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Maria Ina Arnone - One of the best experts on this subject based on the ideXlab platform.

  • the crowns have eyes multiple Opsins found in the eyes of the crown of thorns starfish acanthaster planci
    BMC Evolutionary Biology, 2018
    Co-Authors: Elijah K. Lowe, Anders Garm, Esther Ullrichluter, Claudia Cuomo, Maria Ina Arnone
    Abstract:

    Opsins are G protein-coupled receptors used for both visual and non-visual photoreception, and these proteins evolutionarily date back to the base of the bilaterians. In the current sequencing age, phylogenomic analysis has proven to be a powerful tool, facilitating the increase in knowledge about diversity within the Opsin subclasses and, so far, at least nine types of Opsins have been identified. Within echinoderms, Opsins have been studied in Echinoidea and Ophiuroidea, which do not possess proper image forming eyes, but rather widely dispersed dermal photoreceptors. However, most species of Asteroidea, the starfish, possess true eyes and studying them will shed light on the diversity of Opsin usage within echinoderms and help resolve the evolutionary history of Opsins. Using high-throughput RNA sequencing, we have sequenced and analyzed the transcriptomes of different Acanthaster planci tissue samples: eyes, radial nerve, tube feet and a mixture of tissues from other organs. At least ten Opsins were identified, and eight of them were found significantly differentially expressed in both eyes and radial nerve, with R-Opsin being the most highly expressed in the eye. This study provides new important insight into the involvement of Opsins in visual and nonvisual photoreception. Of relevance, we found the first indication of an r-Opsin photopigment expressed in a well-developed visual eye in a deuterostome animal. Additionally, we provided tissue specific A. planci transcriptomes that will aid in future Evo Devo studies.

  • the crowns have eyes multiple Opsins found in the eyes of the crown of thorns starfish acanthaster planci including the first r Opsin utilized by a deuterostome eye
    bioRxiv, 2017
    Co-Authors: Elijah K. Lowe, Anders Garm, Esther Ullrichluter, Maria Ina Arnone
    Abstract:

    Opsins are G protein-coupled receptors used for both visual and non-visual photoreception, and these proteins evolutionarily date back to the base of the bilaterians. In the current sequencing age, phylogenomic analysis has proven to be a powerful tool, facilitating the increase in knowledge about diversity within the Opsin subclasses and, so far, nine paralogs have been identified. Within echinoderms, Opsins have been studied in Echinoidea and Ophiuroidea, which do not possess proper image forming eyes, but rather widely dispersed dermal photoreceptors. However, most species of Asteroidea, the starfish, possess true eyes and studying them will shed light on the diversity of Opsin usage within echinoderms and help resolve the evolutionary history of Opsins. Using high-throughput RNA sequencing, we have sequenced and analyzed the transcriptomes of different Acanthaster planci tissue samples: eyes, radial nerve, tube feet and a mixture of tissues from other organs. At least ten Opsins were identified, and eight of them were found significantly differentially expressed in both eyes and radial nerve, providing new important insight into the involvement of Opsins in visual and nonvisual photoreception. Of relevance, we found the first evidence of an r-Opsin photopigment expressed in a well developed visual eye in a deuterostome animal.

  • the crowns have eyes multiple Opsins found in the eyes of the crown of thorns starfish acanthaster planci
    bioRxiv, 2017
    Co-Authors: Elijah K. Lowe, Anders Garm, Esther Ullrichluter, Maria Ina Arnone
    Abstract:

    In the late nineteenth century, the examination of visual pigments led to the discovery of a protein -- the Opsin -- covalently bound to a chromophore. Opsins are G protein-coupled receptors (GPCR) used for both visual and non-visual photoreception, and these proteins evolutionarily date back to the base of the bilaterians. In the current sequencing age, phylogenomic analysis has proven to be a powerful tool, facilitating the increase in knowledge about diversity within the Opsin subclasses and so far, nine paralogs have been identified. While phylogeny may help infer function, direct functional studies of Opsins in vertebrates, cephalopod mollusks, and fruit flies have shown that there are multiple pathways involving various Opsins for visual photoreception along with several other processes. Within echinoderms, Opsins have been studied in Echinoidea and Ophiuroidea, but these two groups do not possess proper image forming eyes, but rather widely dispersed dermal photoreceptors. However, most species of Asteroidea, the starfish, possess true eyes and studying them will shed light on the diversity of Opsin usage within echinoderms and help resolve the evolutionary history of Opsins. Using high-throughput RNA sequencing, we have sequenced and analyzed the transcriptomes of different Acanthaster planci tissue samples: eyes, radial nerve, tube feet and a mixture of other organelle tissue. At least 9 Opsins belonging to 7 potential Opsin paralogs were identified, and seven of them were found significantly differentially expressed in both eyes and radial nerve, providing new important insight into the involvement of Opsins in visual and nonvisual photoreception in echinoderms. Of relevance, we found the first evidence of an r-Opsin photopigment expressed in a well developed visual eye in a deuterostome animal.

