Myostatin is a growth factor that regulates the size of muscles beginning in early embryonic development and continuing throughout life. Myostatin acts by inhibiting the growth of muscles, It prevents them from growing too large. Myostatin is also known as growth and differentiation factor 8 (GDF-8). It is a protein made up of two identical subunits. Each subunit contains 110 amino acids. The gene encoding myostatin is termed MSTN (or GDF8) and is on chromosome 2 in band 2q32.1.

Myostatin is a member of the transforming growth factor beta (TGF-beta) family. All of the members of this gene family regulate growth and differentiation from early embryogenesis to mature cell types and tissues.