L is a substrate of PARK2 to drive PARK2-mediated mitophagy. The ubiquitination of BNIP3L by PARK2 recruits NBR1 to mitochondria, thereby targeting mitochondria for degradation. BNIP3L rescues mitochondrial defects in pink1 mutant Drosophila but not in park mutant Drosophila, indicating that the clearance of mitochondria induced by BNIP3L depends on the presence of PARK2. In cells intoxicated with mitochondrial complex I inhibitors rotenone, 6-OHDA or MPP+, the disrupted mitochondria are not appropriately eliminated by mitophagy due to the improper degradation of BNIP3L. Thus, this study study demonstrates that BNIP3L, as a substrate of PARK2, promotes mitophagy in the PINK1/PARK2 pathway is associated with PD pathogenesis.

Tuesday, January 27th

Wong, K.K., Li, W., An, Y., Duan, Y., Li, Z., Kang, Y. and Yan, Y. (2015). β-Spectrin regulates the Hippo signaling pathway and modulates the basal actin network. J Biol Chem. [Epub ahead of print]. PubMed ID: 25589787

Summary: Emerging evidence suggests functional regulation of Hippo pathway by the actin cytoskeleton, although the detailed molecular mechanism remains incomplete. In a genetic screen, this study identified a requirement for β-Spectrin in the posterior follicle cells (PFCs) for the oocyte repolarization process during Drosophila mid-oogenesis. β-spectrin mutations led to loss of Hippo signaling activity in the follicle cells. Similar reduction of Hippo signaling activity was observed after β-Spectrin knockdown in mammalian cells. Further, β-spectrin mutations disrupted the basal actin network in the follicle cells. The abnormal stress-fiber-like actin structure on the basal side of the follicle cells might provide a likely link between the & #946;-spectrin mutations and the loss of Hippo signaling activity phenotype.

Ruiz-Romero, M., Blanco, E., Paricio, N., Serras, F. and Corominas, M. (2015). Cabut/dTIEG associates with the transcription factor Yorkie for growth control. EMBO Rep. PubMed ID: 25572844

Summary: The Drosophila transcription factor Cabut/dTIEG (Cbt) is a growth regulator, whose expression is modulated by different stimuli. This study determined Cbt association with chromatin and identified Yorkie (Yki), the transcriptional co-activator of the Hippo (Hpo) pathway as its partner. Cbt and Yki co-localize on common gene promoters, and the expression of target genes varies according to changes in Cbt levels. Down-regulation of Cbt suppresses the overgrowth phenotypes caused by mutations in expanded (ex) and yki overexpression, whereas its up-regulation promotes cell proliferation. These results imply that Cbt is a novel partner of Yki that is required as a transcriptional co-activator in growth control.

Jolly, M. K., Rizvi, M. S., Kumar, A. and Sinha, P. (2014). Mathematical modeling of sub-cellular asymmetry of fat-dachsous heterodimer for generation of planar cell polarity. PLoS One 9: e97641. PubMed ID: 24841507

Summary: Planar Cell Polarity (PCP) is an evolutionarily conserved characteristic of animal tissues marked by coordinated polarization of cells or structures in the plane of a tissue. In insect wing epithelium, for instance, PCP is characterized by en masse orientation of hairs orthogonal to its apical-basal axis and pointing along the proximal-distal axis of the organ. Directional cue for PCP has been proposed to be generated by complex sets of interactions amongst three proteins - Fat (Ft), Dachsous (Ds) and Four-jointed (Fj). Ft and Ds are two atypical cadherins, which are phosphorylated by Fj, a Golgi kinase. Ft and Ds from adjacent cells bind heterophilically via their tandem cadherin repeats, and their binding affinities are regulated by Fj. Further, in the wing epithelium, sub-cellular levels of Ft-Ds heterodimers are seen to be elevated at the distal edges of individual cells, prefiguring their PCP. Mechanisms generating this sub-cellular asymmetry of Ft-Ds heterodimer in proximal and distal edges of cells, however, have not been resolved yet. Using a mathematical modeling approach, this study provides a framework for generation of this sub-cellular asymmetry of Ft-Ds heterodimer. First, how the known interactions within Ft-Ds-Fj system translate into sub-cellular asymmetry of Ft-Ds heterodimer is explained. Second, this asymmetric localization of Ft-Ds heterodimer was shown to be lost when tissue-level gradient of Fj is flattened, or when phosphorylation of Ft by Fj is abolished, but not when tissue-level gradient of Ds is flattened or when phosphorylation of Ds is abrogated. Finally, distal enrichment of Ds was shown to amplifies Ft-Ds asymmetry. These observations reveal that gradient of Fj expression, phosphorylation of Ft by Fj and sub-cellular distal accumulation of Ds are three critical elements required for generating sub-cellular asymmetry of Ft-Ds heterodimer. This model integrates the known experimental data and presents testable predictions for future studies.

Emran, S., Yang, M., He, X., Zandveld, J. and Piper, M. D. (2014). Target of rapamycin signalling mediates the lifespan-extending effects of dietary restriction by essential amino acid alteration. Aging (Albany NY) 6: 390-398. PubMed ID: 24861087

Summary: Dietary restriction (DR), defined as a moderate reduction in food intake short of malnutrition, has been shown to extend healthy lifespan in a diverse range of organisms, from yeast to primates. Reduced signalling through the insulin/IGF-like (IIS) and Target of Rapamycin (TOR) signalling pathways also extend lifespan. InDrosophila melanogaster the lifespan benefits of DR can be reproduced by modulating only the essential amino acids in yeast based food. This study shows that pharmacological downregulation of TOR signalling, but not reduced IIS, modulates the lifespan response to DR by amino acid alteration. Of the physiological responses flies exhibit upon DR, only increased body fat and decreased heat stress resistance phenotypes correlated with longevity via reduced TOR signalling. These data indicate that lowered dietary amino acids promote longevity via TOR, not by enhanced resistance to molecular damage, but through modified physiological conditions that favour fat accumulation.

Monday, January 26th

Ashwal-Fluss, R., Meyer, M., Pamudurti, N. R., Ivanov, A., Bartok, O., Hanan, M., Evantal, N., Memczak, S., Rajewsky, N. and Kadener, SS (2014). circRNA biogenesis competes with pre-mRNA splicing. Mol Cell 56: 55-66. PubMed ID: 25242144

Summary: Circular RNAs (circRNAs) are widely expressed noncoding RNAs. However, their biogenesis and possible functions are poorly understood. By studying circRNAs that were identified in neuronal tissues, evidence is provided that animal circRNAs are generated cotranscriptionally and that their production rate is mainly determined by intronic sequences. Circularization and splicing compete against each other. These mechanisms are tissue specific and conserved in animals. Interestingly, it was observed that the second exon of the splicing factor muscleblind (MBL/MBNL1) is circularized in flies and humans. This circRNA (circMbl) and its flanking introns contain conserved muscleblind binding sites, which are strongly and specifically bound by MBL. Modulation of MBL levels strongly affects circMbl biosynthesis, and this effect is dependent on the MBL binding sites. Together, these data suggest that circRNAs can function in gene regulation by competing with linear splicing. Furthermore, muscleblind sas identified as a factor involved in circRNA biogenesis.

Westholm, J. O., Miura, P., Olson, S., Shenker, S., Joseph, B., Sanfilippo, P., Celniker, S. E., Graveley, B. R. and Lai, E. C. (2014). Genome-wide analysis of Drosophila circular RNAs reveals their structural and sequence properties and age-dependent neural accumulation. Cell Rep 9: 1966-1980. PubMed ID: 25544350

Summary: Circularization was recently recognized to broadly expand transcriptome complexity. This study exploited massive Drosophila total RNA-sequencing data, >5 billion paired-end reads from >100 libraries covering diverse developmental stages, tissues, and cultured cells, to rigorously annotate >2,500 fruit fly circular RNAs. These mostly derive from back-splicing of protein-coding genes and lack poly(A) tails, and the circularization of hundreds of genes is conserved across multiple Drosophila species. This study elucidate structural and sequence properties of Drosophila circular RNAs, which exhibit commonalities and distinctions from mammalian circles. Notably, Drosophila circular RNAs harbor >1,000 well-conserved canonical miRNA seed matches, especially within coding regions, and coding conserved miRNA sites reside preferentially within circularized exons. Finally, the developmental and tissue specificity of circular RNAs was analyzed and their preferred derivation from neural genes and enhanced accumulation in neural tissues was noted. Interestingly, circular isoforms increase substantially relative to linear isoforms during CNS aging and constitute an aging biomarker.

Wen, J., Duan, H., Bejarano, F., Okamura, K., Fabian, L., Brill, J. A., Bortolamiol-Becet, D., Martin, R., Ruby, J. G. and Lai, E. C. (2015). Adaptive regulation of testis gene expression and control of male fertility by the Drosophila harpin RNA pathway. Mol Cell 57: 165-178. PubMed ID: 25544562

Summary: Although endogenous siRNAs (endo-siRNAs) have been described in many species, still little is known about their endogenous utility. This study shows that Drosophila hairpin RNAs (hpRNAs) generate an endo-siRNA class with predominant expression in testes. Although hairpin RNAs (hpRNAs) are universally recently evolved, this study identified highly complementary protein-coding targets for all hpRNAs. Importantly, broad evidence was found for evolutionary divergences that preferentially maintain compensatory pairing between hpRNAs and targets, serving as first evidence for adaptive selection for siRNA-mediated target regulation in metazoans. Organismal impact of hpRNA activity was demonstrated, since knockout of hpRNA1 derepresses its target ATP synthase-beta in testes and compromises spermatogenesis and male fertility. Moreover, surprising male-specific impact of RNAi factors on germ cell development and fertility was revealed, consistent with testis-directed function of the hpRNA pathway. Finally, the collected hpRNA loci chronicle an evolutionary timeline that reflects their origins from prospective target genes, mirroring a strategy described for plant miRNAs.

Manivannan, S. N., Lai, L. B., Gopalan, V. and Simcox, A. (2015). Transcriptional control of an essential ribozyme in Drosophila reveals an ancient evolutionary divide in animals. PLoS Genet 11: e1004893. PubMed ID: 25569672

Summary: Ribonuclease P (RNase P) is an essential enzyme required for 5'-maturation of tRNA. While an RNA-free, protein-based form of RNase P exists in eukaryotes, the ribonucleoprotein (RNP) form is found in all domains of life. The catalytic component of the RNP is an RNA known as RNase P RNA (RPR). Eukaryotic RPR genes are typically transcribed by RNA polymerase III (pol III). This study showed that the RPR gene in Drosophila, which is annotated in the intron of a pol II-transcribed protein-coding gene, lacks signals for transcription by pol III. Using reporter gene constructs that include the RPR-coding intron from Drosophila, the intron was found to contains all the sequences necessary for production of mature RPR but is dependent on the promoter of the recipient gene for expression. It was also demonstrated that the intron-coded RPR copurifies with RNase P and is required for its activity. Analysis of RPR genes in various animal genomes revealed a striking divide in the animal kingdom that separates insects and crustaceans into a single group in which RPR genes lack signals for independent transcription and are embedded in different protein-coding genes. These findings provide evidence for a genetic event that occurred approximately 500 million years ago in the arthropod lineage, which switched the control of the transcription of RPR from pol III to pol II.

Sunday, January 25th

Tonoki, A. and Davis, R.L. (2015). Aging impairs protein-synthesis-dependent long-term memory in Drosophila. J Neurosci 35:1173-1180. PubMed ID: 25609631

Summary: Although aging is known to impair intermediate-term memory in Drosophila, its effect on protein-synthesis-dependent long-term memory (LTM) is unknown. This study shows that LTM is impaired with age, not due to functional defects in synaptic output of mushroom body (MB) neurons, but due to connectivity defects of dorsal paired medial (DPM) neurons with their postsynaptic MB neurons. GFP reconstitution across synaptic partners (GRASP) experiments revealed structural connectivity defects in aged animals of DPM neurons with MB axons in the α lobe neuropil. As a consequence, a protein-synthesis-dependent LTM trace in the α/β MB neurons failed to form. Aging thus impairs protein-synthesis-dependent LTM along with the α/β MB neuron LTM trace by lessening the connectivity of DPM and α/β MB neurons.

Bourdet, I., Preat, T. and Goguel, V. (2015). The full-length form of the Drosophila amyloid precursor protein is involved in memory formation J Neurosci 35: 1043-1051. PubMed ID: 25609621

Summary: The APP plays a central role in AD, a pathology that first manifests as a memory decline. Understanding the role of APP in normal cognition is fundamental in understanding the progression of AD, and mammalian studies have pointed to a role of secreted APPα in memory. In Drosophila, APPL, the fly APP ortholog, is required for associative memory. This study aimed to characterize which form of APPL is involved in this process. Expression of a secreted-APPL form in the mushroom bodies, the center for olfactory memory, was able to rescue the memory deficit caused by APPL partial loss of function. The study next assessed the impact on memory of the Drosophila α-secretase kuzbanian (KUZ), the enzyme initiating the nonamyloidogenic pathway that produces secreted APPLα. Strikingly, KUZ overexpression not only failed to rescue the memory deficit caused by APPL loss of function, it exacerbated this deficit. Further, in addition to an increase in secreted-APPL forms, KUZ overexpression caused a decrease of membrane-bound full-length species that could explain the memory deficit. Indeed, transient expression of a constitutive membrane-bound mutant APPL form was sufficient to rescue the memory deficit caused by APPL reduction, revealing for the first time a role of full-length APPL in memory formation. This data demonstrates that, in addition to secreted APPL, the noncleaved form is involved in memory, raising the possibility that secreted and full-length APPL act together in memory processes.

Mullin, A. P., Sadanandappa, M. K., Ma, W., Dickman, D. K., VijayRaghavan, K., Ramaswami, M., Sanyal, S. and Faundez, V. (2015). Gene dosage in the dysbindin schizophrenia susceptibility network differentially affect synaptic function and plasticity. J Neurosci 35: 325-338. PubMed ID: 25568125

Summary: Neurodevelopmental disorders arise from single or multiple gene defects. However, the way multiple loci interact to modify phenotypic outcomes remains poorly understood. This paper studied phenotypes associated with mutations in the schizophrenia susceptibility gene dysbindin (dysb), in isolation or in combination with null alleles in the dysb network component Blos1. In humans, the Blos1 ortholog Bloc1s1 encodes a polypeptide that assembles, with dysbindin, into the octameric BLOC-1 complex. Presence of BLOC-1 in Drosophila neurons was biochemically confirmed, and synaptic output and complex adaptive behavior was measured in response to BLOC-1 perturbation. Homozygous loss-of-function alleles of dysb, Blos1, or compound heterozygotes of these alleles impaired neurotransmitter release, synapse morphology, and homeostatic plasticity at the larval neuromuscular junction, and impaired olfactory habituation. This multiparameter assessment indicated that phenotypes were differentially sensitive to genetic dosages of loss-of-function BLOC-1 alleles. These findings suggest that modification of a second genetic locus in a defined neurodevelopmental regulatory network does not follow a strict additive genetic inheritance, but rather, precise stoichiometry within the network determines phenotypic outcomes.

Choi, C. H., et al. (2015). PDE-4 inhibition rescues aberrant synaptic plasticity in Drosophila and mouse models of Fragile X syndrome. J Neurosci 35: 396-408. PubMed ID: 25568131

Summary: Fragile X syndrome (FXS) is the leading cause of both intellectual disability and autism resulting from a single gene mutation. Previous studies have characterized cognitive impairments and brain structural defects in a Drosophila model of FXS and have demonstrated that these impairments were rescued by treatment with metabotropic glutamate receptor (mGluR) antagonists or lithium. A well-documented biochemical defect observed in fly and mouse FXS models and FXS patients is low cAMP levels. cAMP levels can be regulated by mGluR signaling. This study demonstrates PDE-4 inhibition as a therapeutic strategy to ameliorate memory impairments and brain structural defects in the Drosophila model of fragile X. Furthermore, the effects of PDE-4 inhibition were examined by pharmacologic treatment in the fragile X mouse model. Acute inhibition of PDE-4 by pharmacologic treatment in hippocampal slices rescues the enhanced mGluR-dependent LTD phenotype observed in FXS mice. Additionally, it was found that chronic treatment of FXS model mice, in adulthood, also restores the level of mGluR-dependent LTD to that observed in wild-type animals. Translating the findings of successful pharmacologic intervention from the Drosophila model into the mouse model of FXS is an important advance, in that this identifies and validates PDE-4 inhibition as potential therapeutic intervention for the treatment of individuals afflicted with FXS.

Saturday, January 24th

Del Castillo, U., Lu, W., Winding, M., Lakonishok, M. and Gelfand, V. I. (2014). Pavarotti/MKLP1 regulates microtubule sliding and neurite outgrowth in Drosophila neurons. Curr Biol. PubMed ID: 25557664

Summary: Kinesin-1 can slide microtubules against each other, providing the mechanical force required for initial neurite extension in Drosophila neurons. This sliding is only observed in young neurons actively forming neurites and is dramatically downregulated in older neurons. The downregulation is not caused by the global shutdown of kinesin-1, as the ability of kinesin-1 to transport membrane organelles is not diminished in mature neurons, suggesting that microtubule sliding is regulated by a dedicated mechanism. This study has identified the "mitotic" kinesin-6 Pavarotti (Pav-KLP) as an inhibitor of kinesin-1-driven microtubule sliding. Depletion of Pav-KLP in neurons strongly stimulated the sliding of long microtubules and neurite outgrowth, while its ectopic overexpression in the cytoplasm blocked both of these processes. Furthermore, postmitotic depletion of Pav-KLP in Drosophila neurons in vivo reduced embryonic and larval viability, with only a few animals surviving to the third instar larval stage. A detailed examination of motor neurons in the surviving larvae revealed the overextension of axons and mistargeting of neuromuscular junctions, resulting in uncoordinated locomotion. Taken together, these results identify a new role for Pav-KLP as a negative regulator of kinesin-1-driven neurite formation. These data suggest an important parallel between long microtubule-microtubule sliding in anaphase B and sliding of interphase microtubules during neurite formation.

Lee, J., Peng, Y., Lin, W. Y. and Parrish, J. Z. (2015). Coordinate control of terminal dendrite patterning and dynamics by the membrane protein Raw. Development 142: 162-173. PubMed ID: 25480915

Summary: The directional flow of information in neurons depends on compartmentalization: dendrites receive inputs whereas axons transmit them. Axons and dendrites likewise contain structurally and functionally distinct subcompartments. Axon/dendrite compartmentalization can be attributed to neuronal polarization, but the developmental origin of subcompartments in axons and dendrites is less well understood. To identify the developmental bases for compartment-specific patterning in dendrites, a screen was carried out for mutations that affect discrete dendritic domains in Drosophila sensory neurons. From this screen, mutations were identified that affected distinct aspects of terminal dendrite development with little or no effect on major dendrite patterning. Mutation of one gene, raw, affected multiple aspects of terminal dendrite patterning, suggesting that Raw might coordinate multiple signaling pathways to shape terminal dendrite growth. Consistent with this notion, Raw localizes to branch-points and promotes dendrite stabilization together with the Tricornered (Trc) kinase via effects on cell adhesion. Raw independently influences terminal dendrite elongation through a mechanism that involves modulation of the cytoskeleton, and this pathway is likely to involve the RNA-binding protein Argonaute 1 (AGO1), as raw and AGO1 genetically interact to promote terminal dendrite growth but not adhesion. Thus, Raw defines a potential point of convergence in distinct pathways shaping terminal dendrite patterning.

