Reduced PU.1 levels induce reduced expression of transcripts encoding BLNK. (A) Changes in frequencies of mRNA transcripts in CD19^+/CreSfpi1^lox/loxSpib^−/− pre-B ALL cells. Cell sorting was used to enrich B220^low CD19⁺ pre-B ALL cells from the spleen of 17-week-old CD19^+/CreSfpi1^lox/loxSpib^−/− mice, and as a control, B220⁺ CD19⁺ B cells from the spleen of 17-week-old CD19^+/+Sfpi1^lox/loxSpib^−/− mice (see Figure 4D for illustration). RNA was prepared from each sample, and RT-qPCR was used to measure relative frequencies of steady-state mRNA transcript levels for genes indicated in the x-axis. Transcript frequencies were normalized to Gapdh transcript levels. The y-axis represents fold change in transcripts in CD19^+/CreSfpi1^lox/loxSpib^−/− pre-B ALL cells compared with CD19^+/CreSfpi1^lox/loxSpib^−/− B cells. (B) Dose-dependent reduction of Blnk transcript levels in response to reduced PU.1 levels. RNA was prepared from cultured pro-B cells generated from the fetal wild-type (WT), Sfpi1^BN/BN (BN), or Sfpi1^Blac/Blac (Blac) mice. RT-qPCR was performed as described above to determine relative frequencies of Blnk transcripts.