Circadian and Visual Neuroscience, Nuffield Laboratory of Ophthalmology, University of Oxford, Levels 5-6 West Wing, John Radcliffe Hospital, Headley Way, Oxford, UK OX3 9DU.
Photochem Photobiol Sci. 2010 Nov;9(11):1444-57. doi: 10.1039/c0pp00203h. Epub 2010 Oct 5.
Both vertebrates and invertebrates respond to light by utilising a wide-ranging array of photosensory systems, with diverse photoreceptor organs expressing a characteristic photopigment, itself consisting of an opsin apoprotein linked to a light-sensitive retinoid chromophore based on vitamin A. In the eye, the pigments expressed in both cone and rod photoreceptors have been studied in great depth and mediate contrast perception, measurement of the spectral composition of environmental light, and thus classical image forming vision. By contrast, the molecular basis for non-visual and extraocular photoreception is far less understood; however, two photopigment genes have become the focus of much study, the vertebrate ancient (va) opsin and melanopsin (opn4). In this review, we discuss the history of discovery for each gene, as well as focusing on the evolution, expression profile, functional role and broader physiological significance of each photopigment. Recently, it has been suggested independently by Arendt et al. and Lamb that an ancestral opsin bifurcated in early metazoans and evolved into two quite different photopigments, one expressed in rhabdomeric photoreceptors and the other in ciliary photoreceptors. This interpretation of the evolution of the metazoan eye has provided a powerful framework for understanding photobiological organization. Their proposal, however, does not encompass all current experimental observations that would be consistent with what we term a central "Evolution of Photosensory Opsins with Common Heredity (EPOCH)" hypothesis to explain the complexity of animal photosensory systems. Clearly, many opsin genes (e.g. va opsin) simply do not fit neatly within this scheme. Thus, the review concludes with a discussion of these anomalies and their context regarding the phylogeny of photoreceptor and photopigment development.
脊椎动物和无脊椎动物通过利用广泛的光感觉系统对光作出反应，不同的光感受器器官表达一种特征性的光色素，它本身由与基于维生素 A 的光敏感视黄醛发色团相连的视蛋白辅助蛋白组成。在眼睛中，已经对圆锥细胞和杆状细胞光感受器中表达的色素进行了深入研究，这些色素介导对比度感知、环境光光谱组成的测量，从而介导经典的图像形成视觉。相比之下，非视觉和眼外光感受器的分子基础理解得要少得多；然而，两个光色素基因已成为许多研究的焦点，即脊椎动物远古（va）视蛋白和黑视蛋白（opn4）。在这篇综述中，我们讨论了每个基因的发现历史，以及重点关注每个光色素的进化、表达谱、功能作用和更广泛的生理意义。最近，Arendt 等人和 Lamb 独立地提出，一个远古视蛋白在早期后生动物中分支，并进化为两种截然不同的光色素，一种表达在光感受器的纤毛中，另一种表达在睫状光感受器中。这种后生动物眼睛进化的解释为理解光生物学组织提供了一个强大的框架。然而，他们的提议并不能涵盖所有与我们称之为“感光视蛋白遗传进化（EPOCH）”假说一致的当前实验观察结果，该假说用于解释动物感光系统的复杂性。显然，许多视蛋白基因（例如 va 视蛋白）根本不符合这一方案。因此，该综述以讨论这些异常及其与光感受器和光色素发育的系统发育的关系结束。