Liu, J., Lee, D. M., Yu, C. G., Angers, S. and Harris, T. J. (2014). Stepping stone: a cytohesin adaptor for membrane cytoskeleton restraint in the syncytial Drosophila embryo. Mol Biol Cell [Epub ahead of print]. PubMed ID: 25540427

Summary: Cytohesin Arf-GEFs are conserved plasma membrane regulators. The sole Drosophila cytohesin, Steppke, restrains Rho1-dependent membrane cytoskeleton activity at the base of plasma membrane furrows of the syncytial embryo. By mass spectrometry, a single major Steppke-interacting protein from syncytial embryos was identified that was named Stepping stone (Sstn). By sequence, Sstn seems to be a divergent homolog of the mammalian cytohesin adaptor FRMD4A. Experiments supported this relationship. Specifically, heterophilic coiled-coil interactions linked Sstn and Steppke in vivo and in vitro, whereas a separate C-terminal region was required for Sstn localization to furrows. Sstn mutant and RNAi embryos displayed abnormal, Rho1-dependent membrane cytoskeleton expansion from the base of pseudocleavage and cellularization furrows, closely mimicking Steppke loss-of-function embryos. Elevating Sstn furrow levels had no effect on the steppke phenotype, but elevating Steppke furrow levels reversed the sstn phenotype, suggesting Steppke acts downstream of Sstn, and that additional mechanisms can recruit Steppke to furrows. Finally, the coiled-coil domain of Steppke was required for Sstn binding but additionally homo-dimerization, and its removal disrupted Steppke furrow localization and activity in vivo. Overall, it is proposed that Sstn acts as a cytohesin adaptor that promotes Steppke activity for localized membrane cytoskeleton restraint in the syncytial Drosophila embryo.

Bor, B., Bois, J. S. and Quinlan, M. E. (2014). Regulation of the formin Cappuccino is critical for polarity of Drosophila oocytes. Cytoskeleton (Hoboken) [Epub ahead of print]. PubMed ID: 25557988

Summary: The Drosophila formin Cappuccino (Capu) creates an actin mesh-like structure that traverses the oocyte during mid-oogenesis. This mesh is thought to prevent premature onset of fast cytoplasmic streaming which normally happens during late-oogenesis. Proper cytoskeletal organization and cytoplasmic streaming are crucial for localization of polarity determinants such as osk, grk, bcd and nanos mRNAs. Capu mutants disrupt these events, leading to female sterility. Capu is regulated by another nucleator, Spire, as well as by autoinhibition in vitro. Studies in vivo confirm that Spire modulates Capu's function in oocytes; however, how autoinhibition contributes is still unclear. To study the role of autoinhibition in flies, a Capu construct was expressed that is missing the Capu Inhibitory Domain, CapuDeltaN. Consistent with a gain of activity due to loss of autoinhibition, the actin mesh was denser in CapuDeltaN oocytes. Further, cytoplasmic streaming was delayed and fertility levels decreased. Localization of osk mRNA in early stages, and bcd and nanos in late stages, were disrupted in CapuDeltaN-expressing oocytes. Finally, evidence that these phenotypes were due to a loss of autoinhibition comes from co-expression of the N-terminal half of Capu with CapuDeltaN, which suppressed the defects in actin, cytoplasmic streaming and fertility. From these results, it is concluded that Capu can be autoinhibited during Drosophila oocyte development.

Friday, January 23rd

Ohhara, Y., Shimada-Niwa, Y., Niwa, R., Kayashima, Y., Hayashi, Y., Akagi, K., Ueda, H., Yamakawa-Kobayashi, K. and Kobayashi, S. (2015). Autocrine regulation of ecdysone synthesis by β3-octopamine receptor in the prothoracic gland is essential for Drosophila metamorphosis. Proc Natl Acad Sci USA [Epub ahead of print]. PubMed ID: 25605909

Summary:
In Drosophila, pulsed production of the steroid hormone ecdysone plays a pivotal role in developmental transitions such as metamorphosis. Ecdysone production is regulated in the prothoracic gland (PG) by prothoracicotropic hormone (PTTH) and insulin-like peptides (Ilps). This study shows that monoaminergic autocrine regulation of ecdysone biosynthesis in the PG is essential for metamorphosis. PG-specific knockdown of a monoamine G protein-coupled receptor, β3-octopamine receptor (Octβ3R), resulted in arrested metamorphosis due to lack of ecdysone. Knockdown of tyramine biosynthesis genes expressed in the PG caused similar defects in ecdysone production and metamorphosis. Moreover, PTTH and Ilps signaling were impaired by Octβ3R knockdown in the PG, and activation of these signaling pathways rescued the defect in metamorphosis. Thus, monoaminergic autocrine signaling in the PG regulated ecdysone biogenesis in a coordinated fashion on activation by PTTH and Ilps. The study proposes that monoaminergic autocrine signaling acts downstream of a body size checkpoint that allows metamorphosis to occur when nutrients are sufficiently abundant.

Fernandes, V. M., McCormack, K., Lewellyn, L. and Verheyen, E. M. (2014). Integrins regulate apical constriction via microtubule stabilization in the Drosophila eye disc epithelium. Cell Rep 9: 2043-2055. PubMed ID: 25533344

Summary: During morphogenesis, extracellular signals trigger actomyosin contractility in subpopulations of cells to coordinate changes in cell shape. To illuminate the link between signaling-mediated tissue patterning and cytoskeletal remodeling, the progression of the morphogenetic furrow (MF), the wave of apical constriction that traverses the Drosophila eye imaginal disc preceding photoreceptor neurogenesis, was analyzed. Apical constriction depends on actomyosin contractility downstream of the Hedgehog (Hh) and bone morphogenetic protein (BMP) pathways. This study identify a role for integrin adhesion receptors α-PS1 (Mew), α-PS2 (Inflated) and β-PS (Myospheroid) in MF progression. Hh and BMP regulate integrin expression, the loss of which disrupts apical constriction and slows furrow progression; conversely, elevated integrins accelerate furrow progression. Evidence is presented that integrins regulate MF progression by promoting microtubule stabilization, since reducing microtubule stability rescues integrin-mediated furrow acceleration. Thus, integrins act as a genetic link between tissue-level signaling events and morphological change at the cellular level, leading to morphogenesis and neurogenesis in the eye.

Liu, L., Zhang, K., Sandoval, H., Yamamoto, S., Jaiswal, M., Sanz, E., Li, Z., Hui, J., Graham, B.H., Quintana, A. and Bellen, H.J. (2015). Glial lipid droplets and ROS induced by mitochondrial defects promote neurodegeneration. Cell 160: 177-190. PubMed ID: 25594180

Summary: Reactive oxygen species (ROS) and mitochondrial defects in neurons are implicated in neurodegenerative disease. This study finds that a key consequence of ROS and neuronal mitochondrial dysfunction is the accumulation of lipid droplets (LD) in glia. In Drosophila, ROS triggers c-Jun-N-terminal Kinase (JNK) and Sterol Regulatory Element Binding Protein (SREBP) activity in neurons leading to LD accumulation in glia prior to or at the onset of neurodegeneration. The accumulated lipids were peroxidated in the presence of ROS. Reducing LD accumulation in glia and lipid peroxidation via targeted lipase overexpression and/or lowering ROS significantly delayed the onset of neurodegeneration. Furthermore, a similar pathway led to glial LD accumulation in Ndufs4 mutant mice with neuronal mitochondrial defects, suggesting that LD accumulation following mitochondrial dysfunction is an evolutionarily conserved phenomenon, and represents an early, transient indicator and promoter of neurodegenerative disease.

Sachan, N., Mishra, A.K., Mutsuddi, M. and Mukherjee, A. (2015). Chip physically interacts with Notch and their stoichiometry is critical for Notch function in wing development and cell proliferation in Drosophila. Biochim Biophys Acta [Epub ahead of print]. PubMed ID: 25597954

Summary: Notch signaling plays a fundamental role both in metazoan cell fate determination and in the establishment of distinct developmental cell lineages. In a yeast two-hybrid screen, this study identified Chip as a binding partner of Notch and investigated the functional significance of Notch and Chip interactions. Co-immunoprecipitation and GST-pull down experiments confirmed the physical interaction between Notch and Chip. Immunostaining revealed that Chip and Notch-intracellular domain (Notch-ICD) co-localized in cell nuclei. Loss-of-function and gain-of-function analyses of Chip were carried out using FLP/FRT and GAL4-UAS system, respectively. Immunostaining and real-time PCR were performed to analyze the role of Chip on Notch-induced cell proliferation. The study reports the transcriptional cofactor Chip as a novel binding partner of Notch. Chip and Notch also showed strong genetic interactions, and Chip mutant clones in the dorsal compartment induced ectopic wing margins by ectopic expression of Notch and its targets, Wg and Cut. The stoichiometry of Notch and Chip was critical at the dorso-ventral (DV) boundary for wing margin formation. In addition, overexpression of Chip could rescue Notch-induced cell proliferation in larval imaginal discs. These results indicated that Notch function in the DV boundary area was presumably dependent on Notch-Chip heterodimer formation. In addition, overexpression of Chip could rescue Notch-induced cell proliferation presumably through titration of overexpressed Notch-ICD by excess Chip molecules.

Shahab, J., Baratta, C., Scuric, B., Godt, D., Venken, K. J. and Ringuette, M. J. (2014). Loss of SPARC dysregulates basal lamina assembly to disrupt larval fat body homeostasis in Drosophila melanogaster. Dev Dyn [Epub ahead of print]. PubMed ID: 25529377

Summary: SPARC is a collagen-binding glycoprotein whose functions during early development are unknown. It was previously reported that SPARC is expressed in Drosophila by hemocytes and the fat body (FB) and enriched in basal laminae (BL) surrounding tissues, including adipocytes. This study sought to explore if SPARC is required for proper BL assembly in the FB. SPARC deficiency was found to lead to larval lethality, associated with remodeling of the FB. In the absence of SPARC, FB polygonal adipocytes assume a spherical morphology. Loss-of-function clonal analyses revealed a cell autonomous accumulation of BL components around mutant cells that include Collagen IV (Col IV), Laminin and Perlecan. Ultrastructural analyses indicate SPARC-deficient adipocytes are surrounded by an aberrant accumulation of a fibrous extracellular matrix. These data indicate a critical requirement for SPARC for the proper BL assembly in Drosophila FB. Since Col IV within the BL is a prime determinant of cell shape, the rounded appearance of SPARC-deficient adipocytes is due to aberrant assembly of Col IV.

Thursday, January 22nd

Ducuing, A., Keeley, C., Mollereau, B. and Vincent, S. (2015). A DPP-mediated feed-forward loop canalizes morphogenesis during Drosophila dorsal closure. J Cell Biol 208: 239-248. PubMed ID: 25601405

Summary: Development is robust because nature has selected various mechanisms to buffer the deleterious effects of environmental and genetic variations to deliver phenotypic stability. Robustness relies on smart network motifs such as feed-forward loops (FFLs) that ensure the reliable interpretation of developmental signals. This study shows that Decapentaplegic (DPP) and JNK form a coherent FFL that controls the specification and differentiation of leading edge cells during Drosophila melanogaster dorsal closure (DC). The study provided molecular evidence that through repression by Brinker (Brk), the DPP branch of the FFL filters unwanted JNK activity. High-throughput live imaging revealed that this DPP/Brk branch was dispensable for DC under normal conditions but was required when embryos were subjected to thermal stress. These results indicate that the wiring of DPP signaling buffers against environmental challenges and canalizes cell identity. The study proposes that the main function of DPP pathway during Drosophila DC is to ensure robust morphogenesis, a distinct function from its well-established ability to spread spatial information.

Peterson, S.J. and Krasnow, M.A. (2015). Subcellular trafficking of FGF controls tracheal invasion of Drosophila flight muscle. Cell 160: 313-323. PubMed ID: 25557078

Summary: To meet the extreme oxygen demand of insect flight muscle, tracheal (respiratory) tubes ramify not only on its surface, as in other tissues, but also within T-tubules and ultimately surrounding every mitochondrion. Although this remarkable physiological specialization has long been recognized, its cellular and molecular basis is unknown. This study shows that Drosophila tracheoles invade flight muscle T-tubules through transient surface openings. Like other tracheal branching events, invasion required the Branchless FGF pathway. However, localization of the FGF chemoattractant changed from all muscle membranes to T-tubules as invasion began. Core regulators of epithelial basolateral membrane identity localized to T-tubules, and knockdown of Adaptor Protein complex 1, γ subunit, AP-1γ, required for basolateral trafficking, redirected FGF from T-tubules to surface, increasing tracheal surface ramification and preventing invasion. The study proposes that tracheal invasion is controlled by an AP-1-dependent switch in FGF trafficking. Thus, subcellular targeting of a chemoattractant can direct outgrowth to specific domains, including inside the cell.

Trisnadi, N. and Stathopoulos, A. (2014). Ectopic expression screen identifies genes affecting Drosophila mesoderm development including the HSPG Trol. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 25538103

Summary: Gastrulation of the embryo involves coordinate cell movements likely supported by multiple signaling pathways, adhesion molecules, and extracellular matrix components. Fibroblast growth factors (FGFs) have a major role in Drosophila melanogaster mesoderm migration, however few other inputs are known and the mechanism supporting cell movement is unclear. To provide insight, this study carried out an ectopic expression screen to identify secreted or membrane-associated molecules that act to support mesoderm migration. Twenty-four UAS insertions were identified that cause lethality when expressed in either the mesoderm (Twi-Gal4) or ectoderm (69B-Gal4). The list was narrowed to a subset of ten genes that were shown to exhibit loss-of-function mutant phenotypes specifically affecting mesoderm migration. These include the FGF ligand Pyramus, alpha-integrins, E-cadherin, Cueball, EGFR, JAK/STAT signaling components, as well as the heparan sulfate proteoglycan (HSPG) Terribly reduced optic lobes (Trol). Trol encodes the ortholog of mammalian HSPG Perlecan, a demonstrated FGF signaling cofactor. The role of Trol in Drosophila mesoderm migration was studied, and its role was contrasted with that of Syndecan (Sdc), another HSPG, previously implicated in this process. Embryos mutant for Trol or Sdc were obtained and analyzed. The data support the view that both HSPGs function to support FGF-dependent processes in the early embryo as they share phenotypes with FGF mutants: Trol in terms of effects on mesoderm migration and caudal visceral mesoderm (CVM) migration, and Sdc in terms of dorsal mesoderm specification. The differential roles uncovered for these two HSPGs suggest that HSPG cofactor choice may modify FGF-signaling outputs.

Ossipova, O., Chuykin, I., Chu, C. W. and Sokol, S. Y. (2015). Vangl2 cooperates with Rab11 and Myosin V to regulate apical constriction during vertebrate gastrulation. Development 142: 99-107. PubMed ID: 25480917

Summary: Core planar cell polarity (PCP) proteins are well known to regulate polarity in Drosophila and vertebrate epithelia; however, their functions in vertebrate morphogenesis remain poorly understood. This study describes a role for PCP signaling in the process of apical constriction during Xenopus gastrulation. The core PCP protein Vangl2 (Drosophila homolog: Strabismis) is detected at the apical surfaces of cells at the blastopore lip, and it functions during blastopore formation and closure. Further experiments show that Vangl2, as well as Daam1 and Rho-associated kinase (Rock; see Drosophila Rok), regulate apical constriction of bottle cells at the blastopore and ectopic constriction of ectoderm cells triggered by the actin-binding protein Shroom3. At the blastopore lip, Vangl2 is required for the apical accumulation of the recycling endosome marker Rab11 (see Drosophila ). Rab11 and the associated motor protein Myosin V (see Drosophila Didum) play essential roles in both endogenous and ectopic apical constriction, and might be involved in Vangl2 trafficking to the cell surface. Overexpression of Rab11 RNA was sufficient to partly restore normal blastopore formation in Vangl2-deficient embryos. These observations suggest that Vangl2 affects Rab11 to regulate apical constriction during blastopore formation.

Wednesday, January 21nd

Haynes, P.R., Christmann, B.L. and Griffith, L.C. (2015). A single pair of neurons links sleep to memory consolidation in Drosophila melanogaster. Elife. [Epub ahead of print]. PubMed ID: 25564731

Summary: Sleep promotes memory consolidation in humans and many other species, but the physiological and anatomical relationships between sleep and memory remain unclear. This study shows that the dorsal paired medial (DPM) neurons, which are required for memory consolidation in Drosophila, are sleep-promoting inhibitory neurons. DPMs increased sleep via release of GABA onto wake-promoting mushroom body (MB) α'/β' neurons. Functional imaging demonstrated that DPM activation evoked robust increases in chloride in MB neurons, but was unable to cause detectable increases in calcium or cAMP. Downregulation of α'/β' GABAA and GABABR3 receptors resulted in sleep loss, suggesting these receptors were the sleep-relevant targets of DPM-mediated inhibition. Regulation of sleep by neurons necessary for consolidation suggested that these brain processes may be functionally interrelated via their shared anatomy. These findings have important implications for the mechanistic relationship between sleep and memory consolidation, arguing for a significant role of inhibitory neurotransmission in regulating these processes. These results argue for a significant role of inhibitory neurotransmission in memory consolidation and its regulation by sleep.

Klein, M., Afonso, B., Vonner, A. J., Hernandez-Nunez, L., Berck, M., Tabone, C. J., Kane, E. A., Pieribone, V. A., Nitabach, M. N., Cardona, A., Zlatic, M., Sprecher, S. G., Gershow, M., Garrity, P. A. and Samuel, A. D. (2014). Sensory determinants of behavioral dynamics in Drosophila thermotaxis. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 25550513

Summary: Complex animal behaviors are built from dynamical relationships between sensory inputs, neuronal activity, and motor outputs in patterns with strategic value. Connecting these patterns illuminates how nervous systems compute behavior. This paper describes a study of Drosophila larva navigation up temperature gradients toward preferred temperatures (positive thermotaxis). By tracking the movements of animals responding to fixed spatial temperature gradients or random temperature fluctuations, the sensitivity and dynamics of the conversion of thermosensory inputs into motor responses was calculate. Three thermosensory neurons were discovered in each dorsal organ ganglion (DOG) that are required for positive thermotaxis. Random optogenetic stimulation of the DOG thermosensory neurons evokes behavioral patterns that mimic the response to temperature variations. In vivo calcium and voltage imaging reveals that the DOG thermosensory neurons exhibit activity patterns with sensitivity and dynamics matched to the behavioral response. Temporal processing of temperature variations carried out by the DOG thermosensory neurons emerges in distinct motor responses during thermotaxis.

Yamagata, N., Ichinose, T., Aso, Y., Placais, P., Friedrich, A. B., Sima, R. J., Preat, T., Rubin, G. M. and Tanimoto, H. (2014). Distinct dopamine neurons mediate reward signals for short- and long-term memories. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 25548178

Summary: Drosophila melanogaster can acquire a stable appetitive olfactory memory when the presentation of a sugar reward and an odor are paired. However, the neuronal mechanisms by which a single training induces long-term memory are poorly understood. This study shows that two distinct subsets of dopamine neurons in the fly brain signal reward for short-term (STM) and long-term memories (LTM). One subset induces memory that decays within several hours, whereas the other induces memory that gradually develops after training. They convey reward signals to spatially segregated synaptic domains of the mushroom body (MB), a potential site for convergence. Furthermore, a single type of dopamine neuron was identified that conveys the reward signal to restricted subdomains of the mushroom body lobes and induces long-term memory. Constant appetitive memory retention after a single training session thus comprises two memory components triggered by distinct dopamine neurons.

