Comparative analysis of sequence feature and expression of two heat shock cognate 70 genes in mandarin fish Siniperca chuatsi

• Two distinct HSC70 isoforms from mandarin fish were identified and characterized.
• HSC70 isoform expression was activated at different embryonic developmental stages.
• HSC70-2 was markedly induced by heat shock rather than HSC70-1.
• Hypoxia has no effect on HSC70-1 expression but suppressed HSC70-2 expression.
• A. hydrophila infection induced the expression of HSC70-1 rather than HSC70-2.

Heat shock cognate protein 70 (HSC70) is a molecular chaperone that plays essential roles in maintaining the cellular protein homeostasis. In this study, two HSC70 isoforms were identified and characterized from mandarin fish Siniperca chuatsi. They have similar sequence structures, containing seven introns in their coding regions and sharing 94% similarity of their deduced amino acid sequences with 38 substitutions. Transcripts of both isoforms were detected throughout the embryogenesis, at low levels during the early developmental stages and up-regulated at blastula for ScHSC70-1 and appearance of myomere stage for ScHSC70-2. They were ubiquitously expressed in tissues under normal conditions, whereas with tissue-specific variation. Following acute heat shock at 34 °C, the expression of ScHSC70-1 showed no significant changes in the liver, and just a modest increase in the heart and head kidney, while the ScHSC70-2 mRNA levels were markedly up-regulated in these tissues. Compared with their expression under gradual heat shock, the ScHSC70-2 mRNA was rising at a higher rate under fast heat shock, whereas the ScHSC70-1 mRNA increasing rate was lower under fast heat shock. Under hypoxia, transcripts of ScHSC70-1 were not significantly changed, while the expression of ScHSC70-2 was suppressed. Aeromonas hydrophila infection significantly increased the ScHSC70-1 mRNA levels in the head kidney and spleen on early infective stages, while failed to have any significant impact on the expression of ScHSC70-2 in both immune tissues. These results suggest that ScHSC70-1 and ScHSC70-2 are differently involved in the embryogenesis and the stress responses of high temperature, hypoxia and bacterial infection. This study will contribute to further study on enhancing stress tolerance and disease resistance of mandarin fish.