Abstract:Two retinoic acid receptors, RARalpha and RARgamma, were cloned from Cynoglossus semilaevis using RT-PCR and RACE methods, and their spatial expression patterns were investigated using a quantitative PCR assay. The results showed that full-length cDNA sequence encoding the RARalpha gene is 1823 bp in length, its open reading frame (ORF) length is 1332 bp, encoding 443 amino acids; the RARgamma cDNA sequence is 1959 bp in length, and the length of ORF is 1497 bp, encoding 489 amino acids. Homology analysis showed that C. semilaevis RARalpha and RARgamma have homology identity of 60.8%, and both have 97% homology identity with the Japanese flounder. Phylogenetic analysis showed that C. semilaevis RARalpha and RARgamma clustered into a separate branch with other fish counterparts. Spatial expression analysis showed that the highest expression level of RARalpha mRNA occurred in the kidney, whereas the highest expression level of RARgamma mRNA was in the spleen. RARgamma was also highly expressed in the gill, kidney, and heart. Furthermore, RARalpha and RARgamma mRNA expression were detected in all examined tissues, which indicated that these two retinoic acid receptors were both involved in multiple physiological regulation processes. In addition, the differential expression of these two RAR genes were found in the blind side and ocular skins, wherein they both had highest expression levels in the normal blind side skin, followed by the blacking blind side skin and had the lowest expression levels in the ocular side skin. In ocular skin and blind-side blacking skin, the RARalpha expression levels were higher than RARgamma but without significant difference, wherein in blind-side normal skin, the RARgamma expressed significantly higher than RARalpha. This differential expression pattern indicated that they might play important physiological roles in blind-side hypermelanosis regulation of Cynoglossus semilaevis.
