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


Friday, September 29th

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Tian, A., Benchabane, H., Wang, Z., Zimmerman, C., Xin, N., Perochon, J., Kalna, G., Sansom, O. J., Cheng, C., Cordero, J. B. and Ahmed, Y. (2017). Intestinal stem cell overproliferation resulting from inactivation of the APC tumor suppressor requires the transcription cofactors Earthbound and Erect wing. PLoS Genet 13(7): e1006870. PubMed ID: 28708826
Wnt/beta-catenin signal transduction directs intestinal stem cell (ISC) proliferation during homeostasis. Hyperactivation of Wnt signaling initiates colorectal cancer, which most frequently results from truncation of the tumor suppressor Adenomatous polyposis coli (APC). Using a Drosophila model this study demonstrated that two evolutionarily conserved transcription cofactors, Earthbound (Ebd) and Erect wing (Ewg), are essential for all major consequences of Apc1 inactivation in the intestine: the hyperactivation of Wnt target gene expression, excess number of ISCs, and hyperplasia of the epithelium. In contrast, only Ebd, but not Ewg, mediates the Wnt-dependent regulation of ISC proliferation during homeostasis. Therefore, in the adult intestine, Ebd acts independently of Ewg in physiological Wnt signaling, but cooperates with Ewg to induce the hyperactivation of Wnt target gene expression following Apc1 loss. These findings have relevance for human tumorigenesis, as Jerky (JRK/JH8), the human Ebd homolog, promotes Wnt pathway hyperactivation and is overexpressed in colorectal, breast, and ovarian cancers.
Zhai, Z., Boquete, J. P. and Lemaitre, B. (2017). A genetic framework controlling the differentiation of intestinal stem cells during regeneration in Drosophila. PLoS Genet 13(6): e1006854. PubMed ID: 28662029
The speed of stem cell differentiation has to be properly coupled with self-renewal, both under basal conditions for tissue maintenance and during regeneration for tissue repair. Using the Drosophila midgut model, this study analyzed at the cellular and molecular levels the differentiation program required for robust regeneration. The intestinal stem cell (ISC) and its differentiating daughter, the enteroblast (EB), were observed to form extended cell-cell contacts in regenerating intestines. The contact between progenitors is stabilized by cell adhesion molecules, and can be dynamically remodeled to elicit optimal juxtacrine Notch signaling to determine the speed of progenitor differentiation. Notably, increasing the adhesion property of progenitors by expressing Connectin is sufficient to induce rapid progenitor differentiation. It was further demonstrated that JAK/STAT signaling, Sox21a and GATAe form a functional relay to orchestrate EB differentiation. Thus, this study provides new insights into the complex and sequential events that are required for rapid differentiation following stem cell division during tissue replenishment.
Schell, J. C., et al. (2017). Control of intestinal stem cell function and proliferation by mitochondrial pyruvate metabolism. Nat Cell Biol. PubMed ID: 28812582
Most differentiated cells convert glucose to pyruvate in the cytosol through glycolysis, followed by pyruvate oxidation in the mitochondria. These processes are linked by the mitochondrial pyruvate carrier (MPC), which is required for efficient mitochondrial pyruvate uptake. In contrast, proliferative cells, including many cancer and stem cells, perform glycolysis robustly but limit fractional mitochondrial pyruvate oxidation. This study sought to understand the role this transition from glycolysis to pyruvate oxidation plays in stem cell maintenance and differentiation. Loss of the MPC in Lgr5-EGFP-positive stem cells, or treatment of intestinal organoids with an MPC inhibitor, increases proliferation and expands the stem cell compartment. Similarly, genetic deletion of the MPC in Drosophila intestinal stem cells also increases proliferation, whereas MPC overexpression suppresses stem cell proliferation. These data demonstrate that limiting mitochondrial pyruvate metabolism is necessary and sufficient to maintain the proliferation of intestinal stem cells.
Chen, D., Zhu, X., Zhou, L., Wang, J., Tao, X., Wang, S., Sun, F., Kan, X., Han, Z. and Gu, Y. (2017). Gilgamesh is required for the maintenance of germline stem cells in Drosophila testis. Sci Rep 7(1): 5737. PubMed ID: 28720768
Emerging evidence supports that stem cells are regulated by both intrinsic and extrinsic mechanisms. However, factors that determine the fate of stem cells remain incompletely understood. The Drosophila testis provides an exclusive powerful model in searching for potential important regulatory factors and their underlying mechanisms for controlling the fate of germline stem cells (GSCs). This study found that Drosophila gilgamesh (gish), which encodes a homologue of human CK1-gamma (casein kinase 1-gamma), is required intrinsically for GSC maintenance. Genetic analyses indicate gish is not required for Dpp/Gbb signaling silencing of bam and is dispensable for Dpp/Gbb signaling-dependent Dad expression. Finally, it was shown that overexpression of gish fail to dramatically increase the number of GSCs. These findings demonstrate that gish controls the fate of GSCs in Drosophila testis by a novel Dpp/Gbb signaling-independent pathway.

Thursday, September 28th

Li, S., Koe, C. T., Tay, S. T., Tan, A. L. K., Zhang, S., Zhang, Y., Tan, P., Sung, W. K. and Wang, H. (2017). An intrinsic mechanism controls reactivation of neural stem cells by spindle matrix proteins. Nat Commun 8(1): 122. PubMed ID: 28744001
The switch between quiescence and proliferation is central for neurogenesis and its alteration is linked to neurodevelopmental disorders such as microcephaly. However, intrinsic mechanisms that reactivate Drosophila larval neural stem cells (NSCs) to exit from quiescence are not well established. This study shows that the spindle matrix complex containing Chromator (Chro) functions as a key intrinsic regulator of NSC reactivation downstream of extrinsic insulin/insulin-like growth factor signalling. Chro also prevents NSCs from ire-entering quiescence at later stages. NSC-specific in vivo profiling has identified many downstream targets of Chro, including a temporal transcription factor Grainy head (Grh) and a neural stem cell quiescence-inducing factor Prospero (Pros).Spindle matrix proteins promote the expression of Grh and repress that of Pros in NSCs to govern their reactivation. These data demonstrate that nuclear Chro critically regulates gene expression in NSCs at the transition from quiescence to proliferation.The spindle matrix proteins, including Chro, are known to regulate mitotic spindle assembly in the cytoplasm. In Drosophila larval brain, Chro promotes neural stem cell (NSC) reactivation and prevents activated NSCs from entering quiescence, and Chro carries out such a role by regulating the expression of key transcription factors in the nucleus.
Strube-Bloss, M. F., Grabe, V., Hansson, B. S. and Sachse, S. (2017). Calcium imaging revealed no modulatory effect on odor-evoked responses of the Drosophila antennal lobe by two populations of inhibitory local interneurons. Sci Rep 7(1): 7854. PubMed ID: 28798324
Although considerable knowledge is available about how odors are represented in the antennal lobe (AL), the insects' analogue to the olfactory bulb, how the different neurons in the AL network contribute to the olfactory code is not fully understood. In Drosophila it is possible to selectively manipulate specific neuronal populations to elucidate their function in odor processing. This study silenced the synaptic transmission of two distinct subpopulations of multiglomerular GABAergic local interneurons (LN1 and LN2) using shibire (shits) and analyzed their impact on odor-induced glomerular activity at the AL input and output level. Notably, selective silencing of both LN populations did not significantly affect the odor-evoked activity patterns in the AL. It is therefore concluded that these LN subpopulations, which cover one third of the total LN number, are not predominantly involved in odor identity coding per se. As suggested by their broad innervation patterns and contribution to long-term adaptation, they might contribute to AL-computation on a global and longer time scale.
Schoofs, A., Huckesfeld, S. and Pankratz, M. J. (2017). Serotonergic network in the subesophageal zone modulates the motor pattern for food intake in Drosophila. J Insect Physiol [Epub ahead of print]. PubMed ID: 28735009
The functional organization of central motor circuits underlying feeding behaviors is not well understood. This study combined electrophysiological and genetic approaches to investigate the regulatory networks upstream of the motor program underlying food intake in the Drosophila larval central nervous system. The serotonergic network of the CNS was found to be capable of setting the motor rhythm frequency of pharyngeal pumping. Pharmacological experiments verified that modulation of the feeding motor pattern is based on the release of serotonin. Classical lesion and laser based cell ablation indicated that the serotonergic neurons in the subesophageal zone represent a redundant network for motor control of larval food intake.
Mann, K., Gallen, C. L. and Clandinin, T. R. (2017). Whole-brain calcium imaging reveals an intrinsic functional network in Drosophila. Curr Biol 27(15): 2389-2396.e2384. PubMed ID: 28756955
A long-standing goal of neuroscience has been to understand how computations are implemented across large-scale brain networks. By correlating spontaneous activity during "resting states", studies of intrinsic brain networks in humans have demonstrated a correspondence with task-related activation patterns, relationships to behavior, and alterations in processes such as aging and brain disorders, highlighting the importance of resting-state measurements for understanding brain function. This study developed methods to measure intrinsic functional connectivity in Drosophila. This study measured intrinsic functional connectivity in Drosophila by acquiring calcium signals from the central brain. An alignment procedure was developed to assign functional data to atlas regions and correlate activity between regions to generate brain networks. This work reveals a large-scale architecture for neural communication and provides a framework for using Drosophila to study functional brain networks.
Takemura, S. Y., Aso, Y., Hige, T., Wong, A., Lu, Z., Xu, C. S., Rivlin, P. K., Hess, H., Zhao, T., Parag, T., Berg, S., Huang, G., Katz, W., Olbris, D. J., Plaza, S., Umayam, L., Aniceto, R., Chang, L. A., Lauchie, S., Ogundeyi, O., Ordish, C., Shinomiya, A., Sigmund, C., Takemura, S., Tran, J., Turner, G. C., Rubin, G. M. and Scheffer, L. K. (2017). A connectome of a learning and memory center in the adult Drosophila brain. Elife 6. PubMed ID: 28718765
Understanding memory formation, storage and retrieval requires knowledge of the underlying neuronal circuits. In Drosophila, the mushroom body (MB) is the major site of associative learning. This study reconstructed the morphologies and synaptic connections of all 983 neurons within the three functional units, or compartments, that compose the adult MB's alpha lobe, using a dataset of isotropic 8 nm voxels collected by focused ion-beam milling scanning electron microscopy. It was found that Kenyon cells (KCs), whose sparse activity encodes sensory information, each make multiple en passant synapses to MB output neurons (MBONs) in each compartment. Some MBONs have inputs from all KCs, while others differentially sample sensory modalities. Only 6% of KC>MBON synapses receive a direct synapse from a dopaminergic neuron (DAN). Two unanticipated classes of synapses, KC>DAN and DAN>MBON, were identified. DAN activation produces a slow depolarization of the MBON in these DAN>MBON synapses and can weaken memory recall.
Wu, J. K., Tai, C. Y., Feng, K. L., Chen, S. L., Chen, C. C. and Chiang, A. S. (2017). Long-term memory requires sequential protein synthesis in three subsets of mushroom body output neurons in Drosophila. Sci Rep 7(1): 7112. PubMed ID: 28769066
Creating long-term memory (LTM) requires new protein synthesis to stabilize learning-induced synaptic changes in the brain. In the fruit fly, Drosophila melanogaster, aversive olfactory learning forms several phases of labile memory to associate an odor with coincident punishment in the mushroom body (MB). It remains unclear how the brain consolidates early labile memory into LTM. This study surveyed 183 Gal4 lines containing almost all 21 distinct types of MB output neurons (MBONs) and showed that sequential synthesis of learning-induced proteins occurs at three types of MBONs. Downregulation of oo18 RNA-binding proteins (ORBs) in any of these MBONs impaired LTM. And, neurotransmission outputs from these MBONs are all required during LTM retrieval. Together, these results suggest an LTM consolidation model in which transient neural activities of early labile memory in the MB are consolidated into stable LTM at a few postsynaptic MBONs through sequential ORB-regulated local protein synthesis.

Wednesday, September 27th

Wang, G., Gutzwiller, L., Li-Kroeger, D. and Gebelein, B. (2017). A Hox complex activates and potentiates the Epidermal Growth Factor signaling pathway to specify Drosophila oenocytes. PLoS Genet 13(7): e1006910. PubMed ID: 28715417
Hox transcription factors specify distinct cell types along the anterior-posterior axis of metazoans by regulating target genes that modulate signaling pathways. A well-established example is the induction of Epidermal Growth Factor (EGF) signaling by an Abdominal-A (Abd-A) Hox complex during the specification of Drosophila hepatocyte-like cells (oenocytes). Previous studies revealed that Abd-A is non-cell autonomously required to promote oenocyte fate by directly activating a gene (rhomboid) that triggers EGF secretion from sensory organ precursor (SOP) cells. Neighboring cells that receive the EGF signal initiate a largely unknown pathway to promote oenocyte fate. This study shows that Abd-A also plays a cell autonomous role in inducing oenocyte fate by activating the expression of the Pointed-P1 (PntP1) ETS transcription factor downstream of EGF signaling. Genetic studies demonstrate that both PntP1 and PntP2 are required for oenocyte specification. Moreover, PntP1 contains a conserved enhancer (PntP1OE) that is activated in oenocyte precursor cells by EGF signaling via direct regulation by the Pnt transcription factors as well as a transcription factor complex consisting of Abd-A, Extradenticle, and Homothorax. These findings demonstrate that the same Abd-A Hox complex required for sending the EGF signal from SOP cells, enhances the competency of receiving cells to select oenocyte cell fate by up-regulating PntP1. Since PntP1 is a downstream effector of EGF signaling, these findings provide insight into how a Hox factor can both trigger and potentiate the EGF signal to promote an essential cell fate along the body plan.
Suksuwan, W., Cai, X., Ngernsiri, L. and Baumgartner, S. (2017). Segmentation gene expression patterns in Bactrocera dorsalis and related insects: regulation and shape of blastoderm and larval cuticle. Int J Dev Biol 61(6-7): 439-450. PubMed ID: 28695964
The oriental fruit fly, Bactrocera dorsalis, is regarded as a severe pest of fruit production in Asia. Despite its economic importance, only limited information regarding the molecular and developmental biology of this insect is known to date. This study provides a detailed analysis of B. dorsalis embryology, as well as the expression patterns of a number of segmentation genes known to act during patterning of Drosophila and compare these to the patterns of other insect families. An anterior shift of the expression of gap genes was detected when compared to Drosophila. This shift was largely restored during the step where the gap genes control expression of the pair-rule genes. The shapes were analyzed of the embryos of insects of different families, B. dorsalis and the blow fly Lucilia sericata and compared with that of the well-characterized Drosophila melanogaster. Distinct shapes were found as well as differences in the ratios of the length of the anterior-posterior axis and the dorsal-ventral axis. These features were integrated into a profile of how the expression patterns of the gap gene Kruppel and the pair-rule gene even-skipped were observed along the A-P axis in three insects families. Since significant differences were observed, how Kruppel controls the even-skipped stripes is discussed. Furthermore, how the position and angles of the segmentation gene stripes differed from other insects is discussed. Finally, the outcome was analyzed of the expression patterns of the late acting segment polarity genes in relation to the anlagen of the naked-cuticle and denticle belt area of the B. dorsalis larva.
Lin, S. Z., Li, B., Lan, G. and Feng, X. Q. (2017). Activation and synchronization of the oscillatory morphodynamics in multicellular monolayer. Proc Natl Acad Sci U S A 114(31): 8157-8162. PubMed ID: 28716911
Oscillatory morphodynamics provides necessary mechanical cues for many multicellular processes. Owing to their collective nature, these processes require robustly coordinated dynamics of individual cells, which are often separated too distantly to communicate with each other through biomaterial transportation. Although it is known that the mechanical balance generally plays a significant role in the systems' morphologies, it remains elusive whether and how the mechanical components may contribute to the systems' collective morphodynamics. This paper analyzed the collective oscillations in the Drosophila amnioserosa tissue to elucidate the regulatory roles of the mechanical components. The tensile stress was identified as the key activator that switches the collective oscillations on and off. This regulatory role is shown analytically using the Hopf bifurcation theory. The physical properties of the tissue boundary are directly responsible for synchronizing the oscillatory intensity and polarity of all inner cells and for orchestrating the spatial oscillation patterns in the tissue.
Song, Y., Marmion, R. A., Park, J. O., Biswas, D., Rabinowitz, J. D. and Shvartsman, S. Y. (2017). Dynamic control of dNTP synthesis in early embryos. Dev Cell 42(3): 301-308.e303. PubMed ID: 28735680
Exponential increase of cell numbers in early embryos requires large amounts of DNA precursors (deoxyribonucleoside triphosphates (dNTPs)). Little is understood about how embryos satisfy this demand. This study examined dNTP metabolism in the early Drosophila embryo, in which gastrulation is preceded by 13 sequential nuclear cleavages within only 2 hr of fertilization. Surprisingly, despite the breakneck speed at which Drosophila embryos synthesize DNA, maternally deposited dNTPs can generate less than half of the genomes needed to reach gastrulation. The rest of the dNTPs are synthesized 'on the go.' The rate-limiting enzyme of dNTP synthesis, ribonucleotide reductase, is inhibited by endogenous levels of deoxyATP (dATP) present at fertilization and is activated as dATP is depleted via DNA polymerization. This feedback inhibition renders the concentration of dNTPs at gastrulation robust, with respect to large variations in maternal supplies, and is essential for normal progression of embryogenesis.

