The Ultrastructure of Primordial Germinal Cells of the Fetal Testes and of Embryonal Carcinoma Cells of Mice.

This study compares the ultrastructure of murine embryonal carcinoma cells, the multipotential stem cells of teratocarcinomas, with the constituents of the primordial testicular tubules in which they arise. The primordial tubules were composed of Sertoli cells and primordial germinal cells ; the former were well differentiated with Golgi membranes and well developed cisternal endoplasmic reticulum. The ultrastructure of primordial germinal cells bore a striking resemblance to embryonal carcinoma cells. Few profiles of endoplasmic reticulum and numerous dispersed ribosomes imparted a uniform stippled appearance to the cyto plasm. Mitochondria appeared prominently because of the lack of other organelles; desmosomes were absent. Direct cytoplasmic communications through openings in the cellular membranes were observed in primordial germinal cells but never in the cancer cells. It is concluded that the primordial germinal cells of the lo-day-old fetal testis of the mouse satisfy the requirements of multipotentiality and morphological similarity to be the cell of origin of embryonal carcinoma and teratocarcinoma.