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Vers l'identification des facteurs impliqués dans la régulation concertée des gènes soumis à empreinte dans le cerveau

Abstract : One major challenge in genomic imprinting is to understand how the expression of imprinted loci is regulated at different developmental stages and tissues. This issue is of particular importance in brain where the fine-tuned regulation of imprinted expression is involved in various neurological processes. Recently, my host team revealed that the so-called bivalent chromatin structure at Imprinting Control Regions (ICR), combining the permissive H3K4me3 and repressive H3K27me3 marks, contributes to the appropriate tissue-specific expression of imprinted genes. My objective is to identify the transcription factors (TF) controlling H3K27me3 dynamic at ICR during neural lineage commitment by using a validated in vitro model of murine corticogenesis. By a candidate-based approach, I identified TET3 (ten-eleven translocation 3) as a regulator potentially involved in differential DNA methylation maintenance at Peg10, Impact and Zrsr1 ICR. Moreover, TET3 indirectly regulates other imprinted loci, such as Mest and Peg3, possibly by activating the H3K27me3-specific demethylase gene Jmjd3 (jumonji domain containing 3) in neural lineages. Meanwhile, the main part of my thesis aims to identify those TF exhaustively by conducting an original non-biased approach. Our rational is that the regulation of imprinted genes relies on Polycomb- and TF-mediated physical networks that regulate H3K27me3 dynamic at ICR. With the model of corticogenesis, we have recently generated a high-resolution map of allelic molecular signatures and genome architecture at imprinted domains, mainly by the mean of allelic 4C (circular chromosome conformation capture) experiments using 10 ICR as bait. In this manuscript, a preliminary analysis allowed us to observe that ICR are involved in cis-interactions with imprinted genes promoters, and that these contacts are frequently mediated by paternal unmethylated allele of ICR. Those observations raise the question about the potential enhancer function of ICR. Once high-throughput data from RNA-seq, ChIP-seq, RRBS and 4C at two steps of corticogenesis fully analyzed, it will provide an allelic and integrative view of linear genomics features dynamic, such as histone modifications and transcription, in combination with the dynamic of the 3D organization at ICR. This unprecedented resource will be treated by mathematical modeling to identify robust candidate actors of brain-specific imprinted expression. Outcome of this project will provide us relevant, and so far missing, tools to decipher the underlying mechanisms involved in brain-specific imprinting in normal and pathological contexts.
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Jil Cercy. Vers l'identification des facteurs impliqués dans la régulation concertée des gènes soumis à empreinte dans le cerveau. Génétique. Université Clermont Auvergne, 2019. Français. ⟨NNT : 2019CLFAC061⟩. ⟨tel-02521131⟩

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