Elzinga, M. J., van Breugel, F. and Dickinson, M. H. (2014). Strategies for the stabilization of longitudinal forward flapping flight revealed using a dynamically-scaled robotic fly. Bioinspir Biomim 9: 025001. PubMed ID: 24855029

Summary: The ability to regulate forward speed is an essential requirement for flying animals. This study used a dynamically-scaled robot to study how flapping insects adjust their wing kinematics to regulate and stabilize forward flight. The results suggest that the steady-state lift and thrust requirements at different speeds may be accomplished with quite subtle changes in hovering kinematics, and that these adjustments act primarily by altering the pitch moment. This finding is consistent with prior hypotheses regarding the relationship between body pitch and flight speed in fruit flies. Adjusting the mean stroke position of the wings is a likely mechanism for trimming the pitch moment at all speeds, whereas changes in the mean angle of attack may be required at higher speeds. To ensure stability, the flapping system requires additional pitch damping that increases in magnitude with flight speed. A compensatory reflex driven by fast feedback of pitch rate from the halteres could provide such damping, and would automatically exhibit gain scheduling with flight speed if pitch torque was regulated via changes in stroke deviation. Such a control scheme would provide an elegant solution for stabilization across a wide range of forward flight speeds.

Tuesday, January 20th

Wang, L.H. and Baker, N.E. (2015). Salvador-Warts-Hippo pathway in a developmental checkpoint monitoring Helix-Loop-Helix proteins. Dev Cell [Epub ahead of print]. PubMed ID: 25579975

Summary:
The E proteins and Id proteins are, respectively, the positive and negative heterodimer partners for the basic-helix-loop-helix protein family and as such contribute to a remarkably large number of cell-fate decisions. E proteins and Id proteins also function to inhibit or promote cell proliferation and cancer. Using a genetic modifier screen in Drosophila, this study shows that the Id protein Extramacrochaetae enables growth by suppressing activation of the Salvador-Warts-Hippo pathway of tumor suppressors, activation that requires transcriptional activation of the expanded gene by the E protein Daughterless. Daughterless protein bound to an intronic enhancer in the expanded gene, both activated the SWH pathway independently of the transmembrane protein Crumbs and bypassed the negative feedback regulation that targets the same expanded enhancer. Thus, the Salvador-Warts-Hippo pathway has a cell-autonomous function to prevent inappropriate differentiation due to transcription factor imbalance and monitors the intrinsic developmental status of progenitor cells, distinct from any responses to cell-cell interactions

Hamm, D. C., Bondra, E. R. and Harrison, M. M. (2014). Transcriptional activation is a conserved feature of the early embryonic factor Zelda that requires a cluster of four zinc fingers for DNA binding and a low-complexity activation domain. J Biol Chem [Epub ahead of print]. PubMed ID: 25538246

Summary: Delayed transcriptional activation of the zygotic genome is a nearly universal phenomenon in metazoans. Immediately following fertilization, development is controlled by maternally deposited products, and it is not until later stages that widespread activation of the zygotic genome occurs. While the mechanisms driving this genome activation are currently unknown, the transcriptional activator Zelda (ZLD) has been shown to be instrumental in driving this process in Drosophila melanogaster. This study defines functional domains of ZLD required for both DNA binding and transcriptional activation. The C-terminal cluster of four zinc fingers mediates binding to TAGteam DNA elements in the promoters of early expressed genes. All four zinc fingers are required for this activity, and splice isoforms lacking three of the four zinc fingers fail to activate transcription. These truncated splice isoforms dominantly suppress activation by the full-length, embryonically expressed isoform. The transcriptional activation domain of ZLD maps to a central region characterized by low complexity. Despite relatively little sequence conservation within this domain, ZLD orthologs from Drosophila virilis, Anopheles gambiae and Nasonia vitripennis activate transcription in Drosophila melanogaster cells. Transcriptional activation by these ZLD orthologs suggests that ZLD functions through conserved interactions with a protein cofactor(s). Thus, this study has identified distinct DNA-binding and activation domains within the critical transcription factor ZLD that controls the initial activation of the zygotic genome.

Fores, M., Ajuria, L., Samper, N., Astigarraga, S., Nieva, C., Grossman, R., Gonzalez-Crespo, S., Paroush, Z. and Jimenez, G. (2015). Origins of context-dependent gene repression by Capicua. PLoS Genet 11: e1004902. PubMed ID: 25569482

Summary: Receptor Tyrosine Kinase (RTK) signaling pathways induce multiple biological responses, often by regulating the expression of downstream genes. The HMG-box protein Capicua (Cic) is a transcriptional repressor that is downregulated in response to RTK signaling, thereby enabling RTK-dependent induction of Cic targets. In both Drosophila and mammals, Cic is expressed as two isoforms, long (Cic-L) and short (Cic-S), whose functional significance and mechanism of action are not well understood. This study shows that Drosophila Cic relies on the Groucho (Gro) corepressor during its function in the early embryo, but not during other stages of development. This Gro-dependent mechanism requires a short peptide motif, unique to Cic-S and designated N2, which is distinct from other previously defined Gro-interacting motifs and functions as an autonomous, transferable repressor element. Unexpectedly, these data indicate that the N2 motif is an evolutionary innovation that originated within dipteran insects, as the Cic-S isoform evolved from an ancestral Cic-L-type form. Accordingly, the Cic-L isoform lacking the N2 motif is completely inactive in early Drosophila embryos, indicating that the N2 motif endowed Cic-S with a novel Gro-dependent activity that is obligatory at this stage. It is suggested that Cic-S and Gro coregulatory functions have facilitated the evolution of the complex transcriptional network regulated by Torso RTK signaling in modern fly embryos. Notably, the results also imply that mammalian Cic proteins are unlikely to act via Gro and that their Cic-S isoform must have evolved independently of fly Cic-S. Thus, Cic proteins employ distinct repressor mechanisms that are associated with discrete structural changes in the evolutionary history of this protein family.

Kozlov, K., Gursky, V., Kulakovskiy, I. and Samsonova, M. (2014). Sequence-based model of gap gene regulatory network. BMC Genomics 15 Suppl 12: S6. PubMed ID: 25564104

Summary: The detailed analysis of transcriptional regulation is crucially important for understanding biological processes. The gap gene network in Drosophila attracts large interest among researches studying mechanisms of transcriptional regulation. It implements the most upstream regulatory layer of the segmentation gene network. The knowledge of molecular mechanisms involved in gap gene regulation is far less complete than that of genetics of the system. Mathematical modeling goes beyond insights gained by genetics and molecular approaches. It allows reconstruction of wild-type gene expression patterns in silico, infering of underlying regulatory mechanism and proving its sufficiency. This paper developed a new model that provides a dynamical description of gap gene regulatory systems, using detailed DNA-based information, as well as spatial transcription factor concentration data at varying time points. This model correctly reproduces gap gene expression patterns in wild type embryos and is able to predict gap expression patterns in Kr mutants and four reporter constructs. Four-fold cross validation test and fitting to random dataset was used to validate the model and prove its sufficiency in data description. The identifiability analysis showed that most model parameters are well identifiable. The gap gene network topology was reconstructed, and the impact of individual transcription factor binding sites on the model output was studied. This impact was measured by calculating the site regulatory weight as a normalized difference between the residual sum of squares error for the set of all annotated sites and for the set with the site of interest excluded. The reconstructed topology of the gap gene network is in agreement with previous modeling results and data from literature. This study showed that 1) the regulatory weights of transcription factor binding sites show very weak correlation with their PWM score; 2) sites with low regulatory weight are important for the model output; 3) functionally important sites are not exclusively located in cis-regulatory elements, but are rather dispersed through regulatory region. It is of importance that some of the sites with high functional impact in hb, Kr and kni regulatory regions coincide with strong sites annotated and verified in Dnase I footprint assays.

Monday, January 19th

Chen, H., Zheng, X. and Zheng, Y. (2014). Age-associated loss of lamin-B leads to systemic inflammation and gut hyperplasia. Cell 159: 829-843. PubMed ID: 25417159

Summary: Aging of immune organs, termed as immunosenescence, is suspected to promote systemic inflammation and age-associated disease. The cause of immunosenescence and how it promotes disease, however, has remained unclear. This study reports that the Drosophila fat body, a major immune organ, undergoes immunosenescence and mounts strong systemic inflammation that leads to deregulation of immune deficiency (IMD) signaling in the midgut of old animals. Inflamed old fat bodies secrete circulating peptidoglycan recognition proteins that repress IMD activity in the midgut, thereby promoting gut hyperplasia. Further, fat body immunosenecence is caused by age-associated lamin-B reduction specifically in fat body cells, which then contributes to heterochromatin loss and derepression of genes involved in immune responses. As lamin-associated heterochromatin domains are enriched for genes involved in immune response in both Drosophila and mammalian cells, these findings may provide insights into the cause and consequence of immunosenescence during mammalian aging.

Bandarra, D., Biddlestone, J., Mudie, S., Muller, H. A. and Rocha, S. (2014). HIF-1alpha restricts NF-kappaB dependent gene expression to control innate immunity signals. Dis Model Mech [Epub ahead of print]. PubMed ID: 25510503

Summary: Hypoxia and inflammation are intimately linked. It is known that NF-kappaB (Relish, Dorsal and Dif in Drosophila) regulates the HIF system (see Drosophila Similar) but little is known about how HIF regulates NF-kappaB. This study shows that HIF-1alpha represses NF-kappaB dependent gene expression. HIF-1alpha depletion results in increased NF-kappaB transcriptional activity both in mammalian cells and in the model organism Drosophila melanogaster. HIF-1alpha depletion enhanced the NF-kappaB response and this required not only the TAK-IKK complex (see Drosophila immune response deficient 5 and kenny), but also CDK6 (see Cdk4 in Drosophila). Loss of HIF-1alpha results in an increased angiogenic response in mammalian cancer cells and increased mortality in Drosophila following infection. These results indicate that HIF-1alpha is required to restrain the NF-kappaB response, and thus prevents excessive and damaging pro-inflammatory responses.

Neyen, C., Binggeli, O., Roversi, P., Bertin, L., Sleiman, M. B. and Lemaitre, B. (2014). The Black cells phenotype is caused by a point mutation in the Drosophila pro-phenoloxidase 1 gene that triggers melanization and hematopoietic defects. Dev Comp Immunol [Epub ahead of print]. PubMed ID: 25543001

Summary: Melanization contributes to arthropod-specific innate immunity through deposition of melanin at wound sites or around parasites, with concomitant release of microbicidal reactive oxygen species. Melanization requires sequential activation of proteolytic enzymes in the hemolymph, including the final enzyme pro-phenoloxidase. Black cells (Bc) is a mutation causing spontaneous melanization of Drosophila crystal cells, a hemocyte cell type producing phenoloxidases. Bc individuals exhibit circulating Black spots But fail to melanize upon injury. Although Bc is widely used as a loss-of-function mutant of phenoloxidases, the mutation causing Bc remained unknown. This study identified a single point mutation in the pro-phenoloxidase 1 (PPO1) gene of Bc flies causing an Alanine to Valine change in the C-terminal domain of PPO1, predicted to affect the conformation of the N-terminal pro-domain cleavage site at a distance and causing uncontrolled catalytic activity. Genomic insertion of a PPO1A480V transgene phenocopies Black cells, proving that A480V is indeed the causal mutation of the historical Bc phenotype.

Carissimo, G., Pondeville, E., McFarlane, M., Dietrich, I., Mitri, C., Bischoff, E., Antoniewski, C., Bourgouin, C., Failloux, A., Kohl, A. and Vernick, K. D. (2014). Antiviral immunity of Anopheles gambiae is highly compartmentalized, with distinct roles for RNA interference and gut microbiota. Proc Natl Acad Sci U S A. PubMed ID: 25548172

Summary: Arboviruses are transmitted by mosquitoes and other arthropods to humans and animals. The risk associated with these viruses is increasing worldwide, including new emergence in Europe and the Americas. Anopheline mosquitoes are vectors of human malaria but are believed to transmit one known arbovirus, o'nyong-nyong virus, whereas Aedes mosquitoes transmit many. Anopheles interactions with viruses have been little studied, and the initial antiviral response in the midgut has not been examined. This study determined the antiviral immune pathways of the Anopheles gambiae midgut, the initial site of viral infection after an infective blood meal. These responses were compared with the responses of the post-midgut systemic compartment, which is the site of the subsequent disseminated viral infection. Normal viral infection of the midgut requires bacterial flora and is inhibited by the activities of immune deficiency [Imd (see Drosophila Imd), JAK/STAT (see Drosophila JAK/STAT pathway), and Leu-rich repeat immune factors (see Drosophila Toll)]. The exogenous siRNA pathway, thought of as the canonical mosquito antiviral pathway, plays no detectable role in antiviral defense in the midgut but only protects later in the systemic compartment. These results alter the prevailing antiviral paradigm by describing distinct protective mechanisms in different body compartments and infection stages. Importantly, the presence of the midgut bacterial flora is required for full viral infectivity to Anopheles, in contrast to malaria infection, where the presence of the midgut bacterial flora is required for protection against infection. Thus, the enteric flora controls a reciprocal protection tradeoff in the vector for resistance to different human pathogens.

Vitak, N., Johnson, K. N., Sester, D. P. and Stacey, K. J. (2014). A novel pathway of cell death in response to cytosolic DNA in Drosophila cells. J Innate Immun [Epub ahead of print]. PubMed ID: 25472853

Summary: Defence against invading DNA occurs in both mammals and bacteria. Recognition of stray DNA can initiate responses to infection, but may also protect against potentially mutagenic integration of transposons or retrotransposons into the genome. Double-stranded DNA detected in the cytosol of mammalian macrophages can elicit inflammatory cytokines and cell death following assembly of the AIM2 inflammasome. Amongst eukaryotes, responses to cytosolic DNA have so far only been detected in mammals, and AIM2 is mammalian restricted. In protecting genome integrity, it was reasoned that pathways recognising invading DNA should be fundamental to cellular life, and that cell death would be an appropriate response to an overwhelming foreign DNA burden. This study found that Drosophila S2 cells were killed by transfection of DNA from a range of natural sources. Unlike with mammalian cells, responses were not prevented by DNA denaturation. There was an element of sequence specificity, as synthetic single-stranded homopolymers were not toxic, whilst mixed-base synthetic DNA caused significant cell death. Death occurred with rapid loss of membrane integrity, and without the characteristic features of apoptosis. This study has defined a novel defence against invading DNA in Drosophila. An active necrotic pathway has not previously been described in insects.

Sunday, January 18th

Chen, Z., Qi, Y., French, S., Zhang, G., Garcia, R. C., Balaban, R. and Xu, H. (2014). Genetic mosaic analysis of a deleterious mitochondrial DNA mutation in Drosophila reveals novel aspects of mitochondrial regulation and function. Mol Biol Cell [Epub ahead of print]. PubMed ID: 25501370

Summary: Various human diseases are associated with mitochondrial DNA (mtDNA) mutations, but heteroplasmy-the coexistence of mutant and wild-type mtDNA-complicates their study. Previous studies have isolated a temperature lethal mtDNA mutation in Drosophila, mt:CoI^T300I affecting the cytochrome c oxidase subunit I (CoI) locus. In the current study, it was found that the decrease in cytochrome c oxidase (COX) activity was ascribable to a temperature dependent destabilization of cytochrome a heme. Consistently, the viability of homoplasmic flies at 29 ° C was fully restored by expressing an alternative oxidase, which specifically bypasses the cytochrome chains. Heteroplasmic flies are fully viable and were used to explore the age-related and tissue-specific phenotypes of mt:^T300I. The proportion of mt:CoIT300I genome remained constant in somatic tissues along the aging process, suggesting a lack of quality control mechanism to remove defective mitochondria containing a deleterious mtDNA mutation. Using a genetic scheme that expresses a mitochondrially targeted restriction enzyme to induce tissue-specific homoplasmy in heteroplasmic flies, this study found that mt:^T300I homoplasmy in the eye caused severe neurodegeneration at 29 ° C. Degeneration was suppressed by improving mitochondrial Ca2+ uptake, suggesting that Ca2+ mishandling contributed to mt:CoI^T300I pathogenesis. These results demonstrate a novel approach for Drosophila mtDNA genetics, and its application in modeling mtDNA diseases.

Xia, Y., Midoun, S. Z., Xu, Z. and Hong, L. (2014). Heixuedian (heix), a potential melanotic tumor suppressor gene, exhibits specific spatial and temporal expression pattern during Drosophila hematopoiesis. Dev Biol [Epub ahead of print]. PubMed ID: 25530181

Summary: The Drosophila heixuedian (heix) is the ortholog of human UBIAD1 gene (a.k.a TERE1). The protein product of heix/UBIAD1 has multiple enzymatic activities, including the vitamin K2 and the non-mitochondrial CoQ10 biosynthesis. However, the expression pattern of UBIAD1/Heix during metazoan development has not been systematically studied. This study found that loss of function of heix resulted in pathological changes of larval hematopoietic system, including lymph gland hypertrophy, hemocyte overproliferation and aberrant differentiation, and melanin mass formation. Overexpression of heix cDNA under the tubulin Gal4 driver rescued the above hematopoietic defects. Interestingly, Heix was specifically expressed in plasmatocyte/macrophage lineage in srp driven EGFP positive cells on the head mesoderm during embryogenesis, while it was highly expressed in crystal cells in the primary lobes of the third instar larvae lymph glands. Using qRT-PCR analysis, loss of function of heix caused aberrant activation of multiple hemocyte proliferation-related as well as immune-related pathways, including JAK/STAT pathway, Ras/MAPK pathway, IMD pathway and Toll pathway. These data suggested that heix is a potential melanotic tumor suppressor gene and plays a pivotal role in both hemocytes proliferation and differentiation in Drosophila.

Shiraishi, R., Tamura, T., Sone, M. and Okazawa, H. (2014). Systematic analysis of fly models with multiple drivers reveals different effects of ataxin-1 and huntingtin in neuron subtype-specific expression. PLoS One 9: e116567. PubMed ID: 25551764

Summary: The fruit fly, Drosophila melanogaster, is a commonly used model organism for neurodegenerative diseases. Its major advantages include a short lifespan and its susceptibility to manipulation using sophisticated genetic techniques. This study reports the systematic comparison of fly models of two polyglutamine (polyQ) diseases. Expression of the normal and mutant forms of full-length Ataxin-1 and Huntingtin exon 1 was induced in cholinergic, dopaminergic, and motor neurons, and glial cells using cell type-specific drivers. Their effects were systematically analyzed based on multiple phenotypes: eclosion rate, lifespan, motor performance, and circadian rhythms of spontaneous activity. This systematic assay system enabled a quantitative evaluation and comparison the functional disabilities of different genotypes. The results suggest different effects of Ataxin-1 and Huntingtin on specific types of neural cells during development and in adulthood. In addition, the therapeutic effects of LiCl and butyrate was confirmed using representative models. These results support the usefulness of this assay system for screening candidate chemical compounds that modify the pathologies of polyQ diseases.

Lin, Y., He, H., Luo, Y., Zhu, T. and Duan, R. (2014). Inhibition of transglutaminase exacerbates polyglutamine-induced neurotoxicity by increasing the aggregation of mutant Ataxin-3 in an SCA3 Drosophila model. Neurotox Res [Epub ahead of print]. PubMed ID: 25501875

Summary: Transglutaminases (TGs) comprise a family of Ca2+-dependent enzymes that catalyze protein cross-linking, which include nine family members in humans but only a single homolog in Drosophila with three conserved domains. Drosophila Tg plays important roles in cuticle morphogenesis, hemolymph clotting, and innate immunity. Mammalian tissue TG (TG2) is involved in polyglutamine diseases (polyQ diseases), and TG6 has been identified as a causative gene of a novel spinocerebellar ataxia, SCA35. Using a well-established SCA3 fly model, this study found that RNA interference-mediated suppression of Tg aggravated polyQ-induced neurodegenerative phenotypes. The administration of cystamine, a known effective Tg inhibitor, enhanced ommatidial degeneration in SCA3 flies. It was also demonstrated that the aggregates of pathogenic ataxin-3 increased greatly, when the Tg activity was repressed. These findings indicate that Tg is crucial for polyQ-induced neurotoxicity because Tg ablation resulted in more severe neurodegeneration due to the elevated accumulation of insoluble ataxin-3 complexes in the SCA3 Drosophila model.

