Reconstituting expression of IRF4, Ikaros, or Aiolos is sufficient to inhibit the proliferation of IRF4,8^−/− pre-B cells. (A) IRF4,8^−/− pre-B cells were infected with virus expressing ER and IRF4ER. At 24 hours after infection, tamoxifen (1μM) was added to activate IRF4. The cell-cycle status was examined at different time points by staining the cells with Hoechst dye (10 μg/mL). (B) The effect of IRF4 on pre–B-cell proliferation is uncoupled from pre–B-cell differentiation. After 48 hours of treatment with Tamoxifen, the infected cells were stained with anti-kappa and anti-CD19 antibodies and analyzed by FACS. (C) IRF4,8^−/− pre-B cells were infected with control, Ikaros, and Aiolos. The cell-cycle status of the infected cells was analyzed daily for 3 days. Cell-cycle status of the GFP^hi cells was shown, and the numbers represent percentages of the cycling cells. The result is a representative of 3 independent experiments.