MECHANISMS OF NEW BLOOD-VESSEL FORMATION

The formation of new blood vessels includes 1. the de novo formation o f blood vessels during early embryogenesis, a process which is called vasculogenesis, and 2. the formation of new blood vessels from preexis ting ones, called angiogenesis. Vasculogenesis comprises the establish ment of endothelial and blood cell lineages in the blood islands and e nds up in the formation of the primary vascular plexus. Vasculogenesis is closely associated with mesoderm formation and like mesoderm induc tion initiated by the fibroblast growth factor signal transduction sys tem. Angiogenesis is under the control of the vascular endothelial gro wth factor signal transduction system, during embryonic vascular growt h as well as in malignant tumours. The extent and pattern of angiogene sis are further regulated by the interaction of the endothelial cells with the extracellular matrix via matrix receptors, called integrins.