Dicer-2 Regulates Resistance and Maintains Homeostasis against Zika Virus Infection in Drosophila.

Zika virus (ZIKV) outbreaks pose a massive public health threat in several countries. We have developed an in vivo model to investigate the host-ZIKV interaction in Drosophila We have found that a strain of ZIKV replicates in wild-type flies without reducing their survival ability. We have shown that ZIKV infection triggers RNA interference and that mutating Dicer-2 results in enhanced ZIKV load and increased susceptibility to ZIKV infection. Using a flavivirus-specific Ab, we have found that ZIKV is localized in the gut and fat body cells of the infected wild-type flies and results in their perturbed homeostasis. In addition, Dicer-2 mutants display severely reduced insulin activity, which could contribute toward the increased mortality of these flies. Our work establishes the suitability of Drosophila as the model system to study host-ZIKV dynamics, which is expected to greatly advance our understanding of the molecular and physiological processes that determine the outcome of this disease.

Thioester-Containing Proteins 2 and 4 Affect the Metabolic Activity and Inflammation Response in Drosophila.

Drosophila melanogaster is an outstanding model for studying host antipathogen defense. Although substantial progress has been made in understanding how metabolism and immunity are interrelated in flies, little information has been obtained on the molecular players that regulate metabolism and inflammation in Drosophila during pathogenic infection. Recently, we reported that the inactivation of thioester-containing protein 2 (Tep2) and Tep4 promotes survival and decreases the bacterial burden in flies upon infection with the virulent pathogens Photorhabdus luminescens and Photorhabdus asymbiotica Here, we investigated physiological and pathological defects in tep mutant flies in response to Photorhabdus challenge. We find that tep2 and tep4 loss-of-function mutant flies contain increased levels of carbohydrates and triglycerides in the presence or absence of Photorhabdus infection. We also report that Photorhabdus infection leads to higher levels of nitric oxide and reduced transcript levels of the apical caspase-encoding gene Dronc in tep2 and tep4 mutants. We show that Tep2 and Tep4 are upregulated mainly in the fat body rather than the gut in Photorhabdus-infected wild-type flies and that tep mutants contain decreased numbers of Photorhabdus bacteria in both tissue types. We propose that the inactivation of Tep2 or Tep4 in adult Drosophila flies results in lower levels of inflammation and increased energy reserves in response to Photorhabdus, which could confer a survival-protective effect during the initial hours of infection.

Epithelial neoplasia in Drosophila entails switch to primitive cell states.

Only select cell types in an organ display neoplasia when targeted oncogenically. How developmental lineage hierarchies of these cells prefigure their neoplastic propensities is not yet well-understood. Here we show that neoplastic Drosophila epithelial cells reverse their developmental commitments and switch to primitive cell states. In a context of alleviated tissue surveillance, for example, loss of Lethal giant larvae (Lgl) tumor suppressor in the wing primordium induced epithelial neoplasia in its Homothorax (Hth)-expressing proximal domain. Transcriptional profile of proximally transformed mosaic wing epithelium and functional tests revealed tumor cooperation by multiple signaling pathways. In contrast, lgl(-) clones in the Vestigial (Vg)-expressing distal wing epithelium were eliminated by cell death. Distal lgl(-) clones, however, could transform when both tissue surveillance and cell death were compromised genetically and, alternatively, when the transcription cofactor of Hippo signaling pathway, Yorkie (Yki), was activated, or when Ras/EGFR signaling was up-regulated. Furthermore, transforming distal lgl(-) clones displayed loss of Vg, suggesting reversal of their terminal cell fate commitment. In contrast, reinforcing a distal (wing) cell fate commitment in lgl(-) clones by gaining Vg arrested their neoplasia and induced cell death. We also show that neoplasia in both distal and proximal lgl(-) clones could progress in the absence of Hth, revealing Hth-independent wing epithelial neoplasia. Likewise, neoplasia in the eye primordium resulted in loss of Elav, a retinal cell marker; these, however, switched to an Hth-dependent primitive cell state. These results suggest a general characteristic of "cells-of-origin" in epithelial cancers, namely their propensity for switch to primitive cell states.

chinmo-mutant spermatogonial stem cells cause mitotic drive by evicting non-mutant neighbors from the niche.

Niches maintain a finite pool of stem cells via restricted space and short-range signals. Stem cells compete for limited niche resources, but the mechanisms regulating competition are poorly understood. Using the Drosophila testis model, we show that germline stem cells (GSCs) lacking the transcription factor Chinmo gain a competitive advantage for niche access. Surprisingly, chinmo-/- GSCs rely on a new mechanism of competition in which they secrete the extracellular matrix protein Perlecan to selectively evict non-mutant GSCs and then upregulate Perlecan-binding proteins to remain in the altered niche. Over time, the GSC pool can be entirely replaced with chinmo-/- cells. As a consequence, the mutant chinmo allele acts as a gene drive element; the majority of offspring inherit the allele despite the heterozygous genotype of the parent. Our results suggest that the influence of GSC competition may extend beyond individual stem cell niche dynamics to population-level allelic drift and evolution.

