Cell type differences in the sensitivity to radiation-induced apoptosis correlates with localization differences in cyclin B1 protein.

(A) A dose of 200 cGy γ radiation causes apoptosis in mouse primary thymocytes and Ramos cells but not human HF172 fibroblasts, Cos-1, and NIH3T3 cell lines. Apoptosis is determined flow cytometrically by annexin V staining 12 hours after irradiation. (B) A dose of 200 cGy γ radiation causes the nuclear localization of cyclin B1 protein in mouse primary thymocytes and Ramos cells but not human HF172 fibroblasts, Cos-1, and NIH3T3 cell lines. Green fluorescence indicates cyclin B1 staining; red fluorescence indicates nuclear staining with the dye Yo-Pro3 (thymocytes, Ramos) or Hoechst 33342 (HF172, Cos-1, NIH3T3); yellow indicates where the stains overlap. Staining was performed 4 hours after irradiation. Ramos and thymocyte images are confocal, whereas those of HF172, Cos-1, and NIH3T3 are conventional fluorescence microscopy. Original magnification B, × 630.