Evolutionary relationship between human and zebrafish Vegfa isoforms and receptors. Protein sequences were aligned using ClustalW (European Bioinformatics Institute, Cambridge, United Kingdom) with the complete open reading frames. Species are indicated as follows: zf, zebrafish; m, mouse; and h, human. (A) Alignment of VegfA proteins shows a closer relationship of the newly isolated gene to VEGFA than VEGFB, VEGFC, VEGFD, and PLGF. (B) Alignment of RTK sequences. The zebrafish gene (Kdra) formerly referred to as flk1 shows a closer relationship to hFLT1 and mFlt1 than to hKDR (hFLK1) and mKDR (mFlk1). (C) Radiation hybrid mapping of zebrafish kdra, flt1, and kdrb and synteny comparison. Zebrafish kdrb is located on chromosome 20 in a region syntenic to human KDR, nearby the zebrafish orthologues of kit and pdgfra, which map near human KDR on human chromosome 4q12. Zebrafish kdra is on chromosome 14, and flt1 near cdk8 and ipf1 in a region on chromosome 24, which is syntenic to the human 13q12 region where FLT1, CDK8, and IPF1 are located.