The serine/arginine-rich (SR-) family proteins constitute a diverse group of pre-mRNA splicing factors that are essential for viability. They can be characterised based on the presence of one or two RRMs and an RS domain. A subset, of which SRSF1 is the prototype, is capable of nucleocytoplasmic shuttling; a process governed by continual cyclic phosphorylation of the RS domain. In contrast, SRSF2, another member of the SR family, is unable to shuttle due to the presence of a nuclear retention sequence (NRS) at the C-terminus of its RS domain. When this NRS is fused to SRSF1, it prevents nucleocytoplasmic shuttling of the SRSF1-NRS fusion protein. In addition to its nuclear roles, SRSF1 is directly associated with the translation machinery and can activate mRNA translation of target transcripts via an mTOR-dependent mechanism. The specific mRNA translational targets that SRSF1 serves to regulate encode numerous factors including RNA processing factors and cell-cycle proteins. The aim of this work is to study the physiological relevance of SRSF1 cytoplasmic functions, as previous data have relied on overexpression systems. CRISPR/Cas9 editing was used to knock-in the NRS naturally present in SRSF2 at the SRSF1 genomic locus, creating an SRSF1-NRS fusion protein. After numerous attempts, it was only possible to obtain a single viable homozygous clone in mouse embryonic stem cells (mESCs), despite being able to successfully tag the genomic SRSF1 locus. This strongly suggests that the ablation of SRSF1 shuttling ability is highly selected against in mESCs. To assess the physiological importance of SRSF1 nucleocytoplasmic shuttling during development, a mouse model for SRSF1-NRS was also developed. SRSF1-NRS homozygous mice are born at correct Mendelian ratios, but are small in size and present with severe hydrocephalus. Finally, proteomics was used to identify interactors of endogenous cytoplasmic SRSF1 and those that bind the NRS of SRSF2 to gain insights into the mechanism of nuclear retention for non-shuttling SR proteins. In summary, this work analyses the physiological relevance of cytoplasmic SRSF1 function and the consequences of the SRSF1-NRS allele in mouse development.

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TDP-43 est une protéine de liaison aux acides nucléiques qui joue un rôle essentiel dans le métabolisme de l'ARN. À l'état physiologique, un contrôle strict des niveaux d’expression de cette protéine est critique pour la fonction et la survie cellulaire. Une boucle d'autorégulation négative est à la base de ce contrôle du taux intracellulaire de TDP-43. Laquelle a été identifiée comme le constituant principal des inclusions observées chez une majorité des patients atteints de Sclérose Latérale Amyotrophique (SLA) ou de Dégénérescence Lobaire Fronto-Temporale (DLFT). A ce jour, plus de 50 mutations faux-sensdu gène TARDBP/TDP-43 ont été décrites chez des patients DLFT/SLA, démontrant le rôle clé de TDP-43 dans ces pathologies neurodégénératives. Notons cependant que les conséquences fonctionnelles de ces mutations ne sont pas complètement déterminées. Plusieurs études suggèrent qu’une élévation des niveaux d’accumulation de TDP-43 pourraitparticiper aux mécanismes physiopathologiques. La modulation du cycle de production de TDP-43 pourrait donc constituer une nouvelle stratégie thérapeutique. Ce travail de recherche avait donc pour principal objectif d’identifier des modulateurs génétiques de la production de TDP-43 en utilisant un nouveau modèle de drosophile transgénique mimant les principales étapes d’autorégulation de TDP-43. Nous avons ainsi pu montrer que la modulation des niveaux d’expression de la protéine TCERG1 et de plusieurs facteurs d'épissage, parmi lesquels SRSF1, SRSF3 et SF3B1, influe sur les niveaux de production deTDP-43. Nous avons également montré que la présence des mutations DLFT/SLA n’altère pas la capacité de la protéine à s’autoréguler. / TDP-43 is a DNA/RNA binding protein that plays an important role in RNA metabolism. In the physiological state, strict control of its expression levels is critical for cell function and survival. TDP-43 expression is tightly regulated through an autoregulatory negative feedback loop. This protein has been identified as the principal component of the inclusions observed in a majority of patients with Amyotrophic Lateral Sclerosis (ALS) or FrontoTemporal Lobar Degeneration (FTLD). To date, more than 50 missense mutations of the TARDBP / TDP-43 gene have been described in FTLD / ALS patients, demonstrating the key role of TDP-43 in these neurodegenerative pathologies. However, the functional consequences of TDP-43 mutations are not completely determined. Several studies suggest that high accumulation levels of TDP-43 may participate in pathophysiological mechanisms. The modulation of the production cycle of TDP-43 may therefore provide a new therapeutic strategy. The main goal of this research project was to identify genetic modulators of TDP-43 production by using a novel transgenic Drosophila model mimicking main steps of TDP-43 the autoregulatory mechanism. We identified several splicing factors, including SF2, Rbp1 and Sf3b1, as genetic modulators of TDP-43 production. We have also shown that modulation of TCERG1 expression levels affect TDP-43 production levels in flies. Finally, we found that FTLD/ALSlinked TDP-43 mutations do not alter TDP-43’s ability to self-regulate its expression and consequently of the homeostasis of TDP-43 protein levels.