Identification and expression analysis of two HSP70 isoforms in mandarin fish Siniperca chuatsi

Heat shock protein 70 (HSP70) plays important roles in multiple cellular stress responses. Two HSP70 isoforms, ScHSP70a and ScHSP70b, were identified from Siniperca chuatsi in this study. ScHSP70a and ScHSP70b shared all but one of their 639 amino acids and showed a remarkable homology to HSP70s of other species. Expression profile analysis by qRT-PCR revealed that both isoforms were detected throughout embryonic development, and a striking feature of ScHSP70a was its significant up-regulation during the crystal stage. ScHSP70a and ScHSP70b were expressed ubiquitously and at a low level in tissues under non-stressed conditions. However, they were dramatically induced by heat shock at different levels, and their induction was positively correlated with the increasing rate of temperature. Although insensitive to hypoxia in the heart, both genes were greatly induced by hypoxia in the liver, and the induction was returned to the basal level after re-oxygenation for 24 h. Additionally, Aeromonas hydrophila infection also markedly augmented ScHSP70a and ScHSP70b expression in a time-dependent manner in the head kidney and spleen, and the ScHSP70a induction levels were much higher than those of ScHSP70b. These results suggest that ScHSP70a and ScHSP70b contribute differently to embryonic development and protection against damage from high temperature, hypoxia and bacterial infection.