RT-PCR validation of selected HOXA9 gene targets. (A) Confirmation of HOXA9-regulated genes in K562 cells. Gene expression levels were calculated by normalizing PCR data from HOXA9^– and HOXA9⁺ samples to control genes as described in “Materials and methods.” Fold up- or down-regulation was calculated using the ratio of HOXA9⁺/HOXA9^– normalized PCR values and the mean of ratios of HOXA9⁺/HOXA9^– signals from the microarray data. *No expression was detected in one of the HOXA9 conditions such that the ratio could not be calculated, and a lower limit of differential expression is reported. Arrows indicate that the expression of these genes may be higher than what is reported because the HOXA9^– sample value was 0. (B) Quantitative verification of differential expression of HOXA9 target genes in different cell lines. Expression of 3 genes was analyzed by real-time RT-PCR, and fold changes in expression are expressed as the ratio of GAPDH-normalized HOXA9⁺/HOXA9^– values. Fold changes from the arrays represent the mean values from at least 2 hybridizations.