Genome-wide identification and characterization of heat shock protein family 70 provides insight into its divergent functions on immune response and development of .

Flatfish undergo extreme morphological development and settle to a benthic in the adult stage, and are likely to be more susceptible to environmental stress. Heat shock proteins 70 () are involved in embryonic development and stress response in metazoan animals. However, the evolutionary history and functions of in flatfish are poorly understood. Here, we identified 15 genes in the genome of Japanese flounder (), a flatfish endemic to northwestern Pacific Ocean. Gene structure and motifs of the Japanese flounder were conserved, and there were few structure variants compared to other fish species. We constructed a maximum likelihood tree to understand the evolutionary relationship of the genes among surveyed fish. Selection pressure analysis suggested that four genes, , , and , showed signs of positive selection. We then extracted transcriptome data on the Japanese flounder with to induce stress, and found that , , and were highly expressed, likely to protect cells from stress. Interestingly, expression patterns of genes were divergent in different developmental stages of the Japanese flounder. We found that at least one gene was always highly expressed at various stages of embryonic development of the Japanese flounder, thereby indicating that genes were constitutively expressed in the Japanese flounder. Our findings provide basic and useful resources to better understand genes in flatfish.