In-vitro differentiation of germinal epithelium from testes of adult and 12-day rats was studied with the aid of radioautography. Following a single injection of tritiated thymidine, the animals were killed and the testes grown as organ cultures. Tissue samples fixed prior to cultivation and after various time intervals of in-vitro growth, were processed for radioautography. Localization of the label in relation to the germ cell types was determined. In tissues obtained from animals 3 hr after isotope injection, the most advanced labelled germinal cells were spermatogonia and resting primary spermatocytes. Following 3 to 7 days of cultivation, the label was present in the zygotene and leptotene stages of the meiotic prophase and after 2 to 3 weeks of cultivation, in the pachytene stage of primary spermatocytes. No labelled spermatids were found in the cultivated tissues.
Appearance of labelled pachytene spermatocytes in cultures of testicular tissue containing only labelled spermatogonia and resting spermatocytes prior to cultivation constitutes evidence that progressive, although limited, differentiation of germinal epithelium from adult and puberal rats, can take place in vitro.
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