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Maureen Neitz - One of the best experts on this subject based on the ideXlab platform.

  • rod and Cone driven responses in mice expressing human l Cone Pigment
    Journal of Neurophysiology, 2015
    Co-Authors: Tina I Tsai, Jay Neitz, Maureen Neitz, Jenny Atorf, Jan Kremers
    Abstract:

    The mouse is commonly used for studying retinal processing, primarily because it is amenable to genetic manipulation. To accurately study photoreceptor driven signals in the healthy and diseased re...

  • gene therapy for red green colour blindness in adult primates
    Nature, 2009
    Co-Authors: Katherine Mancuso, Matthew C. Mauck, Jay Neitz, James A. Kuchenbecker, William W. Hauswirth, Thomas B Connor, Maureen Neitz
    Abstract:

    Red-green colour blindness, which results from the absence of either the long- (L) or middle- (M) wavelength-sensitive visual photoPigments, is the most common single locus genetic disorder. Here, the possibility of curing colour blindness using gene therapy was explored in experiments on adult monkeys that had been colour blind since birth. A third type of Cone Pigment was added to dichromatic retinas, providing the receptoral basis for trichromatic colour vision. This opened a new avenue to explore the requirements for establishing the neural circuits for a new dimension of colour sensation. Classic visual deprivation experiments1 have led to the expectation that neural connections established during development would not appropriately process an input that was not present from birth. Therefore, it was believed that treatment of congenital vision disorders would be ineffective unless administered to the very young. Here, however, addition of a third opsin in adult red-green colour-deficient primates was sufficient to produce trichromatic colour vision behaviour. Thus, trichromacy can arise from a single addition of a third Cone class and it does not require an early developmental process. This provides a positive outlook for the potential of gene therapy to cure adult vision disorders.

  • Adaptive optics retinal imaging reveals S-Cone dystrophy in tritan color-vision deficiency
    Journal of the Optical Society of America A, 2007
    Co-Authors: Rigmor C. Baraas, K L Gunther, David H. Foster, Joseph Carroll, D.r. Williams, M. Chung, Maureen Neitz
    Abstract:

    Tritan color-vision deficiency is an autosomal dominant disorder associated with mutations in the short-wavelength-sensitive- (S-) Cone-Pigment gene. An unexplained feature of the disorder is that individuals with the same mutation manifest different degrees of deficiency. To date, it has not been possible to examine whether any loss of S-Cone function is accompanied by physical disruption in the Cone mosaic. Two related tritan subjects with the same novel mutation in their S-Cone-opsin gene, but different degrees of deficiency, were examined. Adaptive optics was used to obtain high-resolution retinal images, which revealed distinctly different S-Cone mosaics consistent with their discrepant phenotypes. In addition, a significant disruption in the regularity of the overall Cone mosaic was observed in the subject completely lacking S-Cone function. These results taken together with other recent findings from molecular genetics indicate that, with rare exceptions, tritan deficiency is progressive in nature.

  • A novel mutation in the short-wavelength-sensitive Cone Pigment gene associated with a tritan color vision defect.
    Visual neuroscience, 2006
    Co-Authors: K L Gunther, Jay Neitz, Maureen Neitz
    Abstract:

    Inherited tritan color vision deficiency is caused by defects in the function of the short-wavelength-sensitive (S) Cones. This heterozygous group of disorders has an autosomal dominant pattern of inheritance. Amino acid variations of the S Cone opsin are rare and all that have been identified thus far are associated with inherited tritan color vision defects. Here we report the identification of a 30-year-old male who made errors on standard color vision tests consistent with the presence of a mild tritan color vision deficiency. We tested the hypothesis that his color vision impairment was due to a mutation in the S Cone photoPigment gene. He was found to be heterozygous for a mutation that caused the amino acid proline to be substituted in place of a highly conserved leucine at amino acid position 56 in the S Cone opsin. This mutation was absent in 564 S Cone photoPigment genes from 282 subjects who did not make tritan errors. Thus, we conclude that this mutation disrupts the normal function of S Cones.

