Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “visual opsins”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 343 records · Page 19Linked to original sources
PubMed1985

all-trans-retinoids and dihydroretinoids as probes of the role of chromophore structure in rhodopsin activation.

The absorption of a photon of light by rhodopsin results in the cis to trans isomerization of the 11-cis-retinal Schiff base chromophore. In the studies reported here, an attempt is made to determine the mechanism of the energization of rhodopsin as it relates to the chemistry of the isomerization process and the geometrical state of the chromophore. Studies were performed with vitamin A analogues to probe this mechanism. Both 11-cis-7,8-dihydroretinal and 9-cis-7,8-dihydroretinal form bleachable pigments when combined with opsin. Photolysis of these pigments in the presence of G-protein results in the activation of the latter as revealed by its GTPase activity. Phosphodiesterase is also activated when it is included in the incubation. Therefore, the possibility that rhodopsin is energized by mechanisms involving photochemically induced charge transfer from the protonated Schiff base to the beta-ionone ring can be discarded. Further studies were conducted with all-trans-vitamin A derivatives to determine if these compounds can form the GTPase-activating state R*, a situation that is possible, in principle, by microscopic reversibility. Neither all-trans-retinal nor its oxime, when incubated with bovine opsin in the dark, caused activation of the GTPase, requiring at least a 5 kcal/mol energy gap between them. Furthermore, stoichiometric adducts of all-trans-retinoids and opsin were also unable to mediate activation of the GTPase. Since both all-trans-15,16-dihydroretinylopsin and all-trans-retinoylopsin possess an all-trans-retinoid permanently adducted to opsin, it can be concluded that the all-trans-retinoid chromophore-opsin linkage may be necessary but not sufficient to achieve activation of the visual pigment.

Animals↗
PubMed2005

Molecular characterization and expression of the UV opsin in bumblebees: three ommatidial subtypes in the retina and a new photoreceptor organ in the lamina.

Ultraviolet-sensitive photoreceptors have been shown to be important for a variety of visual tasks performed by bees, such as orientation, color and polarization vision, yet little is known about their spatial distribution in the compound eye or optic lobe. We cloned and sequenced a UV opsin mRNA transcript from Bombus impatiens head-specific cDNA and, using western blot analysis, detected an eye protein band of approximately 41 kDa, corresponding to the predicted molecular mass of the encoded opsin. We then characterized UV opsin expression in the retina, ocelli and brain using immunocytochemistry. In the main retina, we found three different ommatidial types with respect to the number of UV opsin-expressing photoreceptor cells, namely ommatidia containing two, one or no UV opsin-immunoreactive cells. We also observed UV opsin expression in the ocelli. These results indicate that the cloned opsin probably encodes the P350 nm pigment, which was previously characterized by physiological recordings. Surprisingly, in addition to expression in the retina and ocelli, we found opsin expression in different parts of the brain. UV opsin immunoreactivity was detected in the proximal rim of the lamina adjacent to the first optic chiasm, which is where studies in other insects have found expression of proteins involved in the circadian clock, period and cryptochrome. We also found UV opsin immunoreactivity in the core region of the antennal lobe glomeruli and different clusters of perikarya within the protocerebrum, indicating a putative function of these brain regions, together with the lamina organ, in the entrainment of circadian rhythms. In order to test for a possible overlap of clock protein and UV opsin spatial expression, we also examined the expression of the period protein in these regions.

Amino Acid Sequence↗
PubMed1975

Photoreceptor processes: some problems and perspectives.

