Abstract: The present invention relates to a myostatin inhibitor comprising extracellular water-soluble domains of delta-like 1 homolog (DLK1) as active ingredients. More particularly, the present invention relates to a composition for inhibiting myostatin activity, comprising, as active ingredients, extracellular water-soluble domains of DLK1 or a deletion mutant of extracellular water-soluble domains of DLK1. The myostatin inhibitor of the present invention is bonded to the myostatin or activin receptor type IIB so as to inhibit the action mechanism of the myostatin, to thereby promote myogenesis and prevent differentiation into fat cells. Therefore, the myostatin inhibitor of the present invention may be used in preventing and treating diseases such as muscular dysplasia that requires differentiation to muscular cells, or metabolic diseases.

Abstract: The present invention relates to an activin receptor type II B (ACVR2B) inhibitor which comprises the delta-like 1 homolog (DLK1) extracellular water-soluble domain. More specifically, the present invention relates to an extracellular soluble domain of DLK1; fragments of the extracellular soluble domain of DLK1; mutants of the extracellular soluble domain of DLK1; a composition for suppressing ligand linkage with the ACVR2B receptor, which includes a fragment of the mutants as an active ingredient; and a pharmaceutical composition for prevention and treatment of diseases which comprises the same. The composition of the present invention competitively binds to the ACVR2B receptor and inhibits the binding of an ACVR2B ligand to the ACVR2B receptor, which inhibits protein signalling associated with such ligands, and will be useful for prevention and treatment of diseases associated therewith.