Reduced PU.1 gene expression in human AML/ETO leukemia. (A) PU.1 expression (black bars) with respect to hierarchical clustering of the gene expression data set of 285 AML patients from the Erasmus Rotterdam cohort (Affymetrix U133A GeneChips).³⁶  Each cluster demonstrates distinct genetic abnormalities as indicated. (B-C) PU.1 expression profile of cluster t(8;21) compared with low PU.1 and high PU.1 clusters. Red line: all clusters with cluster mean expression higher than the global cluster mean (high PU.1), including clusters 1, 2, 5, 9, 11, and 16 with 118 patients; black line: all clusters with cluster mean expression lower than the global cluster mean (low PU.1), including clusters 3, 4, 6, 7, 8, 10, 12, 14, and 15 with 132 patients; blue line: cluster 13: t(8;21) with 22 patients. (D) PU.1 mRNA levels of E14.5 fetal liver cells (c-kit⁺, GFP⁺c-kit⁺, GFP^–) 48 hours after transduction with either MigR1 or AML/ETO9a-MigR1 (A/E9a). Shown are average levels ± SD as percentage of 18S. n = 4; **P < .01.