Abstract
Pancreatic-duodenal homeobox factor-1 (Pdx1) is highly enriched in islet β cells and integral to proper cell development and adult function. Of the four conserved 5′-flanking sequence blocks that contribute to transcription in vivo, Area II (mouse base pairs -2153/-1923) represents the only mammalian specific control domain. Here we demonstrate that regulation of β-cell-enriched Pdx1 expression by the MafA and MafB transcription factors is exclusively through Area II. Thus, these factors were found to specifically activate through Area II in cell line transfection-based assays, and MafA, which is uniquely expressed in adult islet β cells was only bound to this region in quantitative chromatin immunoprecipitation studies. MafA and MafB are produced in β cells during development and were both bound to Area II at embryonic day 18.5. Expression of a transgene driven by Pdx1 Areas I and II was also severely compromised during insulin+ cell formation in MafB-/- mice, consistent with the importance of this large Maf in β-cell production and Pdx1 expression. These findings illustrate the significance of large Maf proteins to Pdx1 expression in β cells, and in particular MafB during pancreatic development.
Highlights
(Pdx1,5 IPF-1 in humans), the first pancreas-enriched gene product expressed in budding epithelium at embryonic day 8.5 (E8.5) [1, 2]
Chromatin immunoprecipitation (ChIP) analysis illustrated that MafA binding within AII was highly enriched over AI, AIII, and AIV in islet  cell lines, while
Our results demonstrate that large Maf proteins activate Pancreatic-duodenal homeobox factor-1 (Pdx1) transcription by binding to AII and illustrate how expression is compromised in developing  cells in the specific absence of MafB
Summary
Pancreatic-duodenal homeobox factor; ChIP, chromatin immunoprecipitation assay; EMSA, electrophoretic mobility shift assay; -gal, -galactosidase. MafA and MafB Regulate Pdx via Area II transfection-based reporter assays showed that the MafA/MafB binding elements contributed to activation. Both MafA and MafB were bound in vivo to Area II in E18.5 pancreata, and AI/AIIdriven transgene activity was dramatically reduced during -cell development in MafBϪ/Ϫ mice. These data support an essential role for MafA and MafB in AII-mediated activation of Pdx transcription, and highlight the significance of MafB regulation in developing  cells
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