Visual photoreceptors from both vertebrates and invertebrates are characterized by extensive elaboration of membrane which contains visual pigment (rhodopsin). Visual pigments in all phyla examined are chemically similar: the chromophore is 11-cis retinaldehyde attached by an aldimine linkage (Schiff base) to a membrane protein, opsin. The effect of light is to isomerize the chromophore to the all-trans configuration. Beyond these fundamental similarities, several specific areas are discussed in which variations and differences appear. (1) Light causes vertebrate visual pigments to bleach, liberating the chromophore. Most invertebrate visual pigments do not bleach in the light, but instead form a thermally stable metarhodopsin, with the chromophore in the all-trans configuration still attached to the opsin. (2) In the disk membranes of vertebrate rod and cone outer segments, the rhodopsin molecules are oriented with their chromophores nearly coplanar with the disks. Within this plane, however, both rotational and translational diffusion are possible. In the microvillar membranes of arthropod and cephalopod rhabdoms, on the other hand, the situation is less clear. There is evidence for some preferential orientation of chromophores that implies restrictions on Brownian rotation. (3) In the outer segments of vertebrate receptors, absorption of light by rhodopsin causes the plasma membrane to hyperpolarize due to a decrease in sodium conductance, possibly mediated by calcium ions. In most invertebrate photoreceptors, light causes a depolarization due to an increase in conductance, principally to sodium ions. A subsequent entry of calcium causes a partial repolarization of the membrane, due to a decrease in sodium conductance. (4) For vertebrate receptors, log threshold is directly proportional to the fraction of rhodopsin bleached (Dowling-Rushton relationship). The proportionality constant varies in different preparations from less than four to more than 30, and the physical basis for the relationship is unknown. For invertebrates, by contrast, the dependence of sensitivity on rhodopsin concentration is much less dramatic and may well depend simply on the probability of quantum catch. (5) In most species, vertebrate and invertebrate, the accumulation of photoproduct probably has no effect on membrane conductance, but several possible exceptions exist. (6) Photoregeneration of rhodopsin from metarhodopsin is likely an important mechanism of recovery in certain arthropods such as diurnal insects, but dark mechanisms of recovery also exist in all phyla. In no single case are they adequately understood.

Adaptation, Ocular↗
PubMed2005

Mix and match color vision: tuning spectral sensitivity by differential opsin gene expression in Lake Malawi cichlids.

Cichlid fish of the East African Rift Lakes are renowned for their diversity and offer a unique opportunity to study adaptive changes in the visual system in rapidly evolving species flocks. Since color plays a significant role in mate choice, differences in visual sensitivities could greatly influence and even drive speciation of cichlids. Lake Malawi cichlids inhabiting rock and sand habitats have significantly different cone spectral sensitivities. By combining microspectrophotometry (MSP) of isolated cones, sequencing of opsin genes, and spectral analysis of recombinant pigments, we have established the cone complements of four species of Malawi cichlids. MSP demonstrated that each of these species predominately expresses three cone pigments, although these differ between species to give three spectrally different cone complements. In addition, rare populations of spectrally distinct cones were found. In total, seven spectral classes were identified. This was confirmed by opsin gene sequencing, expression, and in vitro reconstitution. The genes represent the four major classes of cone opsin genes that diverged early in vertebrate evolution. All four species possess a long-wave-sensitive (LWS), three spectrally distinct green-sensitive (RH2), a blue-sensitive (SWS2A), a violet-sensitive (SWS2B), and an ultraviolet-sensitive (SWS1) opsin. However, African cichlids determine their spectral sensitivity by differential expression of primarily only three of the seven available cone opsin genes. Phylogenetic analysis suggests that all percomorph fish have similar potential.

Animals↗
PubMed2005

Novel NR2E3 mutations (R104Q, R334G) associated with a mild form of enhanced S-cone syndrome demonstrate compound heterozygosity.

