Faculty of Science, Kyoto University, Kyoto, 606-8502, Japan.
Department of Cytology and Histology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, 700-8558, Japan.
Sci Rep. 2019 Jul 23;9(1):10653. doi: 10.1038/s41598-019-47028-4.
Recent progress in whole genome sequencing has revealed that animals have various kinds of opsin genes for photoreception. Among them, most opsin genes have introns in their coding regions. However, it has been known for a long time that teleost retinas express intron-less rhodopsin genes, which are presumed to have been formed by retroduplication from an ancestral intron-containing rhodopsin gene. In addition, teleosts have an intron-containing rhodopsin gene (exo-rhodopsin) exclusively for pineal photoreception. In this study, to unravel the evolutionary origin of the two teleost rhodopsin genes, we analyzed the rhodopsin genes of non-teleost fishes in the Actinopterygii. The phylogenetic analysis of full-length sequences of bichir, sturgeon and gar rhodopsins revealed that retroduplication of the rhodopsin gene occurred after branching of the bichir lineage. In addition, analysis of the tissue distribution and the molecular properties of bichir, sturgeon and gar rhodopsins showed that the abundant and exclusive expression of intron-containing rhodopsin in the pineal gland and the short lifetime of its meta II intermediate, which leads to optimization for pineal photoreception, were achieved after branching of the gar lineage. Based on these results, we propose a stepwise evolutionary model of teleost intron-containing and intron-less rhodopsin genes.
近年来，全基因组测序的进展揭示了动物具有各种用于光感受的视蛋白基因。其中，大多数视蛋白基因在其编码区都有内含子。然而，长期以来人们一直认为硬骨鱼的视网膜表达无内含子的视蛋白基因，这些基因被认为是通过从含有内含子的视蛋白基因的祖先基因的反转录复制而形成的。此外，硬骨鱼还有一个含有内含子的视蛋白基因（外视蛋白），专门用于松果体的光感受。在这项研究中，为了解开两种硬骨鱼视蛋白基因的进化起源，我们分析了硬骨鱼目中非硬骨鱼的视蛋白基因。比目鱼、鲟鱼和雀鳝视蛋白全长序列的系统发育分析表明，视蛋白基因的反转录复制发生在比目鱼谱系分支之后。此外，比目鱼、鲟鱼和雀鳝视蛋白的组织分布和分子特性分析表明，含有内含子的视蛋白在松果体中的丰富和特异性表达，以及其 meta II 中间体的短寿命，导致了对松果体光感受的优化，是在雀鳝谱系分支之后实现的。基于这些结果，我们提出了一个硬骨鱼含有内含子和无内含子视蛋白基因的逐步进化模型。
