Concerted control of gliogenesis by InR/TOR and FGF signalling in the Drosophila post-embryonic brain

Glial cells are essential for the development and function of the nervous system. In the mammalian brain, vast numbers of glia of several different functional types are generated during late embryonic and early foetal development. However, the molecular cues that instruct gliogenesis and determine glial cell type are poorly understood. During post-embryonic development, the number of glia in the Drosophila larval brain increases dramatically, potentially providing a powerful model for understanding gliogenesis. Using glial-specific clonal analysis we find that perineural glia and cortex glia proliferate extensively through symmetric cell division in the post-embryonic brain. Using pan-glial inhibition and loss-of-function clonal analysis we find that Insulin-like receptor (InR)/Target of rapamycin (TOR) signalling is required for the proliferation of perineural glia. Fibroblast growth factor (FGF) signalling is also required for perineural glia proliferation and acts synergistically with the InR/TOR pathway. Cortex glia require InR in part, but not downstream components of the TOR pathway, for proliferation. Moreover, cortex glia absolutely require FGF signalling, such that inhibition of the FGF pathway almost completely blocks the generation of cortex glia. Neuronal expression of the FGF receptor ligand Pyramus is also required for the generation of cortex glia, suggesting a mechanism whereby neuronal FGF expression coordinates neurogenesis and cortex gliogenesis. In summary, we have identified two major pathways that control perineural and cortex gliogenesis in the post-embryonic brain and have shown that the molecular circuitry required is lineage specific

An in vivo RNA interference screen identifies gene networks controlling Drosophila melanogaster blood cell homeostasis

<p>Abstract</p> <p>Background</p> <p>In metazoans, the hematopoietic system plays a key role both in normal development and in defense of the organism. In Drosophila, the cellular immune response involves three types of blood cells: plasmatocytes, crystal cells and lamellocytes. This last cell type is barely present in healthy larvae, but its production is strongly induced upon wasp parasitization or in mutant contexts affecting larval blood cell homeostasis. Notably, several zygotic mutations leading to melanotic mass (or "tumor") formation in larvae have been associated to the deregulated differentiation of lamellocytes. To gain further insights into the gene regulatory network and the mechanisms controlling larval blood cell homeostasis, we conducted a tissue-specific loss of function screen using hemocyte-specific Gal4 drivers and <it>UAS-dsRNA </it>transgenic lines.</p> <p>Results</p> <p>By targeting around 10% of the Drosophila genes, this <it>in vivo </it>RNA interference screen allowed us to recover 59 melanotic tumor suppressor genes. In line with previous studies, we show that melanotic tumor formation is associated with the precocious differentiation of stem-cell like blood progenitors in the larval hematopoietic organ (the lymph gland) and the spurious differentiation of lamellocytes. We also find that melanotic tumor formation can be elicited by defects either in the fat body, the embryo-derived hemocytes or the lymph gland. In addition, we provide a definitive confirmation that lymph gland is not the only source of lamellocytes as embryo-derived plasmatocytes can differentiate into lamellocytes either upon wasp infection or upon loss of function of the Friend of GATA cofactor U-shaped.</p> <p>Conclusions</p> <p>In this study, we identify 55 genes whose function had not been linked to blood cell development or function before in Drosophila. Moreover our analyses reveal an unanticipated plasticity of embryo-derived plasmatocytes, thereby shedding new light on blood cell lineage relationship, and pinpoint the Friend of GATA transcription cofactor U-shaped as a key regulator of the plasmatocyte to lamellocyte transformation.</p

Systemic and local cues drive neural stem cell niche remodelling during neurogenesis in Drosophila.

Successful neurogenesis requires adequate proliferation of neural stem cells (NSCs) and their progeny, followed by neuronal differentiation, maturation and survival. NSCs inhabit a complex cellular microenvironment, the niche, which influences their behaviour. To ensure sustained neurogenesis, niche cells must respond to extrinsic, environmental changes whilst fulfilling the intrinsic requirements of the neurogenic program and adapting their roles accordingly. However, very little is known about how different niche cells adjust their properties to such inputs. Here, we show that nutritional and NSC-derived signals induce the remodelling of Drosophila cortex glia, adapting this glial niche to the evolving needs of NSCs. First, nutrition-induced activation of PI3K/Akt drives the cortex glia to expand their membrane processes. Second, when NSCs emerge from quiescence to resume proliferation, they signal to glia to promote membrane remodelling and the formation of a bespoke structure around each NSC lineage. The remodelled glial niche is essential for newborn neuron survival

Relative Roles of the Cellular and Humoral Responses in the Drosophila Host Defense against Three Gram-Positive Bacterial Infections