Tuesday, September 26th

Song, W., Owusu-Ansah, E., Hu, Y., Cheng, D., Ni, X., Zirin, J. and Perrimon, N. (2017). Activin signaling mediates muscle-to-adipose communication in a mitochondria dysfunction-associated obesity model. Proc Natl Acad Sci U S A. PubMed ID: 28739899
Mitochondrial dysfunction has been associated with obesity and metabolic disorders. However, whether mitochondrial perturbation in a single tissue influences mitochondrial function and metabolic status of another distal tissue remains largely unknown. This study analyzed the nonautonomous role of muscular mitochondrial dysfunction in Drosophila. Surprisingly, impaired muscle mitochondrial function via complex I perturbation results in simultaneous mitochondrial dysfunction in the fat body (the fly adipose tissue) and subsequent triglyceride accumulation, the major characteristic of obesity. RNA-sequencing (RNA-seq) analysis, in the context of muscle mitochondrial dysfunction, revealed that target genes of the TGF-beta signaling pathway were induced in the fat body. Strikingly, expression of the TGF-beta family ligand, Activin-&beta& (Act&beta&), was dramatically increased in the muscles by NF-kappaB/Relish (Rel) signaling in response to mitochondrial perturbation, and decreasing Actβ expression in mitochondrial-perturbed muscles rescued both the fat body mitochondrial dysfunction and obesity phenotypes. Thus, perturbation of muscle mitochondrial activity regulates mitochondrial function in the fat body nonautonomously via modulation of Activin signaling.
Scholz, N., Guan, C., Nieberler, M., Grotemeyer, A., Maiellaro, I., Gao, S., Beck, S., Pawlak, M., Sauer, M., Asan, E., Rothemund, S., Winkler, J., Promel, S., Nagel, G., Langenhan, T. and Kittel, R. J. (2017). Mechano-dependent signaling by Latrophilin/CIRL quenches cAMP in proprioceptive neurons. Elife 6. PubMed ID: 28784204
Adhesion-type G protein-coupled receptors (aGPCRs), a large molecule family with over 30 members in humans, operate in organ development, brain function and govern immunological responses. Correspondingly, this receptor family is linked to a multitude of diverse human diseases. aGPCRs have been suggested to possess mechanosensory properties, though their mechanism of action is fully unknown. This study shows that the Drosophila aGPCR Latrophilin/dCIRL acts in mechanosensory neurons by modulating ionotropic receptor currents, the initiating step of cellular mechanosensation. This process depends on the length of the extended ectodomain and the tethered agonist of the receptor, but not on its autoproteolysis, a characteristic biochemical feature of the aGPCR family. Intracellularly, dCIRL quenches cAMP levels upon mechanical activation thereby specifically increasing the mechanosensitivity of neurons. These results provide direct evidence that the aGPCR dCIRL acts as a molecular sensor and signal transducer that detects and converts mechanical stimuli into a metabotropic response.
Sakai, K., Tsutsui, K., Yamashita, T., Iwabe, N., Takahashi, K., Wada, A. and Shichida, Y. (2017). Drosophila melanogaster rhodopsin Rh7 is a UV-to-visible light sensor with an extraordinarily broad absorption spectrum. Sci Rep 7(1): 7349. PubMed ID: 28779161
The genome of Drosophila melanogaster contains seven rhodopsin genes. Rh1-6 proteins are known to have respective absorption spectra and function as visual pigments in ocelli and compound eyes. In contrast, Rh7 protein was recently revealed to function as a circadian photoreceptor in the brain. However, its molecular properties have not been characterized yet. This study successfully prepared a recombinant protein of Drosophila Rh7 in mammalian cultured cells. Drosophila Rh7 bound both 11-cis-retinal and 11-cis-3-hydroxyretinal to form photo-pigments which can absorb UV light. Irradiation with UV light caused formation of a visible-light absorbing metarhodopsin that activated Gq-type of G protein. This state could be photoconverted back to the original state and, thus Rh7 is a Gq-coupled bistable pigment. Interestingly, Rh7 (lambda max = 350 nm) exhibited an unusual broad spectrum with a longer wavelength tail reaching 500 nm, whose shape is like a composite of spectra of two pigments. In contrast, replacement of lysine at position 90 with glutamic acid caused the formation of a normal-shaped absorption spectrum with maximum at 450 nm. Therefore, Rh7 is a unique photo-sensor that can cover a wide wavelength region by a single pigment to contribute to non-visual photoreception.
Solis, G. P., Bilousov, O., Koval, A., Luchtenborg, A. M., Lin, C. and Katanaev, V. L. (2017). Golgi-resident Galphao promotes protrusive membrane dynamics. Cell 170(5):939-955. PubMed ID: 28803726
To form protrusions like neurites, cells must coordinate their induction and growth. The first requires cytoskeletal rearrangements at the plasma membrane (PM), the second requires directed material delivery from cell's insides. This study found that the Galphao-subunit of heterotrimeric G proteins localizes dually to PM and Golgi across phyla and cell types. The PM pool of Galphao induces, and the Golgi pool feeds, the growing protrusions by stimulated trafficking. Golgi-residing KDELR binds and activates monomeric Galphao, atypically for G protein-coupled receptors that normally act on heterotrimeric G proteins. Through multidimensional screenings identifying > 250 Galphao interactors, this study pinpoints several basic cellular activities, including vesicular trafficking, as being regulated by Galphao. It was further found small Golgi-residing GTPases Rab1 and Rab3 as direct effectors of Galphao. This KDELR --> Galphao --> Rab1/3 signaling axis is conserved from insects to mammals and controls material delivery from Golgi to PM in various cells and tissues.

Monday, September 25th

Moshe, A. and Kaplan, T. (2017). Genome-wide search for Zelda-like chromatin signatures identifies GAF as a pioneer factor in early fly development. Epigenetics Chromatin 10(1): 33. PubMed ID: 28676122
The protein Zelda was shown to play a key role in early Drosophila development, binding thousands of promoters and enhancers prior to maternal-to-zygotic transition (MZT), and marking them for transcriptional activation. Zelda has been shown to act through specific chromatin patterns of histone modifications to mark developmental enhancers and active promoters. Intriguingly, some Zelda sites still maintain these chromatin patterns in Drosophila embryos lacking maternal Zelda protein. This suggests that additional Zelda-like pioneer factors may act in early fly embryos. A computational method was developed to analyze and refine the chromatin landscape surrounding early Zelda peaks, using a multichannel spectral clustering. The genome was scanned using additional chromatin patterns, and loci-with no Zelda binding- were identified that show similar chromatin patterns, resulting with hundreds of Zelda-independent putative enhancers. These regions were found to be enriched with GAGA factor (GAF, Trl) and are typically located near early developmental zygotic genes. Overall this analysis suggests that GAF, together with Zelda, plays an important role in activating the zygotic genome. This computational approach offers an efficient algorithm for characterizing chromatin signatures around some loci of interest and allows a genome-wide identification of additional loci with similar chromatin patterns.
Shalaby, N. A., Sayed, R., Zhang, Q., Scoggin, S., Eliazer, S., Rothenfluh, A. and Buszczak, M. (2017). Systematic discovery of genetic modulation by Jumonji histone demethylases in Drosophila. Sci Rep 7(1): 5240. PubMed ID: 28701701
Jumonji (JmjC) domain proteins (see Jarid2) influence gene expression and chromatin organization by way of histone demethylation, which provides a means to regulate the activity of genes across the genome. JmjC proteins have been associated with many human diseases including various cancers, developmental and neurological disorders, however, the shared biology and possible common contribution to organismal development and tissue homeostasis of all JmjC proteins remains unclear. This study systematically tested the function of all 13 Drosophila JmjC genes. Generation of molecularly defined null mutants revealed that loss of 8 out of 13 JmjC genes modify position effect variegation (PEV) phenotypes, consistent with their ascribed role in regulating chromatin organization. However, most JmjC genes do not critically regulate development, as 10 members are viable and fertile with no obvious developmental defects. Rather, it was found that different JmjC mutants specifically alter the phenotypic outcomes in various sensitized genetic backgrounds. The data demonstrate that, rather than controlling essential gene expression programs, Drosophila JmjC proteins generally act to "fine-tune" different biological processes.
Li, Y., Wang, C., Cai, W., Sengupta, S., Zavortink, M., Deng, H., Girton, J., Johansen, J. and Johansen, K. M. (2017). H2Av facilitates H3S10 phosphorylation but is not required for heat shock-induced chromatin decondensation or transcriptional elongation. Development. PubMed ID: 28807902
A model has been proposed where JIL-1 kinase-mediated H3S10 and H2Av phosphorylation is required for transcriptional elongation and heat shock-induced chromatin decondensation to occur. However, this study shows that while H3S10 phosphorylation is indeed compromised in the H2Av null mutant. chromatin decondensation at heat shock loci is unaffected both in the absence of JIL-1 as well as of H2Av and that there is no discernable decrease in the elongating form of Pol II in either mutant. Furthermore, mRNA for the major heat shock protein Hsp70 is transcribed at robust levels in both H2Av and JIL-1 null mutants. Using a different chromatin remodeling paradigm that is JIL-1 dependent evidence is provided that ectopic tethering of JIL-1 and subsequent H3S10 phosphorylation recruits PARP-1 to the remodeling site independently of H2Av phosphorylation. Thus these data strongly suggest that H2Av or H3S10 phosphorylation by JIL-1 is not required for chromatin decondensation or transcriptional elongation in Drosophila.
Schauer, T., Ghavi-Helm, Y., Sexton, T., Albig, C., Regnard, C., Cavalli, G., Furlong, E. E. and Becker, P. B. (2017). Chromosome topology guides the Drosophila Dosage Compensation Complex for target gene activation. EMBO Rep. PubMed ID: 28794204
X chromosome dosage compensation in Drosophila requires chromosome-wide coordination of gene activation. The male-specific lethal dosage compensation complex (DCC) identifies and binds to X-chromosomal high-affinity sites (HAS) from which it boosts transcription. A sub-class of HAS, PionX sites, represent first contacts on the X. This study explored the chromosomal interactions of representative PionX sites by high-resolution 4C and determined the global chromosome conformation by Hi-C in sex-sorted embryos. Male and female X chromosomes display similar nuclear architecture, concordant with clustered, constitutively active genes. PionX sites, like HAS, are evenly distributed in the active compartment and engage in short- and long-range interactions beyond compartment boundaries. Long-range, inter-domain interactions between DCC binding sites are stronger in males, suggesting that the complex refines chromatin organization. By de novo induction of DCC in female cells, the extent of activation surrounding PionX sites was monitored. This revealed a remarkable range of DCC action not only in linear proximity, but also at megabase distance if close in space, suggesting that DCC profits from pre-existing chromosome folding to activate genes.

Friday, September 22nd

Moghaddam, M. B., Gross, T., Becker, A., Vilcinskas, A. and Rahnamaeian, M. (2017). The selective antifungal activity of Drosophila melanogaster metchnikowin reflects the species-dependent inhibition of succinate-coenzyme Q reductase. Sci Rep 7(1): 8192. PubMed ID: 28811531
Insect-derived antifungal peptides have a significant economic potential, particularly for the engineering of pathogen-resistant crops. However, the nonspecific antifungal activity of such peptides could result in detrimental effects against beneficial fungi, whose interactions with plants promote growth or increase resistance against biotic and abiotic stress. The antifungal peptide Metchnikowin (Mtk) from Drosophila melanogaster acts selectively against pathogenic Ascomycota, including Fusarium graminearum, without affecting Basidiomycota such as the beneficial symbiont Piriformospora indica. This study investigated the mechanism responsible for the selective antifungal activity of Mtk by using the peptide to probe a yeast two-hybrid library of F. graminearum cDNAs. Mtk was found to specifically target the iron-sulfur subunit (SdhB) of succinate-coenzyme Q reductase (SQR). A functional assay based on the succinate dehydrogenase (SDH) activity of mitochondrial complex II clearly demonstrated that Mtk inhibited the SDH activity of F. graminearum mitochondrial SQR by up to 52%, but that the equivalent enzyme in P. indica was unaffected. A phylogenetic analysis of the SdhB family revealed a significant divergence between the Ascomycota and Basidiomycota. SQR is one of the key targets of antifungal agents and Mtk is therefore proposed as an environmentally sustainable and more selective alternative to chemical fungicides.
Lynch, Z. R., Schlenke, T. A., Morran, L. T. and de Roode, J. C. (2017). Ethanol confers differential protection against generalist and specialist parasitoids of Drosophila melanogaster. PLoS One 12(7): e0180182. PubMed ID: 28700600
As parasites coevolve with their hosts, they can evolve counter-defenses that render host immune responses ineffective. These counter-defenses are more likely to evolve in specialist parasites than generalist parasites; the latter face variable selection pressures between the different hosts they infect. Natural populations of Drosophila are commonly threatened by endoparasitoid wasps in the genus Leptopilina, including the specialist L. boulardi and the generalist L. heterotoma, and both wasp species can incapacitate the cellular immune response of D. melanogaster larvae. Given that ethanol tolerance is high in D. melanogaster and stronger in the specialist wasp than the generalist, whether fly larvae could use ethanol as an anti-parasite defense and whether its effectiveness would differ against the two wasp species was tested. Fly larvae benefited from eating ethanol-containing food during exposure to L. heterotoma; a two-fold decrease in parasitization intensity and a 24-fold increase in fly survival to adulthood were observed. Although host ethanol consumption did not affect L. boulardi parasitization rates or intensities, it led to a modest increase in fly survival. Thus, ethanol conferred stronger protection against the generalist wasp than the specialist. Overall, these results suggest that D. melanogaster larvae obtain protection from certain parasitoid wasp species through their mothers' innate oviposition preferences for ethanol-containing food sources.
Lee, J. E., Rayyan, M., Liao, A., Edery, I. and Pletcher, S. D. (2017). Acute dietary restriction acts via TOR, PP2A, and Myc signaling to boost innate immunity in Drosophila. Cell Rep 20(2): 479-490. PubMed ID: 28700947
Dietary restriction promotes health and longevity across taxa through mechanisms that are largely unknown. This study shows that acute yeast restriction significantly improves the ability of adult female Drosophila melanogaster to resist pathogenic bacterial infections through an immune pathway involving downregulation of target of rapamycin (TOR) signaling, which stabilizes the transcription factor Myc by increasing the steady-state level of its phosphorylated forms through decreased activity of protein phosphatase 2A. Upregulation of Myc through genetic and pharmacological means mimicked the effects of yeast restriction in fully fed flies, identifying Myc as a pro-immune molecule. Short-term dietary or pharmacological interventions that modulate TOR-PP2A-Myc signaling may provide an effective method to enhance immunity in vulnerable human populations.
Trienens, M., Kraaijeveld, K. and Wertheim, B. (2017). Defensive repertoire of Drosophila larvae in response to toxic fungi. Mol Ecol [Epub ahead of print]. PubMed ID: 28746736
Chemical warfare including insecticidal secondary metabolites is a well-known strategy for environmental microbes to monopolize a food source. Insects in turn have evolved behavioural and physiological defences to eradicate or neutralize the harmful microorganisms. This project examined the defensive repertoire of insects in interference competition. Confrontation with the toxic filamentous fungus Aspergillus nidulans severely reduced the survival of Drosophila melanogaster larvae. Nonetheless, the larvae did not behaviourally avoid the fungus, but aggregated at it. Confrontation with fungi strongly affected larval gene expression, including many genes involved in detoxification (e.g., CYP, GST and UGT genes) and the formation of the insect cuticle (e.g., Tweedle genes). The most strongly upregulated genes were several members of the insect-specific gene family Osiris, and CHK-kinase-like domains were over-represented. While internal microbes are widely acknowledged as important, this study emphasizes the underappreciated role of environmental microbes as fierce competitors.