  • Polymorphism of visual Pigment genes in the muriqui (Primates, Atelidae)
    Molecular ecology, 2005
    Co-Authors: Mauricio Talebi, Maureen Neitz, T. R. Pope, Erin R. Vogel, Nathaniel J. Dominy
    Abstract:

    Colour vision varies within the family Atelidae (Primates, Platyrrhini), which consists of four genera with the following cladistic relationship: { Alouatta [ Ateles ( Lagothrix and Brachyteles )]}. Spider monkeys ( Ateles ) and woolly monkeys ( Lagothrix ) are characteristic of platyrrhine monkeys in possessing a colour vision polymorphism. The polymorphism results from allelic variation of the single-locus middle-to-long wavelength (M/L) Cone opsin gene on the X-chromosome. The presence in the population of alleles coding for different M/L photoPigments results in a variety of colour vision phenotypes. Such a polymorphism is absent in howling monkeys ( Alouatta ), which, alone among platyrrhines, acquired uniform trichromatic vision similar to that of Old World monkeys, apes, and humans through opsin gene duplication. Dietary and morphological similarities between howling monkeys and muriquis ( Brachyteles ) raise the possibility that the two genera share a similar form of colour vision, uniform trichromacy. Yet parsimony predicts that the colour vision of Brachyteles will resemble the polymorphism present in Lagothrix and Ateles . Here we test this assumption. We obtained DNA from the blood or faeces of 18 muriquis and sequenced exons 3 and 5 of the M/L opsin gene. Our results affirm the existence of a single M/L Cone opsin gene in the genus Brachyteles . We detected three alleles with predicted λ max values of 530, 550, and 562 nm. Two females were heterozygous and are thus predicted to have different types of M/L Cone Pigment. We discuss the implication of this result towards understanding the evolutionary ecology of trichromatic vision.

Jay Neitz - One of the best experts on this subject based on the ideXlab platform.

  • rod and Cone driven responses in mice expressing human l Cone Pigment
    Journal of Neurophysiology, 2015
    Co-Authors: Tina I Tsai, Jay Neitz, Maureen Neitz, Jenny Atorf, Jan Kremers
    Abstract:

    The mouse is commonly used for studying retinal processing, primarily because it is amenable to genetic manipulation. To accurately study photoreceptor driven signals in the healthy and diseased re...

  • lessons learned from gene therapy for color blindness in primates
    Acta Ophthalmologica, 2014
    Co-Authors: Jay Neitz
    Abstract:

    Color blindness is the most common genetic disorder. The possibility of curing color blindness using gene therapy was explored by adding a third type of Cone Pigment to dichromatic retinas of squirrel monkeys. This opened a new avenue to explore the requirements for establishing the neural circuits for a new dimension of color sensation. The addition of a third opsin in adults was sufficient to produce trichromatic color vision. Thus, trichromacy can arise from a single addition of a third Cone class in a primate and it does not require an early developmental process. This has implications for understanding how our brain processes conscious visual information and it illuminates the opportunities and limits of gene therapy for treating human vision disorders.

  • gene therapy for red green colour blindness in adult primates
    Nature, 2009
    Co-Authors: Katherine Mancuso, Matthew C. Mauck, Jay Neitz, James A. Kuchenbecker, William W. Hauswirth, Thomas B Connor, Maureen Neitz
    Abstract:

    Red-green colour blindness, which results from the absence of either the long- (L) or middle- (M) wavelength-sensitive visual photoPigments, is the most common single locus genetic disorder. Here, the possibility of curing colour blindness using gene therapy was explored in experiments on adult monkeys that had been colour blind since birth. A third type of Cone Pigment was added to dichromatic retinas, providing the receptoral basis for trichromatic colour vision. This opened a new avenue to explore the requirements for establishing the neural circuits for a new dimension of colour sensation. Classic visual deprivation experiments1 have led to the expectation that neural connections established during development would not appropriately process an input that was not present from birth. Therefore, it was believed that treatment of congenital vision disorders would be ineffective unless administered to the very young. Here, however, addition of a third opsin in adult red-green colour-deficient primates was sufficient to produce trichromatic colour vision behaviour. Thus, trichromacy can arise from a single addition of a third Cone class and it does not require an early developmental process. This provides a positive outlook for the potential of gene therapy to cure adult vision disorders.

  • A novel mutation in the short-wavelength-sensitive Cone Pigment gene associated with a tritan color vision defect.
    Visual neuroscience, 2006
    Co-Authors: K L Gunther, Jay Neitz, Maureen Neitz
    Abstract:

    Inherited tritan color vision deficiency is caused by defects in the function of the short-wavelength-sensitive (S) Cones. This heterozygous group of disorders has an autosomal dominant pattern of inheritance. Amino acid variations of the S Cone opsin are rare and all that have been identified thus far are associated with inherited tritan color vision defects. Here we report the identification of a 30-year-old male who made errors on standard color vision tests consistent with the presence of a mild tritan color vision deficiency. We tested the hypothesis that his color vision impairment was due to a mutation in the S Cone photoPigment gene. He was found to be heterozygous for a mutation that caused the amino acid proline to be substituted in place of a highly conserved leucine at amino acid position 56 in the S Cone opsin. This mutation was absent in 564 S Cone photoPigment genes from 282 subjects who did not make tritan errors. Thus, we conclude that this mutation disrupts the normal function of S Cones.

