Caractérisation de régions régulatrices du gène Hnf6
(2005)
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- This thesis deals with the study of tissue-specific transcription factors. Hepatocyte Nuclear Factor 6 (HNF6) is a transcription factor that controls the development of the liver and the pancreas. It is active early in these processes, and is involved in transcriptional cascades. The aim of this thesis is to identify the cis-acting sequences and the trans-acting factors that control the expression of the mouse Hnf6 gene during pancreas and liver development. We focused mainly on the expression of HNF6 in the prepancreatic and prehepatic endoderm. We resorted to in vitro and in vivo analysis of protein-DNA interactions and to transient transfections of cultured cells or whole embryos. We developed a technique that allows to electroporate the endoderm in whole embryos to identify regulatory regions of the Hnf6 gene that are active on the endoderm. We also investigated the role of regulatory regions of the Hnf6 gene by generating transgenic mice harbouring a Hnf6-LacZ construct. <BR> We showed that the transcription of the Hnf6 gene is initiated at two sites, and that the minimal promoter of the gene is localized within 500 bp upstream of the initiator ATG. The main regulators of the promoter are the ubiquitous transcription factors Sp1 and Sp3. the analysis of the Hnf6 gene region that are conserved between mouse and human allowed us to identify an intronic sequence (I3) that strongly stimulates promoter activity in a pancreatic cell line and in the endoderm. When associated with the promoter, this intronic sequence induces the expression of a reporter gene in the endoderm and in the pancreatic and hepatic buds of transgenic embryos. The intronic I3 region contains binding sites for transcription factors. Among these, FoxA and HNF1 bind to the I3 region in vitro and mutation of these sites decreases the transcriptional activity of the I3 region in the endoderm. We also showed that HNF1β binfs the I3 region in vivo, in the endoderm, and that HNF1β is essential for HNF6 expression on the endoderm. <BR> In conclusion, we have localized the Hnf6 promoter and have characterized the regulatory regions that are responsible for the expression of HNF6 in the endoderm and in the pancreatic and hepatic buds. We showed that HNF6 expression on the endoderm depends of HNF1β and we propose the HNF1β -> HNF6 -> Pdx1 cascade controls the generation of the pancreatic precursor cells
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Poll, A. (2005). Caractérisation de régions régulatrices du gène Hnf6. https://hdl.handle.net/2078.5/110661