Expression Analysis Of The RXR Gene During The Moulting And The Ovarian Development Of Portunus Trituberculatus

To elucidate the role of the retinoid X receptor (RXR) in moulting and ovarian development ofcrustaceans, the full-length cDNA of RXR in Portunus trituberculatus (PtRXR) was cloned by nestedreverse transcriptase polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE).The cDNA sequence of PtRXR was determined to be1365bp in length and contained an open readingframe (ORF) of1140bp encoding a379-amino-acid residue protein. The amino acid sequence ofPtRXR contained four independent structural domains, beginning from the N-terminal A/Bdomain to the C-terminal E domain. The deduced amino-acid sequence of PtRXR shared highidentities with other known RXRs. The resulting tree showed that PtRXR was clustered amongcrustacean RXRs and located closer to the vertebrate RXRs than the insect ultraspiracles (USPs, theortholog of RXR). Quantitative real-time PCR (qRT-PCR) was used to analyse the tissue distribution ofPtRXR and its expression patterns during the moulting cycle and the ovarian development of P.trituberculatus. The results showed that PtRXR was widely distributed in the tissues tested. PtRXR mRNAlevels were significantly high in ovary and Y-organs (YO) of intermoult crabs. The mRNA levels of PtRXRin YO and mandibular organs (MO) decreased significantly from intermoult to premoult, then it returned toa higher level after molting. These results demonstrated that PtRXR played an important role in regulatingthe moulting of P. trituberculatus. In addition, PtRXR was expressed at each stage of the ovariandevelopment in ovary, hepatopancreas, YO, and MO. During the first ovarian development, the expressionlevels of PtRXR in ovary and hepatopancreas gradually increased from the earlier stage to the fastdeveloping stages (stage â…¢ and â…£). Themaximum expression levels in YO was at the intermediate stagesof ovary development. During the second ovarian development, the expression levels of PtRXR reachedmaximal values when the ovary reached the final stage of maturation. These results indicate that PtRXR isclosely related to the ovaran development of P. trituberculatus. PtRXR might act as a significant roleduring the ovarian development in P. trituberculatus.