  • Non-directional Photoreceptors in the Pluteus of Strongylocentrotus purpuratus
    Frontiers in Ecology and Evolution, 2016
    Co-Authors: Alberto Valero-gracia, Libero Petrone, Paola Oliveri, Dan-eric Nilsson, Maria Ina Arnone
    Abstract:

    In comparison to complex visual systems, non-directional photoreception – the most primitive form of biological photodetection – has been poorly investigated, although it is essential to many biological processes such as circadian and seasonal rhythms. Here we describe the spatiotemporal expression pattern of the major molecular actors mediating light reception – Opsins – localized in the Strongylocentrotus purpuratus larva. In contrast to other zooplanktonic larvae, the echinopluteus lacks photoreceptor cells with observable shading pigments involved in directional visual tasks. Nonetheless, the echinopluteus expresses two distinct classes of Opsins: a Go-Opsin and a rhabdomeric Opsin. The Go-Opsin, Sp-Opsin3.2, is detectable at early (3 days post fertilization) and four armed pluteus stages (4 days post fertilization) in two cells that flank the apical organ. To rule out the presence of shading pigments involved in directional photoreception, we used electron microscopy to explore the expression domain of Go-Opsin Sp-Opsin3.2 positive cells. The rhabdomeric Opsin Sp-Opsin4 expression is detectable in clusters of cells located around the primary podia at the five-fold ectoderm pentagonal disc stage (day 18-21) and thereafter, thus indicating that Sp-Opsin4 may not be involved in the photoreception mechanism of the larva, but only of the juvenile. We discuss the putative function of the relevant cells in their neural context, and propose a model for understanding simple photodetection in marine larvae.

  • High Opsin diversity in a non-visual infaunal brittle star
    BMC genomics, 2014
    Co-Authors: Jérôme Delroisse, Jérôme Mallefet, Maria Ina Arnone, Esther Ullrich-lüter, Olga Ortega-martinez, Sam Dupont, Patrick Flammang
    Abstract:

    Background: In metazoans, Opsins are photosensitive proteins involved in both vision and non-visual photoreception. Echinoderms have no well-defined eyes but several Opsin genes were found in the purple sea urchin (Strongylocentrotus purpuratus) genome. Molecular data are lacking for other echinoderm classes although many species are known to be light sensitive. Results: In this study focused on the European brittle star Amphiura filiformis, we first highlighted a blue-green light sensitivity using a behavioural approach. We then identified 13 new putative Opsin genes against eight bona fide Opsin genes in the genome of S. purpuratus. Six Opsins were included in the rhabdomeric Opsin group (r-Opsins). In addition, one putative ciliary Opsin (c-Opsin), showing high similarity with the c-Opsin of S. purpuratus (Sp-Opsin 1), one Go Opsin similar to Sp-Opsins 3.1 and 3.2, two basal-branch Opsins similar to Sp-Opsins 2 and 5, and two neurOpsins similar to Sp-Opsin 8, were identified. Finally, two sequences from one putative RGR Opsin similar to Sp-Opsin 7 were also detected. Adult arm transcriptome analysis pinpointed Opsin mRNAs corresponding to one r-Opsin, one neurOpsin and the homologue of Sp-Opsin 2. Opsin phylogeny was determined by maximum likelihood and Bayesian analyses. Using antibodies designed against c- and r-Opsins from S. purpuratus, we detected putative photoreceptor cells mainly in spines and tube feet of A. filiformis, respectively. The r-Opsin expression pattern is similar to the one reported in S. purpuratus with cells labelled at the tip and at the base of the tube feet. In addition, r-Opsin positive cells were also identified in the radial nerve of the arm. C-Opsins positive cells, expressed in pedicellariae, spines, tube feet and epidermis in S. purpuratus were observed at the level of the spine stroma in the brittle star. Conclusion: Light perception in A. filiformis seems to be mediated by Opsins (c- and r-) in, at least, spines, tube feet and in the radial nerve cord. Other non-visual Opsin types could participate to the light perception process indicating a complex expression pattern of Opsins in this infaunal brittle star.

