abstract: Drosophila CORL (dCORL) is a central nervous system (CNS)-specific gene that is hypothesized to function in Transforming Growth Factor β signaling. It is part of the Corl multigene family that includes mouse and human homologs. dCORL is necessary for Ecdysone Receptor isoform B1 (EcR-B1) protein expression in the mushroom body, a brain region responsible for learning and memory. Beyond this, dCORL function is unknown. As dCORL expression is restricted to the CNS, co-expression experiments were performed to identify dCORL-specific neurons. In these experiments, EcR-B1 protein expression was compared to dCORL mRNA expression revealing that they are not expressed in the same cells. Therefore, EcR-B1 is regulated non-autonomously by dCORL. Co-expression analyses were also conducted utilizing dCORL reporters. For example, the reporter AH-lacZ was co-stained with two pars intercerebralis (PI) markers: Drifter (Dfr; a transcription factor found in the nucleus) and Drosophila insulin-like peptide 2 (dILP2; a peptide present in the neurosecretory cells of the pars intercerebralis [PI].) The results showed that there was complete AH-lacZ co-expression with dILP2 in third instar larval and adult brains. Previous work in our lab on dCORL mutant (Df(4)dCORL) adult longevity showed a connection between mating and increased lifespan; mated mutant females had doubled lifespans compared to virgins. Given the published relationship between insulin and longevity, I hypothesized an association between insulin, dCORL, and mating. Df(4)dCORL mutants were used to analyze the effects of dCORL loss-of-function on dILP2. There was a reduction in the number of dILP2-expressing cells in mutants compared to wild type. In wild type larval and adult PI’s, most dILP2-positive neurons also expressed Dfr. Whereas in adult virgin mutants, all dILP2 neurons were Dfr-positive. Both 3-day and 15-day old mated females showed increased dILP2 cell numbers compared to virgin mutants. In these sets of dILP2 cells only a subset expressed Dfr as in wild type. The mutant phenotypes of mated flies showed partial rescue compared to virgins. This led to the conclusion there were associations between mating, longevity, and insulin signaling through dCORL. Homology between Drosophila and mammalian Corl proteins imply these connections may be seen in mammals. / Dissertation/Thesis / Masters Thesis Biology 2018

La taille finale des organismes dépend de la vitesse et de la durée de croissance. Ces paramètres sont contrôlés par différentes hormones. La production d'hormone stéroïdienne détermine la fin de la période de croissance en déclenchant la maturité sexuelle, alors que la vitesse de croissance est régulée par la voie de signalisation de l’insuline/IGF (IIS). La vitesse de croissance des organismes est influencée par la nutrition. En effet, des défauts de croissance sont observés chez les individus souffrant de carence protéique chronique. La nutrition contrôle la croissance grâce à la voie de signalisation de l’insuline/IGF. Cependant, le mécanisme par lequel la nutrition contrôle la voie IIS est complexe et reste à élucider. Afin d’explorer cette régulation, le laboratoire utilise Drosophila melanogaster comme modèle d’étude. Chez la drosophile, il existe 8 insulin-like peptides (Dilps). Parmi eux, Dilp2 est la principale insuline promouvant la croissance systémique. Elle est produite par des neurones spécialisés appelés les Insulin Producing Cells (IPC), homologues des cellules béta du pancréas. La sécrétion de Dilp2 dans l’hémolymphe, équivalent du sang chez les vertébrés, est précisément ajustée en fonction de la nutrition. Cette régulation implique une communication inter-organe avec le corps gras, homologue du foie et du tissu adipeux blanc. Selon les conditions nutritionnelles, plusieurs signaux dérivés du corps gras (FDS) sont sécrétés et contrôlent la sécrétion de Dilp2. Ces FDS agissent directement ou indirectement sur les IPCs, via des relais neuronaux. Mon projet de thèse avait pour but de découvrir et d’étudier de nouvelles cibles neuronales contrôlant l’activité sécrétrice des IPCs, et par conséquent la croissance systémique, en fonction de la nutrition. J’ai identifié une paire de neurones inhibiteurs des IPCs, que l’on a nommé IPC-Connecting Neurons (ICN). Actifs en carence en acides aminés, ils inhibent la sécrétion des Dilps. J’ai montré que la signalisation EGFR réprime l’activité de ces neurones en condition nourrie, ce qui augmente la sécrétion des Dilps et par conséquent la taille des individus. Cette activation est due à un nouveau ligand d’EGFR : Growth Blocking Peptide (GBP). J’ai montré que ce ligand de type EGF possède des propriétés particulières puisqu’il agit de façon endocrinienne. En effet, en condition nourrie, GBP est sécrété par le corps gras dans l’hémolymphe, et atteint les ICN afin d’activer la signalisation EGFR. En conclusion, nous proposons que GBP produit par le corps gras en condition nourrie active la voie EGFR dans les neurones ICN, lève l’inhibition exercée sur les IPCs et stimule la sécrétion des Dilps. Cependant, les mécanismes moléculaires par lequel le couple GBP/EGFR inhibe l’activité neuronale des ICNs reste à élucider. Ce travail a permis d’identifier un nouveau mode de régulation de la sécrétion des insulines et de la croissance des organismes en fonction de la disponibilité et de la qualité nutritionnelle. / Body growth is tightly regulated by nutrient availability. Upon nutritional shortage, animals harmoniously reduce their body size by modulating the activity of the insulin/IGF signaling pathway (IIS). To understand how nutrition controls the IIS, we used Drosophila melanogaster as a model. Drosophila has a conserved IIS with 8 insulin-like peptides (Dilps), a unique insulin receptor and a conserved downstream signaling cascade. Among the Dilps, Dilp2 is the main growth-promoting factor. Dilp2 is produced by specialized neurons located in the brain, the Insulin-Producing-Cells (IPCs), functionally related to vertebrate beta cells. Dilp2 secretion is precisely adjusted in response to nutrition: it is released in the hemolymph under normal nutrient condition, but not upon dietary amino acid scarcity. This regulation requires several inter-organ cross-talks between the producing neurons and the fat body, which is the equivalent of the vertebrate white adipose tissue and liver. Depending on diet composition, several fat-derived signals (FDS) are secreted into the hemolymph and control Dilp2 secretion from the IPCs. These FDS act either directly or indirectly through a neuronal relay, to control the IPCs secretory activity. The aim of my PhD project was to better understand these regulations and to discover new neuronal relay controlling the IPCs secretory activity and body growth, according to nutrition. I identified a pair of neurons harboring synaptic connections with the IPCs (IPC-connecting neurons, ICNs). I determined that the ICNs activity is maximal upon amino acids shortage and is required to exert a blockage of the neighbouring IPCs. Moreover, in rich nutrient conditions, EGFR signaling prevents activation of the ICNs, allowing Dilp2 release from the IPCs. GBP1 and 2 are EGF-like peptides produced by the fat body in response to amino acids, and they can modify insulin release. However, the neural circuitries at play are unknown. I demonstrated that GBPs are atypical ligands for the EGF receptor (EGFR), with endocrine function. Using ex-vivo brain culture, I showed that the presence of the fat body-derived GBP1 in the hemolymph activates EGFR signaling in the ICNs and alleviates their inhibitory input on the IPCs, allowing Dilp2 release and therefore body growth. In conclusion, I identified a novel neural circuitry responding to fat-derived EGF-like GBPs, coupling dietary amino acids to the release of insulin-like peptides and systemic growth.