Saturday, January 17th

Verní, F. and Cenci, G. (2015). The Drosophila histone variant H2A.V works in concert with HP1 to promote kinetochore-driven microtubule formation. Cell Cycle. [Epub ahead of print]. PubMed ID: 25591068

Summary:
Unlike other organisms that have evolved distinct H2A variants for different functions, Drosophila melanogaster has just one variant which is capable of filling many roles. This protein, H2A.V, combines the features of the conserved variants H2A.Z and H2A.X in transcriptional control/heterochromatin assembly and DNA damage response, respectively. This study shows that mutations in the gene encoding H2A.V affect chromatin compaction and perturb chromosome segregation in Drosophila mitotic cells. A microtubule (MT) regrowth assay after cold exposure revealed that loss of H2A.V impaired the formation of kinetochore-driven (k) fibers, which could account for defects in chromosome segregation. All defects were rescued by a transgene encoding H2A.V that lacked the H2A.x function in the DNA damage response, suggesting that the H2A.Z (but not H2A.X) functionality of H2A.V was required for chromosome segregation. Loss of H2A.V weakened HP1 localization, specifically at the pericentric heterochromatin of metaphase chromosomes. Interestingly, loss of HP1 yielded not only telomeric fusions but also mitotic defects similar to those seen in H2A.V null mutants, suggesting a role for HP1 in chromosome segregation. H2A.V precipitated HP1 from larval brain extracts indicating that both proteins were part of the same complex. Moreover, the overexpression of HP1 rescued chromosome missegregation and defects in the kinetochore-driven k-fiber regrowth of H2A.V mutants indicating that both phenotypes were influenced by unbalanced levels of HP1. Collectively, these results suggest that H2A.V and HP1 work in concert to ensure kinetochore-driven MT growth.

Ost, A., Lempradl, A., Casas, E., Weigert, M., Tiko, T., Deniz, M., Pantano, L., Boenisch, U., Itskov, P. M., Stoeckius, M., Ruf, M., Rajewsky, N., Reuter, G., Iovino, N., Ribeiro, C., Alenius, M., Heyne, S., Vavouri, T. and Pospisilik, J. A. (2014). Paternal diet defines offspring chromatin state and intergenerational obesity. Cell 159: 1352-1364. PubMed ID: 25480298

Summary: The global rise in obesity has revitalized a search for genetic and epigenetic factors underlying the disease. This study presents a Drosophila model of paternal-diet-induced intergenerational metabolic reprogramming (IGMR) and identifies genes required for its encoding in offspring. Intriguingly, as little as 2 days of dietary intervention in fathers elicits obesity in offspring. Paternal sugar acts as a physiological suppressor of variegation, desilencing chromatin-state-defined domains in both mature sperm and in offspring embryos. Requirements were identified for H3K9/K27me3-dependent reprogramming of metabolic genes in two distinct germline and zygotic windows. Critically, evidence was found that a similar system may regulate obesity susceptibility and phenotype variation in mice and humans. The findings provide insight into the mechanisms underlying intergenerational metabolic reprogramming and carry profound implications for understanding of phenotypic variation and evolution.

Nikalayevich, E. and Ohkura, H. (2014). The NuRD nucleosome remodelling complex and NHK-1 kinase are required for chromosome condensation in oocytes. J Cell Sci. PubMed ID: 25501812

Summary: Chromosome condensation during cell division is one of the most dramatic events in the cell cycle. Condensin and topoisomerase II are the most studied factors in chromosome condensation. However, their inactivation leads to only mild defects and little is known about roles of other factors. this study took advantage of Drosophila oocytes to elucidate the roles of potential condensation factors by RNAi. Consistent with previous studies, depletion of condensin I subunits or topoisomerase II in oocytes only mildly affected chromosome condensation. In contrast, severe undercondensation of chromosomes after depletion of the Mi-2 containing NuRD nucleosome remodelling complex or the protein kinase NHK-1/ballchen. The further phenotypic analysis suggests that Mi-2 and NHK-1 are involved in different pathways in chromosome condensation. The main role of NHK-1 in chromosome condensation is to phosphorylate BAF and suppress its activity in linking chromosomes to nuclear envelope proteins. Further this study showed that NHK-1 is important for chromosome condensation in mitosis as well as in oocytes.

Zhu, Y., Li, D., Wang, Y., Pei, C., Liu, S., Zhang, L., Yuan, Z. and Zhang, P. (2014). Brahma regulates the Hippo pathway activity through forming complex with Yki-Sd and regulating the transcription of Crumbs. Cell Signal. PubMed ID: 25496831

Summary: The Hippo signaling pathway restricts organ size by inactivating the Yorkie (Yki)/Yes-associated protein (YAP) family proteins. The oncogenic Yki/YAP transcriptional coactivator family promotes tissue growth by activating target gene transcription, but the regulation of Yki/YAP activation remains elusive. In mammalian cells, Brg1, a major subunit of chromatin-remodeling SWI/SNF family proteins, was identified that interacts with YAP. This finding led the authors to investigate the in vivo functional interaction of Yki and Brahma (Brm), the Drosophila homolog of Brg1. Brm was found to function at the downstream of Hippo pathway and interacts with Yki and Scalloped (Sd) to promotes Yki-dependent transcription and tissue growth. Furthermore, it was demonstrated that Brm is required for the Crumbs (Crb) dysregulation-induced Yki activation. Interestingly, it was also found that crb is a downstream target of Yki-Brm complex. Brm physically binds to the promoter of crb and regulates its transcription through Yki. Together, this study has shown that Brm functions as a critical regulator of Hippo signaling during tissue growth and plays an important role in the feedback loop between Crb and Yki.

Bozler, J., Nguyen, H. Q., Rogers, G. C. and Bosco, G. (2014). Condensins exert force on chromatin-nuclear envelope tethers to mediate nucleoplasmic reticulum formation in Drosophila melanogaster. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 25552604

Summary: Although the nuclear envelope is primarily known for its role as a boundary between the nucleus and cytoplasm in eukaryotes, it plays a vital and dynamic role in many cellular processes. Studies of nuclear structure have revealed tissue specific changes in nuclear envelope architecture, suggesting that its three-dimensional structure contributes to its functionality. Despite the importance of the nuclear envelope, the factors that regulate and maintain nuclear envelope shape remain largely unexplored. The nuclear envelope makes extensive and dynamic interactions with the underlying chromatin. Given this inexorable link between chromatin and the nuclear envelope, it is possible that local and global chromatin organization reciprocally impact nuclear envelope form and function. This study used Drosophila salivary glands to show that the three-dimensional structure of the nuclear envelope can be altered with condensin II-mediated chromatin condensation. Both naturally occurring and engineered chromatin-envelope interactions are sufficient to allow chromatin compaction forces to drive distortions of the nuclear envelope. Weakening of the nuclear lamina further enhanced envelope remodeling, suggesting that envelope structure is capable of counterbalancing chromatin compaction forces. These experiments reveal that the nucleoplasmic reticulum is born of the nuclear envelope and remains dynamic, in that they can be reabsorbed into the nuclear envelope. A model is proposed where inner nuclear envelope-chromatin tethers allow interphase chromosome movements to change nuclear envelope morphology. Therefore, interphase chromatin compaction may be a normal mechanism that reorganizes nuclear architecture, while under pathological conditions, such as laminopathies, compaction forces may contribute to defects in nuclear morphology.

Friday, January 16th

Ma, X., Chen, Y., Xu, W., Wu, N., Li, M., Cao, Y., Wu, S., Li, Q. and Xue, L. (2015). Impaired Hippo signaling promotes Rho1-JNK-dependent growth. Proc Natl Acad Sci USA. [Epub ahead of print]. PubMed ID: 25583514
Summary:

The Hippo and c-Jun N-terminal kinase (JNK) pathway both regulate growth and contribute to tumorigenesis when dysregulated. Whereas the Hippo pathway acts via the transcription coactivator Yki/YAP to regulate target gene expression, JNK signaling, triggered by various modulators including Rho GTPases, activates the transcription factors Jun and Fos. This study shows that impaired Hippo signaling induces JNK activation through Rho1. Blocking Rho1-JNK signaling suppressed Yki-induced overgrowth in the wing disk, whereas ectopic Rho1 expression promoted tissue growth when apoptosis was prohibited. Furthermore, Yki directly regulated Rho1 transcription via the transcription factor Sd. These results identify a novel molecular link between the Hippo and JNK pathways and implicate the essential role of the JNK pathway in Hippo signaling-related tumorigenesis.

Sidorov, R., Kucerova, L., Kiss, I. and Zurovec, M. (2014). Mutation in the Drosophila melanogaster adenosine receptor gene selectively decreases the mosaic hyperplastic epithelial outgrowth rates in wts or dco heterozygous flies. Purinergic Signal [Epub ahead of print]. PubMed ID: 25528157

Summary: Adenosine (Ado) is a ubiquitous metabolite that plays a prominent role as a paracrine homeostatic signal of metabolic imbalance within tissues. It quickly responds to various stress stimuli by adjusting energy metabolism and influencing cell growth and survival. Ado is also released by dead or dying cells and is present at significant concentrations in solid tumors. Ado signaling is mediated by Ado receptors (AdoR) and proteins modulating its concentration, including nucleoside transporters and Ado deaminases. This study examined the impact of genetic manipulations of three Drosophila genes involved in Ado signaling on the incidence of somatic mosaic clones formed by the loss of heterozygosity (LOH) of tumor suppressor and marker genes. Genetic manipulations with the AdoR, Equilibrative nucleoside transporter 2 (Ent2), and Ado deaminase growth factor-A (Adgf-A) cause dramatic changes in the frequency of hyperplastic outgrowth clones formed by LOH of the warts (wts) tumor suppressor, while they have almost no effect on control yellow (y) clones. In addition, the effect of AdoR is dose-sensitive and its overexpression leads to the increase in wts hyperplastic epithelial outgrowth rates. Consistently, the frequency of mosaic hyperplastic outgrowth clones generated by the LOH of another tumor suppressor, discs overgrown (dco), belonging to the wts signaling pathway is also dependent on AdoR. These results provide interesting insight into the maintenance of tissue homeostasis at a cellular level.

Wong, D. M., Shen, Z., Owyang, K. E. and Martinez-Agosto, J. A. (2014). Insulin- and Warts-dependent regulation of tracheal plasticity modulates systemic larval growth during hypoxia in Drosophila melanogaster. PLoS One 9: e115297. PubMed ID: 25541690

Summary: Adaptation to dynamic environmental cues during organismal development requires coordination of tissue growth with available resources. More specifically, the effects of oxygen availability on body size have been well-documented, but the mechanisms through which hypoxia restricts systemic growth have not been fully elucidated. This study characterized the larval growth and metabolic defects in Drosophila that result from hypoxia. Hypoxic conditions reduced fat body opacity and increased lipid droplet accumulation in this tissue, without eliciting lipid aggregation in hepatocyte-like cells called oenocytes. Additionally, hypoxia increased the retention of Dilp2 in the insulin-producing cells of the larval brain, associated with a reduction of insulin signaling in peripheral tissues. Overexpression of the wildtype form of the insulin receptor ubiquitously and in the larval trachea rendered larvae resistant to hypoxia-induced growth restriction. Furthermore, Warts downregulation in the trachea was similar to increased insulin receptor signaling during oxygen deprivation, which both rescued hypoxia-induced growth restriction, inhibition of tracheal molting, and developmental delay. Insulin signaling and loss of Warts function increased tracheal growth and augmented tracheal plasticity under hypoxic conditions, enhancing oxygen delivery during periods of oxygen deprivation. These findings demonstrate a mechanism that coordinates oxygen availability with systemic growth in which hypoxia-induced reduction of insulin receptor signaling decreases plasticity of the larval trachea that is required for the maintenance of systemic growth during times of limiting oxygen availability.

Zhou, J., Florescu, S., Boettcher, A., Luo, L., Dutta, D., Kerr, G., Cai, Y., Edgar, B. A. and Boutros, M. (2014). Dpp/Gbb signaling is required for normal intestinal regeneration during infection. Dev Biol [Epub ahead of print]. PubMed ID: 25553980

Summary: Maintaining tissue homeostasis is a critical process during infection and inflammation. Tissues with a high intrinsic turnover, such as the intestinal epithelium, must launch a rapid response to infections while simultaneously coordinating cell proliferation and differentiation decisions. This study sought for genes required for regeneration of the Drosophila intestine, and thereby affecting overall organism survival after infection with pathogenic bacteria. Dpp/Gbb (BMP) signaling was found to be essential for normal midgut regeneration, and infection was found to induce the BMP signaling ligands Dpp and Gbb. Dpp is induced in visceral muscle and required for signaling activation. Subsequently, Gbb is induced in enterocytes after oral infection. Loss-of Dpp signaling in ISCs and transient committed progenitors called enteroblasts (EBs) led to ISC hyperproliferation. This treatment also resulted in an increased number of abnormally small Pdm1-positive cells, suggesting that EBs defective for receiving Dpp/Gbb signaling produce immature enterocytes (ECs) and are therefore defective in EC maturation. Tkv-Mad/Med/Shn activity also promotes EC differentiation and growth, which is epistatic to Notch pathway, and is required for differentiation in normal midgut. These results suggest that Dpp/BMP signaling plays an important role in EBs to maintain tissue integrity and homeostasis during pathogenic infections.

Thursday January 15th

Cong, X., Wang, H., Liu, Z., He, C., An, C. and Zhao, Z. (2015). Regulation of sleep by Insulin-like peptide system in Drosophila melanogaster. Sleep. [Epub ahead of print]. PubMed ID: 25581915

Summary: Most organisms have behavioral and physiological circadian rhythms, which are controlled by an endogenous clock. Although genetic analysis has revealed the intracellular mechanism of the circadian clock, the manner in which this clock communicates its temporal information to produce systemic regulation is still largely unknown. In this study, sleep behavior was measured using the Drosophila Activity Monitoring System (DAMS) monitor under a 12 h light:12 h dark cycle and constant darkness (DD), and 5 min without recorded activity were defined as a bout of sleep. The study reports that Drosophila insulin-like peptides (DILPs) and their receptor (DInR) regulate sleep behavior. All mutants of the seven dilps and the mutant of their receptor exhibited decreases of total sleep except dilp4 mutants, whereas upregulation of DILP and DInR in the nervous system led to increased sleep. Histological analysis identified four previously unidentified neurons expressing DILP: D1, P1, L1, and L2, of which L1 and L2 belong to the LNd and LNv clock neurons that separately regulate different times of sleep. In addition, dilp2 levels significantly decreased when flies were fasted, which was consistent with a previous report that starvation inhibits sleep, further indicating that the dilp system was involved in sleep regulation. Taken together, the results indicate that the DILP system is a crucial regulator of sleep.

Ramdya, P., Lichocki, P., Cruchet, S., Frisch, L., Tse, W., Floreano, D. and Benton, R. (2014). Mechanosensory interactions drive collective behaviour in Drosophila. Nature [Epub ahead of print]. PubMed ID: 25533959

Summary: Collective behaviour enhances environmental sensing and decision-making in groups of animals. Experimental and theoretical investigations of schooling fish, flocking birds and human crowds have demonstrated that simple interactions between individuals can explain emergent group dynamics. These findings indicate the existence of neural circuits that support distributed behaviours, but the molecular and cellular identities of relevant sensory pathways are unknown. This study shows that Drosophila melanogaster exhibits collective responses to an aversive odour: individual flies weakly avoid the stimulus, but groups show enhanced escape reactions. Using high-resolution behavioural tracking, computational simulations, genetic perturbations, neural silencing and optogenetic activation this collective odour avoidance was demonstrated to arise from cascades of appendage touch interactions between pairs of flies. Inter-fly touch sensing and collective behaviour require the activity of distal leg mechanosensory sensilla neurons and the mechanosensory channel NOMPC. Remarkably, through these inter-fly encounters, wild-type flies can elicit avoidance behaviour in mutant animals that cannot sense the odour - a basic form of communication. These data highlight the unexpected importance of social context in the sensory responses of a solitary species and open the door to a neural-circuit-level understanding of collective behaviour in animal groups.

Sadaf, S., Reddy, O. V., Sane, S. P. and Hasan, G. (2014). Neural control of wing coordination in flies. Curr Biol [Epub ahead of print]. PubMed ID: 25496964

Summary: At the onset of each flight bout in flies, neural circuits in the CNS must rapidly integrate multimodal sensory stimuli and synchronously engage hinges of the left and right wings for coordinated wing movements. Whereas anatomical and physiological investigations of flight have been conducted on larger flies, molecular genetic studies in Drosophila have helped identify neurons that mediate various levels of flight control. However, neurons that might mediate bilateral coordination of wing movements to precisely synchronize left and right wing engagement at flight onset and maintain their movement in perfect coordination at rapid frequencies during flight maneuvers remain largely unexplored. Wing coordination could be directly modulated via bilateral sensory inputs to motoneurons of steering muscles and/or through central interneurons. Using a Ca2+-activity-based GFP reporter, this study identified three flight-activated central dopaminergic interneurons in the ventral ganglion, which connect to and activate motoneurons that innervate a pair of direct-steering flight muscles. The activation of these newly identified dopaminergic interneurons is context specific. Whereas bilateral wing engagement for flight requires these neurons, they do not control unilateral wing extension during courtship. Thus, independent central circuits function in the context of different natural behaviors to control the motor circuit for Drosophila wing movement.

Fedotov, S. A., Bragina, J. V., Besedina, N. G., Danilenkova, L. V., Kamysheva, E. A., Panova, A. A. and Kamyshev, N. G. (2014). The effect of neurospecific knockdown of candidate genes for locomotor behavior and sound production in Drosophila melanogaster. Fly (Austin) 8: 176-187. PubMed ID: 25494872

Summary: Molecular mechanisms underlying the functioning of central pattern generators (CPGs) are poorly understood. Investigations using genetic approaches in the model organism Drosophila may help to identify unknown molecular players participating in the formation or control of motor patterns. This study reports Drosophila genes as candidates for involvement in the neural mechanisms responsible for motor functions, such as locomotion and courtship song. Twenty-two Drosophila lines, used for gene identification, were isolated from a previously created collection of 1064 lines, each carrying a P element insertion in one of the autosomes. The lines displayed extreme deviations in locomotor and/or courtship song parameters compared with the whole collection. The behavioral consequences of CNS-specific RNAi-mediated knockdowns for 10 identified genes were estimated. The most prominent changes in the courtship song interpulse interval (IPI) were seen in flies with Sps2 or CG15630 knockdown. Glia-specific knockdown of these genes produced no effect on the IPI. Estrogen-induced knockdown of CG15630 in adults reduced the IPI. The product of the CNS-specific gene, CG15630 (a predicted cell surface receptor), is likely to be directly involved in the functioning of the CPG generating the pulse song pattern. Future studies should ascertain its functional role in the neurons that constitute the song CPG. Other genes (Sps2, CG34460), whose CNS-specific knockdown resulted in IPI reduction, are also worthy of detailed examination.

