Global gene expression analysis of gill tissues from normal and thermally selected strains of rainbow trout

The objective of the study reported here was to investigate genes related to upper temperature tolerance in rainbow trout Oncorhynchus mykiss, a cold-water species with considerable economic importance, by global gene expression analysis using a next generation sequencing system. Fifty million paired sequences were collected from the gill tissues of each of five individuals of a thermally selected strain developed by selective breeding and from the gill tissues of a standard Donaldson strain and assembled into transcripts. The data of both strains were integrated, and a BLASTX search identified 13,092 independent, known genes. A back-mapping of raw reads from both strains onto the genes, conducted to investigate their frequency of expression, revealed that 324 genes showed at least a twofold higher expression in the thermally selected strain than in the Donaldson strain. In addition, 44.4 % of commonly expressed genes were categorized into 38 functional groups by annotation. Genes encoding heat shock proteins and c-fos-related proteins were highly expressed in the thermally selected strain. Our strategy to employ next generation sequencing proved to be very useful to find genes responsible for upper temperature tolerance of rainbow trout.