Fig. 7. Proposed model for how blood vessel function contributes to pancreas development subsequent to endoderm specification. Blood vessel (aorta)-derived S1P binds S1P receptors on dorsal pancreatic mesenchymal cells (1) or endothelial cells (2), resulting in heterotrimeric G-protein-mediated intracellular signalling and enhanced mesenchymal cell proliferation/survival in a cell-autonomous manner (1) or indirectly via S1PR-triggered signalling from endothelial cells (2). Mesenchymal cells accumulate around the committed dorsal pancreatic endoderm and secrete soluble factors necessary for further growth/differentiation of the endoderm. Da, dorsal aorta; m, mesenchymal cells; e, endothelial cells; dp, dorsal pancreas; arrows, recruitment of dorsal pancreatic mesenchymal cells from lateral plate mesenchyme.