Iigo Masayuki, Abe Tomotaka, Kambayashi Saori, Oikawa Kaoru, Masuda Tomohiro, Mizusawa Kanta, Kitamura Shoji, Azuma Teruo, Takagi Yasuaki, Aida Katsumi, Yanagisawa Tadashi
Department of Applied Biochemistry, Utsunomiya University, 350 Mine-machi, Utsunomiya, Tochigi 321-8505, Japan.
Gen Comp Endocrinol. 2007 Oct-Dec;154(1-3):91-7. doi: 10.1016/j.ygcen.2007.06.013. Epub 2007 Jun 21.
In many teleost species, the photoreceptive pineal organ harbors the circadian clock that regulates melatonin release in the pineal organ itself. However, the pineal organ of three salmonids (rainbow trout Oncorhynchus mykiss, masu salmon Oncorhynchus masou, and sockeye salmon Oncorhynchus nerka) did not exhibit circadian rhythms in melatonin release when maintained under constant darkness (DD) in vitro, suggesting that the pineal organs of all salmonids lack the circadian regulation of melatonin production. To test this hypothesis, the pineal organ of seven salmonids (common whitefish Coregonus lavaretus, grayling Thymallus thymallus, Japanese huchen Hucho perryi, Japanese charr Salvelius leucomaenis pluvius, brook trout Salvelius fontinalis, brown trout Salmo trutta and chum salmon Oncorhynchus keta) and closely related osmerids (ayu Plecoglossus altivelis altivelis and Japanese smelt Hypomesus nipponensis) were individually maintained in flow-through culture at 15 degrees C under several light conditions. Under light-dark cycles, the pineal organ of all species showed a rhythmic melatonin release with high rates during the dark phase. Under DD, the osmerid pineal organs exhibited circadian rhythms in melatonin release with high rates only during the subjective-night but the salmonid pineal organs constantly released melatonin at high rates. Under constant light, melatonin release was suppressed in all species. The pineal organ of rainbow trout maintained at different temperature (15, 20 or 25 degrees C) under DD released melatonin with high rates but the amount of melatonin released was temperature-sensitive (highest at 20 degrees C). Thus, melatonin release from the pineal organ of osmerids is regulated by both light and circadian clock but the circadian regulation is lacking in salmonids. These results indicate that ancestral salmonids lost the circadian regulation of melatonin production after the divergence from osmerid teleosts.
在许多硬骨鱼物种中，具有感光性的松果体器官含有昼夜节律钟，该节律钟调节松果体自身褪黑素的释放。然而，三种鲑科鱼类（虹鳟Oncorhynchus mykiss、马苏大马哈鱼Oncorhynchus masou和红大马哈鱼Oncorhynchus nerka）的松果体在体外持续黑暗（DD）条件下培养时，褪黑素释放并未表现出昼夜节律，这表明所有鲑科鱼类的松果体缺乏褪黑素分泌的昼夜节律调节。为了验证这一假设，将七种鲑科鱼类（白鲑Coregonus lavaretus、茴鱼Thymallus thymallus、石川哲罗鱼Hucho perryi、日本红点鲑Salvelius leucomaenis pluvius、溪红点鲑Salvelius fontinalis、褐鳟Salmo trutta和大麻哈鱼Oncorhynchus keta）以及亲缘关系较近的胡瓜鱼科鱼类（香鱼Plecoglossus altivelis altivelis和日本公鱼Hypomesus nipponensis）的松果体分别在15摄氏度的几种光照条件下进行流通培养。在明暗循环条件下，所有物种的松果体在黑暗阶段均表现出褪黑素释放的节律性，且释放速率较高。在持续黑暗条件下，胡瓜鱼科鱼类的松果体仅在主观夜间表现出褪黑素释放的昼夜节律，且释放速率较高，但鲑科鱼类的松果体持续以较高速率释放褪黑素。在持续光照条件下，所有物种的褪黑素释放均受到抑制。虹鳟的松果体在持续黑暗条件下于不同温度（15、20或25摄氏度）下培养时，均以较高速率释放褪黑素，但褪黑素的释放量对温度敏感（在20摄氏度时最高）。因此，胡瓜鱼科鱼类松果体的褪黑素释放受光照和昼夜节律钟的双重调节，但鲑科鱼类缺乏昼夜节律调节。这些结果表明，原始鲑科鱼类在与胡瓜鱼科硬骨鱼分化后失去了褪黑素分泌的昼夜节律调节。
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