Role for VPAC2 Receptor-Mediated Signals in Pancreas Development

Abstract

T he pancreas originates from the dorsal and ventral regions of the foregut endoderm immediately behind the stomach. The endoderm evaginates to form epithelial buds that subsequently enlarge. During this period, exocrine and endocrine cells that will constitute the functional pancreatic unit undergo differentiation.Inductive signals have been shown to be important for normal pancreatic development. Such signals derive from various sources, such as the primitive streak mesoderm, notochord, blood vessels, cardiogenic mesoderm, septum transversum mesenchyme, mesoderm, and mesenchyme (1-6). Research has been conducted to define the exact nature of the inductive signals involved in pancreatic development, and several secreted factors have emerged as likely candidates. These factors belong to a variety of families. A large number of ligands for receptor tyrosine kinases such as fibroblast growth factor-1, -2, -4, -7, and -10; vascular endothelial growth factor; epidermal growth factor; and hepatocyte growth factor have been shown to be involved at various steps of pancreatic development (2,6 -13). Several members of the transforming growth factor (TGF)-␤ superfamily (e.g., activin, bone morphogenetic proteins, TGF-␤) have also been implicated in pancreas development (3,8,14,15).Various ligands of protein G-coupled receptors that increase cAMP accumulation have been shown to exert an important influence on pancreatic function and regeneration during postnatal life (16 -19). In other tissues, these ligands are important for normal development (20,21). However, to our knowledge, few data are available on their role in prenatal pancreas development. In the present study, we used a recently described in vitro system of immature embryonic pancreatic epithelium to look for evidence that ligands of protein G-coupled receptors that increase cAMP accumulation may contribute to the control of pancreas development.Our data indicate that embryonic pancreatic epithelial cells are sensitive to vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP). These factors signal via the VPAC2 receptor, which is highly expressed in the pancreatic epithelium between embryonic days 12 and 16. They increase the proliferation and survival of immature pancreatic epithelial cells, leading to a final increase in the number of insulin-expressing cells. RESEARCH DESIGN AND METHODSAnimals. Pregnant Wistar rats were purchased from the Janvier breeding center (Le Genet, France). The morning of the discovery of the vaginal plug was designated embryonic day 0.5 (E0.5). The animals had free access to food pellets and water. Pregnant rats at different stages of gestation were killed by CO 2 asphyxiation. Dissection of pancreatic epithelium. E13.5 embryos were harvested, and their dorsal pancreatic buds were dissected. The pancreatic epithelium was separated from its surrounding mesenchyme as described previously (22), with minor modifications. Briefly, the stomach, pancreas, and a small portion of the intestine were...

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