The fine morphology of mouse primordial germ cells in extragonadal locations

Abstract

The localization and morphologic characteristics of mouse primordial germ cells at stages of embryonal development preceding formation of the undifferentiated gonads have been studied by means of high resolution light microscopy and electron microscopy. At day 9 of intrauterine life, the germ cells are found in the wall of the hind‐gut, at days 10 and 11 in the dorsal mesentery, and at day 12 they are mostly in the genital ridges or adjacent areas. Our observations confirm the hypothesis that germ cells attain their definitive location by ameboid movements. On the basis of morphologic characteristics displayed during migration, germ cells appear to be highly undifferentiated elements; for their energy requirements, they may depend on close association with somatic cells and on availability of exogenous substances of metabolic importance. Upon arrival at the genital ridges, the cells lose their ameboid features and assume a structural organization which is much simpler than that of precedinng stages. This indicates that migration is followed by a period of relative quiescence; mitosis is now the only evident activity. Interphase cells may occasionally be connected by intercellular bridges; it would seem that the first mitotic divisions with incomplete cytokinesis, a feature known to characterize oogonia and spermatogonia in sexually differentiated gonads, occur shortly after arrival of the germ cells in the genital ridges.