Acts specifically as a negative regulator of skeletal muscle growth. Homodimer; disulfide-linked (PubMed:19644449). Interacts with WFIKKN2, leading to inhibit its activity (PubMed:12595574). Interacts with FSTL3 (PubMed:22052913). Expressed specifically in developing and adult skeletal muscle. Weak expression in adipose tissue. First detected 9.5 dpc in one-third of developing somites. At 10.5 dpc, expressed in the myotome compartment of somites. At later stages of development, detected in a wide range of developing muscles. Expression continues in adulthood. Synthesized as large precursor molecule that undergoes proteolytic cleavage to generate an N-terminal propeptide and a disulfide linked C-terminal dimer, which is the biologically active molecule. The circulating form consists of a latent complex of the C-terminal dimer and other proteins, including its propeptide, which maintain the C-terminal dimer in a latent, inactive state. Ligand activation requires additional cleavage of the prodomain by a tolloid-like metalloproteinase (PubMed:14671324). Mutant animals exhibit muscle hypertrophy. Belongs to the TGF-beta family.