In the mouse, one spermatogenic cycle from spermatogonia to mature spermatozoa is estimated to take about 35 days. Therefore, in about 1 mo all the differentiating germ cells in the premeiotic as well as postmeiotic stages finish maturing to spermatozoa and are released from the seminiferous epithelium to the epididymis. Nevertheless, our finding that p-gal-positive cells were still detected in a clump of spermatogenic germ cells even after 1 mo of CMV-lacZ transfection (Fig. 3B) suggests that beyond the blood-testis barrier the foreign gene was transferred into the spermatogenic stem cells and the proliferating spermatogonia residing on the basal membrane. buy birth control online
This possibility was supported by the results obtained with transfection to busulfan-treated testes. The anti-cancer drug acts predominantly by killing proliferating active cells such as undifferentiated spermatogonia and transiently inhibiting the spermatogenic cycle. As a result, all developing spermatogenic cells disappear within 3 wk while some slowly dividing spermatogenic stem cells and nonproliferating somatic cells remain alive in busulfan-treated testes. After 2 mo of CMV-lacZ transfection to the busulfan-treat-ed testis, we found a clump of p-gal-positive cells in the repopulating spermatogenic cell layers (Fig. 3D), as well as characteristic localization of the transfectant cells along the axis of the seminiferous tubules (Fig. 3C).