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

Sunday May 31st, 2015

Choi, S., Lim, D.S. and Chung, J. (2015). Feeding and fasting signals converge on the LKB1-SIK3 pathway to regulate lipid metabolism in Drosophila. PLoS Genet 11: e1005263. PubMed ID: 25996931
Summary:
LKB1 plays important roles in governing energy homeostasis by regulating AMP-activated protein kinase (AMPK) and other AMPK-related kinases, including the salt-inducible kinases (SIKs). However, the roles and regulation of LKB1 in lipid metabolism are poorly understood. This study shows that Drosophila LKB1 mutants display decreased lipid storage and increased gene expression of brummer, the Drosophila homolog of adipose triglyceride lipase (ATGL). These phenotypes were consistent with those of SIK3 mutants and were rescued by expression of constitutively active SIK3 in the fat body, suggesting that SIK3 is a key downstream kinase of LKB1. Using genetic and biochemical analyses, HDAC4, a class IIa histone deacetylase, was identified as a lipolytic target of the LKB1-SIK3 pathway. Interestingly, it was found that the LKB1-SIK3-HDAC4 signaling axis was modulated by dietary conditions. In short-term fasting, the adipokinetic hormone (AKH) pathway, related to the mammalian glucagon pathway, inhibited the kinase activity of LKB1 as shown by decreased SIK3 Thr196 phosphorylation, and consequently induced HDAC4 nuclear localization and brummer gene expression. However, under prolonged fasting conditions, AKH-independent signaling decreased the activity of the LKB1-SIK3 pathway to induce lipolytic responses. It was also identified that the Drosophila insulin-like peptides (DILPs) pathway, related to mammalian insulin pathway, regulated SIK3 activity in feeding conditions independently of increasing LKB1 kinase activity. Overall, these data suggest that fasting stimuli specifically control the kinase activity of LKB1 and establish the LKB1-SIK3 pathway as a converging point between feeding and fasting signals to control lipid homeostasis in Drosophila.

Eriksson, A., et al. (2015). Implication of coronin 7 in body weight regulation in humans, mice and flies. BMC Neurosci 16: 13. PubMed ID: 25887538
Summary:
Obesity is a growing global concern with strong associations with cardiovascular disease, cancer and type-2 diabetes. Although various genome-wide association studies have identified more than 40 genes associated with obesity, these genes cannot fully explain the heritability of obesity, suggesting there may be other contributing factors, including epigenetic effects. This study performed genome wide DNA methylation profiling comparing normal-weight and obese 9-13 year old children to investigate possible epigenetic changes correlated with obesity. Of note, obese children had significantly lower methylation levels at a CpG site located near coronin 7 (CORO7), which encodes a tryptophan-aspartic acid dipeptide (WD)-repeat containing protein most likely involved in Golgi complex morphology and function. Anatomical profiling of coronin 7 (Coro7) mRNA expression in mice revealed that it was highly expressed in appetite and energy balance regulating regions, including the hypothalamus, striatum and locus coeruleus, the main noradrenergic brain site. Interestingly, food deprivation in mice downregulated hypothalamic Coro7 mRNA levels, and injecting ethanol, an appetite stimulant, increased the number of Coro7 expressing cells in the locus coeruleus. Finally, by employing the genetically-tractable Drosophila melanogaster model they were able to demonstrate an evolutionarily conserved metabolic function for the CORO7 homologue pod1. Knocking down the pod1 in the Drosophila adult nervous system increased their resistance to starvation. Furthermore, feeding flies a high-calorie diet significantly increased pod1 expression. The study concludes that coronin 7 is involved in the regulation of energy homeostasis and this role stems, to some degree, from the effect on feeding for calories and reward.

Saturday, May 30th

Friday, May 29th

Thursday, May 28th

Wednesday, May27th

Tuesday, May 26th

Bouzaiane, E., Trannoy, S., Scheunemann, L., Plaçais, P.Y. and Preat, T. (2015). Two independent mushroom body output circuits retrieve the six discrete components of Drosophila aversive memory. Cell Rep [Epub ahead of print]. PubMed ID: 25981036
Summary:
Understanding how the various memory components are encoded and how they interact to guide behavior requires knowledge of the underlying neural circuits. Currently, aversive olfactory memory in Drosophila is behaviorally subdivided into four discrete phases. Among these, short- and long-term memories rely, respectively, on the γ and α/β Kenyon cells (KCs), two distinct subsets of the ∼2,000 neurons in the mushroom body (MB). Whereas V2 efferent neurons retrieve memory from α/β KCs, the neurons that retrieve short-term memory are unknown. This study identified a specific pair of MB efferent neurons, named M6, that retrieve memory from γ KCs. Moreover, network analysis revealed that six discrete memory phases actually existed, three of which had been conflated in the past. At each time point, two distinct memory components separately recruited either V2 or M6 output pathways. Memory retrieval thus features a dramatic convergence from KCs to MB efferent neurons.

Monday, May 25th

Sunday, May 24th

Saturday, May 23rd

Friday, May 22nd

Thursday, May 21st

Wednesday, May 20th

Tuesday, May 19th

Monday, May 18th

Sunday, May 17th

Saturday, May 16th

Vanha-Aho, L.M., Anderl, I., Vesala, L., Hultmark, D., Valanne, S and Rämet, M. (2015). Edin expression in the fat body is required in the defense against parasitic wasps in Drosophila melanogaster. PLoS Pathog 11: e1004895. PubMed ID: 25965263
Summary:
The cellular immune response against parasitoid wasps in Drosophila involves the activation, mobilization, proliferation and differentiation of different blood cell types. This study has assessed the role of Edin (elevated during infection) in the immune response against the parasitoid wasp Leptopilina boulardi in Drosophila melanogaster larvae. Blast search revels that edin is a novel gene confined to dipteran species. The expression of edin is induced within hours after a wasp infection in larval fat bodies. Tissue-specific RNAi showed that Edin is an important determinant of the encapsulation response. Although edin expression in the fat body is required for the larvae to mount a normal encapsulation response, it is dispensable in hemocytes. Edin expression in the fat body is not required for lamellocyte differentiation, but it is needed for the increase in plasmatocyte numbers and for the release of sessile hemocytes into the hemolymph. The study concludes that edin expression in the fat body affects the outcome of a wasp infection by regulating the increase of plasmatocyte numbers and the mobilization of sessile hemocytes in Drosophila larvae

Friday, May 16th

Bajgar, A., Kucerova, K., Jonatova, L., Tomcala, A., Schneedorferova, I., Okrouhlik, J. and Dolezal, T. (2015). Extracellular adenosine mediates a systemic metabolic switch during immune response. PLoS Biol 13: e1002135. PubMed ID: 25915062 Summary: Immune defense is energetically costly, and thus an effective response requires metabolic adaptation of the organism to reallocate energy from storage, growth, and development towards the immune system. The natural infection of Drosophila with a parasitoid wasp was used to study energy regulation during immune response. To combat the invasion, the host must produce specialized immune cells (lamellocytes) that destroy the parasitoid egg. A significant portion of nutrients are allocated to differentiating lamellocytes when they would otherwise be used for development. This systemic metabolic switch is mediated by extracellular adenosine released from immune cells. The switch is crucial for an effective immune response. Preventing adenosine transport from immune cells or blocking adenosine receptor precludes the metabolic switch and the deceleration of development, dramatically reducing host resistance. Adenosine thus serves as a signal that the "selfish" immune cells send during infection to secure more energy at the expense of other tissues.

Seelig, J. D. and Jayaraman, V. (2013). Neural dynamics for landmark orientation and angular path integration. Nature 521: [Epub ahead of print]. Nature Summary: Many animals navigate using a combination of visual landmarks and path integration. In mammalian brains, head direction cells integrate these two streams of information by representing an animal's heading relative to landmarks, yet maintaining their directional tuning in darkness based on self-motion cues. This study used two-photon calcium imaging in head-fixed Drosophila melanogaster walking on a ball in a virtual reality arena to demonstrate that landmark-based orientation and angular path integration are combined in the population responses of neurons whose dendrites tile the ellipsoid body, a toroidal structure in the centre of the fly brain. The neural population encodes the fly's azimuth relative to its environment, tracking visual landmarks when available and relying on self-motion cues in darkness. When both visual and self-motion cues are absent, a representation of the animal's orientation is maintained in this network through persistent activity, a potential substrate for short-term memory. Several features of the population dynamics of these neurons and their circular anatomical arrangement are suggestive of ring attractors, network structures that have been proposed to support the function of navigational brain circuits. See Online videos

Owald, D., Felsenberg, J., Talbot, C. B., Das, G., Perisse, E., Huetteroth, W. and Waddell, S. (2015). Activity of defined mushroom body output neurons underlies learned olfactory behavior in Drosophila. Neuron 86: 417-427. PubMed ID: 25864636 Summary: During olfactory learning in fruit flies, dopaminergic neurons assign value to odor representations in the mushroom body Kenyon cells. This study identified a class of downstream glutamatergic mushroom body output neurons (MBONs) called M4/6, or MBON-β2β'2a, MBON-β'2mp, and MBON-γ5&beta'2a, whose dendritic fields overlap with dopaminergic neuron projections in the tips of the β, β', and γ lobes. This anatomy and their odor tuning suggests that M4/6 neurons pool odor-driven Kenyon cell synaptic outputs. Like that of mushroom body neurons, M4/6 output is required for expression of appetitive and aversive memory performance. Moreover, appetitive and aversive olfactory conditioning bidirectionally alters the relative odor-drive of M4β' neurons (MBON-β'2mp). Direct block of M4/6 neurons in naive flies mimics appetitive conditioning, being sufficient to convert odor-driven avoidance into approach, while optogenetically activating these neurons induces avoidance behavior. It is therefore proposed that drive to the M4/6 neurons reflects odor-directed behavioral choice. See Three Pairs of Glutamatergic Output Neurons Innervate the Tips of the Horizontal Mushroom Body Lobes

Tastekin, I., Riedl, J., Schilling-Kurz, V., Gomez-Marin, A., Truman, J. W. and Louis, M. (2015). Role of the subesophageal zone in sensorimotor control of Orientation in Drosophila larva. Curr Biol. PubMed ID: 25959970 Summary: In the Drosophila melanogaster larva, chemotaxis mainly consists of an alternation of distinct behavioral modes: runs and directed turns. During locomotion, turns are triggered by the integration of temporal changes in the intensity of the stimulus. While the anatomy of the peripheral olfactory circuits is reasonably well documented, the neural circuits connecting the sensory neurons to the motor neurons remain unknown. This study combined a loss-of-function behavioral screen with optogenetics-based clonal gain-of-function manipulations to identify neurons that are necessary and sufficient for the initiation of reorientation maneuvers in odor gradients. The results indicate that a small subset of neurons residing in the subesophageal zone controls the rate of transition from runs to turns-a premotor function compatible with observations made in other invertebrates. After having shown that this function pertains to the processing of inputs from different sensory modalities (olfaction, vision, thermosensation), it is concluded that the subesophageal zone operates as a general premotor center that regulates the selection of different behavioral programs based on the integration of sensory stimuli. The present analysis paves the way for a systematic investigation of the neural computations underlying action selection in a miniature brain amenable to genetic manipulations.

Gepner, R., Mihovilovic Skanata, M., Bernat, N. M., Kaplow, M. and Gershow, M. (2015). Computations underlying photo-taxis, odor-taxis, and multi-sensory integration. Elife 4 [Epub ahead of print]. PubMed ID: 25945916 Summary: To better understand how organisms make decisions on the basis of temporally varying multi-sensory input, this study identified computations made by Drosophila larvae responding to visual and optogenetically induced fictive olfactory stimuli. The larva's navigational decision to initiate turns was modeled as the output of a Linear-Nonlinear-Poisson cascade. Reverse-correlation was used to fit parameters to this model; the parameterized model predicted larvae's responses to novel stimulus patterns. For multi-modal inputs, it was found that larvae linearly combine olfactory and visual signals upstream of the decision to turn. This prediction was verified by measuring larvae's responses to coordinated changes in odor and light. Other navigational decisions were studied, and it was found that larvae integrated odor and light according to the same rule in all cases. These results suggest that photo-taxis and odor-taxis are mediated by a shared computational pathway.

