FIG. 4.
Comparison of transcriptional response in kidney and liver. Following preprocessing and general-linear modeling of the microarray data, we compared the specific genes altered by Ahr genotype (A) and TCDD exposure (B) in liver and kidney. Large numbers of genes were altered by Ahr genotype in each tissue, and a significant fraction (p < 10−64) was common to both (A). By contrast, only five few genes were TCDD responsive in both tissues, which were again more than expected by chance (p = 3.99 × 10−18). To determine if these differences were related to genes just below our selected thresholds we plotted the fold-changes in liver against those in kidney for both genotype-responsive (C) and TCDD-responsive (D) genes. Although a number of genes lie on the diagonal in (C) many are along the axes indicating strong evidence of tissue specificity. Similarly, the TCDD-responsive genes are largely tissue-specific. The outlier in the top right of (D) with high fold changes in both liver and kidney is CYP1A1.