Régulation traductionnelle en réponse à la fécondation et en conditions perturbées dans l'embryon d'oursin

Abstract : Translation is a critical step in gene expression regulation. In sea urchin embryos, fertilization induces an increase in protein synthesis, which depends mainly on the translation of maternal messenger RNAs. This protein synthesis is essential for the first cell cycles. Embryonic development of the sea urchin is an excellent model for studying translational control. In this thesis, translational regulation in sea urchin embryos was studied in two situations: the physiological context of fertilization and the context of apoptosis induction. We first examined the regulatory mechanisms involved in protein synthesis after fertilization. Initiation is one of the limiting steps of translation. In this context, the initiation factor eIF2 plays a key role. eIF2 is responsible for bringing the initiator methionine to the ribosome. When the alpha subunit of eIF2 is phosphorylated, global protein synthesis is inhibited and the selective translation of certain mRNAs is stimulated. In the sea urchin unfertilized eggs, eIF2alpha is physiologically phosphorylated and fertilization induces its dephosphorylation. By microinjecting a variant mimicking the phosphorylated state of eIF2alpha into the unfertilized eggs, we showed that dephosphorylation of eIF2alpha is required for the first mitotic division in the sea urchin. We were interested in the relationship between the phosphorylation of eIF2alpha and induction of apoptosis in the sea urchin. Indeed, the translation of mRNAs encoding proteins pro- or anti-apoptotic directly influences cell survival. The sea urchin has the molecular tool kit for apoptotic induction. Exposing embryos to MMS, a DNA-damaging agent, causes phosphorylation of eIF2alpha and apoptosis activation. In this situation, we found that the GCN2 kinase is involved in the phosphorylation of eIF2alpha. In order to study how the translational machinery modulates the polysomal recruitment, we analyzed the translatome in response to fertilization and after exposure to MMS. We conducted deep sequencing of transcripts that are present in polysomes. Analysis of these transcripts, following annotation, will allow a better understanding of the genes regulatory network at the translational level during fertilization and the induction of apoptosis in sea urchin embryos.
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Submitted on : Monday, June 11, 2012 - 9:15:46 AM
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Vlad Costache. Régulation traductionnelle en réponse à la fécondation et en conditions perturbées dans l'embryon d'oursin. Biologie cellulaire. Université Rennes 1, 2012. Français. ⟨NNT : 2011REN1S162⟩. ⟨tel-00706548⟩

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