Fig. 5. Granulosa cell apoptosis is not increased in Cx43 null mutant follicles as indicated by the TUNEL assay. (A) In wild-type ovaries, apoptosis can be readily detected in some follicles, indicative of atresia. (B) Very few apoptotic cells were observed within Gja1^–/Gja1^– follicles, although apoptotic cells were observed in the stroma. (C) GDF9 null mutant ovaries did not display evidence of any apoptotic granulosa or stromal cells. (D) A positive control section, treated with DNase before TUNEL staining. (E) A quantitative comparison of TUNEL staining in wild-type and Cx43 null mutant follicles failed to reveal a significant difference (P>0.3). The bars indicate the total pixel intensity normalized to follicle area, the error bars indicate s.e. and the number of follicles surveyed is indicated in parentheses above each bar. Bar, 100 µm.