Wednesday, January 14th

Fairchild, M.J., Smendziuk, C.M. and Tanentzapf, G. (2015). A somatic permeability barrier around the germline is essential for Drosophila spermatogenesis. Development. 142: 268-281. PubMed ID: 25503408

Summary: Interactions between the soma and germline are essential for gametogenesis. In the Drosophila testis, differentiating germ cells are encapsulated by two somatic cells that surround the germline throughout spermatogenesis. chickadee (chic), the fly ortholog of Profilin, mediates soma-germline interactions. Knockdown of Chic in the soma results in sterility and severely disrupted spermatogenesis due to defective encapsulation. This study reports a permeability assay to analyze whether the germline is isolated from the surrounding environment by the soma. Germline encapsulation by the soma was, by itself, insufficient for the formation of a permeability barrier, but such a barrier gradually developed during early spermatogenesis. Thus, germline stem cells, gonialblasts and early spermatogonia were not isolated from the outside environment. By late spermatocyte stages, however, a permeability barrier was formed by the soma. Furthermore, concomitant with formation of the permeability barrier, septate junction markers were expressed in the soma and localized to junctional sites connecting the two somatic cells that surround the germline. Importantly, knockdown of septate junction components also disrupted the permeability barrier. Germline differentiation was delayed when the permeability barrier was compromised. The study proposes that the permeability barrier around the germline serves an important regulatory function during spermatogenesis by shaping the signaling events that take place between the soma and the germline.

Tseng, C.Y., Kao, S.H., Wan, C.L., Cho, Y., Tung, S.Y. and Hsu, H.J. (2014). Notch signaling mediates the age-associated decrease in adhesion of germline stem cells to the niche. PLoS Genet. 10: e1004888. PubMed ID: 25521289

Summary: Stem cells have an innate ability to occupy their stem cell niche, which in turn, is optimized to house stem cells. Organ aging is associated with reduced stem cell occupancy in the niche, but the mechanisms involved are poorly understood. This study reports that Notch signaling is increased with age in Drosophila female germline stem cells (GSCs), and this results in their removal from the niche. Clonal analysis revealed that GSCs with low levels of Notch signaling exhibited increased adhesiveness to the niche, thereby out-competing their neighbors with higher levels of Notch; adhesiveness was altered through regulation of E-cadherin expression. Experimental enhancement of Notch signaling in GSCs hastened their age-dependent loss from the niche, and such loss was at least partially mediated by Sex lethal. However, disruption of Notch signaling in GSCs did not delay GSC loss during aging, and nor did it affect BMP signaling, which promotes self-renewal of GSCs. Finally, in contrast to GSCs, Notch activation in the niche (which maintains niche integrity, and thus mediates GSC retention) was reduced with age, indicating that Notch signaling regulated GSC niche occupancy both intrinsically and extrinsically. These findings expose a novel role of Notch signaling in controlling GSC-niche adhesion in response to aging, and are also of relevance to metastatic cancer cells, in which Notch signaling suppresses cell adhesion.

Wei, Y., Reveal, B., Reich, J., Laursen, W. J., Senger, S., Akbar, T., Iida-Jones, T., Cai, W., Jarnik, M. and Lilly, M. A. (2014). TORC1 regulators Iml1/GATOR1 and GATOR2 control meiotic entry and oocyte development in Drosophila. Proc Natl Acad Sci U S A. PubMed ID: 25512509

Summary: In single-cell eukaryotes the pathways that monitor nutrient availability are central to initiating the meiotic program and gametogenesis. In Saccharomyces cerevisiae an essential step in the transition to the meiotic cycle is the down-regulation of the nutrient-sensitive target of rapamycin complex 1 (TORC1; see Drosophila Tor pathway) by the increased minichromosome loss 1/ GTPase-activating proteins toward Rags 1 (Iml1/GATOR1) complex in response to amino acid starvation. How metabolic inputs influence early meiotic progression and gametogenesis remains poorly understood in metazoans. This study defined opposing functions for the TORC1 regulatory complexes Iml1/GATOR1 and GATOR2 during Drosophila oogenesis. As is observed in yeast, the Iml1/GATOR1 complex inhibits TORC1 activity to slow cellular metabolism and drive the mitotic/meiotic transition in developing ovarian cysts. In iml1 germline depletions, ovarian cysts undergo an extra mitotic division before meiotic entry. The TORC1 inhibitor rapamycin can suppress this extra mitotic division. Thus, high TORC1 activity delays the mitotic/meiotic transition. Conversely, mutations in Tor, which encodes the catalytic subunit of the TORC1 complex, result in premature meiotic entry. Later in oogenesis, the GATOR2 components Missing oocyte (Mio) and Seh1 are required to oppose Iml1/GATOR1 activity to prevent the constitutive inhibition of TORC1 and a block to oocyte growth and development. These studies represent the first examination of the regulatory relationship between the Iml1/GATOR1 and GATOR2 complexes within the context of a multicellular organism. The data imply that the central role of the Iml1/GATOR1 complex in the regulation of TORC1 activity in the early meiotic cycle has been conserved from single cell to multicellular organisms.

Luo, J., Zuo, J., Wu, J., Wan, P., Kang, D., Xiang, C., Zhu, H. and Chen, J. (2014). In vivo RNAi screen identifies candidate signaling genes required for collective cell migration in Drosophila ovary. Sci China Life Sci. PubMed ID: 25528253

Summary: Collective migration of loosely or closely associated cell groups is prevalent in animal development, physiological events, and cancer metastasis. However, understanding of the mechanisms of collective cell migration is incomplete. Drosophila border cells provide a powerful in vivo genetic model to study collective migration and identify essential genes for this process. Using border cell-specific RNAi-silencing in Drosophila, 360 conserved signaling transduction genes were knocked down in adult flies to identify essential pathways and genes for border cell migration. A plethora of signaling genes were uncovered, a large proportion of which had not been reported for border cells, including Rack1 (Receptor of activated C kinase) and brk (brinker), Mad (Mother against dpp), and sax (saxophone), which encode three components of TGF-beta signaling. The RNAi knock down phenotype was validated by clonal analysis of Rack1 mutants. These data suggest that inhibition of Src activity by Rack1 may be important for border cell migration and cluster cohesion maintenance. Lastly, results from the screen not only would shed light on signaling pathways involved in collective migration during embryogenesis and organogenesis in general but also could help in understanding for the functions of conserved human genes involved in cancer metastasis.

Tuesday, January 13th

Sen, S., Cao, D., Choudhary, R., Biagini, S., Wang, J.W., Reichert, H. and VijayRaghavan, K. (2014). Genetic transformation of structural and functional circuitry rewires the Drosophila brain. Elife. [Epub ahead of print]. PubMed ID: 25546307

Summary: Acquisition of distinct neuronal identities during development is critical for the assembly of diverse functional neural circuits in the brain. In both vertebrates and invertebrates, intrinsic determinants are thought to act in neural progenitors to specify their identity and the identity of their neuronal progeny. However, the extent to which individual factors can contribute to this is poorly understood. This study investigates the role of orthodenticle in the specification of an identified neuroblast (neuronal progenitor) lineage in the Drosophila brain. Loss of orthodenticle from this neuroblast affected molecular properties, neuroanatomical features and functional inputs of progeny neurons, such that an entire central complex lineage transformed into a functional olfactory projection neuron lineage. This ability to change functional macrocircuitry of the brain through changes in gene expression in a single neuroblast revealed a surprising capacity for novel circuit formation in the brain and provided a paradigm

Apitz, H. and Salecker, I. (2014). A region-specific neurogenesis mode requires migratory progenitors in the Drosophila visual system. Nat Neurosci [Epub ahead of print]. PubMed ID: 25501037

Summary: Brain areas each generate specific neuron subtypes during development. However, underlying regional variations in neurogenesis strategies and regulatory mechanisms remain poorly understood. In Drosophila, neurons in four optic lobe ganglia originate from two neuroepithelia, the outer (OPC) and inner (IPC) proliferation centers. Using genetic manipulations, this study found that one IPC neuroepithelial domain progressively transformed into migratory progenitors that matured into neural stem cells (neuroblasts) in a second domain. Progenitors emerged by an epithelial-mesenchymal transition-like mechanism that required the Snail-family member Escargot and, in subdomains, Decapentaplegic signaling. The proneural factors Lethal of scute and Asense differentially controlled progenitor supply and maturation into neuroblasts. These switched expression from Asense to a third proneural protein, Atonal. Dichaete and Tailless mediated this transition, which was essential for generating two neuron populations at defined positions. It is proposed that this neurogenesis mode is central for setting up a new proliferative zone to facilitate spatio-temporal matching of neurogenesis and connectivity across ganglia.

Aso, Y., Hattori, D., Yu, Y., Johnston, R. M., Iyer, N. A., Ngo, T. T., Dionne, H., Abbott, L., Axel, R., Tanimoto, H. and Rubin, G. M. (2014). The neuronal architecture of the mushroom body provides a logic for associative learning. Elife 3. PubMed ID: 25535793. Mushroom body output neurons encode valence and guide memory-based action selection in Drosophila. Elife 3 [Epub ahead of print]. PubMed ID: 25535794

Summary: Animals discriminate stimuli, learn their predictive value and use this knowledge to modify their behavior. In Drosophila, the mushroom body (MB) plays a key role in these processes. Sensory stimuli are sparsely represented by approximately 2000 Kenyon cells, which converge onto 34 output neurons (MBONs) of 21 types (see Circuit diagrams of the mushroom body). The role of MBONs were studied in several associative learning tasks and in sleep regulation, revealing the extent to which information flow is segregated into distinct channels and suggesting possible roles for the multi-layered MBON network. Optogenetic activation of MBONs can, depending on cell type, induce repulsion or attraction in flies. The behavioral effects of MBON perturbation are combinatorial, suggesting that the MBON ensemble collectively provides an adaptive mechanism to assign valence—positive or negative survival value—to a sensory stimulus then store that information, and recall it when that same stimulus is encountered again. It is proposed that local, stimulus-specific dopaminergic modulation selectively alters the balance within the MBON network for those stimuli. These results suggest that valence encoded by the MBON ensemble biases memory-based action selection.

Urwyler, O., Izadifar, A., Dascenco, D., Petrovic, M., He, H., Ayaz, D., Kremer, A., Lippens, S., Baatsen, P., Guerin, C. J. and Schmucker, D. (2014). Investigating CNS synaptogenesis at single-synapse resolution by combining reverse genetics with correlative light and electron microscopy. Development [Epub ahead of print]. PubMed ID: 25503410

Summary: Determining direct synaptic connections of specific neurons in the central nervous system (CNS) is a major technical challenge in neuroscience. As a corollary, molecular pathways controlling developmental synaptogenesis in vivo remain difficult to address. This study presents genetic tools for efficient and versatile labeling of organelles, cytoskeletal components and proteins at single-neuron and single-synapse resolution in Drosophila mechanosensory (ms) neurons. The imaging analysis was extended to the ultrastructural level by developing a protocol for correlative light and 3D electron microscopy (3D CLEM). In ms neurons, synaptic puncta revealed by genetically encoded markers serve as a reliable indicator of individual active zones. Block-face scanning electron microscopy analysis of ms axons revealed T-bar-shaped dense bodies and other characteristic ultrastructural features of CNS synapses. For a mechanistic analysis, the single-neuron labeling approach was directly combined with cell-specific gene disruption techniques. In proof-of-principle experiments evidence was found for a highly similar requirement for the scaffolding molecule Liprin-α and its interactors Lar and DSyd-1 (RhoGAP100F) in synaptic vesicle recruitment. This suggests that these important synapse regulators might serve a shared role at presynaptic sites within the CNS. In principle, the CLEM approach is broadly applicable to the developmental and ultrastructural analysis of any cell type that can be targeted with genetically encoded markers.

Monday, January 12th

Figueiredo, M. L., Kim, M., Philip, P., Allgardsson, A., Stenberg, P. and Larsson, J. (2014). Non-coding roX RNAs prevent the binding of the MSL-complex to heterochromatic regions. PLoS Genet 10: e1004865. PubMed ID: 25501352

Summary: Long non-coding RNAs contribute to dosage compensation in both mammals and Drosophila by inducing changes in the chromatin structure of the X-chromosome. In Drosophila melanogaster, roX1 and roX2 are long non-coding RNAs that together with proteins form the male-specific lethal (MSL) complex, which coats the entire male X-chromosome and mediates dosage compensation by increasing its transcriptional output. Studies on polytene chromosomes have demonstrated that when both roX1 and roX2 are absent, the MSL-complex becomes less abundant on the male X-chromosome and is relocated to the chromocenter and the 4th chromosome. This study addresses the role of roX RNAs in MSL-complex targeting and the evolution of dosage compensation in Drosophila. ChIP-seq experiments were performed that showed that MSL-complex recruitment to high affinity sites (HAS) on the X-chromosome is independent of roX and that the HAS sequence motif is conserved in D. simulans. Additionally, a complete and enzymatically active MSL-complex is recruited to six specific genes on the 4th chromosome. Interestingly, the sequence analysis showed that in the absence of roX RNAs, the MSL-complex has an affinity for regions enriched in Hoppel transposable elements and repeats in general. It is hypothesized that roX mutants reveal the ancient targeting of the MSL-complex and propose that the role of roX RNAs is to prevent the binding of the MSL-complex to heterochromatin.

Spletter, M.L., Barz, C., Yeroslaviz, A., Schönbauer, C., Ferreira, I.R., Sarov, M., Gerlach, D., Stark, A., Habermann, B.H. and Schnorrer, F. (2014). The RNA-binding protein Arrest (Bruno) regulates alternative splicing to enable myofibril maturation in Drosophila flight muscle. EMBO Rep. [Epub ahead of print]. PubMed ID: 25532219

Summary: In Drosophila, fibrillar flight muscles (IFMs) enable flight, while tubular muscles mediate other body movements. This study uses RNA-sequencing and isoform-specific reporters to show that spalt major (salm) determines fibrillar muscle physiology by regulating transcription and alternative splicing of a large set of sarcomeric proteins. The RNA-binding protein Arrest (Aret, Bruno) acted downstream of salm. Aret shuttled between the cytoplasm and nuclei and was essential for myofibril maturation and sarcomere growth of IFMs. Molecularly, Aret regulated IFM-specific splicing of various salm-dependent sarcomeric targets, including Stretchin and wupA (TnI), and thus maintained muscle fiber integrity. As Aret and its sarcomeric targets are evolutionarily conserved, similar principles may regulate mammalian muscle morphogenesis.

Oktaba, K., Zhang, W., Lotz, T. S., Jun, D. J., Lemke, S. B., Ng, S. P., Esposito, E., Levine, M. and Hilgers, V. (2014). ELAV links paused Pol II to alternative polyadenylation in the Drosophila nervous system. Mol Cell [Epub ahead of print]. PubMed ID: 25544561

Summary: Alternative polyadenylation (APA) has been implicated in a variety of developmental and disease processes. A particularly dramatic form of APA occurs in the developing nervous system of flies and mammals, whereby various developmental genes undergo coordinate 3' UTR extension. In Drosophila, the RNA-binding protein ELAV inhibits RNA processing at proximal polyadenylation sites, thereby fostering the formation of exceptionally long 3' UTRs. This study presents evidence that paused Pol II promotes recruitment of ELAV to extended genes. Replacing promoters of extended genes with heterologous promoters blocks normal 3' extension in the nervous system, while extension-associated promoters can induce 3' extension in ectopic tissues expressing ELAV. Computational analyses suggest that promoter regions of extended genes tend to contain paused Pol II and associated cis-regulatory elements such as GAGA. ChIP-seq assays identify ELAV in the promoter regions of extended genes. This study provides evidence for a regulatory link between promoter-proximal pausing and APA.

Chen, Y. W., Song, S., Weng, R., Verma, P., Kugler, J. M., Buescher, M., Rouam, S. and Cohen, S. M. (2014). Systematic study of Drosophila microRNA functions using a collection of targeted knockout mutations. Dev Cell 31: 784-800. PubMed ID: 25535920

Summary: MicroRNAs are abundant in animal genomes, yet little is known about their functions in vivo. This study reports the production of 80 new Drosophila miRNA mutants by targeted homologous recombination. These mutants remove 104 miRNAs. Together with 15 previously reported mutants, this collection includes 95 mutants deleting 130 miRNAs. Collectively, these genes produce over 99% of all Drosophila miRNAs, measured by miRNA sequence reads. A survey is presented of developmental and adult miRNA phenotypes. Over 80% of the mutants showed at least one phenotype using a p < 0.01 significance threshold. A significant correlation was observed between miRNA abundance and phenotypes related to survival and lifespan, but not to most other phenotypes. miRNA cluster mutants were no more likely than single miRNA mutants to produce significant phenotypes. This mutant collection will provide a resource for future analysis of the biological roles of Drosophila miRNAs.

Sunday, January 11th

Clough, E., Jimenez, E., Kim, Y.A., Whitworth, C., Neville, M.C., Hempel, L.U., Pavlou, H.J., Chen, Z.X., Sturgill, D., Dale, R.K., Smith, H.E., Przytycka, T.M., Goodwin, S.F., Van Doren, M. and Oliver, B. (2014). Sex- and tissue-specific functions of Drosophila doublesex transcription factor target genes. Dev Cell 31: 761-773. PubMed ID: 25535918

Summary: Primary sex-determination 'switches' evolve rapidly, but Doublesex (DSX)-related transcription factors (DMRTs) act downstream of these switches to control sexual development in most animal species. Drosophila dsx encodes female- and male-specific isoforms (DSX^F and DSX^M), but little is known about how dsx controls sexual development, whether DSX^F and DSX^M bind different targets, or how DSX proteins direct different outcomes in diverse tissues. This study undertook genome-wide analyses to identify DSX targets using in vivo occupancy, binding site prediction, and evolutionary conservation. It finds that DSX^F and DSX^M bind thousands of the same targets in multiple tissues in both sexes, yet these targets have sex- and tissue-specific functions. Interestingly, DSX targets showed considerable overlap with targets identified for mouse DMRT1. DSX targets included transcription factors and signaling pathway components providing for direct and indirect regulation of sex-biased expression.

Potier, D., Davie, K., Hulselmans, G., Naval Sanchez, M., Haagen, L., Huynh-Thu, V. A., Koldere, D., Celik, A., Geurts, P., Christiaens, V. and Aerts, S. (2014). Mapping gene regulatory networks in Drosophila eye development by large-scale transcriptome perturbations and motif inference. Cell Rep 9: 2290-2303. PubMed ID: 25533349

Summary: Genome control is operated by transcription factors (TFs) controlling their target genes by binding to promoters and enhancers. Conceptually, the interactions between TFs, their binding sites, and their functional targets are represented by gene regulatory networks (GRNs). Deciphering in vivo GRNs underlying organ development in an unbiased genome-wide setting involves identifying both functional TF-gene interactions and physical TF-DNA interactions. To reverse engineer the GRNs of eye development in Drosophila, this study performed RNA-seq across 72 genetic perturbations and sorted cell types and inferred a coexpression network. Next, direct TF-DNA interactions were derived using computational motif inference, ultimately connecting 241 TFs to 5,632 direct target genes through 24,926 enhancers. Using this network, network motifs, cis-regulatory codes, and regulators of eye development were found. The predicted target regions of Grainyhead were validated by ChIP-seq and this factor was identified as a general cofactor in the eye network, being bound to thousands of nucleosome-free regions.

