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PubMed2003

Coexpression of two visual pigments in a photoreceptor causes an abnormally broad spectral sensitivity in the eye of the butterfly Papilio xuthus.

The compound eye of the butterfly Papilio xuthus consists of three different types of ommatidia, each containing nine photoreceptor cells (R1-R9). We have found previously that the R5-R8 photoreceptors of type II ommatidia coexpress two different mRNAs, encoding opsins of green- and orange-red-absorbing visual pigments (Kitamoto et al., 1998). Do these cells contain two functionally distinct visual pigments? First, we identified the sensitivity spectrum of these photoreceptors by using combined intracellular recording and dye injection. We thus found that the R5-R8 of type II ommatidia have a characteristic sensitivity spectrum extending over an excessively broad spectral range, from the violet to the red region; the photoreceptors are therefore termed broadband photoreceptors. The spectral shape was interpreted with a computational model for type II ommatidia, containing a UV visual pigment in cells R1 and R2, two green visual pigments in cells R3 and R4, a far-UV-absorbing screening pigment (3-hydroxyretinol) in the distal part of the ommatidium, and a red-screening pigment that surrounds the rhabdom. The modeling suggests that both visual pigments in the R5-R8 photoreceptors participate in phototransduction. This work provides the first compelling evidence that multiple visual pigments participate in phototransduction in single invertebrate photoreceptors.

Animals↗
PubMed2005

Rod and cone opsin families differ in spectral tuning domains but not signal transducing domains as judged by saturated evolutionary trace analysis.

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.

Amino Acid Sequence↗
PubMed1999

Direct visual resolution of gene copy number in the human photopigment gene array.

PURPOSE: To visualize by direct fluorescent in situ hybridization the entire human visual pigment gene array on single X-chromosome fibers and to compare the results with values obtained by other molecular techniques. METHODS: The size of the opsin gene array on the X-chromosome in eight male subjects was investigated by (i) direct visual in situ hybridization (DIRVISH) on elongated DNA fibers: (ii) quantitation of genomic restriction fragments after Southern blot hybridization; (iii) quantitation of restriction fragment length polymorphism after PCR amplification (PCR/RFLP), and (iv) sizing of NotI fragments by pulsed field gel electrophoresis and Southern blot detection. Each male subject's color vision was assessed by Rayleigh matches on a Nagel Type 1 anomaloscope. RESULTS: The number of genes resolved by the DIRVISH protocol, which ranges from 1 to 6, agrees exactly with the gene array sizes obtained in the same male subjects from pulsed field gel electrophoresis, but differs from the estimates derived from the commonly used indirect Southern blot hybridization and PCR/RFLP quantitation methods. In particular, the PCR/RFLP method overestimates the copy number in all but the smallest arrays. CONCLUSIONS: Visualization of the X-chromosome opsin gene array by DIRVISH provides a new, direct method for obtaining exact copy numbers and helps to resolve the controversy about the range and the average visual pigment gene number in the human population in favor of smaller average array sizes.

Blotting, Southern↗
PubMed2003

Intraspecific variation in retinal cone distribution in the bluefin killifish, Lucania goodei.

Studies of visual ecology have typically focused on differences among species while paying less attention to variation among populations and/or individuals. Here, we show that the relative abundance of UV, violet, yellow, and red cones varies between two populations of bluefin killifish, Lucania goodei. Animals from a spring population (high-transmission UV/blue light) have a higher frequency of UV and violet cones and a lower frequency of yellow and red cones than animals from a swamp population (low-transmission UV/blue light). Visual sensitivity does not vary significantly between the populations, but spring animals tend to be more sensitive in the UV/blue wavelengths (360-440 nm) and less sensitive in longer wavelengths (560-600 nm) than swamp animals. The results have two important implications. First, the tight conservation of functional regions of opsin genes across taxa does not imply that visual systems are constrained in their evolution; differential sensitivity can arise through differential expression of cone classes within the retina. Second, intraspecific visual signals in this species may evolve to maximize contrast between the signaler and the background (as opposed to brightness); males with blue anal fins are most abundant in swamp habitats where animals express fewer UV and violet cones.

