KAP1-deficient mice display reduced numbers of mature B cells. (A) Bone marrow (top), spleen (middle), and PE (bottom) cells from 8- to 12-week-old CD19-Cre/KAP1flox (KO) and littermate wt/KAP1flox control mice (ctrl) were counted and analyzed by flow cytometry. Left panels, total number of B cells; middle panels, representative flow cytometric analysis; right panels, average and SD of the percentage of the indicated populations, n ≥ 15. (B) CD19-Cre/YFPflox/Kap1flox (KO) and CD19-Cre/YFPflox/Kap1flox^het (ctrl) mice analyzed by flow cytometry as in panel A. Percentages of YFP⁺ and YFP⁻ cells in the depicted populations are given as average and SEM (n = 5). (C) Chimeric mice obtained by transplantation of 50% CD45.2⁺CD19-Cre/YFPflox/Kap1flox plus 50% CD45.1⁺ wild-type (KO 50/50; n = 8), 50% CD45.2⁺CD19-Cre/YFPflox/KAP1wt plus 50% CD45.1⁺ wild-type (ctrl 50/50; n = 8), 100% CD45.2⁺CD19-Cre/YFP-flox/Kap1flox (KO 100; n = 3) and 100% CD45.2⁺CD19-Cre/YFPflox/Kap1wt (ctrl 100; n = 4) lineage-depleted cells were analyzed by flow cytometry 6-10 weeks after injection. Only CD45.2⁺ deleted (YFP⁺) cell frequencies are shown. For CD45.2⁺ nondeleted (YFP⁻) frequencies, see supplemental Figure 1. Subpopulations were analyzed as in panel A. Average and SD are shown. P values are for the indicated populations comparing KO50/50 with ctrl 50/50. Pre indicates Pre-B cell progenitors; Imm, immature B-cell progenitors; Mat, mature B-cell progenitors; T1, transitional 1 progenitors; T2-FP, transitional 2 follicular progenitors; and T2-MZP, transitional 2 MZ progenitors. Also see supplemental Figure 1. P values analyzed by Mann-Whitney test.