  • Cone Pigment gene expression in individual photoreceptors and the chromatic topography of the retina
    Journal of The Optical Society of America A-optics Image Science and Vision, 2000
    Co-Authors: Stephanie A Hagstrom, Maureen Neitz, Jay Neitz
    Abstract:

    Human trichromatic vision is based on three classes of Cones: L, M, and S (long-, middle-, and short-wavelength sensitive, respectively). Individuals can have more than one M and/or more than one L Pigment gene on the X chromosome along with an S Pigment gene on chromosome 7. In some people the X-linked Pigment gene array can include polymorphic variants that encode multiple, spectrally distinct Cone photoPigment subtypes. A single-cell, polymerase chain reaction approach was used to examine visual Pigment gene expression in individual human Cone cells and identify them as L or M. The ratio of L:M Pigment gene expression was assayed in homogenized retinal tissues taken from the same eyes. Results indicate that there is a close correspondence between the Cone ratio determined from counting single cells and the L:M Pigment mRNA ratio estimated from homogenized pieces of retina. The results also show that the different Pigment genes in one array are often expressed at very different levels, giving rise to unequal numbers of L and M Cones. Expression of only one photoPigment gene was detected in each Cone cell. However, individual males can have more than the classically described three spectrally distinct Cone types in their retinas.

Jeremy Nathans - One of the best experts on this subject based on the ideXlab platform.

  • proximal and distal sequences control uv Cone Pigment gene expression in transgenic zebrafish
    Journal of Biological Chemistry, 2004
    Co-Authors: Wenqin Luo, Philip M Smallwood, John Williams, Jeffrey W Touchman, Laura M Roman, Jeremy Nathans
    Abstract:

    The molecular basis of Cone photoreceptor-specific gene expression is largely unknown. In this study, we define cis-acting DNA sequences that control the cell type-specific expression of the zebrafish UV Cone Pigment gene by transient expression of green fluorescent protein transgenes following their injection into zebrafish embryos. These experiments show that 4.8 kb of 5′-flanking sequences from the zebrafish UV Pigment gene direct expression specifically to UV Cones and that this activity requires both distal and proximal sequences. In addition, we demonstrate that a proximal region located between -215 and -110 bp (with respect to the initiator methionine codon) can function in the context of a zebrafish rhodopsin promotor to convert its specificity from rod-only expression to rod and UV Cone expression. These experiments demonstrate the power of transient transgenesis in zebrafish to efficiently define cis-acting regulatory sequences in an intact vertebrate.

  • role of a locus control region in the mutually exclusive expression of human red and green Cone Pigment genes
    Proceedings of the National Academy of Sciences of the United States of America, 2002
    Co-Authors: Philip M Smallwood, Yanshu Wang, Jeremy Nathans
    Abstract:

    Trichromacy in humans and other Old World primates evolved from a dichromatic color vision system ≈30–40 million years ago. One essential part of this evolution was the duplication and divergence of sequences on the X chromosome to create the present-day red and green Cone Pigment genes. Earlier work demonstrated that a locus control region (LCR) located upstream of these genes is essential for their expression. In the present work, we have generated a variety of modified human red and green Pigment gene arrays that direct the expression of distinguishable histochemical reporters from each gene promoter. Transgenic mice carrying a single copy of each modified array were studied to define the role of three variables in producing mutually exclusive expression of red and green Pigment transgenes: the distance between the promoter and the LCR, the identity of the visual Pigment promoter, and LCR copy number. The results support a model in which the mutually exclusive expression of these genes in their respective Cone types is controlled by competition between visual Pigment promoters for pairing with the LCR, and they suggest a facile mechanism for the evolution of trichromacy after visual Pigment gene duplication.

  • mechanisms of spectral tuning in the mouse green Cone Pigment
    Proceedings of the National Academy of Sciences of the United States of America, 1997
    Co-Authors: Hui Sun, Jennifer P Macke, Jeremy Nathans
    Abstract:

    Diversification of Cone Pigment spectral sensitivities during evolution is a prerequisite for the development of color vision. Previous studies have identified two naturally occurring mechanisms that produce variation among vertebrate Pigments by red-shifting visual Pigment absorbance: addition of hydroxyl groups to the putative chromophore binding pocket and binding of chloride to a putative extracellular loop. In this paper we describe the use of two blue-shifting mechanisms during the evolution of rodent long-wave Cone Pigments. The mouse green Pigment belongs to the long-wave subfamily of Cone Pigments, but its absorption maximum is 508 nm, similar to that of the rhodopsin subfamily of visual Pigments, but blue-shifted 44 nm relative to the human red Pigment, its closest homologue. We show that acquisition of a hydroxyl group near the retinylidene Schiff base and loss of the chloride binding site mentioned above fully account for the observed blue shift. These data indicate that the chloride binding site is not a universal attribute of long-wave Cone Pigments as generally supposed, and that, depending upon location, hydroxyl groups can alter the environment of the chromophore to produce either red or blue shifts.

