GDF9 is a member of the bone morphogenetic protein (BMP) family and the TGF-beta superfamily. This group of proteins is characterized by a polybasic proteolytic processing site which is cleaved to produce a mature protein containing seven conserved cysteine residues. The members of this family are regulators of cell growth and differentiation in both embryonic and adult tissues. Growth factors synthesized by ovarian somatic cells directly affect oocyte growth and function. GDF9 is expressed in oocytes and is thought to be required for ovarian folliculogenesis. GDF9/4262 can be used in assays to detect GDF9 expression and help diagnose ovarian disorders.