The role of FGF and VEGF in angioblast induction and migration during vascular development

The embryonic vasculature forms by the processes of vasculogenesis and angi ogenesis. Angioblasts (endothelial cell precursors) appear to be induced by fibroblast growth factor 2 (FGF-2). The angioblasts contributing to the do rsal aortae arise by an epithelial to mesenchymal transformation of cells o riginating from the splanchnic mesoderm, QH-1 and vascular endothelial grow th factor receptor 2 (VEGFR-2) both appear to label these cells as they ado pt a mesenchymal morphology, Since VEGFR-2 is the earliest known VEGF recep tor this suggests that VEGF is not involved in angioblast induction. VEGF d oes appear to be critical, however, for growth and morphogenesis of angiobl asts into the initial vascular pattern. Controlled delivery of FGF-2 from b eads and aggregates of cells transfected with quail VEGF have been used in our laboratory to study the role of these growth factors in angioblast indu ction and migration. We have induced cells from the epithelial quail somite to differentiate into angioblasts with FGF-2 both in the embryo and in cul ture, This is a useful model system to study the origins of endothelial cel ls that are normally more diffusely induced during gastrulation by an obscu re process probably involving signals from the embryonic endoderm. The orig ins of arterial versus venous endothelial cells is also poorly understood b ut recent findings on the distribution of ephrins and Eph receptors suggest that molecular differences exist prior to the onset of circulation. Finall y, studies on the role of growth factors in such diverse phenomena as stem cell biology, angiogenesis, and molecular medicine in addition to vascular development suggest multiple roles for FGF-2 and VEGF in vascular developme nt. (C) 2001 Wiley-Liss, Inc.