RAD6B-knockout mice and RNF8-knockout mice present a histone replacement disorder during spermatogenesis. (A) Sections of testes from WT, RNF8−/− and RAD6B−/− mice stained with anti-tH2B (testis-specific histone H2B) are shown. Bar, 20 μm. (B) We used the ratio of tH2B IOD (sum) to DAPI IOD (sum) to analyze the difference in expression levels of tH2B among WT, RNF8−/− and RAD6B−/− mice. All values are presented as the mean ± SEM (WT n = 6; RNF8−/− n = 6; RAD6B−/− n = 6). Student's t-test; ***P < 0.001; ****P < 0.0001; ns, not significant. (C) Histone tH2B was not replaced in RNF8−/− and RAD6B−/− mice sperm. Images of immunostained sperm from WT, RNF8−/− and RAD6B−/− mice are shown. Bar, 20 μm.