Radiation resistance of engrafted hematopoietic stem cells in the absence of Puma. (A) Radioprotection of HSCs by deletion of Puma in competitive transplantation model. The experimental design was shown in detail in supplemental Figure 1A. The hematopoietic contribution in blood by 100 LT-HSCs before and after 4-Gy irradiation was indicated by the ratios of CD45.2 to CD45.1/.2 cells (n = 4 in both Puma^+/+ and Puma^−/− groups). (B-C) Self-renewing capacities of Puma^−/− HSCs remained after serial competitive transplantation and 4-Gy radiation. The experimental design was shown in detail in supplemental Figure 1B. The engraftment levels of Puma^−/− HSCs relative to competitor cells in primary recipients (B) and secondary recipients (C) were shown, respectively. (D-E) Kaplan-Meier analysis of overall survival of the mice reconstituted with Puma^+/+ or Puma^−/− hematopoietic cells (supplemental Figure 1C) exposed to first round 9-Gy irradiation (D) and second round 9-Gy irradiation (E). P values are indicated in the graphs.