Gene expression profiling of copper-induced responses in the intertidal copepod Tigriopus japonicus using a 6K oligochip microarray

The intertidal copepod Tigriopus japonicus has shown promising results in classical acute and chronic toxicity studies. Recently, a large number of genes have been identified from this species and their mRNA expression has been studied independently against exposure to marine environmental pollutants. T. japonicus is a promising organism for the study of mechanistic aspects of marine environmental pollutants using genomics. In this study, a 6K oligochip for T. japonicus that included mostly unique sets of genes from ~26K ESTs, was developed. A total of 5463 spots (2313 mRNAs upregulated and 3150 downregulated) were identified to be significantly expressed on microarray by hierarchical clustering of genes after exposure to copper for different time durations (10μg/L for 6, 12 and 24h). However, mRNAs of only 138 and 375 genes were observed to be consistently upregulated and downregulated, respectively, at all time points. Most of the changes of mRNA expression were observed at the short exposure of 6h. It was observed that mRNA expression of several genes involved in growth, metabolism, reproduction and hormonal regulation was modulated in Cu-exposed T. japonicus. mRNA expression of genes involved in detoxification and antioxidant functions was also modulated. This indicates that Cu-induced gene transcription is complicated in T. japonicus similar to other crustaceans. Cu specifically upregulated mRNAs of genes of some isoforms of cytochrome P450 (CYP). On the other hand, a majority of downregulated mRNAs were of genes encoding for proteins important for growth and development. The expression profile of mRNAs of selected genes was verified by the quantitative real time RT-PCR. The mRNA expression profiles provide insight into the mechanism of action of copper in T. japonicus. These results demonstrate the suitability of a T. japonicus oligochip microarray for risk assessment of trace metals in the marine environment. As yet, major breakthroughs in invertebrate toxicogenomics have mainly been in Daphnia and Drosophila. Daphnia's use is limited to freshwater ecotoxicogenomics. Here we propose an oligochip microarray-based approach for risk assessment of trace metals in a potential model marine test species.