PAX5 and acute lymphoblastic leukemia: While the Ptprc (CD45) gene was similarly expressed in the Pax5Jak2/+ and control B‐ALL tumors (Appendix Fig S2H), the increased expression of the repressed Pax5 target gene Hnrnpll (Fig 2E) may explain the decreased B220 expression on Pax5Jak2/+ B‐ALL cells, as the RNA‐binding protein hnRNPLL regulates the alternative splicing of exons 4–6 of the Ptprc (CD45) mRNA (Oberdoerffer et al, 2008) (Fig 2H and Appendix Fig S2I).