Myostatin in fish: current understanding of its characterization, function, and signaling pathways.

Myostatin (Mstn), a secretory protein from the transforming growth factor-β (TGF-β) superfamily, is mostly present in skeletal muscle across vertebrates. The mstn gene exhibits a conserved genomic structure consisting of three exons and two introns in both teleost fish and mammals. Unlike mammals which typically possess a single mstn copy, most fish species harbor two or more copies derived from whole-genome duplication events, and these paralogs show broader tissue expression profiles including muscle, brain, liver, kidney, and gonads. The function and mechanism of action in fish appear generally similar to those of other animals, although fish-specific gene duplication and tissue distribution patterns suggest possible functional divergence. Mstn primarily exerts its growth-inhibitory effect by suppressing muscle satellite cell activation, inhibiting myoblast proliferation, and downregulating myogenic regulatory factor (MRF) family expression. These molecular actions collectively restrict both hyperplastic and hypertrophic muscle growth. Disruptive mutations, including nucleotide deletions or substitutions, in the coding sequence of the fish mstn gene lead to a loss of Mstn function, which in turn stimulates myoblast proliferation and differentiation, potentially leading to pronounced muscle hyperplasia and hypertrophy. Emerging evidence further indicates that fish Mstn also plays pleiotropic roles in lipid metabolism regulation and immune modulation. In this paper, we evaluate the sequence structure, tissue distribution, function, and mechanism of mstn action in fish, with a focus on mstn's role and molecular mechanism in controlling fish muscle growth, to provide fundamental information for fish quality improvement.