Thursday, September 21st

Muzzopappa, M., Murcia, L. and Milan, M. (2017). Feedback amplification loop drives malignant growth in epithelial tissues. Proc Natl Acad Sci U S A. PubMed ID: 28808034
Interactions between cells bearing oncogenic mutations and the surrounding microenvironment, and cooperation between clonally distinct cell populations, can contribute to the growth and malignancy of epithelial tumors. The genetic techniques available in Drosophila have contributed to identify important roles of the TNF-alpha ligand Eiger and mitogenic molecules in mediating these interactions during the early steps of tumor formation. This study unraveled the existence of a tumor-intrinsic-and microenvironment-independent-self-reinforcement mechanism that drives tumor initiation and growth in an Eiger-independent manner. This mechanism relies on cell interactions between two functionally distinct cell populations, and evidence is presented that these cell populations are not necessarily genetically different. Tumor-specific and cell-autonomous activation of the tumorigenic JNK stress-activated pathway drives the expression of secreted signaling molecules and growth factors to delaminating cells, which nonautonomously promote proliferative growth of the partially transformed epithelial tissue. Evidence is presented that cross-feeding interactions between delaminating and nondelaminating cells increase each other's sizes and that these interactions can explain the unlimited growth potential of these tumors. These results will open avenues toward molecular understanding of those social cell interactions with a relevant function in tumor initiation in humans.
Miller, M., Chen, A., Gobert, V., Auge, B., Beau, M., Burlet-Schiltz, O., Haenlin, M. and Waltzer, L. (2017). Control of RUNX-induced repression of Notch signaling by MLF and its partner DnaJ-1 during Drosophila hematopoiesis. PLoS Genet 13(7): e1006932. PubMed ID: 28742844
In Drosophila, Myeloid Leukemia Factor (MLF) has been shown to control blood cell development by stabilizing the RUNX transcription factor Lozenge (Lz). This study further characterized MLF's mode of action in Drosophila blood cells using proteomic, transcriptomic and genetic approaches. The results show that MLF and the Hsp40 co-chaperone family member DnaJ-1 interact through conserved domains and demonstrate that both proteins bind and stabilize Lz in cell culture, suggesting that MLF and DnaJ-1 form a chaperone complex that directly regulates Lz activity. Importantly, dnaj-1 loss causes an increase in Lz+ blood cell number and size similarly as in mlf mutant larvae. Moreover dnaj-1 was found to genetically interact with mlf to control Lz level and Lz+ blood cell development in vivo. In addition, mlf and dnaj-1 loss was shown to alter Lz+ cell differentiation, and the increase in Lz+ blood cell number and size observed in these mutants is caused by an overactivation of the Notch signaling pathway. Finally, high levels of Lz were shown to be required to repress Notch transcription and signaling. These data indicate that the MLF/DnaJ-1-dependent increase in Lz level allows the repression of Notch expression and signaling to prevent aberrant blood cell development. Thus these findings establish a functional link between MLF and the co-chaperone DnaJ-1 to control RUNX transcription factor activity and Notch signaling during blood cell development in vivo.
Saadaoui, M., Konno, D., Loulier, K., Goiame, R., Jadhav, V., Mapelli, M., Matsuzaki, F. and Morin, X. (2017). Loss of the canonical spindle orientation function in the Pins/LGN homolog AGS3. EMBO Rep [Epub ahead of print]. PubMed ID: 28684399
In many cell types, mitotic spindle orientation relies on the canonical "LGN complex" composed of Pins/LGN, Mud/NuMA, and Gαi subunits. Membrane localization of this complex recruits motor force generators that pull on astral microtubules to orient the spindle. Drosophila Pins shares highly conserved functional domains with its two vertebrate homologs LGN and AGS3. Whereas the role of Pins and LGN in oriented divisions is extensively documented, involvement of AGS3 remains controversial. This study shows that AGS3 is not required for planar divisions of neural progenitors in the mouse neocortex. AGS3 is not recruited to the cell cortex and does not rescue LGN loss of function. Despite conserved interactions with NuMA and Gαi in vitro, comparison of LGN and AGS3 functional domains in vivo reveals unexpected differences in the ability of these interactions to mediate spindle orientation functions. Finally, Drosophila Pins was found to be is unable to substitute for LGN loss of function in vertebrates, highlighting that species-specific modulations of the interactions between components of the Pins/LGN complex are crucial in vivo for spindle orientation.
Matsushima, Y., Hirofuji, Y., Aihara, M., Yue, S., Uchiumi, T., Kaguni, L. S. and Kang, D. (2017). Drosophila protease ClpXP specifically degrades DmLRPPRC1 controlling mitochondrial mRNA and translation. Sci Rep 7(1): 8315. PubMed ID: 28814717
ClpXP is the major protease in the mitochondrial matrix in eukaryotes, and is well conserved among species. ClpXP is composed of a proteolytic subunit, ClpP, and a chaperone-like subunit, ClpX. Although it has been proposed that ClpXP is required for the mitochondrial unfolded protein response, additional roles for ClpXP in mitochondrial biogenesis are unclear. This study found that Drosophila leucine-rich pentatricopeptide repeat domain-containing protein 1 (DmLRPPRC1) is a specific substrate of ClpXP. Depletion or introduction of catalytically inactive mutation of ClpP increases DmLRPPRC1 and causes non-uniform increases of mitochondrial mRNAs, accumulation of some unprocessed mitochondrial transcripts, and modest repression of mitochondrial translation in Drosophila Schneider S2 cells. Moreover, DmLRPPRC1 over-expression induces the phenotypes similar to those observed when ClpP is depleted. Taken together, ClpXP regulates mitochondrial gene expression by changing the protein level of DmLRPPRC1 in Drosophila Schneider S2 cells.

Wednesday, September 20th

Lei, Y., Liu, K., Hou, L., Ding, L., Li, Y. and Liu, L. (2017). Small chaperons and autophagy protected neurons from necrotic cell death. Sci Rep 7(1): 5650. PubMed ID: 28720827
Neuronal necrosis occurs during early phase of ischemic insult. However, knowledge of neuronal necrosis is still inadequate. To study the mechanism of neuronal necrosis, a Drosophila genetic model has been established of neuronal necrosis by calcium overloading through expression of a constitutively opened cation channel mutant. Further genetic screens have been performed, and a suppressor of neuronal necrosis, CG17259, has been identified that encodes a seryl-tRNA synthetase. Loss-of-function (LOF) CG17259 activated eIF2alpha phosphorylation and subsequent up-regulation of chaperons (Hsp26 and Hsp27) and autophagy. Genetically, down-regulation of eIF2alpha phosphorylation, Hsp26/Hsp27 or autophagy reduced the protective effect of LOF CG17259, indicating they function downstream of CG17259. The protective effect of these protein degradation pathways indicated activation of a toxic protein during neuronal necrosis. The data indicated that p53 was likely one such protein, because p53 was accumulated in the necrotic neurons and down-regulation of p53 rescued necrosis. In the SH-SY5Y human cells, tunicamycin (TM), a PERK activator, promoted transcription of hsp27; and necrosis induced by glutamate could be rescued by TM, associated with reduced p53 accumulation. In an ischemic stroke model in rats, p53 protein was also increased, and TM treatment could reduce the p53 accumulation and brain damage.
Choutka, C., DeVorkin, L., Go, N. E., Hou, Y. C., Moradian, A., Morin, G. B. and Gorski, S. M. (2017). Hsp83 loss suppresses proteasomal activity resulting in an upregulation of caspase-dependent compensatory autophagy. Autophagy: 1-17. PubMed ID: 28806103
The two main degradative pathways that contribute to proteostasis are the ubiquitin-proteasome system and autophagy but how they are molecularly coordinated is not well understood. This study demonstrates an essential role for an effector caspase in the activation of compensatory autophagy when proteasomal activity is compromised. Functional loss of Hsp83, the Drosophila ortholog of human HSP90 (heat shock protein 90), resulted in reduced proteasomal activity and elevated levels of the effector caspase Dcp-1. Surprisingly, genetic analyses showed that the caspase was not required for cell death in this context, but instead was essential for the ensuing compensatory autophagy, female fertility, and organism viability. The zymogen pro-Dcp-1 was found to interact with Hsp83 and undergo proteasomal regulation in an Hsp83-dependent manner. This work not only reveals unappreciated roles for Hsp83 in proteasomal activity and regulation of Dcp-1, but identifies an effector caspase as a key regulatory factor for sustaining adaptation to cell stress in vivo.
Neukomm, L. J., Burdett, T. C., Seeds, A. M., Hampel, S., Coutinho-Budd, J. C., Farley, J. E., Wong, J., Karadeniz, Y. B., Osterloh, J. M., Sheehan, A. E. and Freeman, M. R. (2017). Axon death pathways converge on Axundead to promote functional and structural axon disassembly. Neuron 95(1): 78-91.e75. PubMed ID: 28683272
Axon degeneration is a hallmark of neurodegenerative disease and neural injury. Axotomy activates an intrinsic pro-degenerative axon death signaling cascade involving loss of the NAD+ biosynthetic enzyme Nmnat/Nmnat2 in axons, activation of dSarm/Sarm1, and subsequent Sarm-dependent depletion of NAD+. This study has identified Axundead (Axed) as a mediator of axon death. axed mutants suppress axon death in several types of axons for the lifespan of the fly and block the pro-degenerative effects of activated dSarm in vivo. Neurodegeneration induced by loss of the sole fly Nmnat ortholog is also fully blocked by axed, but not dsarm, mutants. Thus, pro-degenerative pathways activated by dSarm signaling or Nmnat elimination ultimately converge on Axed. Remarkably, severed axons morphologically preserved by axon death pathway mutations remain integrated in circuits and able to elicit complex behaviors after stimulation, indicating that blockade of axon death signaling results in long-term functional preservation of axons.
Ren, P., Li, W. and Xue, L. (2017). GLYAT regulates JNK-mediated cell death in Drosophila. Sci Rep 7(1): 5183. PubMed ID: 28701716
Cell death is a fundamental progress that regulates cell number, tissue homeostasis and organ size in development. The c-Jun N-terminal kinase (JNK) pathway has been evolutionarily conserved from fly to human, and plays essential roles in regulating cell death. To characterize additional genes that regulate JNK signaling, a genetic screen was performed in Drosophila and dGLYAT (CG34010), a novel gene whose function was previously unknown, was identified as a modulator of JNK-mediated cell death. Loss of dGLYAT suppressed JNK activation and cell death triggered by over-expression of Eiger or Hemipterous, or depletion of puckered or lgl in development, suggesting dGLYAT regulates both ectopic and physiological functions of JNK pathway. Furthermore, loss of dGLYAT was shown to inhibit JNK-mediated ROS production, suggesting dGLYAT regulates multiple functions of JNK signaling in vivo.

Tuesday, September 19th

Monsanto-Hearne, V., Asad, S., Asgari, S. and Johnson, K. N. (2017). Drosophila microRNA modulates viral replication by targeting a homologue of mammalian cJun. J Gen Virol [Epub ahead of print]. PubMed ID: 28691661
MicroRNAs (miRNAs) are important regulators of biological processes, including host-virus interaction. This study investigated the involvement of Drosophila miR-8-5p in host-virus interaction. Drosophila flies and cells challenged with Drosophila C virus (DCV) were found to have lower miR-8-5p abundance compared to uninfected samples. Lowering miR-8-5p abundance by experimental inhibition of the miRNA led to an increase in viral accumulation, suggesting that the observed decrease in the miR-8-5p abundance during DCV infection enhances viral replication. miR-8-5p putative targets were identified and included dJun. Increasing miR-8-5p abundance using miR-8-5p mimics resulted in a decrease in dJun and GFP reporter levels. Furthermore, when the putative target in dJun was mutated, addition of miR-8-5p mimics did not result in the same antagonistic effect on dJun. These results show negative regulation of dJun by miR-8-5p and suggest that an miRNA-mediated pathway is involved in dJun regulation during viral infection. To analyse the role of dJun during DCV infection, dJun was knocked down in cells prior to DCV infection. Knockdown of dJun decreased DCV replication, providing evidence that dJun up-regulation that is concomitant with miR-8-5p down-regulation during DCV infection supports viral replication. These results highlight the role of miRNA in regulating the transcription factor gene dJun and uncover a previously unrecognized mechanism by which dJun is regulated during host-virus interaction.
Chen, T. and van Steensel, B. (2017). Comprehensive analysis of nucleocytoplasmic dynamics of mRNA in Drosophila cells. PLoS Genet 13(8): e1006929. PubMed ID: 28771467
Eukaryotic mRNAs undergo a cycle of transcription, nuclear export, and degradation. A major challenge is to obtain a global, quantitative view of these processes. This study measured the genome-wide nucleocytoplasmic dynamics of mRNA in Drosophila cells by metabolic labeling in combination with cellular fractionation. By mathematical modeling of these data rates of transcription, export and cytoplasmic decay were determined for 5420 genes. These kinetic rates were characterized and investigated links with mRNA features, RNA-binding proteins (RBPs) and chromatin states were investigated. Prominent correlations were found between mRNA decay rate and transcript size, while nuclear export rates are linked to the size of the 3'UTR. Transcription, export and decay rates are each associated with distinct spectra of RBPs. Specific classes of genes, such as those encoding cytoplasmic ribosomal proteins, exhibit characteristic combinations of rate constants, suggesting modular control. Binding of splicing factors is associated with faster rates of export, and the data suggest coordinated regulation of nuclear export of specific functional classes of genes. Finally, correlations between rate constants suggest global coordination between the three processes. This approach provides insights into the genome-wide nucleocytoplasmic kinetics of mRNA and should be generally applicable to other cell systems.
Foo, L. C. (2017). Cyclin-dependent kinase 9 is required for the survival of adult Drosophila melanogaster glia. Sci Rep 7(1): 6796. PubMed ID: 28754981
Neuronal and glial progenitor cells exist in the adult Drosophila brain. The primarily glial progenitor cells rely on a microRNA, mir-31a, to inhibit the expression of a predicted E3 ubiquitin ligase, CG16947. Erroneous inheritance of CG16947 by the progeny when the neural progenitor cell divides leads to death of the progeny, however how CG16947 achieves glial cell death is unknown. This study has identified the interacting partner of CG16947 to be Cdk9. Reduction of cdk9 expression in glia causes glial loss; highlighting the importance of cdk9 in mediating the survival of glia. Further, glial loss observed in mir-31a mutants was prevented with adult-specific expression of cdk9 in glia. Biochemical evidence is provided that the binding of CG16947 to Cdk9 causes its degradation. Taken together, this data shows that cdk9 plays a role in the survival of adult glia in the Drosophila brain. Thus, a fine balance exists between mir-31a and CG16947 expression in the progenitor cells that in turn regulates the levels of cdk9 in the progeny. This serves to allow the progenitor cells to regulate the number of glia in the adult brain.
Gotze, M., Dufourt, J., Ihling, C., Rammelt, C., Pierson, S., Sambrani, N., Temme, C., Sinz, A., Simonelig, M. and Wahle, E. (2017). Translational repression of the Drosophila nanos mRNA involves the RNA helicase Belle and RNA coating by Me31B and Trailer hitch. RNA [Epub ahead of print]. PubMed ID: 28701521
Translational repression of maternal mRNAs is an essential regulatory mechanism during early embryonic development. Repression of the Drosophila nanos mRNA, required for the formation of the anterior-posterior body axis, depends on the protein Smaug binding to two Smaug recognition elements (SREs) in the nanos 3' UTR. In a comprehensive mass-spectrometric analysis of the SRE-dependent repressor complex, Smaug, Cup, Me31B, Trailer hitch, eIF4E and PABPC were identified, in agreement with earlier data. As a novel component, the RNA-dependent ATPase Belle (DDX3) was found, and its involvement in deadenylation and repression of nanos was confirmed in vivo. Smaug, Cup and Belle bound stoichiometrically to the SREs, independently of RNA length. Binding of Me31B and Tral was also SRE-dependent, but their amounts were proportional to the length of the RNA and equimolar to each other. It is suggested that 'coating' of the RNA by a Me31B*Tral complex may be at the core of repression.

Monday, June 18th

Makhijani, K., Alexander, B., Rao, D., Petraki, S., Herboso, L., Kukar, K., Batool, I., Wachner, S., Gold, K. S., Wong, C., O'Connor, M. B. and Bruckner, K. (2017). Regulation of Drosophila hematopoietic sites by Activin-beta from active sensory neurons. Nat Commun 8: 15990. PubMed ID: 28748922
An outstanding question in animal development, tissue homeostasis and disease is how cell populations adapt to sensory inputs. During Drosophila larval development, hematopoietic sites are in direct contact with sensory neuron clusters of the peripheral nervous system (PNS), and blood cells (hemocytes) require the PNS for their survival and recruitment to these microenvironments, known as Hematopoietic Pockets. This study reports that Activin-β, a TGF-beta family ligand, is expressed by sensory neurons of the PNS and regulates the proliferation and adhesion of hemocytes. These hemocyte responses depend on PNS activity, as shown by agonist treatment and transient silencing of sensory neurons. Activin-β has a key role in this regulation, which is apparent from reporter expression and mutant analyses. This mechanism of local sensory neurons controlling blood cell adaptation invites evolutionary parallels with vertebrate hematopoietic progenitors and the independent myeloid system of tissue macrophages, whose regulation by local microenvironments remain undefined.
Kuleesha, Feng, L. and Wasser, M. (2017). Spatial pattern analysis of nuclear migration in remodelled muscles during Drosophila metamorphosis. BMC Bioinformatics 18(1): 329. PubMed ID: 28693471
During metamorphosis in Drosophila, multi-nucleated larval dorsal abdominal muscles either undergo cell death or are remodeled to temporary adult muscles. Muscle remodeling is associated with anti-polar nuclear migration and atrophy during early pupation followed by polar migration and muscle growth during late pupation. Loss of Cathepsin-L has been shown to inhibit anti-polar movements, while knockdown of autophagy-related genes affected nuclear positioning along the medial axis in late metamorphosis. This study has developed new descriptors of myonuclear distribution. Nuclear tracks were used to distinguish between fast moving nuclei associated with fragments of dead muscles (sarcolytes) and slow-moving nuclei inside remodelled muscles. Anti-polar migration leads to a longitudinal nuclear spread decrease. Unexpectedly, the decrease in longitudinal nuclear spread was significantly enhanced by Atg9, Atg5 and Atg18 silencing, indicating that the loss of autophagy promotes the migration and clustering of nuclei. In vivo imaging and quantitative image analysis of Drosophila metamorphosis promise to provide novel insights into the relationship between muscle wasting and myonuclear positioning.
Ku, H. Y. and Sun, Y. H. (2017). Notch-dependent epithelial fold determines boundary formation between developmental fields in the Drosophila antenna. PLoS Genet 13(7): e1006898. PubMed ID: 28708823
Compartment boundary formation plays an important role in development by separating adjacent developmental fields. Drosophila imaginal discs have proven valuable for studying the mechanisms of boundary formation. This study examined the boundary separating the proximal A1 segment and the distal segments, defined respectively by Lim1 and Dll expression in the eye-antenna disc. Sharp segregation of the Lim1 and Dll expression domains precedes activation of Notch at the Dll/Lim1 interface. By repressing bantam miRNA and elevating the actin regulator Enabled, Notch signaling then induces actomyosin-dependent apical constriction and epithelial fold. Disruption of Notch signaling or the actomyosin network reduces apical constriction and epithelial fold, so that Dll and Lim1 cells become intermingled. These results demonstrate a new mechanism of boundary formation by actomyosin-dependent tissue folding, which provides a physical barrier to prevent mixing of cells from adjacent developmental fields.
Martin, M., Ostale, C. M. and de Celis, J. F. (2017). Patterning of the Drosophila L2 vein is driven by regulatory interactions between region-specific transcription factors expressed in response to Dpp signalling. Development [Epub ahead of print]. PubMed ID: 28760811
Pattern formation relies on the generation of transcriptional landscapes regulated by signalling pathways. A paradigm of epithelial patterning is the distribution of vein territories in the Drosophila wing disc. In this tissue, Decapentaplegic signalling regulates its target genes at different distances from the source of the ligand. The transformation of signalling into coherent territories of gene expression requires regulatory cross-interactions between these target genes. This study analysed the mechanisms generating the domain of knirps expression in the presumptive L2 vein of the wing imaginal disc. knirps is regulated by four Decapentaplegic target genes encoding transcription factors: aristaless, spalt mayor, spalt related and optix. The expression of optix is activated by Dpp and repressed by the Spalt proteins, becoming restricted to the most anterior region of the wing blade. In turn, the expression of knirps is activated by Aristaless and repressed by Optix and the Spalt proteins. In this manner, the expression of Knirps became restricted to those cells where Spalt levels are sufficient to repress optix, but not sufficient to repress knirps.

