Vascular endothelial growth factor and vascular endothelial growth factor receptor-2 expression in the chick embryo area vasculosa

Vascular endothelial growth factor is an angiogenic factor in vivo and in v itro that plays a crucial role in the control of blood vessel development a nd in pathological angiogenesis. The vascularized extraembryonic membranes of the chick embryo include the area vasculosa and the chorioallantoic memb rane. In this study, we investigated the expression of vascular endothelial growth factor and of its receptor-2, specifically expressed by the endothe lial cells, in the chick area vasculosa at days 6, 10 and 14 of incubation. Our results indicate that, in all the three developmental stages examined, vascular endothelial growth factor is clearly expressed in the endodermal cells immediately adjacent to the mesodermal endothelial cells which, in tu rn, expressed vascular endothelial growth factor receptor-2. These observat ions suggest that during the development of the vascular system, endodermal cells, expressing vascular endothelial growth factor, initiate angiogenesi s by stimulating directly mesodermal cells, which express vascular endothel ial growth factor receptor-2. Moreover, our data demonstrate that vascular endothelial growth factor receptor-2 expression is also maintained by endot helial cells in the later stages of development, until day 14 of incubation . In accord with other literature data, this suggests that vascular endothe lial growth factor is required not only for proliferation, but also for the survival of endothelial cells.