A ROLE FOR NOTOCHORD IN AXIAL VASCULAR DEVELOPMENT REVEALED BY ANALYSIS OF PHENOTYPE AND THE EXPRESSION OF VEGR-2 IN ZEBRAFISH FLH AND NTL MUTANT EMBRYOS

The notochord is required for the differentiation of nearby tissues, i ncluding the neural tube and the floor plate. Because the dorsal aorta and axial vein are midline structures, their development might also b e influenced by the notochord. To investigate this possibility, we clo ned zebrafish VEGR-2, homologous to the earliest known marker of endot helial cells in mammals. In flh and ntl mutant embryos, which lack a n otochord, we found a defect in axial blood vessel formation, and a del ay in the fusion of VEGR-2 positive endothelial progenitor cells into the primary vascular plexus and a block in the establishment of mature vessels. Differences in the vascular phenotype between the two mutati ons correlated with the severity of their axial mesodermal defects. Th ese observations support a role for the notochord in vasculogenesis. ( C) 1997 Elsevier Science Ireland Ltd.