Insulin-like Growth Factor 2 Regulates Skeletal Muscle Development in Spotted Sea Bass (Lateolabrax maculatus).

Insulin-like growth factor 2 (IGF2) is a conserved member of the insulin superfamily, playing essential roles in growth and skeletal muscle development in vertebrates. However, its molecular functions in marine teleosts remain largely unexplored. In this study, we cloned and characterized the igf2 gene from the spotted sea bass (Lateolabrax maculatus), a commercially important aquaculture species. Bioinformatic analysis revealed that the IGF2 protein contains conserved structural domains and forms a phylogenetically clade with teleost IGF2b sequences. Tissue expression profiling and in situ hybridization confirmed strong hepatic expression of igf2, with localized cytoplasmic signals in hepatocytes. In skeletal muscle, expression analyses further indicated differential expression patterns among IGF receptors, with igf1ra transcripts prominently localized to the subsarcolemmal region of muscle fibers. To assess its function, recombinant IGF2 (rIGF2) was expressed and purified in Escherichia coli. Functional assays demonstrated that rIGF2 significantly enhanced myoblast proliferation in a dose-dependent manner, as evidenced by EdU incorporation and CCK-8 assays. Furthermore, rIGF2 promoted myotube formation and upregulated the expression of myogenic regulatory factors (myod, myog) and mitochondrial dynamics-related genes (mfn1b, mfn2, opa1, and fis1), suggesting a role in both differentiation and mitochondrial remodeling. Collectively, these findings provide new insights into IGF2 function in teleost skeletal muscle development and offer a molecular basis for future studies on growth regulation and selective breeding in marine aquaculture species.