Duplicate VegfA genes and orthologues of the KDR receptor tyrosine kinase family mediate vascular development in the zebrafish

Vascular endothelial growth factor A (VEGFA) and the type III receptor tyrosine kinase receptors (RTKs), are both required for the differentiation of endothelial cells (vasculogenesis) and for the sprouting of new capillaries (angiogenesis). We have isolated a duplicated zebrafish VegfA locus, termed VegfAb, and a duplicate RTK locus with homology to KDR/FLK1 (named Kdrb). Morpholino disrupted VegfAb embryos develop a normal circulatory system until approximately 2-3 dpf, when defects in angiogenesis permits blood to extravasate into many tissues. Unlike the VegfAa121 and VegfAa165 isoforms, the VegfAb isoforms VegfAb171 and VegfAb210 are not normally secreted when expressed in mammalian tissue culture cells. The Kdrb locus encodes a 1361 amino acid transmembrane receptor with strong homology to mammalian KDR. Combined knockdown of both RTKs leads to defects in vascular development, suggesting that they cooperate in mediating the vascular effects of VegfA in zebrafish development. Both VegfAa and VegfAb can individually bind and promote phosporylation of both Flk1 (Kdra), and Kdrb proteins in vitro. Taken together, our data support a model in the zebrafish, in which duplicated VegfA and multiple type III RTKs mediate vascular development.