Vasculogenesis in early human placental villi: an ultrastructural study

In this study we examined the chorionic villi of 5 normal human placentas a t 12-14 weeks of gestation ultrastructurally with regard to differentiation of the vascular components. The aim of the present report is to discuss th e factors influencing vasculogenesis (in situ formation of blood vessels) a t the ultrastructural level. Our observations have led us to think that the cytotrophoblast influences v asculogenesis in human chorionic villi. Mesenchymal-preendothelial cell gro ups were always found in very close association with the cytotrophoblast at the periphery of the villi, forming blood vessels. The cytotrophoblast pro bably attracts mesenchymal cells towards the margin of the villi by secreti ng vascular endothelial growth factor (VEGF). Once cells attach to the trop hoblastic basement membrane they begin to differentiate into endothelial ce lls. This close structural relation between two Cell types (cytotrophoblast and mesenchymal cells) may not be the only mechanism controlling vasculoge nesis, but it seems to be one of the factors influencing the differentiatio n of mesenchymal cells into the endothelial cells of blood vessels in early human chorionic villi.