Peirson Stuart N, Halford Stephanie, Foster Russell G
Nuffield Laboratory of Ophthalmology, University of Oxford, The John Radcliffe Hospital, Headley Way, Headington, Oxford OX3 9DU, UK.
Philos Trans R Soc Lond B Biol Sci. 2009 Oct 12;364(1531):2849-65. doi: 10.1098/rstb.2009.0050.
Circadian rhythms are endogenous 24 h cycles that persist in the absence of external time cues. These rhythms provide an internal representation of day length and optimize physiology and behaviour to the varying demands of the solar cycle. These clocks require daily adjustment to local time and the primary time cue (zeitgeber) used by most vertebrates is the daily change in the amount of environmental light (irradiance) at dawn and dusk, a process termed photoentrainment. Attempts to understand the photoreceptor mechanisms mediating non-image-forming responses to light, such as photoentrainment, have resulted in the discovery of a remarkable array of different photoreceptors and photopigment families, all of which appear to use a basic opsin/vitamin A-based photopigment biochemistry. In non-mammalian vertebrates, specialized photoreceptors are located within the pineal complex, deep brain and dermal melanophores. There is also strong evidence in fish and amphibians for the direct photic regulation of circadian clocks in multiple tissues. By contrast, mammals possess only ocular photoreceptors. However, in addition to the image-forming rods and cones of the retina, there exists a third photoreceptor system based on a subset of melanopsin-expressing photosensitive retinal ganglion cells (pRGCs). In this review, we discuss the range of vertebrate photoreceptors and their opsin photopigments, describe the melanopsin/pRGC system in some detail and then finally consider the molecular evolution and sensory ecology of these non-image-forming photoreceptor systems.
昼夜节律是一种内源性的24小时周期，在没有外部时间线索的情况下依然存在。这些节律提供了白昼长度的内部表征，并根据太阳周期的不同需求优化生理机能和行为。这些生物钟需要每天根据当地时间进行调整，大多数脊椎动物使用的主要时间线索（授时因子）是黎明和黄昏时环境光量（辐照度）的每日变化，这一过程称为光诱导。试图理解介导对光的非成像反应（如光诱导）的光感受器机制，已促成了一系列不同光感受器和光色素家族的发现，所有这些似乎都使用基于视蛋白/维生素A的基本光色素生物化学。在非哺乳类脊椎动物中，专门的光感受器位于松果体复合体、脑深部和真皮黑素细胞内。在鱼类和两栖动物中，也有强有力的证据表明昼夜生物钟在多个组织中受到直接的光调节。相比之下，哺乳动物仅拥有眼部光感受器。然而，除了视网膜的成像视杆细胞和视锥细胞外，还存在基于表达黑素视蛋白的光敏视网膜神经节细胞（pRGCs）子集的第三种光感受器系统。在这篇综述中，我们讨论了脊椎动物光感受器及其视蛋白光色素的范围，详细描述了黑素视蛋白/pRGC系统，最后考虑了这些非成像光感受器系统的分子进化和感觉生态学。