Dose-Response Relationship, Radiation↗
PubMedDate not supplied

Evaluation of S-cone sensitivity in reattached macula following macula-off retinal detachment surgery.

PURPOSE: To investigate the recovery of short-wavelength sensitivity in patients who had undergone successful reattachment of a rhegmatogenous retinal detachment with macular involvement. METHODS: Postoperative assessment of the visual acuity and the visual fields by standard achromatic automated perimetry (SAP), and short-wavelength automated perimetry (SWAP, Humphrey visual field analyzer; macula test pattern) was performed on 12 patients after the macula was reattached. The follow-up period was up to 12 months. RESULTS: The visual acuity and SAP sensitivity recovered rapidly after reattachment, with further moderate improvements up to 6 months after reattachment. The improvements stabilized by 9 to 12 months. The SWAP sensitivities improved more slowly than the visual acuity or SAP sensitivities, but they continued to improve even when visual acuity or SAP sensitivities had stabilized. CONCLUSION: We conclude that measurement of the sensitivities of the short-wavelength-sensitive cones (S-cones) with SWAP may be a sensitive method to evaluate the visual recovery of the reattached macula following macula-off retinal detachment.

Adult↗
PubMedDate not supplied

Evidence for the prolonged photoactivated lifetime of an analogue visual pigment containing 11-cis 9-desmethylretinal.

Following bright flashes, rod photoreceptors exhibit a period of photocurrent saturation that increases linearly with the logarithm of flash intensity. In a recent report, Pepperberg et al. (1992) presented evidence that the slope of the function relating the saturation period (T) to the natural logarithm of flash intensity (ln If) represents the exponential lifetime (tau) of photoactivated visual pigment: tau = delta T/delta [ln If]. In salamander rods, 11-cis 9-desmethylretinal combines with opsin to form 9-desmethyl rhodopsin. Dim flash responses mediated by this analogue visual pigment exhibited slow recovery kinetics relative to those of native pigment (Corson et al., 1991). This observation raises the hypothesis that the physiological lifetime of photoactivated 9-desmethyl rhodopsin is substantially longer than that of native visual pigment. To test this hypothesis, we have examined the relation between the period of photocurrent saturation and flash intensity in salamander rods containing a mixture of the two pigments. Brief stimuli at two widely separated wavelengths (440 and 640 nm) elicited saturating photocurrent responses that were preferentially mediated by 9-desmethyl rhodopsin or residual native pigment, respectively. Plots of T vs. ln If revealed a linear increase in the period of response saturation over a large range of saturating intensities at both wavelengths. However, the slope of the relation between T and ln If with 440-nm flashes was more than twice as large (4.1 +/- 0.5 s, n = 5) as that measured with 640-nm flashes (1.7 +/- 0.4 s). For rods subjected only to bleaching of the native pigment, or to bleaching and resensitization with 11-cis retinal, the slope of the relation between T and ln If remained independent of wavelength and indistinguishable from that of native pigment in unbleached cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2002

Developmental changes in the cone visual pigments of black bream Acanthopagrus butcheri.

The spectral absorption characteristics of the visual pigments in the photoreceptors of the black bream Acanthopagrus butcheri Munro (Sparidae, Teleostei), were measured using microspectrophotometry. A single cohort of fish aged 5-172 days post-hatch (dph), aquarium-reared adults and wild-caught juveniles were investigated. During the larval stage and in juveniles younger than 100 dph, two classes of visual pigment were found, with wavelengths of maximum absorbance (lambda(max)) at approximately 425 nm and 535 nm. Following double cone formation, from 40 dph onwards, the short wavelength-sensitive pigment was recorded in single cones and the longer wavelength-sensitive pigment in double cones. From 100 dph, a gradual shift in the lambda(max) towards longer wavelengths was observed in both cone types. By 160 dph, and in adults, all single cones had a lambda(max) at approximately 475 nm while the lambda(max) in double cones ranged from 545 to 575 nm. The relationships between the lambda(max) and the ratio of bandwidth:lambda(max), for changes in either chromophore or opsin, were modelled mathematically for the long-wavelength-sensitive visual pigments. Comparing our data with the models indicated that changes in lambda(max) were not mediated by a switch from an A(1) to A(2) chromophore, rather a change in opsin expression was most likely. The shifts in the lambda(max) of the visual pigments occur at a stage when the juvenile fish begin feeding in deeper, tanninstained estuarine waters, which transmit predominantly longer wavelengths, so the spectral sensitivity changes may represent an adaptation by the fish to the changing light environment.