Yoshii, T., Hermann-Luibl, C., Kistenpfennig, C., Schmid, B., Tomioka, K. and Helfrich-Forster, C. (2015). Cryptochrome-dependent and -independent circadian entrainment circuits in Drosophila. J Neurosci 35: 6131-6141. PubMed ID: 25878285 Summary: Entrainment to environmental light/dark (LD) cycles is a central function of circadian clocks. In Drosophila, entrainment is achieved by Cryptochrome (Cry) and input from the visual system. During activation by brief light pulses, Cry triggers the degradation of Timeless and subsequent shift in circadian phase. This is less important for LD entrainment, leading to questions regarding light input circuits and mechanisms from the visual system. Recent studies show that different subsets of brain pacemaker clock neurons, the morning (M) and evening (E) oscillators, have distinct functions in light entrainment. However, the role of Cry in M and E oscillators for entrainment to LD cycles is unknown. This study addresses this question by selectively expressing Cry in different subsets of clock neurons in a cry-null (cry0) mutant background. It was possible to rescue the light entrainment deficits of cry0 mutants by expressing Cry in E oscillators but not in any other clock neurons. Par domain protein 1 molecular oscillations in the E, but not M, cells of cry0 mutants still responded to the LD phase delay. This residual light response was stemming from the visual system because it disappeared when all external photoreceptors were ablated genetically. It is concluded that the E oscillators are the targets of light input via Cry and the visual system and are required for normal light entrainment.

Bushey, D., Tononi, G. and Cirelli, C. (2015). Sleep- and wake-dependent changes in neuronal activity and reactivity demonstrated in fly neurons using in vivo calcium imaging. Proc Natl Acad Sci U S A 112: 4785-4790. PubMed ID: 25825756 Summary: Sleep in Drosophila shares many features with mammalian sleep, but it remains unknown whether spontaneous and evoked activity of individual neurons change with the sleep/wake cycle in flies as they do in mammals. This study used calcium imaging to assess how the Kenyon cells in the fly mushroom bodies change their activity and reactivity to stimuli during sleep, wake, and after short or long sleep deprivation. As before, sleep was defined as a period of immobility of >5 min associated with a reduced behavioral response to a stimulus. Calcium levels in Kenyon cells were found to decline when flies fall asleep and increase when they wake up. Moreover, calcium transients in response to two different stimuli are larger in awake flies than in sleeping flies. The activity of Kenyon cells is also affected by sleep/wake history: in awake flies, more cells are spontaneously active and responding to stimuli if the last several hours (5-8 h) before imaging were spent awake rather than asleep. By contrast, long wake (>/=29 h) reduces both baseline and evoked neural activity and decreases the ability of neurons to respond consistently to the same repeated stimulus. The latter finding may underlie some of the negative effects of sleep deprivation on cognitive performance and is consistent with the occurrence of local sleep during wake as described in behaving rats. Thus, calcium imaging uncovers new similarities between fly and mammalian sleep: fly neurons are more active and reactive in wake than in sleep, and their activity tracks sleep/wake history. See: Identification of sleep and wake states during calcium imaging

Thursday, May 14th

Irizarry, J. and Stathopoulos, A. (2015). FGF signaling supports Drosophila fertility by regulating development of ovarian muscle tissues. Dev Biol [Epub ahead of print]. PubMed ID: 25958090 Summary: The thisbe (ths) gene encodes a Drosophila FGF, and mutant females are viable but sterile suggesting a link between FGF signaling and fertility. Ovaries exhibit abnormal morphology including lack of epithelial sheaths, muscle tissues that surround ovarioles. This study investigated how FGF influences Drosophila ovary morphogenesis. Heartless (Htl) FGF receptor was found expressed within somatic cells at the larval and pupal stages, and phenotypes were uncovered using RNAi. Differentiation of terminal filament cells was affected, but this effect did not alter ovariole number. In addition, proliferation of epithelial sheath progenitors, the apical cells, was decreased in both htl and ths mutants, while ectopic expression of the Ths ligand led to these cells' over-proliferation suggesting that FGF signaling supports ovarian muscle sheath formation by controlling apical cell number in the developing gonad. Additionally, live imaging of adult ovaries was used to show that htl RNAi mutants, hypomorphic mutants in which epithelial sheaths were present, exhibited abnormal muscle contractions. Collectively, these results demonstrate that proper formation of ovarian muscle tissues is regulated by FGF signaling in the larval and pupal stages through control of apical cell proliferation and is required to support fertility.

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 U S A 112: 1065-1070. PubMed ID: 25583514 Summary: The Hippo and c-Jun N-terminal kinase (JNK) pathways 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 suppresses Yki-induced overgrowth in the wing disk, whereas ectopic Rho1 expression promotes tissue growth when apoptosis is prohibited. Furthermore, Yki directly regulates Rho1 transcription via the transcription factor Sd. Thus, these results have identified a novel molecular link between the Hippo and JNK pathways and implicated the essential role of the JNK pathway in Hippo signaling-related tumorigenesis.

Wang, Z. H., Rabouille, C. and Geisbrecht, E. R. (2015). Loss of a Clueless-dGRASP complex results in ER stress and blocks integrin exit from the perinuclear endoplasmic reticulum in Drosophila larval muscle. Biol Open. PubMed ID: 25862246 Summary: Drosophila Clueless (Clu) and its conserved orthologs are known for their role in the prevention of mitochondrial clustering. This study uncovered a new role for Clu in the delivery of integrin subunits in muscle tissue. In clu mutants, αPS2 integrin (Inflated), but not βPS integrin, abnormally accumulates in a perinuclear endoplasmic reticulum (ER) subdomain, a site that mirrors the endogenous localization of Clu. Loss of components essential for mitochondrial distribution do not phenocopy the clu mutant alphaPS2 phenotype. Conversely, RNAi knockdown of the Drosophila Golgi reassembly and stacking protein GRASP55/65 recapitulates clu defects, including the abnormal accumulation of αPS2 and larval locomotor activity. Both Clu and dGRASP proteins physically interact and loss of Clu displaces dGRASP from ER exit sites, suggesting that Clu cooperates with dGRASP for the exit of alphaPS2 from a perinuclear subdomain in the ER. This study also found that Clu and dGRASP loss of function leads to ER stress and that the stability of the ER exit site protein Sec16 is severely compromised in the clu mutants, thus explaining the ER accumulation of αPS2. Remarkably, exposure of clu RNAi larvae to chemical chaperones restores both αPS2 delivery and functional ER exit sites. It is proposed that Clu together with dGRASP prevents ER stress and therefore maintains Sec16 stability essential for the functional organization of perinuclear early secretory pathway. This, in turn, is essential for integrin subunit αPS2 ER exit in Drosophila larval myofibers.

Slade, J. D. and Staveley, B. E. (2015). Compensatory growth in novel Drosophila Akt1 mutants. BMC Res Notes 8: 77. PubMed ID: 25889856 Summary: The insulin receptor signalling pathway with its central component, the Akt1 kinase, and endpoint regulator, the transcription factor Foxo, plays a significant role in the control of growth. Imprecise excision of a PZ P-element inserted in the upstream region of Akt1 generated several mutations that lead to small, viable flies that presented with delays in development. Suppression of this phenotype by the directed expression of Akt1- indicates that the phenotypes observed are Akt1 dependent. Somatic clones of the eyes, consisting of homozygous tissue in otherwise heterozygous organisms that develop within a standard timeframe, signify that more severe phenotypes are masked by an extension in the time of development of homozygous mutants. Generation of flies having the hypomorphic Akt1 alleles and a null allele of the downstream target foxo result in a phenotype very similar to that of the foxo mutant and do not resemble the Akt1 mutants. It is concluded that developmental delay of these novel Akt1 hypomorphs results in a latent phenotype uncovered by generation of somatic clones. The compensatory growth occurring during the extended time of development appears to be implemented through alteration of foxo activity. Production of clones is an effective and informative way to observe the effects of mutations that result in small, viable, developmentally delayed flies.

Wednesday, May 13th

Means, J.C., et al. (2015). Drosophila Spaghetti and Doubletime link the circadian clock and light to caspases, apoptosis and tauopathy. PLoS Genet 11: e1005171. PubMed ID: 25951229 Summary: While circadian dysfunction and neurodegeneration are correlated, the mechanism for this is not understood. This study shows that the knock-down of a regulator (spag) of the circadian kinase Dbt in circadian cells lowers Dbt levels abnormally, lengthens circadian rhythms and causes expression of activated initiator caspase (Dronc) in the optic lobes during the middle of the day or after light pulses at night. Likewise, reduced Dbt activity lengthened circadian period and caused expression of activated Dronc, and a loss-of-function mutation in Clk also lead to expression of activated Dronc in a light-dependent manner. Genetic epistasis experiments placed Dbt downstream of Spag in the pathway, and Spag-dependent reductions of Dbt were shown to require the proteasome. Importantly, activated Dronc expression due to reduced Spag or Dbt activity occurred in cells that did not express the spag RNAi or dominant negative Dbt and required PDF neuropeptide signaling from the same neurons that support behavioral rhythms. Furthermore, reduction of Dbt or Spag activity lead to Dronc-dependent Drosophila Tau cleavage and enhanced neurodegeneration produced by human Tau in a fly eye model for tauopathy. Aging flies with lowered Dbt or Spag function showed markers of cell death as well as behavioral deficits and shortened lifespans, and even old wild type flies exhibited Dbt modification and activated caspase at particular times of day. These results suggest that circadian clock defects confer sensitivity to expression of activated Dronc in response to prolonged light. This study has established a link between the circadian clock factors, light, cell death pathways and Tau toxicity.

Shi, Q., Li, S., Li, S., Jiang, A., Chen, Y. and Jiang, J. (2014). Hedgehog-induced phosphorylation by CK1 sustains the activity of Ci/Gli activator.Proc Natl Acad Sci U S A 111: E5651-5660. PubMed ID: 25512501 Summary: Hedgehog (Hh) signaling governs many developmental processes by regulating the balance between the repressor (CiR/GliR) and activator (CiA/GliA) forms of Cubitus interruptus (Ci)/glioma-associated oncogene homolog (Gli) transcription factors. Although much is known about how CiR/GliR is controlled, the regulation of CiA/GliA remains poorly understood. This study, carried out in larval wing discs demonstrates that Casein kinase 1 (CK1) sustains Hh signaling downstream of Costal2 and Suppressor of fused (Sufu) by protecting CiA) from premature degradation. Hh stimulates Ci phosphorylation by CK1 at multiple Ser/Thr-rich degrons to inhibit its recognition by the Hh-induced MATH and BTB domain containing protein (HIB), a substrate receptor for the Cullin 3 family of E3 ubiquitin ligases. In Hh-receiving cells, reduction of CK1 activity accelerated HIB-mediated degradation of CiA, leading to premature loss of pathway activity. Evidence that GliA is regulated by CK1 in a similar fashion and that CK1 acts downstream of Sufu to promote Sonic hedgehog signaling. Taken together, this study not only reveals an unanticipated and conserved mechanism by which phosphorylation of Ci/Gli positively regulates Hh signaling but also provides the first evidence that substrate recognition by the Cullin 3 family of E3 ubiquitin ligases is negatively regulated by a kinase.

