Differentiation of rhabdomyosarcoma and neonatal muscle cells in vitro

Differentiating cells in monolayer cultures of neonatal rat muscle and nickelsulfide-induced rhabdomyosarcoma tissues were studied at the light and electron-microscopic levels. The strap cells in cultures of both tissues exhibited such common features as tube-like shape, centrally aligned uniform nuclei, large nucleoli and longitudinal cytoplasmic striations. Neonatal muscle cultures, however started to differentiate much earlier than tumor cultures and frequently showed cross- striations and spontaneous contractions whereas tumor cultures were characterized by a heterogeneous cell population with limited abilities to differentiate. Electron microscope examinations of strap cells from both types of cultures revealed abundant free ribosomes and parallel alignment of cytoplasmic filaments with Z bodies. These observations suggest that the initial stages of myogenesis are identical in some cells from both tumors and neonatal muscles. The main differences between the 2 types of strap cells are concerned with the rate and extent of differentiation. The significance of the observations with regard to the origin of the tumor strap cells is discussed.