Characterization of muscle morphology and satellite cells,and expression of muscle-related genes in skeletal muscle of juvenile and adult Megalobrama amblycephala

Hyperplasia and hypertrophy are two distinct processes of skeletal muscle growth regulated by four myogenic regulatory factors (MRFs, contains MyoD, Myf5, Mrf4 and myogenin (MyoG)) and myostatin (MSTN). In this study, characterization of muscle morphology and satellite cells in juvenile (1-year-old) and adult (2-year-old) Megalobrama amblycephala was described. Compared with 1-year-old M. amblycephala, the diameter scope of epaxial, horizontal septum and hypaxial muscle fibers including red and white muscle in 2-year-old fish exhibited broader with dramatic reduction in frequency distribution of <20 μm diameter, nevertheless observable increase in frequency distribution of >50 μm diameter. Intermyofibrillar (IM) nuclei were also found except numerous subsarcolemmal (SS) nuclei in 2-year-old fish, whereas only SS nuclei were observed in 1-year-old fish. Immunofluorescence results showed that more satellite cells existed in red muscle than white muscle in 1-year-old fish, rather than 2-year-old fish. Moreover, we observed predominant increase in the mRNA levels of MyoD, Myf5, Mrf4, and MSTN during muscle development of fish in 2-year-old fish except MyoG.