BACKGROUND: Two NF-kappaB signaling pathways, Toll and immune deficiency (imd), are required for survival to bacterial infections in Drosophila. In response to septic injury, these pathways mediate rapid transcriptional activation of distinct sets of effector molecules, including antimicrobial peptides, which are important components of a humoral defense response. However, it is less clear to what extent macrophage-like hemocytes contribute to host defense. METHODOLOGY/PRINCIPAL FINDINGS: In order to dissect the relative importance of humoral and cellular defenses after septic injury with three different gram-positive bacteria (Micrococcus luteus, Enterococcus faecalis, Staphylococcus aureus), we used latex bead pre-injection to ablate macrophage function in flies wildtype or mutant for various Toll and imd pathway components. We found that in all three infection models a compromised phagocytic system impaired fly survival--independently of concomitant Toll or imd pathway activation. Our data failed to confirm a role of the PGRP-SA and GNBP1 Pattern Recognition Receptors for phagocytosis of S. aureus. The Drosophila scavenger receptor Eater mediates the phagocytosis by hemocytes or S2 cells of E. faecalis and S. aureus, but not of M. luteus. In the case of M. luteus and E. faecalis, but not S. aureus, decreased survival due to defective phagocytosis could be compensated for by genetically enhancing the humoral immune response. CONCLUSIONS/SIGNIFICANCE: Our results underscore the fundamental importance of both cellular and humoral mechanisms in Drosophila immunity and shed light on the balance between these two arms of host defense depending on the invading pathogen

Effective but Costly, Evolved Mechanisms of Defense against a Virulent Opportunistic Pathogen in Drosophila melanogaster

Drosophila harbor substantial genetic variation for antibacterial defense, and investment in immunity is thought to involve a costly trade-off with life history traits, including development, life span, and reproduction. To understand the way in which insects invest in fighting bacterial infection, we selected for survival following systemic infection with the opportunistic pathogen Pseudomonas aeruginosa in wild-caught Drosophila melanogaster over 10 generations. We then examined genome-wide changes in expression in the selected flies relative to unselected controls, both of which had been infected with the pathogen. This powerful combination of techniques allowed us to specifically identify the genetic basis of the evolved immune response. In response to selection, population-level survivorship to infection increased from 15% to 70%. The evolved capacity for defense was costly, however, as evidenced by reduced longevity and larval viability and a rapid loss of the trait once selection pressure was removed. Counter to expectation, we observed more rapid developmental rates in the selected flies. Selection-associated changes in expression of genes with dual involvement in developmental and immune pathways suggest pleiotropy as a possible mechanism for the positive correlation. We also found that both the Toll and the Imd pathways work synergistically to limit infectivity and that cellular immunity plays a more critical role in overcoming P. aeruginosa infection than previously reported. This work reveals novel pathways by which Drosophila can survive infection with a virulent pathogen that may be rare in wild populations, however, due to their cost

Bacterial Communities of Diverse Drosophila Species: Ecological Context of a Host–Microbe Model System

Drosophila melanogaster is emerging as an important model of non-pathogenic host–microbe interactions. The genetic and experimental tractability of Drosophila has led to significant gains in our understanding of animal–microbial symbiosis. However, the full implications of these results cannot be appreciated without the knowledge of the microbial communities associated with natural Drosophila populations. In particular, it is not clear whether laboratory cultures can serve as an accurate model of host–microbe interactions that occur in the wild, or those that have occurred over evolutionary time. To fill this gap, we characterized natural bacterial communities associated with 14 species of Drosophila and related genera collected from distant geographic locations. To represent the ecological diversity of Drosophilids, examined species included fruit-, flower-, mushroom-, and cactus-feeders. In parallel, wild host populations were compared to laboratory strains, and controlled experiments were performed to assess the importance of host species and diet in shaping bacterial microbiome composition. We find that Drosophilid flies have taxonomically restricted bacterial communities, with 85% of the natural bacterial microbiome composed of only four bacterial families. The dominant bacterial taxa are widespread and found in many different host species despite the taxonomic, ecological, and geographic diversity of their hosts. Both natural surveys and laboratory experiments indicate that host diet plays a major role in shaping the Drosophila bacterial microbiome. Despite this, the internal bacterial microbiome represents only a highly reduced subset of the external bacterial communities, suggesting that the host exercises some level of control over the bacteria that inhabit its digestive tract. Finally, we show that laboratory strains provide only a limited model of natural host–microbe interactions. Bacterial taxa used in experimental studies are rare or absent in wild Drosophila populations, while the most abundant associates of natural Drosophila populations are rare in the lab