Animals↗
PubMedDate not supplied

Temporal and spatial patterns of opsin gene expression in zebrafish (Danio rerio).

In zebrafish, the first class of cone photoreceptor to become morphologically distinct is the ultraviolet-sensitive short single cone, at 4 days postfertilization, whereas the last class, the red- and green-sensitive double cone, becomes distinct at 10 days postfertilization. We have examined the time course of visual pigment gene expression in zebrafish using whole-mount in situ hybridization. Within the retina, opsins may be detected as early as 40 h postfertilization with the ultraviolet and rod visual pigments being expressed before the blue- (48 h) and red- (60 h) sensitive pigments. In the pineal, red-sensitive opsin is expressed at 48 h postfertilization. Visual pigment expression provides a useful tool for investigations of early cell fate in zebrafish.

Animals↗
PubMed1983

Rhodopsin chromophore exchanges among opsin molecules in the dark.

Turnover of rhodopsin chromophore in vertebrate visual cells has been explored by light microscope autoradiography (LMARG) and radiobiochemical techniques. Retinol-binding protein (RBP) was isolated from human serum, its native ligand removed and replaced with [3H]-retinol. After reconstitution, [3H]-retinol-RBP was reassociated with prealbumin (PA), and the protein complex injected intravenously into dark-adapted animals. After selected intervals in the dark, animals were killed, and ocular tissues dissected under infrared illumination. Eyecups from frogs and mice were fixed (4 C) and after in situ reduction of the chromophore-protein linkage of rhodopsin with borane dimethyl amine (BDMA), processed histologically to retain lipids, or alternatively to extract them with chloroform-methanol (C-M), and LMARG performed. Rhodopsin was purified from detergent-solubilized mouse retinas by Concanavalin A (Con A) affinity chromatography and analyzed for radioactivity. Autoradiographic labeling of frog rod outer segments (ROS) was first detectable at 1 day postinjection, increasing over the duration of the experiment. At all times, label was distributed throughout the organelle in a diffuse pattern, although in certain cases a band of silver grains was also evident at the proximal end of the ROS, the site of new membrane assembly. Similar autoradiographic patterns were noted in mouse rods, although the kinetics of labeling differed in certain respects. In biochemical experiments, incorporation of [3H]-retinol into mouse rhodopsin was seen to occur very rapidly (less than 30 min), without an appreciable lag period. We interpret the diffuse labeling of ROS to result from an exchange in the dark of [3H]-vitamin A aldehyde for unlabeled opsin-bound chromophore, whereas the formation of a reaction band no doubt reflects the continual renewal of ROS membrane occurring in the dark. With respect to the former, the turnover of chromophore qualitatively resembles that found for membrane fatty acids.

Animals↗
PubMed1996

Blue and ultraviolet light-absorbing opsin from the retinal pigment epithelium.

The retinal pigment epithelium (RPE) contains an abundant opsin that is distinct from rhodopsin and cone visual pigments and is able to bind the retinaldehyde chromophore. The putative retinal G protein-coupled receptor (RGR) was isolated in digitonin solution from bovine RPE microsomes and copurified consistently with a minor 34-kDa protein. The absorption spectrum of RGR revealed endogenous pH-sensitive absorbance in the blue and near-ultraviolet regions of light. Membrane-bound RGR was incubated with exogenously added all-trans-retinal and formed two long-lived pH-dependent photopigments with absorption maxima of 469 +/- 2.4 and 370 +/- 7.3 nm. The effects of hydrogen ion concentration suggest that the blue and near-UV photopigments are tautomeric forms of RGR, in which an all-trans-retinal Schiff base is protonated or unprotonated, respectively. The RPE pigment was also demonstrable by its reactivity to hydroxylamine in the dark. The retinaldehyde-RGR conjugate at neutral pH favors the near-UV pigment and is a novel light-absorbing opsin in the vertebrate eye.

