[Electron microscopic study of differentiation in rhabdomyoblast clone lines]

The ultrastructure of rabdomyoblasts has been studied. Rhabdomyoblasts were removed from rhabdomyosarcoma M-38 induced in mice by 20-methylcholantren, from clon-line M-38/13 (5 passages) originating from this rhabdomyosarcoma, and from two line of rhabdomyosarcomas cultivated for several years. Throughout the passaging (progression) of tumors, both highly and poorly differentiated ((cambial) cells were seen to disappear from tumor cell populations. The intracellular differentiation of rhabdomyoblastse manifested itself as formation of specific contractile structures, can occur only in those rhabdomyoblasts which enter the cell complexes. These complexes have narrow intercellular spaces and intercellular contracts. It is suggested that the rhabdomyoblast with features of cytotypical differentiation may be considered as a structural functional unit of the differentiating cell complex.