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Battelle BA. Opsins and Their Expression Patterns in the Xiphosuran Limulus polyphemus. THE BIOLOGICAL BULLETIN 2017; 233:3-20. [PMID: 29182506 DOI: 10.1086/693730] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The American horseshoe crab Limulus polyphemus (Linnaeus, 1758) is one of four extant species of xiphosuran chelicerates, the sister group to arachnids. Because of their position in the arthropod family tree and because they exhibit many plesiomorphic characteristics, Xiphosura are considered a proxy for the euchelicerate ancestor and therefore important for understanding the evolution and diversification of chelicerates and arthropods. Limulus polyphemus is the most extensively studied xiphosuran, and its visual system has long been a focus of studies critical for our understanding of basic mechanisms of vision and the evolution of visual systems in arthropods. Building upon a wealth of information about the anatomy and physiology of its visual system, advances in genetic approaches have greatly expanded possibilities for understanding its biochemistry. This review focuses on studies of opsin expression in L. polyphemus, which have been significantly advanced by the availability of transcriptomes and a recent high-quality assembly of its genome. These studies show that the repertoire of expressed opsins in L. polyphemus is far larger than anticipated, that the regulation of their expression in rhabdoms is far more complex than anticipated, and that photosensitivity may be distributed widely throughout the L. polyphemus central nervous system. The visual system of L. polyphemus is now arguably the best understood among chelicerates, and as such, it is a critical resource for furthering our understanding of the evolution and diversification of visual systems in arthropods.
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Key Words
- CNS, central nervous system
- LE, lateral eye
- LWS, long wavelength-sensitive
- LpArthOps, Limulus arthropsin
- LpCOps, Limulus C-type opsin
- LpOps, Limulus opsin
- LpPerOps, Limulus peropsin
- ME, median eye
- MWS, medium wavelength-sensitive
- Rh-LpOps, Limulus opsin in rhabdoms
- SWS, short wavelength-sensitive
- VE, ventral eye
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Battelle BA. Simple Eyes, Extraocular Photoreceptors and Opsins in the American Horseshoe Crab. Integr Comp Biol 2016; 56:809-819. [DOI: 10.1093/icb/icw093] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
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Battelle BA, Kempler KE, Saraf SR, Marten CE, Dugger DR, Speiser DI, Oakley TH. 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. J Exp Biol 2015; 218:466-79. [PMID: 25524988 PMCID: PMC4317242 DOI: 10.1242/jeb.116087] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Accepted: 12/09/2014] [Indexed: 11/20/2022]
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.
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Affiliation(s)
- Barbara-Anne Battelle
- Whitney Laboratory for Marine Bioscience and Departments of Neuroscience and Biology, 9505 Ocean Shore Blvd, University of Florida, St Augustine, FL 32080, USA
| | - Karen E Kempler
- Whitney Laboratory for Marine Bioscience and Departments of Neuroscience and Biology, 9505 Ocean Shore Blvd, University of Florida, St Augustine, FL 32080, USA
| | - Spencer R Saraf
- Whitney Laboratory for Marine Bioscience and Departments of Neuroscience and Biology, 9505 Ocean Shore Blvd, University of Florida, St Augustine, FL 32080, USA
| | - Catherine E Marten
- Whitney Laboratory for Marine Bioscience and Departments of Neuroscience and Biology, 9505 Ocean Shore Blvd, University of Florida, St Augustine, FL 32080, USA
| | - Donald R Dugger
- Department of Ophthalmology, University of Florida, Gainesville, FL 32080, USA
| | - Daniel I Speiser
- 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
| | - Todd H Oakley
- Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA 93106, USA
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Battelle BA, Kempler KE, Harrison A, Dugger DR, Payne R. 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. ACTA ACUST UNITED AC 2014; 217:3133-45. [PMID: 24948643 DOI: 10.1242/jeb.107383] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
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.
