B cell developmental block at the pre-proB cell stage in E2AER/ER mice. (A) Representative staining of bone marrow cells from E2A+/+, E2AER/+, E2AER/ER, E2AE47bm/+, and E2AE47bm/E47bm mice. Cells are pre-gated on 7AAD- lymphocytes and relative percentages are given in each plot. Cells from the CD43+B220+ gate are displayed in histograms analyzing CD19 expression. Pre-proB (CD19-) and proB (CD19+) cell percentages are shown. (B) Occasional CD19+ B cell population detected in E2AER/ER mice. Staining of bone marrow from E2AER/ER and E2A+/+ mice for B220, CD43, CD19, and IgM expression. All plots are pre-gated on 7AAD- lymphocytes. Histograms are pre-gated on B220+CD43+ cells as above and relative percentages are shown.