Tissue-specific and embryonic expression of the retinoid X receptors in Sebastiscus marmoratus

Retinoid X receptors (RXRs) are highly conserved members of the nuclear receptor family and mediate various physiological processes in vertebrates. Most studies on RXRs have concentrated on their structure and function in mammals and their characterization and developmental expression in Danio rerio. However, there is little information concerning the distribution of RXRs in teleost tissues. In the present study, we cloned partial sequences of three RXR subtypes (RXRa, -b, -g) from Sebastiscus marmoratus by RACE PCR and analyzed the phylogeny of the teleost and the tetrapod RXR genes, and identified some inconsistencies with previous studies. The tissue-specific and embryonic expression profiles of each RXR gene were explored using real time quantitative PCR. This analysis demonstrated that these RXRs were expressed in all test tissues indicating their participation in many physiological processes. However, we found a great difference in the distribution of RXRg between teleosts and mammals. Furthermore, we followed expression of the three subtypes through various embryo developmental stages and found that the RXRa orthologues of teleosts might be involved in the development of the anterior hindbrain, tailbud and neural crest and in the formation of the pharynx and fin, that RXRb played ubiquitous roles in fish early development, and that RXRg probably played a role in brain and nervous system development and function.