Evolutionary scenario of the FGF3 subfamily. (a) Genomic events leading to the birth of the FGF3 subfamily. From a single FGF3/4/5/6 gene, a tandem duplication occurred before the chordate diversification giving rise to an FGF3 and an FGF4/5/6 gene (brown box). The two rounds of whole genome duplication, followed by several gene losses and by a specific translocation of the chromosome region containing FGF5 (grey box) conducted to the gene content currently found in vertebrates. (b) Evolutionary relationships between FGFs 3, 4, 5, and 6 in chordates. Here, the chordate ancestor had both FGF3 and FGF4/5/6. This gene content was kept in amphioxus, whereas FGF3 was lost in urochordates and different gene losses account in vertebrates for the presence of a single FGF3 gene and three genes of the FGF4/5/6 paralogy group. This implies that in amphioxus FGF3 and FGFB are orthologs, as well as FGF4/5/6 and FGFE.
