Dual lack of RXRα and RXRβ in HSCs leads to cell-cycle activation and quiescence exit. (A) Representative flow cytometry density plots showing 5-bromo-2′-deoxyuridine (BrdU) incorporation by LSKs and CD150⁺CD48⁻ LT-HSCs after a 24-hour pulse (left); the plot (right) shows the frequencies of cells with BrdU incorporation (data are pooled from 2 independent experiments). (B) Representative flow cytometry density plots showing pyronin Y and Hoechst 33342 staining by LSKs and CD150⁺CD48⁻ LT-HSCs (upper plots); the lower plots show frequencies of cells with double pyronin Y and Hoechst 33342 staining (data are pooled from 2 independent experiments). (C-E) Recovery of hematopoietic cells after 5-fluorouracil (5-FU) administration to Vav^Cre+Rxrab^fl/fl and WT mice. (C) Experimental design. (D) Time course of PB-cell counts (baseline was defined as the mean reading on day 0, expressed as 100%; n = 9-11 mice per genotype). (E) Absolute HSC/P numbers in total BM 20 days after 5-FU administration. (F-H) HSC/P proliferation 5 days after 5-FU administration to Vav^Cre+Rxrab^fl/fl and WT mice. (F) Experimental design. (G) Representative flow cytometry density plots showing BrdU incorporation by LSKs and CD150⁺CD48⁻ LT-HSCs. (H) Frequencies of BrdU-positive cells. All data are presented as means ± SEM, and dots represent individual animals. Significance was determined by unpaired Student t test (A, B, E, and H) or 2-way analysis of variance followed by the Sidak multiple comparisons test (D; age-paired mice), and is represented as follows: ∗P ≤ .05, ∗∗P ≤ .01, ∗∗∗P ≤ .001, and ∗∗∗∗P ≤ .0001. n.s., not significant.