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Affiliation(s)
- Barbara-Anne Battelle
- 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
| | - Karen E Kempler
- 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
| | - Alexandra Harrison
- 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
| | - Donald R Dugger
- Department of Ophthalmology, University of Florida, Gainesville, FL 32610, USA
| | - Richard Payne
- Department of Biology, University of Maryland, College Park, MD 20742, USA
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Katti C, Kempler K, Porter ML, Legg A, Gonzalez R, Garcia-Rivera E, Dugger D, Battelle BA. Opsin co-expression in Limulus photoreceptors: differential regulation by light and a circadian clock. ACTA ACUST UNITED AC 2010; 213:2589-601. [PMID: 20639420 DOI: 10.1242/jeb.043869] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A long-standing concept in vision science has held that a single photoreceptor expresses a single type of opsin, the protein component of visual pigment. However, the number of examples in the literature of photoreceptors from vertebrates and invertebrates that break this rule is increasing. Here, we describe a newly discovered Limulus opsin, Limulus opsin5, which is significantly different from previously characterized Limulus opsins, opsins1 and 2. We show that opsin5 is co-expressed with opsins1 and 2 in Limulus lateral and ventral eye photoreceptors and provide the first evidence that the expression of co-expressed opsins can be differentially regulated. We show that the relative levels of opsin5 and opsin1 and 2 in the rhabdom change with a diurnal rhythm and that their relative levels are also influenced by the animal's central circadian clock. An analysis of the sequence of opsin5 suggests it is sensitive to visible light (400-700 nm) but that its spectral properties may be different from that of opsins1 and 2. Changes in the relative levels of these opsins may underlie some of the dramatic day-night changes in Limulus photoreceptor function and may produce a diurnal change in their spectral sensitivity.
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Affiliation(s)
- C Katti
- Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Boulevard, St Augustine, FL 32080, USA
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Rudloe A, Herrnkind WF. Orientation ofLimulus polyphemusin the Vicinity of Breeding Beaches. ACTA ACUST UNITED AC 2009. [DOI: 10.1080/10236247609386943] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Dalal JS, Jinks RN, Cacciatore C, Greenberg RM, Battelle BA. Limulus opsins: diurnal regulation of expression. Vis Neurosci 2004; 20:523-34. [PMID: 14977331 DOI: 10.1017/s095252380320506x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Much has been learned from studies of Limulus photoreceptors about the role of the circadian clock and light in the removal of photosensitive membrane. However, little is known in this animal about mechanisms regulating photosensitive membrane renewal, including the synthesis of proteins in, and associated with, the photosensitive membrane. To begin to understand renewal, this study examines diurnal changes in the levels of mRNAs encoding opsin, the integral membrane protein component of visual pigment, and the relative roles of light and the circadian clock in producing these changes. We show that at least two distinct opsin genes encoding very similar proteins are expressed in both the lateral and ventral eyes, and that during the day and night in the lateral eye, the average level of mRNA encoding opsinl is consistently higher than that encoding opsin2. Northern blot assays showed further that total opsin mRNA in the lateral eyes of animals maintained under natural illumination increases during the afternoon (9 & 12 h after sunrise) in the light and falls at night in the dark. This diurnal change occurs whether or not the eyes receive input from the circadian clock, but it is eliminated in eyes maintained in the dark. Thus, it is regulated by light and darkness, not by the circadian clock, with light stimulating an increase in opsin mRNA levels. The rise in opsin mRNA levels observed under natural illumination was seasonal; it occurred during the summer but not the spring and fall. However, a significant increase in opsin mRNA levels could be achieved in the fall by exposing lateral eyes to 3 h of natural illumination followed by 9 h of artificial light. The diurnal regulation of opsin mRNA levels contrasts sharply with the circadian regulation of visual arrestin mRNA levels (Battelle et al., 2000). Thus, in Limulus, distinctly different mechanisms regulate the levels of mRNA encoding two proteins critical for the photoresponse.
