Role of p19Arf in the Rag1-deficient Sca1⁺CD19⁺ population. (A) BrdU incorporation is shown both as a percentage of the Sca1⁺CD19⁺ population and as a cell count (×10³; Sca1⁺CD19⁺BrdU⁺). The FACS histograms show the mean level of BrdU incorporation in percent by the Sca1⁺CD19⁺ population (n = 3). (B) The histograms indicate ckit expression gated on the Sca1⁺CD19⁺ population in AR, A, R, and WT BM in an immunofluorescence analysis. One of 4 representative experiments is shown here. (C) Frequency (%) and absolute cell numbers (×10⁵) of Sca1^lowckit^low CD19⁺ cells in AR, A, R, and WT BM (P < .037 for AR vs A; n = 4) is indicated. (D) cDNA was synthesized from BM-derived R and WT flow-sorted Sca1^lowckit^lowCD19⁺ cells. After 5-fold dilution of the cDNA, RT-PCR assays were used to analyze expression of p19Arf and the control housekeeping gene actin. One of 3 representative experiments is shown here.