Abstract
In arthropods, retinoid X receptor (RXR) is a highly conserved nuclear hormone receptor. By forming a heterodimeric complex with the ecdysone receptor (EcR), RXR is known to be vital importance for various physiological processes. However, in comparison to EcR, the RXR signaling pathway and its roles in crustacean reproduction are poorly understood. In the present study, the RXR mRNA was detected in the ovarian follicular cells of mud crab Scylla paramamosain (SpRXR) and during ovarian maturation, its expression level was found to increase significantly. In vitro experiment showed that both SpRXR and vitellogenin (SpVg) mRNA in the ovarian explants were significantly induced by 20-hydroxyecdysone (20E) but not methyl farnesoate (MF). However, differing from the in vitro experiment, injection of MF in in vivo experiment significantly stimulated the expressions of SpRXR and SpVg in female crabs at early vitellogenic stage, but the ecdysone and insect juvenile hormone (JH) signaling pathway genes were not induced. The results together suggest that both MF and SpRXR play significant roles in regulating the expression of SpVg and ovarian development of S. paramamosain through their own specific signaling pathway rather than sharing with the ecdysone or the insect JH.
Highlights
In arthropods, retinoid X receptor (RXR) is a highly conserved nuclear hormone receptor
It has been reported that following injection of exogenous methyl farnesoate (MF), the ovarian index of C. maenas was significantly enhanced when compared to those control crabs injecting crab saline[10]
SpRXR1 consisted of a 364 bp 3′-untranslated region (UTR) with a poly A tail and 192 bp 5′-UTR while 5 aa and 42 aa insert sequences were found in the T-box domain of SpRXR2 and the ligand binding domain (LBD) of SpRXR1, respectively (Fig. 1A,B)
Summary
Retinoid X receptor (RXR) is a highly conserved nuclear hormone receptor. Differing from the in vitro experiment, injection of MF in in vivo experiment significantly stimulated the expressions of SpRXR and SpVg in female crabs at early vitellogenic stage, but the ecdysone and insect juvenile hormone (JH) signaling pathway genes were not induced. Many important physiological processes, including molting, appendage regeneration and reproduction, are regulated by the biological active forms of ecdysone (e.g. 20-hydroxyecdysone, 20E), a group of steroid hormones[1]. To mediate these processes, ecdysone needs to bind to the ecdysone receptor (EcR) first to activate the early response genes[2]. To date its receptor remains poorly understood, and the molecular basis of the signaling pathway as well as underlying functional mechanisms are largely unknown
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