Kristin Tessmarraible - One of the best experts on this subject based on the ideXlab platform.

  • a g o type Opsin mediates the shadow reflex in the annelid platynereis dumerilii
    BMC Biology, 2018
    Co-Authors: Thomas Ayers, Vinoth Babu Veedin Rajan, Kristin Tessmarraible, Martin Guhmann, Hisao Tsukamoto
    Abstract:

    The presence of photoreceptive molecules outside the eye is widespread among animals, yet their functions in the periphery are less well understood. Marine organisms, such as annelid worms, exhibit a ‘shadow reflex’, a defensive withdrawal behaviour triggered by a decrease in illumination. Herein, we examine the cellular and molecular underpinnings of this response, identifying a role for a photoreceptor molecule of the Go-Opsin class in the shadow response of the marine bristle worm Platynereis dumerilii. We found Pdu-Go-Opsin1 expression in single specialised cells located in adult Platynereis head and trunk appendages, known as cirri. Using gene knock-out technology and ablation approaches, we show that the presence of Go-Opsin1 and the cirri is necessary for the shadow reflex. Consistently, quantification of the shadow reflex reveals a chromatic dependence upon light of approximately 500 nm in wavelength, matching the photoexcitation characteristics of the Platynereis Go-Opsin1. However, the loss of Go-Opsin1 does not abolish the shadow reflex completely, suggesting the existence of a compensatory mechanism, possibly acting through a ciliary-type Opsin, Pdu-c-Opsin2, with a Lambdamax of approximately 490 nm. We show that a Go-Opsin is necessary for the shadow reflex in a marine annelid, describing a functional example for a peripherally expressed photoreceptor, and suggesting that, in different species, distinct Opsins contribute to varying degrees to the shadow reflex.

Jon Vidar Helvik - One of the best experts on this subject based on the ideXlab platform.

  • environmental population and life stage plasticity in the visual system of atlantic cod
    The Journal of Experimental Biology, 2018
    Co-Authors: Ragnhild Valen, Rita Karlsen, Jon Vidar Helvik
    Abstract:

    The visual system is for many fishes essential in guiding behaviors such as foraging, predator avoidance and mate choice. The marine environment is characterized by large spatiotemporal fluctuations in light intensity and spectral composition. However, visual capabilities are restricted by both space limitations set by eye size, and by the genomic content of light absorbing Opsin genes. The rich array of visual Opsins in teleosts may be used differentially to tune vision towards specific needs during ontogeny, and to changing light. Yet, to what extent visual plasticity is a pre-programmed developmental event, or is triggered by photic environment, is unclear. Our previous studies on Atlantic cod revealed an evolutionary genomic loss of UV-sensitive sws1 and red-sensitive lws Opsin families, while blue-sensitive sws2 and green-sensitive rh2 Opsins had duplicated. The current study have taken an Opsin expression approach to characterize visual plasticity in cod towards; different spectral light during the larval stage, to maturation, and extreme seasonal changes in the Barents Sea. Our data suggest that Opsin plasticity in cod larvae is controlled by developmental program rather than immediate light environment. The lack of expressional changes during maturation, suggest a less important role for visual modulation related to mate choice. Although no seasonal effects on visual Opsins were detected in migratory North East Arctic cod, the expressed Opsin subset differed from the more stationary Norwegian Coastal cod described in previous studies. Interestingly these data provide the first indications of a population difference in actively used visual Opsins associated with cod ecotypes.