Saturday, September 16th

Keesey, I. W., Koerte, S., Khallaf, M. A., Retzke, T., Guillou, A., Grosse-Wilde, E., Buchon, N., Knaden, M. and Hansson, B. S. (2017). Pathogenic bacteria enhance dispersal through alteration of Drosophila social communication. Nat Commun 8(1): 265. PubMed ID: 28814724
Pathogens and parasites can manipulate their hosts to optimize their own fitness. For instance, bacterial pathogens have been shown to affect their host plants' volatile and non-volatile metabolites, which results in increased attraction of insect vectors to the plant, and, hence, to increased pathogen dispersal. Behavioral manipulation by parasites has also been shown for mice, snails and zebrafish as well as for insects. This study shows that infection by pathogenic bacteria alters the social communication system of Drosophila melanogaster. More specifically, infected flies and their frass emit dramatically increased amounts of fly odors, including the aggregation pheromones methyl laurate, methyl myristate, and methyl palmitate, attracting healthy flies, which in turn become infected and further enhance pathogen dispersal. Thus, olfactory cues for attraction and aggregation are vulnerable to pathogenic manipulation, and the alteration of social pheromones can be beneficial to the microbe while detrimental to the insect host. Behavioral manipulation of host by pathogens has been observed in vertebrates, invertebrates, and plants. This study shows that in Drosophila, infection with pathogenic bacteria leads to increased pheromone release, which attracts healthy flies. This process benefits the pathogen since it enhances bacterial dispersal, but is detrimental to the host.
Kim, I. S. and Dickinson, M. H. (2017). Idiothetic path Integration in the fruit fly Drosophila melanogaster. Curr Biol 27(15): 2227-2238.e2223. PubMed ID: 28736164
After discovering a small drop of food, hungry flies exhibit a peculiar behavior in which they repeatedly stray from, but then return to, the newly discovered resource. To study this behavior in more detail, hungry Drosophila were tracked as they explored a large arena, focusing on the question of how flies remain near the food. To determine whether flies use external stimuli, visual, olfactory, and pheromonal cues were individually eliminated. In all cases, flies still exhibited a centralized search behavior, suggesting that none of these cues are absolutely required for navigation back to the food. To simultaneously eliminate visual and olfactory cues associated with the position of the food, an apparatus was constructed in which the food could be rapidly translated from the center of the arena. Flies continued to search around the original location, even after the food was moved to a new position. A random search model based on measured locomotor statistics could not reproduce the centered nature of the animal's trajectory. It is concluded that this behavior is best explained by a form of path integration in which the flies use idiothetic cues to search near the location of the food. It is argued that the use of path integration to perform a centered local search is not a specialization of Drosophila but rather represents an ancient behavioral mode that is homologous to the more elaborate foraging strategies of central place foragers such as ants.
Le Page, S., Sepil, I., Flintham, E., Pizzari, T., Carazo, P. and Wigby, S. (2017). Male relatedness and familiarity are required to modulate male-induced harm to females in Drosophila. Proc Biol Sci 284(1860). PubMed ID: 28794215
Males compete over mating and fertilization, and often harm females in the process. Inclusive fitness theory predicts that increasing relatedness within groups of males may relax competition and discourage male harm of females as males gain indirect benefits. Recent studies in Drosophila melanogaster are consistent with these predictions, and have found that within-group male relatedness increases female fitness, though others have found no effects. Importantly, these studies did not fully disentangle male genetic relatedness from larval familiarity, so the extent to which modulation of harm to females is explained by male familiarity remains unclear. This study performed a fully factorial design, isolating the effects of male relatedness and larval familiarity on female harm. While no differences were found in male courtship or aggression, there was a significant interaction between male genetic relatedness and familiarity on female reproduction and survival. Relatedness among males increased female lifespan, reproductive lifespan and overall reproductive success, but only when males were familiar. By showing that both male relatedness and larval familiarity are required to modulate female harm, these findings reconcile previous studies, shedding light on the potential role of indirect fitness effects on sexual conflict and the mechanisms underpinning kin recognition in fly populations.
Martelli, C., Pech, U., Kobbenbring, S., Pauls, D., Bahl, B., Sommer, M. V., Pooryasin, A., Barth, J., Arias, C. W. P., Vassiliou, C., Luna, A. J. F., Poppinga, H., Richter, F. G., Wegener, C., Fiala, A. and Riemensperger, T. (2017). SIFamide translates hunger signals into appetitive and feeding behavior in Drosophila. Cell Rep 20(2): 464-478. PubMed ID: 28700946
Animal behavior is, on the one hand, controlled by neuronal circuits that integrate external sensory stimuli and induce appropriate motor responses. On the other hand, stimulus-evoked or internally generated behavior can be influenced by motivational conditions, e.g., the metabolic state. Motivational states are determined by physiological parameters whose homeostatic imbalances are signaled to and processed within the brain, often mediated by modulatory peptides. This study investigate the regulation of appetitive and feeding behavior in the fruit fly, Drosophila melanogaster. Four neurons in the fly brain that release SIFamide were found to be integral elements of a complex neuropeptide network that regulates feeding. SIFamidergic cells integrate feeding stimulating (orexigenic) and feeding suppressant (anorexigenic) signals to appropriately sensitize sensory circuits, promote appetitive behavior, and enhance food intake. This study advances the cellular dissection of evolutionarily conserved signaling pathways that convert peripheral metabolic signals into feeding-related behavior.

Friday, September 15th

Li, Q., Tjong, H., Li, X., Gong, K., Zhou, X. J., Chiolo, I. and Alber, F. (2017). The three-dimensional genome organization of Drosophila melanogaster through data integration. JGenome Biol 18(1): 145. PubMed ID: 28760140
Genome structures are dynamic and non-randomly organized in the nucleus of higher eukaryotes. To maximize the accuracy and coverage of three-dimensional genome structural models, it is important to integrate all available sources of experimental information about a genome's organization. It remains a major challenge to integrate such data from various complementary experimental methods. This study presents an approach for data integration to determine a population of complete three-dimensional genome structures that are statistically consistent with data from both genome-wide chromosome conformation capture (Hi-C) and lamina-DamID experiments. The structures defined in this paper resolve the genome at the resolution of topological domains, and reproduce simultaneously both sets of experimental data. Importantly, this data deconvolution framework allows for structural heterogeneity between cells, and hence accounts for the expected plasticity of genome structures. As a case study, Drosophila melanogaster embryonic cells, for which both data types are available, were chosen. Three-dimensional genome structures have strong predictive power for structural features not directly visible in the initial data sets, and reproduce experimental hallmarks of the D. melanogaster genome organization from previous and current imaging experiments. Also they reveal a number of new insights about genome organization and its functional relevance, including the preferred locations of heterochromatic satellites of different chromosomes, and observations about homologous pairing that cannot be directly observed in the original Hi-C or lamina-DamID data. This approach allows systematic integration of Hi-C and lamina-DamID data for complete three-dimensional genome structure calculation, while also explicitly considering genome structural variability.
Li, W., Yi, J., Agbu, P., Zhou, Z., Kelley, R. L., Kallgren, S., Jia, S. and He, X. (2017). Replication stress affects the fidelity of nucleosome-mediated epigenetic inheritance. PLoS Genet 13(7): e1006900. PubMed ID: 28749973
The fidelity of epigenetic inheritance or, the precision by which epigenetic information is passed along, is an essential parameter for measuring the effectiveness of the process. How the precision of the process is achieved or modulated, however, remains largely elusive. This study performed quantitative measurement of epigenetic fidelity, using position effect variegation (PEV) in Schizosaccharomyces pombe as readout, to explore whether replication perturbation affects nucleosome-mediated epigenetic inheritance. Replication stresses, due to either hydroxyurea treatment or various forms of genetic lesions of the replication machinery, were shown to reduce the inheritance accuracy of CENP-A/Cnp1 (see Drosophila Centromere identifier) nucleosome positioning within centromere. Mechanistically, it was demonstrated that excessive formation of single-stranded DNA, a common molecular abnormality under these conditions, might have correlation with the reduction in fidelity of centromeric chromatin duplication. Furthermore, this study showed that replication stress broadly changes chromatin structure at various loci in the genome, such as telomere heterochromatin expanding and mating type locus heterochromatin spreading out of the boundaries. Interestingly, the levels of inheritable expanding at sub-telomeric heterochromatin regions are highly variable among independent cell populations. Finally, this study showed that HU treatment of the multi-cellular organisms C. elegans and D. melanogaster affects epigenetically programmed development and PEV, illustrating the evolutionary conservation of the phenomenon. Replication stress, in addition to its demonstrated role in genetic instability, promotes variable epigenetic instability throughout the epigenome.
Lee, Y. C. G. and Karpen, G. H. (2017). Pervasive epigenetic effects of Drosophila euchromatic transposable elements impact their evolution. Elife 6. PubMed ID: 28695823
Transposable elements (TEs) are widespread genomic parasites, and their evolution has remained a critical question in evolutionary genomics. This paper describes a study of the relatively unexplored epigenetic impacts of TEs and provides the first genome-wide quantification of such effects in D. melanogaster and D. simulans. Surprisingly, the spread of repressive epigenetic marks (histone H3K9me2) to nearby DNA occurs at >50% of euchromatic TEs, and can extend up to 20 kb. This results in differential epigenetic states of genic alleles and, in turn, selection against TEs. Interestingly, the lower TE content in D. simulans compared to D. melanogaster correlates with stronger epigenetic effects of TEs and higher levels of host genetic factors known to promote epigenetic silencing. This study demonstrates that the epigenetic effects of euchromatic TEs, and host genetic factors modulating such effects, play a critical role in the evolution of TEs both within and between species.
Eagen, K. P., Aiden, E. L. and Kornberg, R. D. (2017). Polycomb-mediated chromatin loops revealed by a subkilobase-resolution chromatin interaction map. Proc Natl Acad Sci U S A 114(33): 8764-8769. PubMed ID: 28765367
The locations of chromatin loops in Drosophila were determined by Hi-C (chemical cross-linking, restriction digestion, ligation, and high-throughput DNA sequencing). Whereas most loop boundaries or 'anchors' are associated with CTCF protein in mammals, loop anchors in Drosophila were found most often in association with the polycomb group (PcG) protein Polycomb (Pc), a subunit of polycomb repressive complex 1 (PRC1). Loops were frequently located within domains of PcG-repressed chromatin. Promoters located at PRC1 loop anchors regulate some of the most important developmental genes and are less likely to be expressed than those not at PRC1 loop anchors. Although DNA looping has most commonly been associated with enhancer-promoter communication, the results indicate that loops are also associated with gene repression.

Thursday, September 14th

Hinnant, T. D., Alvarez, A. A. and Ables, E. T. (2017). Temporal remodeling of the cell cycle accompanies differentiation in the Drosophila germline. Dev Biol 429(1): 118-131. PubMed ID: 28711427
During Drosophila oogenesis, mature oocytes are created through a series of precisely controlled division and differentiation steps, originating from a single tissue-specific stem cell. To describe how the cell cycle is remodeled in germ cells as they differentiate in situ, the Drosophila Fluorescence Ubiquitin-based Cell Cycle Indicator (Fly-FUCCI) system was used, in which degradable versions of GFP::E2f1 and RFP::CycB fluorescently label cells in each phase of the cell cycle. The lengths of the G1, S, and G2 phases of the cell cycle were found to change dramatically over the course of differentiation, and the 4/8-cell cyst was identified as a key developmental transition state in which cells prepare for specialized cell cycles. The data suggest that the transcriptional activator E2f1, which controls the transition from G1 to S phase, is a key regulator of mitotic divisions in the early germline. These data support the model that E2f1 is necessary for proper GSC proliferation, self-renewal, and daughter cell development. In contrast, while E2f1 degradation by the Cullin 4 (Cul4)-containing ubiquitin E3 ligase (CRL4) is essential for developmental transitions in the early germline, the data do not support a role for E2f1 degradation as a mechanism to limit GSC proliferation or self-renewal. Taken together, these findings provide further insight into the regulation of cell proliferation and the acquisition of differentiated cell fate, with broad implications across developing tissues.
Yang, S. Y., Chang, Y. C., Wan, Y. H., Whitworth, C., Baxter, E. M., Primus, S., Pi, H. and Van Doren, M. (2017). Control of a novel spermatocyte-promoting factor by the male germline sex determination factor PHF7 of Drosophila melanogaster. Genetics [Epub ahead of print]. PubMed ID: 28588035
A key aspect of germ cell development is to establish germline sexual identity and initiate a sex-specific developmental program to promote spermatogenesis or oogenesis. The histone reader Plant Homeodomain Finger 7 (PHF7) has been identified as an important regulator of male germline identity. To understand how PHF7 directs sexual differentiation of the male germline, this study investigated the downstream targets of PHF7 by combining transcriptome analyses, which reveal genes regulated by Phf7, with genomic profiling of histone H3K4me2, the chromatin mark that is bound by PHF7. Through these genomic experiments, a novel spermatocyte factor Receptor Accessory Protein Like 1 (REEPL1) was identified that can promote spermatogenesis and whose expression is kept off by PHF7 in the spermatogonial stage. Loss of Reepl1 significantly rescues the spermatogenesis defects in Phf7 mutants, indicating that regulation of Reepl1 is an essential aspect of PHF7 function. Further, increasing REEPL1 expression facilitates spermatogenic differentiation. These results indicate that PHF7 controls spermatogenesis by regulating the expression patterns of important male germline genes.
LeBlanc, M. G. and Lehmann, R. (2017). Domain-specific control of germ cell polarity and migration by multifunction Tre1 GPCR. J Cell Biol [Epub ahead of print]. PubMed ID: 28687666
The migration of primordial germ cells (PGCs) from their place of origin to the embryonic gonad is an essential reproductive feature in many animal species. In Drosophila melanogaster, a single G protein-coupled receptor, Trapped in endoderm 1 (Tre1), mediates germ cell polarization at the onset of active migration and directs subsequent migration of PGCs through the midgut primordium. How these different aspects of cell behavior are coordinated through a single receptor is not known. This study demonstrates that two highly conserved domains, the E/N/DRY and NPxxY motifs, have overlapping and unique functions in Tre1. The Tre1-NRY domain via G protein signaling is required for reading and responding to guidance and survival cues controlled by the lipid phosphate phosphatases Wunen and Wunen2. In contrast, the Tre1-NPIIY domain has a separate role in Rho1- and E-cadherin-mediated polarization at the initiation stage independent of G protein signaling. It is proposed that this bifurcation of the Tre1 G protein-coupled receptor signaling response via G protein-dependent and independent branches enables distinct spatiotemporal regulation of germ cell migration.
Couderc, J. L., Richard, G., Vachias, C. and Mirouse, V. (2017). Drosophila LKB1 is required for the assembly of the polarized actin structure that allows spermatid individualization. PLoS One 12(8): e0182279. PubMed ID: 28767695
In mammals, a testis-specific isoform of the protein kinase LKB1 is required for spermiogenesis, but its exact function and specificity are not known. Human LKB1 rescues the functions of Drosophila Lkb1 essential for viability, but these males are sterile, revealing a new function for this genes in fly. A testis-specific transcript was identified, generated by an alternative promoter; it only differs by a longer 5'UTR. dLKB1 is required in the germline for the formation of the actin cone, the polarized structure that allows spermatid individualization and cytoplasm excess extrusion during spermiogenesis. Three of the nine LKB1 classical targets in the Drosophila genome (AMPK, NUAK and KP78b) are required for proper spermiogenesis, but later than dLKB1. dLkb1 mutant phenotype is reminiscent of that of myosin V mutants, and both proteins show a dynamic localization profile before actin cone formation. Together, these data highlight a new dLKB1 function and suggest that dLKB1 posttranscriptional regulation in testis and involvement in spermatid morphogenesis are evolutionarily conserved features.

