Identification of ecdysteroid signaling late-response genes from different tissues of the Pacific white shrimp, Litopenaeus vannamei

Ecdysteroids initiate signaling along multiple pathways that regulate various aspects of development, maturation, and reproduction in arthropods. This study was carried out to seek the late target genes of ecdysteroid signaling from different tissues of the Pacific white shrimp, Litopenaeus vannamei. In the present study, eight isoforms of ecdysteroid receptor (EcR), two isoforms of retinoic acid X receptor (RXR), and one homolog of E75 were characterized from L. vannamei. The overall protein sequences and specific functional sites of EcR, RXR and E75 among crustacean species were found highly conserved. Tissue-specific, development stage-specific, and molt stage-specific expression patterns of LvEcR, LvRXR, and LvE75 were detected by qPCR. Double stranded RNA (dsRNA)-mediated RNA interference (RNAi) of any one of the three genes LvEcR, LvRXR and LvE75 caused specific expression changes of the other two, and resulted in corresponding expression changes of two molting related genes Cathepsin-L (LvCHSL) and Hemocyanin (LvHCyn) in the hepatopancreas, two chitin metabolism related genes chitin synthase (LvChS) and chitinase isoenzyme (LvChi2) in the epidermis, and two muscle growth related genes LvActin and myosin heavy chain (LvMHC) in the muscle. In correspondence, after in vivo injections of 20 hydroxyecdysone, specific expression changes of LvEcR, LvRXR, LvE75, LvCHSL and LvHCyn in the hepatopancreas, LvEcR, LvRXR, LvE75, LvChS and LvChi2 in the epidermis, and LvEcR, LvRXR, LvE75, LvActin and LvMHC in the muscle were also observed, respectively. Results in our study indicate multiple functions of ecdysteroids signaling in L. vannamei and the function may be time- and space-specific; ecdysteroids may act through different pathways via its functional receptor heterodimer EcR-RXR and the early responsive gene E75 to perform specific regulation roles on the target genes in different shrimp tissues; LvCHSL and LvHCyn in the hepatopancreas, LvChS and LvChi2 in the epidermis, and LvActin and LvMHC in the muscle are potential targets for ecdysteroid control. This is the first report on nuclear receptors in the economically important shrimp L. vannamei.