FGF-4, also named FGFKandKFGF, belongs to the fibroblast growth factor (FGF) family. By signaling through the FGFR1c,2c,3cand4 receptors, FGF-4 has functions that maintain a population of progenitor cells in the epiblast that generates mesoderm, and contribute to the stem cell population that is incorporated in the tailbud. It is also required for axial elongation of the mouse embryo after gastrulation. Mature human FGF4 (71206 a.a.) shares 91 %, 82 %, 94 % and 91 % a.a. identity with murine, rat, canine and bovine FGF4. Additionally, FGF-4 shares about 30 % sequence identity with the prototypical members of the FGF family.