Principal component expression patterns. The average gene expression profiles are shown for all 10 clusters. In PC1, the genes having a common expression profile in the C57BL/6J (B6) and DBA/2J (D2) strains are clustered. PC1 positive represents genes in both strains that have decreased expression after ONC. PC1 negative has the reverse of this pattern, with genes increasing in expression. PC2 appears to represent genes that are differentially expressed in the two strains. These gene cluster patterns are almost mirror images of each other. In the remaining clusters (PC3 to PC5), very different patterns appear to represent interactions between strain differences and the effects of ONC.