  • a sequence upstream of the mouse blue visual Pigment gene directs blue Cone specific transgene expression in mouse retinas
    Visual Neuroscience, 1994
    Co-Authors: Isabel M Chiu, Jeremy Nathans
    Abstract:

    A 6.4-kb sequence upstream of the mouse blue visual Pigment gene has been assayed in transgenic mice for the ability to direct cell-type-specific expression of a linked beta-galactosidase (lacZ) reporter. The construct is expressed specifically in Cone photoreceptors in three independent lines. Transgene expression is found in the developing retina on the first postnatal day, increases rapidly in subsequent days, and persists through adulthood. A gradient of transgene expression is observed across the retina, with the transgene-expressing Cones found almost exclusively in the lower retina and rarely in the upper retina, a pattern that parallels the distribution of blue Cones in the mouse retina. Double-labeling with anti-Cone Pigment antibodies shows that transgene expression is confined to blue Cones. These results imply that all of the sequence elements necessary for the control of blue Cone-specific expression are encoded within the 6.4-kb DNA fragment tested.

  • blue Cones and Cone bipolar cells share transcriptional specificity as determined by expression of human blue visual Pigment derived transgenes
    The Journal of Neuroscience, 1994
    Co-Authors: M I Chiu, Jeremy Nathans
    Abstract:

    Sequences 5' of the human blue visual Pigment gene have been assayed in transgenic mice for their ability to direct cell-type-specific expression of linked beta-galactosidase (lacZ) and placental alkaline phosphatase (P ALP1) reporters. Constructs containing either 5.4 kilobases (kb) or 0.47 kb of 5' flanking DNA direct expression exclusively to the retina. Within the retina, transgene expression is confined to blue Cones and Cone bipolar cells, as determined, respectively, by double labeling with anti-Cone Pigment antibodies and by morphologic analyses. These results imply that blue Cones and Cone bipolar cells have partially overlapping transcriptional specificities.

Vladimir J Kefalov - One of the best experts on this subject based on the ideXlab platform.

  • cis retinol oxidation regulates photoreceptor access to the retina visual cycle and Cone Pigment regeneration
    The Journal of Physiology, 2016
    Co-Authors: Shinya Sato, Vladimir J Kefalov
    Abstract:

    Key points This study explores the nature of the cis retinol that Muller cells in the retina provide to Cones for the regeneration of their visual Pigment. We report that the retina visual cycle provides Cones exclusively with 11-cis chromophore in both salamander and mouse and show that this selectivity is dependent on the 11-cis-specific cellular retinaldehyde binding protein (CRALBP) present in Muller cells. Even though salamander blue Cones and green rods share the same visual Pigment, only blue Cones but not green rods are able to dark-adapt in the retina following a bleach and to use exogenous 9-cis retinol for Pigment regeneration, suggesting that access to the retina visual cycle is Cone-specific and Pigment-independent. Our results show that the retina produces 11-cis retinol that can be oxidized and used for Pigment regeneration and dark adaptation selectively in Cones and not in rods. Abstract Chromophore supply by the retinal Muller cells (retina visual cycle) supports the efficient Pigment regeneration required for Cone photoreceptor function in bright light. Surprisingly, a large fraction of the chromophore produced by dihydroceramide desaturase-1, the putative all-trans retinol isomerase in Muller cells, appears to be 9-cis retinol. In contrast, the canonical retinal Pigment epithelium (RPE) visual cycle produces exclusively 11-cis retinal. Here, we used the different absorption spectra of 9-cis and 11-cis Pigments to identify the isoform of the chromophore produced by the visual cycle of the intact retina. We found that the spectral sensitivity of salamander and mouse Cones dark-adapted in the isolated retina (with only the retina visual cycle) was similar to that of Cones dark-adapted in the intact eye (with both the RPE and retina visual cycles) and consistent with pure 11-cis Pigment composition. However, in mice lacking the cellular retinaldehyde binding protein (CRALBP), Cone spectral sensitivity contained a substantial 9-cis component. Thus, the retina visual cycle provides Cones exclusively with 11-cis chromophore and this process is mediated by the 11-cis selective CRALBP in Muller cells. Finally, despite sharing the same Pigment, salamander blue Cones, but not green rods, recovered their sensitivity in the isolated retina. Exogenous 9-cis retinol produced robust sensitivity recovery in bleached red and blue Cones but not in red and green rods, suggesting that cis retinol oxidation restricts access to the retina visual cycle to Cones.