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Affiliation(s)
- Jasbir S Dalal
- Whitney Laboratory and Department of Neuroscience, University of Florida, St. Augustine 32080, USA
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Abstract
An UV-sensitive class of photoreceptors exists in all regions of the retinas of mantis shrimps. UV photosensitivity apparently resides in rhabdomeres of the eighth retinular cell (R8) that lies atop each rhabdom; and in ommatidia where the R8 rhabdomere consists of microvilli parallel in a single direction, sensitivity is maximal when the e-vector of plane-polarized light is parallel to the microvilli. Spectral sensitivity of the UV photoreceptor peaks at 345 nm and is best explained by the presence of a photopigment with lambda max near 325 nm overlain by material that absorbs UV light at wavelengths below approximately 350 nm. Rhabdomeres of R8 cells in several different retinal regions of a variety of species examined contain a photopigment absorbing maximally below 340 nm. Under appropriate conditions, a metapigment with lambda max near 460 nm can be formed. UV vision may be useful for enhancing the visual contrast of midwater predators or prey.
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Affiliation(s)
- T W Cronin
- Department of Biological Sciences, University of Maryland Baltimore County 21228
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Gribakin FG. Light scattering in the eye of the blowfly chalky mutant: the effect on spectral sensitivity of photoreceptors R1-6. Vision Res 1993; 33:1185-91. [PMID: 8333168 DOI: 10.1016/0042-6989(93)90207-d] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
In non-pigmented insect eyes, stray light causes the narrowing of the spectral sensitivity functions of the visual cells, and this effect is shown to be a sensitive tool for estimation of the stray light absorption by a photoreceptor. Spectral sensitivity functions of single cells of Calliphora chalky mutants were obtained in three sets of experiments with different contribution of stray light in total light absorption by a visual cell, and the relative parasitic absorption due to stray light appeared to be as high as 70% of total absorption even with a point light source. The effect of light scattering may be of some functional significance in non-pigmented parts of the wild type eyes as, for instance, in the dorsal rim area of the crickets.
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Affiliation(s)
- F G Gribakin
- Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St Petersburg
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Abstract
Ventral photoreceptors of the horseshoe crab, Limulus polyphemus, have been important in the study of visual transduction, due to their large size and hardiness in vitro. This study shows that there are two classes of ventral photoreceptors that can be distinguished on the basis of differences in cellular and nuclear dimensions, soma and rhabdom morphology, and axon size. Large protoreceptors, which have been the subject of many physiological studies, have an extensive superficial rhabdom, a nuclear diameter of 20-24 microns, and measure 100-150 microns in length. In contrast, small photoreceptors measure 45-65 microns in length and have a nucleus 13-16 microns across. Small photoreceptors are found singly or in association with large photoreceptors. The rhabdom of isolated small photoreceptors is surrounded by a calyx originating from the soma, so that it appears to be located internally. The rhabdomeral lobe of small photoreceptors associated with large photoreceptors characteristically is divided into several segments, each of which invaginates the rhabdomeral lobe of the adjacent large photoreceptor. The entire external rhabdom of the associated small photoreceptor abuts the rhabdom of the large photoreceptor. Morphometric analysis of the ventral nerves shows that there are two size classes of photoreceptor axons, corresponding to the two classes of photoreceptors. The numbers of axons in each size class are nearly equal. Unlike the ventral eye, none of the other eyes of Limulus have been reported to have more than one morphological class of photoreceptor. Functional differences between the two classes of ventral photoreceptors are suggested by experiments, reported in the accompanying paper (Herman (1991), J. Comp. Neurol. 303:11-21), showing that the large photoreceptors exhibit light-stimulated rhabdom turnover while the small ones do not.
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Affiliation(s)
- K G Herman
- Laboratory of Neurobiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892
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Kirkwood A, Weiner D, Lisman JE. An estimate of the number of G regulator proteins activated per excited rhodopsin in living Limulus ventral photoreceptors. Proc Natl Acad Sci U S A 1989; 86:3872-6. [PMID: 2498877 PMCID: PMC287243 DOI: 10.1073/pnas.86.10.3872] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Previous work by others on Limulus photoreceptors has shown that application of a variety of guanine nucleotide-binding regulatory protein (G protein) activators produces discrete waves of depolarization similar to those generated by single photos, but smaller in size. We investigated whether these events might originate at a site other than the G protein. Initiation of the events did not depend on the state of the visual pigment, suggesting that the events do not originate at the pigment level. The events could be blocked by the G-protein blocker guanosine 5'-[beta-thio]diphosphate (GDP[betaS]) and thus support the conclusion that these discrete events are due to the activation of G protein itself. Quantitative measurements indicate that the average size of these events is approximately 8 times smaller than that evoked by single photons under the same conditions. Given certain reasonable assumptions, these results imply that the gain of the first stage of transduction in vivo is approximately 8, a value considerably lower than that measured in vitro in vertebrate rods (gain, 100-500). Furthermore, independent evidence for a low first-stage gain in Limulus is derived from the observation that GDP[betaS] barely affects the size of the response to single photons, but greatly reduces the probability that a photon evokes a response. These results can be explained if rhodopsin normally activates only a few G proteins.
