Deletion of Puma enhances repopulation of hematopoiesis after a single lethal dose of radiation. (A) Diagram for in vivo HSC competitive repopulating assay. PUMA−/− BM cells (Ly5.2+) were mixed with an equal number (1 × 106) of helper BM cells (Ly5.1+/Ly5.2+), and then transplanted into lethally irradiated recipients (Ly5.1+). The percentage of donor-derived cells (Ly5.2+) among hematopoietic cells derived from transplanted BM cells (Ly5.1+/Ly5.2+ and Ly5.2+) was determined by flow cytometric analysis in each recipient at 2 months after radiation. Reconstituted mice were then given a second course of γ-irradiation (9 Gy), and the percentage of donor-derived cells (Ly5.2+) in each recipient was determined by flow cytometric analysis at 2 months after the second radiation. (B) The percentage of donor-derived cells (Ly5.2+) in reconstituted mice in panel A. The percentage of donor-derived cells (Ly5.2+) in each of the reconstituted mice was significantly increased after a second course of γ-irradiation (9 Gy). The data shown are the means ± SD (n = 4 mice/group). P < .001. (C) Hematoxylin and eosin staining of the BM cavities of femurs from mice after TBI (9 Gy) or without treatment. Ten days after irradiation, hematopoietic cell clusters were evident in the BM of Puma−/− mice but not those of Puma+/+ mice.
