[Pattern of skeletal muscle differentiation in fish: molecular and biological approaches]

The initial stages of myogenesis going in myoblasts include the stages of induction, determination, and differentiation. The induction and determination of cells in the myotomes are controlled by morphogenetic signals from neighboring tissues of the notochord and neural tube manifested as expression of genes of Shh and Wnt families, respectively. In fish (at the example of danio), this signal is passed to somite cells neighboring the notochord; later the cells migrate to the embryo surface and differentiate into slow muscle fibers. Synthesis of the main contractile proteins, primarily the components of myosin molecule--heavy chain (MHC) and individual isoforms of light chains (MLC1, MLC2, and MLC3)--are encoded by different genes during different ontogenetic stages. The peptide maps obtained after alpha-chymotrypsin digestion of MHCs from larvae, fast and slow skeletal muscle of loach are different, which points to differences in their primary structure. In addition, considerable differences were revealed in the structure of MLC isoforms at different ontogenetic stages. The definitive fast muscle contained three light chain types, MLC1, MLC2, and MLC3; slow muscle, MLC1 and MLC3; while the larval muscle fibers included a specific larval MLCL in addition to MLC3.