A pair as a minimum: the two fibroblast growth factors of the nematode Caenorhabditis elegans

Fibroblast growth factors (FGFs) regulate many important developmental and homeostatic physiological events. The FGF superfamily contains several families. In this review, we present recent findings on the two FGFs of the nematode Caenorhabditis elegans from both functional and phylogenic points of view. C. elegans has a single FGFR (EGL-15) with two functionally exclusive isoforms, and two FGFs (LET-756 and EGL-17), which play distinct roles: an essential function for the former, and guidance of the migrating sex myoblasts for the latter. Regulation of homeostasis by control of the fluid balance could be the basis for the essential function of LET-756. Phylogenetic and functional studies suggest that LET-756, like vertebrate FGF9, -16, and -20, belongs to the FGF9 family, whereas EGL-17, like vertebrate FGF8, -17, and -18, could be included in the FGF8 family.