[Divergent differentiation during embryonal histogenesis of skeletal muscle tissue].

Morphometric analysis of the developmental processes of the satellite cells and myosimplasts has been performed in embryonal histogenesis of the skeletal muscle tissue in 17 human fetuses 8-27 weeks of the intrauterine development. The sequence of death of some myoblasts in embryonal histogenesis is described in details. Basing on the data obtained, a conception on existance of muscular-proliferative units (MPU) in composition of the skeletal muscles is put forward. The amount of the MPU determines the whole number of muscle fibers in the muscle. The anlage of the MPU occurs as a result of divergent differentiation of the stem myogenic cells at early stages of myogenesis (myosimplasts and myotubes) from the cells commited to mutual fusion. The fund of these cells is determined by the number of myogenic elements that are at the state of the proliferative rest. One of the mechanisms regulating the number of the resting cells is the growth rate of the simplast lengthwise. The resting cells, appearing at late stages of myogenesis (of the muscle fibers), are the sources for development of the myosatellites in mature muscle fibers. In dying myotubes there is a sharp disturbance in growth processes lengthwise, in biosynthesis of contractile proteins, in correlation between the number of nuclei in the satellite cells and those of simplasts.