Wednesday, September 13th

Kreko-Pierce, T. and Eaton, B. A. (2017). The Drosophila LC8 homologue Cut-up specifies the axonal transport of proteasomes. J Cell Sci [Epub ahead of print]. PubMed ID: 28808087
Because of their functional polarity and elongated morphologies, microtubule-based transport of proteins and organelles is critical for normal neuronal function. The proteasome is required throughout the neuron for the highly regulated degradation of a broad set of protein targets whose functions underlie key physiological responses including synaptic plasticity and axonal degeneration. Molecularly, the relationship between proteasome transport and the transport of the targets of proteasomes is unclear. The dynein motor complex is required for the microtubule-based motility of numerous proteins and organelles in neurons. This study demonstrates that microtubule-based transport of proteasomes within the neuron utilizes a distinct dynein light chain compared to synaptic proteins. Live imaging of proteasomes and synaptic vesicle proteins in axons and synapses finds that these cargoes traffic independently and that proteasomes exhibit significantly reduced retrograde transport velocities compared to synaptic vesicle proteins. Genetic and biochemical analyses reveals that the Drosophila homologue of the LC8 dynein light chain Cut-up binds proteasomes and functions specifically during their transport. These data support the model that Cut-up functions to specify the dynein-mediated transport of neuronal proteasomes.
Dewey, E. B. and Johnston, C. A. (2017). Diverse mitotic functions of the cytoskeletal crosslinking protein Shortstop suggest a role in Dynein/Dynactin activity. Mol Biol Cell [Epub ahead of print]. PubMed ID: 28747439
Proper assembly and orientation of the bipolar mitotic spindle is critical to the fidelity of cell division. Mitotic precision fundamentally contributes to cell fate specification, tissue development and homeostasis, and chromosome distribution within daughter cells. Defects in these events is thought to contribute to several human diseases. The underlying mechanisms that function in spindle morphogenesis and positioning remain incompletely defined, however. This study describes diverse roles for the actin-microtubule crosslinker, Shortstop (Shot), in mitotic spindle function in Drosophila Shot localizes to mitotic spindle poles and its knockdown results in an unfocused spindle pole morphology and a disruption of proper spindle orientation. Loss of Shot also leads to chromosome congression defects, cell cycle progression delay, and defective chromosome segregation during anaphase. These mitotic errors trigger apoptosis in Drosophila epithelial tissue, and blocking this apoptotic response results in a marked induction of the EMT marker MMP-1. The Actin-binding domain of Shot directly interacts with Actin-related protein-1 (Arp-1), a key component of the Dynein/Dynactin complex. Knockdown of Arp-1 phenocopies Shot loss universally, whereas chemical disruption of F-actin does so selectively. This work highlights novel roles for Shot in mitosis and suggests a mechanism involving Dynein/Dynactin activation.
Ding, Z. Y., Wang, Y. H., Huang, Y. C., Lee, M. C., Tseng, M. J., Chi, Y. H. and Huang, M. L. (2017). Outer nuclear membrane protein Kuduk modulates the LINC complex and nuclear envelope architecture. J Cell Biol [Epub ahead of print]. PubMed ID: 28716842
Linker of nucleoskeleton and cytoskeleton (LINC) complexes spanning the nuclear envelope (NE) contribute to nucleocytoskeletal force transduction. A few NE proteins have been found to regulate the LINC complex. This study identified one, Kuduk (Kud), which can reside at the outer nuclear membrane and is required for the development of Drosophila melanogaster ovarian follicles and NE morphology of myonuclei. Kud associates with LINC complex components in an evolutionarily conserved manner. Loss of Kud increases the level but impairs functioning of the LINC complex. Overexpression of Kud suppresses NE targeting of cytoskeleton-free LINC complexes. Thus, Kud acts as a quality control mechanism for LINC-mediated nucleocytoskeletal connections. Genetic data indicate that Kud also functions independently of the LINC complex. Overexpression of the human orthologue TMEM258 in Drosophila proved functional conservation. These findings expand understanding of the regulation of LINC complexes and NE architecture.
Hiraiwa, T., Kuranaga, E. and Shibata, T. (2017). Wave propagation of junctional remodeling in collective cell movement of epithelial tissue: Numerical simulation study. Front Cell Dev Biol 5: 66. PubMed ID: 28770197
During animal development, epithelial cells forming a monolayer sheet move collectively to achieve the morphogenesis of epithelial tissues. One driving mechanism of such collective cell movement is junctional remodeling, which is found in the process of clockwise rotation of Drosophila male terminalia during metamorphosis. However, it still remains unknown how the motions of cells are spatiotemporally organized for collective movement by this mechanism. Since these moving cells undergo elastic deformations, the influence of junctional remodeling may mechanically propagate among them, leading to spatiotemporal pattern formations. Using a numerical cellular vertex model, this study found that the junctional remodeling in collective cell movement exhibits spatiotemporal self-organization without requiring spatial patterns of molecular signaling activity. The junctional remodeling propagates as a wave in a specific direction with a much faster speed than that of cell movement. Such propagation occurs in both the absence and presence of fluctuations in the contraction of cell boundaries.

Tuesday, September 12th

Chowdhary, S., Tomer, D., Dubal, D., Sambre, D. and Rikhy, R. (2017). Analysis of mitochondrial organization and function in the Drosophila blastoderm embryo. Sci Rep 7(1): 5502. PubMed ID: 28710464
Mitochondria are inherited maternally as globular and immature organelles in metazoan embryos. This study used the Drosophila blastoderm embryo to characterize their morphology, distribution and functions in embryogenesis. Mitochondria are relatively small, dispersed and distinctly distributed along the apico-basal axis in proximity to microtubules by motor protein transport. Live imaging, photobleaching and photoactivation analyses of mitochondrially targeted GFP show that they are mobile in the apico-basal axis along microtubules and are immobile in the lateral plane thereby associating with one syncytial cell. Photoactivated mitochondria distribute equally to daughter cells across the division cycles. ATP depletion by pharmacological and genetic inhibition of the mitochondrial electron transport chain (ETC) activates AMPK and decreases syncytial metaphase furrow extension. In summary, this study shows that small and dispersed mitochondria of the Drosophila blastoderm embryo localize by microtubule transport and provide ATP locally for the fast syncytial division cycles. This study opens the possibility of use of Drosophila embryogenesis as a model system to study the impact of maternal mutations in mitochondrial morphology and metabolism on embryo patterning and differentiation.
Choe, C. P., Stellabotte, F. and Brown, S. J. (2017). Regulation and function of odd-paired in Tribolium segmentation. Dev Genes Evol. PubMed ID: 28791475
The pair-rule gene odd-paired (opa) is required for the patterning of alternate segment boundaries in the early Drosophila embryo. Mutant phenotypes of opa display a typical pair-rule phenotype in which most of each odd-numbered denticle belt is eliminated. However, among the nine Drosophila pair-rule genes, opa is the only gene that is not expressed in stripes with double segmental periodicity; its transcript and protein are expressed in a broad domain within segmenting embryos. While expression patterns of orthologs of opa have been analyzed in several arthropod species, their regulation and function in segmentation were largely unknown. This study analyzed the expression patterns, regulation, and function of the Tribolium ortholog of opa (Tc-opa). Tc-opa is expressed in segmental stripes in the early stages of segmentation and then is expressed in a broad domain at the growth zone of elongating germbands where new segments form. This broad expression of Tc-opa is processed into segmental stripes once the trunk has become segmented. Tc-opa expression is regulated positively and negatively by even-skipped and >odd-skipped, respectively. However, knock-down of Tc-opa does not affect embryonic segmentation. These findings suggest that Tc-opa expression is regulated by the pair-rule gene network even though its requirement for segmentation is uncertain in Tribolium.
Huang, A., Amourda, C., Zhang, S., Tolwinski, N. S. and Saunders, T. E. (2017). Decoding temporal interpretation of the morphogen Bicoid in the early Drosophila embryo. Elife 6. PubMed ID: 28691901
Morphogen gradients provide essential spatial information during development. Not only the local concentration but also duration of morphogen exposure is critical for correct cell fate decisions. Yet, how and when cells temporally integrate signals from a morphogen remains unclear. This study used optogenetic manipulation to switch off Bicoid-dependent transcription in the early Drosophila embryo with high temporal resolution, allowing time-specific and reversible manipulation of morphogen signalling. Bicoid transcriptional activity was found to be dispensable for embryonic viability in the first hour after fertilization, but persistently required throughout the rest of the blastoderm stage. Short interruptions of Bicoid activity alter the most anterior cell fate decisions, while prolonged inactivation expands patterning defects from anterior to posterior. Such anterior susceptibility correlates with high reliance of anterior gap gene expression on Bicoid. Therefore, cell fates exposed to higher Bicoid concentration require input for longer duration, demonstrating a previously unknown aspect of Bicoid decoding.
Koromila, T. and Stathopoulos, A. (2017). Broadly expressed repressors integrate patterning across orthogonal axes in embryos. Proc Natl Acad Sci U S A. PubMed ID: 28720706
The role of spatially localized repressors in supporting embryonic patterning is well appreciated, but, alternatively, the role ubiquitously expressed repressors play in this process is not well understood. This study investigated the function of two broadly expressed repressors, Runt (Run) and Suppressor of Hairless [Su(H)], in patterning the Drosophila embryo. Previous studies have shown that Run and Su(H) regulate gene expression along anterior-posterior (AP) or dorsal-ventral (DV) axes, respectively, by spatially limiting activator action, but this study characterizes a different role. The data show that broadly expressed repressors silence particular enhancers within cis-regulatory systems, blocking their expression throughout the embryo fully but transiently, and, in this manner, regulate spatiotemporal outputs along both axes. These results suggest that Run and Su(H) regulate the temporal action of enhancers and are not dedicated regulators of one axis but, instead, act coordinately to pattern both axes, AP and DV.

Monday, September 11th

Khoueiry, P., Girardot, C., Ciglar, L., Peng, P. C., Gustafson, E. H., Sinha, S. and Furlong, E. E. (2017). Uncoupling evolutionary changes in DNA sequence, transcription factor occupancy and enhancer activity. Elife 6. PubMed ID: 28792889
Sequence variation within enhancers plays a major role in both evolution and disease, yet its functional impact on transcription factor (TF) occupancy and enhancer activity remains poorly understood. This study assayed the binding of five essential TFs over multiple stages of embryogenesis in two distant Drosophila species (with 1.4 substitutions per neutral site), identifying thousands of orthologous enhancers with conserved or diverged combinatorial occupancy. The five factors examined, Twist, Mef2, Tinman (Tin), Bagpipe and Biniou, are the major drivers of the subdivision of the mesoderm into different muscle primordia and form part of a highly interconnected gene regulatory network. These binding signatures were used to dissect two properties of developmental enhancers: (1) potential TF cooperativity, using signatures of co-associations and co-divergence in TF occupancy. This revealed conserved combinatorial binding despite sequence divergence, suggesting protein-protein interactions sustain conserved collective occupancy. (2) Enhancer in-vivo activity, revealing orthologous enhancers with conserved activity despite divergence in TF occupancy. Taken together, this study has identified enhancers with diverged motifs yet conserved occupancy and others with diverged occupancy yet conserved activity, emphasising the need to functionally measure the effect of divergence on enhancer activity.
Kaieda, Y., Masuda, R., Nishida, R., Shimell, M., O'Connor, M. B. and Ono, H. (2017). Glue protein production can be triggered by steroid hormone signaling independent of the developmental program in Drosophila melanogaster. Dev Biol [Epub ahead of print]. PubMed ID: 28782527
Steroid hormones regulate life stage transitions, allowing animals to appropriately follow a developmental timeline. During insect development, the steroid hormone ecdysone is synthesized and released in a regulated manner by the prothoracic gland (PG) and then hydroxylated to the active molting hormone, 20-hydroxyecdysone (20E), in peripheral tissues. This study manipulated ecdysteroid titers, through temporally controlled over-expression of the ecdysteroid-inactivating enzyme, CYP18A1, in the PG using the GeneSwitch-GAL4 system in the fruit fly Drosophila melanogaster. Expression was monitored of a 20E-inducible glue protein gene, Salivary gland secretion 3 (Sgs3), using a Sgs3:GFP fusion transgene. In wild type larvae, Sgs3-GFP expression is activated at the midpoint of the third larval instar stage in response to the rising endogenous level of 20E. By first knocking down endogenous 20E levels during larval development and then feeding 20E to these larvae at various stages, it was found that Sgs3-GFP expression could be triggered at an inappropriate developmental stage after a certain time lag. This stage-precocious activation of Sgs3 required expression of the Broad-complex, similar to normal Sgs3 developmental regulation, and a small level of nutritional input. It is suggested that these studies provide evidence for a tissue-autonomic regulatory system for a metamorphic event independent from the primary 20E driven developmental progression.
Kaye, E. G., Kurbidaeva, A., Wolle, D., Aoki, T., Schedl, P. and Larschan, E. (2017). Drosophila dosage compensation loci associate with a boundary forming insulator complex. Mol Cell Biol. [Epub ahead of print] PubMed ID: 28784719
CES (chromatin entry sites) are 100-1,500 bp elements that recruit MSL (Male Specific Lethal) complexes to the X-chromosome to upregulate expression of X-linked genes in male flies. CES contain one or more approximately 20 bp GA rich sequences called MREs (MSL recognition elements) that are critical for dosage compensation. Recent studies indicate that CES also correspond to boundaries of X-chromosomal TADs (topologically associated domains). This study shows that an approximately 1,000 kDa complex called the LBC, which is required for the functioning of the Bithorax complex boundary Fab-7, interacts specifically with a special class of CES that contain multiple MREs. Mutations in the MRE sequences of three of these CES that disrupt function in vivo abrogate interactions with the LBC. Moreover, reducing the levels of two LBC components compromises MSL recruitment. Finally, it was shown that several of the CES that are physically linked to each other in vivo are LBC interactors.
Jaksic, A. M., Kofler, R. and Schlotterer, C. (2017). Regulation of transposable elements: Interplay between TE-encoded regulatory sequences and host-specific trans-acting factors in Drosophila melanogaster. Mol Ecol [Epub ahead of print]. PubMed ID: 28742942
Transposable elements (TEs) are mobile genetic elements that can move around the genome, and their expression is one precondition for this mobility. Because the insertion of TEs in new genomic positions is largely deleterious, the molecular mechanisms for transcriptional suppression have been extensively studied. In contrast, very little is known about their primary transcriptional regulation. This study characterized the expression dynamics of TE families in Drosophila melanogaster across a broad temperature range (13-29 ° C). In 71% of the expressed TE families, the expression is modulated by temperature. This temperature-dependent regulation is specific for TE families and strongly affected by the genetic background. It is deduced that TEs carry family-specific regulatory sequences, which are targeted by host-specific trans-acting factors, such as transcription factors. Consistent with the widespread dominant inheritance of gene expression, the prevailing dominance of TE family expression was found. It is concluded that TE family expression across a range of temperatures is regulated by an interaction between TE family-specific regulatory elements and trans-acting factors of the host.