Wong, H. W., Shaukat, Z., Wang, J., Saint, R. and Gregory, S. L. (2014). JNK signaling is needed to tolerate chromosomal instability. Cell Cycle 13: 622-631. PubMed ID: 24335260 Summary: Chromosomal instability (CIN), as a common feature of tumors, represents a potential therapeutic target if ways can be found to specifically cause apoptosis in unstably dividing cells. Previous studies has shown that if signaling through the JNK pathway is reduced, apoptosis is triggered in models of chromosomal instability induced by loss of the spindle checkpoint (reducing Mad2 in adult flies by RNAi). This study identified components upstream and downstream of JNK that are able to mediate this effect, and tested the involvement of p53 and DNA damage in causing apoptosis when JNK signaling is reduced in CIN cells. Cell cycle progression timing has shown to have a strong effect on the apoptosis seen when JNK signaling is reduced in genetically unstable cells: a shortened G 2 phase enhances the apoptosis, while lengthening G 2 rescues the JNK-deficient CIN cell death phenotype. These findings suggest that chromosomal instability represents a significant stress to dividing cells, and that without JNK signaling, cells undergo apoptosis because they lack a timely and effective response to DNA damage.

Andersen, D. S., et al. (2015). The Drosophila TNF receptor Grindelwald couples loss of cell polarity and neoplastic growth. Nature [Epub ahead of print]. PubMed ID: 25874673 Summary: Disruption of epithelial polarity is a key event in the acquisition of neoplastic growth. JNK signalling is known to play an important part in driving the malignant progression of many epithelial tumours, although the link between loss of polarity and JNK signalling remains elusive. In a Drosophila genome-wide genetic screen designed to identify molecules implicated in neoplastic growth, this study identified grindelwald (grnd; CG10176), a gene encoding a transmembrane protein with homology to members of the tumour necrosis factor receptor (TNFR) superfamily. This study shows that Grnd mediates the pro-apoptotic functions of Eiger (Egr), the unique Drosophila TNF, and that overexpression of an active form of Grnd lacking the extracellular domain is sufficient to activate JNK signalling in vivo. Grnd also promotes the invasiveness of RasV12/scrib-/- tumours through Egr-dependent Matrix metalloprotease-1 (Mmp1) expression. Grnd localizes to the subapical membrane domain with the cell polarity determinant Crumbs (Crb) and couples Crb-induced loss of polarity with JNK activation and neoplastic growth through physical interaction with Veli (also known as Lin-7). Therefore, Grnd represents the first example of a TNFR that integrates signals from both Egr and apical polarity determinants to induce JNK-dependent cell death or tumour growth.

Tuesday, May 12th

Beehler-Evans, R. and Micchelli, C. A. (2015). Generation of enteroendocrine cell diversity in# #Drosophila #midgut #stemcell #lineages. Development 142: 654-664. PubMed ID: 25670792 Summary: The endocrine system mediates long-range peptide hormone signaling to broadcast changes in metabolic status to distant target tissues via the circulatory system. In many animals, the diffuse endocrine system of the gut is the largest endocrine tissue, with the full spectrum of endocrine cell subtypes not yet fully characterized. This study combine molecular mapping, lineage tracing and genetic analysis in the adult fruit fly to gain new insight into the cellular and molecular mechanisms governing enteroendocrine cell diversity. Neuropeptide hormone distribution was used as a basis to generate a high-resolution cellular map of the diffuse endocrine system. These studies show that cell diversity is seen at two distinct levels: regional and local. Class I and class II enteroendocrine cells can be distinguished locally by combinatorial expression of secreted neuropeptide hormones. Cell lineage tracing studies demonstrate that class I and class II cells arise from a common stem cell lineage and that peptide profiles are a stable feature of enteroendocrine cell identity during homeostasis and following challenge with the enteric pathogen Pseudomonas entomophila. Genetic analysis shows that Notch signaling controls the establishment of class II cells in the lineage, but is insufficient to reprogram extant class I cells into class II enteroendocrine cells. Thus, one mechanism by which secretory cell diversity is achieved in the diffuse endocrine system is through cell-cell signaling interactions within individual adult stem cell lineages.

Hasan, S., Hétié, P. and Matunis, E.L. (2015). Niche signaling promotes stem cell survival in the Drosophila testis via the Jak-STAT target DIAP1. Dev Biol [Epub ahead of print]. PubMed ID: 25941003 Summary: Tissue-specific stem cells are thought to resist environmental insults better than their differentiating progeny, but this resistance varies from one tissue to another, and the underlying mechanisms are not well-understood. This study uses the Drosophila testis as a model system to study the regulation of cell death within an intact niche. This niche contains sperm-producing germline stem cells (GSCs) and accompanying somatic cyst stem cells (or CySCs). Although many signals are known to promote stem cell self-renewal in this tissue, including the highly conserved JAK-STAT pathway, the response of these stem cells to potential death-inducing signals, and factors promoting stem cell survival, have not been characterized. The study found that both GSCs and CySCs resisted cell death better than their differentiating progeny, under normal laboratory conditions and in response to potential death-inducing stimuli such as irradiation or starvation. To ask what might be promoting stem cell survival, the study characterized the role of the anti-apoptotic gene Drosophila inhibitor of apoptosis 1 (diap1) in testis stem cells. DIAP1 protein was enriched in the GSCs and CySCs and was a Jak-STAT target. diap1 was necessary for survival of both GSCs and CySCs, and ectopic up-regulation of DIAP1 in somatic cyst cells was sufficient to non-autonomously rescue stress-induced cell death in adjacent differentiating germ cells (spermatogonia). Altogether, these results show that niche signals can promote stem cell survival by up-regulation of highly conserved anti-apoptotic proteins, and suggest that this strategy may underlie the ability of stem cells to resist death more generally.

Ren, W., Zhang, Y., Li, M., Wu, L., Wang, G., Baeg, G.H., You, J., Li, Z. and Lin, X. (2015). Windpipe controls Drosophila intestinal homeostasis by regulating JAK/STAT pathway via promoting receptor endocytosis and lysosomal degradation. PLoS Genet 11: e1005180. PubMed ID: 25923769 Summary: The adult intestinal homeostasis is tightly controlled by proper proliferation and differentiation of intestinal stem cells. The JAK/STAT (Janus Kinase/Signal Transducer and Activator of Transcription) signaling pathway is essential for the regulation of adult stem cell activities and maintenance of intestinal homeostasis. Currently, it remains largely unknown how JAK/STAT signaling activities are regulated in these processes. This study has identified windpipe (wdp) as a novel component of the JAK/STAT pathway. Wdp was positively regulated by JAK/STAT signaling in Drosophila adult intestines. Loss of wdp activity resulted in the disruption of midgut homeostasis under normal and regenerative conditions. Conversely, ectopic expression of Wdp inhibited JAK/STAT signaling activity. Importantly, Wdp interacted with the receptor Domeless (Dome), and promoted its internalization for subsequent lysosomal degradation. Together, these data led the study to propose that Wdp acts as a novel negative feedback regulator of the JAK/STAT pathway in regulating intestinal homeostasis.

Wang, L., Ryoo, H.D., Qi, Y. and Jasper, H. (2015). PERK limits Drosophila lifespan by promoting intestinal stem cell proliferation in response to ER stress. PLoS Genet 11: e1005220. PubMed ID: 25945494 Summary: Intestinal homeostasis requires precise control of intestinal stem cell (ISC) proliferation. In Drosophila, this control declines with age largely due to chronic activation of stress signaling and associated chronic inflammatory conditions. An important contributor to this condition is the age-associated increase in endoplasmic reticulum (ER) stress. This study shows that the PKR-like ER kinase (PERK) integrates both cell-autonomous and non-autonomous ER stress stimuli to induce ISC proliferation. In addition to responding to cell-intrinsic ER stress, PERK was also specifically activated in ISCs by JAK/Stat signaling in response to ER stress in neighboring cells. The activation of PERK was required for homeostatic regeneration, as well as for acute regenerative responses, yet the chronic engagement of this response became deleterious in aging flies. Accordingly, knocking down PERK in ISCs was sufficient to promote intestinal homeostasis and extend lifespan. These studies highlight the significance of the PERK branch of the unfolded protein response of the ER (UPRER) in intestinal homeostasis and provide a viable strategy to improve organismal health- and lifespan.

Monday, May 11th

Bozzetti, M.P., Specchia, V., Cattenoz, P., Laneve, P., Geusa, A., Sahin, H.B., Di Tommaso, S., Friscini, A., Massari, S., Diebold, C. and Giangrande, A. (2015). The Drosophila Fragile X Mental Retardation Protein participates in the piRNA pathway. J Cell Sci [Epub ahead of print]. PubMed ID: 25908854 Summary: RNA metabolism controls multiple biological processes and a specific class of small RNAs, called piRNAs, act as genome guardians by silencing the expression of transposons and repetitive sequences in the gonads. Defects in the piRNA pathway affect genome integrity and fertility. The possible implications in physiopathological mechanisms of human diseases have made the piRNA pathway the object of intense investigation and recent work calls for a role of this pathway in somatic processes including synaptic plasticity. The RNA-binding Fragile X Mental Retardation Protein (FMRP) controls translation and its loss triggers the most frequent syndromic form of mental retardation as well as gonadal defects in humans. This study demonstrates for the first time that germline as well as somatic expression of dFmr1, the Drosophila ortholog of FMRP, are necessary in a pathway mediated by piRNAs. Moreover, dFmr1 interacted genetically and biochemically with Aubergine, an Argonaute protein and a key player in this pathway. These data open novel perspectives for understanding the phenotypes observed in Fragile X patients and support the view that piRNAs may be at work in the nervous system.

Antic, S., Wolfinger, M.T., Skucha, A., Hosiner, S. and Dorner, S. (2015). General and miRNA-mediated mRNA degradation occurs on ribosome complexes in Drosophila cells. Mol Cell Biol [Epub ahead of print]. PubMed ID: 25918245 Summary: The translation and degradation of mRNAs are two key steps in gene expression that are highly regulated and targeted by many factors including miRNAs. While it is well established that translation and mRNA degradation are tightly coupled, it is still not entirely clear where in the cell mRNA degradation takes place. This study has investigated the possibility of mRNA degradation on the ribosome in Drosophila cells. Using polysome profiles and ribosome affinity purification, the co-purification of various deadenylation and decapping factors with ribosome complexes was demonstrated. Also AGO1 and GW182, two key factors in the miRNA-mediated mRNA degradation pathway, were associated with ribosome complexes. Their co-purification was dependent on intact mRNAs suggesting the association of these factors with the mRNA rather than the ribosome itself. Furthermore, decapped mRNA degradation intermediates were isolated from ribosome complexes, and HiSeq analysis was performed. Interestingly, 93 % of decapped mRNA fragments (approx. 12,000) could be detected with the same relative abundance on ribosome complexes as in cell lysates. In summary, these findings strongly indicate the association of the majority of bulk mRNAs but also mRNAs targeted by miRNAs with the ribosome during their degradation.

Roy, C. K., Olson, S., Graveley, B. R., Zamore, P. D. and Moore, M. J. (2015). Assessing long-distance RNA sequence connectivity via RNA-templated DNA-DNA ligation. Elife 4. PubMed ID: 25866926 Summary: Many RNAs, including pre-mRNAs and long non-coding RNAs, can be thousands of nucleotides long and undergo complex post-transcriptional processing. Multiple sites of alternative splicing within a single gene exponentially increases the number of possible spliced isoforms, with most human genes currently estimated to express at least ten. To understand the mechanisms underlying these complex isoform expression patterns, methods are needed that faithfully maintain long-range exon connectivity information in individual RNA molecules. This study describes SeqZip, a methodology that uses RNA-templated DNA-DNA ligation to retain and compress connectivity between distant sequences within single RNA molecules. Using this assay, proposed coordination between distant sites of alternative exon utilization in mouse Fn1 was tested and the extraordinary exon diversity of Drosophila melanogaster Dscam1 was characterized. Consistent with previous reports, it is concluded that individual Dscam1 isoforms are produced via stochastic alternative splicing.

