Pancreatic beta cell-specific transcription of the pdx-1 gene. The role of conserved upstream control regions and their hepatic nuclear factor 3beta sites.
To identify potential transactivators of pdx-1, we sequenced approximately 4.5 kilobases of the 5' promoter region of the human and chicken homologs, assuming that sequences conserved with the mouse gene would contain critical cis-regulatory elements. The sequences associated with hypersensitive site 1 (HSS1) represented the principal area of homology within which three conserved subdomains were apparent: area I (-2694 to -2561 base pairs (bp)), area II (-2139 to -1958 bp), and area III (-1879 to -1799 bp). The identities between the mouse and chicken/human genes are very high, ranging from 78 to 89%, although only areas I and III are present within this region in chicken. Pancreatic beta cell-selective expression was shown to be controlled by mouse and human area I or area II, but not area III, from an analysis of pdx-1-driven reporter activity in transfected beta- and non-beta cells. Mutational and functional analyses of conserved hepatic nuclear factor 3 (HNF3)-like sites located within area I and area II demonstrated that activation by these regions was mediated by HNF3beta. To determine if a similar regulatory relationship might exist within the context of the endogenous gene, pdx-1 expression was measured in embryonic stem cells in which one or both alleles of HNF3beta were inactivated. pdx-1 mRNA levels induced upon differentiation to embryoid bodies were down-regulated in homozygous null HNF3beta cells. Together, these results suggest that the conserved sequences represented by areas I and II define the binding sites for factors such as HNF3beta, which control islet beta cell-selective expression of the pdx-1 gene.
Gerrish
K
K
Department of Molecular Physiology, Vanderbilt Medical Center, Nashville, Tennessee 37232, USA.
Gannon
M
M
Shih
D
D
Henderson
E
E
Stoffel
M
M
Wright
C V
CV
Stein
R
R
D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D002645:Chickens; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D051542:Hepatocyte Nuclear Factor 3-beta; D018398:Homeodomain Proteins / Q000096:biosynthesis / Q000235:genetics; D006801:Humans; D007515:Islets of Langerhans / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D015534:Trans-Activators / Q000096:biosynthesis / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection
D004268:DNA-Binding Proteins; C496502:FOXA2 protein, human; C496503:Foxa2 protein, mouse; D018398:Homeodomain Proteins; D009687:Nuclear Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C084010:pancreatic and duodenal homeobox 1 protein; D051542:Hepatocyte Nuclear Factor 3-beta