To date, 22 members of the Fibroblast Growth Factor (FGF) family have been identified in vertebrates; however, only 18 of them are FGFR ligands. FGF11, FGF12, FGF13, and FGF14 cannot bind with FGFR, and are known as FGF homologous factors. For human, there is no FGF15; for mouse, there is no FGF19. Due to the sequence similarity between human FGF19 and mouse FGF15, they are considered as orthologous genes.
Table 1. Chromosomal localizations of FGFs in human and mouse
Based on phylogenetic analysis, the human FGF family can be further divided into seven subfamilies; FGF 1/2, FGF 4/5/6, FGF 3/7/10/22, FGF 8/17/18, FGF 9/16/20, FGF 11/12/13/14, and FGF 19/21/23. According to their mechanisms of action, the FGF family can also be classified into three categories, which are paracrine, endocrine, and intracrine FGFs. Paracrine FGFs refers to members of subfamilies FGF1/2, FGF 4/5/6, FGF 3/7/10/22, FGF 8/17/18, FGF 9/16/20; endocrine FGFs includes the three members of FGF 19/21/23 subfamily; and the four members of subfamily FGF 11/12/13/14 are identified as intracrine FGFs.
Fig 2. Action mechanisms of FGFs