Matsumoto, N., Sato, K., Nishimasu, H., Namba, Y., Miyakubi, K., Dohmae, N., Ishitani, R., Siomi, H., Siomi, M. C. and Nureki, O. (2015). Crystal structure and activity of the endoribonuclease domain of the piRNA pathway factor Maelstrom. Cell Rep 11: 366-375. PubMed ID: 25865890 Summary: PIWI-interacting RNAs (piRNAs) protect the genome from transposons in animal gonads. Maelstrom (Mael) is an evolutionarily conserved protein, composed of a high-mobility group (HMG) domain and a MAEL domain, and is essential for piRNA-mediated transcriptional transposon silencing in various species, such as Drosophila and mice. However, its structure and biochemical function have remained elusive. This study reports the crystal structure of the MAEL domain from Drosophila melanogaster Mael, at 1.6 A resolution. The structure reveals that the MAEL domain has an RNase H-like fold but lacks canonical catalytic residues conserved among RNase H-like superfamily nucleases. The biochemical analyses reveal that the MAEL domain exhibits single-stranded RNA (ssRNA)-specific endonuclease activity. Cell-based analyses further indicate that ssRNA cleavage activity appears dispensable for piRNA-mediated transcriptional transposon silencing in Drosophila. These findings provide clues toward understanding the multiple roles of Mael in the piRNA pathway.

Sinha, N. K., Trettin, K. D., Aruscavage, P. J. and Bass, B. L. (2015). Drosophila Dicer-2 cleavage is mediated by helicase- and dsRNA termini-dependent states that are modulated by Loquacious-PD. Mol Cell. PubMed ID: 25891075 Summary: Previous studies have shown that the helicase domain of Drosophila Dicer-2 (dmDcr-2) governs substrate recognition and cleavage efficiency, and that dsRNA termini are key to this discrimination. This study now provides a mechanistic basis for these observations. Discrimination of termini was shown to occur during initial binding. Without ATP, dmDcr-2 binds 3' overhanging, but not blunt, termini. By contrast, with ATP, dmDcr-2 binds both types of termini, with highest-affinity binding observed with blunt dsRNA. In the presence of ATP, binding, cleavage, and ATP hydrolysis are optimal with blunt termini compared to 3'overhang termini. Limited proteolysis experiments suggest the optimal reactivity of blunt dsRNA is mediated by a conformational change that is dependent on ATP and the helicase domain. dmDcr-2's partner protein, Loquacious-PD, alters termini dependence, enabling dmDcr-2 to cleave substrates normally refractory to cleavage, such as dsRNA with blocked, structured, or frayed ends.

Herter, E. K., Stauch, M., Gallant, M., Wolf, E., Raabe, T. and Gallant, P. (2015). snoRNAs are a novel class of biologically relevant Myc targets. BMC Biol 13: 25. PubMed ID: 25888729 Summary: Myc proteins are essential regulators of animal growth during normal development, and their deregulation is one of the main driving factors of human malignancies. They function as transcription factors that (in vertebrates) control many growth- and proliferation-associated genes, and in some contexts contribute to global gene regulation. This study combined ChIPseq and RNAseq approaches in Drosophila tissue culture cells to identify a core set of less than 500 Myc target genes, whose salient function resides in the control of ribosome biogenesis. Among these genes, the non-coding snoRNA genes were found to be a large novel class of Myc targets. All assayed snoRNAs are affected by Myc, and many of them are subject to direct transcriptional activation by Myc, both in Drosophila and in vertebrates. The loss of snoRNAs impairs growth during normal development, whereas their overexpression increases tumor mass in a model for neuronal tumors. This work shows that Myc acts as a master regulator of snoRNP biogenesis. In addition, in combination with recent observations of snoRNA involvement in human cancer, it raises the possibility that Myc's transforming effects are partially mediated by this class of non-coding transcripts.

Sunday, May 9th

Spencer, A.K., Siddiqui, B.A. and Thomas, J.H. (2015). Cell shape change and invagination of the cephalic furrow involves reorganization of F-actin. Dev Biol [Epub ahead of print]. PubMed ID: 25929228 Summary: Invagination of epithelial sheets to form furrows is a fundamental morphogenetic movement and is found in a variety of developmental events including gastrulation and vertebrate neural tube formation. The cephalic furrow is a deep epithelial invagination that forms during Drosophila gastrulation. In the first phase of cephalic furrow formation, the initiator cells that will lead invagination undergo apicobasal shortening and apical constriction in the absence of epithelial invagination. In the second phase of cephalic furrow formation, the epithelium starts to invaginate, accompanied by both basal expansion and continued apicobasal shortening of the initiator cells. The cells adjacent to the initiator cells also adopt wedge shapes, but only after invagination is well underway. Myosin II did not appear to drive apical constriction in cephalic furrow formation. However, cortical F-actin was increased in the apices of the initiator cells and in invaginating cells during both phases of cephalic furrow formation. These findings suggest that a novel mechanism for epithelial invagination is involved in cephalic furrow formation.

Biersmith, B., Wang, Z. H. and Geisbrecht, E. R. (2015). Fine-tuning of the actin cytoskeleton and cell adhesion during Drosophila development by guanine nucleotide exchange factors Myoblast city and Sponge. Genetics [Epub ahead of print]. PubMed ID: 25908317 Summary: The evolutionarily conserved Dock proteins function as unconventional guanine nucleotide exchange factors (GEFs). Upon binding to Engulfment and cell motility (ELMO) proteins, Dock-ELMO complexes activate the Rho family of small GTPases to mediate a diverse array of biological processes. Both in vertebrate and invertebrate systems, the actin dynamics regulator, Rac, is the target GTPase of the Dock-A subfamily. However, it remains unclear whether Rac or Rap1 are the in vivo downstream GTPases of the Dock-B subfamily. Drosophila melanogaster is an excellent genetic model organism to understand Dock protein function as its genome encodes one ortholog per subfamily: Myoblast city (Mbc; Dock-A) and Sponge (Spg; Dock-B). This study shows that the roles of Spg and Mbc are not redundant in the Drosophila somatic muscle or the dorsal vessel (dv). Moreover, this study confirms the in vivo role of Mbc upstream of Rac and provides evidence that Spg functions in concert with Rap1, possibly to regulate aspects of cell adhesion. Together these data show that Mbc and Spg can have different downstream GTPase targets. These findings predict that the ability to regulate downstream GTPases is dependent on cellular context and allows for the fine-tuning of actin cytoskeletal or cell adhesion events in biological processes that undergo cell morphogenesis.

Babic, M., Russo, G. J., Wellington, A. J., Sangston, R. M., Gonzalez, M. and Zinsmaier, K. E. (2015). Miro's N-Terminal GTPase domain is required for transport of mitochondria into axons and dendrites. J Neurosci 35: 5754-5771. PubMed ID: 25855186 Summary: Mitochondria are dynamically transported in and out of neuronal processes to maintain neuronal excitability and synaptic function. In higher eukaryotes, the mitochondrial GTPase Miro binds Milton/TRAK adaptor proteins linking microtubule motors to mitochondria. This study shows that Drosophila Miro (dMiro), which has previously been shown to be required for kinesin-driven axonal transport, is also critically required for the dynein-driven distribution of mitochondria into dendrites. In addition, the loss-of-function mutations dMiroT25N and dMiroT460N were used to determine the significance of dMiro's N-terminal and C-terminal GTPase domains, respectively. Expression of dMiroT25N in the absence of endogenous dMiro caused premature lethality and arrested development at a pupal stage. dMiroT25N accumulated mitochondria in the soma of larval motor and sensory neurons, and prevented their kinesin-dependent and dynein-dependent distribution into axons and dendrites, respectively. dMiroT25N mutant mitochondria also were severely fragmented and exhibited reduced kinesin and dynein motility in axons. In contrast, dMiroT460N did not impair viability, mitochondrial size, or the distribution of mitochondria. However, dMiroT460N reduced dynein motility during retrograde mitochondrial transport in axons. Finally, this study showed that substitutions analogous to the constitutively active Ras-G12V mutation in dMiro's N-terminal and C-terminal GTPase domains cause neomorphic phenotypic effects that are likely unrelated to the normal function of each GTPase domain. Overall, this analysis indicates that dMiro's N-terminal GTPase domain is critically required for viability, mitochondrial size, and the distribution of mitochondria out of the neuronal soma regardless of the employed motor, likely by promoting the transition from a stationary to a motile state.

Brust-Mascher, I., Civelekoglu-Scholey, G. and Scholey, J. M. (2015). Mechanism for anaphase B: Evaluation of "slide-and-cluster" versus "slide-and-flux-or-elongate" models. Biophys J 108: 2007-2018. PubMed ID: 25902440 Summary: Elongation of the mitotic spindle during anaphase B contributes to chromosome segregation in many cells. This study quantitatively tested the ability of two models for spindle length control to describe the dynamics of anaphase B spindle elongation using experimental data from Drosophila embryos. In the slide-and-flux-or-elongate (SAFE) model, kinesin-5 motors persistently slide apart antiparallel interpolar microtubules (ipMTs). During pre-anaphase B, this outward sliding of ipMTs is balanced by depolymerization of their minus ends at the poles, producing poleward flux, while the spindle maintains a constant length. Following cyclin B degradation, ipMT depolymerization ceases so the sliding ipMTs can push the poles apart. The competing slide-and-cluster (SAC) model proposes that MTs nucleated at the equator are slid outward by the cooperative actions of the bipolar kinesin-5 and a minus-end-directed motor, which then pulls the sliding MTs inward and clusters them at the poles. In assessing both models, it is assumed that kinesin-5 preferentially cross-links and slides apart antiparallel MTs while the MT plus ends exhibit dynamic instability. However, in the SAC model, minus-end-directed motors bind the minus ends of MTs as cargo and transport them poleward along adjacent, parallel MT tracks, whereas in the SAFE model, all MT minus ends that reach the pole are depolymerized by kinesin-13. Remarkably, the results show that within a narrow range of MT dynamic instability parameters, both models can reproduce the steady-state length and dynamics of pre-anaphase B spindles and the rate of anaphase B spindle elongation. However, only the SAFE model reproduces the change in MT dynamics observed experimentally at anaphase B onset. Thus, although both models explain many features of anaphase B in this system, the quantitative evaluation of experimental data regarding several different aspects of spindle dynamics suggests that the SAFE model provides a better fit.

Saturday, May 9th

O'Connell, M.D. and Reeves G.T. (2015). The presence of nuclear Cactus in the early Drosophila embryo may extend the dynamic range of the dorsal gradient. PLoS Comput Biol 11: e1004159. PubMed ID: 25879657 Summary: In a developing embryo, the spatial distribution of a signaling molecule, or a morphogen gradient, has been hypothesized to carry positional information to pattern tissues. Recent measurements of morphogen distribution have allowed this hypothesis to be subjected to rigorous physical testing. In the early Drosophila embryo, measurements of the morphogen Dorsal, which is a transcription factor responsible for initiating the earliest zygotic patterns along the dorsal-ventral axis, have revealed a gradient that is too narrow to pattern the entire axis. This study uses a mathematical model of Dorsal dynamics, fit to experimental data, to determine the ability of the Dorsal gradient to regulate gene expression across the entire dorsal-ventral axis. Two assumptions were required for the model to match experimental data in both Dorsal distribution and gene expression patterns. First, Cactus, an inhibitor that binds to Dorsal and prevents it from entering the nuclei, must itself be present in the nuclei. And second, fluorescence measurements of Dorsal reflect both free Dorsal and Cactus-bound Dorsal. The model explains the dynamic behavior of the Dorsal gradient at lateral and dorsal positions of the embryo, the ability of Dorsal to regulate gene expression across the entire dorsal-ventral axis, and the robustness of gene expression to stochastic effects. These results have a general implication for interpreting fluorescence-based measurements of signaling molecules.

