B cell development in B-Fip200 ^−/− mice, related to Fig. 1. (A) Naïve B cells and CD4⁺ T cells were isolated from the spleens of WT or B-Fip200^−/− mice (n = 3), and FIP200 expression was detected by western blot. (B and C) Flow cytometry analysis of BM (B) or spleen (C) from WT and Fip200-KO-B mice. (B) BM samples were stained with antibodies against CD43, CD24, BP-1, IgM, IgD, and B220, and populations were identified following the Hardy classification system: B cells (B220⁺), early progenitors (B220⁺CD43⁺), late progenitors (B220⁺CD43⁻), fraction A (CD43⁺CD24⁻BP-1⁻), fraction B (CD43⁺CD24⁺BP-1⁻), fraction C (CD43⁺ CD24⁺ BP-1⁺), fraction D (CD43⁻IgM⁻IgD⁻), fraction E (CD43⁻IgM⁺IgD⁻), fraction F (CD43⁻IgM⁺IgD⁺). Left to right: **P = 0.0043, **P = 0.0043. (C) Spleen samples were stained with antibodies against CD21, CD23, CD24, and B220, and transitional or mature B cell populations were identified—B cells (B220⁺), T0-T1 cells (B220⁺CD21^loCD24^hi), T2-MZB cells (B220⁺CD21^hiCD24^hi), MZB cells (B220⁺CD21^hiCD23^lo), follicular B cells (B220⁺CD21^hiCD23⁺). Two replicates were performed with three to five animals in each group; one representative experiment is shown. Significant P values were determined by an unpaired t test. Top to bottom: *P = 0.0286, *P = 0.0286. Source data are available for this figure: SourceData FS1.