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Ultrastructure of a transplantable murine rhabdomyosarcoma.

A spontaneous rhabdomyosarcoma from a BALB/cAnN mouse was transplanted several times in the same strain of mice and was developed in vitro .

Electron microscopic observations confirmed the muscular nature of the transplantable tumor which is composed of multinucleated and mononucleated cells. The ultrastructure of the muscle fibers appeared abnormal in that multinucleated myofibers with a majority of irregular sarcomeres and undefined transverse tubular systems were produced. Many nuclei of the tumor muscle cells contained large cytoplasmic inclusions of varying structures. Virus-like particles were found in sarcoplasmic vesicles of the muscle cell.