Study for the physiological characteristics of the pineal ultraviolet photoreceptor cells.

低等脊椎动物可以独立于眼睛用松果体复合体探测紫外线。电生理研究和发色团提取分析表明，七鳃鳗松果体中潜在的色素具有双稳态性质，即在紫外线和可见光下发生可逆的光反应，这是已知的紫外线色素所无法实现的。本文讨论了松果体紫外线受体的分子鉴定。我们的研究结果表明，长期假设的色素是七鳃鳗的parapinopsin同源物，其在370 nm处表现出最大的吸收。紫外光引起视黄醛_2发色团的顺反异构化。形成稳定的光产物，在515nm处具有最大的吸收。光产物在可见光吸收后恢复到原来的色素，表现出色素的光再生。原位杂交结果表明，旁apapinopsin在松果体器官背侧的细胞中选择性表达。我们成功地获得了最大灵敏度约为380 nm的背区光感受器细胞的超极化反应，其中外段明显被抗副apapinopsin抗体染色。这些结果表明，副松果体紫外光素是具有光交换两种稳定状态的松果体紫外光色素。副松果体视蛋白的双稳态性质可以解释松果体在背景绿光下的光恢复。此外，我们从鱼类和青蛙的松果体复合体中分离出具有紫外线敏感性的副松果体蛋白同源物，这表明副松果体蛋白是脊椎动物松果体接受紫外线的共同分子基础。

Lower vertebrates can detect UV light with the pineal complex independently of eyes. Electrophysiological studies, together with chromophore extraction analysis, have suggested that the underlying pigment in the lamprey pineal exhibits a bistable nature, that is, reversible photoreaction by UV and visible lights, which is never achieved by known UV pigments. Here we addressed the molecular identification of the pineal UV receptor. Our results showed that the long-hypothesized pigment is a lamprey homologue ofparapinopsin, which exhibits an absorption maximum at 370 nm. UV light causes cis-trans isomerization of its retinal_2 chromophore,.forming a stable photoproduct having an absorption maximum at 515 nm. The photoproduct reverts to the original pigment upon visible light absorption, showing photoregeneration of the pigment. In situ hybridization showed that parapinopsin is selectively expressed in the cells located at the dorsal region of the pineal organ. We successfully obtained the hyperpolarizing responses with a maximum sensitivity about 380 nm from the photoreceptor cells at the dorsal region, in which the outer segment was clearly stained with anti-parapinopsin antibody. These results demonstrated that parapinopsin is the pineal UV pigment having photo-interconvertible two stable states. The bistable nature of the parapinopsin can account for the photorecovery of the pineal UV-sensitivity by background green light in the lamprey. Furthermore, we isolated the parapinopsin homologues from fish and frog pineal complexes which exhibit UV-sensitivity, suggesting that parapinopsin is a common molecular basis for pineal UV reception in the vertebrate.