Molecular cloning,tissue specific expression of three retinoid X receptors of Lateolabrax japonicus

The retinoid X receptor(RXR)is a member of nuclear hormone receptor family proteins and plays an important role in the regulation of intracellular receptor signaling pathways.Three retinoid X receptor subtypes(RXRα,RXRβ and RXRγ)cDNAs were obtained from Lateolabrax japonicus by RT-PCR and RACE.The obtained cDNA sequence of RXRα was 1 686 bp in length,containing a 5′-untranslated region(UTR)of 364 bp and an uncompleted CDS of 1 322 bp,and encoded a putative protein of 440 amino acids.The full length cDNA sequence of RXRβ was 1 741 bp in length,containing a 5′ UTR of 150 bp,3′UTR of 256 bp and an ORF of 1 335 bp which encoded a putative protein of 444 amino acids with an estimated molecular weight of 49.5 ku.The RXRγ cDNA was 1 847 bp in length with 88 bp of 5′-UTR,397 bp of 3′-UTR and an ORF of 1 362 bp which encoded a putative protein of 453 amino acids with an estimated molecular weight of 49.9 ku.Like other RXRs,the DNA-binding domain(DBD)of L.japonicus RXRα, RXRβ and RXRγ contain P box and D box and the ligand binding domain(LBD)contains 12 α-helices and 2 β-sheets with a ligand-dependent activation function AF-2 in the COOH terminus of the H12. In the phylogenetic tree, L. japonicus RXRα, RXRβ and RXRγ were clustered with corresponding subtypes respectively.The tissue-specific expression of each RXR gene was explored using RT-PCR.The mRNA of RXRα were expressed in all tissues examined with low level.The mRNA of RXRβ were expressed homogeneously in all tested tissues excepting a low expression in heart. RXRγ mRNA were also expressed in all tissues tested with high levels in muscle, intestine,kidney,fat and spleen.The results lay the foundation for further study of the functions of RXRα, RXRβ and RXRγ.