Transcriptomic analysis of feminizing somatic stem cells in the Drosophila testis reveals putative downstream effectors of the transcription factor Chinmo.

One of the best examples of sexual dimorphism is the development and function of the gonads, ovaries and testes, which produce sex-specific gametes, oocytes, and spermatids, respectively. The development of these specialized germ cells requires sex-matched somatic support cells. The sexual identity of somatic gonadal cells is specified during development and must be actively maintained during adulthood. We previously showed that the transcription factor Chinmo is required to ensure the male sexual identity of somatic support cells in the Drosophila melanogaster testis. Loss of chinmo from male somatic gonadal cells results in feminization: they transform from squamous to epithelial-like cells that resemble somatic cells in the female gonad but fail to properly ensheath the male germline, causing infertility. To identify potential target genes of Chinmo, we purified somatic cells deficient for chinmo from the adult Drosophila testis and performed next-generation sequencing to compare their transcriptome to that of control somatic cells. Bioinformatics revealed 304 and 1549 differentially upregulated and downregulated genes, respectively, upon loss of chinmo in early somatic cells. Using a combination of methods, we validated several differentially expressed genes. These data sets will be useful resources to the community.

Tumor induction in Drosophila imaginal epithelia triggers modulation of fat body lipid droplets.

Our understanding of cancer-specific metabolic changes is currently unclear. In recent years, the fruit fly Drosophila melanogaster with its powerful genetic tools has become an attractive model for studying both tumor autonomous and the systemic processes resulting from the tumor growth. Here we investigated the effect of tumorigenesis on the modulation of lipid droplets (LDs) in the larval fat bodies (mammalian equivalent of adipose tissue). We have overexpressed Notch signaling alone or in combination with the developmental regulator Myocyte enhancer factor 2 (Mef2) using wing-specific and eye-specific drivers, quantified the size of LDs in the fat body of the different tumor bearing larvae, and estimated the expression of genes associated with lipolysis and lipogenesis. We have found that hyperplastic and neoplastic tumor induced by overexpression of Notch and co-expression of Notch and Mef2 respectively triggers impaired lipid metabolism marked by increased size of fat body LDs. The impaired lipid metabolism in tumor carrying larvae is linked to the altered expression of genes that participate in lipolysis and lipogenesis. These findings reveal modulation of LDs as one of the host's specific response upon tumor initiation. This information could potentially uncover mechanisms for designing innovative approaches to modulate cancer growth.

Zika virus non-structural protein NS4A restricts eye growth in Drosophila through regulation of JAK/STAT signaling.

To gain a comprehensive view of the changes in host gene expression underlying Zika virus (ZIKV) pathogenesis, we performed whole-genome RNA sequencing (RNA-seq) of ZIKV-infected Drosophila adult flies. RNA-seq analysis revealed that ZIKV infection alters several and diverse biological processes, including stress, locomotion, lipid metabolism, imaginal disc morphogenesis and regulation of JAK/STAT signaling. To explore the interaction between ZIKV infection and JAK/STAT signaling regulation, we generated genetic constructs overexpressing ZIKV-specific non-structural proteins NS2A, NS2B, NS4A and NS4B. We found that ectopic expression of non-structural proteins in the developing Drosophila eye significantly restricts growth of the larval and adult eye and correlates with considerable repression of the in vivo JAK/STAT reporter, 10XStat92E-GFP At the cellular level, eye growth defects are associated with reduced rate of proliferation without affecting the overall rate of apoptosis. In addition, ZIKV NS4A genetically interacts with the JAK/STAT signaling components; co-expression of NS4A along with the dominant-negative form of domeless or StatRNAi results in aggravated reduction in eye size, while co-expression of NS4A in HopTuml (also known as hopTum ) mutant background partially rescues the hop-induced eye overgrowth phenotype. The function of ZIKV NS4A in regulating growth is maintained in the wing, where ZIKV NS4A overexpression in the pouch domain results in reduced growth linked with diminished expression of Notch targets, Wingless (Wg) and Cut, and the Notch reporter, NRE-GFP Thus, our study provides evidence that ZIKV infection in Drosophila results in restricted growth of the developing eye and wing, wherein eye phenotype is induced through regulation of JAK/STAT signaling, whereas restricted wing growth is induced through regulation of Notch signaling. The interaction of ZIKV non-structural proteins with the conserved host signaling pathways further advance our understanding of ZIKV-induced pathogenesis.This article has an associated First Person interview with the first author of the paper.

Intestinal lipid droplets as novel mediators of host-pathogen interaction in Drosophila.

Lipid droplets (LDs) are lipid-carrying multifunctional organelles, which might also interact with pathogens and influence the host immune response. However, the exact nature of these interactions remains currently unexplored. Here we show that systemic infection of Drosophila adult flies with non-pathogenic Escherichia coli, the extracellular bacterial pathogen Photorhabdus luminescens or the facultative intracellular pathogen Photorhabdus asymbiotica results in intestinal steatosis marked by lipid accumulation in the midgut. Accumulation of LDs in the midgut also correlates with increased whole-body lipid levels characterized by increased expression of genes regulating lipogenesis. The lipid-enriched midgut further displays reduced expression of the enteroendocrine-secreted hormone, Tachykinin. The observed lipid accumulation requires the Gram-negative cell wall pattern recognition molecule, PGRP-LC, but not PGRP-LE, for the humoral immune response. Altogether, our findings indicate that Drosophila LDs are inducible organelles, which can serve as markers for inflammation and, depending on the nature of the challenge, they can dictate the outcome of the infection.

