FIG. 2.

p53-mediated apoptosis does not require Atm. (A) Apoptotic cells in CP (arrows) were detected by the TUNEL assay. No qualitative changes were detected between TgT₁₂₁ and TgT₁₂₁ Atm^−/− CP tumor cells. (B) Quantitative apoptotic indices in TgT₁₂₁ and TgT₁₂₁ Atm^−/− CP. The percentages of apoptotic cells were determined for TgT₁₂₁ (open bars) and TgT₁₂₁ Atm^−/− (solid bars) littermates at different ages. Each bar in the left panel represents the averaged counts from 10 fields of one sample from one mouse at the specified age. The averages of all four mice are shown at the right. The error bars represent the standard deviations among microscopic fields (left) or among mice (right). (C) Impact of Atm deficiency on apoptosis compared with impact of p53 and E2F1 deficiency. Atm deficiency has no effect on apoptosis in TgT₁₂₁ CP cells, while p53 and E2F1 account for 85 and 80% of the apoptosis, respectively (26, 34).