Sunday, September 10th

Khan, S. J., Abidi, S. N. F., Skinner, A., Tian, Y. and Smith-Bolton, R. K. (2017). The Drosophila Duox maturation factor is a key component of a positive feedback loop that sustains regeneration signaling. PLoS Genet 13(7): e1006937. PubMed ID: 28753614
Regenerating tissue must initiate the signaling that drives regenerative growth, and sustain that signaling long enough for regeneration to complete. How these key signals are sustained is unclear. To gain a comprehensive view of the changes in gene expression that occur during regeneration, whole-genome mRNAseq was performed of actively regenerating tissue from damaged Drosophila wing imaginal discs. Genetic tools to ablate the wing primordium to induce regeneration, and transcriptional profiling of the regeneration blastema was carried out by fluorescently labeling and sorting the blastema cells, thus identifying differentially expressed genes. Importantly, by using genetic mutants of several of these differentially expressed genes it was confirmed that they have roles in regeneration. This approach showed that high expression of the gene moladietz (mol), which encodes the Duox-maturation factor NIP, is required during regeneration to produce reactive oxygen species (ROS), which in turn sustain JNK signaling during regeneration. JNK signaling was shown to upregulate mol expression, thereby activating a positive feedback signal that ensures the prolonged JNK activation required for regenerative growth. Thus, by whole-genome transcriptional profiling of regenerating tissue this study has identified a positive feedback loop that regulates the extent of regenerative growth.
Huang, H. W., Zeng, X., Rhim, T., Ron, D. and Ryoo, H. D. (2017). The requirement of IRE1-XBP1 in resolving physiological stress during Drosophila development. J Cell Sci. PubMed ID: 28775151
IRE1 mediates the Unfolded Protein Response (UPR) in part by regulating XBP1 mRNA splicing in response to endoplasmic reticulum (ER) stress. In cultured metazoan cells, IRE1 also exhibits XBP1-independent biochemical activities. IRE1 and XBP1 are developmentally essential genes in Drosophila and mammals, but the source of the physiological ER stress and the relative contributions of XBP1 activation versus other IRE1 functions to development remain unknown. This study employed Drosophila to address this question. Specifically, specific regions of the developing alimentary canal, fat body and the male reproductive organ are the sources of physiological stress that requires ire1 and xbp1 for resolution. In particular, the developmental lethality associated with xbp1 nulls was rescued by transgenic expression of xbp1 in the alimentary canal. IRE1's domains involved in detecting unfolded proteins, cleaving RNAs and activating XBP1 splicing were all essential for development. The earlier onset of developmental defects of ire1 mutant larvae compared to xbp1-null flies supports a developmental role for XBP1-independent IRE1 RNase activity while challenging the importance of RNase-independent effector mechanisms of Drosophila IRE1 function.
Katz, B., Voolstra, O., Tzadok, H., Yasin, B., Rhodes-Modrov, E., Bartels, J. P., Strauch, L., Huber, A. and Minke, B. (2017). The latency of the light response is modulated by the phosphorylation state of Drosophila TRP at a specific site. Channels (Austin): [Epub ahead of print]. PubMed ID: 28762890
Drosophila photoreceptors respond to oscillating light of high frequency (approximately 100 Hz), while increasing the oscillating light intensity raises the maximally detected frequency. Dephosphorylation of the light-activated TRP ion channel at S936 is a fast, graded, light-, and Ca2+-dependent process. It was further found that this process affects the detection limit of high frequency oscillating light. Accordingly, transgenic Drosophila, which do not undergo phosphorylation at the S936-TRP site (trpS936A), revealed a short time-interval before following the high stimulus frequency (oscillation-lock response) in both dark- and light-adapted flies. In contrast, the trpS936D transgenic flies, which mimic constant phosphorylation, showed a long-time interval to oscillation-lock response in both dark- and light-adapted flies. This study extends these findings by showing that dark-adapted trpS936A flies reveal light-induced current (LIC) with short latency relative to trpWT or trpS936D flies, indicating that the channels are a limiting factor of response kinetics. The results indicate that properties of the light-activated channels together with the dynamic light-dependent process of TRP phosphorylation at the S936 site determine response kinetics.
Hochapfel, F., Denk, L., Mendl, G., Schulze, U., Maassen, C., Zaytseva, Y., Pavenstadt, H., Weide, T., Rachel, R., Witzgall, R. and Krahn, M. P. (2017). Distinct functions of Crumbs regulating slit diaphragms and endocytosis in Drosophila nephrocytes. Cell Mol Life Sci. PubMed ID: 28717874
Mammalian podocytes, the key determinants of the kidney's filtration barrier, differentiate from columnar epithelial cells and several key determinants of apical-basal polarity in the conventional epithelia have been shown to regulate podocyte morphogenesis and function. However, little is known about the role of Crumbs, a conserved polarity regulator in many epithelia, for slit-diaphragm formation and podocyte function. This study used Drosophila nephrocytes as model system for mammalian podocytes and identified a conserved function of Crumbs proteins for cellular morphogenesis, nephrocyte diaphragm assembly/maintenance, and endocytosis. Nephrocyte-specific knock-down of Crumbs results in disturbed nephrocyte diaphragm assembly/maintenance and decreased endocytosis, which can be rescued by Drosophila Crumbs as well as human Crumbs2 and Crumbs3, which were both expressed in human podocytes. In contrast to the extracellular domain, which facilitates nephrocyte diaphragm assembly/maintenance, the intracellular FERM-interaction motif of Crumbs is essential for regulating endocytosis. Moreover, Moesin, which binds to the FERM-binding domain of Crumbs, is essential for efficient endocytosis. Thus, this study describes a new mechanism of nephrocyte development and function, which is likely to be conserved in mammalian podocytes.

Saturday, September 9th

Kaneko, T., Macara, A. M., Li, R., Hu, Y., Iwasaki, K., Dunnings, Z., Firestone, E., Horvatic, S., Guntur, A., Shafer, O. T., Yang, C. H., Zhou, J. and Ye, B. (2017). Serotonergic modulation enables pathway-specific plasticity in a developing sensory circuit in Drosophila. Neuron 95(3): 623-638.e624. PubMed ID: 28712652
How experiences during development cause long-lasting changes in sensory circuits and affect behavior in mature animals are poorly understood. This study establish a novel system for mechanistic analysis of the plasticity of developing neural circuits by showing that sensory experience during development alters nociceptive behavior and circuit physiology in Drosophila larvae. Despite the convergence of nociceptive and mechanosensory inputs on common second-order neurons (SONs), developmental noxious input modifies transmission from nociceptors to their SONs, but not from mechanosensors to the same SONs, which suggests striking sensory pathway specificity. These SONs activate serotonergic neurons to inhibit nociceptor-to-SON transmission; stimulation of nociceptors during development sensitizes nociceptor presynapses to this feedback inhibition. The results demonstrate that, unlike associative learning, which involves inputs from two sensory pathways, sensory pathway-specific plasticity in the Drosophila nociceptive circuit is in part established through feedback modulation. This study elucidates a novel mechanism that enables pathway-specific plasticity in sensory systems.
Iliadi, K. G., Iliadi, N. and Boulianne, G. L. (2017). Drosophila mutants lacking octopamine exhibit impairment in aversive olfactory associative learning. Eur J Neurosci [Epub ahead of print]. PubMed ID: 28715094
Octopamine is a biogenic amine in invertebrates that is considered a functional homolog of vertebrate norepinephrine. Octopamine regulates many physiological processes such as metabolism, reproduction and different types of behaviour including learning and memory. Previous studies in insects led to the notion that acquisition of an olfactory memory depends on the octopaminergic system during appetitive (reward-based) learning, but not in the case of aversive (punishment-based) learning. This study provides several lines of evidence demonstrating that aversive associative olfactory learning in Drosophila is also dependent on octopamine signaling. Specifically, Drosophila Tβh (Tyramine-β-hydroxylase) mutants, which lack octopamine and are female sterile, were examined to determine whether octopamine plays a role in aversive learning. Tβh mutant flies are shown to exhibit a significant reduction in learning compared to control lines that is independent of either genetic background or the methods used to induce aversive olfactory memory. To unambiguously demonstrate that octopamine synthesis plays a role in aversive olfactory learning, rescue experiments were performed using the Gal4/UAS system. Expression of UAS-Tβh in octopamine/tyraminergic neurons using Tdc2-Gal4 in Tβh null mutant flies fully rescued both the aversive learning defects and female sterility observed in Tβh mutants.
Inada, K., Tsuchimoto, Y. and Kazama, H. (2017). Origins of cell-type-specific olfactory processing in the Drosophila mushroom body circuit. Neuron 95(2): 357-367. PubMed ID: 28728024
How cell-type-specific physiological properties shape neuronal functions in a circuit remains poorly understood. This issue has been addressed in the Drosophila mushroom body (MB), a higher olfactory circuit, where neurons belonging to distinct glomeruli in the antennal lobe feed excitation to three types of intrinsic neurons, α/β, α'/&beta', and γ Kenyon cells (KCs). Two-photon optogenetics and intracellular recording revealed that whereas glomerular inputs add similarly in all KCs, spikes were generated most readily in α'/β' KCs. This cell type was also the most competent in recruiting GABAergic inhibition fed back by anterior paired lateral neuron, which responded to odors either locally within a lobe or globally across all lobes depending on the strength of stimuli. Notably, as predicted from these physiological properties, α'/β' KCs had the highest odor detection speed, sensitivity, and discriminability. This enhanced discrimination required proper GABAergic inhibition. These results link cell-type-specific mechanisms and functions in the MB circuit.
Han, Y., Xiong, L., Xu, Y., Tian, T. and Wang, T. (2017). The beta-alanine transporter BalaT is required for visual neurotransmission in Drosophila. Elife 6 [Epub ahead of print]. PubMed ID: 28806173
The recycling of neurotransmitters is essential for sustained synaptic transmission. In Drosophila, histamine recycling is required for visual synaptic transmission. Synaptic histamine is rapidly taken up by laminar glia, and is converted to carcinine. After delivered back to photoreceptors, carcinine is hydrolyzed to release histamine and β-alanine. This histamine is repackaged into synaptic vesicles, but it is unclear how the β-alanine is returned to the laminar glial cells. This study identified a new beta-alanine transporter, which has been named BalaT (Beta-alanine Transporter). Null balat mutants exhibited lower levels of β-alanine, as well as less β-alanine accumulation in the retina. Moreover, BalaT is expressed and required in retinal pigment cells for maintaining visual synaptic transmission and phototaxis behavior. These results provide the first genetic evidence that retinal pigment cells play a critical role in visual neurotransmission, and suggest that a BalaT-dependent beta-alanine trafficking pathway is required for histamine homeostasis and visual neurotransmission.

Friday, September 8th

Huser, A., Eschment, M., Gullu, N., Collins, K. A. N., Bopple, K., Pankevych, L., Rolsing, E. and Thum, A. S. (2017). Anatomy and behavioral function of serotonin receptors in Drosophila melanogaster larvae. PLoS One 12(8): e0181865. PubMed ID: 28777821
The biogenic amine serotonin (5-HT) is an important neuroactive molecule in the central nervous system of the majority of animal phyla. 5-HT binds to specific G protein-coupled and ligand-gated ion receptors to regulate particular aspects of animal behavior. In Drosophila, as in many other insects this includes the regulation of locomotion and feeding. Due to its genetic amenability and neuronal simplicity the Drosophila larva has turned into a useful model for studying the anatomical and molecular basis of chemosensory behaviors. This is particularly true for the olfactory system, which is mostly described down to the synaptic level over the first three orders of neuronal information processing. This study focused on the 5-HT receptor system of the Drosophila larva. In a bipartite approach consisting of anatomical and behavioral experiments, the distribution and the implications are described of individual 5-HT receptors on naive and acquired chemosensory behaviors. The data suggest that 5-HT1A, 5-HT1B, and 5-HT7 are dispensable for larval naive olfactory and gustatory choice behaviors as well as for appetitive and aversive associative olfactory learning and memory. In contrast, 5-HT/5-HT2A signaling throughout development, but not as an acute neuronal function, affects associative olfactory learning and memory using high salt concentration as a negative unconditioned stimulus. These findings describe for the first time an involvement of 5-HT signaling in learning and memory in Drosophila larvae. In the longer run these results may uncover developmental, 5-HT dependent principles related to reinforcement processing possibly shared with adult Drosophila and other insects.
de la Flor, M., Chen, L., Manson-Bishop, C., Chu, T. C., Zamora, K., Robbins, D., Gunaratne, G. and Roman, G. (2017). Drosophila increase exploration after visually detecting predators. PLoS One 12(7): e0180749. PubMed ID: 28746346
Novel stimuli elicit behaviors that are collectively known as specific exploration. These behaviors allow the animal to become more familiar with the novel objects within its environment. Specific exploration is frequently suppressed by defensive reactions to predator cues. This study examined if this suppression occurs in Drosophila melanogaster by measuring the response of these flies to wild harvested predators. The flies used in these experiments have been cultured and had not lived under predator threat for multiple decades. In a circular arena with centrally-caged predators, wild type Drosophila actively avoided the pantropical jumping spider, Plexippus paykulli, and the Texas unicorn mantis, Phyllovates chlorophaena, indicating an innate defensive reaction to these predators. Interestingly, wild type Drosophila males also avoided a centrally-caged mock spider, and the avoidance of the mock spider became exaggerated when it was made to move within the cage. Visually impaired Drosophila failed to detect and avoid the Plexippus paykulli and the moving mock spider, while the broadly anosmic orco2 mutants were fully capable of detecting and avoiding Plexippus paykulli, indicating that these flies principally relied upon vison to perceive the predator stimuli. During early exploration of the arena, exploratory activity increased in the presence of Plexippus paykulli and the moving mock spider. The elevated activity induced by Plexippus paykulli disappeared after the fly had finished exploring, suggesting the flies were capable of habituating the predator cues. Taken together, these results indicate that despite being isolated from predators for decades Drosophila will visually detect these predators, retain innate defensive behaviors, respond by increasing exploratory activity in the arena rather than suppressing activity, and may habituate to normal predator cues.
Fedina, T. Y., Arbuthnott, D., Rundle, H. D., Promislow, D. E. L. and Pletcher, S. D. (2017). Tissue-specific insulin signaling mediates female sexual attractiveness. PLoS Genet 13(8): e1006935. PubMed ID: 28817572
Individuals choose their mates so as to maximize reproductive success, and one important component of this choice is assessment of traits reflecting mate quality. Previous work has shown that global manipulation of insulin signaling, a nutrient-sensing pathway governing investment in survival versus reproduction, affects female sexual attractiveness in Drosophila. This study demonstrates that these effects on attractiveness derive from insulin signaling in the fat body and ovarian follicle cells, whose signals are integrated by pheromone-producing cells called oenocytes. Functional ovaries were required for global insulin signaling effects on attractiveness, and manipulations of insulin signaling specifically in late follicle cells recapitulated effects of global manipulations. Interestingly, modulation of insulin signaling in the fat body produced opposite effects on attractiveness, suggesting a competitive relationship with the ovary. Furthermore, all investigated tissue-specific insulin signaling manipulations that changed attractiveness also changed fecundity in the corresponding direction, pointing to insulin pathway activity as a reliable link between fecundity and attractiveness cues. The cues themselves, cuticular hydrocarbons, responded distinctly to fat body and follicle cell manipulations, indicating independent readouts of the pathway activity from these two tissues. Thus, this study describes a system in which female attractiveness results from an apparent connection between attractiveness cues and an organismal state of high fecundity, both of which are created by lowered insulin signaling in the fat body and increased insulin signaling in late follicle cells.
Gupta, T., Morgan, H. R., Andrews, J. C., Brewer, E. R. and Certel, S. J. (2017). Methyl-CpG binding domain proteins inhibit interspecies courtship and promote aggression in Drosophila. Sci Rep 7(1): 5420. PubMed ID: 28710457
Reproductive isolation and speciation are driven by the convergence of environmental and genetic variation. The integration of these variation sources is thought to occur through epigenetic marks including DNA methylation. Proteins containing a methyl-CpG-binding domain (MBD) bind methylated DNA and interpret epigenetic marks, providing a dynamic yet evolutionarily adapted cellular output. This study reports the Drosophila MBD-containing proteins, dMBD-R2 and dMBD2/3, contribute to reproductive isolation and survival behavioral strategies. Drosophila melanogaster males with a reduction in dMBD-R2 specifically in octopamine (OA) neurons exhibit courtship toward divergent interspecies D. virilis and D. yakuba females and a decrease in conspecific mating success. Conspecific male-male courtship is increased between dMBD-R2-deficient males while aggression is reduced. These changes in adaptive behavior are separable as males with a hypermethylated OA neuronal genome exhibited a decrease in aggression without altering male-male courtship. These results suggest Drosophila MBD-containing proteins are required within the OA neural circuitry to inhibit interspecies and conspecific male-male courtship and indicate that the genetically hard-wired neural mechanisms enforcing behavioral reproductive isolation include the interpretation of the epigenome.

