miR-125b Orchestrates the Proliferation and Fusion of Myoblasts in Chinese Perch by Targeting the MyoD and Myomaker.

Fish skeletal muscle serves as a crucial source of high-quality protein for human consumption. MicroRNAs (miRNAs) are important epigenetic regulators for the growth and development of skeletal muscle. Although the functions of many myogenic miRNAs have been studied, the regulatory functions of miRNAs in fish skeletal muscle have not been fully investigated. Here we show miR-125b is highly expressed in fast muscle of Chinese perch (Siniperca chuatsi) at 30-60 days post-hatching (dph), with transient downregulation during the skeletal muscle injury repair stage, implying its essential regulatory role in fast muscle growth and injury repair. Moreover, inhibiting miR-125b in Chinese perch resulted in an increase in muscle fiber diameter, the number of proliferating myoblasts and nuclei in single muscle fiber. In contrast, overexpression of miR-125b in Chinese perch led to a significant reduction in muscle fiber diameter, accompanied by a significant decrease in the number of proliferating myoblasts and the number of nuclei in single muscle fiber. Bioinformatics analysis and dual luciferase assays confirmed MyoD and Myomaker as direct targets of miR-125b. In summary, our findings demonstrate that miR-125b modulates the expression of MyoD and Myomaker, thereby regulating the proliferation and fusion of myoblasts, and ultimately controlling the hypertrophy of muscle fibers in Chinese perch. This finding holds significant relevance in unraveling the genetic mechanisms that govern the developmental traits of muscle fibers in fish during the postembryonic phase.