ABSTRACT

Introduction .................................................................................................. 89 Netrins and their receptors ........................................................................ 91 Roundabouts and Slits in vessel development....................................... 94 Semaphorin-Plexin signaling .................................................................... 96 Neuropilin receptors ................................................................................... 98 Ephrins and Eph receptors....................................................................... 100 Discussion and perspectives .................................................................... 102 References.................................................................................................... 103

Introduction Blood vessel formation during embryonic development is initiated by the differentiation of endothelial precursor cells from the mesoderm and their subsequent proliferation, differentiation, and coalescence into tubes to form the primary vascular plexus. This process is termed vasculogenesis (Risau 1997). The primary vascular plexus consists of the major embryonic vessels, the dorsal aorta, the cardinal veins, and a meshwork of homogeneously sized capillaries. This primitive network subsequently expands via angiogenesis, which involves sprouting and splitting of pre-existing vessels to form new ones, bridging and branching of vessels to set up new connections, and pruning to remove excess vessel tracts.