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Mol. Cell. Biol., Oct 1997, 6002-6013, Vol 17, No. 10
KL Wu, M Gannon, M Peshavaria, MF Offield, E Henderson, M Ray, A Marks, LW Gamer, CV Wright and R Stein
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 beta 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
beta-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 beta-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 beta-cell and non-beta-cell
lines. Furthermore, we also established that this region was important in
vivo by demonstrating that expression from a site 1-driven
beta-galactosidase reporter construct was directed to islet beta-cells in
transgenic mice. The activity of the site 1-driven constructs was reduced
substantially in beta-cell lines by mutating a hepatocyte nuclear factor 3
(HNF3)-like site located between nucleotides -2007 and -1996. Gel shift
analysis indicated that HNF3beta present in islet beta cells binds to this
element. Immunohistochemical studies revealed that HNF3beta was present
within the nuclei of almost all islet beta cells and subsets of pancreatic
acinar cells. Together, these results suggest that HNF3beta, 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.
Copyright © 1997, American Society for Microbiology
Hepatocyte nuclear factor 3beta is involved in pancreatic beta-cell- specific transcription of the pdx-1 gene
Department of Molecular Physiology and Biophysics, Vanderbilt Medical Center, Nashville, Tennessee 37232, USA.
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