Loss of Skp2 triggers the HSCs entering the cell cycle. (A) Analysis of apoptosis in LT-HSCs from WT and Skp2^−/− mice by flow cytometry (P > .05; n = 3). (B) Cell cycle profile of LT-HSCs from WT and Skp2^−/− mice was determined by flow cytometric analysis (*P < .05; n = 3). The representative histogram is shown in supplemental Figure 4. (C-D) Flow cytometric dot plot and statistical results of G₀ and G₁ phase cells in LT-HSCs from WT and Skp2^−/− (*P < .05; n = 3). (E) The BrdU incorporated rates of Flk⁻LSK cells from WT and Skp2^−/− mice were 0.578% ± 0.199% versus 1.389% ± 0.742% in BM (**P < .01; n = 3) and 3.122% ± 2.553% versus 5.722% ± 1.340% in spleen (*P < .05; n = 3).