  • Molecular Evidence that Only Two Opsin Subfamilies, the Blue Light- (SWS2) and Green Light-Sensitive (RH2), Drive Color Vision in Atlantic Cod (Gadus morhua)
    PLoS ONE, 2014
    Co-Authors: Ragnhild Valen, Øyvind Drivenes, Rolf B. Edvardsen, Anne Mette Søviknes, Jon Vidar Helvik
    Abstract:

    Teleosts show a great variety in visual Opsin complement, due to both gene duplication and gene loss. The repertoire ranges from one subfamily of visual Opsins (scotopic vision) including rod Opsin only retinas seen in many deep-sea species to multiple subfamilies of visual Opsins in some pelagic species. We have investigated the Opsin repertoire of Atlantic cod (Gadus morhua) using information in the recently sequenced cod genome and found that despite cod not being a deep sea species it lacks visual subfamilies sensitive towards the most extreme parts of the light spectra representing UV and red light. Furthermore, we find that Atlantic cod has duplicated paralogs of both blue-sensitive SWS2 and green-sensitive RH2 subfamilies, with members belonging to each subfamily linked in tandem within the genome (two SWS2-, and three RH2A genes, respectively). The presence of multiple cone Opsin genes indicates that there have been duplication events in the cod ancestor SWS2 and RH2 Opsins producing paralogs that have been retained in Atlantic. Our results are supported by expressional analysis of cone Opsins, which further revealed an ontogenetic change in the array of cone Opsins expressed. These findings suggest life stage specific programs for Opsin regulation which could be linked to habitat changes and available light as the larvae is transformed into an early juvenile. Altogether we provide the first molecular evidence for color vision driven by only two families of cone Opsins due to gene loss in a teleost.

  • Topography of different photoreceptor cell types in the larval retina of Atlantic halibut (Hippoglossus hippoglossus)
    The Journal of Experimental Biology, 2001
    Co-Authors: Jon Vidar Helvik, Øyvind Drivenes, Torstein Harboe
    Abstract:

    SUMMARY The identities of single cone cells in the retina of Atlantic halibut (Hippoglossus hippoglossus) larvae were studied by in situ hybridisation using RNA probes for the five different halibut Opsins. Four different cone Opsins (ultraviolet-, blue-, green- and red-sensitive) are expressed in Atlantic halibut at the end of the yolk-sac period, whereas rod Opsin is expressed later in development. Photoreceptor cells expressing ultraviolet-sensitive Opsin are found only in the ventral retina, presumably to optimise detection of the downwelling ultraviolet light. The majority of the photoreceptors (approximately 90%) in the retina express green-sensitive Opsin and its distribution shows no regional differences. In contrast, blue- and red-sensitive Opsins are expressed much less frequently (in approximately 10% of photoreceptors), although these two Opsins are also found over the entire retina. The expression patterns of the different visual pigments indicate some form of mosaic expression in the single-coned larval retina, and this is reminiscent of the square mosaic expression found in post-metamorphic Atlantic halibut. These findings suggest plasticity in green-Opsin-expressing cells during development, resulting in a square mosaic expression pattern.

Rosalie K. Crouch - One of the best experts on this subject based on the ideXlab platform.

  • coexpression of three Opsins in cone photoreceptors of the salamander ambystoma tigrinum
    The Journal of Comparative Neurology, 2014
    Co-Authors: Tomoki Isayama, Masahiro Kono, Rosalie K. Crouch, Ying Chen, Eduard Fabre, Michael Slavsky, Willem J Degrip, Jian Xing, Clint L Makino
    Abstract:

    Although more than one type of visual Opsin is present in the retina of most vertebrates, it was thought that each type of photoreceptor expresses only one Opsin. However, evidence has accumulated that some photoreceptors contain more than one Opsin, in many cases as a result of a developmental transition from the expression of one Opsin to another. The salamander UV-sensitive (UV) cone is particularly notable because it contains three Opsins (Makino and Dodd [1996] J Gen Physiol 108:27-34). Two Opsin types are expressed at levels more than 100 times lower than the level of the primary Opsin. Here, immunohistochemical experiments identified the primary component as a UV cone Opsin and the two minor components as the short wavelength-sensitive (S) and long wavelength-sensitive (L) cone Opsins. Based on single-cell recordings of 156 photoreceptors, the presence of three components in UV cones of hatchlings and terrestrial adults ruled out a developmental transition. There was no evidence for multiple Opsin types within rods or S cones, but immunohistochemistry and partial bleaching in conjunction with single-cell recording revealed that both single and double L cones contained low levels of short wavelength-sensitive pigments in addition to the main L visual pigment. These results raise the possibility that coexpression of multiple Opsins in other vertebrates was overlooked because a minor component absorbing at short wavelengths was masked by the main visual pigment or because the expression level of a component absorbing at long wavelengths was exceedingly low.

