Regulation of the Pancreatic Pro-Endocrine Gene Neurogenin3
- Jane C. Lee12,
- Stewart B. Smith1,
- Hirotaka Watada1,
- Joseph Lin1,
- David Scheel1,
- Juehu Wang1,
- Raghavendra G. Mirmira1 and
- Michael S. German13
- 1Hormone Research Institute and the Departments of
- 2Pediatrics and
- 3Medicine, University of California, San Francisco, California
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.
R.G.M. is currently affiliated with the Department of Medicine, University of Virginia, Charlottesville, Virginia.
Address correspondence and reprint requests to Michael S. German, MD, University of California, San Francisco, HSW 1090, Box 0534, 513 Parnassus Ave., San Francisco, CA 94143. E-mail:.
Received for publication 17 December 2000 and accepted in revised form 20 February 2001. Posted on the World Wide Web at www.diabetes.org/diabetes on 11 April 2001.
bHLH, basic helix-loop-helix; CMV, cytomegalovirus; DMEM, Dulbecco’s modified Eagle’s medium; E, embryonic day; EMSA, elecrophoretic mobility shift assay; GST, glutathione S-transferase; HNF, hepatocyte nuclear factor; ngn3, neurogenin3; PCR, polymerase chain reaction; RACE, rapid amplification of cDNA end; TK, thymidine kinase.