– Growth/differentiation factor 8(Mstn, GDF-8) 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. It is expressed specifically in developing and adult skeletal muscle. It exists as a homodimer, and interacts with WFIKKN2, leading to inhibit its activity. This protein can act specifically as a negative regulator of skeletal muscle growth. It regulates cell growth and differentiation in both embryonic and adult tissues.