(A) Flow cytometric gating of different developmental stages of B lymphopoiesis in the bone marrow (BM) of WT, Setx-/-Rnaseh2bf/f, and Setx-/-Rnaseh2bf/f mice (n = 4). Pre-pro-B cells are defined as B220+CD19- CD43+IgM-, pro-B cells are defined as B220+CD19+CD43+IgM-, large and small pre-B cells are defined as B220+ CD19+CD43−IgM−FSChi and B220+CD19+CD43−IgM−FSClo, respectively, and immature B cells are defined as B220+CD19+CD43−IgM+ FSC, forward scatter. (B) Absolute number of cells per mouse at different stages of B cell development in the BM of WT, Setx-/-, Rnaseh2bf/f, and Setx-/-Rnaseh2bf/f mice (n = 4). (C) Number of mature naïve B lymphocytes isolated from spleen. (D) Absolute number of myeloid compartment cells (CD11b + cells) in BM.