Gene responses to TCDD exposure in livers of Ahr-null versus wildtype mice: measurement of selected mRNA levels by real-time RT-PCR. Hepatic RNA was prepared, as described in Materials and Methods, from male adult Ahr-null mice (Ahr-/-) and wildtype C57BL/6J mice (Ahr+/+) after treatment with a single dose of 1000 μg/kg TCDD or corn oil vehicle for 19 hours. There were 3 TCDD-treated and 3 control mice in the Ahr-null groups and 4 TCDD-treated and 4 control mice in the wildtype groups. Levels for selected mRNAs used in the RT-PCR array validity experiments in rats were measured by real-time RT-PCR and normalized to Actb in this mouse model . For each gene, the highest mRNA level across all experiments was set at 100% and all other mRNA levels for that gene are shown as a percentage of that maximal level. Error bars represent standard deviation of the mean. Asterisks indicate differences in mRNA levels (ANOVA followed by Bonferroni post hoc tests, * p < 0.05, *** p < 0.001). Note that for CYP1A1 the mRNA level in control animals or in TCDD-treated Ahr-/- mice or control Ahr-/- mice is below the detection limit of the assay; thus there are no bars visible for these groups in this plot (ND).