Opsins play important roles in the image-forming visual pathways and numerous biological systems such as the biological clock and circadian rhythm. However, the nonvisual opsins involved in nonimage forming process are not clear to date. The aim of this study was to characterize nonvisual opsins in Paralichthys olivaceus. A total of 24 nonvisual opsin genes were identified. Expressions of these genes in eye, brain, heart, testis, and fin were investigated by quantitative real-time polymerase chain reaction (qRT-PCR). Testis contained a surprisingly large number of nonvisual opsins including Opn4m2, Tmt2a, Tmt3b, Opn3, RRH, Opn7a, and Opn7b. Syntenic and phylogenetic analyses confirmed that the RGRa and RGRb originated from the teleost-specific genome duplication (TSGD). qRT-PCR results demonstrated high RGRa and RGRb expression in the eye, while the expression levels in the brain, heart, testis, and fin were relatively weak. In situ hybridization results presented here revealed the presence of both RGRa and RGRb mRNA-positive signals in the ganglion cell layer but absence in the intracellular compartment of retinal pigment epithelium (RPE) and Müller glial cells. Therefore, we hypothesized that RGRa and RGRb had undergone subfunctionalization in P. olivaceus after TSGD. In conclusion, this study provides novel insights into the evolutionary fates of the RGR genes, still, further studies need to be done to explore the mechanism about the lack of RGR genes' expression in RPE.

中文翻译：

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非视觉视蛋白家族的全基因组鉴定揭示了RPE视网膜G蛋白受体基因（RGR）的扩增，并提供了对RGR（s）在oliparaeus olivaceus（Paralichthyidae，Teleostei）中功能的新颖见解。

视蛋白在图像形成的视觉通路和众多生物系统（例如生物钟和昼夜节律）中发挥着重要作用。但是，目前尚不清楚参与非图像形成过程的非视觉视蛋白。这项研究的目的是表征橄榄肉眼中的非视觉视蛋白。总共鉴定了24个非视觉视蛋白基因。通过定量实时聚合酶链反应（qRT-PCR）研究了这些基因在眼，脑，心脏，睾丸和鳍中的表达。睾丸包含大量令人惊讶的非视觉视蛋白，包括Opn4m2，TMT2a，TMT3b，Opn3，RRH，Opn7a和Opn7b。序列分析和系统发育分析证实，RGRa和RGRb来源于硬骨鱼特异性基因组复制（TSGD）。qRT-PCR结果表明眼中RGRa和RGRb的表达较高，而在脑，心脏，睾丸和鳍中的表达水平相对较弱。此处显示的原位杂交结果表明，神经节细胞层中同时存在RGRa和RGRb mRNA阳性信号，而视网膜色素上皮（RPE）和Müller胶质细胞的细胞内区室则不存在。因此，我们假设TSGD后RGRa和RGRb在橄榄假单胞菌中经历了亚功能化。总之，这项研究为RGR基因的进化命运提供了新颖的见解，但是，仍需要做进一步的研究以探索RGR基因在RPE中缺乏表达的机制。此处显示的原位杂交结果表明，神经节细胞层中同时存在RGRa和RGRb mRNA阳性信号，而视网膜色素上皮（RPE）和Müller胶质细胞的细胞内区室则不存在。因此，我们假设TSGD后RGRa和RGRb在橄榄假单胞菌中经历了亚功能化。总之，这项研究为RGR基因的进化命运提供了新颖的见解，但是，仍需要做进一步的研究以探索RGR基因在RPE中缺乏表达的机制。此处显示的原位杂交结果表明，神经节细胞层中同时存在RGRa和RGRb mRNA阳性信号，而视网膜色素上皮（RPE）和Müller胶质细胞的细胞内区室则不存在。因此，我们假设TSGD后RGRa和RGRb在橄榄假单胞菌中经历了亚功能化。总之，这项研究为RGR基因的进化命运提供了新颖的见解，但是，仍需要做进一步的研究以探索RGR基因在RPE中缺乏表达的机制。