Fig. 7. Apoptotic delays during involution in E2f3 mutant mice. (A) Involution in the wild-type control, E2f1-knockout and E2f3 heterozygous samples. (B) To examine apoptosis in the wild type and E2f3 mutant, a TUNEL analysis was conducted at day 2 and day 3 of involution. TUNEL-positive cells stain brown and the sections are lightly counterstained with Hematoxylin. (C) The results of the TUNEL staining were quantitated, with the day 2 and day 3 differences being significant (P<0.0001 and P=0.0073, respectively). (D) An involution signature from a wild-type mammary involution dataset was generated and the probability of fitting the signature was assessed for the wild type and E2f3 mutant at successive days of involution. Red indicates a high probability of matching the involution day 4 signature; blue indicates a high probability of matching the involution day 1 signature.