Molecular cloning, characterization and expression analysis of the retinoid X receptor in the swimming crab, Portunus trituberculatus (Miers, 1876) (Decapoda, Portunidae)

Abstract

To elucidate the role of the retinoid X receptor (RXR) in moulting and ovarian development of crustaceans, the full-length cDNA of RXR (PtRXR) in Portunus trituberculatus (Miers, 1876) was cloned by nested reverse transcriptase polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). The cDNA sequence of PtRXR was determined to be 1365 bp in length and contained an open reading frame (ORF) of 1140 bp encoding a 379-amino-acid residue protein. The deduced amino-acid sequence of PtRXR shared high identities with other known RXRs. Phylogenetic analysis showed that PtRXR was clustered among crustacean RXRs and located closer to the vertebrate RXRs than the insect ultraspiracle (USP, an orthologue of RXR). Quantitative real-time PCR (qRT-PCR) was used to analyse the tissue distribution of PtRXR and its expression patterns during the moulting cycle and the second ovarian development of P. trituberculatus. The results showed that PtRXR was widely distributed in the tested tissues. PtRXR mRNA levels were significantly high in ovary and Y-organs (YO) of intermoult crabs. The mRNA levels of PtRXR in YO and mandibular organs (MO) decreased significantly from intermoult to premoult. In addition, PtRXR was expressed at each stage of the second ovarian development in ovary, hepatopancreas, YO and MO, and the expression levels reached maximal values when the ovary reached the final stage of maturation. These results indicate that PtRXR might have an important role in regulating the moulting and ovarian development of P. trituberculatus.