[Fibrillary structures in tumor myoblasts]

An electron microscope study was made of fibrillar structures in various types of cell elements in mice rhabdomyosarcoma. Different stages of myofibril development were followed in such differentiated cell elements as large spindle cells, large round cells and middle spindle cells. In the former two cells, the evolution has riched a stage of bundles of myofibrills with Z-like bands. The highest degree of myofibril maturation occurs in multinuclear myosymplasts. The occurrence of myofibrils being at different stages of evolution within the same cells is characteristic of tumor myoblasts in addition to an excentric unipolarity of cell differentiation and atypical structure of Z-brands. Cytotypical differentiation (myofibrillogenesis in uninuclear cells) may be the case only in those types of rhabdomyosarcoma cell elements which are able to undergo histottypical differentiation (fussion and formation of multinuclear myosymplasts).