Molecular characterization of four actin cDNAs and effects of 20-hydroxyecdysone on their expression in swimming crab, Portunus trituberculatus (Miers, 1876)

Abstract

Crustacean muscle fibers exhibit a high level of plasticity in various growth and developmental stages and understanding its mechanism is one of the important factors to improve the commercial value of the decapod products including shrimp, lobsters, and crabs. In the present study, four cDNAs encoding actins (PotActinSK1, PotActinSK2, PotActinHT, and PotActinCT) were identified from the swimming crab (Portunus trituberculatus) using a PCR-based cloning strategy. Although the four cDNA encoding actins exhibit similarities in size and deduced amino acid sequences, their tissue expression profiles differ significantly from one another. Phylogenetic analysis revealed that muscular and cytoplasmic actins have been diverged before vertebrates were evolved and cardiac and skeletal muscular actins were branched out after the vertebrates were evolved. Based on the phylogenetic analysis and expression patterns, PotActinSK1 and SK2 belong to the slow-type skeletal muscle actins and the fast-type skeletal muscle actin has not been identified. PotActinHT showed the highest sequence similarity to Ha-ActinHT from H. americanus and appeared to be an ortholog of heart muscle actins in decapod crustaceans. PotActinCT exhibited the highest sequence similarity to the cytoplasmic actin of L. vannamei ActinT1. End-point RT-PCR results showed that PotActinSK1 and PotActinSK2 were strongly expressed in skeletal muscular tissues including chela propodus muscle, chela merus muscle, leg muscle, thoracic muscle, and there was no significant difference in the expression ratio between the two genes of those four tissues. PotActinCT was ubiquitously expressed in all the tissues, whereas PotActinHT was exclusively expressed in the heart. Interestingly, a considerable level of PotActinCT was expressed in the heart, which is similar to those of PotActinHT. The transcriptional response to 20-hydroxyecdysone (20E) injection was different in each PotActin suggesting that effects of muscle plasticity by 20E may differ in each tissue of decapod crustaceans.