Characterization of the zebrafish vascular endothelial growth factor A gene: comparison with vegf-A genes in mammals and Fugu
Vascular endothelial growth factor (VEGF-A) is a key angiogenic growth factor which regulates vertebrate embryonic vascularization, adult physiology such as wound healing and reproduction as well as many human diseases. To understand the evolution and regulation of this gene in vertebrates, we have isolated and characterized the zebrafish vegf-A gene and compared it with VEGF-A genes of human, mouse as well as an in silico isolated VEGF-A homologue from pufferfish. Our results indicate that the zebrafish vegf-A gene is organized similarly to mammalian and Fugu VEGF-A genes, with eight exons interrupted by seven introns. However, zebrafish vegf-A introns are generally larger than mammalian introns while Fugu VEGF-A introns are much smaller. Furthermore, zebrafish exon 6 (z6) has a unique sequence while Fugu's exon 6 is highly homologous to the mammalian counterparts. Alternative splicing generates multiple vegf-A mRNA isoforms in zebrafish with Vegf121 as the dominant isoform in adult and Vegf165 as the dominant isoform in early embryos. The exon z6 containing isoform Vegf12345z678 is only detected in heart, muscle, and early embryos while another isoform Vegf-A1234577a8 is only detected in heart. Furthermore, no conserved 5′ flanking sequences between zebrafish and Fugu were observed while numerous conserved regions exist between human and mouse in this area. These results suggest both conserved and diverged functions of VEGF-A from fish to mammals since the separation of these two groups from their common ancestor about 450 million years ago and a diverged regulation of this gene since the separation of zebrafish from Fugu. These data will be valuable for future studies of VEGF-A gene regulation and function in different vertebrates.