Shen Baoguo, Wada Seiji, Nishioka Haruka, Nagata Takashi, Kawano-Yamashita Emi, Koyanagi Mitsumasa, Terakita Akihisa
Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Osaka, 558-8585, Japan.
The OCU Advanced Research Institute for Natural Science and Technology, Osaka City University, Osaka, 558-8585, Japan.
Zoological Lett. 2021 Feb 12;7(1):1. doi: 10.1186/s40851-021-00171-1.
In the pineal organ of zebrafish larvae, the bistable opsin parapinopsin alone generates color opponency between UV and visible light. Our previous study suggested that dark inactivation of the parapinopsin photoproduct, which activates G-proteins, is important for the regulation of the amount of the photoproduct. In turn, the photoproduct is responsible for visible light sensitivity in color opponency. Here, we found that an opsin kinase or a G-protein-coupled receptor kinase (GRK) is involved in inactivation of the active photoproduct of parapinopsin in the pineal photoreceptor cells of zebrafish larvae. We investigated inactivation of the photoproduct in the parapinopsin cells of various knockdown larvae by measuring the light responses of the cells using calcium imaging. We found that GRK7a knockdown slowed recovery of the response of parapinopsin photoreceptor cells, whereas GRK1b knockdown or GRK7b knockdown did not have a remarkable effect, suggesting that GRK7a, a cone-type GRK, is mainly responsible for inactivation of the parapinopsin photoproduct in zebrafish larvae. We also observed a similar knockdown effect on the response of the parapinopsin photoreceptor cells of mutant larvae expressing the opsin SWS1, a UV-sensitive cone opsin, instead of parapinopsin, suggesting that the parapinopsin photoproduct was inactivated in a way similar to that described for cone opsins. We confirmed the immunohistochemical distribution of GRK7a in parapinopsin photoreceptor cells by comparing the immunoreactivity to GRK7 in GRK7a-knockdown and control larvae. These findings suggest that in pineal photoreceptor cells, the cone opsin kinase GRK7a contributes greatly to the inactivation of parapinopsin, which underlies pineal color opponency.
在斑马鱼幼体的松果体器官中，双稳态视蛋白副视蛋白单独产生紫外线与可见光之间的颜色拮抗。我们之前的研究表明，激活G蛋白的副视蛋白光产物的暗失活对于调节光产物的量很重要。反过来，光产物负责颜色拮抗中的可见光敏感性。在这里，我们发现一种视蛋白激酶或G蛋白偶联受体激酶（GRK）参与斑马鱼幼体松果体光感受器细胞中副视蛋白活性光产物的失活。我们通过使用钙成像测量细胞的光反应，研究了各种基因敲低幼体副视蛋白细胞中光产物的失活情况。我们发现，敲低GRK7a会减缓副视蛋白光感受器细胞反应的恢复，而敲低GRK1b或GRK7b则没有显著影响，这表明作为视锥细胞型GRK的GRK7a主要负责斑马鱼幼体中副视蛋白光产物的失活。我们还观察到，对于表达视蛋白SWS1（一种紫外线敏感的视锥细胞视蛋白）而非副视蛋白的突变幼体的副视蛋白光感受器细胞反应，也有类似的基因敲低效应，这表明副视蛋白光产物的失活方式与视锥细胞视蛋白的情况类似。我们通过比较GRK7a基因敲低幼体和对照幼体中与GRK7的免疫反应性，确认了GRK7a在副视蛋白光感受器细胞中的免疫组织化学分布。这些发现表明，在松果体光感受器细胞中，视锥细胞视蛋白激酶GRK7a对副视蛋白失活有很大贡献，而副视蛋白失活是松果体颜色拮抗的基础。
