Accumulation of DNA damage in irradiated-Parp-2^−/− HSPCs. (A) Representative staining profiles of γH2AX in LSK and MP cells derived from Parp-2^+/+ and Parp-2^−/− mice at basal level and 2 hours after γ-irradiation (5 Gy). (B) Graph showing the percentage of γH2AX-positive cells. Bars represent the mean ± SEM obtained from at least 5 mice per genotype. (C) Representative images showing DNA damage in LSK and MP cells derived from Parp-2^+/+ and Parp-2^−/− mice at different time points after irradiation (5 Gy), visualized by alkaline comet assay. (D) Graph showing the percentage of cells with comet. An average of 100 cells was scored for each time point from each mouse. Bars represent the mean ± SEM obtained from 3 mice per genotype from independent experiments.