MCL1 and lymphoma: Moreover, lymphomas that arose in Eμ-Myc;CD19-Cre;Mcl-1fl/+ and Eμ-Myc;CD19-Cre;Mcl-1fl/fl mice despite loss of one Mcl-1 allele appeared to have undergone selection for upregulation of BCL-XL and/or a reduction in pro-apoptotic BIM.