  • retinol dehydrogenase 8 and atp binding cassette transporter 4 modulate dark adaptation of m Cones in mammalian retina
    The Journal of Physiology, 2015
    Co-Authors: Akiko Maeda, Vladimir J Kefalov, Krzysztof Palczewski, Yoshikazu Imanishi, Alexander V Kolesnikov, Peter H Tang
    Abstract:

    KEY POINTS This study explores the molecular mechanisms that regulate the recycling of chromophore required for Pigment regeneration in mammalian Cones. We report that two chromophore binding proteins, retinol dehydrogenase 8 (RDH8) and photoreceptor-specific ATP-binding cassette transporter (ABCA4) accelerate the dark adaptation of Cones, first, directly, by facilitating the processing of chromophore in Cones, and second, indirectly, by accelerating the turnover of chromophore in rods, which is then recycled and delivered to both rods and Cones. Preventing competition with the rods by knocking out rhodopsin accelerated Cone dark adaptation, demonstrating the interplay between rod and Cone Pigment regeneration driven by the retinal Pigment epithelium (RPE). This novel interdependence of rod and Cone Pigment regeneration should be considered when developing therapies targeting the recycling of chromophore for rods, and evaluating residual Cone function should be a critical test for such regimens targeting the RPE. ABSTRACT Rapid recycling of visual chromophore and regeneration of the visual Pigment are critical for the continuous function of mammalian Cone photoreceptors in daylight vision. However, the molecular mechanisms modulating the supply of visual chromophore to Cones have remained unclear. Here we explored the roles of two chromophore-binding proteins, retinol dehydrogenase 8 (RDH8) and photoreceptor-specific ATP-binding cassette transporter 4 (ABCA4), in dark adaptation of mammalian Cones. We report that young adult RDH8/ABCA4-deficient mice have normal M-Cone morphology but reduced visual acuity and photoresponse amplitudes. Notably, the deletion of RDH8 and ABCA4 suppressed the dark adaptation of M-Cones driven by both the intraretinal visual cycle and the retinal Pigmented epithelium (RPE) visual cycle. This delay can be caused by two separate mechanisms: direct involvement of RDH8 and ABCA4 in Cone chromophore processing, and an indirect effect from the delayed recycling of chromophore by the RPE due to its slow release from RDH8/ABCA4-deficient rods. Intriguingly, our data suggest that RDH8 could also contribute to the oxidation of cis-retinoids in Cones, a key reaction of the retina visual cycle. Finally, we dissected the roles of rod photoreceptors and RPE for dark adaptation of M-Cones. We found that rods suppress, whereas RPE promotes, Cone dark adaptation. Thus, therapeutic approaches targeting the RPE visual cycle could have adverse effects on the function of Cones, making the evaluation of residual Cone function a critical test for regimens targeting the RPE.

  • Regulation of Mammalian Cone Phototransduction by Recoverin and Rhodopsin Kinase
    The Journal of biological chemistry, 2015
    Co-Authors: Keisuke Sakurai, Shahrokh C. Khani, Jeannie Chen, Vladimir J Kefalov
    Abstract:

    Cone photoreceptors function under daylight conditions and are essential for color perception and vision with high temporal and spatial resolution. A remarkable feature of Cones is that, unlike rods, they remain responsive in bright light. In rods, light triggers a decline in intracellular calcium, which exerts a well studied negative feedback on phototransduction that includes calcium-dependent inhibition of rhodopsin kinase (GRK1) by recoverin. Rods and Cones share the same isoforms of recoverin and GRK1, and photoactivation also triggers a calcium decline in Cones. However, the molecular mechanisms by which calcium exerts negative feedback on Cone phototransduction through recoverin and GRK1 are not well understood. Here, we examined this question using mice expressing various levels of GRK1 or lacking recoverin. We show that although GRK1 is required for the timely inactivation of mouse Cone photoresponse, gradually increasing its expression progressively delays the Cone response recovery. This surprising result is in contrast with the known effect of increasing GRK1 expression in rods. Notably, the kinetics of Cone responses converge and become independent of GRK1 levels for flashes activating more than ∼1% of Cone Pigment. Thus, mouse Cone response recovery in bright light is independent of Pigment phosphorylation and likely reflects the spontaneous decay of photoactivated visual Pigment. We also find that recoverin potentiates the sensitivity of Cones in dim light conditions but does not contribute to their capacity to function in bright light.