Staller, M.V., Vincent, B.J., Bragdon, M.D., Lydiard-Martin, T., Wunderlich, Z., Estrada, J. and DePace, A.H. (2015). Shadow enhancers enable Hunchback bifunctionality in the Drosophila embryo. Proc Natl Acad Sci USA. [Epub ahead of print]. PubMed ID: 25564665

Summary: Hunchback (Hb) is a bifunctional transcription factor that activates and represses distinct enhancers. This study investigates the hypothesis that Hb can activate and repress the same enhancer. Computational models predicted that Hb bifunctionally regulated the even-skipped (eve) stripe 3+7 enhancer (eve3+7) in Drosophila blastoderm embryos. The study measured and modeled eve expression at cellular resolution under multiple genetic perturbations and found that the eve3+7 enhancer could not explain endogenous eve stripe 7 behavior. Instead, eve stripe 7 was controlled by two enhancers: the canonical eve3+7 and a sequence encompassing the minimal eve stripe 2 enhancer (eve2+7). Hb bifunctionally regulated eve stripe 7, but it executed these two activities on different pieces of regulatory DNA-it activated the eve2+7 enhancer and repressed the eve3+7 enhancer. These two "shadow enhancers" used different regulatory logic to create the same pattern.

Asada, R., Takemata, N., Hoffman, C. S., Ohta, K. and Hirota, K. (2014). Antagonistic controls of chromatin and mRNA start site selection by Tup family corepressors and the CCAAT-binding factor. Mol Cell Biol [Epub ahead of print]. PubMed ID: 25535331

Summary: The Tup family corepressors contribute to critical cellular responses, such as stress response and differentiation, presumably by inducing repressive chromatin, though the precise repression mechanism remains to be elucidated. Fission yeast Tup family corepressors Tup11 and Tup12, which are orthologs of Tup1 in budding yeast and Groucho in Drosophila, negatively control chromatin and transcriptional activity of some stress-responsive genes. This study demonstrates that Tup11/12 repress transcription of a gluconeogenesis gene fbp1⁺ by three distinct mechanisms. First, Tup11/12 inhibit chromatin remodeling in the fbp1⁺ promoter region where the Atf1 and Rst2 transcriptional activators bind. Second, they repress the formation of an open chromatin configuration at the fbp1⁺ TATA box. Third, they repress mRNA transcription per se, by regulating basic transcription factors. These inhibitory actions of Tup11/12 are antagonized by three different types of transcriptional activators: CREB/ATF-type Atf1, C2H2 zinc finger-type Rst2, and CBF/NF-Y-type Php5 proteins. Impaired chromatin remodeling and fbp1⁺mRNA transcription were found in php5^Δ strains are rescued by the double deletions of tup11⁺ and tup12⁺, although the distribution of the transcription start sites becomes broader than in wild-type cells. These data reveal a new mechanism of precise determination of mRNA start site by Tup family corepressors and CBF/NF-Y proteins.

Saturday, January 10th

Bell, G.P., Fletcher, G.C., Brain, R. and Thompson, B.J. (2015). Aurora kinases phosphorylate Lgl to induce mitotic spindle orientation in Drosophila epithelia. Curr Biol. 25: 61-68. PubMed ID: 25484300

Summary: The Lethal giant larvae (Lgl) protein was discovered in Drosophila as a tumor suppressor in both neural stem cells (neuroblasts) and epithelia. In neuroblasts, Lgl relocalizes to the cytoplasm at mitosis, an event attributed to phosphorylation by mitotically activated aPKC kinase and thought to promote asymmetric cell division. This study shows that Lgl also relocalizes to the cytoplasm at mitosis in epithelial cells, which divide symmetrically. The Aurora A and Aurora B kinases directly phosphorylated Lgl to promote its mitotic relocalization, whereas aPKC kinase activity was required only for polarization of Lgl. A form of Lgl that was a substrate for aPKC, but not Aurora kinases, could restore cell polarity in lgl mutants but revealed defects in mitotic spindle orientation in epithelia. The study proposes that removal of Lgl from the plasma membrane at mitosis allows Pins/LGN to bind Dlg and thus orient the spindle in the plane of the epithelium. These findings suggest a revised model for Lgl regulation and function in both symmetric and asymmetric cell divisions.

Carvalho, C.A., Moreira, S., Ventura, G., Sunkel, C.E. and Morais-de-Sá, E. (2015). Aurora A triggers Lgl cortical release during symmetric division to control planar spindle orientation. Curr Biol. 25: 53-60. PubMed ID: 25484294

Summary: Mitotic spindle orientation is essential to control cell-fate specification and epithelial architecture. The tumor suppressor Lgl localizes to the basolateral cortex of epithelial cells, where it acts together with Dlg and Scrib to organize apicobasal polarity. Dlg and Scrib also control planar spindle orientation but how the organization of polarity complexes is adjusted to control symmetric division is largely unknown. Lgl redistribution during epithelial mitosis is reminiscent of asymmetric cell division, where it is proposed that Aurora A promotes aPKC activation to control the localization of Lgl and cell-fate determinants. This study shows that the Dlg complex is remodeled during Drosophila follicular epithelium cell division, when Lgl is released to the cytoplasm. Aurora A controlled Lgl localization directly, triggering its cortical release at early prophase in both epithelial and S2 cells. This relied on double phosphorylation within the putative aPKC phosphorylation site, which was required and sufficient for Lgl cortical release during mitosis and could be achieved by a combination of aPKC and Aurora A activities. Cortical retention of Lgl disrupted planar spindle orientation, but only when Lgl mutants that could bind Dlg were expressed. Taken together, Lgl mitotic cortical release is not specifically linked to the asymmetric segregation of fate determinants, and the study proposes that Aurora A activation breaks the Dlg/Lgl interaction to allow planar spindle orientation during symmetric division via the Pins (LGN)/Dlg pathway.

Venkei, Z. G. and Yamashita, Y. M. (2015). The centrosome orientation checkpoint is germline stem cell specific and operates prior to the spindle assembly checkpoint in Drosophila testis. Development 142: 62-69. PubMed ID: 25480919

Summary: Asymmetric cell division is utilized by a broad range of cell types to generate two daughter cells with distinct cell fates. In stem cell populations asymmetric cell division is believed to be crucial for maintaining tissue homeostasis, failure of which can lead to tissue degeneration or hyperplasia/tumorigenesis. Asymmetric cell divisions also underlie cell fate diversification during development. Accordingly, the mechanisms by which asymmetric cell division is achieved have been extensively studied, although the check points that are in place to protect against potential perturbation of the process are poorly understood. Drosophila melanogaster male germline stem cells (GSCs) possess a checkpoint, termed the centrosome orientation checkpoint (COC), that monitors correct centrosome orientation with respect to the component cells of the niche to ensure asymmetric stem cell division. The COC is the only checkpoint mechanism identified to date that specializes in monitoring the orientation of cell division in multicellular organisms. By establishing colcemid-induced microtubule depolymerization as a sensitive assay, this study examined the characteristics of COC activity and found that it functions uniquely in GSCs but not in their differentiating progeny. The COC operates in the G2 phase of the cell cycle, independently of the spindle assembly checkpoint. This study may provide a framework for identifying and understanding similar mechanisms that might be in place in other asymmetrically dividing cell types.

Elenbaas, J. S., Mouawad, R., Henry, W. R., Arnosti, D. N. and Payankaulam, S. (2014). Role of Drosophila retinoblastoma protein instability element in cell growth and proliferation. Cell Cycle: [Epub ahead of print]. PubMed ID: 25496208

Summary: The RB tumor suppressor, a regulator of the cell cycle, apoptosis, senescence, and differentiation, is frequently mutated in human cancers. An evolutionarily conserved C-terminal 'instability element' (IE) of the Drosophila Rbf1 retinoblastoma protein regulates its turnover. Misexpression of wild-type or non-phosphorylatable forms of the Rbf1 protein leads to repression of cell cycle genes. In contrast, overexpression of a defective form of Rbf1 lacking the IE (DeltaIE), a stabilized but transcriptionally less active form of the protein, induced ectopic S phase in cell culture. To determine how mutations in the Rbf1 IE may induce dominant effects in a developmental context, the impact was assessed of in vivo expression of mutant Rbf1 proteins on wing development. DeltaIE expression resulted in overgrowth of larval wing imaginal discs and larger adult wings containing larger cells. In contrast, a point mutation in a conserved lysine of the IE (K774A) generated severely disrupted, reduced wings. These contrasting effects appear to correlate with control of apoptosis; expression of the pro-apoptotic reaper gene and DNA fragmentation measured by acridine orange stain increased in flies expressing the K774A isoform and was suppressed by expression of Rbf1DeltaIE. Intriguingly, cancer associated mutations affecting RB homologs p130 and p107 may similarly induce dominant phenotypes.

Friday, January 9th

Kaneuchi, T., Sartain, C.V., Takeo, S., Horner, V.L., Buehner, N.A., Aigaki, T. and Wolfner, M.F. (2015). Calcium waves occur as Drosophila oocytes activate. Proc Natl Acad Sci USA. [Epub ahead of print]. PubMed ID: 25564670

Summary: Egg activation is the process by which a mature oocyte becomes capable of supporting embryo development. In vertebrates and echinoderms, activation is induced by fertilization. Molecules introduced into the egg by the sperm trigger progressive release of intracellular calcium stores in the oocyte. Calcium wave(s) spread through the oocyte and induce completion of meiosis, new macromolecular synthesis, and modification of the vitelline envelope to prevent polyspermy. However, arthropod eggs activate without fertilization: in the insects examined, eggs activate as they move through the female's reproductive tract. This study shows that a calcium wave is, nevertheless, characteristic of egg activation in Drosophila. The calcium rise required influx of calcium from the external environment and was induced as the egg ovulated. Pressure on the oocyte (or swelling by the oocyte) could induce a calcium rise through the action of mechanosensitive ion channels. Visualization of calcium fluxes in activating eggs in oviducts showed a wave of increased calcium initiating at one or both oocyte poles and spreading across the oocyte. In vitro, waves also spread inward from oocyte pole(s). Wave propagation required the IP3 system. Thus, although a fertilizing sperm was not necessary for egg activation in Drosophila, the characteristic of increased cytosolic calcium levels spreading through the egg was conserved. Because many downstream signaling effectors are conserved in Drosophila, this system offers the unique perspective of egg activation events due solely to maternal components.

Le Droguen, P.M., Claret, S., Guichet, A. and Brodu, V. (2015). Microtubule-dependent apical restriction of recycling endosomes sustains adherens junctions during morphogenesis of the Drosophila tracheal system. Development 142: 363-374. PubMed ID: 25564624

Summary: Epithelial remodelling is an essential mechanism for organogenesis, during which cells change shape and position while maintaining contact with each other. Adherens junctions (AJs) mediate stable intercellular cohesion but must be actively reorganised to allow morphogenesis. Vesicle trafficking and the microtubule (MT) cytoskeleton contribute to regulating AJs but their interrelationship remains elusive. This study reports a detailed analysis of the role of MTs in cell remodelling during formation of the tracheal system in the Drosophila embryo. Induction of MT depolymerisation specifically in tracheal cells showed that MTs were essential during a specific time frame of tracheal cell elongation while the branch extended. In the absence of MTs, one tracheal cell per branch overelongated, ultimately leading to branch break. Three-dimensional quantifications revealed that MTs were crucial to sustain E-Cadherin (Shotgun) and Par-3 (Bazooka) levels at AJs. Maintaining E-Cadherin/Par-3 levels at the apical domain required de novo synthesis rather than internalisation and recycling from and to the apical plasma membrane. However, apical targeting of E-Cadherin and Par-3 required functional recycling endosomes, suggesting an intermediate role for this compartment in targeting de novo synthesized E-Cadherin to the plasma membrane. The apical enrichment of recycling endosomes was dependent on the MT motor Dynein and essential for the function of this vesicular compartment. In addition, E-Cadherin dynamics and MT requirement differed in remodelling tracheal cells versus planar epithelial cells. Altogether, these results uncover an MT-Dynein-dependent apical restriction of recycling endosomes that controls adhesion by sustaining Par-3 and E-Cadherin levels at AJs during morphogenesis.

Schulman, V. K., Folker, E. S., Rosen, J. N. and Baylies, M. K. (2014). Syd/JIP3 and JNK signaling are required for myonuclear positioning and muscle function. PLoS Genet 10: e1004880. PubMed ID: 25522254

Summary: Highlighting the importance of proper intracellular organization, many muscle diseases are characterized by mispositioned myonuclei. Proper positioning of myonuclei is dependent upon the microtubule motor proteins, Kinesin-1 and cytoplasmic Dynein, and there are at least two distinct mechanisms by which Kinesin and Dynein move myonuclei. The motors exert forces both directly on the nuclear surface and from the cell cortex via microtubules. How these activities are spatially segregated yet coordinated to position myonuclei is unknown. Using Drosophila melanogaster, Sunday Driver (Syd), a homolog of mammalian JNK-interacting protein 3 (JIP3), was shown to specifically regulate Kinesin- and Dynein-dependent cortical pulling of myonuclei without affecting motor activity near the nucleus. Specifically, Syd mediates Kinesin-dependent localization of Dynein to the muscle ends, where cortically anchored Dynein then pulls microtubules and the attached myonuclei into place. Proper localization of Dynein also requires activation of the JNK signaling cascade. Furthermore, Syd functions downstream of JNK signaling because without Syd, JNK signaling is insufficient to promote Kinesin-dependent localization of Dynein to the muscle ends. The significance of Syd-dependent myonuclear positioning is illustrated by muscle-specific depletion of Syd, which impairs muscle function. Moreover, both myonuclear spacing and locomotive defects in syd mutants can be rescued by expression of mammalian JIP3 in Drosophila muscle tissue, indicating an evolutionarily conserved role for JIP3 in myonuclear movement and highlighting the utility of Drosophila as a model for studying mammalian development. Collectively, this study implicated Syd/JIP3 as a novel regulator of myogenesis that is required for proper intracellular organization and tissue function.

Luan, Q., Chen, Q. and Friedrich, M. (2014). The Pax6 genes eyeless and twin of eyeless are required for global patterning of the ocular segment in the Tribolium embryo. Dev Biol 394: 367-381. PubMed ID: 25149513

Summary: The transcription factor gene Pax6 is widely considered a master regulator of eye development in bilaterian animals. However, the existence of visual organs that develop without Pax6 input and the considerable pleiotropy of Pax6 outside the visual system dictate further studies into defining ancestral functions of this important regulator. Previous work has shown that the combinatorial knockdown of the insect Pax6 orthologs eyeless (ey) and twin of eyeless (toy) perturbs the development of the visual system but also other areas of the larval head in the red flour beetle Tribolium castaneum. To elucidate the role of Pax6 during Tribolium head development in more detail, head cuticle morphology, brain anatomy, embryonic head morphogenesis, and developmental marker gene expression were studied in combinatorial ey and toy knockdown animals. These experiments reveal that Pax6 is broadly required for patterning the anterior embryonic head. One of the earliest detectable roles is the formation of the embryonic head lobes, which originate from within the ocular segment and give rise to large parts of the supraesophageal brain including the mushroom body, a part of the posterior head capsule cuticle, and the visual system. Further evidence is presented that toy continues to be required for the development of the larval eyes after formation of the embryonic head lobes in cooperation with the eye developmental transcription factor dachshund (dac). The sum of these findings suggests that Pax6 functions as a competence factor throughout the development of the insect ocular segment. Comparative evidence identifies this function as an ancestral aspect of bilaterian head development.

Thursday, January 8th

Dent, L. G., Poon, C. L., Zhang, X., Degoutin, J. L., Tipping, M., Veraksa, A. and Harvey, K. F. (2014). The GTPase regulatory proteins Pix and Git control tissue growth via the Hippo pathway. Curr Biol 25(1):124-30. PubMed ID: 25484297

Summary: The Salvador-Warts-Hippo (Hippo) pathway is a conserved regulator of organ size and is deregulated in human cancers. In epithelial tissues, the Hippo pathway is regulated by fundamental cell biological properties, such as polarity and adhesion, and coordinates these with tissue growth. Despite its importance in disease, development, and regeneration, the complete set of proteins that regulate Hippo signaling remain undefined. This study used proteomics to identify proteins that bind to the Hippo (Hpo) kinase. Prominent among these were PAK-interacting exchange factor (known as Pix or RtGEF) and G-protein-coupled receptor kinase-interacting protein (Git). Pix is a conserved Rho-type guanine nucleotide exchange factor (Rho-GEF) homologous to Beta-PIX and Alpha-PIX in mammals. Git is the single Drosophila melanogaster homolog of the mammalian GIT1 and GIT2 proteins, which were originally identified in the search for molecules that interact with G-protein-coupled receptor kinases. Pix and Git form an oligomeric scaffold to facilitate sterile 20-like kinase activation and have also been linked to GTPase regulation. Pix and Git regulate Hippo-pathway-dependent tissue growth in D. melanogaster, and they do this in parallel to the known upstream regulator Fat cadherin. Pix and Git influence activity of the Hpo kinase by acting as a scaffold complex, rather than enzymes, and promote Hpo dimerization and autophosphorylation of Hpo's activation loop. Therefore, this study provides important new insights into an ancient signaling network that controls the growth of metazoan tissues.

Zhang, H., Li, C., Chen, H., Wei, C., Dai, F., Wu, H., Dui, W., Deng, W. and Jiao, R. (2014). SCF E3 ligase-mediated degradation of Expanded is inhibited by the Hippo pathway in Drosophila. Cell Res 25(1):93-109. PubMed ID: 25522691

Summary: Deregulation of the evolutionarily conserved Hippo pathway has been implicated in abnormal development of animals and in several types of cancer. One mechanism of Hippo pathway regulation is achieved by controlling the stability of its regulatory components. However, the executive E3 ligases that are involved in this process, and how the process is regulated, remain poorly defined. This study identified, through a genetic candidate screen, the SCFSlmb E3 ligase as a novel negative regulator of the Hippo pathway in Drosophila imaginal tissues via mediation of the degradation of Expanded (Ex). Mechanistic study shows that Slmb-mediated degradation of Ex is inhibited by the Hippo signaling. Considering the fact that Hippo signaling suppresses the transcription of ex, it is proposed that the Hippo pathway employs a double security mechanism to ensure fine-tuned homeostasis during development.

Zhang, T., Liao, Y., Hsu, F. N., Zhang, R., Searle, J. S., Pei, X., Li, X., Ryoo, H. D., Ji, J. Y. and Du, W. (2014). Hyperactivated Wnt signaling induces synthetic lethal interaction with Rb inactivation by elevating TORC1 activities. PLoS Genet 10: e1004357. PubMed ID: 24809668

Summary: Inactivation of the Rb tumor suppressor can lead to increased cell proliferation or cell death depending on specific cellular context. Therefore, identification of the interacting pathways that modulate the effect of Rb loss will provide novel insights into the roles of Rb in cancer development and promote new therapeutic strategies. This study identified a novel synthetic lethal interaction between Rb inactivation and deregulated Wg/Wnt signaling through unbiased genetic screens. A weak allele of axin, which deregulates Wg signaling and increases cell proliferation without obvious effects on cell fate specification, significantly alters metabolic gene expression, causes hypersensitivity to metabolic stress induced by fasting, and induces synergistic apoptosis with mutation of fly Rb ortholog, rbf. Furthermore, hyperactivation of Wg signaling by other components of the Wg pathway also induces synergistic apoptosis with rbf. hyperactivated Wg signaling significantly increases TORC1 activity and induces excessive energy stress with rbf mutation. Inhibition of TORC1 activity significantly suppressed synergistic cell death induced by hyperactivated Wg signaling and rbf inactivation, which is correlated with decreased energy stress and decreased induction of apoptotic regulator expression. Finally the synthetic lethality between Rb and deregulated Wnt signaling is conserved in mammalian cells, and inactivation of Rb and APC induces synergistic cell death through a similar mechanism. These results suggest that elevated TORC1 activity and metabolic stress underpin the evolutionarily conserved synthetic lethal interaction between hyperactivated Wnt signaling and inactivated Rb tumor suppressor.

