Growth differentiation factor 8 (GDF8), also known as myostatin, is a unique member of the transforming growth factor-β superfamily that is expressed in human granulosa cells and has important roles in regulating a variety of ovarian functions. GDF8 acts as a negative regulator of skeletal muscle growth and differentiation. In addition to the expression in the musculoskeletal system, GDF8 is also expressed in various tissues, including the reproductive system.