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Molecular and Cellular Biology, June 2007, p. 4093-4104, Vol. 27, No. 11
0270-7306/07/$08.00+0 doi:10.1128/MCB.01978-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Departments of Medicine, Division of Diabetes, Endocrinology, and Metabolism,1 Molecular Physiology and Biophysics,2 Cell and Developmental Biology, Vanderbilt University, Nashville, Tennessee 37232,3 Cell and Developmental Biology Program, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, Pennsylvania 191114
Received 20 October 2006/ Returned for modification 18 December 2006/ Accepted 23 March 2007
The critical pancreatic transcription factor Pdx1 is expressed throughout the pancreas early but enriched in insulin-producing ß cells postnatally. Previous studies showed that the 5' conserved promoter regions areas I and II (Pdx1PB) direct endocrine cell expression, while an adjacent region (Pdx1XB) containing conserved area III directs transient ß-cell expression. In this study, we used Cre-mediated lineage tracing to track cells that activated these regions. Pdx1PBCre mediated only endocrine cell recombination, while Pdx1XBCre directed broad and early recombination in the developing pancreas. Also, a reporter transgene containing areas I, II, and III was expressed throughout the embryonic day 10.5 (E10.5) pancreas and gradually became ß cell enriched, similar to endogenous Pdx1. These data suggested that sequences within area III mediate early pancreas-wide Pdx1 expression. Area III contains a binding site for PTF1, a transcription factor complex essential for pancreas development. This site contributed to area III-dependent reporter gene expression in the acinar AR42J cell line, while PTF1 specifically trans-activated area III-containing reporter expression in a nonpancreatic cell line. Importantly, Ptf1a occupied sequences spanning the endogenous PTF1 site in area III of E11.5 pancreatic buds. These data strongly suggest that PTF1 is an important early activator of Pdx1 in acinar and endocrine progenitor cells during pancreas development.
Published ahead of print on 2 April 2007.
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