Expression and localization of some retinoid receptors during European sea bass ( Dicentrarchus labrax) larvae development

Abstract

In the present study, we report the characterization in European sea bass of the partial cDNA sequences of three nuclear receptors, retinoic acid receptor (RAR)α, RARγ, retinoid X receptor (RXR)α, involved in retinoid pathways. These pathways participate to vertebrates morphogenesis processes and may be responsible for the appearance of skeletal malformations. The predicted polypeptide encoded by each cDNA sequence contains the ligand-binding domain (LBD) characteristic of nuclear hormone receptors, and the RXRα cDNA sequence also includes a partial zinc finger domain corresponding to the DNA-binding domain (DBD) of this receptor. The relative expression levels of the three receptors were determined by real-time polymerase chain reaction (RT–PCR) in European sea bass larvae. Between 10 and 42 days posthatch (dph), the expression of RARα and RARγ increased 7.3- and 35.6-fold, respectively, while RXRα expression was down-regulated with a factor of 35.4. The same trend was observed between 10 and 21 dph but was not statistically different. Using RNA/RNA hybridizations, RARα antisense probes were revealed in jaws at 5 dph, and, at 37 dph, they were detected in jaws, vertebra, liver, muscle, pectoral fins, brain, neural tissues, eyes, and branchial arches. At 37 dph, RARγ expression was found in the cartilage, eyes, and operculum, while the presence of RXRα mRNA was localised in the exocrine pancreas, liver, thyroid, kidney, heart, jaws, and teeth. These results suggested that RARα and RARγ were used for European sea bass development. RARγ would play a key role in the morphogenesis of the cephalic region, while RXRα would be essential during the early stages of development in European sea bass larvae when an intense process of differentiation occurred.