title: Opsin expression in Limulus eyes: a UV opsin is expressed in each eye type and co-expressed with a visible light-sensitive opsin in ventral larval eyes.
abstract: The eyes of the horseshoe crab, Limulus polyphemus, are a model for studies of visual function and the visual systems of euarthropods. Much is known about the structure and function of L. polyphemus photoreceptors, much less about their photopigments. Three visible-light-sensitive L. polyphemus opsins were characterized previously (LpOps1, 2 and 5). Here we characterize a UV opsin (LpUVOps1) that is expressed in all three types of L. polyphemus eyes. It is expressed in most photoreceptors in median ocelli, the only L. polyphemus eyes in which UV sensitivity was previously detected, and in the dendrite of eccentric cells in lateral compound eyes. Therefore, eccentric cells, previously thought to be non-photosensitive second-order neurons, may actually be UV-sensitive photoreceptors. LpUVOps1 is also expressed in small photoreceptors in L. polyphemus ventral larval eyes, and intracellular recordings from these photoreceptors confirm that LpUVOps1 is an active, UV-sensitive photopigment. These photoreceptors also express LpOps5, which we demonstrate is an active, long-wavelength-sensitive photopigment. Thus small photoreceptors in ventral larval eyes, and probably those of the other larval eyes, have dual sensitivity to UV and visible light. Interestingly, the spectral tuning of small ventral photoreceptors may change day to night, because the level of LpOps5 in their rhabdoms is lower during the day than during the night, whereas LpUVOps1 levels show no diurnal change. These and previous findings show that opsin co-expression and the differential regulation of co-expressed opsins in rhabdoms is a common feature of L. polyphemus photoreceptors.
authors.affiliation: Whitney Laboratory for Marine Bioscience, University of Florida, St Augustine, FL 32080, USA Departments of Neuroscience and Biology, University of Florida, Gainesville, FL 32611, USA Battelle@whitney.ufl.edu.
authors.forename: Barbara-Anne
authors.initials: BA
authors.lastname: Battelle
authors.affiliation: Whitney Laboratory for Marine Bioscience, University of Florida, St Augustine, FL 32080, USA Departments of Neuroscience and Biology, University of Florida, Gainesville, FL 32611, USA.
authors.forename: Karen E
authors.initials: KE
authors.lastname: Kempler
authors.affiliation: Whitney Laboratory for Marine Bioscience, University of Florida, St Augustine, FL 32080, USA Departments of Neuroscience and Biology, University of Florida, Gainesville, FL 32611, USA.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Harrison
authors.affiliation: Department of Ophthalmology, University of Florida, Gainesville, FL 32610, USA.
authors.forename: Donald R
authors.initials: DR
authors.lastname: Dugger
authors.affiliation: Department of Biology, University of Maryland, College Park, MD 20742, USA.
authors.forename: Richard
authors.initials: R
authors.lastname: Payne
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D054910:Compound Eye, Arthropod / Q000737:chemistry / Q000502:physiology; D005123:Eye / Q000378:metabolism; D005786:Gene Expression Regulation / Q000528:radiation effects; D006737:Horseshoe Crabs / Q000737:chemistry* / Q000528:radiation effects*; D008027:Light; D055355:Opsins / Q000737:chemistry* / Q000378:metabolism; D017956:Photoreceptor Cells, Invertebrate / Q000737:chemistry* / Q000502:physiology*; D014466:Ultraviolet Rays; D014785:Vision, Ocular / Q000502:physiology
chemical_list: D055355:Opsins
keywords: Diurnal rhythms; Limulus photoreceptors; Opsin co-expression; UV opsin; UV sensitivity