Cloning,sequencing of the HSC70 gene in Ctenopharyngodon idella

A cDNA encoding heat shock cognate protein 70 (HSC70) was cloned from liver of grass carp (Ctenopharyngodon idella) (GenBank JF436930). This cDNA was found out to contain 2 346 bp in length, including 1 950 bp of complete coding sequence encoding 649 amino acids (aa), plus 89 bp of 5′-UTR and 307 bp of 3′-UTR. Analysis of its genomic structure revealed that its corresponding gene contained seven exons and six introns. Homology analysis indicated that it shared 99% of identity with HSC70 of breams and 86% of identity with HSP70 of Drosophila. Fluorescent RT-PCR analysis revealed that at 28 °C, this gene was expressed in abdominal fat, muscle, intestines, brain, middle kidney, head kidney, gonads, swim bladder, liver, heart, spleen, gills, and fins with expression level in liver being the highest (p<0.05), followed by that in the gonads; at 36 °C, its mRNA expression level was increased at first but then decreased thereafter under heat shock stress, indicating that its expression can be regulated by heat shock. In conclusion, cloning and expression analysis identified a cDNA encoding a constitutive HSP70 gene that is expressed in many tissues of Ctenopharyngodon idella and its expression was down-regulated by heat shock.