Use of reverse genetics and cDNA arrays to understand ‘dioxin’ toxicity

The molecular mechanisms of toxic agents are rarely likely to be the result of change in the expression of a single gene. Even apparently simple actions of chemicals are probably the consequence of genetically variable multigene expression. One strategy for attacking this problem is to take advantage of the genetic variation of response in mice to search for susceptibility genes using genetic linkage analysis in combination with comparisons of gene expression in the parent strains by cDNA microarray technology. Genetic variation in mice and toxicogenomics were used to explore mechanisms of gene interaction leading to cell malfunction and injury in the liver caused by dioxin. This demonstrated susceptibility loci, other than the Ahr gene, pertinent to the development of porphyria (a disruption of heme synthesis) and liver injury. cDNA arrays of 4000 IMAGE clones pertinent to toxicology were used to compare candidate multiple gene expression in strains relative to their initial hepatic response e.g. induction of drug metabolism enzymes, and to their subsequent development of porphyria and liver injury. Phenotypic response was compared with gene expression by metabolic system including groups of genes for heme and iron metabolism, the AH battery and oxidative stress.