Ultrastructure of ovarian teratomas in LT mice.

Stem cells of these tumors formed nests consisting of undifferentiated embryonic cells in the center with more differentiated cells towards the periphery. A type viral particles were seen in the cisternae of rough endoplasmic reticulum. Ultrastructurally the stem cells of ovarian teratomas did not differ from stem cells of testicular or embryo-derived teratomas. They were however distinct from the cleavage stage embryonic cells and/or the unfertilized ovum, they stemmed from. They correspond both cytologically and developmentally to ectodermal embryonic cells from the egg-cylinder, the most advanced developmental stage of parthenotes observed previously in the ovary of LT mice.