Expression of PML-RARα mRNA in nonleukemic and leukemic spleen cells. Real time quantitative PCR was performed on the bone marrow RNA derived from 3 nonleukemic animals of each genotype at 3 to 6 months of age and on 3 independent splenic tumors each from leukemic mCG^+/PR (ΔPGK-neo) or transgenic hCG–PML-RARα animals. Each sample was analyzed in duplicate at least twice. Levels of human PML-RARα mRNA were normalized to levels of endogenous mouse neutrophil elastase mRNA to control for the contribution of early myeloid cells, which express abundant neutrophil elastase mRNA, in each sample. All of the normalized data were pooled and averaged; means and standard errors of the mean are shown. Statistical significance was determined by a 2-tailed Student t test. Inset: enlarged view of PML-RARα expression in the nonleukemic bone marrow RNAs of C57Bl/6 wild-type, mCG^+/PR (+PGK-neo), and mCG^+/PR (ΔPGK-neo) animals. *P < .005 versus mCG^+/PR (ΔPGK-neo). #P < .005 versus mCG^+/PR (+PKG-neo).