Ablation of Puma confers protection of primitive hematopoietic cells against a single dose of γ-irradiation. (A-D) Total number of surviving CD150⁺ LSK cells (A), Flk2^low LSK cells (B), Flk2^high LSK cells (C), and multipotent progenitor (MPP; CD150⁻CD48⁻CD244⁺) cells (D) in mice before and after 9 Gy TBI. The total number of CD150⁺ LSK cells, Flk2^low LSK cells, and Flk2^highLSK cells in 1 pair of femurs of Puma^−/− mice (n = 6) was comparable with those in Puma^+/+ mice (n = 5) under normal conditions but was significantly higher in Puma^−/− mice than in Puma^+/+ mice at 3 days after 9 Gy TBI. In contrast, the number of MPP cells (CD150⁻CD48⁻CD244⁺) was similar in both Puma^−/− mice and Puma^+/+ mice before and 3 days after 9 Gy TBI, respectively; ***P < .001. All data are shown as mean ± SD.