Senthilan Pingkalai R, Grebler Rudi, Reinhard Nils, Rieger Dirk, Helfrich-Förster Charlotte
Neurobiology & Genetics, Theodor-Boveri Institute, Biocenter, Julius-Maximilians University Würzburg, Am Hubland, 97074 Würzburg, Germany.
Biology (Basel). 2019 Jan 10;8(1):6. doi: 10.3390/biology8010006.
Light profoundly affects the circadian clock and the activity levels of animals. Along with the systematic changes in intensity and spectral composition, over the 24-h day, light shows considerable irregular fluctuations (noise). Using light as the Zeitgeber for the circadian clock is, therefore, a complex task and this might explain why animals utilize multiple photoreceptors to entrain their circadian clock. The fruit fly possesses light-sensitive Cryptochrome and seven Rhodopsins that all contribute to light detection. We review the role of Rhodopsins in circadian entrainment, and of direct light-effects on the activity, with a special emphasis on the newly discovered Rhodopsin 7 (Rh7). We present evidence that Rhodopsin 6 in receptor cells 8 of the compound eyes, as well as in the extra retinal Hofbauer-Buchner eyelets, plays a major role in entraining the fly's circadian clock with an appropriate phase-to-light⁻dark cycles. We discuss recent contradictory findings regarding Rhodopsin 7 and report original data that support its role in the compound eyes and in the brain. While Rhodopsin 7 in the brain appears to have a minor role in entrainment, in the compound eyes it seems crucial for fine-tuning light sensitivity to prevent overshooting responses to bright light.
光对动物的昼夜节律钟和活动水平有着深远影响。在一天24小时中，随着光照强度和光谱组成的系统性变化，光还呈现出相当大的不规则波动（噪声）。因此，将光用作昼夜节律钟的授时因子是一项复杂的任务，这或许可以解释为什么动物会利用多种光感受器来校准它们的昼夜节律钟。果蝇拥有对光敏感的隐花色素和七种视紫红质，它们都有助于光检测。我们综述了视紫红质在昼夜节律校准中的作用以及光对活动的直接影响，特别强调新发现的视紫红质7（Rh7）。我们提供证据表明，复眼中8号受体细胞中的视紫红质6以及视网膜外的霍夫鲍尔 - 布赫纳小眼在使果蝇的昼夜节律钟与合适的明暗周期同步方面发挥着主要作用。我们讨论了最近关于视紫红质7的相互矛盾的研究结果，并报告了支持其在复眼和大脑中作用的原始数据。虽然大脑中的视紫红质7在昼夜节律校准中似乎作用较小，但在复眼中它对于微调光敏感性以防止对强光的过度反应似乎至关重要。