The Drosophila melanogaster host model

The deleterious and sometimes fatal outcomes of bacterial infectious diseases are the net result of the interactions between the pathogen and the host, and the genetically tractable fruit fly, Drosophila melanogaster, has emerged as a valuable tool for modeling the pathogen–host interactions of a wide variety of bacteria. These studies have revealed that there is a remarkable conservation of bacterial pathogenesis and host defence mechanisms between higher host organisms and Drosophila. This review presents an in-depth discussion of the Drosophila immune response, the Drosophila killing model, and the use of the model to examine bacterial–host interactions. The recent introduction of the Drosophila model into the oral microbiology field is discussed, specifically the use of the model to examine Porphyromonas gingivalis–host interactions, and finally the potential uses of this powerful model system to further elucidate oral bacterial-host interactions are addressed

ROLE DE L'EXOENZYME S DE PSEUDOMONAS AERUGINOSA DANS LA VIRULENCE BACTERIENNE : ETUDE FONCTIONNELLE DU DOMAINE GAP ET DE SES CIBLES SUR LA REPONSE IMMUNITAIRE CHEZ DROSOPHILA MELANOGASTER

The type III exoenzyme S toxin of Pseudomonas aeruginosa possesses a GAP domain (GTPase Activating Protein) (ExosGAP) inhibiting the Rho GTPases (Rho, Rac and Cdc42) and phagocytosis in Mammal cell lines. We have used a transgenesis approach in Drosophila melanogaster using a tissue-specific inducible expression system (UAS-Gal4) to express ExoSGAP. We have demonstrated that ExoSGAP targeted in vivo the Rho GTPases Rho, Rac1, Rac2 and Cdc42. The ExoSGAP expression affects fly resistance to infection by inhibiting phagocytosis of bacteria by plasmatocytes, a macrophage cell line, but has no effect on NF-kB signalling pathways. A genetic approach has allowed the identification of new ExoSGAP targets by looking for genes whose misexpression modifies the eye or wing phenotype induced by the toxin expression. We have identified several genes which can be implicated in JNK and NF-kB signalling pathways. All these results validate a new strategy to study type III toxins by transgenesis in Drosophila.In parallel, I have demonstrated GTPase Rac2 specificity in Drosophila resistance to infection. Rac2 participates notably in phagocytosis.The works of Dr. H. Tricoire led to the identification of 180 genes whose misexpression modifies fly response to oxidative stress. We have tested 105 of these lines for their resistance to infections to study a possible correlation between the oxidative and infectious stress response. This screen allows to demonstrate the implication of a protein with a lectin domain called PSLR (Pseudomonas Sensitive Lectin Receptor) in fly immunity.L'exoenzyme S, une toxine de type III, de Pseudomonas aeruginosa possède un domaine GAP (GTPase Activating Protein) (ExoSGAP) inhibant les Rho GTPases (Rho, Rac, Cdc42) et la phagocytose dans les cellules de Mammifères en culture. J'ai utilisé une approche de transgenèse chez Drosophila melanogaster en utilisant un système d'expression tissu-spécifique inductible (UAS-Gal4) afin d'exprimer ExoSGAP. Nous avons montré qu'ExoSGAP cible in vivo les Rho GTPases Rho, Rac1, Rac2 et Cdc42. ExoSGAP affecte la résistance des mouches aux infections en inhibant la phagocytose des bactéries par les plasmatocytes, des cellules de type macrophage, mais n'a pas d'effet sur les voies NF-kB. Une approche génétique a permis d'identifier de nouvelles cibles de la toxine, en recherchant des gènes dont la dérégulation modifie le phénotype d'œil ou d'aile induit par l'expression d'ExoSGAP. Nous avons identifié plusieurs gènes pouvant avoir un rôle dans les voies des JNK et NF-kB Ces résultats valident une stratégie d'étude des toxines de type III par transgenèse chez la drosophile.J'ai parallèlement montré la spécificité de la GTPase Rac2 dans la résistance des mouches aux infections bactériennes. Rac2 participe notamment à la phagocytose.Les travaux du Dr. H. Tricoire ont permis d'identifier 180 gènes dont la dérégulation modifie la réponse des mouches à un stress oxydant. J'ai testé 105 de ces lignées pour leur résistance aux infections, afin d'étudier une corrélation possible entre la réponse aux stress oxydant et infectieux. Ce crible a permis de montrer l'implication d'une protéine à domaine lectine PSLR (Pseudomonas Sensitive Lectin Receptor) dans la réponse immunitaire de la drosophile