Oncogenes in the study of endothelial cell growth and differentiation.

During embryogenesis endothelial cells differentiate from mesodermal blood islands, proliferate and form new blood vessels throughout embryonic and early postnatal life by the processes of vasculogenesis and angiogenesis. Proliferation then ceases and is very low in the adult, although it resumes under certain physiological and pathological conditions, such as wound healing, tumor growth and hemangiomatous diseases. Expression of the polyoma middle T (PymT) oncogene in mouse endothelial cells leads to their rapid transformation and to the development of hemangiomas. These endothelial tumors allow the establishment of endothelioma (End) cell lines, which resemble normal endothelial cells yet exhibit a drastically altered proteolytic activity. The specific effects of PymT on the growth of endothelial cells appear in part to be mediated through the activation of cellular tyrosine kinases.