Differentiation of hepatic and pancreatic cells is controlled by HNF6 and microRNAs

(eng) The present thesis addresses the role of microRNAs and of the ONECUT factors HNF6 and OC2 in liver and pancreas development. ONECUT factors play an important role in the specification of the pancreas and in the differentiation of hepatocytes, cholangiocytes, pancreatic endocrine and ductal cells. MicroRNAs recently emerged as novel posttranscriptional regulators that control several biological processes, including embryonic development. The first aim of this thesis is to identify microRNAs that regulate the expression of ONECUT factors during liver and pancreas development. We used cloning and microarray techniques to describe the expression of the microRNAs in liver and pancreas at different stages in mouse liver and pancreas organogenesis, and bioinformatic predictions to select microRNAs that target HNF6 and OC2. The function of selected microRNAs was verified by transfection experiments. With this approach we found that miR-495 and miR-218 downregulate the expression of HNF6 and OC2, respectively. The second objective of the thesis is to characterize the role of microRNAs in liver and pancreas development. This was investigated by characterizing the function of mice with liver- and pancreas-specific depletion of Dicer (Foxa3-Cre x Dicer-flox). Depletion of Dicer was rapidly achieved in developing liver and near complete in pancreas at the end of gestation. The liver showed perturbed differentiation of hepatocytes and biliary cells. The pancreas showed acinar-to-ductal metaplasia (ADM), asssociated with overexpression of HNF6 in the transdifferentiating acinar cells. We next tried to decipher the role of HNF6 in ADM. By inducing ADM by various means in wild-type and Hnf6-/- mice we found that HNF6 is expressed in exocrine cells upon acinar injury, that HNF6 is necessary for progression of ADM, and that it is able to downregulate acinar markers and induce expression of ductal markers. We also found expression of HNF6 in human pancreatic ADM.