PBX1 and leukemia: We tested a subset of Hox and Hox cofactor genes, HOXA5, HOXA7, HOXA9, HOXA10, PBX1, PBX2, PBX3, and MEIS1, and possible Hox target genes FLT3, HLF, JAG2, MEF2C, DDX4, and PRNP. The gene expressions in leukemia samples were normalized with the housekeeping gene GUS as an endogenous control and the expression levels were calculated relative to pooled normal bone marrow (Table 3).