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GENETIC INTERACTION BETWEEN HNF4alpha AND HNF1alpha IN THE INTESTINAL MUCOSA IS ESSENTIAL FOR ENTEROCYTE FUNCTIONS AND EARLY POST-NATAL SURVIVAL IN MICE
CR Lussier, J-P Babeu, F Boudreau
Department of Anatomy and Cell Biology, Université de Sherbrooke, Sherbrooke, PQ
Hepatocyte nuclear factor-1alpha (HNF1alpha) and 4-alpha (HNF4alpha) are transcription factors expressed in the liver, pancreas and intestine. Deficiencies in HNF1A and HNF4A locus have been recently linked to various human diabetes subtypes. We previously identified HNF-4alpha as an important regulator of intestinal epithelial cell (IEC) differentiation. HNF-4alpha induces the expression of HNF-1alpha and cooperates with it in transcriptional intestinal specific gene modulation.
AIM: To investigate the cooperative function of Hnf4alpha and Hnf1alpha in differentiation and maintenance of the intestinal epithelium.
HYPOTHESIS: Mice deficient for intestinal Hnf4alpha (Hnf4alphaKO) should present mucosal functional defects and a reduced level of Hnf1alpha expression.
METHODS AND RESULTS: Hnf4alphaKO mice were generated by crossing floxed Hnf4alpha mice with Villin-Cre line. Immunolocalization and real time PCR confirmed that the deletion of Hnf4alpha was effective (diminution > 90%) in the small intestine at post-natal day 1. Unexpectedly, these mice developed normally and displayed an intestinal mucosa apparently normal. Moreover, real time PCR analysis performed on total small intestine mRNA extracts demonstrated that Hnf1alpha was expressed at similar levels in Hnf4alphaKO as compared to control mice. On the other hand, the characterization of the intestinal phenotype for Hnf1alpha classical KO mice revealed that the mRNA expression level of Hnf4alpha was reduced more then 60% at post-natal day 1 as compared to the control mice. Real time PCR analysis showed a drastic (80%) diminution of lactase and FABP1 expression level at this period of time. Analysis of the Hnf1alphaKO mice having survived to the perinatal period indicated that the small intestinal expression of Hnf4alpha has recovered to similar levels as compared to control mice. Mice totally deficient for Hnf1alpha and with Hnf4alpha exclusively deleted in the gut epithelium were then generated (Hnf4alphaKO-Hnf1alphaKO). No double mutant mice survived more than 36 hours after birth. The detailed phenotypic and gene profiling characterization of these mutant mice are presently ongoing.
CONCLUSION: Our results indicate that Hnf4alpha and Hnf1alpha are, in common, crucial regulators of gut epithelium functions.
Supported by CCFC and CIHR