  • In vitro assays of rod and cone Opsin activity: retinoid analogs as agonists and inverse agonists.
    Methods in Molecular Biology, 2010
    Co-Authors: Masahiro Kono, Rosalie K. Crouch
    Abstract:

    Upon absorption of a photon, the bound 11-cis-retinoid isomerizes to the all-trans form resulting in a protein conformational change that enables it to activate its G protein, transducin, to begin the visual signal transduction cascade. The native ligand, 11-cis-retinal, acts as an inverse agonist to both the apoproteins of rod and cone visual pigments (Opsins); all-trans-retinal is an agonist. Truncated analogs of retinal have been used to characterize structure–function relationships with rod Opsins, but little has been done with cone Opsins. Activation of transducin by an Opsin is one method to characterize the conformational state of the Opsin. This chapter describes an in vitro transducin activation assay that can be used with cone Opsins to determine the degree to which different ligands can act as an agonist or an inverse agonist to gain insight into the ligand-binding pocket of cone Opsins and differences between the different classes of Opsins. The understanding of the effects of ligands on cone Opsin activity can potentially be applied to future therapeutic agents targeting Opsins.

  • Rpe65-/- and Lrat-/- mice: comparable models of leber congenital amaurosis.
    Investigative Opthalmology & Visual Science, 2008
    Co-Authors: Jie Fan, Jeanne M Frederick, Wolfgang Baehr, Baerbel Rohrer, Rosalie K. Crouch
    Abstract:

    PURPOSE. The Rpe65 -/- mouse, used as a model for Leber congenital amaurosis, has slow rod degeneration and rapid cone loss, presumably because of the mistrafficking of cone Opsins. This animal does not generate 11-cis retinal, and both cone loss and rod response are restored by 11-cis retinal administration. Similarly, the Lrat -/- mouse does not produce 11-cis retinal. The authors sought to determine whether the same effects on rod and cone Opsins in the Rpe65 -/- mouse are also present in the Lrat -/- mouse, thereby establishing that these changes can be attributed to the lack of 11-cis retinal rather than to some unknown function of RPE65. METHODS. Rod and cone Opsins were localized by immunohistochemical methods. Functional Opsin levels were determined by regeneration with 11-cis retinal. IsorhodOpsin levels were determined from pigment extraction. Opsin phosphorylation was determined by mass spectrometry. RESULTS. Rods in both models degenerated slowly. Regenerable rod Opsin levels were similar over the 6-month time course investigated, rod Opsin was phosphorylated at a low level (approximately 10%), and minimal 9-cis retinal was generated by a nonphotic process, giving a trace light response. In both models, S-Opsin and M/L-Opsin failed to traffic to the cone outer segments appropriately, and rapid cone degeneration occurred. Cone Opsin mistrafficking in both models was arrested on 11-cis retinal administration. CONCLUSIONS. These data show that the Lrat -/- and Rpe65 -/- mice are comparable models for studies of Leber congenital amaurosis and that the destructive cone Opsin mistrafficking is caused by the lack of 11-cis retinal.

  • rpe65 and lrat mice comparable models of leber congenital amaurosis
    Investigative Ophthalmology & Visual Science, 2008
    Co-Authors: Jie Fan, Jeanne M Frederick, Wolfgang Baehr, Baerbel Rohrer, Rosalie K. Crouch
    Abstract:

