Figure 1

TCDD-Induced Changes in mRNA in Rat and Mouse. The hepatic mRNA abundance profiles of C57BL/6 mice and L-E rats were determined using microarray methods. Following GCRMA pre-processing, ProbeSet-wise linear-models were fit to identify differentially expressed genes. A) A plot of the number of distinct genes (Entrez Gene IDs) called differentially-expressed in each species (y-axis) as a function of threshold (x-axis) suggests more mouse genes than rat genes are TCDD-responsive. B) In a threshold-independent manner (x-axis) a larger fraction of mouse genes than rat genes are induced by TCDD. C) The variance of each rat ProbeSet was calculated and those having a variance above 1.0 were mean-centered and root-mean-square-scaled and subjected to divisive hierarchical clustering using the DIANA algorithm. TCDD-treated animals (rows with red annotation bars) cluster independently from vehicle controls (rows with blue annotation bars) in this unsupervised analysis. D) The variance of each mouse ProbeSet was calculated and those having a variance above 1.0 were mean-centered and root-mean-square-scaled and subjected to divisive hierarchical clustering using the DIANA algorithm. TCDD-treated animals (rows with red annotation bars) cluster independently from vehicle controls (rows with blue annotation bars) in this unsupervised analysis.