GDF 9 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 synthesized by ovarian somatic cells directly affect oocyte growth and function. GDF 9 is expressed in oocytes and is thought to be required for ovarian folliculogenesis.