FGF-6 is a member of the fibroblast growth factor (FGF) family, and it is closely related in structure to FGF-4. FGF-6 exhibits a very restricted expression profile predominantly in the developing muscle in embryos. FGF-6 mRNA can also be detected in testis, heart, and skeletal muscle in adults. FGF-6 is involved in both proliferation and differentiation of the myogenic lineages. In vitro studies have shown that the effects of FGF-6 are concentration dependent. At lower concentration, FGF-6 can increase the expression of many muscle cell differentiation markers. At higher concentrations, FGF-6 can downregulate the expression of myogenic markers and some myogenic transcription factors, and can delay C2 myogenic cell differentiation. Injection of FGF-6 recombinant protein into damaged mouse muscle can induce cyclin D1 mRNA and differentiation markers, including Cdkl1, MHC I and Tn1, which results in the acceleration of muscle regeneration. It has been shown that the expression of FGF-6 can transiently be upregulated by muscle injuries in both fast and slow myofibers. FGF-6 can stimulate migration of myogenic stem cells and also control the maintenance of muscle progenitor cells. During muscle regeneration, it has been shown that FGF-6 can be released from necrotic myofibers and be sequestered by basal laminae. FGF-6 regulates muscle differentiation through a calcineurin-dependent pathway and regulates myofiber size through IGF-II/TGF2R pathway. FGF-6 is also involved in bone metabolism.