Requirement for antiapoptotic function in initiation of BCR-ABL leukemia. (A) BM from Mcl-1^wt, Mcl-l^f/f, Bax^f/fBax^KO, Bax^f/fBax^KOMcl-1^f/f, Bim^f/f, and Mcl-1^f/fBim^f/f mice (on an Arf^wt background) was transduced with p185-IRES-Cre retrovirus to transform and delete floxed alleles. Viable cell concentration was determined every 24 hours. Each time point represents the average of 3 independent experiments (n = 3) each composed of 2 separate initiations, and the error bars denote the SEM. (B) Representative Mcl-1, Mcl-1–deleted, Bax, Bak, and Cre genomic genotyping post outgrowth from experiment detailed in panel A. (C) Representative Mcl-1, Mcl-1–deleted, Bim, Bim-deleted, and Cre genomic genotyping shown from post-outgrowth cells detailed in panel A. (D) Representative immunoblot of the cells that grew out in culture from the experiment detailed in panel A. Lysates were blotted for MCL-1, BAX, BAK, Cre, and BCR-ABL (as detected by anti-ABL antibody) (loading control). (E) Representative immunoblot analysis of the cells that grew out in culture from the experiment detailed in panel A. Lysates were blotted for MCL-1, BIM, Cre, and BCR-ABL (loading control). (F) Mcl-1^f/fArf^−/− pre–B cells were cotransduced with Mcl-1, BCL-2, BCL-X_L, or Mcl-1^GRRL constructs and p185-IRES-Cre retrovirus. Cell viability was determined every 24 hours. Each time point represents 3 independent experiments (n = 3) composed of 2 separate initiations, and the error bars denote the SEM. (G) Representative Mcl-1 and Mcl-1–deleted genotyping from Mcl-1^f/fArf^−/− pre–B cells cotransduced with indicated construct and p185-IRES-Cre retrovirus post outgrowth. (H) Lysates from Mcl-1^f/fArf^−/− pre–B cells cotransduced with indicated constructs and p185-IRES-Cre retrovirus post outgrowth were western blotted for MCL-1, BCL-X_L, BCL-2 (human-specific antibody), and BCR-ABL (loading control). Results indicate 2 independent cultures.