  • the mammalian Cone visual cycle promotes rapid m l Cone Pigment regeneration independently of the interphotoreceptor retinoid binding protein
    The Journal of Neuroscience, 2011
    Co-Authors: Alexander V Kolesnikov, Ryan O. Parker, Rosalie K Crouch, Peter H Tang, Vladimir J Kefalov
    Abstract:

    Rapid regeneration of the visual Pigment following its photoactivation is critical for the function of Cone photoreceptors throughout the day. Though the reactions of the visual cycle in the retinal Pigment epithelium (RPE) that recycle chromophore for rod Pigment regeneration are well characterized, the corresponding mechanisms that enable rapid regeneration of Cone Pigment are poorly understood. A key remaining question is the relative contribution of the recently discovered Cone-specific retina visual cycle and the classic RPE-dependent visual cycle to mammalian Cone Pigment regeneration. In addition, it is not clear what role, if any, the abundant interphotoreceptor retinoid-binding protein (IRBP) presumed to facilitate the traffic of chromophore, plays in accelerating mammalian Cone Pigment regeneration. To address these issues, we used transretinal recordings to evaluate M/L-Cone Pigment regeneration in isolated retinas and eyecups from control and IRBP-deficient mice. Remarkably, the mouse retina promoted M/L-Cone dark adaptation eightfold faster than the RPE. However, complete Cone recovery required both visual cycles. We conclude that the retina visual cycle is critical for the initial rapid regeneration of mouse M/L-Cone Pigment during dark adaptation, whereas the slower RPE visual cycle is required to complete the process. While the deletion of IRBP reduced the amplitude and slowed the kinetics of mouse M/L-Cone photoresponses, Cone adaptation in bright, steady light and the kinetics of Cone dark adaptation were not affected in isolated retina or in intact eyecup. Thus, IRBP does not accelerate Cone Pigment regeneration and is not critical for the function of mouse M/L-Cones in bright light.

  • physiological studies of the interaction between opsin and chromophore in rod and Cone visual Pigments
    Methods of Molecular Biology, 2010
    Co-Authors: Vladimir J Kefalov, Gordon L. Fain
    Abstract:

    Visual Pigments are photon-absorbing molecules that enable rod and Cone photoreceptors to produce electrical signals in response to light. They consist of a protein called opsin and a chromophore, in vertebrates usually 11-cis retinal. In contrast to other G protein-coupled receptors, the ligand (retinal) in the visual Pigment is covalently attached to the protein and functions both as reverse agonist in the dark (11-cis configuration), and as an agonist upon absorption of a photon (all-trans configuration). The relative ease of delivering light stimuli of known strength and duration allows the detailed characterization of the function of visual Pigments in intact photoreceptors. As a result, it is possible to use physiological measurements from single rod and Cone photoreceptors to investigate the interaction between opsin and chromophore, as well as the relation between the properties of visual Pigments and the function of photoreceptors. There are two complementary approaches to the study of visual Pigments under physiological conditions. The first involves the modification of the chromophore by substituting the native form with a retinoid analog. The second is the transgenic expression of exogenous opsin in place of, or in addition to, the native opsin. The first approach is based on the light-induced decay of the photoactivated (bleached) visual Pigment. Following photon absorption, the activated complex decays into free opsin and all-trans retinal (1). All-trans retinal is then reduced to all-trans retinol by a retinol dehydrogenase and is translocated from the photoreceptors to the retinal Pigment epithelium (RPE), where it is converted back into 11-cis retinal. The recycled 11-cis retinal is then sent back to the photoreceptors where it recombines covalently with opsin to form the ground-state visual Pigment molecule (2). However, experimental detachment of the retina from the RPE interrupts this visual cycle and prevents the recycling of chromophore and regeneration of the bleached visual Pigment. As a result, after exposure of the isolated retina or isolated photoreceptors to bright light, most of the visual Pigment is converted to free opsin which is now available for Pigment regeneration (3, 4). Application of exogenous retinoid analogs to such bleached photoreceptors allows investigating the noncovalent and covalent binding properties of chromophore to opsin by physiological techniques. The second approach is based on the tremendous progress in the techniques of molecular biology that has occurred during the last two decades, which has made possible the expression of mutant or foreign opsins in photoreceptors. These techniques allow studies of the effects of opsin mutations on the signaling properties of the visual Pigments. Furthermore, as rods and Cones use distinct forms of opsin but share the same chromophore (11-cis retinal) (5), transgenic expression of rod and Cone opsins allows examination of the differences in sensitivity and response kinetics that derive from differences in opsin structure. 1.1 Animal models Salamander (Ambystoma tigrinum) has been the animal of choice for single-cell recordings from rod and Cone photoreceptors to investigate different aspects of the interaction between retinoid and opsin using retinoid analogs (6, 7). This well-established preparation offers large and abundant rods (Fig. 1A) and Cones that can be easily dissociated and maintained in culture. Physiological recordings from salamander photoreceptors are stable over hours and allow extended and rigorous experimental protocols. This greatly facilitates experimental approaches involving replacement of the native chromophore, because the decay of photoactivated Pigments and their subsequent regeneration with exogenous chromophore can take as much as 1–2 hours. Figure 1 Suction electrode configuration for recording from single photoreceptors. A, Dissociated salamander rod with its inner segment drawn in the suction electrode and the outer segment protruding out of it. B, Mouse rod with its outer segment drawn in the ... The animals of choice for studies of transgenic opsins have been Xenopus laevis and mouse. Xenopus photoreceptors are relatively large and provide stable and reproducible recordings (8). In addition, the high yield of transgenic Xenopus animals produced by oocyte injection makes unnecessary the breeding and maintenance of transgenic lines for extended periods of time. However, the native chromophore in Xenopus (11-cis 3,4-dehydroreltinal, or A2) is slightly different from the native chromophore in most mammals, including mouse and human (11-cis retinal, or A1). As a result, Pigment properties that depend on the chromophore are likely to differ in Xenopus and mammalian photoreceptors. Another drawback of this preparation has been the lack of developed tools for deleting endogenous genes. This has limited Xenopus studies to the transgenic expression of exogenous opsin genes. Mice, on the other hand, are amenable to both transgenic and gene knockout manipulations. In addition, mouse studies can take advantage of the wide and continuously increasing number of genetically modified lines including transgenic and knockout animals. Finally, mouse rod recordings (see Fig. 1B) have been used routinely for over a decade to investigate rod phototransduction (9). Although the methods developed for regenerating salamander visual Pigments with exogenous retinoid analogs are yet to be widely used in mouse photoreceptors, recent studies indicate that the same methods might be applicable there (10–12). Finally, although mouse Cone recordings have been challenging, the recent development of genetically modified mice and the creative use of single-cell and electroretinographic (ERG) recording techniques have proven successful (13, 14). This indicates the feasibility of physiological studies of mouse Cone Pigment properties in their native environment.

Gerald H. Jacobs - One of the best experts on this subject based on the ideXlab platform.

  • Contributions of the mouse UV photoPigment to the ERG and to vision
    Documenta Ophthalmologica, 2007
    Co-Authors: Gerald H. Jacobs, Gary A Williams
    Abstract:

    The mouse retina contains two classes of Cone photoPigment with respective peak sensitivities in the middle (M) wavelengths and in the ultraviolet (UV) portion of the spectrum. To examine the functional roles subserved by the UV Pigment, the absorption of light by the mouse lens was measured and voltage versus intensity ( V –log  I ) functions were derived from recordings of the flicker ERG made under test conditions designed to maximize the relative sensitivities of the two Pigment types. These V –log  I data accurately predict ERG-based spectral sensitivity functions, but they fail to provide a similarly accurate account of behaviorally based measurements of spectral sensitivity in that the ERG spectral sensitivity function has much higher sensitivity in the UV wavelengths than does the behavioral spectral sensitivity function. The disparity between these two is argued to be a consequence of the widespread receptor co-expression of the two types of Cone Pigment in the mouse and of the pattern of retinal wiring that is thought to be characteristic of all mammalian retinas.

  • influence of Cone Pigment coexpression on spectral sensitivity and color vision in the mouse
    Vision Research, 2004
    Co-Authors: Gerald H. Jacobs, Gary A Williams, John A Fenwick
    Abstract:

    Abstract The mouse retina contains both middle-wavelength-sensitive (M) and ultraviolet-sensitive (UV) photoPigments that are coexpressed in Cones. To examine some potential visual consequences of Cone Pigment coexpression, spectral sensitivity functions were measured in mice (Mus musculus) using both the flicker electroretinogram (ERG) and behavioral discrimination tests. Discrimination tests were also employed to search for the presence of color vision in the mouse. Spectral sensitivity functions for the mouse obtained from ERG measurements and from psychophysical tests each reveal contributions from two classes of Cone having peak sensitivities (λmax) of approximately 360 and 509–512 nm. The relative contributions of the two Pigment types to spectral sensitivity differ significantly in the two types of measurements with a relationship reversed from that often seen in mammals. Mice were capable of discriminating between some pairs of spectral stimuli under test conditions where luminance-related cues were irrelevant. Since mice can make dichromatic color discriminations, their visual systems must be able to exploit differences in the spectral absorption properties among the Cones. Complete selective segregation of opsins into individual photoreceptors is apparently not a prerequisite for color vision.

