Genome-Wide Characterization of the Myostatin Gene (MSTN) Ligand–Receptor System and Its Expression Patterns Associated with Growth Variation in Trachinotus ovatus

Myostatin (MSTN), a member of the transforming growth factor-β (TGF-β) superfamily, is a conserved negative regulator of muscle growth in vertebrates. In this study, nine MSTN-related genes were identified in Trachinotus ovatus, including two MSTN ligand genes (ToMSTNa and ToMSTNb) and seven putative receptor genes (ToACVR1A, ToACVR1Ba, ToACVR1Bb, ToACVR2Aa, ToACVR2Ab, ToACVR2Ba, and ToACVR2Bb). Comprehensive evolutionary and expression analyses revealed the conservation and potential functional diversification of MSTN-related genes in T. ovatus. The two MSTN ligands showed relatively conserved gene structures and motif compositions, whereas the receptor genes displayed greater structural diversity. Tissue expression analysis showed that ToMSTNa was relatively highly expressed in muscle, while ToMSTNb was relatively highly expressed in brain, suggesting potential tissue-specific functional divergence between the two MSTN paralogs. In addition, expression analysis between large and small individuals showed that ToMSTNa was more highly expressed in the brain and intestine of small individuals than in large individuals, whereas ToACVR1A and ToACVR2Bb showed higher expression levels in the liver of small individuals, suggesting their potential association with growth variation. The homology-based predicted protein association network suggested potential associations of ACVR1B- and ACVR2A-type receptors with components of MSTN-related signaling. Overall, this study provides new insights into the evolutionary conservation, tissue-specific functional divergence, and potential growth-associated roles of the MSTN ligand–receptor system in T. ovatus, providing a foundation for further functional studies of MSTN-related signaling and the identification of candidate molecular targets associated with growth traits in teleost fish.