The protein encoded by this gene is a member of the fibroblast growth factor (FGF) family. FGF family members possess broad mitogenic and cell survival activities, and are involved in a variety of biological processes, including embryonic development, cell growth, morphogenesis, tissue repair, tumor growth and invasion. This protein was isolated as a secreted factor that exhibits a growth-stimulating effect on cultured glial cells. In nervous system, this protein is produced mainly by neurons and may be important for glial cell development. Expression of the mouse homolog of this gene was found to be dependent on Sonic hedgehog (Shh) signaling. Mice lacking the homolog gene displayed a male-to-female sex reversal phenotype, which suggested a role in testicular embryogenesis.
FGF9 has also been shown to play a vital role in male development. Once activated by SOX9, it is responsible for forming a feedforward loop with Sox9, increasing the levels of both genes. The absence of Fgf9 causes an individual, even an individual with X and Y chromosomes, to develop into a female, as it is needed to carry out important masculinizing developmental functions such as the multiplication of Sertoli cells and creation of the testis cords.
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