Les anomalies congénitales du rein et du tractus urinaire (CAKUT) sont l’une des malformations les plus fréquentes chez l’homme, et résultent d’un défaut du programme de dévelopement des organes. La famille de gènes Sox code pour 20 facteurs de transcription qui assurent des fonctions multiples et essentielles pendant l’organogenèse chez l’homme et la souris. Nous avons précedemment montré que Sox8 et Sox9 sont nécessaires au branchement de l’uretère, et la perte de ces gènes résulte en une agénésie rénale. L’objectif de ce projet de thèse était de caractériser le role des gènes Sox-C (Sox4/11/12) in vivo chez la souris. L’analyse des patrons d’expression a révélé que Sox4 , Sox11 et Sox12 sont co-exprimés dans les cellules progénitirices des néphrons, destinées à subir une transition mésenchyme epithelium (MET) pour former des vésicules qui s'allongent pour aboutir au néphron fonctionnel. L’analyse phénotypique a révélé une redondance fonctionnelle entre Sox4 et Sox11 pendant les processus de MET et de maturation des néphrons: les double mutants développent une hypodysplasie rénale dûe à une réduction dramatique du nombre et de la taille des néphrons. Le pool de progéniteurs de néphrons est intact chez ces mutants mais incapable de s’engager dans la nephrogenèse, probablement dû à un changement d’identité cellulaire. Par ailleurs, en l’absence de Sox11, des bourgeons uretéraux ectopiques se forment, conduisant à des reins duplex, phénotype présent dans une proportion de patients CAKUT. De manière importante, nous avons identifié une série de variants SOX11 dans une cohorte de patients CAKUT, suggérant l'implication de mutations SOX11 dans cette maladie chez l'homme. / Congenital abnormalities of the kidney and the urinary tract (CAKUT) belong to the mostcommon birth defects in human and are caused by defects in the program governing organ development. The Sox gene family encodes 20 transcription factors that ensure multiple and essential functions during mouse and human organogenesis. We have previously shown that the homologous genes Sox8 and Sox9 are required for the branching process of the ureter and their loss results in renal agenesis. In this thesis project, we aimed to identify and characterize the role of the Sox-C genes (Sox4/11/12), in vivo using mouse models. Expression analysis revealed that Sox4, Sox11 and Sox12 are coexpressed in the self-renewing nephron precursors cells that are destined to undergo mesenchyme-to-eptihelial transition (MET) to form vesicles that elongate to give rise to the functional nephrons. Phenotypical analysis revealed a functional redundancy between Sox4 and Sox11 in MET and nephron maturation processes: double mutants display renal hypodysplasia, due to a dramatic reduction in the number and size of nephrons. The nephron precursor pool is intact in these mutants but unable to commit to nephrogenesis, probably because of a cell identity change. In addition, in the absence of Sox11, ectopic ureteric buds form, leading to duplex kidneys, a phenotype found in a proportion of CAKUT patients. Importantly, mutation analysis of a cohort suffering from CAKUT syndrome identified a series of SOX11 variants, thus suggesting an involvement of SOX11 mutations in this human disease.

In aquaculture, short term chilled storage has been used to transport brood stock fish embryos for genetic improvement programmes. It is therefore important to understand the effect of chilling on embryos at both developmental and molecular levels. In the present study, gene expression patterns in zebrafish embryos were studied before investigations were carried out on the effect of chilling on gene and protein expression in these embryos. The gene expression results obtained in different developmental stages using conventional PCR showed that, only sox genes were expressed throughout the tested developmental stages from 30% epiboly to 6 somites. Quantitative RT-PCR was then used to investigate sox gene expression patterns during chilling of 50% epiboly stage embryos at 0°C for up to 180 min and also after warming. Significant decreases in sox2 and sox3 expressions were observed when compared to those of controls following chilling whilst significant increases of expressions of the two genes were observed after warming in the embryos chilled for 30 and 60 min. Studies on the impact of cryoprotectant MeOH on sox genes and protein expression showed that 50% epiboly stage zebrafish embryos could tolerate chilling for up to 6 h with or without MeOH. It was observed that expression of all three sox genes were significantly decreased following chilling for 3 h at 0°C. However the degree of decrease was less pronounced in embryos chilled with different concentrations of MeOH. Significant increases in sox genes were observed in hatching stage embryos chilled with 1 M MeOH for 3h but subsequent sox2 and sox19a protein expression was not affected. The effect of long term chilling (18h) on sox gene and protein expression in 50% epiboly stage embryos was also investigated. Improved hatching rates (56% ± 5) were achieved when embryos were chilled with 1 M MeOH + 0.1 M sucrose. Results from gene expression studies showed a stable sox2 gene expression in 18 h chilled embryos in cryoprotectant mixture when compared to that of embryos chilled without cryoprotectant mixture. Similar patterns were observed when the expression of sox2 and sox3 protein was investigated. This is the first study carried out on the effect of chilling in early stage zebrafish embryos at the molecular level. The results obtained from the present study provided useful information on the molecular mechanisms of the effect of chilling on zebrafish embryos and will have important implications in designing chilled storage protocols for fish embryos.