Hepatocyte Nuclear Factor 3β is Involved in Pancreatic β-Cell-Specific Transcription of the pdx-1 Gene

• Published in: Molecular and cellular biology 1997-10, Vol.17 (10), p.6002-6013
• Main Authors: Wu, Kuo-Liang, Gannon, Maureen, Peshavaria, Mina, Offield, Martin F., Henderson, Eva, Ray, Michael, Marks, Antonio, Gamer, Laura W., Wright, Christopher V. E., Stein, Roland
• Format: Article
• Language: English
• ISSN: 1098-5549; 0270-7306; 1098-5549
• DOI: 10.1128/MCB.17.10.6002

The mammalian homeobox gene pdx-1 is expressed in pluripotent precursor cells in the dorsal and ventral pancreatic bud and duodenal endoderm, which will produce the pancreas and the rostral duodenum. In the adult, pdr-1 is expressed principally within insulin-secreting pancreatic islet β cells and cells of the duodenal epithelium. Our objective in this study was to localize sequences within the mouse pdx-1 gene mediating selective expression within the islet. Studies of transgenic mice in which a genomic fragment of the mouse pdx-1 gene from kb -4.5 to +8.2 was used to drive a β-galactosidase reporter showed that the control sequences sufficient for appropriate developmental and adult specific expression were contained within this region. Three nuclease-hypersensitive sites, located between bp -2560 and -1880 (site 1), bp -1330 and -800 (site 2), and bp -260 and +180 (site 3), were identified within the 5′-flanking region of the endogenous pdx-1 gene. Pancreatic β-cell-specific expression was shown to be controlled by sequences within site 1 from an analysis of the expression pattern of various pdr-1-herpes simplex virus thymidine kinase promoter expression constructs in transfected β-cell and non-β-cell lines. Furthermore, we also established that this region was important in vivo by demonstrating that expression from a site 1-driven β-galactosidase reporter construct was directed to islet β-cells in transgenic mice. The activity of the site 1-driven constructs was reduced substantially in β-cell lines by mutating a hepatocyte nuclear factor 3 (HNF3)-like site located between nucleotides -2007 and -1996. Gel shift analysis indicated that HNF3β present in islet β cells binds to this element. Immunohistochemical studies revealed that HNF3β was present within the nuclei of almost all islet β cells and subsets of pancreatic acinar cells. Together, these results suggest that HNF3β, a key regulator of endodermal cell lineage development, plays an essential role in the cell-type-specific transcription of the pdx-1 gene in the pancreas.