The effect of Sirt1 loss is cell-autonomous and linked to stress but not developmental HSPC expansion. (A) Hematopoietic lineage-specific Sirt1-E4^fl/fl, vav-iCre mice (SIRT1^Δ/Δ, n = 5), Sirt1-E4^fl/fl (WT, n = 5), and vav-iCre (Cre, n = 2) control mice were treated with 4-OHT at 5 mo of age for 11 wk and the frequency of the indicated LSK subsets was analyzed by FACS. Cell numbers from two hind legs are shown. P-values are based on comparison of SIRT1^Δ/Δ to combined controls. (B) Sirt1-E4^fl/fl, vav-iCre mice (SIRT1^Δ/Δ, n = 3) and Sirt1-E4^fl/fl controls (WT, n = 3) were treated with 5-FU at 4–5 mo of age and analyzed 2 wk later as in A. Representative gating strategies are shown in Fig. S2. Total BM cell number from two hind legs is shown for the indicated subsets. (C) Frequency of CD150⁺CD34⁺ LSK progenitors and total LSKs in 2-wk-old Sirt1-E4^fl/fl, vav-iCre mice (SIRT1^Δ/Δ, n = 6), WT (n = 12), or vav-iCre (n = 3) controls. 5-mo-old mice from B are shown for comparison (n = 3 per group). (D) Total BM cell numbers of indicated HSPC subsets in 2-wk-old Sirt1-E4^fl/fl, vav-iCre mice (SIRT1^Δ/Δ) and WT or vav-iCre controls (Cre). Panels represent individual litters of either WT (n = 9) and SIRT1^Δ/Δ (n = 3) or WT (n = 2) and Cre mice (n = 6). Error bars represent SD. *, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.001.