Fibroblast growth factor-9 (FGF-9) is a member of the fibroblast growth factor (FGF) family. All FGF family members are heparin binding growth factors with a core 120 amino acid (a.a.) FGF domain that allows for a common tertiary structure. FGF-9 plays an important role in the regulation of embryonic development, cell proliferation, cell differentiation and cell migration. This protein was isolated as a secreted factor that exhibits a growth-stimulating effect on cultured glial cells. FGF-9 is a monomer and interacts with FGFR1, FGFR2, FGFR3 and FGFR4. The rat FGF-9 shares 98 % a.a. sequence identity with human FGF-9.