PURPOSE: We investigated the ophthalmic features of a mild form of enhanced S-cone syndrome (ESCS) in a 33-year-old Japanese female proband and 3 unaffected family members. A genetic analysis was performed. DESIGN: Genetic and observational case study. METHODS: Fundus examinations, optical coherence tomography (OCT), Goldmann visual field (VF) perimetry, color vision tests, spectral sensitivity, and full-field and spectral electroretinography (ERG) were performed. Mutation screening of the NR2E3 gene, which encodes a photoreceptor-specific orphan nuclear receptor, was performed with polymerase chain reaction amplification and direct sequencing. MAIN OUTCOME MEASURES: Mutations in the NR2E3 gene, fundus photographs, OCT images, VFs, spectral sensitivity, and ERG findings. RESULTS: The diagnosis of ESCS was made based on the distinctive spectral ERG findings: hypersensitivity to blue stimuli and hyposensitivity to red stimuli. The proband had good visual acuity, normal color vision, good central VFs, and nearly normal spectral sensitivity. Funduscopy showed degenerative lesions in the vascular arcades to the midperipheral retina. The OCT images showed a morphologically normal macular thickness. In the full-field ERG, low amplitudes of rod b-waves were detected. Waveforms between rod-plus-cone and cone ERGs were very similar. Mutation analysis identified 2 novel compound heterozygous missense mutations, p.R104Q and p.R334G, which reside in the DNA-binding domain (DBD) and ligand-binding domain (LBD), respectively. The unaffected parents carried one of these mutations each, consistent with autosomal recessive transmission. CONCLUSIONS: Our study suggests that the expression of these 2 mutants of NR2E3, acting as a dimer, is correlated with a mild form of ESCS in that full foveal function and retinal laminar structure are maintained, and certain rod responses are present. This may be explained by the possibility that the heterodimers encoded by the 2 mutant alleles retain certain NR2E3 functions through the respective intact DBD and LBD.

Adult↗
PubMed1999

Photoreceptor autophagy: effects of light history on number and opsin content of degradative vacuoles.

PURPOSE: To investigate whether regulation of rhodopsin levels as a response to changed lighting environment is performed by autophagic degradation of opsin in rod inner segments (RISs). METHODS: Groups of albino rats were kept in 3 lux or 200 lux. At 10 weeks of age, one group was transferred from 3 lux to 200 lux, another group was switched from 200 lux to 3 lux, and two groups remained in their native lighting (baselines). Rats were killed at days 1, 2, and 3 after switching. Another group was switched from 3 lux to 200 lux, and rats were killed at short intervals after the switch. Numbers of autophagic vacuoles (AVs) in RISs were counted, and immunogold labeling was performed for opsin and ubiquitin in electron microscopic sections. RESULTS: The number of AVs increased significantly after switching from 3 lux to 200 lux at days 1 and 2 and declined at day 3, whereas the reverse intensity change did not cause any increase. Early time points after change from 3 lux to 200 lux showed a significant increase of AVs 2 and 3 hours after switching. Distinct opsin label was observed in AVs of rats switched to 200 lux. Ubiquitin label was present in all investigated specimens and was also seen in AVs especially in 200-lux immigrants. CONCLUSIONS: Earlier studies had shown that an adjustment to new lighting environment is performed by changes in rhodopsin levels in ROSs. Autophagic degradation of opsin or rhodopsin may subserve, at least in part, the adaptation to abruptly increased habitat illuminance by removing surplus visual pigment.

Adaptation, Ocular↗
PubMed1989

Transplantation of photoreceptors to light-damaged retina.

We investigated the possibility of reconstructing light-damaged retinas by photoreceptor transplantation. The outer nuclear layer containing the photoreceptor cells was eliminated in adult albino rat retinas by exposure to constant high-level illumination. Photoreceptors for transplantation were harvested from neonatal rats using a novel isolation technique that maintained the cellular organization of the outer nuclear layer. Transplantation was accomplished using a transcorneal approach to the subretinal space, which minimized trauma to the eye. The retina reattached to the back of the eye with transplanted photoreceptors interposed between the retina and the overlying tissues. Prelabelling with fluorescent dye enabled positive identification of the transplanted cells. The transplanted photoreceptors appeared to survive transplantation for at least 6 weeks and were immunohistochemically reactive for opsin. The antibody staining for opsin identifies the transplanted cells as photoreceptors and indicates that they are still capable of producing visual pigment and therefore may have the capacity to transduce light. These findings indicate that photoreceptors can be transplanted to form a new outer nuclear layer in a damaged mature retina.

