ABSTRACT
The development of a vasculature is critical to the survival of the higher vertebrate embryo. Recent work has further shown that signals from vascular endothelial cells play an inductive role in differentiation of the Purkinje fiber network from cardio-myocytes (1) and the formation of pancreas from gut endoderm (2). Endothelial cells line all vascular structures including the endocardium, both venous and arterial beds, and lymphatic vessels. Endothelial cell precursors or angioblasts arise in most mesoderm including both intra and extraembryonic mesoderm, where they coalesce to form primitive vascular chords de novo, a vasculogenic mechanism. Some angio-blasts are highly migratory in nature originating far from their eventual location (3). Later elaboration of the vascular structure is achieved primarily through the sprouting of new blood vessels from the existing vasculature via angiogenesis (4-7).
