Fig. 4. Apoptotic loss of spermatogenic precursors in CIT-K^-/- mice. E14.5 embryos from CIT-K heterozygous intercrossing were labeled for 1 hour in utero with BrdU and then processed for immunohistochemistry. (A,B) Apoptotic gonocytes were identified by immunohistochemistry for activated Caspase-3, as intratubular-positive cells (red arrowheads). The assay was performed on comparable sections from CIT-K^+/+ (A) and ^-/- (B) testes. Interstitial cells displayed a background cytoplasmic positivity in both control and knockout samples. (C,D) The tubular proliferative index was determined on sections adjacent to those used for the apoptosis assay, labeled by anti-BrdU immunostaining. (E) Graphic representation of the apoptotic (Cas-3) and proliferative (BrdU) indexes at E14.5 in testes of CIT-K^+/+ (open bars) and ^-/- (closed bars). Values are expressed as the relative increase compared with the control. Error bars showstandard deviation, P<0.01.