Liu, N. and Lasko, P. (2015). Analysis of RNA interference lines identifies new functions of maternally-expressed genes involved in embryonic patterning in Drosophila melanogaster. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 25834215 Summary: Embryonic patterning inhttp://www.sdbonline.org/sites/fly Drosophila melanogaster is initially established through the activity of a number of maternally expressed genes that are expressed during oogenesis. mRNAs from some of these genes accumulate in the posterior pole plasm of the oocyte and early embryo, and localize further into RNA islands, transient ring-like structures that form around the nuclei of future primordial germ cells (pole cells) at stage 3 of embryogenesis. As mRNAs from several genes with known functions in anterior-posterior patterning and/or germ cell specification accumulate in RNA islands, it was hypothesized that some other mRNAs that localize in this manner might also function in these developmental processes. To test this, the developmental functions of 51 genes whose mRNAs accumulate in RNA islands were investigated by abrogating their activity in the female germline using RNA interference. This analysis revealed requirements for ttk, pbl, Hip14, eIF5, eIF4G, and CG9977 for progression through early oogenesis. Dorsal appendage defects were observed in a proportion of eggs produced by females expressing double-stranded RNA targeting Mkrn1 or jvl, implicating these two genes in dorsal-ventral patterning. In addition, posterior patterning defects and a reduction in pole cell number were seen in the progeny of Mkrn1 females. As the mammalian orthologue of Mkrn1 acts as an E3 ubiquitin ligase, these results suggest an additional link between protein ubiquitination and pole plasm activity.

Wong, M. M., Liu, M. F. and Chiu, S. K. (2015). Cropped, Drosophila transcription factor AP-4, controls tracheal terminal branching and cell growth. BMC Dev Biol 15: 20. PubMed ID: 25888431 Summary: Endothelial or epithelial cellular branching is vital in development and cancer progression; however, the molecular mechanisms of these processes are not clear. In Drosophila, terminal cell at the end of some tracheal tube ramifies numerous fine branches on the internal organs to supply oxygen. To discover more genes involved in terminal branching, mutants were sought with very few terminal branches using the Kiss enhancer-trap line collection. This analysis identified cropped (crp), encoding the Drosophila homolog of the transcription activator protein AP-4. Overexpressing the wild-type crp gene or a mutant that lacks the DNA-binding region in either the tracheal tissues or terminal cells led to a loss-of-function phenotype, implying that crp can affect terminal branching. Unexpectedly, the ectopic expression of crp also led to enlarged organs, and cell-counting experiments on the salivary glands suggest that elevated levels of AP-4 increase cell size and organ size. Like its mammalian counterpart, cropped is controlled by dMyc, as ectopic expression of dMyc in terminal cells increased cellular branching and the Cropped protein levels in vivo. This study has found that the branching morphogenesis of terminal cells of the tracheal tubes in Drosophila requires the dMyc-dependent activation of Cropped/AP-4 protein to increase the cell growth of terminal cells.

Sharma, R., et al. (2015). The single FGF receptor gene in the beetle Tribolium castaneum codes for two isoforms that integrate FGF8- and Branchless-dependent signals. Dev Biol [Epub ahead of print]. PubMed ID: 25864412 Summary: In Drosophila, the FGF ligand / receptor combinations of FGF8 (Pyramus and Thisbe) / Heartless (Htl) and Branchless (Bnl) / Breathless (Btl) are required for the migration of mesodermal cells and for the formation of the tracheal network respectively with both the receptors functioning independently of each other. However, only a single fgf-receptor gene (Tc-fgfr) has been identified in the genome of the beetle Tribolium. It was therefore asked whether both the ligands Fgf8 and Bnl could transduce their signal through a common fgf-receptor in Tribolium. Indeed, it was found that the function of the single Tc-fgfr gene is essential for mesoderm differentiation as well as for the formation of the tracheal network during early development. Ligand specific RNAi for Tc-fgf8 and Tc-bnl resulted in two distinct non-overlapping phenotypes of impaired mesoderm differentiation and abnormal formation of the tracheal network in Tc-fgf8- and Tc-bnlRNAi embryos respectively. It was further shown that the single Tc-fgfr gene encodes at least two different receptor isoforms that are generated through alternative splicing. Exon-specific RNAi additionally demonstrated their distinct tissue-specific functions. Finally, the structure of the FGF-receptor gene esd discussed from an evolutionary perspective.

Friday, May 8th

Han, T.H., Dharkar, P., Mayer, M.L. and Serpe, M. (2015). Functional reconstitution of Drosophila melanogaster NMJ glutamate receptors. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 25918369 Summary: The Drosophila larval neuromuscular junction (NMJ), at which glutamate acts as the excitatory neurotransmitter, is a widely used model for genetic analysis of synapse function and development. Despite decades of study, the inability to reconstitute NMJ glutamate receptor function using heterologous expression systems has complicated the analysis of receptor function, such that it is difficult to resolve the molecular basis for compound phenotypes observed in mutant flies. This study finds that Drosophila Neto functions as an essential component required for the function of NMJ glutamate receptors, permitting analysis of glutamate receptor responses in Xenopus oocytes. In combination with a crystallographic analysis of the GluRIIB ligand binding domain, the Serpe lab used this system to characterize the subunit dependence of assembly, channel block, and ligand selectivity for Drosophila NMJ glutamate receptors.

Sugie, A., Hakeda-Suzuki, S., Suzuki, E., Silies, M., Shimozono, M., Mohl, C., Suzuki, T. and Tavosanis, G. (2015). Molecular remodeling of the presynaptic active zone of Drosophila photoreceptors via activity-dependent feedback. Neuron [Epub ahead of print]. PubMed ID: 25892303 Summary: Neural activity contributes to the regulation of the properties of synapses in sensory systems, allowing for adjustment to a changing environment. Little is known about how synaptic molecular components are regulated to achieve activity-dependent plasticity at central synapses. This study found that after prolonged exposure to natural ambient light the presynaptic active zone in Drosophila photoreceptors undergoes reversible remodeling, including loss of Bruchpilot, DLiprin-alpha, and DRBP, but not of DSyd-1 or Cacophony. The level of depolarization of the postsynaptic neurons is critical for the light-induced changes in active zone composition in the photoreceptors, indicating the existence of a feedback signal. In search of this signal, this study has identified a crucial role of microtubule meshwork organization downstream of the divergent canonical Wnt pathway, potentially via Kinesin-3 Imac. These data reveal that active zone composition can be regulated in vivo and identify the underlying molecular machinery.

Lee, J. and Littleton, J. T. (2015). Transmembrane tethering of synaptotagmin to synaptic vesicles controls multiple modes of neurotransmitter release. Proc Natl Acad Sci U S A 112: 3793-3798. PubMed ID: 25775572 Summary: Synaptotagmin 1 (Syt1) is a synaptic vesicle integral membrane protein that regulates neurotransmitter release by activating fast synchronous fusion and suppressing slower asynchronous release. The cytoplasmic C2 domains of Syt1 interact with SNAREs and plasma membrane phospholipids in a Ca(2+)-dependent manner and can substitute for full-length Syt1 in in vitro membrane fusion assays. To determine whether synaptic vesicle tethering of Syt1 is required for normal fusion in vivo, this study performed a structure-function study with tethering mutants at the Drosophila larval neuromuscular junction. Transgenic animals expressing only the cytoplasmic C2 domains or full-length Syt1 tethered to the plasma membrane failed to restore synchronous synaptic vesicle fusion, and also failed to clamp spontaneous vesicle release. In addition, transgenic animals with shorter, but not those with longer, linker regions separating the C2 domains from the transmembrane segment abolished Syt1's ability to activate synchronous vesicle fusion. Similar defects were observed when C2 domain alignment was altered to C2B-C2A from the normal C2A-C2B orientation, leaving the tether itself intact. Although cytoplasmic and plasma membrane-tethered Syt1 variants could not restore synchronous release in syt1 null mutants, they were very effective in promoting fusion through the slower asynchronous pathway. As such, the subcellular localization of Syt1 within synaptic terminals is important for the temporal dynamics that underlie synchronous and asynchronous neurotransmitter release.

Wong, M. Y., Cavolo, S. L. and Levitan, E. S. (2015). Synaptic neuropeptide release by Dynamin-dependent partial release from circulating vesicles. Mol Biol Cell [Epub ahead of print]. PubMed ID: 25904335 Summary: Neurons release neuropeptides, enzymes and neurotrophins by exocytosis of dense-core vesicles (DCVs). Peptide release from individual DCVs has been imaged in vitro with endocrine cells and at the neuron soma, growth cones, neurites, axons, and dendrites, but not at nerve terminals where peptidergic neurotransmission occurs. Here dynamin (encoded by the shibire gene) is shown to enhance activity-evoked peptide release at the Drosophila neuromuscular junction. Simultaneous photobleaching and imaging (SPAIM) demonstrates that activity depletes only a portion of a single presynaptic DCV's content. Activity initiates exocytosis within seconds, but subsequent release occurs slowly. Synaptic neuropeptide release is further sustained by DCVs undergoing multiple rounds of exocytosis. Synaptic neuropeptide release is surprisingly similar regardless of anterograde or retrograde DCV transport into boutons, bouton location and time of arrival in the terminal. Thus, vesicle circulation and bidirectional capture supplies synapses with functionally competent DCVs. These results show that activity-evoked synaptic neuropeptide release is independent of a DCV's past traffic and occurs by slow dynamin-dependent partial emptying of DCVs suggestive of kiss and run exocytosis.

Thursday, May 7th

Mannava, A. G. and Tolwinski, N. S. (2015). Membrane bound GSK-3 activates Wnt signaling through Disheveled and Arrow. PLoS One 10: e0121879. PubMed ID: 25848770 Summary: Wnt ligands and their downstream pathway components coordinate many developmental and cellular processes. In adults, they regulate tissue homeostasis through regulation of stem cells. Mechanistically, signal transduction through this pathway is complicated by pathway components having both positive and negative roles in signal propagation. This study examined the positive role of GSK-3/Zw3 in promoting signal transduction at the plasma membrane. Targeting GSK-3 to the plasma membrane activates signaling in Drosophila embryos. This activation requires the presence of the co-receptor Arrow-LRP5/6 and the pathway activating protein Disheveled. These results provide genetic evidence for evolutionarily conserved, separable roles for GSK-3 at the membrane and in the cytosol, and are consistent with a model where the complex cycles from cytosol to membrane in order to promote signaling at the membrane and to prevent it in the cytosol.

Ricolo, D., Butí, E. and Araújo, S.J. (2015). Drosophila melanogaster Hedgehog cooperates with Frazzled to guide axons through a non-canonical signalling pathway. Mech Dev [Epub ahead of print]. PubMed ID: 25936631 Summary: This study reports that the morphogen Hedgehog (Hh) is an axonal chemoattractant in the midline of D. melanogaster embryos. Hh is present in the ventral nerve cord during axonal guidance and overexpression of hh in the midline causes ectopic midline crossing of FasII-positive axonal tracts. In addition, Hh influenced axonal guidance via a non-canonical signalling pathway dependent on Ptc. These results reveal that the Hh pathway cooperates with the Netrin/Frazzled pathway to guide axons through the midline in invertebrates.

