LEDGF/p75 is essential for MLL-rearranged transformation. (A) Schematic representation of the experimental setup. BM cells were harvested from 10-week-old Psip^Fl/Fl and Psip^Vav/Vav mice. After depletion of lineage-committed progenitors, cells were transduced with MLL-ENL or E2A-HLF fusions and assessed for leukemogenic activities in vitro in CFU assays and in vivo in BMT. CFU per 10⁴Psip^Fl/Fl or Psip^Vav/Vav cells transduced with MSCV encoding MLL-ENL (B) and E2A-HLF (C) fusions. Representative images of tetrazolium-stained colonies after the third plating are shown. Error bars represent standard deviation of triplicate measurements. Differences were determined using Student t test; **P < .01; ***P < .001. (D) Kaplan-Meier survival curve for lethally irradiated recipients transplanted with Psip^Fl/Fl or Psip^Vav/Vav cells transduced with MLL-ENL (Psip^Fl/Fl.MLL-ENL and Psip^Vav/Vav.MLL-ENL, respectively) or control cells (Psip^Fl/Fl cells transduced with mock vector). Number of transplanted animals (n) per group is indicated. (E) PCR analysis of whole BM cells of moribund mice transplanted with Psip^Fl/Fl.MLL-ENL cells and whole BM cells of Psip^Vav/Vav.MLL-ENL or control animals (described in panel D) harvested at 180 days posttransplantation. Primers were designed to specifically detect the MLL-ENL fusion gene. A vertical line has been inserted to indicate a repositioned gel lane. (F) Replating CFU transformation assay for lin⁻ cells transduced with MLL-ENL fusion or MLL-ENL mutated in the LEDGF/p75-binding domain (mut.MLL-ENL). Error bars represent standard deviation of triplicate measurements. Differences were determined using Student t test; **P < .01.