An experimental mouse testicular teratoma as a model for neuroepithelial neoplasia and differentiation. II. Electron microscopy.

The electron microscopic features of the stages of divergent neuroepithelial differentiation in the solid implants of a transplantable mouse testicular teratoma (OTT-6050) are presented and compared to the sequential stages of cytogenesis that have been described in the developing avian and mammalian central nervous system. Primitive neuroepithelial tumor cells showed the features of undifferentiated multipotential matrix (or ventricular) cells of the neural tube. They formed primitive medullary rosettes, from which various transitions were traced to more differentiated, cilia-containing ependymoblastomatous rosettes; the transitional features included increased granular endoplasmic reticulum and microvilli formation. Glial differentiation was characterized by the presence of mature ependymal rosettes and of astrocytes containing glial filaments. Neuronal differentiation included the development of synapses and the presence of dense-core vesicles in nerve cell processes. No intermediate cell forms were found that suggested multiple lines of differentiation occurring within a single cell.