title: Opsins in Limulus eyes: characterization of three visible light-sensitive opsins unique to and co-expressed in median eye photoreceptors and a peropsin/RGR that is expressed in all eyes.
abstract: 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.
authors.affiliation: Whitney Laboratory for Marine Bioscience and Departments of Neuroscience and Biology, 9505 Ocean Shore Blvd, University of Florida, St Augustine, FL 32080, USA Battelle@whitney.ufl.edu.
authors.forename: Barbara-Anne
authors.initials: BA
authors.lastname: Battelle
authors.affiliation: Whitney Laboratory for Marine Bioscience and Departments of Neuroscience and Biology, 9505 Ocean Shore Blvd, University of Florida, St Augustine, FL 32080, USA.
authors.forename: Karen E
authors.initials: KE
authors.lastname: Kempler
authors.affiliation: Whitney Laboratory for Marine Bioscience and Departments of Neuroscience and Biology, 9505 Ocean Shore Blvd, University of Florida, St Augustine, FL 32080, USA.
authors.forename: Spencer R
authors.initials: SR
authors.lastname: Saraf
authors.affiliation: Whitney Laboratory for Marine Bioscience and Departments of Neuroscience and Biology, 9505 Ocean Shore Blvd, University of Florida, St Augustine, FL 32080, USA.
authors.forename: Catherine E
authors.initials: CE
authors.lastname: Marten
authors.affiliation: Department of Ophthalmology, University of Florida, Gainesville, FL 32080, USA.
authors.forename: Donald R
authors.initials: DR
authors.lastname: Dugger
authors.affiliation: Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA 93106, USA Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA.
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Speiser
authors.affiliation: Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA 93106, USA.
authors.forename: Todd H
authors.initials: TH
authors.lastname: Oakley
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D054910:Compound Eye, Arthropod / Q000378:metabolism*; D006737:Horseshoe Crabs / Q000378:metabolism* / Q000528:radiation effects; D008027:Light; D055355:Opsins / Q000378:metabolism*; D017956:Photoreceptor Cells, Invertebrate / Q000378:metabolism*; D010802:Phylogeny
chemical_list: D055355:Opsins
keywords: Limulus photoreceptor; Ocellar specific opsin; Opsin co-expression; Peropsin