Sun Lanfang, Kawano-Yamashita Emi, Nagata Takashi, Tsukamoto Hisao, Furutani Yuji, Koyanagi Mitsumasa, Terakita Akihisa
Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Osaka, Japan.
Department of life and Coordination-Complex Molecular Science, Institute for Molecular Science, Okazaki, Japan; Department of Structural Molecular Science, The Graduate University for Advanced Studies (SOKENDAI), Okazaki, Japan.
PLoS One. 2014 Sep 24;9(9):e108209. doi: 10.1371/journal.pone.0108209. eCollection 2014.
Mammals contain 1 melanopsin (Opn4) gene that is expressed in a subset of retinal ganglion cells to serve as a photopigment involved in non-image-forming vision such as photoentrainment of circadian rhythms. In contrast, most nonmammalian vertebrates possess multiple melanopsins that are distributed in various types of retinal cells; however, their functions remain unclear. We previously found that the lamprey has only 1 type of mammalian-like melanopsin gene, which is similar to that observed in mammals. Here we investigated the molecular properties and localization of melanopsin in the lamprey and other cyclostome hagfish retinas, which contribute to visual functions including image-forming vision and mainly to non-image-forming vision, respectively. We isolated 1 type of mammalian-like melanopsin cDNA from the eyes of each species. We showed that the recombinant lamprey melanopsin was a blue light-sensitive pigment and that both the lamprey and hagfish melanopsins caused light-dependent increases in calcium ion concentration in cultured cells in a manner that was similar to that observed for mammalian melanopsins. We observed that melanopsin was distributed in several types of retinal cells, including horizontal cells and ganglion cells, in the lamprey retina, despite the existence of only 1 melanopsin gene in the lamprey. In contrast, melanopsin was almost specifically distributed to retinal ganglion cells in the hagfish retina. Furthermore, we found that the melanopsin-expressing horizontal cells connected to the rhodopsin-containing short photoreceptor cells in the lamprey. Taken together, our findings suggest that in cyclostomes, the global distribution of melanopsin in retinal cells might not be related to the melanopsin gene number but to the extent of retinal contribution to visual function.
哺乳动物含有1个黑视蛋白（Opn4）基因，该基因在一部分视网膜神经节细胞中表达，作为一种光色素参与非成像视觉，如昼夜节律的光调节。相比之下，大多数非哺乳动物脊椎动物拥有多个黑视蛋白，分布于各种类型的视网膜细胞中；然而，它们的功能仍不清楚。我们之前发现七鳃鳗只有1种类似哺乳动物的黑视蛋白基因，这与在哺乳动物中观察到的情况相似。在这里，我们研究了七鳃鳗和其他圆口纲盲鳗视网膜中黑视蛋白的分子特性和定位，它们分别有助于包括成像视觉的视觉功能和主要的非成像视觉功能。我们从每个物种的眼睛中分离出1种类似哺乳动物的黑视蛋白cDNA。我们发现重组七鳃鳗黑视蛋白是一种对蓝光敏感的色素，七鳃鳗和盲鳗的黑视蛋白都能使培养细胞中的钙离子浓度以类似于哺乳动物黑视蛋白的方式依赖光增加。我们观察到，尽管七鳃鳗中仅存在1个黑视蛋白基因，但黑视蛋白分布于七鳃鳗视网膜的几种类型的视网膜细胞中，包括水平细胞和神经节细胞。相比之下，黑视蛋白在盲鳗视网膜中几乎特异性地分布于视网膜神经节细胞。此外，我们发现表达黑视蛋白的水平细胞与七鳃鳗中含有视紫红质的短光感受器细胞相连。综上所述，我们的研究结果表明，在圆口纲动物中，黑视蛋白在视网膜细胞中的整体分布可能与黑视蛋白基因数量无关，而是与视网膜对视觉功能的贡献程度有关。
