Characterization of CCTα and evaluating its expression in the mud crab Scylla paramamosain when challenged by low temperatures alone and in combination with high and low salinity.

Chaperonin containing the T-complex polypeptide-1 (CCT), which is known to be involved in intracellular assembly and folding of proteins, is a class of chaperonin omnipresent in all forms of life. Previous studies showed that CCT played a vital role in cold hardiness of various animals. In order to understand the response of the polypeptide complex to low temperature challenge and other environmental stresses, a subunit of CCT (CCTα) was cloned from the mud crab Scylla paramamosain by expressed sequence tag (EST) analysis and rapid amplification of cDNA ends (RACE). The full-length cDNA SpCCTα was of 1972 bp and contained a 1668 bp open reading frame (ORF) encoding a polypeptide of 555 amino acids with four conserved motifs. The messenger ribonucleic acid (mRNA) levels of SpCCTα in ten tissues of adult S. paramamosain was subsequently examined and the highest expression was found in muscle, followed by gill, hepatopancreas, thoracic ganglion, hemocyte, heart, cerebral ganglion, stomach, eyestalk ganglion, and epidermis. The expressions of SpCCTα in the muscle of sub-adult crabs (pre-acclimated to 28 °C) subjected to the challenges of both lower temperatures (25, 20, 15, and 10 °C) alone and low temperatures (15 and 10 °C) in combination with salinity of 35 and 10 were further investigated by fluorescent quantitative real-time PCR (qPCR). It was revealed that when exposed to lower temperatures alone, the mRNA transcripts of the SpCCTα gene in the muscle were generally induced for significant higher expression at 10 °C treatment than the 25, 20, and 15 °C treatments; meanwhile, exposure to 15 °C also frequently led to significantly higher expression than those at 20 and 25 °C. This finding indicated that the up-regulation of SpCCTα was closely related to the cold hardiness of S. paramamosain. The results of an additional experiment challenging the sub-adult crabs with various combinations of low temperatures with different salinity conditions generally demonstrated that at both 10 and 15 °C, the expression of SpCCTα under the high salinity of 35 was significantly lower than that at low salinity of 10, implying that the damages caused by low temperatures with high salinity were less than that under low salinity.