Regulation of the pancreatic pro-endocrine gene neurogenin3.
Neurogenin3 (ngn3), a basic helix-loop-helix (bHLH) transcription factor, functions as a pro-endocrine factor in the developing pancreas: by itself, it is sufficient to force undifferentiated pancreatic epithelial cells to become islet cells. Because ngn3 expression determines which precursor cells will differentiate into islet cells, the signals that regulate ngn3 expression control islet cell formation. To investigate the factors that control ngn3 gene expression, we mapped the human and mouse ngn3 promoters and delineated transcriptionally active sequences within the human promoter. Surprisingly, the human ngn3 promoter drives transcription in all cell lines tested, including fibroblast cell lines. In contrast, in transgenic animals the promoter drives expression specifically in regions of ngn3 expression in the developing pancreas and gut; and the addition of distal sequences greatly enhances transgene expression. Within the distal enhancer, binding sites for several pancreatic transcription factors, including hepatocyte nuclear factor (HNF)-1 and HNF-3, form a tight cluster. HES1, an inhibitory bHLH factor activated by Notch signaling, binds to the proximal promoter and specifically blocks promoter activity. Together with previous genetic data, these results suggest a model in which the ngn3 gene is activated by the coordinated activities of several pancreatic transcription factors and inhibited by Notch signaling through HES1.
Lee
J C
JC
Hormone Research Institute, Department of Pediatrics, University of California, San Francisco 94143, USA.
Smith
S B
SB
Watada
H
H
Lin
J
J
Scheel
D
D
Wang
J
J
Mirmira
R G
RG
German
M S
MS
D000818:Animals; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000235:genetics; D005934:Glucagon / Q000032:analysis; D051537:Hepatocyte Nuclear Factor 1; D051538:Hepatocyte Nuclear Factor 1-alpha; D051539:Hepatocyte Nuclear Factor 1-beta; D051541:Hepatocyte Nuclear Factor 3-alpha; D006801:Humans; D007515:Islets of Langerhans / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D005810:Multigene Family; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000235:genetics*; D009687:Nuclear Proteins / Q000235:genetics; D016366:Open Reading Frames; D011401:Promoter Regions, Genetic; D016385:TATA Box; D014157:Transcription Factors / Q000235:genetics; D014162:Transfection; D001616:beta-Galactosidase / Q000032:analysis / Q000235:genetics
D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D005934:Glucagon; D051537:Hepatocyte Nuclear Factor 1; D051538:Hepatocyte Nuclear Factor 1-alpha; D051539:Hepatocyte Nuclear Factor 1-beta; D051541:Hepatocyte Nuclear Factor 3-alpha; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D014157:Transcription Factors; D001616:beta-Galactosidase; C496499:FOXA1 protein, human; C496500:Foxa1 protein, mouse; C496487:HNF1A protein, human; C496495:HNF1B protein, human; C496488:Hnf1a protein, mouse; C496496:Hnf1b protein, mouse; C498695:NEUROG3 protein, human; C407737:Neurog3 protein, mouse