  • Cone Pigment polymorphism in New World monkeys: are all Pigments created equal?
    Visual Neuroscience, 2004
    Co-Authors: Mickey P. Rowe, Gerald H. Jacobs
    Abstract:

    Most platyrrhine monkeys have a triallelic M/L opsin gene polymorphisin that underlies significant individual variations in color vision. A survey of the frequencies of these polymorphic genes Suggests that the three alleles occur with equal frequency among squirrel monkeys (subfamily Cebinae), but are not equally frequent in a number of species from the subfamily Callitrichinae. This departure from equal frequency in the Callitrichids should slightly increase the ratio of dichromats to trichromats in the population and significantly after the relative representation of the three possible dichromatic and trichromatic phenotypes. A particular feature of the inequality is that it leads to a relative increase in the number of trichromats whose M/L Pigments have the largest possible spectral separation. To assess whether these trichromatic phenotypes are equally well equipped to make relevant visual discriminations, psychophysical experiments were run on human observers. A technique involving the functional substitution of photoPigments was as used to simulate the discrimination between fruits among a back-ground of leaves. The goal of the simulation was to reproduce in the Cones of human observers excitations equivalent to those produced in monkey Cones as the animals view fruit. Three different viewing conditions were examined involving variations in the relative luminances of fruit and leaves and the spectrum of the illuminant. In all cases, performance was best for simulated trichromacies including M/L Pigments with the largest spectral separation. Thus, the inequality of opsin gene frequency in Callitrichid monkeys may reflect adaptive pressures.

  • Diurnality and Cone photoPigment polymorphism in strepsirrhines: examination of linkage in Lemur catta.
    American Journal of Physical Anthropology, 2003
    Co-Authors: Gerald H. Jacobs, Jess F. Deegan
    Abstract:

    Trichromatic color vision is routine among catarrhine primates, but occurs only as a variant form of color vision in some individuals in most platyrrhine genera. This arises from a fundamental difference in the organization of X-chromosome Cone opsin genes in these two lineages: catarrhines have two opsin genes specifying middle- and long-wavelength-sensitive Cone Pigments, while platyrrhines have only a single gene. Some female platyrrhine monkeys achieve trichromacy because of a species polymorphism that allows the possibility of different opsin gene alleles on the two X-chromosomes. Recently, a similar opsin gene polymorphism was detected in some diurnal strepsirrhines, while at the same time appearing to be absent in any nocturnal genera. The aim of this study was to assess whether Cone Pigment polymorphism is inevitably linked to diurnality in strepsirrhines. Cone photoPigments were measured in a species usually classified as diurnal, the ring-tailed lemur (Lemur catta), using electroretinogram flicker photometry, a noninvasive electrophysiological procedure. Each of 12 animals studied was found to have the same middle-wavelength Cone Pigment, with peak sensitivity at about 547 nm. In conjunction with earlier results, this implies that Cone Pigment polymorphism is unlikely to exist in this species and that, accordingly, such variation is not a consistently predictable feature of vision in diurnal strepsirrhines.

  • Cone Pigment variations in four genera of new world monkeys
    Vision Research, 2003
    Co-Authors: Gerald H. Jacobs, Jess F. Deegan
    Abstract:

    Previous research revealed significant individual variations in opsin genes and Cone photoPigments in several species of platyrrhine (New World) monkeys and showed that these in turn can yield significant variations in color vision. To extend the understanding of the nature of color vision in New World monkeys, electroretinogram flicker photometry was used to obtain spectral sensitivity measurements from representatives of four platyrrhine genera (Cebus, Leontopithecus, Saguinus, Pithecia). Animals from each genus were found to be polymorphic for middle to long-wavelength (M/L) sensitive Cones. The presence of a short-wavelength sensitive photoPigment was established as well so these animals conform to the earlier pattern in predicting that all male monkeys are dichromats while, depending on their opsin gene array, individual females can be either dichromatic or trichromatic. Across subjects a total of five different M/L Cone Pigments were inferred with a subset of three of these present in each species.