FIG. 3.

Characteristics of transcriptional response in kidney and liver. Following microarray preprocessing and general-linear modeling, we explored transcriptome-wide characteristics of genes altered in kidney and liver. Because very few genes displayed AHR-independent responses to TCDD these were not included in our analyses. First, we looked at the fraction of genes that were induced (A). Genes that were responsive to TCDD in either liver or kidney, as well as those altered by Ahr genotype in kidney, are much more likely to be inductive than repressive. By contrast genes responsive to Ahr genotype in liver were balanced slightly enriched for repressive responses. Next, to study intertissue responses to TCDD, we performed a coclustering analysis (B). The strongest trend was Ahr genotype, with both TCDD exposure and tissue having effects of similar magnitude. The color bar on the right side of the heatmap indicates tissue (yellow, kidney; green, liver), Ahr genotype (blue, AHR^−/−; white, AHR^+/+), and TCDD exposure (red, TCDD treated; white, vehicle treated).