Animals↗
PubMed1990

Phototransduction: different mechanisms in vertebrates and invertebrates.

The photoreceptor cells of invertebrate animals differ from those of vertebrates in morphology and physiology. Our present knowledge of the different structures and transduction mechanisms of the two animal groups is described. In invertebrates, rhodopsin is converted by light into a meta-rhodopsin which is thermally stable and is usually re-isomerized by light. In contrast, photoisomerization in vertebrates leads to dissociation of the chromophore from opsin, and a metabolic process is necessary to regenerate rhodopsin. The electrical signals of visual excitation have opposite character in vertebrates and invertebrates: the vertebrate photoreceptor cell is hyperpolarized because of a decrease in conductance and invertebrate photoreceptors are depolarized owing to an increase in conductance. Single-photon-evoked excitatory events, which are believed to be a result of concerted action (the opening in invertebrates and the closing in vertebrates) of many light-modulated cation channels, are very different in terms of size and time course of photoreceptors for invertebrates and vertebrates. In invertebrates, the single-photon events (bumps) produced under identical conditions vary greatly in delay (latency), time course and size. The multiphoton response to brighter stimuli is several times as long as a response evoked by a single photon. The single-photon response of vertebrates has a standard size, a standard latency and a standard time course, all three parameters showing relatively small variations. Responses to flashes containing several photons have a shape and time scale that are similar to the single-photon-evoked events, varying only by an amplitude scaling factor, but not in latency and time course. In both vertebrate and invertebrate photoreceptors the single-photon-evoked events become smaller (in size) and faster owing to light adaptation. Calcium is mainly involved in these adaptation phenomena. All light adaptation in vertebrates is primarily, or perhaps exclusively, attributable to calcium feedback. In invertebrates, cyclic AMP (cAMP) is apparently another controller of sensitivity in dark adaptation. The interaction of photoexcited rhodopsin with a G-protein is similar in both vertebrate and invertebrate photoreceptors. However, these G-proteins activate different photoreceptor enzymes (phosphodiesterases): phospholipase C in invertebrates and cGMP phosphodiesterase in vertebrates. In the photoreceptors of vertebrates light leads to a rapid hydrolysis of cGMP which results in closing of cation channels. At present, the identity of the internal terminal messenger in invertebrate photoreceptors is still unsolved.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1994

Parallel regulation of fetal gene expression in different photoreceptor cell types.

Transcriptional induction for multiple bovine rod-specific photoreceptor genes has been shown to coincide with the first emergence of rod outer segments (two-thirds gestation) suggesting a coordinate regulation of these genes. Since cone visual transduction proteins are encoded for by distinct genes and mammalian cone cell genesis has been found to precede rod cell genesis it is important to determine when induction of photoreceptor-specific gene expression occurs in cone cells and how the timing of this event compares to that in rods. RNase protection assays specific for each cell type-specific gene were used to compare mRNA levels for bovine rod and blue cone gamma subunits of cGMP phosphodiesterase and rhodopsin and red cone opsin from before transcriptional induction (4 months gestation) to the adult. Both pairs of rod and cone visual transduction mRNAs exhibit indistinguishable transcriptional induction points at around 6 months of gestation. Before this time, transcripts of all four genes are present at low, but detectable levels. Thus, although rod and cone cells are distinct cell types and cone cells may be committed well before rod cells early in development, during the final trimester when elaboration of outer segments begins, there appears to be a coordinated regulation of both rod- and cone-specific visual transduction genes.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1992

Rod opsin cDNA sequence from the sand goby (Pomatoschistus minutus) compared with those of other vertebrates.

The absorbance spectra of rods from the sand goby were measured by using microspectrophotometry. Analysis of the averaged spectra shows that the rod visual pigment has a maximum absorbance (lambda max) at approximately 501 nm. A sand goby retinal cDNA library was constructed and then screened with a partial sand goby rod opsin clone obtained by the polymerase chain reaction (PCR). The screening of the library yielded a full length rod opsin clone. The cDNA sequence and deduced amino acid sequence of this clone are compared with those of other vertebrate rod opsins.