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Affiliation(s)
- A Kirkwood
- Department of Biology, Brandeis University, Waltham, MA 02254
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Lisman J. The role of metarhodopsin in the generation of spontaneous quantum bumps in ultraviolet receptors of Limulus median eye. Evidence for reverse reactions into an active state. J Gen Physiol 1985; 85:171-87. [PMID: 3981127 PMCID: PMC2215799 DOI: 10.1085/jgp.85.2.171] [Citation(s) in RCA: 35] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The origin of spontaneous quantum bumps has been examined in the ultraviolet photoreceptors of Limulus median eye. These cells have a rhodopsin with a lambda max at 360 nm and a stable photoproduct, metarhodopsin, with a lambda max at 470 nm. The steady state rate of spontaneous quantum bumps was found to be higher when the metarhodopsin concentration was high than when the rhodopsin concentration was high. This result implicates metarhodopsin in the generation of spontaneous quantum bumps. Furthermore, this result is consistent with the idea that the reaction which inactivates metarhodopsin (terminates the ability of metarhodopsin to initiate the reactions leading to a quantum bump) is reversible and that such reversions can be a significant source of spontaneous quantum bumps. Given that the rate of spontaneous quantum bumps is approximately 1/s under conditions where the number of inactive metarhodopsin molecules is approximately 10(9), it follows that the molecular switch that inactivates metarhodopsin reverses with a probability of less than 10(-9). A model is presented of how a molecular switch with this reliability might be constructed.
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Lisman JE, Strong JA. The initiation of excitation and light adaptation in Limulus ventral photoreceptors. J Gen Physiol 1979; 73:219-43. [PMID: 438771 PMCID: PMC2215242 DOI: 10.1085/jgp.73.2.219] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Two types of experiments indicate that light adaptation and excitation are initiated by the same, rather than different, populations of visual pigment. (a) The criterion action spectra of light adaptation and excitation are the same. (b) Increment-threshold curves were measured with a voltage-clamp technique under conditions of high and low concentration of plasma membrane rhodopsin (Rhpm). SD, the dark-adapted sensitivity, and 1/I2, the inverse of the background irradiance that desensitized by 0.3 log units, underwent the same fractional change when the rhodopsin concentration was changed. Both quantities appear to be linearly related to Rhpm. Reversible reductions in Rhpm were achieved by orange irradiation during a brief increase of extracellular pH from 7.8 to 10. This procedure would be unlikely to produce similar concentration changes in a hypothetical intracellular pigment because the concurrent change in intracellular pH, measured using the dye, phenol red, was only 0.45 pH units. It is thus unlikely that an intracellular pigment initiates light adaptation. On the assumption that light adaptation is mediated by a light-induced release of Ca++ from an intracellular store. the results reported here imply that an intracellular transmitter is needed to couple Rhpm to the intracellular store.