Swarup, S., Pradhan-Sundd, T. and Verheyen, E. M. (2015). Genome-wide identification of phospho-regulators of Wnt signaling in Drosophila. Development 142: 1502-1515. PubMed ID: 25852200 Summary: Evolutionarily conserved intercellular signaling pathways regulate embryonic development and adult tissue homeostasis in metazoans. The precise control of the state and amplitude of signaling pathways is achieved in part through the kinase- and phosphatase-mediated reversible phosphorylation of proteins. In this study, a genome-wide in vivo RNAi screen for was performed for kinases and phosphatases that regulate the Wnt pathway under physiological conditions in the Drosophila wing disc. The analyses have identified 54 high-confidence kinases and phosphatases capable of modulating the Wnt pathway, including 22 novel regulators. These candidates were also assayed for a role in the Notch pathway, and numerous phospho-regulators were identified. Additionally, each regulator of the Wnt pathway was evaluated in the wing disc for its ability to affect the mechanistically similar Hedgehog pathway. Twenty-nine dual regulators were identifed that that have the same effect on the Wnt and Hedgehog pathways. As proof of principle, it was established that Cdc37 and Gilgamesh/CK1γ inhibit and promote signaling, respectively, by functioning at analogous levels of these pathways in both Drosophila and mammalian cells. The Wnt and Hedgehog pathways function in tandem in multiple developmental contexts, and the identification of several shared phospho-regulators serve as potential nodes of control under conditions of aberrant signaling and disease.

Sen, A., Sun, R. and Krahn, M. P. (2015). Localization and function of Pals1 associated tight junction protein in Drosophila is regulated by two distinct apical complexes. J Biol Chem [Epub ahead of print]. PubMed ID: 25847234 Summary: The transmembrane protein Crumbs (Crb) and its intracellular adaptor protein Pals1 (Stardust, Sdt in Drosophila) play a crucial role in the establishment and maintenance of apical-basal polarity in epithelial cells in various organisms. In contrast, the multiple-PDZ-domain containing protein PATJ, which has been described to form a complex with Crb/Sdt, is not essential for apical basal polarity or for the stability of the Crb/Sdt complex in the Drosophila epidermis. This study shows that in the embryonic epidermis Sdt is essential for the correct subcellular localization of PATJ in differentiated epithelial cells but not during cellularization. Consistently, the L27-domain of PATJ is crucial for the correct localization and function of the protein. These data further indicate that the four PDZ domains of PATJ function to a large extent in redundancy regulating the proteins function. Interestingly the PATJ-Sdt heterodimer is not only recruited to the apical cell-cell contacts by binding to Crb but depends on functional Bazooka (Baz). However biochemical experiments show that PATJ associates with both complexes, the Baz-Sdt and the Crb-Sdt complex in the mature epithelium of the embryonic epidermis, suggesting a role of these two complexes for PATJs function during development of Drosophila.

Wednesday, May 6th

Sherrard, K.M. and Fehon, R.G. (2015). The transmembrane protein Crumbs displays complex dynamics during follicular morphogenesis and is regulated competitively by Moesin and aPKC. Development [Epub ahead of print]. PubMed ID: 25926360 Summary: The transmembrane protein Crumbs (Crb) functions in apical polarity and epithelial integrity. To better understand its role in epithelial morphogenesis, this study examined Crb localization and dynamics in the late follicular epithelium of Drosophila. Crb was unexpectedly dynamic during middle-to-late stages of egg chamber development, being lost from the marginal zone (MZ) in stage 9 before abruptly returning at the end of stage 10b, then undergoing a pulse of endocytosis in stage 12. The reappearance of MZ Crb was necessary to maintain an intact adherens junction and MZ. Although Crb has been proposed to interact through its juxtamembrane domain with Moesin (Moe), a FERM domain protein that regulates the cortical actin cytoskeleton, the functional significance of this interaction is poorly understood. This study found that whereas the Crb juxtamembrane domain was not required for adherens junction integrity, it was necessary for MZ localization of Moe, aPKC and F-actin. Furthermore, Moe and aPKC functioned antagonistically, suggesting that Moe limits Crb levels by reducing its interactions with the apical Par network. Additionally, Moe mutant cells lost Crb from the apical membrane and accumulated excess Crb at the MZ, suggesting that Moe regulates Crb distribution at the membrane. Together, these studies reveal reciprocal interactions between Crb, Moe and aPKC during cellular morphogenesis.

Little, S. C., Sinsimer, K. S., Lee, J. J., Wieschaus, E. F. and Gavis, E. R. (2015). Independent and coordinate trafficking of single Drosophila germ plasm mRNAs. Nat Cell Biol. PubMed ID: 25848747 Summary: Messenger RNA localization is a conserved mechanism for spatial control of protein synthesis, with key roles in generating cellular and developmental asymmetry. Whereas different transcripts may be targeted to the same subcellular domain, the extent to which their localization is coordinated is unclear. Using quantitative single-molecule imaging, this study analysed the assembly of Drosophila germ plasm mRNA granules inherited by nascent germ cells. The germ-cell-destined transcripts nanos, cyclin B and polar granule component travel within the oocyte as ribonucleoprotein particles containing single mRNA molecules but co-assemble into multi-copy heterogeneous granules selectively at the posterior of the oocyte. The stoichiometry and dynamics of assembly indicate a defined stepwise sequence. The data suggest that co-packaging of these transcripts ensures their effective segregation to germ cells. In contrast, compartmentalization of the germline determinant oskar mRNA into different granules limits its entry into germ cells. This exclusion is required for proper germline development.

Hsu, S.J., Plata, M.P., Ernest, B., Asgarifar, S. and Labrador, M. (2015). The insulator protein Suppressor of Hairy wing is required for proper ring canal development during oogenesis in Drosophila. Dev Biol [Epub ahead of print]. PubMed ID: 25882370 Summary: Chromatin insulators orchestrate gene transcription during embryo development and cell differentiation by stabilizing interactions between distant genomic sites. Mutations in genes encoding insulator proteins are generally lethal, making in vivo functional analyses of insulator proteins difficult. In Drosophila, however, mutations in the gene encoding the Suppressor of Hairy wing insulator protein [Su(Hw)] are viable and female sterile, providing an opportunity to study insulator function during oocyte development. Whereas previous reports suggest that the function of Su(Hw) in oogenesis is independent of its insulator activity, many aspects of the role of Su(Hw) in Drosophila oogenesis remain unexplored. This study shows that mutations in su(Hw) result in smaller ring canal lumens and smaller outer ring diameters, which likely obstruct molecular and vesicle passage from nurse cells to the oocyte. Fluorescence microscopy revealed that lack of Su(Hw) lead to excess accumulation of Kelch (Kel) and Filament-actin (F-actin) proteins in the ring canal structures of developing egg chambers. Furthermore, misexpression of the Src oncogene at 64B (Src64B) may cause ring canal development defects as microarray analysis and real-time RT-PCR revealed there was a three fold decrease in Src64B expression in su(Hw) mutant ovaries. Restoration of Src64B expression in su(Hw) mutant female germ cells rescued the ring phenotype but did not restore fertility. The study concluded that loss of su(Hw) affects expression of many oogenesis related genes and down-regulates Src64B, resulting in ring canal defects potentially contributing to obstruction of molecular flow and an eventual failure of egg chamber organization.

Vogel, K. J., Brown, M. R. and Strand, M. R. (2015). Ovary ecdysteroidogenic hormone requires a receptor tyrosine kinase to activate egg formation in the mosquito Aedes aegypti. Proc Natl Acad Sci U S A 112: 5057-5062. PubMed ID: 25848040 Summary: Mosquitoes are major disease vectors because most species must feed on blood from a vertebrate host to produce eggs. Blood feeding by the vector mosquito Aedes aegypti triggers the release of two neurohormones, ovary ecdysteroidogenic hormone (OEH) and insulin-like peptides (ILPs), which activate multiple processes required for oogenesis egg formation. ILPs function by binding to the insulin receptor, which activates downstream components in the canonical insulin signaling pathway. OEH in contrast belongs to a neuropeptide family called neuroparsins, whose receptor is unknown. This study demonstrated that a previously orphanized receptor tyrosine kinase (RTK) from A. aegypti encoded by the gene AAEL001915 is an OEH receptor. Phylogenetic studies indicated that the protein encoded by this gene, designated AAEL001915, belongs to a clade of RTKs related to the insulin receptor, which are distinguished by an extracellular Venus flytrap module. Knockdown of AAEL001915 by RNAi disabled OEH-mediated egg formation in A. aegypti. AAEL001915 was primarily detected in the mosquito ovary in association with follicular epithelial cells. Both monomeric and dimeric AAEL001915 were detected in mosquito ovaries and transfected Drosophila S2 cells. Functional assays further indicated that OEH bound to dimeric AAEL001915, which resulted in downstream phosphorylation of dbzhnsky/akt1-1.htmAkt. It is hypothesized that orthologs of AAEL001915 in other insects are neuroparsin receptors.

Tuesday, May 5th

Bartok, O., Teesalu, M., Ashwall-Fluss, R., Pandey, V., Hanan, M., Rovenko, B.M., Poukkula, M., Havula, E., Moussaieff, A., Vodala, S., Nahmias, Y., Kadener, S. and Hietakangas, V. (2015). The transcription factor Cabut coordinates energy metabolism and the circadian clock in response to sugar sensing. EMBO J [Epub ahead of print]. PubMed ID: 25916830 Summary: Nutrient sensing pathways adjust metabolism and physiological functions in response to food intake. For example, sugar feeding promotes lipogenesis by activating glycolytic and lipogenic genes through the Mondo/ChREBP-Mlx transcription factor complex. Concomitantly, other metabolic routes are inhibited, but the mechanisms of transcriptional repression upon sugar sensing have remained elusive. This study characterizes cabut (cbtDrosophila. cbt was rapidly induced upon sugar feeding through direct regulation by Mondo-Mlx. CBT repressed several metabolic targets in response to sugar feeding, including both isoforms of phosphoenolpyruvate carboxykinase (pepck). Deregulation of pepck1 (CG17725) in mlx mutants underlay imbalance of glycerol and glucose metabolism as well as developmental lethality. Furthermore, cbt provided a regulatory link between nutrient sensing and the circadian clock. Specifically, a subset of genes regulated by the circadian clock were also targets of CBT. Moreover, perturbation of CBT levels led to deregulation of the circadian transcriptome and circadian behavioral patterns.

Zhang, Y., Liu, G., Yan, J., Zhang, Y., Li, B. and Cai, D. (2015). Metabolic learning and memory formation by the brain influence systemic metabolic homeostasis. Nat Commun 6: 6704. PubMed ID: 25848677 Summary: Metabolic homeostasis is regulated by the brain, but whether this regulation involves learning and memory of metabolic information remains unexplored. This study use a calorie-based, taste-independent learning/memory paradigm to show that Drosophila form metabolic memories that help in balancing food choice with caloric intake; however, this metabolic learning or memory is lost under chronic high-calorie feeding. Loss of individual learning/memory-regulating genes causes a metabolic learning defect, leading to elevated trehalose and lipid levels. Importantly, this function of metabolic learning requires not only the mushroom body but also the hypothalamus-like pars intercerebralis, while NF-κB activation in the pars intercerebralis mimics chronic overnutrition in that it causes metabolic learning impairment and disorders. Finally, this study evaluated this concept of metabolic learning/memory in mice, suggesting that the hypothalamus is involved in a form of nutritional learning and memory, which is critical for determining resistance or susceptibility to obesity. In conclusion, these data indicate that the brain, and potentially the hypothalamus, direct metabolic learning and the formation of memories, which contribute to the control of systemic metabolic homeostasis.