Amino Acid Sequence↗
PubMed2003

Diminished pupillary light reflex at high irradiances in melanopsin-knockout mice.

In the mammalian retina, a small subset of retinal ganglion cells (RGCs) are intrinsically photosensitive, express the opsin-like protein melanopsin, and project to brain nuclei involved in non-image-forming visual functions such as pupillary light reflex and circadian photoentrainment. We report that in mice with the melanopsin gene ablated, RGCs retrograde-labeled from the suprachiasmatic nuclei were no longer intrinsically photosensitive, although their number, morphology, and projections were unchanged. These animals showed a pupillary light reflex indistinguishable from that of the wild type at low irradiances, but at high irradiances the reflex was incomplete, a pattern that suggests that the melanopsin-associated system and the classical rod/cone system are complementary in function.

Adaptation, Ocular↗
PubMed1997

Control of Drosophila retinoid and fatty acid binding glycoprotein expression by retinoids and retinoic acid: northern, western and immunocytochemical analyses.

In Drosophila, thorough retinoid deprivation is possible, optimizing investigation of the effects of vitamin A metabolites and retinoic acid on the visual system. Retinoids had been found to control transcription and translation of Drosophila's opsin gene. To follow this line of inquiry, we examined the effect of retinoids on the translation and transcription of a Drosophila Retinoid and Fatty Acid Binding Glycoprotein. Western blots showed that this protein is high in retinoid replete flies and low in deprived flies. Flies grown on media capable of activating the opsin gene's transcription and which contain alternate transcription activators including retinoic acid yielded extracts containing significant amounts of Retinoid and Fatty Acid Binding Glycoprotein. Immunocytochemistry confirmed its absence in deprived flies and its presence in flies reared or replaced on these diverse media containing retinoids or general nutrients. Immunocytochemistry localized Retinoid and Fatty Acid Binding Glycoprotein to the Semper (cone) cells and the intraommatidial matrix (the interphotoreceptor matrix of the ommatidium). Positive staining of Semper cells in mutants of the opsin gene and a mutant lacking receptors suggests that Retinoid and Fatty Acid Binding Glycoprotein does not depend on presence of opsin and that it is not synthesized in receptor cells respectively. Northern blots demonstrated greatly diminished mRNA for Retinoid and Fatty Acid Binding Glycoprotein in flies grown on deprivation food relative to flies grown on normal food. Although the synthesis of Retinoid and Fatty Acid Binding Glycoprotein does not require chromophore precursors as does that of opsin, the control of Retinoid and Fatty Acid Binding Glycoprotein and opsin transcription by retinoids including retinoic acid might very well be the same. Our results suggest that Retinoid and Fatty Acid Binding Glycoprotein may be involved in retinoid transport. Also, Semper cells may be analogous to vertebrate retinal pigment epithelium in retinoid metabolism and/or delivery.

Animals↗
PubMed1994

Two different visual pigments in one retinal cone cell.

The retina of the mouse, rabbit, and guinea pig is divided into a superior area dominated by green-sensitive (M) cones and an inferior area in which cones possess practically only short wavelength-sensitive (S) photopigments. The present study shows that the transitional zone between these retinal areas is populated by cones labeled by both the M and S cone photopigment-specific antibodies COS-1 and OS-2. It is concluded that the overwhelming majority of the transitional cones express both visual pigments. A small population of the transitional cones was strongly labeled exclusively by OS-2 (genuine S cones). The results indicate that, in contrast to the generally accepted idea of one visual pigment per one cone cell, cones of certain mammalian species can express different opsins simultaneously under natural conditions. We speculate that the coexpression may be due to the overlapping of regulatory factors determining the M and S fields.

Animals↗
PubMed2000

Visual pigment reconstitution in intact goldfish retina using synthetic retinaldehyde isomers.