>Jakobs, P., Exner, S., Schurmann, S., Pickhinke, U., Bandari, S., Ortmann, C., Kupich, S., Schulz, P., Hansen, U., Seidler, D. G. and Grobe, K. (2014). Scube2 enhances proteolytic Shh processing from the surface of Shh-producing cells. J Cell Sci 127: 1726-1737. PubMed ID: 24522195

Summary: All morphogens of the Hedgehog (Hh; see Drosophila Hedgehog) family are synthesized as dual-lipidated proteins, which results in their firm attachment to the surface of the cell in which they were produced. Thus, Hh release into the extracellular space requires accessory protein activities. Previous studies suggested that the proteolytic removal of N- and C-terminal lipidated peptides (shedding) could be one such activity. The secreted glycoprotein Scube2 (signal peptide, cubulin domain, epidermal-growth-factor-like protein 2) was also implicated in the release of Shh from the cell membrane. This activity strictly depended on the CUB domains of Scube2, which derive their name from the complement serine proteases and from bone morphogenetic protein-1/tolloid metalloproteinases (C1r/C1s, Uegf and Bmp1). CUB domains function as regulators of proteolytic activity in these proteins. This suggested that sheddases and Scube2 might cooperate in Shh release. This study confirmed that sheddases and Scube2 act cooperatively to increase the pool of soluble bioactive Shh, and that Scube2-dependent morphogen release is unequivocally linked to the proteolytic processing of lipidated Shh termini, resulting in truncated soluble Shh. Thus, Scube2 proteins act as protease enhancers in this setting, revealing newly identified Scube2 functions in Hh signaling regulation.

Wednesday, January 7th

Guo, C., Du, Y., Yuan, D., Li, M., Gong, H., Gong, Z. and Liu, L. (2014). A conditioned visual orientation requires the ellipsoid body in Drosophila. Learn Mem 22: 56-63. PubMed ID: 25512578

Summary: Orientation, the spatial organization of animal behavior, is an essential faculty of animals. Bacteria and lower animals such as insects exhibit taxis, innate orientation behavior, directly toward or away from a directional cue. Organisms can also orient themselves at a specific angle relative to the cues. This study, using Drosophila as a model system, established a visual orientation conditioning paradigm based on a flight simulator in which a stationary flying fly could control the rotation of a visual object. By coupling aversive heat shocks to a fly's orientation toward one side of the visual object, this study found that the fly could be conditioned to orientate toward the left or right side of the frontal visual object and retain this conditioned visual orientation. The lower and upper visual fields have different roles in conditioned visual orientation. Transfer experiments showed that conditioned visual orientation could generalize between visual targets of different sizes, compactness, or vertical positions, but not of contour orientation. Rut-Type I adenylyl cyclase and Dnc-phosphodiesterase were dispensable for visual orientation conditioning. Normal activity and scb signaling in R3/R4d neurons of the ellipsoid body were required for visual orientation conditioning. These studies established a visual orientation conditioning paradigm and examined the behavioral properties and neural circuitry of visual orientation, an important component of the insect's spatial navigation.

Strutz, A., Soelter, J., Baschwitz, A., Farhan, A., Grabe, V., Rybak, J., Knaden, M., Schmuker, M., Hansson, B. S. and Sachse, S. (2014). Decoding odor quality and intensity in the Drosophila brain. Elife 3 [Epub ahead of print]. PubMed ID: 25512254

Summary: To internally reflect the sensory environment, animals create neural maps encoding the external stimulus space. From that primary neural code relevant information has to be extracted for accurate navigation. This study analyzed how different odor features such as hedonic valence and intensity are functionally integrated in the lateral horn (LH) of the vinegar fly, Drosophila melanogaster. Olfactory-processing pathway, comprised of inhibitory projection neurons (iPNs) that target the LH exclusively, at morphological, functional and behavioral levels. iPNs are subdivided into two morphological groups encoding positive hedonic valence or intensity information and conveying these features into separate domains in the LH. Silencing iPNs severely diminished flies' attraction behavior. Moreover, functional imaging disclosed a LH region tuned to repulsive odors comprised exclusively of third-order neurons. Evidence is provided for a feature-based map in the LH, and elucidate its role as the center for integrating behaviorally relevant olfactory information.

Kumar, S., Chen, D., Jang, C., Nall, A., Zheng, X. and Sehgal, A. (2014). An ecdysone-responsive nuclear receptor regulates circadian rhythms in Drosophila. Nat Commun 5: 5697. PubMed ID: 25511299

Summary: Little is known about molecular links between circadian clocks and steroid hormone signalling, although both are important for normal physiology. This study reports a circadian function for a nuclear receptor, ecdysone-induced protein 75 (Eip75/E75), which was identified through a gain-of-function screen for circadian genes in Drosophila melanogaster. Overexpression or knockdown of E75 in clock neurons disrupts rest:activity rhythms and dampens molecular oscillations. E75 represses expression of the gene encoding the transcriptional activator, Clock (Clk), and may also affect circadian output. Per inhibits the activity of E75 on the Clk promoter, thereby providing a mechanism for a previously proposed de-repressor effect of Per on Clk transcription. The Ecdysone receptor is also expressed in central clock cells and manipulations of its expression produce effects similar to those of E75 on circadian rhythms. E75 protects rhythms under stressful conditions, suggesting a function for steroid signalling in the maintenance of circadian rhythms in Drosophila.

Mast, J. D., De Moraes, C. M., Alborn, H. T., Lavis, L. D. and Stern, D. L. (2014). Evolved differences in larval social behavior mediated by novel pheromones. Elife 3 [Epub ahead of print]. PubMed ID: 25497433

Summary: Pheromones, chemical signals that convey social information, mediate many insect social behaviors, including navigation and aggregation. Several studies have suggested that behavior during the immature larval stages of Drosophila development is influenced by pheromones, but none of these compounds or the pheromone-receptor neurons that sense them have been identified. This study reports a larval pheromone-signaling pathway. Larvae produce two novel long-chain fatty acids that are attractive to other larvae. A single larval chemosensory neuron was identified that detects these molecules. Two members of the pickpocket family of DEG/ENaC channel subunits (ppk23 and ppk29) are required to respond to these pheromones. This pheromone system is evolving quickly, since the larval exudates of D. simulans, the sister species of D. melanogaster, are not attractive to other larvae. These results define a new pheromone signaling system in Drosophila that shares characteristics with pheromone systems in a wide diversity of insects.

Tuesday, January 6th

Nandi, N., Tyra, L. K., Stenesen, D. and Kramer, H. (2014). Acinus integrates AKT1 and subapoptotic caspase activities to regulate basal autophagy. J Cell Biol 207: 253-268. PubMed ID: 25332163

Summary: How cellular stresses up-regulate autophagy is not fully understood. One potential regulator is the Drosophila melanogaster protein Acinus (Acn), which is necessary for autophagy induction and triggers excess autophagy when overexpressed. Cell type-specific regulation of Acn depends on proteolysis by the caspase Dcp-1. Basal Dcp-1 activity in developing photoreceptors is sufficient for this cleavage without a need for apoptosis to elevate caspase activity. On the other hand, Acn was stabilized by loss of Dcp-1 function or by the presence of a mutation in Acn that eliminates its conserved caspase cleavage site. Acn stability also was regulated by AKT1-mediated phosphorylation. Flies that expressed stabilized forms of Acn, either the phosphomimetic Acn(S641,731D) or the caspase-resistant Acn(D527A), exhibited enhanced basal autophagy. Physiologically, these flies showed improvements in processes known to be autophagy dependent, including increased starvation resistance, reduced Huntingtin-induced neurodegeneration, and prolonged life span. These data indicate that AKT1 and caspase-dependent regulation of Acn stability adjusts basal autophagy levels.

Anding, A. L. and Baehrecke, E. H. (2014). Vps15 is required for stress induced and developmentally triggered autophagy and salivary gland protein secretion in Drosophila . Cell Death Differ [Epub ahead of print]. PubMed ID: 25342466

Summary: Autophagy is a catabolic process used to deliver cellular material to the lysosome for degradation. The core Vps34/class III phosphatidylinositol 3-kinase (PI3K) complex, consisting of Atg6, Vps15, and Vps34, is highly conserved throughout evolution, critical for recruiting autophagy-related proteins to the preautophagosomal structure and for other vesicular trafficking processes, including vacuolar protein sorting. Atg6 and Vps34 have been well characterized, but the Vps15 kinase remains poorly characterized with most studies focusing on nutrient deprivation-induced autophagy. This study investigate the function of Vps15 in different cellular contexts and found that it is necessary for both stress-induced and developmentally programmed autophagy in various tissues in Drosophila melanogaster. Vps15 is required for autophagy that is induced by multiple forms of stress, including nutrient deprivation, hypoxia, and oxidative stress. Furthermore, autophagy that is triggered by physiological stimuli during development in the fat body, intestine, and salivary gland also require the function of Vps15. In addition, Vps15 is necessary for efficient salivary gland protein secretion. These data illustrate the broad importance of Vps15 in multiple forms of autophagy in different animal cells, and also highlight the pleiotropic function of this kinase in multiple vesicle-trafficking pathways.

Ochaba, J., Lukacsovich, T., Csikos, G., Zheng, S., Margulis, J., Salazar, L., Mao, K., Lau, A. L., Yeung, S. Y., Humbert, S., Saudou, F., Klionsky, D. J., Finkbeiner, S., Zeitlin, S. O., Marsh, J. L., Housman, D. E., Thompson, L. M. and Steffan, J. S. (2014). Potential function for the Huntingtin protein as a scaffold for selective autophagy. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 25385587

Summary: Although dominant gain-of-function triplet repeat expansions in the Huntingtin (HTT) gene are the underlying cause of Huntington disease (HD), understanding the normal functions of nonmutant HTT protein has remained a challenge. This study reports findings that suggest that HTT plays a significant role in selective autophagy. Loss of HTT function in Drosophila disrupts starvation-induced autophagy in larvae and conditional knockout of HTT in the mouse CNS causes characteristic cellular hallmarks of disrupted autophagy, including an accumulation of striatal p62/SQSTM1 over time. Specific domains of HTT have structural similarities to yeast Atg proteins that function in selective autophagy, and in particular that the C-terminal domain of HTT shares structural similarity to yeast Atg11, an autophagic scaffold protein. To explore possible functional similarity between HTT and Atg11, whether the C-terminal domain of HTT interacts with mammalian counterparts of yeast Atg11-interacting proteins was examined. Strikingly, this domain of HTT coimmunoprecipitates with several key Atg11 interactors, including the Atg1 /Unc-51-like autophagy activating kinase 1 kinase complex, autophagic receptor proteins, and mammalian Atg8 homologs. Mutation of a phylogenetically conserved WXXL domain in a C-terminal HTT fragment reduces coprecipitation with mammalian Atg8 homolog GABARAPL1, suggesting a direct interaction. Collectively, these data support a possible central role for HTT as an Atg11-like scaffold protein. These findings have relevance to both mechanisms of disease pathogenesis and to therapeutic intervention strategies that reduce levels of both mutant and normal HTT.

Summary: The RB tumor suppressor, a regulator of the cell cycle, apoptosis, senescence, and differentiation, is frequently mutated in human cancers. An evolutionarily conserved C-terminal "instability element" (IE) of the Drosophila Rbf1 retinoblastoma protein regulates its turnover. Misexpression of wild-type or non-phosphorylatable forms of the Rbf1 protein leads to repression of cell cycle genes. In contrast, overexpression of a defective form of Rbf1 lacking the IE (DeltaIE), a stabilized but transcriptionally less active form of the protein, induced ectopic S phase in cell culture. To determine how mutations in the Rbf1 IE may induce dominant effects in a developmental context, the impact was assessed of in vivo expression of mutant Rbf1 proteins on wing development. DeltaIE expression resulted in overgrowth of larval wing imaginal discs and larger adult wings containing larger cells. In contrast, a point mutation in a conserved lysine of the IE (K774A) generated severely disrupted, reduced wings. These contrasting effects appear to correlate with control of apoptosis; expression of the pro-apoptotic reaper gene and DNA fragmentation measured by acridine orange stain increased in flies expressing the K774A isoform and was suppressed by expression of Rbf1DeltaIE. Intriguingly, cancer associated mutations affecting RB homologs p130 and p107 may similarly induce dominant phenotypes.

Monday, January 5th

Yamazaki, D., Horiuchi, J., Ueno, K., Ueno, T., Saeki, S., Matsuno, M., Naganos, S., Miyashita, T., Hirano, Y., Nishikawa, H., Taoka, M., Yamauchi, Y., Isobe, T., Honda, Y., Kodama, T., Masuda, T. and Saitoe, M. (2014). Glial dysfunction causes age-related memory impairment in Drosophila. Neuron 84: 753-763. PubMed ID: 25447741

Summary: Several aging phenotypes, including age-related memory impairment (AMI), are thought to be caused by cumulative oxidative damage. In Drosophila, age-related impairments in 1 hr memory can be suppressed by reducing activity of protein kinase A (PKA). However, the mechanism for this effect has been unclear. This study shows that decreasing PKA suppresses AMI by reducing activity of pyruvate carboxylase (PC), a glial metabolic enzyme whose amounts increase upon aging. Increased PC activity causes AMI through a mechanism independent of oxidative damage. Instead, increased PC activity is associated with decreases in D-serine, a glia-derived neuromodulator that regulates NMDA receptor activity. D-serine feeding suppresses both AMI and memory impairment caused by glial overexpression of dPC, indicating that an oxidative stress-independent dysregulation of glial modulation of neuronal activity contributes to AMI in Drosophila.

Stratoulias, V. and Heino, T. I. (2014). MANF silencing, immunity induction or autophagy trigger an unusual cell type in metamorphosing Drosophila brain. Cell Mol Life Sci [Epub ahead of print]. PubMed ID: 25511196

Summary: Glia are abundant cells in the brain of animals ranging from flies to humans. They perform conserved functions not only in neural development and wiring, but also in brain homeostasis. This study shows that by manipulating gene expression in glia, a previously unidentified cell type appears in the Drosophila brain during metamorphosis. More specifically, this cell type appears in three contexts: (1) after the induction of either immunity, or (2) autophagy, or (3) by silencing of neurotrophic factor Mesencephalic astrocyte-derived neurotrophic factor ortholog (DmMANF) in glial cells. These cells were called MANF immunoreactive Cells (MiCs). MiCs are migratory based on their shape, appearance in brain areas where no cell bodies exist and the nuclear localization of dSTAT. They are labeled with a unique set of molecular markers including the conserved neurotrophic factor DmMANF and the transcription factor Zfh1. They possess the nuclearly localized protein Relish, which is the hallmark of immune response activation. They also express the conserved engulfment receptor Draper, therefore indicating that they are potentially phagocytic. Surprisingly, they do not express any of the common glial and neuronal markers. In addition, ultrastructural studies show that MiCs are extremely rich in lysosomes. These findings reveal critical molecular and functional components of an unusual cell type in the Drosophila brain. It is suggested that MiCs resemble macrophages/hemocytes and vertebrate microglia based on their appearance in the brain upon genetically challenged conditions and the expression of molecular markers. Interestingly, macrophages/hemocytes or microglia-like cells have not been reported in the fly nervous system before.

Jang, W., Kim, J. Y., Cui, S., Jo, J., Lee, B. C., Lee, Y., Kwon, K. S., Park, C. S. and Kim, C. (2014). The Anoctamin family channel Subdued mediates thermal nociception in Drosophila. J Biol Chem [Epub ahead of print]. PubMed ID: 25505177

Summary: Calcium-permeable and thermo-sensitive transient receptor potential (TRP) channels mediate the nociceptive transduction of noxious temperature in Drosophila nociceptors; yet the underlying molecular mechanisms are not completely understood. This study fond that Subdued, a calcium-activated chloride channel of the Drosophila anoctamin family, functions in conjunction with the thermo-TRPs in thermal nociception. Genetic analysis with deletion and the RNAi-mediated reduction of subdued show that subdued is required for thermal nociception in nociceptors. Further genetic analysis of subdued mutant and thermo-TRP mutants show that they interact functionally in thermal nociception. Subdued expressed in heterologous cells mediates a strong chloride conductance in the presence of both heat and calcium ions. Thus this analysis suggests that Subdued channels may amplify the nociceptive neuronal firing that is initiated by thermo-TRP channels in response to thermal stimuli.

Beckwith, E. J. and Ceriani, M. F. (2014). Experimental assessment of the network properties of the Drosophila circadian clock. J Comp Neurol [Epub ahead of print]. PubMed ID: 25504089

Summary: Circadian rhythms are conserved across kingdoms and coordinate physiology and behavior for appropriate time-keeping. The neuronal populations that govern circadian rhythms are described in many animal models, and the current challenge is to understand how they interact to control overt rhythms remaining plastic to respond and adapt to a changing environment. In Drosophila melanogaster, the circadian network comprises about 150 neurons and the main synchronizer is the neuropeptide Pigment Dispersing Factor (PDF), released by the well characterized central pacemaker neurons, the sLNvs. However, the rules and properties governing the communication and coupling between this central pacemaker and downstream clusters are not fully elucidated. Along this work, the speed of the molecular clock was genetically manipulated specifically in the central pacemaker neurons of Drosophila, and experimental evidence is provided of their restricted ability to synchronize downstream clusters. It was also demonstrated that the sLNv-controlled clusters have an asymmetric entrainment range and are able to experimentally assess it. This data implies that different clusters are subjected to different coupling strength, and display independent endogenous periods. Finally, the manipulation employed in this study established a suitable paradigm to test other network properties as well as the cell autonomous mechanisms running in different circadian relevant clusters.

Sunday, January 4th

Wei, K. H., Grenier, J. K., Barbash, D. A. and Clark, A. G. (2014). Correlated variation and population differentiation in satellite DNA abundance among lines of Drosophila melanogaster. Proc Natl Acad Sci U S A. PubMed ID: 25512552

Summary: Tandemly repeating satellite DNA elements in heterochromatin occupy a substantial portion of many eukaryotic genomes. Although often characterized as genomic parasites deleterious to the host, they also can be crucial for essential processes such as chromosome segregation. Adding to their interest, satellite DNA elements evolve at high rates; among Drosophila, closely related species often differ drastically in both the types and abundances of satellite repeats. However, due to technical challenges, the evolutionary mechanisms driving this rapid turnover remain unclear. This study characterized natural variation in simple-sequence repeats of 2-10 bp from inbred Drosophila melanogaster lines derived from multiple populations, using a method called k-Seek that analyzes unassembled Illumina sequence reads. In addition to quantifying all previously described satellite repeats, this study identified many novel repeats of low to medium abundance. Many of the repeats show population differentiation, including two that are present in only some populations. Interestingly, the population structure inferred from overall satellite quantities does not recapitulate the expected population relationships based on the demographic history of D. melanogaster. It was also found that some satellites of similar sequence composition are correlated across lines, revealing concerted evolution. Moreover, correlated satellites tend to be interspersed with each other, further suggesting that concerted change is partially driven by higher order structure. Surprisingly, negative correlations were observed among some satellites, suggesting antagonistic interactions. This study demonstrates that current genome assemblies vastly underestimate the complexity, abundance, and variation of highly repetitive satellite DNA and presents approaches to understand their rapid evolutionary divergence.

