Conditional deletion of STAT5 causes rapid and sustained loss of HSC quiescence. (A) Representative flow cytometry analysis of Pyronin Y and Hoechst 33342 staining on KLS cells. (B) The percentage of KLS cells in G₀, G₁, and S/G₂/M phase is shown as mean plus or minus SD values from wild-type (n = 9) and KO (n = 6) analyses. (C) Wild-type or KO mice were injected intraperitoneally with a single dose of BrdU (as described in “BrdU staining and cell-cycle analysis of HSC”) and killed 3 days later. Representative flow cytometric analysis is shown for BrdU incorporation into gated KLS cells. (D) Bars represent the percentage of BrdU⁺ cells per KLS cells expressed as mean plus or minus SD values for n = 3 per group. P values are indicated when significant differences were observed between WT and KO groups. (E) The 7-dose pI:pC treatment regimen with treatments on alternating days for 2 weeks. These mice were analyzed 4 months later in LT-HSC subsets defined as CD34⁻ KLS. (F) Mice that received 7 doses of pI:pC were analyzed for cell-cycle status by Hoechst/Pyronin Y staining. Shown are values for G₀, G₁, and S/G₂/M fractions for both wild-type and KO mice (n = 3).