Ecdysone and retinoid-X receptors of the blue crab, Callinectes sapidus: Cloning and their expression patterns in eyestalks and Y-organs during the molt cycle

Jun 15, 2013Gene

Hormone receptors in blue crab eyestalks and molting organs and how their levels change during molting

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Abstract

The expression levels of CasRXRs in eyestalks are 3-5 times higher than those of CasEcRs.

Crustacean molting is primarily regulated by ecdysteroids and the crustacean hyperglycemic hormone neuropeptide family.
Four putative isoforms of CasEcRs and CasRXRs were identified in the Y-organs, differing in the length of their coding regions but sharing typical nuclear receptor structures.
The presence of specific insertions in the receptor sequences indicates possible variations in receptor functions.
Y-organs and eyestalks co-express CasEcRs and CasRXRs, but expression levels differ significantly between these tissues.
Changes in hemolymphatic ecdysteroid levels may lead to tissue-specific responses, suggesting differences in sensitivity to these hormones.
In silico analysis reveals potential regulatory mechanisms controlling the translation of EcR/RXR/USP receptors in C. sapidus and related arthropods.

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Crustacean molting is known to be regulated largely by ecdysteroids and crustacean hyperglycemic hormone (CHH) neuropeptide family including molt-inhibiting hormone (MIH) and CHH. The surge of 20-OH ecdysone and/or ponasterone A initiates the molting process through binding to its conserved heterodimeric nuclear receptor: Ecdysone Receptor (EcR) and Ultraspiracle (USP)/Retinoid-X Receptor (RXR). To better understand the role of ecdysteroids in the molt regulation, the full-length cDNAs of the blue crab, Callinectes sapidus EcR1 and RXR1 were isolated from the Y-organs and their expression levels were determined in both Y-organs and eyestalks at various molt stages. Y-organs show the expression of four putative isoforms of CasEcRs and CasRXRs which differ in the length of the open reading frame but share the same domain structures as in typical nuclear receptors: AF1, DBD, HR, LBD, and AF2. The putative CasEcR isoforms are derived from a 27-aa insert in the HR and a 49-aa residue substitution in the LBD. In contrast, an insertion of a 5-aa and/or a 45-aa in the DBD and LBD gives rise to CasRXR isoforms. The eyestalks and Y-organs show the co-expression of CasEcRs and CasRXRs but at the different levels. In the eyestalks, the expression levels of CasRXRs are 3-5 times higher than those of CasEcRs, while in Y-organs, CasRXRs are 2.5-4 times higher than CasEcRs. A tissue-specific response to the changes in the levels of hemolymphatic ecdysteroids indicates that these tissues may have differences in the sensitivity or responsiveness to ecdysteroids. The presence of upstream open reading frame and internal ribosome entry site in 5' UTR sequences of C. sapidus and other arthropod EcR/RXR/USP analyzed by in silico indicates a plausible, strong control(s) of the translation of these receptors.

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Ecdysone and retinoid-X receptors of the blue crab, Callinectes sapidus: Cloning and their expression patterns in eyestalks and Y-organs during the molt cycle

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