Thursday, September 7th

Aguilera-Gomez, A., Zacharogianni, M., van Oorschot, M. M., Genau, H., Grond, R., Veenendaal, T., Sinsimer, K. S., Gavis, E. R., Behrends, C. and Rabouille, C. (2017). Phospho-Rasputin stabilization by Sec16 is required for stress granule formation upon amino acid starvation. Cell Rep 20(4): 935-948. PubMed ID: 28746877
Most cellular stresses induce protein translation inhibition and stress granule formation. Stress granules are well-studied, cytoplasmic reversible, pro-survival stress assemblies where untranslated free RNAs (resulting from protein translation inhibition) are stored and protected together with RNA-binding proteins, translation initiation factors, and the 40S ribosomal subunits. This study used Drosophila S2 cells to investigate the role of G3BP/Rasputin in this process. In contrast to arsenite treatment, where dephosphorylated Ser142 Rasputin is recruited to stress granules, this study found that, upon amino acid starvation, only the phosphorylated Ser142 form is recruited. Furthermore, Sec16, a component of the endoplasmic reticulum exit site, was identified as a Rasputin interactor and stabilizer. Sec16 depletion results in Rasputin degradation and inhibition of stress granule formation. However, in the absence of Sec16, pharmacological stabilization of Rasputin is not enough to rescue the assembly of stress granules. This is because Sec16 specifically interacts with phosphorylated Ser142 Rasputin, the form required for stress granule formation upon amino acid starvation. Taken together, these results demonstrate that stress granule formation is fine-tuned by specific signaling cues that are unique to each stress. These results also expand the role of Sec16 as a stress response protein.
Highfill, C. A., Tran, J. H., Nguyen, S. K. T., Moldenhauer, T. R., Wang, X. and Macdonald, S. J. (2017). Naturally-segregating variation at Ugt86Dd contributes to nicotine resistance in Drosophila melanogaster. Genetics [Epub ahead of print]. PubMed ID: 28743761
Identifying the sequence polymorphisms underlying complex trait variation is a key goal of genetics research, since knowing the precise causative molecular events allows insight into the pathways governing trait variation. Genetic analysis of complex traits in model systems regularly starts by constructing QTL maps, but generally fails to identify causative sequence polymorphisms. Previous studies mapped a series of QTL contributing to resistance to nicotine in a Drosophila melanogaster multiparental mapping resource, and this study use a battery of functional tests to resolve QTL to the molecular level. One large-effect QTL resided over a cluster of UDP-glucuronosyltransferases, and quantitative complementation tests using deficiencies eliminating subsets of these detoxification genes revealed allelic variation impacting resistance. RNAseq showed that Ugt86Dd had significantly higher expression in genotypes that are more resistant to nicotine, and anterior midgut-specific RNAi of this gene reduced resistance. A segregating 22-bp frameshift deletion in Ugt86Dd, and accounting for the InDel during mapping largely eliminates the QTL, implying the event explains the bulk of the effect of the mapped locus. CRISPR/Cas9 editing a relatively resistant genotype to generate lesions in Ugt86Dd that recapitulate the naturally-occurring putative loss-of-function allele leads to a large reduction in resistance. Despite this major effect of the deletion, the allele appears to be very rare in wild-caught populations, and likely explains only a small fraction of the natural variation for the trait. Nonetheless, this putatively causative coding InDel can be a launchpad for future mechanistic exploration of xenobiotic detoxification.
Harvanek, Z. M., Lyu, Y., Gendron, C. M., Johnson, J. C., Kondo, S., Promislow, D. E. L. and Pletcher, S. D. (2017). Perceptive costs of reproduction drive ageing and physiology in male Drosophila. Nat Ecol Evol 1(6): 152. PubMed ID: 28812624
Costs of reproduction are thought to result from natural selection optimizing organismal fitness within putative physiological constraints. Phenotypic and population genetic studies of reproductive costs are plentiful across taxa, but an understanding of their mechanistic basis would provide important insight into the diversity in life-history traits, including reproductive effort and ageing. This study dissected the causes and consequences of specific costs of reproduction in male Drosophila melanogaster. Key survival and physiological costs of reproduction arise from perception of the opposite sex, and they are reversed by the act of mating. In the absence of pheromone perception, males are free from reproductive costs on longevity, stress resistance and fat storage. The costs of perception and the benefits of mating are both mediated by evolutionarily conserved neuropeptidergic signalling molecules, as well as the transcription factor dFoxo. These results provide a molecular framework in which certain costs of reproduction arise as a result of self-imposed 'decisions' in response to perceptive neural circuits, which then orchestrate the control of life-history traits independently of physical or energetic effects associated with mating itself.
Biolchini, M., Murru, E., Anfora, G., Loy, F., Banni, S., Crnjar, R. and Sollai, G. (2017). Fat storage in Drosophila suzukii is influenced by different dietary sugars in relation to their palatability. PLoS One 12(8): e0183173. PubMed ID: 28817633
The peripheral sensitivity and palatability of different carbohydrates was evaluated and their nutritional value assessed in adult females of D. suzukii by means of an electrophysiological, behavioural and metabolic approach. The electrophysiological responses were recorded from the labellar "l" type sensilla stimulated with metabolizable mono- and disaccharides (glucose and maltose) and a non-metabolizable sugar (sucralose); the response rating and the palatability to the same sugars, evaluated by recording the proboscis extension reflex (PER), was maltose>glucose>sucralose. The nutritional value of carbohydrates was assessed by means of survival trials and fatty acids profile. Flies fed on a diet containing maltose had a longer lifespan than flies on monosaccharides, while flies fed on a diet containing sucralose had a shorter one. In addition, the ability to store fat seems to be influenced by the different sugars in the diet and is in relationship with their palatability. In fact, data showed a higher synthesis of palmitic and palmitoleic acids, most likely derived from de-novo lipogenesis with glucose as precursor, in flies fed with maltose and glucose than with non-metabolizable sucralose. In conclusion, these results suggest that the ability to select different sugars on the basis of their palatability may favour the storage of energy reserves such as fat by de-novo lipogenesis, determining a longer survival capability during prolonged periods of fasting.

Wednesday, September 6th

Fujii, S., Emery, P. and Amrein, H. (2017). SIK3-HDAC4 signaling regulates Drosophila circadian male sex drive rhythm via modulating the DN1 clock neurons. Proc Natl Acad Sci U S A 114(32): E6669-e6677. PubMed ID: 28743754
The physiology and behavior of many organisms are subject to daily cycles. In Drosophila melanogaster the daily locomotion patterns of single flies are characterized by bursts of activity at dawn and dusk. Two distinct clusters of clock neurons-morning oscillators (M cells) and evening oscillators (E cells)-are largely responsible for these activity bursts. In contrast, male-female pairs of flies follow a distinct pattern, most notably characterized by an activity trough at dusk followed by a high level of male courtship during the night. This male sex drive rhythm (MSDR) is mediated by the M cells along with DN1 neurons, a cluster of clock neurons located in the dorsal posterior region of the brain. This study reports that males lacking Salt-inducible kinase 3 (SIK3) expression in M cells exhibit a short period of MSDR but a long period of single-fly locomotor rhythm (SLR). Moreover, lack of Sik3 in M cells decreases the amplitude of Period (Per) cycling in DN1 neurons, suggesting that SIK3 non-cell-autonomously regulates DN1 neurons' molecular clock. This study also shows that Sik3 reduction interferes with circadian nucleocytoplasmic shuttling of Histone deacetylase 4 (HDAC4), a SIK3 phosphorylation target, in clock neurons and that constitutive HDAC4 localization in the nucleus shortens the period of MSDR. Taking these findings together, it is concluded that SIK3-HDAC4 signaling in M cells regulates MSDR by regulating the molecular oscillation in DN1 neurons.
Frank, D. D., Enjin, A., Jouandet, G. C., Zaharieva, E. E., Para, A., Stensmyr, M. C. and Gallio, M. (2017). Early integration of temperature and humidity stimuli in the Drosophila brain. Curr Biol 27(15): 2381-2388.e2384. PubMed ID: 28736172
The Drosophila antenna contains receptor neurons for mechanical, olfactory, thermal, and humidity stimuli. Neurons expressing the ionotropic receptor IR40a have been implicated in the selection of an appropriate humidity range, but although previous work indicates that insect hygroreceptors may be made up by a 'triad' of neurons (with a dry-, a cold-, and a humid-air-responding cell), IR40a expression included only cold- and dry-air cells. This study reports the identification of the humid-responding neuron that completes the hygrosensory triad in the Drosophila antenna. This cell type expresses the Ir68a gene, and Ir68a mutation perturbs humidity preference. Next, the projections of Ir68a neurons were followed to the brain, and they were shown to form form a distinct glomerulus in the posterior antennal lobe (PAL). In the PAL, a simple sensory map represents related features of the external environment with adjacent 'hot,' 'cold,' 'dry,' and 'humid' glomeruli - an organization that allows for both unique and combinatorial sampling by central relay neurons. Indeed, flies avoided dry heat more robustly than humid heat, and this modulation was abolished by silencing of dry-air receptors. Consistently, at least one projection neuron type received direct synaptic input from both temperature and dry-air glomeruli. These results further understanding of humidity sensing in the Drosophila antenna, uncover a neuronal substrate for early sensory integration of temperature and humidity in the brain, and illustrate the logic of how ethologically relevant combinations of sensory cues can be processed together to produce adaptive behavioral responses.
Eichler, K., Li, F., Litwin-Kumar, A., Park, Y., Andrade, I., Schneider-Mizell, C. M., Saumweber, T., Huser, A., Eschbach, C., Gerber, B., Fetter, R. D., Truman, J. W., Priebe, C. E., Abbott, L. F., Thum, A. S., Zlatic, M. and Cardona, A. (2017). The complete connectome of a learning and memory centre in an insect brain. Nature 548(7666): 175-182. PubMed ID: 28796202
Associating stimuli with positive or negative reinforcement is essential for survival, but a complete wiring diagram of a higher-order circuit supporting associative memory has not been previously available. This study reconstructed one such circuit at synaptic resolution, the Drosophila larval mushroom body. Most Kenyon cells were found to integrate random combinations of inputs, but a subset receives stereotyped inputs from single projection neurons. This organization maximizes performance of a model output neuron on a stimulus discrimination task. A novel canonical circuit in each mushroom body compartment with previously unidentified connections is reported: reciprocal Kenyon cell to modulatory neuron connections, modulatory neuron to output neuron connections, and a surprisingly high number of recurrent connections between Kenyon cells. Stereotyped connections found between output neurons could enhance the selection of learned behaviours. The complete circuit map of the mushroom body should guide future functional studies of this learning and memory centre.
Foley, B. R., Marjoram, P. and Nuzhdin, S. V. (2017). Basic reversal-learning capacity in flies suggests rudiments of complex cognition. PLoS One 12(8): e0181749. PubMed ID: 28813432
The most basic models of learning are reinforcement learning models (for instance, classical and operant conditioning) that posit a constant learning rate; however many animals change their learning rates with experience. This process is sometimes studied by reversing an existing association between cues and rewards, and measuring the rate of relearning. Augmented reversal-learning, where learning rates increase with practice, can be an important component of behavioral flexibility; and may provide insight into higher cognition. Previous studies of reversal-learning in Drosophila have not measured learning rates, but have tended to focus on measuring gross deficits in reversal-learning, as the ratio of two timepoints. These studies have uncovered a diversity of mechanisms underlying reversal-learning, but natural genetic variation in this trait has yet to be assessed. A reversal-learning regime was conducted on a diverse panel of Drosophila melanogaster genotypes. Highly significant genetic variation was found in their baseline ability to learn. It was also found that they have a consistent, and strong (1.3x), increase in their learning speed with reversal. No evidence was found, however, that there was genetic variation in their ability to increase their learning rates with experience. This may suggest that Drosophila have a hitherto unrecognized ability to integrate acquired information, and improve their decision making; but that their mechanisms for doing so are under strong constraints.

Tuesday, September 5th

Flack, J. E., Mieszczanek, J., Novcic, N. and Bienz, M. (2017). Wnt-Dependent Inactivation of the Groucho/TLE Co-repressor by the HECT E3 Ubiquitin Ligase Hyd/UBR5. Mol Cell 67(2): 181-193.e185. PubMed ID: 28689657
Extracellular signals are transduced to the cell nucleus by effectors that bind to enhancer complexes to operate transcriptional switches. For example, the Wnt enhanceosome is a multiprotein complex associated with Wnt-responsive enhancers through T cell factors (TCF; see Pangolin) and kept silent by Groucho/TLE co-repressors. Wnt-activated β-catenin (see Armadillo) binds to TCF to overcome this repression, but how it achieves this is unknown. This study discovered that this process depends on the HECT E3 ubiquitin ligase Hyd/UBR5, which is required for Wnt signal responses in Drosophila and human cell lines downstream of activated Armadillo/β-catenin. Groucho/TLE was identified as a functionally relevant substrate, whose ubiquitylation by UBR5 is induced by Wnt signaling and conferred by β-catenin. Inactivation of TLE by UBR5-dependent ubiquitylation also involves VCP/p97, an AAA ATPase regulating the folding of various cellular substrates including ubiquitylated chromatin proteins. Thus, Groucho/TLE ubiquitylation by Hyd/UBR5 is a key prerequisite that enables Armadillo/β-catenin to activate transcription.
Gleason, R. J., Vora, M., Li, Y., Kane, N. S., Liao, K. and Padgett, R. W. (2017). C. elegans SMA-10 regulates BMP receptor trafficking. PLoS One 12(7): e0180681. PubMed ID: 28704415
The C. elegans type I bone morphogenetic protein (BMP) receptor SMA-6 (see Drosophila Thickveins), part of the TGFβ family, is recycled through the retromer complex while the type II receptor, DAF-4 (see Drosophila Punt) is recycled in a retromer-independent, ARF-6 dependent manner. From genetic screens in C. elegans aimed at identifying new modifiers of BMP signaling, SMA-10, a conserved LRIG (leucine-rich and immunoglobulin-like domains) transmembrane protein, has been reported. It is a positive regulator of BMP signaling that binds to the SMA-6 receptor. This study shows that the loss of sma-10 leads to aberrant endocytic trafficking of SMA-6, resulting in its accumulation in distinct intracellular endosomes including the early endosome, multivesicular bodies (MVB), and the late endosome with a reduction in signaling strength. Trafficking defects caused by the loss of sma-10 are not universal, but affect only a limited set of receptors. Likewise, in Drosophila, the fly homolog of sma-10, lambik (lbk), reduces signaling strength of the BMP pathway, consistent with its function in C. elegans and suggesting evolutionary conservation of function. Loss of sma-10 results in reduced ubiquitination of the type I receptor SMA-6, suggesting a possible mechanism for its regulation of BMP signaling.
Garcia, C. J., Khajeh, J., Coulanges, E., Chen, E. I. and Owusu-Ansah, E. (2017). Regulation of mitochondrial complex I biogenesis in Drosophila flight muscles. Cell Rep 20(1): 264-278. PubMed ID: 28683319
The flight muscles of Drosophila are highly enriched with mitochondria, but the mechanism by which mitochondrial complex I (CI) is assembled in this tissue has not been described. This paper reports the mechanism of CI biogenesis in Drosophila flight muscles and shows that it proceeds via the formation of approximately 315, approximately 550, and approximately 815 kDa CI assembly intermediates. Additionally, specific roles are defined for several CI subunits in the assembly process. In particular, this study shows that dNDUFS5 is required for converting an approximately 700 kDa transient CI assembly intermediate into the approximately 815 kDa assembly intermediate. Importantly, incorporation of dNDUFS5 into CI is necessary to stabilize or promote incorporation of dNDUFA10 into the complex. These findings highlight the potential of studies of CI biogenesis in Drosophila to uncover the mechanism of CI assembly in vivo and establish Drosophila as a suitable model organism and resource for addressing questions relevant to CI biogenesis in humans.
Damulewicz, M., Loboda, A., Jozkowicz, A., Dulak, J. and Pyza, E. (2017). Haeme oxygenase protects against UV light DNA damages in the retina in clock-dependent manner. Sci Rep 7(1): 5197. PubMed ID: 28701782
This study showed that in the retina of Drosophila, the expression of the Ho gene, encoding Heme oxygenase (Ho), is regulated by light but only at the beginning of the day. This timing must be set by the circadian clock, as light pulses applied at other time points during the day do not increase the ho mRNA level. Moreover, light-induced activation of HO does not depend on the canonical phototransduction pathway but instead involves Cryptochrome and is enhanced by ultraviolet (UV) light. Interestingly, the level of DNA damage in the retina after UV exposure was inversely related to the circadian oscillation of the Ho mRNA level during the night, being the highest when the Ho level is low and reverses during the day. Accordingly, induction of Ho by the iron containing metalloporphyrin hemin was associated with low DNA damage, while inhibition of Ho activity by SnPPIX aggravated the damage. These data suggest that Ho acts in the retina to decrease oxidative DNA damage in photoreceptors caused by UV-rich light in the morning.

Monday, September 4th

Dylla, K. V., Raiser, G., Galizia, C. G. and Szyszka, P. (2017). Trace conditioning in Drosophila induces associative plasticity in mushroom body kenyon cells and dopaminergic neurons. Front Neural Circuits 11: 42. PubMed ID: 28676744
Dopaminergic neurons (DANs) signal punishment and reward during associative learning. In mammals, DANs show associative plasticity that correlates with the discrepancy between predicted and actual reinforcement (prediction error) during classical conditioning. Also in insects, such as Drosophila, DANs show associative plasticity that is, however, less understood. Associative plasticity in DANs and their synaptic partners, the Kenyon cells (KCs) in the mushroom bodies (MBs), has been studied while training Drosophila to associate an odorant with a temporally separated electric shock (trace conditioning). In most MB compartments DANs strengthened their responses to the conditioned odorant relative to untrained animals. This response plasticity preserved the initial degree of similarity between the odorant- and the shock-induced spatial response patterns, which decreased in untrained animals. Contrary to DANs, KCs (α'/β'-type) decreased their responses to the conditioned odorant relative to untrained animals. No evidence was fpimd for prediction error coding by DANs during conditioning. Rather, the data supports the hypothesis that DAN plasticity encodes conditioning-induced changes in the odorant's predictive power.
Boyan, G., Liu, Y., Khalsa, S. K. and Hartenstein, V. (2017). A conserved plan for wiring up the fan-shaped body in the grasshopper and Drosophila. Dev Genes Evol 227(4): 253-269. PubMed ID: 28752327
The central complex comprises an elaborate system of modular neuropils which mediate spatial orientation and sensory-motor integration. The neuroarchitecture of the largest of these modules, the fan-shaped body, is characterized by its stereotypic set of decussating fiber bundles. These are generated during development by axons from four homologous protocerebral lineages which enter the commissural system and subsequently decussate at stereotypic locations across the brain midline. It is not clear how the decussating bundles relate to individual lineages, or if the projection pattern is conserved across species. This study traced the axonal projections from the homologous central complex lineages into the commissural system of the embryonic and larval brains of both the grasshopper and Drosophila. Projections into the primordial commissures of both species are found to be lineage-specific and allow putatively equivalent fascicles to be identified. Comparison of the projection pattern before and after the commencement of axon decussation in both species reveals that equivalent commissural fascicles are involved in generating the columnar neuroarchitecture of the fan-shaped body. Further, the tract-specific columns in both the grasshopper and Drosophila can be shown to contain axons from identical combinations of central complex lineages, suggesting that this columnar neuroarchitecture is also conserved.
Doll, C. A., Vita, D. J. and Broadie, K. (2017). Fragile X mental retardation protein requirements in activity-dependent critical period neural circuit refinement. Curr Biol 27(15): 2318-2330.e2313. PubMed ID: 28756946
Activity-dependent synaptic remodeling occurs during early-use critical periods, when naive juveniles experience sensory input. Fragile X mental retardation protein (FMRP) sculpts synaptic refinement in an activity sensor mechanism based on sensory cues, with FMRP loss causing the most common heritable autism spectrum disorder (ASD), fragile X syndrome (FXS). In the well-mapped Drosophila olfactory circuitry, projection neurons (PNs) relay peripheral sensory information to the central brain mushroom body (MB) learning/memory center. FMRP-null PNs reduce synaptic branching and enlarge boutons, with ultrastructural and synaptic reconstitution MB connectivity defects. Critical period activity modulation via odorant stimuli, optogenetics, and transgenic tetanus toxin neurotransmission block show that elevated PN activity phenocopies FMRP-null defects, whereas PN silencing causes opposing changes. FMRP-null PNs lose activity-dependent synaptic modulation, with impairments restricted to the critical period. It is concluded that FMRP is absolutely required for experience-dependent changes in synaptic connectivity during the developmental critical period of neural circuit optimization for sensory input.
Sun, Y., Nern, A., Franconville, R., Dana, H., Schreiter, E. R., Looger, L. L., Svoboda, K., Kim, D. S., Hermundstad, A. M. and Jayaraman, V. (2017). Neural signatures of dynamic stimulus selection in Drosophila. Nat Neurosci [Epub ahead of print]. PubMed ID: 28604683
Many animals orient using visual cues, but how a single cue is selected from among many is poorly understood. This study shows that Drosophila ring neurons-central brain neurons implicated in navigation-display visual stimulus selection. Using in vivo two-color two-photon imaging with genetically encoded calcium indicators, this study demonstrates that individual ring neurons inherit simple-cell-like receptive fields from their upstream partners. Stimuli in the contralateral visual field suppressed responses to ipsilateral stimuli in both populations. Suppression strength depended on when and where the contralateral stimulus was presented, an effect stronger in ring neurons than in their upstream inputs. This history-dependent effect on the temporal structure of visual responses, which was well modeled by a simple biphasic filter, may determine how visual references are selected for the fly's internal compass. This approach highlights how two-color calcium imaging can help identify and localize the origins of sensory transformations across synaptically connected neural populations.