    PURPOSE. The Rpe65 -/- mouse, used as a model for Leber congenital amaurosis, has slow rod degeneration and rapid cone loss, presumably because of the mistrafficking of cone Opsins. This animal does not generate 11-cis retinal, and both cone loss and rod response are restored by 11-cis retinal administration. Similarly, the Lrat -/- mouse does not produce 11-cis retinal. The authors sought to determine whether the same effects on rod and cone Opsins in the Rpe65 -/- mouse are also present in the Lrat -/- mouse, thereby establishing that these changes can be attributed to the lack of 11-cis retinal rather than to some unknown function of RPE65. METHODS. Rod and cone Opsins were localized by immunohistochemical methods. Functional Opsin levels were determined by regeneration with 11-cis retinal. IsorhodOpsin levels were determined from pigment extraction. Opsin phosphorylation was determined by mass spectrometry. RESULTS. Rods in both models degenerated slowly. Regenerable rod Opsin levels were similar over the 6-month time course investigated, rod Opsin was phosphorylated at a low level (approximately 10%), and minimal 9-cis retinal was generated by a nonphotic process, giving a trace light response. In both models, S-Opsin and M/L-Opsin failed to traffic to the cone outer segments appropriately, and rapid cone degeneration occurred. Cone Opsin mistrafficking in both models was arrested on 11-cis retinal administration. CONCLUSIONS. These data show that the Lrat -/- and Rpe65 -/- mice are comparable models for studies of Leber congenital amaurosis and that the destructive cone Opsin mistrafficking is caused by the lack of 11-cis retinal.

  • Palmitylation of cone Opsins.
    Vision Research, 2006
    Co-Authors: Zsolt Ablonczy, Masahiro Kono, Daniel R. Knapp, Rosalie K. Crouch
    Abstract:

    Palmitylation is a widespread modification in G-protein-coupled receptors and often a dynamic process. In rhodOpsins, palmitylation is static on C322/C323. Red/green (M/LWS) cone Opsins have no cysteines at corresponding positions and no palmitylation. Blue (SWS2) cone Opsins have a single corresponding cysteine and mass spectrometric analysis showed partial palmitylation of salamander SWS2 cone Opsin. Ultraviolet (SWS1) cone Opsins have one corresponding cysteine, but only unpalmitylated Opsin was observed for mouse and salamander. The results show that the static palmitylation found on rhodOpsin is not found on cone Opsins and suggest the possibility of an unidentified role for Opsin palmitylation in cones.

Karen L. Carleton - One of the best experts on this subject based on the ideXlab platform.

  • Multiple trans QTL and one cis-regulatory deletion are associated with the differential expression of cone Opsins in African cichlids
    BMC Genomics, 2018
    Co-Authors: Sri Pratima Nandamuri, Matthew A. Conte, Karen L. Carleton
    Abstract:

    Background Dissecting the genetic basis of phenotypic diversity is one of the fundamental goals in evolutionary biology. Despite growing evidence for gene expression divergence being responsible for the evolution of complex traits, knowledge about the proximate genetic causes underlying these traits is still limited. African cichlids have diverse visual systems, with different species expressing different combinations of seven cone Opsin genes. Using Opsin expression variation in African cichlids as a model for gene expression evolution, this study aims to investigate the genetic architecture of Opsin expression divergence in this group. Results Results from a genome-wide linkage mapping on the F_2 progeny of an intergeneric cross, between two species with differential Opsin expression show that Opsins in Lake Malawi cichlids are controlled by multiple quantitative trait loci (QTLs). Most of these QTLs are located in trans to the Opsins except for one cis -QTL for SWS1 on LG17. A closer look at this major QTL revealed the presence of a 691 bp deletion in the promoter of the SWS1 Opsin (located 751 bp upstream of the start site) that is associated with a decrease in its expression. Phylogenetic footprinting indicates that the region spanning the deletion harbors a microRNA miR-729 and a conserved non-coding element (CNE) that also occurs in zebrafish and other teleosts. This suggests that the deletion might contain ancestrally preserved regulators that have been tuned for SWS1 gene expression in Lake Malawi. While this deletion is not common, it does occur in several other species within the lake. Conclusions Differential expression of cichlid Opsins is associated with multiple overlapping QTL, with all but one in trans to the Opsins they regulate. The one cis -acting factor is a deletion in the promoter of the SWS1 Opsin, suggesting that ancestral polymorphic deletions may contribute to cichlid’s visual diversity. In addition to expanding our understanding of the molecular landscape of Opsin expression in African cichlids, this study sheds light on the molecular mechanisms underlying phenotypic variation in natural populations.

