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Etude fonctionnelle du transporteur d'ammonium Rh50 dans le système neuromusculaire de Drosophila melanogaster

Abstract : Ammonia (acid/base pair NH4+/NH3) is implicated in many biological processes, such as the maintenance of acid-base balance by the kidney and the synthesis and recycling of neurotransmitters. Specific transporters, such as the Rhesus glycoproteins (Rh50), make cellular membranes permeable to ammonium. The Rh50 proteins have been described in red blood cells, liver and kidney, where they are involved in NH3 transport and in the maintenance of cell architecture. Drosophila melanogaster has a unique Rh50 gene, expressed in the central nervous system (CNS) and the neuromuscular system. Therefore, Drosophila is a model of choice for the in vivo functional study of Rh50 proteins in the nervous system.In this thesis work, we show that Rh50 is strongly expressed in muscles and enriched at the neuromuscular junction (NMJ) of the Drosophila larva, where it co-localizes with Discs large (Dlg) and other postsynaptic density proteins. Inactivation of the Rh50 gene induced muscle atrophy, larval locomotion defects, overexpression of postsynaptic glutamate receptors, and pupal lethality. Electrophysiological recordings at the larval NMJ showed that the frequency of spontaneous excitatory postsynaptic potentials increases when Rh50 is down-regulated in muscles. Rh50-deficient larvae were also more susceptible than the wild type to exposure to high concentrations of ammonium. In the CNS, Rh50 is expressed in neuroendocrine cells and our results suggest that it controls the expression of FMRFamides, neuropeptides involved in the regulation of NMJ activity.In conclusion, our work identifies Rh50 as a new essential protein in Drosophila, which is involved in synaptic development and physiology, and regulates ammonium levels and acid-base homeostasis in the neuromuscular system.
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Mathilde Lecompte. Etude fonctionnelle du transporteur d'ammonium Rh50 dans le système neuromusculaire de Drosophila melanogaster. Neurosciences [q-bio.NC]. Université Paris sciences et lettres, 2018. Français. ⟨NNT : 2018PSLET009⟩. ⟨tel-03408227⟩

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