Schematic diagram of strategies for mapping MLL fusion target genes. All 5 human cell lines (top left) are derived from acute leukemia patients and represent early progenitor cells of myeloid origin. MV4;11 (expressing MLL-AF4) and THP-1 (expressing MLL-AF9) have one rearranged MLL allele and one wild-type (WT) MLL allele. ML-2 cells possess 2 alleles of MLL-AF6 but no WT MLL allele. U937 and HL60 cells contain 2 copies of WT MLL. The inducible mouse cells express MLL-ENL in the presence of the inducer. The MLL-ENL fusion protein is inactivated on withdrawal of the inducer. Target genes of MLL wild-type and MLL fusion proteins were obtained from MLL binding analysis in both human leukemic cells and the mouse inducible system.