Battelle Barbara-Anne
Whitney Laboratory for Marine Bioscience and Departments of Neuroscience and Biology, University of Florida, St Augustine, FL 32080, and Gainesville, FL 36611, USA
Integr Comp Biol. 2016 Nov;56(5):809-819. doi: 10.1093/icb/icw093. Epub 2016 Jul 21.
The eyes and photoreceptors of the American horseshoe crab Limulus polyphemus have been studied since the 1930s, and this work has been critical for understanding basic mechanisms of vision. One of the attractions of Limulus as a preparation for studies of vision is that it has three different types of eyes-a pair of later compound, image-forming eyes and two types of simple eyes, a pair of median ocelli, and three pair of larval eyes. Each eye type is tractable for experimentation. Limulus also has extraocular photoreceptors in its segmental ganglia and tail. The current contribution focuses on photoreceptors in Limulus larval eyes and ocelli and its extraocular photoreceptors with the goal of summarizing what is currently known and not known about their physiology and function and the opsins they express. The Limulus genome encodes a surprisingly large number of opsins (18), and studies of their expression pattern have raised new questions about the role of opsin co-expression, the functions of peropsins expressed outside of eyes, and the physiological relevance of opsins with apparently very low expression levels. Studies of opsin expression in Limulus lead one to wonder whether photoreceptors yet to be discovered might be present throughout its central nervous system.
自20世纪30年代以来，人们一直在研究美洲鲎（Limulus polyphemus）的眼睛和光感受器，这项工作对于理解视觉的基本机制至关重要。鲎作为视觉研究的实验对象，其吸引人之处在于它有三种不同类型的眼睛——一对复眼、成像眼以及两种单眼，一对中眼和三对幼虫眼。每种眼睛类型都便于进行实验。鲎在其节段神经节和尾部也有眼外光感受器。本文的贡献集中在鲎幼虫眼和中眼以及眼外光感受器中的光感受器，目的是总结目前关于它们的生理学、功能以及所表达视蛋白的已知和未知情况。鲎的基因组编码了数量惊人的视蛋白（18种），对其表达模式的研究提出了关于视蛋白共表达的作用、眼外表达的视黄醛结合蛋白的功能以及表达水平明显很低的视蛋白的生理相关性等新问题。对鲎视蛋白表达的研究让人不禁思考，在其整个中枢神经系统中是否可能存在尚未被发现的光感受器。
