Se and selenoproteins are required in early SEPs. (A-D) Analysis of Se-A and Se-D mice treated with 50% PHZ. (A) Survival of Se-A and Se-D mice treated with 50% PHZ; n = 8 per diet. (B) Analysis of hematocrit during recovery from treatment with 50% PHZ; n = 10-15 per diet. (C) Representative flow cytometry graphs of Kit⁺CD133⁺early SEPs during recovery from PHZ treatment. (D) Quantitation of spleen Kit⁺CD133⁺early SEPs and Kit single-positive cells during recovery; n = 3-4 per diet. (E-F) In vitro analysis of Trsp^Δ/Δ and control cells using 2-phase stress erythropoiesis culture; n = 4 per group. (E) Total cell numbers postexpansion culture (in stress erythropoiesis expansion medium [SEEM]) and differentiation culture (in stress erythropoiesis differentiation medium [SEDM]). (F) Stress BFU-E colony assays of cells after differentiation culture. (G-J) In vivo short-term radioprotective model. Donor BM cells were obtained from Trsp^fl/Δ;CreERT or control Trsp^fl/Δ mice. Trsp gene deletion was induced by treating cells with 4-hydroxytamoxifen in vitro 48 hours before bone marrow transplant. (G) Survival rate and (H) hematocrit measurements of transplanted mice on the indicated days posttransplant. Two independent repeats; n = 5 for each group. (I) Total spleen SEPs on days 8 and 10 after BMT; n = 4 per group. (J) Stress BFU-E colony assays of spleen cells on day 10 after BMT; n = 4 per group. Bars are representative of mean ± SEM. *P < .05; ***P < .005; ****P < .0001.