Toomey, M. E. and Frydman, H. M. (2014). Extreme divergence of Wolbachia tropism for the stem-cell-niche in the Drosophila testis. PLoS Pathog 10: e1004577. PubMed ID: 25521619

Summary: Microbial tropism, the infection of specific cells and tissues by a microorganism, is a fundamental aspect of host-microbe interactions. The intracellular bacteria Wolbachia have a peculiar tropism for the stem cell niches in the Drosophila ovary, the microenvironments that support the cells producing the eggs. The molecular underpinnings of Wolbachia stem cell niche tropism are unknown. Previously studies have shown that the patterns of tropism in the ovary show a high degree of conservation across the Wolbachia lineage, with closely related Wolbachia strains usually displaying the same pattern of stem cell niche tropism. It has also been shown that tropism to these structures in the ovary facilitates both vertical and horizontal transmission, providing a strong selective pressure towards evolutionary conservation of tropism. This study shows great disparity in the evolutionary conservation and underlying mechanisms of stem cell niche tropism between male and female gonads. In contrast to females, niche tropism in the male testis is not pervasive, present in only 45% of niches analyzed. The patterns of niche tropism in the testis are not evolutionarily maintained across the Wolbachia lineage, unlike what was shown in the females. Furthermore, hub tropism does not correlate with cytoplasmic incompatibility, a Wolbachia-driven phenotype imprinted during spermatogenesis. Towards identifying the molecular mechanism of hub tropism, hybrid analyses of Wolbachia strains were performed in non-native hosts. These results indicate that both Wolbachia and host derived factors play a role in the targeting of the stem cell niche in the testis. Surprisingly, even closely related Wolbachia strains in Drosophila melanogaster, derived from a single ancestor only 8,000 years ago, have significantly different tropisms to the hub, highlighting that stem cell niche tropism is rapidly diverging in males. These findings provide a powerful system to investigate the mechanisms and evolution of microbial tissue tropism.

MacMillan, H. A., Ferguson, L. V., Nicolai, A., Donini, A., Staples, J. F. and Sinclair, B. J. (2014). Parallel ionoregulatory adjustments underlie phenotypic plasticity and evolution of Drosophila cold tolerance. J Exp Biol [Epub ahead of print]. PubMed ID: 25524989

Summary: Low temperature tolerance is the main predictor of variation in the global distribution and performance of insects, yet the molecular mechanisms underlying cold tolerance variation are poorly known, and it is unclear whether the mechanisms that improve cold tolerance within the lifetime of an individual insect are similar to those that underlie evolved differences among species. The accumulation of cold-induced injuries by hemimetabolous insects is associated with loss of Na+ and K+ homeostasis. This study shows that this model holds true for Drosophila; cold exposure increases hemolymph [K+] in D. melanogaster, and cold-acclimated flies maintain low hemolymph [Na+] and [K+], both at rest and during a cold exposure. This pattern holds across 24 species of the Drosophila phylogeny, where improvements in cold tolerance have been consistently paired with reductions in hemolymph [Na+] and [K+]. Cold-acclimated D. melanogaster have low activity of Na+/K+-ATPase, which may contribute to the maintenance of low hemolymph [Na+] and underlie improvements in cold tolerance. Modifications to ion balance are associated with both phenotypic plasticity within D. melanogaster and evolutionary differences in cold tolerance across the Drosophila phylogeny, which suggests that adaptation and acclimation of cold tolerance in insects may occur through similar mechanisms. Cold-tolerant flies maintain hemolymph osmolality despite low hemolymph [Na+] and [K+], possibly through modest accumulations of organic osmolytes. It is proposed that this could have served as an evolutionary route by which chill-susceptible insects developed more extreme cold tolerance strategies.

Cogni, R., Kuczynski, K., Lavington, E., Koury, S., Behrman, E. L., O'Brien, K. R., Schmidt, P. S. and Eanes, W. F. (2015). Variation in Drosophila melanogaster central metabolic genes appears driven by natural selection both within and between populations. Proc Biol Sci 282. PubMed ID: 25520361

Summary: This report examined the hypothesis that the drivers of latitudinal selection observed in the eastern US Drosophila melanogaster populations are reiterated within seasons in a temperate orchard population in Pennsylvania, USA. Specifically, it was asked whether alleles that are apparently favoured in northern populations are also favoured early in the spring, and decrease in frequency from the spring to autumn with the population expansion. SNP data collected for 46 metabolic genes and 128 SNPs representing the central metabolic pathway was used, and these were examined for the aggregate SNP allele frequencies whether the association of allele change with latitude and that with increasing days of spring-autumn season are reversed. Testing by random permutation, a highly significant negative correlation was observed between these associations that was consistent with this expectation. This correlation is stronger when the analysis was confined to only those alleles that show significant latitudinal changes. This pattern is not caused by association with chromosomal inversions. When data are resampled using SNPs for amino acid change the relationship is not significant but is supported when SNPs associated with cis-expression are only considered. These results suggest that climate factors driving latitudinal molecular variation in a metabolic pathway are related to those operating on a seasonal level within populations.

Saturday, January 3rd

Rodenfels, J., Lavrynenko, O., Ayciriex, S., Sampaio, J. L., Carvalho, M., Shevchenko, A. and Eaton, S. (2014). Production of systemically circulating Hedgehog by the intestine couples nutrition to growth and development. Genes Dev 28: 2636-2651. PubMed ID: 25452274

Summary: In Drosophila larvae, growth and developmental timing are regulated by nutrition in a tightly coordinated fashion. The networks that couple these processes are far from understood. This study shows that the intestine responds to nutrient availability by regulating production of a circulating lipoprotein-associated form of the signaling protein Hedgehog (Hh). Levels of circulating Hh tune the rates of growth and developmental timing in a coordinated fashion. Circulating Hh signals to the fat body to control larval growth. It regulates developmental timing by controlling ecdysteroid production in the prothoracic gland. Circulating Hh is especially important during starvation, when it is also required for mobilization of fat body triacylglycerol (TAG) stores. Thus, this study demonstrates that Hh, previously known only for its local morphogenetic functions, also acts as a lipoprotein-associated endocrine hormone, coordinating the response of multiple tissues to nutrient availability.

Ferguson, G. B. and Martinez-Agosto, J. A. (2014). Yorkie and Scalloped signaling regulates Notch-dependent lineage specification during Drosophila hematopoiesis. Curr Biol 24: 2665-2672. PubMed ID: 25454586

Summary: Cellular microenvironments established by the spatial and temporal expression of specific signaling molecules are critical for both the maintenance and lineage-specific differentiation of progenitor cells. In Drosophila, a population of hematopoietic progenitors, or prohemocytes, within the larval lymph gland gives rise to three mature cell types: plasmatocytes, lamellocytes, and crystal cells. Removal of the secreted signaling molecules Hedgehog and PVF1 from the posterior signaling center (PSC), which acts as a niche, leads to a loss of progenitors and complete differentiation of the lymph gland. This study characterizes a novel population of signaling cells within the lymph gland, distinct from the PSC, that are required for lineage-specific differentiation of crystal cells. Evidence is provided that Yorkie and ScallopedSerrate, the Notch ligand responsible for the initiation of the crystal cell differentiation program. Genetic manipulation of yorkie and scalloped in the lymph gland specifically alters Serrate expression and crystal cell differentiation. Furthermore, Serrate expression in lineage-specifying cells is eliminated in the lymph gland upon the immune response induced by wasp parasitization to ensure the proper differentiation of lamellocytes at the expense of crystal cells. These findings expand the roles for Yorkie/Scalloped beyond growth to encompass specific cell-fate determination in the context of blood development. Similar regulatory functions may extend to their homologs in vertebrate progenitor cell niches that are required for specifying cell fate.

Jia, Q., Liu, Y., Liu, H. and Li, S. (2014). Mmp1 and Mmp2 cooperatively induce Drosophila fat body cell dissociation with distinct roles. Sci Rep 4: 7535. PubMed ID: 25520167

Summary: During Drosophila metamorphosis, the single-cell layer of fat body tissues gradually dissociates into individual cells. Via a fat body-specific RNAi screen this study found that two matrix metalloproteinases (MMPs), Mmp1 and Mmp2, are both required for fat body cell dissociation. As revealed through a series of cellular, biochemical, molecular, and genetic experiments, Mmp1 preferentially cleaves DE-cadherin-mediated cell-cell junctions, while Mmp2 preferentially degrades basement membrane (BM) components and thus destroy cell-BM junctions, resulting in the complete dissociation of the entire fat body tissues into individual cells. Moreover, several genetic interaction experiments demonstrated that the roles of Mmp1 and Mmp2 in this developmental process are cooperative. In conclusion, Mmp1 and Mmp2 induce fat body cell dissociation during Drosophila metamorphosis in a cooperative yet distinct manner, a finding that sheds light on the general mechanisms by which MMPs regulate tissue remodeling in animals.

Shimada-Niwa, Y. and Niwa, R. (2014). Serotonergic neurons respond to nutrients and regulate the timing of steroid hormone biosynthesis in Drosophila. Nat Commun 5: 5778. PubMed ID: 25502946

Summary: The temporal transition of development is flexibly coordinated in the context of the nutrient environment, and this coordination is essential for organisms to increase their survival fitness and reproductive success. Steroid hormone, a key player of the juvenile-to-adult transition, is biosynthesized in a nutrient-dependent manner; however, the underlying genetic mechanism remains unclear. This study reports that the biosynthesis of insect steroid hormone, ecdysteroid, is regulated by a subset of serotonergic neurons in Drosophila melanogaster. These neurons directly innervate the prothoracic gland (PG), an ecdysteroid-producing organ and share tracts with the stomatogastric nervous system. Interestingly, the projecting neurites morphologically respond to nutrient conditions. Moreover, reduced activity of the PG-innervating neurons or of serotonin signalling in the PG strongly correlates with a delayed developmental transition. These results suggest that serotonergic neurons form a link between the external environment and the internal endocrine system by adaptively tuning the timing of steroid hormone biosynthesis.

Friday, January 2

Huang, F., Paulson, A., Dutta, A., Venkatesh, S., Smolle, M., Abmayr, S. M. and Workman, J. L. (2014). Histone acetyltransferase Enok regulates oocyte polarization by promoting expression of the actin nucleation factor spire. Genes Dev 28: 2750-2763. PubMed ID: 25512562

Summary: KAT6 histone acetyltransferases (HATs) are highly conserved in eukaryotes and have been shown to play important roles in transcriptional regulation. This study demonstrates that the Drosophila KAT6 Enok acetylates histone H3 Lys 23 (H3K23) in vitro and in vivo. Mutants lacking functional Enok exhibited defects in the localization of Oskar (Osk) to the posterior end of the oocyte, resulting in loss of germline formation and abdominal segments in the embryo. RNA sequencing (RNA-seq) analysis revealed that spire (spir) and maelstrom (mael), both required for the posterior localization of Osk in the oocyte, were down-regulated in enok mutants. Chromatin immunoprecipitation showed that Enok is localized to and acetylates H3K23 at the spir and mael genes. Furthermore, Gal4-driven expression of spir in the germline can largely rescue the defective Osk localization in enok mutant ovaries. These results suggest that the Enok-mediated H3K23 acetylation (H3K23Ac) promotes the expression of spir, providing a specific mechanism linking oocyte polarization to histone modification.

Lee, M. C. and Spradling, A. C. (2014). The progenitor state is maintained by lysine-specific demethylase 1-mediated epigenetic plasticity during Drosophila follicle cell development. Genes Dev 28: 2739-2749. PubMed ID: 25512561

Summary: Progenitors are early lineage cells that proliferate before the onset of terminal differentiation. Although widespread, the epigenetic mechanisms that control the progenitor state and the onset of differentiation remain elusive. By studying Drosophila ovarian follicle cell progenitors, lysine-specific demethylase 1 (lsd1) and CoRest were identified as differentiation regulators using a GAL4Colon, two colonsGFP variegation assay. The follicle cell progenitors in lsd1 or CoRest heterozygotes prematurely lose epigenetic plasticity, undergo the Notch-dependent mitotic-endocycle transition, and stop dividing before a normal number of follicle cells can be produced. Simultaneously reducing the dosage of the histone H3K4 methyltransferase Trithorax reverses these effects, suggesting that an Lsd1/CoRest complex times progenitor differentiation by controlling the stability of H3K4 methylation levels. Individual cells or small clones initially respond to Notch; hence, a critical level of epigenetic stabilization is acquired cell-autonomously and initiates differentiation by making progenitors responsive to pre-existing external signals.

Vlachos, S., Jangam, S., Conder, R., Chou, M., Nystul, T. and Harden, N. (2015). A Pak-regulated cell intercalation event leading to a novel radial cell polarity is involved in positioning of the follicle stem cell niche in the Drosophila ovary. Development 142: 82-91. PubMed ID: 25516970

Summary: In the germarium of the Drosophila ovary, germline cysts are encapsulated one at a time by a follicular epithelium derived from two follicle stem cells (FSCs). Ovaries in flies mutant for the serine/threonine kinase Pak-kinase exhibit a novel phenotype, in which two side-by-side cysts are encapsulated at a time, generating paired egg chambers. This striking phenotype originates in the pupal ovary, where the developing germarium is shaped by the basal stalk, a stack of cells formed by cell intercalation. The process of basal stalk formation is not well understood, and this study provides evidence that the cell intercalation is driven by actomyosin contractility of DE-Cadherin-adhered cells, leading to a column of disk-shaped cells exhibiting a novel radial cell polarity. Cell intercalation fails in Pak mutant ovaries, leading to abnormally wide basal stalks and consequently wide germaria with side-by-side cysts. Evidence is presented that Pak mutant germaria have extra FSCs, and it is proposed that contact of a germline cyst with the basal stalk in the pupal ovary contributes to FSC niche formation. The wide basal stalk in Pak mutants enables the formation of extra FSC niches which are mispositioned and yet functional, indicating that the FSC niche can be established in diverse locations.

Mahala Burn, K., Shimada, Y., Ayers, K., Lu, F., Hudson, A. M. and Cooley, L. (2014). Somatic insulin signaling regulates a germline starvation response in Drosophila egg chambers. Dev Biol [Epub ahead of print]. PubMed ID: 25481758

Summary: Egg chambers from starved Drosophila females contain large aggregates of processing (P) bodies and cortically enriched microtubules. As this response to starvation is rapidly reversed upon re-feeding females or culturing egg chambers with exogenous bovine insulin, the role of endogenous insulin signaling was examined in mediating the starvation response. Systemic Drosophila insulin-like peptides (dILPs) were found to activate the insulin pathway in follicle cells, which then regulate both microtubule and P body organization in the underlying germline cells. This organization is modulated by the motor proteins Dynein and Kinesin. Dynein activity is required for microtubule and P body organization during starvation, while Kinesin activity is required during nutrient-rich conditions. Blocking the ability of egg chambers to form P body aggregates in response to starvation correlated with reduced progeny survival. These data suggest a potential mechanism to maximize fecundity even during periods of poor nutrient availability, by mounting a protective response in immature egg chambers.

Thursday, January 1st

Rovenko, B. M., Perkhulyn, N. V., Gospodaryov, D. V., Sanz, A., Lushchak, O. V. and Lushchak, V. I. (2014). High consumption of fructose rather than glucose promotes a diet-induced obese phenotype in Drosophila melanogaster. Comp Biochem Physiol A Mol Integr Physiol 180C: 75-85. PubMed ID: 25461489

Summary: During the last 20 years, there has been a considerable scientific debate about the possible mechanisms of induction of metabolic disorders by reducing monosaccharides such as glucose or fructose. This study reports the metabolic rearrangement in response to consumption of these monosaccharides at concentrations ranging from 0.25% to 20% in a Drosophila model. Flies raised on high-glucose diet displayed delay in pupation and increased developmental mortality compared with fructose consumers. Both monosaccharides at high concentrations promoted an obese-like phenotype indicated by increased fly body mass, levels of uric acid, and circulating and stored carbohydrates and lipids; and decreased percentage of water in the body. However, flies raised on fructose showed lower levels of circulating glucose and higher concentrations of stored carbohydrates, lipids, and uric acid. The preferential induction of obesity caused by fructose in Drosophila was associated with increased food consumption and reduced mRNA levels of DILP2 and DILP5 in the brain of adult flies. These data show that glucose and fructose differently affect carbohydrate and lipid metabolism in Drosophila in part by modulation of insulin/insulin-like growth factor signaling. Some reported similarities with effects observed in mammals make Drosophila as a useful model to study carbohydrate influence on metabolism and development of metabolic disorders.

AMatsuda, H., Yamada, T., Yoshida, M. and Nishimura, T. (2014). Flies without Trehalose. J Biol Chem [Epub ahead of print]. PubMed ID: 25451929

Summary: Living organisms adapt to environmental changes through metabolic homeostasis. Sugars are primarily used for the metabolic production of ATP energy and carbon sources. Trehalose is a non-reducing disaccharide that is present in many organisms. In insects, the principal hemolymph sugar is trehalose instead of glucose. As in mammals, hemolymph sugar levels in Drosophila are regulated by the action of endocrine hormones. Therefore, the mobilization of trehalose to glucose is thought to be critical for metabolic homeostasis. However, the physiological role of trehalose as a hemolymph sugar during insect development remains largely unclear. This study demonstrates that mutants of the trehalose synthesis enzyme, Tps1, failed to produce trehalose as expected but survived into the late pupal period and died before eclosion. Larvae without trehalose grew normally, with a slight body size reduction, under normal food conditions. However, these larvae were extremely sensitive to starvation, possibly due to a local defect in the central nervous system. Furthermore, Tps1 mutant larvae failed to grow on a low-sugar diet and exhibited severe growth defects on a low-protein diet. These diet-dependent phenotypes of Tps1 mutants demonstrate the critical role of trehalose during development in Drosophila and reveal how animals adapt to changes in nutrient availability.

Kim, G., Lee, Y., Lee, G., Cho, Y., Lee, Y., Jang, Y., Paik, D. and Park, J. (2014). Overexpression of malic enzyme in the larval stage extends Drosophila lifespan. Biochem Biophys Res Commun [Epub ahead of print]. PubMed ID: 25511696

Summary: Metabolic modifications during the developmental period can extend longevity. This study found that Malic enzyme (Men) overexpression during the larval period lengthened the lifespan of Drosophila. Men overexpression by S106-GeneSwitch-Gal4 driver increased pyruvate content and NADPH/NADP+ ratio but reduced triglyceride, glycogen, and ATP levels in the larvae. ROS levels increased unexpectedly in Men-overexpressing larvae. Interestingly, adults exposed to larval Men-overexpression maintained ROS tolerance with enhanced expression levels of glutathione-S-transferase D2 and thioredoxin-2. These results suggest that metabolic changes mediated by Men during development might be related to the control of ROS tolerance and the longevity of Drosophila.

Maass, A., Schutze, H., Speck, O., Yonelinas, A., Tempelmann, C., Heinze, H. J., Berron, D., Cardenas-Blanco, A., Brodersen, K. H., Enno Stephan, K. and Duzel, E. (2014). Laminar activity in the hippocampus and entorhinal cortex related to novelty and episodic encoding. Nat Commun 5: 5547. PubMed ID: 25424131

Summary: The ability to form long-term memories for novel events depends on information processing within the hippocampus (HC) and entorhinal cortex (EC). The HC-EC circuitry shows a quantitative segregation of anatomical directionality into different neuronal layers. Whereas superficial EC layers mainly project to dentate gyrus (DG), CA3 and apical CA1 layers, HC output is primarily sent from pyramidal CA1 layers and subiculum to deep EC layers. This study utilized this directionality information by measuring encoding activity within HC/EC subregions with 7 T high resolution functional magnetic resonance imaging (fMRI). Multivariate Bayes decoding within HC/EC subregions shows that processing of novel information most strongly engages the input structures (superficial EC and DG/CA2-3), whereas subsequent memory is more dependent on activation of output regions (deep EC and pyramidal CA1). This suggests that while novelty processing is strongly related to HC-EC input pathways, the memory fate of a novel stimulus depends more on HC-EC output.

This month

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