Next-Generation Sequencing Reveals Increased Anti-oxidant Response and Ecdysone Signaling in STAT Supercompetitors in Drosophila.

Cell competition is the elimination of one viable population of cells (the losers) by a neighboring fitter population (the winners) and was discovered by studies in the Drosophila melanogaster wing imaginal disc. Supercompetition is a process in which cells with elevated JAK/STAT signaling or increased Myc become winners and outcompete wild-type neighbors. To identify the genes that are differentially regulated in STAT supercompetitors, we purified these cells from Drosophila wing imaginal discs and performed next-generation sequencing. Their transcriptome was compared to those of control wing disc cells and Myc supercompetitors. Bioinformatics revealed that STAT and Myc supercompetitors have distinct transcriptomes with only 41 common differentially regulated genes. Furthermore, STAT supercompetitors have elevated reactive oxygen species, an anti-oxidant response and increased ecdysone signaling. Using a combination of methods, we validated 13 differentially expressed genes. These data sets will be useful resources to the community.

Enhancer of Polycomb and the Tip60 complex repress hematological tumor initiation by negatively regulating JAK/STAT pathway activity.

Myeloproliferative neoplasms (MPNs) are clonal hematopoietic disorders that cause excessive production of myeloid cells. Most MPN patients have a point mutation in JAK2 (JAK2V617F ), which encodes a dominant-active kinase that constitutively triggers JAK/STAT signaling. In Drosophila, this pathway is simplified, with a single JAK, Hopscotch (Hop), and a single STAT transcription factor, Stat92E. The hopTumorous-lethal [hopTum ] allele encodes a dominant-active kinase that induces sustained Stat92E activation. Like MPN patients, hopTum mutants have significantly more myeloid cells, which form invasive tumors. Through an unbiased genetic screen, we found that heterozygosity for Enhancer of Polycomb [E(Pc)], a component of the Tip60 lysine acetyltransferase complex (also known as KAT5 in humans), significantly increased tumor burden in hopTum animals. Hematopoietic depletion of E(Pc) or other Tip60 components in an otherwise wild-type background also induced blood cell tumors. The E(Pc) tumor phenotype was dependent on JAK/STAT activity, as concomitant depletion of hop or Stat92E inhibited tumor formation. Stat92E target genes were significantly upregulated in E(Pc)-mutant myeloid cells, indicating that loss of E(Pc) activates JAK/STAT signaling. Neither the hop nor Stat92E gene was upregulated upon hematopoietic E(Pc) depletion, suggesting that the regulation of the JAK/STAT pathway by E(Pc) is dependent on substrates other than histones. Indeed, E(Pc) depletion significantly increased expression of Hop protein in myeloid cells. This study indicates that E(Pc) works as a tumor suppressor by attenuating Hop protein expression and ultimately JAK/STAT signaling. Since loss-of-function mutations in the human homologs of E(Pc) and Tip60 are frequently observed in cancer, our work could lead to new treatments for MPN patients.This article has an associated First Person interview with the first author of the paper.

Endosymbiont-based immunity in Drosophila melanogaster against parasitic nematode infection.

Associations between endosymbiotic bacteria and their hosts represent a complex ecosystem within organisms ranging from humans to protozoa. Drosophila species are known to naturally harbor Wolbachia and Spiroplasma endosymbionts, which play a protective role against certain microbial infections. Here, we investigated whether the presence or absence of endosymbionts affects the immune response of Drosophila melanogaster larvae to infection by Steinernema carpocapsae nematodes carrying or lacking their mutualistic Gram-negative bacteria Xenorhabdus nematophila (symbiotic or axenic nematodes, respectively). We find that the presence of Wolbachia alone or together with Spiroplasma promotes the survival of larvae in response to infection with S. carpocapsae symbiotic nematodes, but not against axenic nematodes. We also find that Wolbachia numbers are reduced in Spiroplasma-free larvae infected with axenic compared to symbiotic nematodes, and they are also reduced in Spiroplasma-containing compared to Spiroplasma-free larvae infected with axenic nematodes. We further show that S. carpocapsae axenic nematode infection induces the Toll pathway in the absence of Wolbachia, and that symbiotic nematode infection leads to increased phenoloxidase activity in D. melanogaster larvae devoid of endosymbionts. Finally, infection with either type of nematode alters the metabolic status and the fat body lipid droplet size in D. melanogaster larvae containing only Wolbachia or both endosymbionts. Our results suggest an interaction between Wolbachia endosymbionts with the immune response of D. melanogaster against infection with the entomopathogenic nematodes S. carpocapsae. Results from this study indicate a complex interplay between insect hosts, endosymbiotic microbes and pathogenic organisms.