Fibroblast Growth Factor-9 (FGF-9),  also known as Glia-activating factor (GAF) and HBGF-9, belongs to the heparin-binding growth factors family. It is a secreted protein that exists as monomer or homodimer. It interacts with FGFR-1, FGFR-2, FGFR-3, and FGFR-4 and plays an important role in regulating cell proliferation, differentiation and migration. It is reported that FGF-9 may be involved in glial cell growth and differentiation during development, gliosis during brain tissue regeneration, and glial tumor growth stimulation. Other reports indicate that FGF-9 plays a role in male development.