A protocol has been developed for reconstituting visual pigments in intact retinae by delivering synthetic isomers of retinal incorporated in phospholipid vesicles. Calibration curves have been constructed relating the lambda(max) of the native porphyropsins (visual pigments based on 11-cis 3-dehydroretinal) of the rods and four spectral classes of cone in the goldfish, and the equivalent photosensitive pigments regenerated from 11-cis retinal (rhodopsins) and the commercially available isomer, 9-cis retinal (isorhodopsins). The relationship between the lambda(max) of rhodopsins and isorhodopsins appears to be linear, such that the difference in lambda(max) changes sign at about 380 nm. We therefore conclude that the protocol for reconstituting visual pigments with 9-cis retinal is suitable for all classes of vertebrate opsin-based photopigments.

Animals↗
PubMed1992

Defective colour vision associated with a missense mutation in the human green visual pigment gene.

All red/green colour vision defects described so far have been associated with gross rearrangements within the red/green opsin gene array (Xq28). We now describe a male with severe deuteranomaly without such a rearrangement. A substitution of a highly conserved cysteine by arginine at position 203 in the green opsins presumably accounted for his colour vision defect. Surprisingly, this mutation was fairly common (2%) in the population but apparently was not always expressed. In analogy with nonexpression of some 5'green-red hybrid genes in persons with normal colour vision, we suggest that failure of manifestation occurs when the mutant gene is located at a distal (3') position among several green opsin genes. This mutation might also predispose to certain X-linked retinal dystrophies.

Amino Acid Sequence↗
PubMed1996

High-level inducible expression of visual pigments in transfected cells.

A method for high-level expression of a functionally active, recombinant human red cone opsin was developed by adding the coding sequence for the C-terminal epitope of bovine rhodopsin onto the C terminus of the cone opsin and cloning the resulting construct into the vector pMEP4 beta. The recombinant pMEP4 beta vector was transfected stably into 293-EBNA cells, and expression of the cone opsin was induced by the addition of CdCl2 into the medium. The recombinant cone opsin was reconstituted with 11-cis retinal and purified by immunoaffinity chromatography. Spectral analysis prior to and following photobleaching confirmed its identity as a red cone opsin. The protein was targeted to the cell membrane and activated bovine transducin.

Animals↗
PubMed1994

The primary structure of mantid opsin.

The sequence encoding opsin from the mantid Sphodromantis sp. has been determined by dideoxynucleotide sequencing of PCR products from a cDNA derived from eye cup tissue. The 376-amino-acid (aa) residues show approx. 56% identity and 85% similarity to known insect opsins (Drosophila melanogaster and Calliphora erythrocephala). The predicted protein structure, based on the hydropathy profile and placement of key aa residues, reveals a seven-transmembrane structure typical of a rhodopsin. Unlike the previously characterised insect visual pigments which have 3-hydroxy retinal in their binding sites, mantid rhodopsin contains 11-cis retinal. Comparison of transmembrane sequences from the opsin family was performed in order to identify any specific aa substitutions which are able to account for the selection of retinal or its 3-hydroxy derivative by insect opsins.

Amino Acid Sequence↗
PubMed2005

Molecular properties of rod and cone visual pigments from purified chicken cone pigments to mouse rhodopsin in situ.

We have investigated the molecular properties of rod and cone visual pigments to elucidate the differences in the molecular mechanism(s) of the photoresponses between rod and cone photoreceptor cells. We have found that the cone pigments exhibit a faster pigment regeneration and faster decay of meta-II and meta-III intermediates than the rod pigment, rhodopsin. Mutagenesis experiments have revealed that the amino acid residues at positions 122 and 189 in the opsins are the determinants for these differences. In order to study the relationship between the molecular properties of visual pigments and the physiology of rod photoreceptors, we used mouse rhodopsin as a model pigment because, by gene-targeting, the spectral properties of the pigment can be directly correlated to the physiology of the cells. In the present paper, we summarize the spectroscopic properties of cone pigments and describe our studies with mouse rhodopsin utilizing a high performance charge coupled device (CCD) spectrophotometer.

Animals↗