Targeted salmon (SalArray) gene chip: a toxicogenomic tool for gene expression profiling in complex chemical mixture exposure scenarios

In toxicogenomics, gene arrays are valuable tools in the identification of differentially-expressed genes and potentially identify new gene biomarkers altered by exposure of organisms to xenobiotic compounds. We have constructed a targeted salmon cDNA array containing 300 differentially-expressed genes using suppression Subtractive Hybridisation (SSH) after exposure of salmon to complex chemical mixtures targeted towards estrogen receptor (ER) and aryl hydrocarbon receptor (AhR) pathways. The functional distribution of the genes up-regulated in exposed as opposed to control fish were as follows; 26% biometabolism and biosynthesis, 19% intra- and extra-cellular structure, 10% apoptosis and protein degradation, 9% transcription and translation, 5% cell growth control, 5 % transport and binding and 2% of the genes belonged to the chromatin and DNA structure groups. The genes that were down-regulated in exposed fish as opposed to control fish were distributed as follows; 28% biometabolism and biosynthesis, 16% transport and binding, 12% intra- and extra-cellular structure, 9% apoptosis and protein degradation, 7% chromatin and DNA structure, 5% transcription and translation, 3% hormonal regulation and 2% of each of the categories ell growth control and signal transduction. 17% of the genes obtained did not presently have an assigned or known function in fish. Genes found to have altered expressions were quantified using quantitative PCR. We found that exposure of salmon hepatocytes to a combination of estrogen receptor agonist (nonylphenol) and aryl hydrocarbon receptor agonist (PCB-77) inhibited mRNA expression of nonylphenol-induced ERs and their target genes. The potentials of our Salarray gene chip in pollution biomonitoring and discovery of new chemical molecular target pathways will be presented and discussed.