Battelle Barbara-Anne, Kempler Karen E, Saraf Spencer R, Marten Catherine E, Dugger Donald R, Speiser Daniel I, Oakley Todd H
Whitney Laboratory for Marine Bioscience and Departments of Neuroscience and Biology, 9505 Ocean Shore Blvd, University of Florida, St Augustine, FL 32080, USA
Whitney Laboratory for Marine Bioscience and Departments of Neuroscience and Biology, 9505 Ocean Shore Blvd, University of Florida, St Augustine, FL 32080, USA.
J Exp Biol. 2015 Feb 1;218(Pt 3):466-79. doi: 10.1242/jeb.116087. Epub 2014 Dec 18.
The eyes of the horseshoe crab Limulus polyphemus have long been used for studies of basic mechanisms of vision, and the structure and physiology of Limulus photoreceptors have been examined in detail. Less is known about the opsins Limulus photoreceptors express. We previously characterized a UV opsin (LpUVOps1) that is expressed in all three types of Limulus eyes (lateral compound eyes, median ocelli and larval eyes) and three visible light-sensitive rhabdomeric opsins (LpOps1, -2 and -5) that are expressed in Limulus lateral compound and larval eyes. Physiological studies showed that visible light-sensitive photoreceptors are also present in median ocelli, but the visible light-sensitive opsins they express were unknown. In the current study we characterize three newly identified, visible light-sensitive rhabdomeric opsins (LpOps6, -7 and -8) that are expressed in median ocelli. We show that they are ocellar specific and that all three are co-expressed in photoreceptors distinct from those expressing LpUVOps1. Our current findings show that the pattern of opsin expression in Limulus eyes is much more complex than previously thought and extend our previous observations of opsin co-expression in visible light-sensitive Limulus photoreceptors. We also characterize a Limulus peropsin/RGR (LpPerOps1). We examine the phylogenetic relationship of LpPerOps1 with other peropsins and RGRs, demonstrate that LpPerOps1 transcripts are expressed in each of the three types of Limulus eyes and show that the encoded protein is expressed in membranes of cells closely associated with photoreceptors in each eye type. These finding suggest that peropsin was in the opsin repertoire of euchelicerates.
鲎（Limulus polyphemus）的眼睛长期以来一直被用于视觉基本机制的研究，并且对鲎光感受器的结构和生理学进行了详细研究。关于鲎光感受器所表达的视蛋白，人们了解得较少。我们之前鉴定了一种紫外线视蛋白（LpUVOps1），它在鲎的三种眼睛类型（侧复眼、中眼和幼虫眼）中均有表达，还鉴定了三种对可见光敏感的视杆视蛋白（LpOps1、-2和-5），它们在鲎的侧复眼和幼虫眼中表达。生理学研究表明，中眼中也存在对可见光敏感的光感受器，但它们所表达的对可见光敏感的视蛋白尚不清楚。在当前的研究中，我们鉴定了三种新发现的、在中眼中表达的对可见光敏感的视杆视蛋白（LpOps6、-7和-8）。我们表明它们是眼特异性的，并且这三种视蛋白在与表达LpUVOps1的光感受器不同的光感受器中共表达。我们目前的研究结果表明，鲎眼中视蛋白的表达模式比之前认为的要复杂得多，并扩展了我们之前关于鲎对可见光敏感的光感受器中视蛋白共表达的观察结果。我们还鉴定了一种鲎视黄醛结合蛋白/视黄醛异构酶（LpPerOps1）。我们研究了LpPerOps1与其他视黄醛结合蛋白和视黄醛异构酶的系统发育关系，证明LpPerOps1转录本在鲎的三种眼睛类型中均有表达，并表明编码的蛋白质在与每种眼睛类型的光感受器紧密相关的细胞的膜中表达。这些发现表明视黄醛结合蛋白存在于真螯肢动物的视蛋白库中。
