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, including the neural tube and the floor plate. Because the dorsal aorta and axial vein are midline structures, their development might also be influenced by the notochord. To investigate this possibility, we cloned zebrafish VEGR-2, homologous to the earliest known marker of endothelial cells in mammals. In flh and ntl mutant embryos, which lack a notochord, we found a defect in axial blood vessel formation, and a delay 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 mutations correlated with the severity of their axial mesodermal defects. These observations support a role for the notochord in vasculogenesis.