c-Myc is induced during β-catenin lymphomagenesis and it is required for transformation. (A) Northern blot analyses using RNAs extracted from LckCre (lanes 1-2), LckCre-Ctnnb^Δex3 (lane 3), CD4Cre-Ctnnb^Δex3 (lane 4) thymocytes, as well as from 2 independent LckCre-Ctnnb^Δex3 (lanes 5-6) and 1 CD4Cre-Ctnnb^Δex3 (lanes 7-9) lymphomas. Blots were hybridized with P³²-labeled probes for the indicated genes (“Materials and methods”). (B) Western blot analysis showing stabilization of β-catenin and DNA-PCR showing deletion of c-Myc floxed allele in sorted DP thymocytes from CD4Cre (lane 1), CD4Cre-Ctnnb^Δex3 (lane 2), CD4Cre-Myc^fl/fl (lane 3), and CD4Cre-Ctnnb^Δex3-Myc^fl/fl (lane 4) mice. (C) CD4/CD8 profiles of CD4Cre-Myc^fl/fl and CD4Cre-Ctnnb^Δex3-Myc^fl/fl thymi. (D) Kaplan-Meyer tumor-free survival curves of CD4Cre-Ctnnb^Δex3-Myc^fl/+ and CD4Cre-Ctnnb^Δex3-Myc^fl/fl mice. The median latency of lymphoma was 101 days and the incidence of lymphoma was 70% in CD4Cre-Ctnnb^Δex3-Myc^fl/+ mice.