Pax-2 activates the proglucagon gene promoter but is not essential for proglucagon gene expression or development of proglucagon-producing cell lineages in the murine pancreas or intestine

Abstract

Tissue-specific proglucagon gene transcription is achieved through combinations of transcription factors expressed in pancreatic A cells and enteroendocrine L cells of the small and large intestine. Cell transfection and electrophoretic mobility shift assay experiments previously identified Pax-2 as a regulator of islet proglucagon gene expression. We examined whether Pax-2 regulates gut proglucagon gene expression using enteroendocrine cell lines and Pax21NEU mutant mice. Immunoreactive Pax-2 was detected in STC-1 enteroendocrine cells, and Pax-2 activated proglucagon promoter activity in transfected baby hamster kidney and GLUTag cells. Pax-2 antisera diminished the formation of a Pax-2-G3 complex in electrophoretic mobility shift assay studies using nuclear extracts from islet and enteroendocrine cell lines. Surprisingly, Pax-2 mRNA transcripts were not detected by RT-PCR in RNA isolated from adult rat pancreas, rat islets, embryonic d 19 or adult murine pancreas and gastrointestinal tract. Furthermore, embryonic d 19 or neonatal d 1 Pax21NEU mice exhibited normal islet A cells and gut endocrine L cells, and no decrement in pancreatic or intestinal glucagon gene expression. These findings demonstrate that Pax-2 is not essential for the developmental formation of islet A or gut L cells and does not play a role in the physiological control of proglucagon gene expression in vivo.