  • determination of the genetic architecture underlying short wavelength sensitivity in lake malawi cichlids
    Journal of Heredity, 2017
    Co-Authors: Sri Pratima Nandamuri, Brian E Dalton, Karen L. Carleton
    Abstract:

    African cichlids are an exemplary system to study organismal diversity and rapid speciation. Species differ in external morphology including jaw shape and body coloration, but also differ in sensory systems including vision. All cichlids have 7 cone Opsin genes with species differing broadly in which Opsins are expressed. The differential Opsin expression results in closely related species with substantial differences in spectral sensitivity of their photoreceptors. In this work, we take a first step in determining the genetic basis of Opsin expression in cichlids. Using a second generation cross between 2 species with different Opsin expression patterns, we make a conservative estimate that short wavelength Opsin expression is regulated by a few loci. Genetic mapping in 96 F2 hybrids provides clear evidence of a cis-regulatory region for SWS1 Opsin that explains 34% of the variation in expression between the 2 species. Additionally, in situ hybridization has shown that SWS1 and SWS2B Opsins are coexpressed in individual single cones in the retinas of F2 progeny. Results from this work will contribute to a better understanding of the genetic architecture underlying Opsin expression. This knowledge will help answer long-standing questions about the evolutionary processes fundamental to Opsin expression variation and how this contributes to adaptive cichlid divergence.

  • spectral tuning by Opsin coexpression in retinal regions that view different parts of the visual field
    Proceedings of The Royal Society B: Biological Sciences, 2014
    Co-Authors: Brian E Dalton, Ellis R. Loew, Thomas W. Cronin, Karen L. Carleton
    Abstract:

    Vision frequently mediates critical behaviours, and photoreceptors must respond to the light available to accomplish these tasks. Most photoreceptors are thought to contain a single visual pigment, an Opsin protein bound to a chromophore, which together determine spectral sensitivity. Mechanisms of spectral tuning include altering the Opsin, changing the chromophore and incorporating pre-receptor filtering. A few exceptions to the use of a single visual pigment have been documented in which a single mature photoreceptor coexpresses Opsins that form spectrally distinct visual pigments, and in these exceptions the functional significance of coexpression is unclear. Here we document for the first time photoreceptors coexpressing spectrally distinct Opsin genes in a manner that tunes sensitivity to the light environment. Photoreceptors of the cichlid fish, Metriaclima zebra , mix different pairs of Opsins in retinal regions that view distinct backgrounds. The mixing of visual pigments increases absorbance of the corresponding background, potentially aiding the detection of dark objects. Thus, Opsin coexpression may be a novel mechanism of spectral tuning that could be useful for detecting prey, predators and mates. However, our calculations show that coexpression of some Opsins can hinder colour discrimination, creating a trade-off between visual functions.

  • Rod and Cone Opsin Families Differ in Spectral Tuning Domains but Not Signal Transducing Domains as Judged by Saturated Evolutionary Trace Analysis
    Journal of Molecular Evolution, 2005
    Co-Authors: Karen L. Carleton, Tyrone C Spady, Rick H. Cote
    Abstract:

    The visual receptor of rods and cones is a covalent complex of the apoprotein, Opsin, and the light-sensitive chromophore, 11-cis-retinal. This pigment must fulfill many functions including photoactivation, spectral tuning, signal transmission, inactivation, and chromophore regeneration. Rod and cone photoreceptors employ distinct families of Opsins. Although it is well known that these Opsin families provide unique ranges in spectral sensitivity, it is unclear whether the families have additional functional differences. In this study, we use evolutionary trace (ET) analysis of 188 vertebrate Opsin sequences to identify functionally important sites in each Opsin family. We demonstrate the following results. (1) The available vertebrate Opsin sequences produce a definitive description of all five vertebrate Opsin families. This is the first demonstration of sequence saturation prior to ET analysis, which we term saturated ET (SET). (2) The cone Opsin classes have class-specific sites compared to the rod Opsin class. These sites reside in the transmembrane region and tune the spectral sensitivity of each Opsin class to its characteristic wavelength range. (3) The cytoplasmic loops, primarily responsible for signal transmission and inactivation, are essentially invariant in rod versus cone Opsins. This indicates that the electrophysiological differences between rod and cone photoreceptors cannot be ascribed to differences in the protein interaction regions of the Opsins. SET shows that chromophore binding and regeneration are the only aspects of Opsin structure likely to have functionally significant differences between rods and cones, whereas excitatory and adaptational properties of the Opsin families appear to be functionally invariant.