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Miller WH. Ocular Optical Filtering. COMPARATIVE PHYSIOLOGY AND EVOLUTION OF VISION IN INVERTEBRATES 1979. [DOI: 10.1007/978-3-642-66999-6_3] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Spectral Sensitivity and Color Vision in Invertebrates. COMPARATIVE PHYSIOLOGY AND EVOLUTION OF VISION IN INVERTEBRATES 1979. [DOI: 10.1007/978-3-642-66999-6_9] [Citation(s) in RCA: 104] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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Benolken RM, Maude MB, Anderson RE. Photopigments of the lateral eye ofLimulus. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 1976. [DOI: 10.1007/bf00656742] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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MEECH ROBERTW, BROWN HMACK. INVERTEBRATE PHOTORECEPTORS: A SURVEY OF RECENT EXPERIMENTS ON PHOTORECEPTORS FROM BALANUS AND LIMULUS. ZOOLOGY 1976. [DOI: 10.1016/b978-0-08-018767-9.50034-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Brown HM, Cornwall MC. Spectral correlates of a quasi-stable depolarization in barnacle photoreceptor following red light. J Physiol 1975; 248:555-78. [PMID: 1151837 PMCID: PMC1309539 DOI: 10.1113/jphysiol.1975.sp010988] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
1. Illumination of B. eburneus photoreceptors with intense red light produces a membrane depolarization that persists in darkness. This quasistable depolarization (latch-up) can be terminated with green light. The phenomenon was investigated with electrophysiological, spectrochemical, and microspectrophotometric techniques. 2. Latch-up was associated with a stable inward current in cells with the membrane potential voltage-clamped at the resting potential in darkness. The stable current could only be elicited at wave-lengths greater than 580 nm. 3. Light-induced current (LIC) was measured at various wave-lengths in dark-adapted photoreceptors with the membrane voltage-clamped to the resting potential. The minimum number of photons required to elicit a fixed amount of LIC occurred at 540 nm, indicating that the photoreceptor is maximally sensitive to this wave-length of light. The photoreceptor was also sensitive to wave-lengths in the near-U.V. region of the spectrum (380-420 nm). 4. Steady red adapting light reduced the magnitude of the LIC uniformly at all wave-lengths except in the near-U.V. region of the spectrum; sensitivity was reduced less in this region. 5. The spectrum for termination of the stable inward current following or during red light was shifted to the blue (peak about 510 nm) compared to the peak for LIC (peak about 540 nm). 6. Absorbance of single cells prepared under bright, red light decreased maximally at 480 nm following exposure to wave-lengths of light longer than 540 nm. 7. A pigment extract of 1000 barnacle ocelli prepared under dim, red light had a maximum absorbance change at 480 nm when bleached with blue-gree light. 8. There was no evidence in the latter two experiments of photointerconversion of pigments with absorbance maxima at 480 and 540 nm. Rather, the maximum absorption of the bleaching products seemed to occur at wave-lengths shorter than 420 nm. 9. Since latch-up induction occurs at wave-lengths longer than 580 nm, it may depend on the 540 pigment or on an undetected red absorbing pigment. 10. A photolabile pigment at 480 nm correlated most closely with termination of the stable inward current associated with latch-up.
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Fahrenbach WH, Griffin AJ. The morphology of the Limulus visual system. VI. Connectivity in the ocellus. Cell Tissue Res 1975; 159:39-47. [PMID: 1149089 DOI: 10.1007/bf00231993] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
An ocellus of the horseshoe crab, Limulus polyphemus, has been serially sectioned for light and electron microscopy, its sensory cells have been indexed, and the interconnections of a third of these traced. The ocellus contains 155 retinula cells and 26 arhabdomeric cells, which are secondary sensory neurons. Of these, 55 retinula cells constitute 7 quasi-ommatidial assemblages, each innervated by at least one and a total of 9 arhabdomeric cells. When known electrotonic coupling patterns are compared with gap-junctional connections, retinula cells sensitive to visible or ultraviolet light can be tentatively identified. Retinula cell axons contribute collaterals to a synaptic plexus, in which the arhabdomeric cells apparently do not participate.
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Fahrenbach WH. The visual system of the horseshoe crab Limulus polyphemus. INTERNATIONAL REVIEW OF CYTOLOGY 1975; 41:285-349. [PMID: 1093990 DOI: 10.1016/s0074-7696(08)60970-5] [Citation(s) in RCA: 97] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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Jones C, Nolte J, Brown JE. The anatomy of the median ocellus of Limulus. ZEITSCHRIFT FUR ZELLFORSCHUNG UND MIKROSKOPISCHE ANATOMIE (VIENNA, AUSTRIA : 1948) 1971; 118:297-309. [PMID: 5566319 DOI: 10.1007/bf00331188] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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