Epidermal growth factor induces terminal differentiation in human epidermoid carcinoma cells

In this study, spermatogenesis in the adult Djungarian hamster is described. Undifferentiated spermatogonia topographically arranged as Asingle (A(s)), Apaired (Apr), and Aaligned (Aal) spermatogonia were observed, as were six generations of differentiating spermatogonia (A1, A2, A3, intermediate, B1, and B2). The differentiating spermatogonia divided at regular intervals during the cycle of the seminiferous epithelium. Mitosis of these cells was observed at the transition from stage IX to stage X (mitosis of A1 into A2 spermatogonia), at the transition from stage XII to stage I, at the transition from stage II to stage III, at the transition from stage IV to stage V, at the end of stage VI, and at approximately the middle of stage VII. Cellular associations in the cycle of the seminiferous epithelium are described. The seminiferous epithelium was divided into 12 stages, based upon the developmental steps in spermiogenesis, and the frequency of these stages was determined. The duration of the cycle of the seminiferous epithelium, determined by 3H]thymidine incorporation, was shown to be 7.90 +/- 0.01 (mean +/- SEM) days.