Fig. 3. Quantification of cell cycle and cell death analysis in the CNS of E13.5 germline Rb^–/– and chimeric embryos. (A) S-phase activity (assessed by BrdU incorporation) and apoptosis (by TUNEL analysis) in hindbrain region on sagittal sections of germline Rb^–/–, chimeric and wild-type (wt) E13.5 embryos. S-phase entry was increased in the brains of both germline Rb-deficient and chimeric embryos as compared with wild type. However, apoptosis was significantly suppressed in chimeras as compared with germline Rb^–/– embryos. (B) FACS cell cycle profile analysis of Rb^–/– and wild-type cells in chimeric CNS at E13.5. Rb^–/– cells show reduced G₁, and increased S-phase and G₂/M fraction. (C) PH3 (a mitotic marker) expression in wild-type, germline Rb-deficient and chimeric embryo CNS at E13.5. M-phase entry was increased in germline Rb^–/– embryos but not in chimeras as compared with wild type.