Fig. 3. Histology of testes at various ages. Testes from control (Brca2 Ko/+; Tg/+, A and C) and rescued males (Brca2 Ko/Ko; Tg/+, B,D,E) at 3 weeks (A,B), 2 months (C,D) and 7 months (E) of age were analyzed. (A,B) In young control males at 3 weeks of age, the seminiferous tubules are filled with spermatocytes. The rescued testes show presence of several seminiferous tubules with spermatocytes but there are few that have reduced number of spermatocytes. (C,D) At 2 months, adult male control testes contain spermatocytes at various stages of maturation as well as spermatozoa in the seminiferous tubules. In rescued males, the spermatocytes appear to be arrested in meiotic prophase I and no postmeiotic cells are visible. Several seminiferous tubules containing only Sertoli cells are observed. There appears to be a relative increase in the number of Sertoli cells per seminiferous tubule in the mutants (see insets, arrows indicate the Sertoli cells). (E) In rescued testes, by 7 months of age, most of the seminiferous tubules are completely devoid of germ cells and none contain normal looking spermatocytes, while control tubules exhibit normal spermatogenesis. (F,G) In rescued testes, there is an increase in apoptosis, as indicated by the TUNEL-positive staining cells (brown precipitate). Very few spermatocytes show brown staining in 3-week-old control males where as majority of the spermatocytes show positive staining in the rescued testes. In the control testis, some tubules show TUNEL-positive cells next to the basal lamina of the tubules, indicating that they are the spermatogonial cells. S, spermatozoa; Sp, spermatocytes. Scale bars: 50 µm.