p53 deletion, but not p21 deletion, rescues the B-cell development defect in the bone marrow of Wip1KO mice. (A) Western blot analysis of phospho-p53 (ser 15) expression in sorted B220⁺ cells from the bone marrow of WT and Wip1KO mice. Western blots are representative of 3 independent experiments. (B) Relative expression of p53 in FACS sorted pre–B cells. Data are expressed as means ± SD (n = 6). (C) The percentage of immature B cells and mature B cells in the bone marrow of WT, Wip1KO, p53KO, and Wip1/p53-DKO mice. (D) The number of immature B cells and mature B cells in the bone marrow of WT, Wip1KO, p53KO, and Wip1/p53-DKO mice. Data are expressed as means ± SD (n = 7). Representative histograms show the cell-cycle profile of early B-cell precursors, including pre-pro–B cells (E), pro–B cells (F), and pre–B cells (G). The bar graphs show the percentage of pre-pro–B, pro-B, and pre–B cells in SG2M phase. Data are expressed as means ± SD (n = 9). (H) The bar graphs show the percentage of B cells that are Annexin V positive in pre-pro–B, pro-B, and pre–B cells in WT and Wip1KO mice. Data are expressed as means ± SD (n = 8). (I) The bar graphs show the percentage of Annexin V–positive pre–B cells in the bone marrow of WT, Wip1KO, p53KO, and Wip1/p53 DKO mice (n = 6). (J) The bar graphs show the apoptosis of pre-B cells in the bone marrow of WT, Wip1KO, p21KO, and Wip1/p21 DKO mice. (K) The percentage of Annexin V–positive pro–B cells in the bone marrow of WT, Wip1KO, p53KO, and Wip1/p53 DKO mice. No significant difference was observed when comparing apoptosis in pro–B cells in Wip1KO, p53KO, and Wip1/p53-DKO mice with that in WT mice. Data are expressed as means ± SD (n = 5). *P < .05, **P < .01, and ***P < .001 compared with WT mice or between the indicated groups. NS, not significant.