Molecular characterization of calreticulin gene in mud crabScylla paramamosain(Estampador): implications for the regulation of calcium homeostasis during moult cycle

Abstract

Calreticulin (CRT), a well conserved endoplasmic reticulum-resident protein for Ca2+-binding, is widely expressed in multicellular eukaryotes. CRT plays a key role in many cellular processes, including Ca2+ homeostasis. To address the role of CRT underlying the Ca2+ homeostasis alternation during the mineralization cycle of the mud crab (Scylla paramamosain), we cloned the full-length cDNA of CRT gene (SpCRT) from S. paramamosain, and its protein contains all signature domains of CRT. Tissue distribution showed the SpCRT transcript was far more abundant in hepatopancreas than in others. Meanwhile, seven moult stages of the crab were characterized by observing the third maxilliped under microscope and clear uropod images were presented. During the moult cycle, the total calcium levels in the hepatopancreas were determined using ICP-AES. It decreased significantly at stage A and B (p < 0.05), and was relatively steady between inter-moult C and early pre-moult D0 (p > 0.05). It was then gradually increased thereafter by nearly 274.2% until stage E (compared with stage C) (p < 0.05). Additionally, the expression of SpCRT in the hepatopancreas was the lowest in the moult stage E and post-moult stage A, and then it maintained at a high level in other stages. Taken together, the relative retard timing of calcium incrument corresponding to the higher expression of SpCRT may suggest CRT plays a critical role in Ca2+ storage in hepatopancreas during the moult cycle of crustaceans.