May, C. M., Doroszuk, A. and Zwaan, B. J. (2015). The effect of developmental nutrition on life span and fecundity depends on the adult reproductive environment in Drosophila melanogaster. Ecol Evol 5: 1156-1168. PubMed ID: 25859322 Summary: Both developmental nutrition and adult nutrition affect life-history traits; however, little is known about whether the effect of developmental nutrition depends on the adult environment experienced. This study used the fruit fly to determine whether life-history traits, particularly life span and fecundity, are affected by developmental nutrition, and whether this depends on the extent to which the adult environment allows females to realize their full reproductive potential. Flies on three different developmental food levels containing increasing amounts of yeast and sugar: poor, control, and rich. Development on poor or rich larval food resulted in several life-history phenotypes indicative of suboptimal conditions, including increased developmental time, and, for poor food, decreased adult weight. However, development on poor larval food actually increased adult virgin life span. In addition, the reproductive potential of the adult environment was manipulated by adding yeast or yeast and a male. This manipulation interacted with larval food to determine adult fecundity. Specifically, under two adult conditions, flies raised on poor larval food had higher reproduction at certain ages - when singly mated this occurred early in life and when continuously mated with yeast this occurred during midlife. Poor larval food is not necessarily detrimental to key adult life-history traits, but does exert an adult environment-dependent effect, especially by affecting virgin life span and altering adult patterns of reproductive investment. These findings are relevant because (1) they may explain differences between published studies on nutritional effects on life-history traits; (2) they indicate that optimal nutritional conditions are likely to be different for larvae and adults, potentially reflecting evolutionary history; and (3) they urge for the incorporation of developmental nutritional conditions into the central life-history concept of resource acquisition and allocation.

Jensen, K., McClure, C., Priest, N. K. and Hunt, J. (2015). Sex-specific effects of protein and carbohydrate intake on reproduction but not lifespan in Drosophila melanogaster. Aging Cell [Epub ahead of print]. PubMed ID: 25808180 Summary: Modest dietary restriction extends lifespan (LS) in a diverse range of taxa and typically has a larger effect in females than males. Traditionally, this has been attributed to a stronger trade-off between LS and reproduction in females than in males that is mediated by the intake of calories. Recent studies, however, suggest that it is the intake of specific nutrients that extends LS and mediates this trade-off. This study, used the geometric framework (GF) to examine the sex-specific effects of protein (P) and carbohydrate (C) intake on LS and reproduction in Drosophila melanogaster. This study found that LS was maximized at a high intake of C and a low intake of P in both sexes, whereas nutrient intake had divergent effects on reproduction. Male offspring production rate and LS were maximized at the same intake of nutrients, whereas female egg production rate was maximized at a high intake of diets with a P:C ratio of 1:2. This resulted in larger differences in nutrient-dependent optima for LS and reproduction in females than in males, as well as an optimal intake of nutrients for lifetime reproduction that differed between the sexes. Under dietary choice, the sexes followed similar feeding trajectories regulated around a P:C ratio of 1:4. Consequently, neither sex reached their nutritional optimum for lifetime reproduction, suggesting intralocus sexual conflict over nutrient optimization. This study shows clear sex differences in the nutritional requirements of reproduction in D. melanogaster and joins the growing list of studies challenging the role of caloric restriction in extending LS.

Monday, May 4th

Ramos, C. I., Igiesuorobo, O., Wang, Q. and Serpe, M. (2015). Neto-mediated intracellular interactions shape postsynaptic composition at the Drosophila neuromuscular junction. PLoS Genet 11: e1005191. PubMed ID: 25905467 Summary: The molecular mechanisms controlling the subunit composition of glutamate receptors are crucial for the formation of neural circuits and for the long-term plasticity underlying learning and memory. This study use the Drosophila neuromuscular junction (NMJ) to examine how specific receptor subtypes are recruited and stabilized at synaptic locations. In flies, clustering of ionotropic glutamate receptors (iGluRs) requires Neto (Neuropillin and Tolloid-like), a highly conserved auxiliary subunit that is essential for NMJ assembly and development. Drosophila neto encodes two isoforms, Neto-α and Neto-β, with common extracellular parts and distinct cytoplasmic domains. Mutations that specifically eliminate Netoβ or its intracellular domain were generated. When Neto-β is missing or is truncated, the larval NMJs show profound changes in the subtype composition of iGluRs due to reduced synaptic accumulation of the GluRIIA subunit. Furthermore, neto-β mutant NMJs fail to accumulate p21-activated kinase (PAK), a critical postsynaptic component implicated in the synaptic stabilization of GluRIIA. Muscle expression of either Neto-α or Neto-β rescued the synaptic transmission at neto null NMJs, indicating that Neto conserved domains mediate iGluRs clustering. However, only Neto-β restored PAK synaptic accumulation at neto null NMJs. Thus, Neto engages in intracellular interactions that regulate the iGluR subtype composition by preferentially recruiting and/or stabilizing selective receptor subtypes.

Stephan, R., Goellner, B., Moreno, E., Frank, C. A., Hugenschmidt, T., Genoud, C., Aberle, H. and Pielage, J. (2015). Hierarchical microtubule organization controls axon caliber and transport and determines synaptic structure and stability. Dev Cell 33: 5-21. PubMed ID: 25800091 Summary: The dimensions of axons and synaptic terminals determine cell-intrinsic properties of neurons; however, the cellular mechanisms selectively controlling establishment and maintenance of neuronal compartments remain poorly understood. This study shows that two giant Drosophila Ankyrin2 isoforms, Ank2-L and Ank2-XL, and the MAP1B homolog Futsch form a membrane-associated microtubule-organizing complex that determines axonal diameter, supports axonal transport, and provides independent control of synaptic dimensions and stability. Ank2-L controls microtubule and synaptic stability upstream of Ank2-XL that selectively controls microtubule organization. Synergistically with Futsch, Ank2-XL provides three-dimensional microtubule organization and is required to establish appropriate synaptic dimensions and release properties. In axons, the Ank2-XL/Futsch complex establishes evenly spaced, grid-like microtubule organization and determines axonal diameter in the absence of neurofilaments. Reduced microtubule spacing limits anterograde transport velocities of mitochondria and synaptic vesicles. These data identify control of microtubule architecture as a central mechanism to selectively control neuronal dimensions, functional properties, and connectivity.

West, R. J., Lu, Y., Marie, B., Gao, F. B. and Sweeney, S. T. (2015). Rab8, POSH, and TAK1 regulate synaptic growth in a Drosophila model of frontotemporal dementia. J Cell Biol 208: 931-947. PubMed ID: 25800055 Summary: Mutations in genes essential for protein homeostasis have been identified in frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) patients. Why mature neurons should be particularly sensitive to such perturbations is unclear. This study identified mutations in Rab8 in a genetic screen for enhancement of an FTD phenotype associated with ESCRT-III dysfunction. Examination of Rab8 mutants or motor neurons expressing a mutant ESCRT-III subunit, CHMP2B(Intron5), at the Drosophila melanogaster neuromuscular junction synapse revealed synaptic overgrowth and endosomal dysfunction. Expression of Rab8 rescued overgrowth phenotypes generated by CHMP2B(Intron5). In Rab8 mutant synapses, c-Jun N-terminal kinase (JNK)/activator protein-1 and TGF-beta signaling were overactivated and acted synergistically to potentiate synaptic growth. Novel roles were identified for endosomal JNK-scaffold POSH (Plenty-of-SH3s) and a JNK kinase kinase, TAK1, in regulating growth activation in Rab8 mutants. These data uncover Rab8, POSH, and TAK1 as regulators of synaptic growth responses and point to recycling endosome as a key compartment for synaptic growth regulation during neurodegenerative processes

Gavino, M. A., Ford, K. J., Archila, S. and Davis, G. W. (2015). Homeostatic synaptic depression is achieved through a regulated decrease in presynaptic calcium channel abundance. Elife 4. PubMed ID: 25884248 Summary: Homeostatic signaling stabilizes synaptic transmission at the neuromuscular junction (NMJ) of Drosophila, mice, and human. It is believed that homeostatic signaling at the NMJ is bi-directional and considerable progress has been made identifying mechanisms underlying the homeostatic potentiation of neurotransmitter release. However, very little is understood mechanistically about the opposing process, homeostatic depression, and how bi-directional plasticity is achieved. This study shows that homeostatic potentiation and depression can be simultaneously induced, demonstrating true bi-directional plasticity. Next, it was shown that mutations that block homeostatic potentiation do not alter homeostatic depression, demonstrating that these are genetically separable processes. Finally, homeostatic depression was shown to be achieved by decreased presynaptic calcium channel abundance and calcium influx, changes that are independent of the presynaptic action potential waveform. Thus, this study identified a novel mechanism of homeostatic synaptic plasticity and proposes a model that can account for the observed bi-directional, homeostatic control of presynaptic neurotransmitter release.

Sunday, May 3rd

Kwon, Y., Song, W., Droujinine, I. A., Hu, Y., Asara, J. M. and Perrimon, N. (2015). Systemic organ wasting induced by localized expression of the secreted Insulin/IGF antagonist ImpL2. Dev Cell 33: 36-46. PubMed ID: 25850671 Summary: Organ wasting, related to changes in nutrition and metabolic activity of cells and tissues, is observed under conditions of starvation and in the context of diseases, including cancers. A model for organ wasting in adult Drosophila is described, whereby overproliferation induced by activation of Yorkie, the Yap1 oncogene ortholog, in intestinal stem cells leads to wasting of the ovary, fat body, and muscle. These organ-wasting phenotypes are associated with a reduction in systemic insulin/IGF signaling due to increased expression of the secreted insulin/IGF antagonist ImpL2 from the overproliferating gut. Strikingly, expression of rate-limiting glycolytic enzymes and central components of the insulin/IGF pathway is upregulated with activation of Yorkie in the gut, which may provide a mechanism for this overproliferating tissue to evade the effect of ImpL2. Altogether, this study provides insights into the mechanisms underlying organ-wasting phenotypes in Drosophila and how overproliferating tissues adapt to global changes in metabolism.

Chen, H., Zheng, X. and Zheng, Y. (2015). Lamin-B in systemic inflammation, tissue homeostasis, and aging. Nucleus [Epub ahead of print]. PubMed ID: 25875575 Summary: Gradual loss of tissue function (or homeostasis) is a natural process of aging and is believed to cause many age-associated diseases. In human epidemiology studies, the low-grade and chronic systemic inflammation in elderly has been correlated with the development of aging related pathologies. Although it is suspected that tissue decline is related to systemic inflammation, the cause and consequence of these aging phenomena are poorly understood. By studying the Drosophila fat body and gut, this study has uncovered a mechanism by which lamin-B loss in the fat body upon aging induces age-associated systemic inflammation. This chronic inflammation results in the repression of gut local immune response, which in turn leads to the over-proliferation and mis-differentiation of the intestinal stem cells, thereby resulting in gut hyperplasia. Implications and remaining questions are discussed in light of these new observations.

Jeon, H. J., Kim, Y. S., Park, J. S., Pyo, J. H., Na, H. J., Kim, I. J., Kim, C. M., Chung, H. Y., Kim, N. D., Arking, R. and Yoo, M. A. (2015). Age-related change in gammaH2AX of Drosophila muscle: its significance as a marker for muscle damage and longevity. Biogerontology. PubMed ID: 25860864 Summary: Muscle aging is closely related to unhealthy late-life and organismal aging. Recently, the state of differentiated cells was shown to be critical to tissue homeostasis. Thus, understanding how fully differentiated muscle cells age is required for ensuring healthy aging. Adult Drosophila muscle is a useful model for exploring the aging process of fully differentiated cells. This study investigated age-related changes of γH2AX, an indicator of DNA strand breaks, in adult Drosophila muscle to document whether its changes are correlated with muscle degeneration and lifespan. The results demonstrate that γH2AX accumulation increases in adult Drosophila thoracic and leg muscles with age. Analyses of short-, normal-, and long-lived strains indicate that the age-related increase of γH2AX is closely associated with the extent of muscle degeneration, cleaved caspase-3 and poly-ubiquitin aggregates, and longevity. Further analysis of muscle-specific knockdown of heterochromatin protein 1a revealed that the excessive γH2AX accumulation in thoracic and leg muscles induces accelerated degeneration and decreases longevity. These data suggest a strong correlation between age-related muscle damage and lifespan in Drosophila. These findings indicate that γH2AX may be a reliable biomarker for assessing muscle aging in Drosophila.