Sunday, September 3rd

Ries, A. S., Hermanns, T., Poeck, B. and Strauss, R. (2017). Serotonin modulates a depression-like state in Drosophila responsive to lithium treatment. Nat Commun 8: 15738. PubMed ID: 28585544
Major depressive disorder (MDD) affects millions of patients; however, the pathophysiology is poorly understood. Rodent models have been developed using chronic mild stress or unavoidable punishment (learned helplessness) to induce features of depression, like general inactivity and anhedonia. This study reports a three-day vibration-stress protocol for Drosophila that reduces voluntary behavioural activity. As in many MDD patients, lithium-chloride treatment can suppress this depression-like state in flies. The behavioural changes correlate with reduced serotonin (5-HT) release at the mushroom body (MB) and can be relieved by feeding the antidepressant 5-hydroxy-L-tryptophan or sucrose, which results in elevated 5-HT levels in the brain. This relief is mediated by 5-HT-1A receptors in the α-/β-lobes of the MB, whereas 5-HT-1B receptors in the γ-lobes control behavioural inactivity. The central role of serotonin in modulating stress responses in flies and mammals indicates evolutionary conserved pathways that can provide targets for treatment and strategies to induce resilience.
Galasso, A., Cameron, C. S., Frenguelli, B. G. and Moffat, K. G. (2017). An AMPK-dependent regulatory pathway in tau-mediated toxicity. Biol Open [Epub ahead of print]. PubMed ID: 28808138
Neurodegenerative tauopathies are characterized by accumulation of hyperphosphorylated tau aggregates primarily degraded by autophagy. The 5'AMP-activated protein kinase (AMPK) is expressed in most cells, including neurons. Alongside its metabolic functions, it is also known to be activated in Alzheimer's brains, phosphorylate tau, and be a critical autophagy activator. While stress conditions can result in AMPK activation enhancing tau-mediated toxicity, AMPK activation is not always concomitant with autophagic induction. This study analysed in Drosophila the impact of AMPK and autophagy on tau-mediated toxicity, recapitulating the AMPK-mediated tauopathy condition: increased tau phosphorylation, without corresponding autophagy activation. It was demonstrated that AMPK, binding to and phosphorylating tau at Ser-262, a site reported to facilitate soluble tau accumulation, affects its degradation. This phosphorylation results in exacerbation of tau toxicity and is ameliorated via rapamycin-induced autophagy stimulation. These findings support the development of combinatorial therapies effective at reducing tau toxicity targeting tau phosphorylation and AMPK-independent autophagic induction. The proposed in vivo tool represents an ideal readout to perform preliminary screening for drugs promoting this process.
Saras, A., Wu, V. V., Brawer, H. J. and Tanouye, M. A. (2017).. Investigation of seizure-susceptibility in a Drosophila model of human epilepsy with optogenetic stimulation. Genetics [Epub ahead of print]. PubMed ID: 28630111
This study examined seizure-susceptibility in a Drosophila model of human epilepsy using optogenetic stimulation of ReaChR opsin. Photostimulation of the seizure-sensitive mutant parabss1 causes behavioral paralysis that resembles paralysis caused by mechanical stimulation, in many aspects. Electrophysiology shows that photostimulation evokes abnormal seizure-like neuronal firing in parabss1 followed by a quiescent period resembling synaptic failure and apparently responsible for paralysis. The pattern of neuronal activity concludes with seizure-like activity just prior to recovery. This study tentatively identifies the mushroom body as one apparent locus of optogenetic seizure initiation. The α/β lobes may be primarily responsible for mushroom body seizure induction.
Brandt, T., Mourier, A., Tain, L. S., Partridge, L., Larsson, N. G. and Kuhlbrandt, W. (2017). Changes of mitochondrial ultrastructure and function during ageing in mice and Drosophila. Elife 6. PubMed ID: 28699890
Ageing is a progressive decline of intrinsic physiological functions. This study examined the impact of ageing on the ultrastructure and function of mitochondria in mouse and fruit flies by electron cryo-tomography and respirometry and discovered distinct age-related changes in both model organisms. Mitochondrial function and ultrastructure are maintained in mouse heart, whereas subpopulations of mitochondria from mouse liver show age-related changes in membrane morphology. Subpopulations of mitochondria from young and old mouse kidney resemble those described for apoptosis. In aged flies, respiratory activity is compromised and the production of peroxide radicals is increased. In about 50% of mitochondria from old flies, the inner membrane organization breaks down. This establishes a clear link between inner membrane architecture and functional decline. Mitochondria were affected by ageing to very different extents, depending on the organism and possibly on the degree to which tissues within the same organism are protected against mitochondrial damage.

Saturday, September 2nd

Zhu, J., Palliyil, S., Ran, C. and Kumar, J. P. (2017). Drosophila Pax6 promotes development of the entire eye-antennal disc, thereby ensuring proper adult head formation. Proc Natl Acad Sci U S A 114(23): 5846-5853. PubMed ID: 28584125
Paired box 6 (Pax6) is considered to be the master control gene for eye development in all seeing animals studied so far. In vertebrates, it is required not only for lens/retina formation but also for the development of the CNS, olfactory system, and pancreas. Although Pax6 plays important roles in cell differentiation, proliferation, and patterning during the development of these systems, the underlying mechanism remains poorly understood. In the fruit fly, Drosophila melanogaster, Pax6 also functions in a range of tissues, including the eye and brain. This report describes the function of Pax6 in Drosophila eye-antennal disc development. Previous studies have suggested that the two fly Pax6 genes, eyeless (ey) and twin of eyeless (toy), initiate eye specification, whereas eyegone (eyg) and the Notch (N) pathway independently regulate cell proliferation. This study shows that Pax6 controls eye progenitor cell survival and proliferation through the activation of teashirt (tsh) and eyg, thereby indicating that Pax6 initiates both eye specification and proliferation. Although simultaneous loss of ey and toy during early eye-antennal disc development disrupts the development of all head structures derived from the eye-antennal disc, overexpression of N or tsh in the absence of Pax6 rescues only antennal and head epidermis development. Furthermore, overexpression of tsh induces a homeotic transformation of the fly head into thoracic structures. Taking these data together, this study demonstrates that Pax6 promotes development of the entire eye-antennal disc and that the retinal determination network works to repress alternative tissue fates, which ensures proper development of adult head structures.
Aggarwal, P., Gera, J., Ghosh, S., Mandal, L. and Mandal, S. (2017). Non-canonical Decapentaplegic signaling activates Matrix metalloproteinase 1 to restrict hedgehog activity and limit ectopic eye differentiation in Drosophila. Genetics [Epub ahead of print]. PubMed ID: 28696218
One of the pertinent issues associated with cellular plasticity is to understand how the delicate balance between the determined state of cells and the extent to which they can transdetermine is maintained. Employing the well-established model of generating ectopic eyes in developing wing discs of Drosophila by ectopic eyeless expression, this study provides evidence for the genetic basis of this mechanism. By both loss-of-function and gain-of-function genetic analyses, Matrix metalloproteinase 1 (Mmp1) was demonstrated to play an important role in regulating the extent of ectopic ommatidial differentiation. Transcriptional activation of ectopic Mmp1 by the morphogen Decapentaplegic (Dpp) is not triggered by its canonical signaling pathway that involves Mad. Rather, Dpp activates an alternate cascade involving dTak1 and JNK, to induce ectopic Mmp1 expression. Mutational analyses reveal that Mmp1 negatively regulates ectopic eye differentiation by restricting the rate of proliferation and the levels of expression of retinal determining genes dachshund and eyes absent This is primarily achieved by restricting the range of Hh signaling. Importantly, the increase in proliferation and up-regulation of target retinal determining genes, as observed upon attenuating Mmp1 activity, get significantly rescued when ectopic eyes are generated in wing discs of hh heterozygous mutants. In conjunction with the previously established instructive and permissive roles of Dpp in facilitating ectopic eye differentiation in wing discs, the outcome of this study sheds light on a mechanism by which Dpp plays a dual role in modulating the delicate balance between the determined state of cells and the extent they can transdetermine.
Chen, W., Huang, H., Hatori, R. and Kornberg, T. B. (2017). Essential basal cytonemes take up Hedgehog in the Drosophila wing imaginal disc. Development [Epub ahead of print]. PubMed ID: 28743798
Morphogen concentration gradients that extend across developmental fields form by dispersion from source cells. In the Drosophila wing disc, Hedgehog (Hh) produced by posterior compartment cells distributes in a concentration gradient to adjacent cells of the anterior compartment. This study monitored Hh:GFP after pulsed expression and analyzed movements and co-localization of Hh, Patched (Ptc) and Smoothened (Smo) proteins tagged with GFP or mCherry and expressed at physiological levels from bacterial artificial chromosome transgenes. Hh:GFP moved to basal sub-cellular locations prior to release from posterior compartment cells that express it, and was taken up by basal cytonemes that extend to the source cells. Hh and Ptc were present in puncta that moved along the basal cytonemes and formed characteristic apical-basal distributions in the anterior compartment cells. The basal cytonemes required diaphanous, Scar, neuroglian, and synaptobrevin, and both the Hh gradient and Hh signaling declined under conditions in which the cytonemes were compromised. These findings show that in the wing disc, Hh distributions and signaling are dependent upon basal release and uptake, and on cytoneme-mediated movement. No evidence for apical dispersion was obtained.
Ma, M., Cao, X., Dai, J. and Pastor-Pareja, J. C. (2017). Basement membrane manipulation in Drosophila wing discs affects Dpp retention but not growth mechanoregulation. Dev Cell 42(1): 97-106.e104. PubMed ID: 28697337
Basement membranes (BMs) are extracellular matrix polymers basally underlying epithelia, where they regulate cell signaling and tissue mechanics. Constriction by the BM shapes Drosophila wing discs, a well-characterized model of tissue growth. Recently, the hypothesis that mechanical factors govern wing growth has received much attention, but it has not been definitively tested. This study manipulated BM composition to cause dramatic changes in tissue tension. Increased tissue compression was found when perlecan was knocked down did not affect adult wing size. BM elimination, decreasing compression, reduced wing size but did not visibly affect Hippo signaling, widely postulated to mediate growth mechanoregulation. BM elimination, in contrast, attenuated signaling by bone morphogenetic protein/transforming growth factor beta ligand Dpp, which was not efficiently retained within the tissue and escaped to the body cavity. These results challenge mechanoregulation of wing growth, while uncovering a function of BMs in preserving a growth-promoting tissue environment.

Friday, September 1st

Li, L. and Wunderlich, Z. (2017). An enhancer's length and composition are shaped by its regulatory task. Front Genet 8: 63. PubMed ID: 28588608
Enhancers drive the gene expression patterns required for virtually every process in metazoans. It is proposed that enhancer length and transcription factor (TF) binding site composition-the number and identity of TF binding sites-reflect the complexity of the enhancer's regulatory task. In development, regulatory task complexity is defined as the number of fates specified in a set of cells at once. It is hypothesized that enhancers with more complex regulatory tasks will be longer, with more, but less specific, TF binding sites. Larger numbers of binding sites can be arranged in more ways, allowing enhancers to drive many distinct expression patterns, and therefore cell fates, using a finite number of TF inputs. This study compared ~100 enhancers patterning the more complex anterior-posterior (AP) axis and the simpler dorsal-ventral (DV) axis in Drosophila and found that the AP enhancers are longer with more, but less specific binding sites than the (DV) enhancers. Using a set of ~3,500 enhancers, enhancer length and TF binding site number were found to increase with increasing regulatory task complexity. Therefore, to be broadly applicable, computational tools to study enhancers must account for differences in regulatory task.
Kyrchanova, O., Zolotarev, N., Mogila, V., Maksimenko, O., Schedl, P. and Georgiev, P. (2017). Architectural protein Pita cooperates with dCTCF in organization of functional boundaries in Bithorax Complex. Development [Epub ahead of print]. PubMed ID: 28619827
Boundaries in the Bithorax Complex (BX-C) of Drosophila delimit autonomous regulatory domains that drive parasegment-specific expression of homeotic genes. BX-C boundaries have two critical functions: they must block crosstalk between adjacent regulatory domains, and at the same time facilitate boundary bypass. The C2H2 zinc finger Pita protein binds to several BX-C boundaries including Fab-7 and Mcp. To study Pita functions, a boundary replacement strategy was used by substituting modified DNAs for the Fab-7 boundary, which is located between the iab-6 and iab-7 regulatory domains. Multimerized Pita sites block iab-6<-->ab-7 crosstalk but fail to support iab-6 regulation of Abd-B (bypass). In the case of Fab-7 a novel sensitized background was used to show that the two Pita sites contribute its boundary function. Although Mcp is from BX-C, it does not function appropriately when substituted for Fab-7; it blocks crosstalk but does not support bypass. Mutation of the Mcp Pita site disrupts blocking activity and also eliminates dCTCF binding. In contrast, mutation of the Mcp dCTCF site does not affect Pita binding, and this mutant boundary retains partial function.
Barr, K. A. and Reinitz, J. (2017). A sequence level model of an intact locus predicts the location and function of nonadditive enhancers. PLoS One 12(7): e0180861. PubMed ID: 28715438
Metazoan gene expression is controlled through the action of long stretches of noncoding DNA that contain enhancers-shorter sequences responsible for controlling a single aspect of a gene's expression pattern. Models built on thermodynamics have shown how enhancers interpret protein concentration in order to determine specific levels of gene expression, but the emergent regulatory logic of a complete regulatory locus shows qualitative and quantitative differences from isolated enhancers. Such differences may arise from steric competition limiting the quantity of DNA that can simultaneously influence the transcription machinery. This competition was incorporated into a mechanistic model of gene regulation, generated efficient algorithms for this computation, and applied it to the regulation of Drosophila even-skipped (eve). This model finds the location of enhancers and identifies which factors control the boundaries of eve expression. This model predicts a new enhancer that, when assayed in vivo, drives expression in a non-eve pattern. Incorporation of chromatin accessibility eliminates this inconsistency.
Crocker, J. and Stern, D. L. (2017). Functional regulatory evolution outside of the minimal even-skipped stripe 2 enhancer. Development [Epub ahead of print]. PubMed ID: 28760812
Transcriptional enhancers are regions of DNA that drive precise patterns of gene expression. While many studies have elucidated how individual enhancers can evolve, most of this work has focused on what are called "minimal" enhancers, the smallest DNA regions that drive expression that approximates an aspect of native gene expression. This study explored how the Drosophila erecta even-skipped (eve) locus has evolved by testing its activity in the divergent D. melanogaster genome. As has been reported previously, it was found that the D. erecta eve stripe 2 enhancer (eveS2) fails to drive appreciable expression in D. melanogaster. However, it was found that a large transgene carrying the entire D. erecta eve locus drives normal eve expression, including in stripe 2. A functional dissection of the region upstream of the D. erecta eveS2 region was performed and multiple Zelda motifs were found that are required for normal expression. These results illustrate how sequences outside of minimal enhancer regions can evolve functionally through mechanisms other than changes in transcription factor binding sites that drive patterning.
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