Regulatory regions driving developmental and tissue-specific expression ofthe essential pancreatic gene pdx1

pdx1 (pancreatic and duodenal homeobox gene-1), which is expressed broadly in the embryonic pancreas and, later, in a more restricted manner in the ma ture beta cells in the islets of Langerhans, is essential both for organ fo rmation and beta cell gene expression and function. We carried out a transg enic reporter gene analysis to identify region- and cell type-specific regu latory regions in pdx1. A 14.5-kb pdx1 genomic fragment corrected the gluco se intolerance of pdx1(+/-) animals but, moreover, fully rescued the severe gut and pancreas defects in pdx1(-/-) embryos. Sequences sufficient to dir ect reporter expression to the entire endogenous pdx1 expression domain lie within 4.3 kb of 5' flanking DNA. In this region, we identified two distin ct fragments that drive reporter gene expression to different sets of islet neuroendocrine cells. One shows pan-endocrine cell specificity, the other is selectively activated in insulin-producing beta cells. The endocrine-spe cific regulatory regions overlap a localized region of 5' flanking DNA that is remarkably conserved in sequence between vertebrate pdx1 genes, and whi ch has been associated with beta cell-selective expression in cultured cell lines. This region contains potential binding sites for several transcript ion factors implicated in endodermal development and the pathogenesis of so me forms of type-2 diabetes. These results are consistent with our previous proposal that conserved upstream pdx1 sequences exert control over pdx1 du ring embryonic organogenesis and islet endocrine cell differentiation. We p ropose that mutations affecting the expression and/or activity of transcrip tion factors operating via these sequences may predispose towards diabetes, at least in part by direct effects on endocrine pdx1 expression. (C) 2001 Academic Press.