Identification of Meis1 domains implicated in acceleration of HOXA9-induced leukemia. (A) Schematic representation of Meis1 mutants (left), and average onset of AML in recipients of bone marrow cells transduced with the indicated mutants, and HOXA9 (right). (B, top) Survival curves of mice that received a transplant of HOXA9-transduced, HOXA9 plus Meis1–transduced, or HOXA9 plus Meis1ΔHD–transduced bone marrow cells. (Bottom) Survival curves of mice that received a transplant of HOXA9-transduced, HOXA9 plus Meis1–transduced, or HOXA9 plus Meis1ΔPIM–transduced bone marrow cells. (C) Schematic representation of Meis1a and PBX1 domain-swapping mutants. (D) In vitro analysis of interactions between the domain-swapping mutants. (Top blots) Western blot analysis of FLAG-tagged Meis1 and Meis1(PIM>MIM) expression in lysates of 293 cells transfected with vectors expressing the indicated Meis1 and PBX1 mutants. Lysates of cells transfected with vectors indicated at the left of the panel were subjected to immunoprecipitation with anti-HA antibodies. The amount of HA-tagged PBX1 mutants was determined by Western blot analysis with HA antibody (middle blots), and interaction of these proteins with Meis1 was determined using anti-FLAG antibody (bottom blots). (E) Survival curves of mice that received a transplant of HOXA9 or of HOXA9 plus Meis(PIM>MIM) plus PBX1(MIM>PIM) cells. Mice that received cells expressing HOXA9 plus individual swapping mutant (others) survived past the time when majority of HOXA9 recipients succumbed to AML. (F) Survival curves of mice that received a transplant of triply transduced bone marrow cells. □ indicates HOXA9 plus FLAG-Meis1(PIM>MIM) plus PBX1(MIM>PIM, GKFQ>HA); •, HOXA9 plus Meis1(PIM>MIM) plus PBX1(MIM>PIM); ▦, HOXA9 plus FLAG-Meis1(PIM>MIM) plus PBX1(MIM>PIM, NH2>HA); and ▵, HOXA9 plus Meis1(PIM>MIM) plus PBX1(MIM>PIM, N51S).