Hine, C., Harputlugil, E., Zhang, Y., Ruckenstuhl, C., Lee, B. C., Brace, L., Longchamp, A., Trevino-Villarreal, J. H., Mejia, P., Ozaki, C. K., Wang, R., Gladyshev, V. N., Madeo, F., Mair, W. B. and Mitchell, J. R. (2015). Endogenous hydrogen sulfide production is essential for dietary restriction benefits. Cell 160: 132-144. PubMed ID: 25542313 Summary: Dietary restriction (DR) without malnutrition encompasses numerous regimens with overlapping benefits including longevity and stress resistance, but unifying nutritional and molecular mechanisms remain elusive. In a mouse model of DR-mediated stress resistance, this study found that sulfur amino acid (SAA) restriction increased expression of the transsulfuration pathway (TSP) enzyme cystathionine gamma-lyase (CGL), resulting in increased hydrogen sulfide (H2S) production and protection from hepatic ischemia reperfusion injury. SAA supplementation, mTORC1 activation, or chemical/genetic CGL inhibition reduced H2S production and blocked DR-mediated stress resistance. In vitro, the mitochondrial protein SQR was required for H2S-mediated protection during nutrient/oxygen deprivation. Finally, TSP-dependent H2S production was observed in yeast, worm, fruit fly, and rodent models of DR-mediated longevity. Together, these data are consistent with evolutionary conservation of TSP-mediated H2S as a mediator of DR benefits with broad implications for clinical translation.

Saturday, May 2nd

Dissel, S., Angadi, V., Kirszenblat, L., Suzuki, Y., Donlea, J., Klose, M., Koch, Z., English, D., Winsky-Sommerer, R., van Swinderen, B. and Shaw, P.J. (2015). Sleep restores behavioral plasticity to Drosophila mutants. Curr Biol [Epub ahead of print]. PubMed ID: 25913403 Summary: Given the role that sleep plays in modulating plasticity, this study hypothesized that increasing sleep would restore memory to canonical memory mutants without specifically rescuing the causal molecular lesion. Sleep was increased using three independent strategies: activating the dorsal fan-shaped body, increasing the expression of Fatty acid binding protein (dFabp), or by administering the GABA-A agonist 4,5,6,7-tetrahydroisoxazolo-[5,4-c]pyridine-3-ol (THIP). Short-term memory (STM) or long-term memory (LTM) was evaluated in rutabaga (rut) and dunce (dnc) mutants using aversive phototaxic suppression and courtship conditioning. Each of the three independent strategies increased sleep and restored memory to rut and dnc mutants. Importantly, inducing sleep also reversed memory defects in a Drosophila model of Alzheimer's disease. Together, these data demonstrate that sleep plays a more fundamental role in modulating behavioral plasticity than previously appreciated and suggest that increasing sleep may benefit patients with certain neurological disorders.

Gao, X. J., Clandinin, T. R. and Luo, L. (2015). Extremely sparse olfactory inputs are sufficient to mediate innate aversion in Drosophila. PLoS One 10: e0125986. PubMed ID: 25927233 Summary: Innate attraction and aversion to odorants are observed throughout the animal kingdom, but how olfactory circuits encode such valences is not well understood, despite extensive anatomical and functional knowledge. In Drosophila melanogaster, ~50 types of olfactory receptor neurons (ORNs) each express a unique receptor gene, and relay information to a cognate type of projection neurons (PNs). To examine the extent to which the population activity of ORNs is required for olfactory behavior, a genetic strategy was developed to block all ORN outputs, and then to restore output in specific types. Unlike attraction, aversion was unaffected by simultaneous silencing of many ORNs, and even single ORN types previously shown to convey neutral valence sufficed to mediate aversion. Thus, aversion may rely on specific activity patterns in individual ORNs rather than the number or identity of activated ORNs. ORN activity is relayed into the brain by downstream circuits, with excitatory PNs (ePN) representing a major output. This study found that silencing the majority of ePNs did not affect aversion, even when ePNs directly downstream of single restored ORN types were silenced. The data demonstrate the robustness of olfactory aversion, and suggest that its circuit mechanism is qualitatively different from attraction.

Yang, Z., Yu, Y., Zhang, V., Tian, Y., Qi, W. and Wang, L. (2015). Octopamine mediates starvation-induced hyperactivity in adult Drosophila. Proc Natl Acad Sci U S A 112: 5219-5224. PubMed ID: 25848004 Summary: Starved animals often exhibit elevated locomotion, which has been speculated to partly resemble foraging behavior and facilitate food acquisition and energy intake. Despite its importance, the neural mechanism underlying this behavior remains unknown in any species. This study confirmed and extended previous findings that starvation induces locomotor activity in adult fruit flies Drosophila melanogaster. This study also showed that starvation-induced hyperactivity was directed toward the localization and acquisition of food sources, because it could be suppressed upon the detection of food cues via both central nutrient-sensing and peripheral sweet-sensing mechanisms, via induction of food ingestion. It was further found that octopamine, the insect counterpart of vertebrate norepinephrine, as well as the neurons expressing octopamine, were both necessary and sufficient for starvation-induced hyperactivity. Octopamine was not required for starvation-induced changes in feeding behaviors, suggesting independent regulations of energy intake behaviors upon starvation. Taken together, these results establish a quantitative behavioral paradigm to investigate the regulation of energy homeostasis by the CNS and identify a conserved neural substrate that links organismal metabolic state to a specific behavioral output.

Schleyer, M., et al. (2015). The impact of odor-reward memory on chemotaxis in larval Drosophila. Learn Mem 22: 267-277. PubMed ID: 25887280 Summary: How do animals adaptively integrate innate with learned behavioral tendencies? This study tackles this question using chemotaxis as a paradigm. Chemotaxis in the Drosophila larva largely results from a sequence of runs and oriented turns. Thus, the larvae minimally need to determine (1) how fast to run, (2) when to initiate a turn, and (3) where to direct a turn. The study first reported how odor-source intensities modulated these decisions to bring about higher levels of chemotactic performance for higher odor-source intensities during innate chemotaxis. The study then examined whether the same modulations were responsible for alterations of chemotactic performance by learned odor "valence" (understood throughout as level of attractiveness). Run speed (1) was neither modulated by the innate nor by the learned valence of an odor. Turn rate (2), however, was modulated by both. Likewise, turning direction (3) was modulated concordantly by innate and learned valence. Using numerical simulations, the paper showed that a modulation of both turn rate and of turning direction was sufficient to account for the empirically found differences in preference scores across experimental conditions. These results suggest that innate and learned valence organize adaptive olfactory search behavior by their summed effects on turn rate and turning direction, but not on run speed. This work should aid studies into the neural mechanisms by which memory impacts specific aspects of behavior.

Friday, May 1st

Katsuyama, T., Comoglio, F., Seimiya, M., Cabuy, E. and Paro, R. (2015). During Drosophila disc regeneration, JAK/STAT coordinates cell proliferation with Dilp8-mediated developmental delay. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 25902518 Summary: Regeneration of fragmented Drosophila imaginal discs occurs in an epimorphic manner involving local cell proliferation at the wound site. After disc fragmentation, cells at the wound site activate a restoration program through wound healing, regenerative cell proliferation, and repatterning of the tissue. However, the interplay of signaling cascades driving these early reprogramming steps is not well-understood. This study profiled the transcriptome of regenerating cells in the early phase within 24 h after wounding. JAK/STAT signaling was found to become activated at the wound site and to promote regenerative cell proliferation in cooperation with Wingless (Wg) signaling. In addition, the expression of Insulin-like peptide 8 (dilp8), which encodes a paracrine peptide to delay the onset of pupariation, was found to be controlled by JAK/STAT signaling in early regenerating discs. These findings suggest that JAK/STAT signaling plays a pivotal role in coordinating regenerative disc growth with organismal developmental timing.

Hatfield, I., Harvey, I., Yates, E.R., Redd, J.R., Reiter, L.T. and Bridges, D. (2015). The role of TORC1 in muscle development in Drosophila. Sci Rep 5: 9676. PubMed ID: 25866192 Summary: Myogenesis is an important process during both development and muscle repair. Previous studies suggest that mTORC1 plays a role in the formation of mature muscle from immature muscle precursor cells. This study shows that gene expression for several myogenic transcription factors including Myf5, Myog and Mef2c but not MyoD and myosin heavy chain isoforms decrease when C2C12 cells are treated with rapamycin, supporting a role for mTORC1 pathway during muscle development. To investigate the possibility that mTORC1 can regulate muscle in vivo, the essential dTORC1 subunit Raptor was ablated in Drosophila melanogaster, and it was found that muscle-specific knockdown of Raptor caused flies to be too weak to emerge from their pupal cases during eclosion. Using a series of GAL4 drivers it was also shown that muscle-specific Raptor knockdown also caused shortened lifespan, even when eclosure was unaffected. Together these results highlight an important role for TORC1 in muscle development, integrity and function in both Drosophila and mammalian cells.

Arias, C., Fussero, G., Zacharonok, M. and Macias, A. (2015). Dpp-expressing and non-expressing cells: two different populations of growing cells in Drosophila. PLoS One 10: e0121457. PubMed ID: 25798905 Summary: There are different models that explain growth during development. One model is based on insect and amphibian regeneration studies. This model proposes that growth is directed by pattern, and growth takes place by intercalation at a growth discontinuity; therefore, proliferation should surround the discontinuity. Currently, this model, apart from regenerative studies on mostly adult patterning, has not found supporting evidence in Drosophila that shows proliferation surrounding a discontinuity. Despite this lack of evidence, the importance of discontinuities has been shown in different experiments, even under wt conditions, more specifically in the formation of the leg joints because of the occurrence of cell death at their boundaries. This study shows the existence of a sharp discontinuity in Decapentaplegic (Dpp) in the genital discs at the third larvae stage (L3), which determines the upregulation in the Jun-NH2-Terminal-Kinase (JNK) pathway, reaper (rpr), head involution defective (hid) and active caspases from its boundaries. The proliferation and cell death surrounding the discontinuity suggest that growth can proceed by intercalation and competitive death takes place in this area. Finally, the Rpr, Grim and Hid (RGH) products are a few of the factors that define the growth discontinuity because they are negative regulators of growth, a new function that is unique from their known functions in apoptosis.

Fernandes, V. M., Pradhan-Sundd, T., Blaquiere, J. A. and Verheyen, E. M. (2015). Ras/MEK/MAPK-mediated regulation of heparin sulphate proteoglycans promotes retinal fate in the Drosophila eye-antennal disc. Dev Biol [Epub ahead of print]. PubMed ID: 25848695 Summary: The Drosophila eye-antennal imaginal disc is a well-characterised system in which to study regional specification; it is first divided into antennal and eye fates and subsequently retinal differentiation occurs within only the eye field. During development, signalling pathways and selector genes compete with and mutually antagonise each other to subdivide the tissue. Wingless (Wg) signalling is the main inhibitor of retinal differentiation; it does so by promoting antennal/head-fate via selector factors and by antagonising Hedgehog (Hh), the principal differentiation-initiating signal. Wg signalling must be suppressed by JAK/STAT at the disc posterior in order to initiate retinal differentiation. Ras/MEK/MAPK signalling has also been implicated in initiating retinal differentiation but its mode of action is not known. This study found that compromising Ras/MEK/MAPK signalling in the early larval disc results in expanded antennal/head cuticle at the expense of the compound eye. These phenotypes correspond both to perturbations in selector factor expression, and to de-repressed wg. Indeed, STAT activity is reduced due to decreased mobility of the ligand Unpaired (Upd) along with a corresponding loss in Dally-like protein (Dlp), a heparan sulphate proteoglycan (HSPG) that aids Upd diffusion. Strikingly, blocking HSPG biogenesis phenocopies compromised Ras/MEK/MAPK, while restoring HSPG expression rescues the adult phenotype significantly. This study identifies a novel mode by which the Ras/MEK/MAPK pathway regulates regional-fate specification via HSPGs during development.

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