A transgenic construct was designed with the CMV enhancer/chicken beta-actin promoter, loxP-flanked STOP sequence (beta-geo reporter followed by SV40 polyadenylation signal), human TEL-AML1 fusion protein sequence (coding for the translocation t(12;21)(p13;q22)), internal ribosomal entry site, and an enhanced green fluorescent protein (EGFP) gene. Prior to Cre-mediated excision of the "floxed" STOP sequence, high expression of lacZ is observed in cells and tissues. When bred to Cre recombinase expressing mice, the STOP sequence (and beta-geo) is removed in the resulting offspring, allowing transcription/co-expression of both the human TEL-AML1 fusion protein and EGFP to proceed in the Cre recombinase expressing cells. (J:119130)