Cbfβ-SMMHC impairs early B-lineage differentiation as early as the commitment step from CLPs to pre–pro-B cells. (A) Flow cytometric analysis of CLP cells (Lin⁻/IL-7R⁺/Sca-1^lo/AA4.1⁺) in whole BM from wild-type control and restored Cbfb^+/56M/Mx1Cre mice. Representative results of 3 independent experiments are shown. (B) Flow cytometric analysis of pre–pro-B (Ly6C⁻/DX5⁻/IgM⁻/B220⁺/CD43⁺/CD24⁻/CD19⁻), pro-B (Ly6C⁻/DX5⁻/IgM⁻/B220⁺/CD43⁺/CD24⁺/CD19⁺), and pre-B (Ly6C⁻/DX5⁻/IgM⁻/B220⁺/CD43⁻) cells in whole BM from control and restored Cbfb^+/56M/Mx1Cre mice. Representative results of 3 independent experiments are shown. (C) Flow cytometric analysis of a time course of sorted CLPs from wild-type control or restored Cbfb^+/56M/Mx1Cre mice cultured on OP9-MIGR1 stromal cells supplemented with IL-7 and Flt3 ligand. The number of pro-B cells produced at each time point is shown below each panel. Shown are representative results from 2 independent experiments. Numbers on plots are percentages of total cells. (D) Percentage of cells retaining the restored Cbfb-MYH11 allele over the 4-day culture, analyzed by qPCR. Shown are means plus or minus SD from 2 independent experiments, each performed in duplicate.