Animals↗
PubMed1998

Genetic analyses of the green visual pigments of rabbit (Oryctolagus cuniculus) and rat (Rattus norvegicus).

We have cloned and sequenced the green opsin genes of rabbit and rat. When these genes are expressed in cultured cells and reconstituted with 11-cis retinal, the resulting visual pigments have wavelengths of maximal absorption (lambdamax) of 509nm. These blue-shifted lambdamax values are fully explained by their aa composition A, Y, Y, T, and S at sites 180, 197, 277, 285, and 308, respectively. The inference on the ancestral pigment sequences strongly suggests that the rabbit and rat (and mouse) green pigments attained the extant lambdamax values independently, mainly by the single aa replacement A308S.

Amino Acid Sequence↗
PubMed1995

Bovine opsin gene expression exhibits a late fetal to adult regulatory switch.

Rates of bovine photoreceptor gene transcription, as measured by nuclear run-on assays, exhibit gene-specific patterns of regulation. Here we investigate initiation and elongation in nuclear run-on assays with the use of sarkosyl to further understand the nature of these gene-specific elements. Opsin transcription, alone among several genes tested, proved sarkosyl-sensitive. This sensitivity is maximal in adult retinas, with inhibition first detected in mid-third trimester fetal retinas. Therefore, opsin transcription appears to involve different regulatory elements in adult and fetal retinas, implying a fetal to adult switch in the control of opsin gene expression. Although this regulatory switch is initially activated at a time when the fetal outer nuclear layer of the retina first achieves adult-like morphology, further maturation of opsin regulation takes place postpartum since levels of sarkosyl sensitivity are almost 5-fold greater in adult retinas compared to the 7.5 month fetus. We also show that the sarkosyl-induced reduction of opsin transcription is not due to prevention of de novo RNA polymerase II initiation in the run-on reaction, suggesting the detergent alters a positive-acting, postinitiation component of the transcriptional apparatus. Since levels of opsin transcription with sarkosyl are similar to those of the other visual transduction genes with or without sarkosyl, this detergent-sensitive transcriptional component appears to account for the singularly high, gene-specific rate of opsin transcription in retinal photoreceptor cells.

Aging↗
PubMed1996

Molecular evolution of retinal and nonretinal opsins.

Vision and the circadian rhythms of various biological functions are triggered by phototransduction. The retinal and nonretinal (pineal gland-specific) opsins are traced back to a single common ancestor. Evolutionary analyses of these opsins identify amino acid changes that are potentially important in the regulation of wavelength absorption of photosensitive molecules-visual pigments. Such theoretical predictions can now be tested experimentally using site-directed mutagenesis; expressing the mutagenized opsins in tissue culture cells, reconstituting with 11-cis retinal, and measuring the absorption spectra of the regenerated visual pigments.

Animals↗
PubMed2006

Central projections of melanopsin-expressing retinal ganglion cells in the mouse.

A rare type of ganglion cell in mammalian retina is directly photosensitive. These novel retinal photoreceptors express the photopigment melanopsin. They send axons directly to the suprachiasmatic nucleus (SCN), intergeniculate leaflet (IGL), and olivary pretectal nucleus (OPN), thereby contributing to photic synchronization of circadian rhythms and the pupillary light reflex. Here, we sought to characterize more fully the projections of these cells to the brain. By targeting tau-lacZ to the melanopsin gene locus in mice, ganglion cells that would normally express melanopsin were induced to express, instead, the marker enzyme beta-galactosidase. Their axons were visualized by X-gal histochemistry or anti-beta-galactosidase immunofluorescence. Established targets were confirmed, including the SCN, IGL, OPN, ventral division of the lateral geniculate nucleus (LGv), and preoptic area, but the overall projections were more widespread than previously recognized. Targets included the lateral nucleus, peri-supraoptic nucleus, and subparaventricular zone of the hypothalamus, medial amygdala, margin of the lateral habenula, posterior limitans nucleus, superior colliculus, and periaqueductal gray. There were also weak projections to the margins of the dorsal lateral geniculate nucleus. Co-staining with the cholera toxin B subunit to label all retinal afferents showed that melanopsin ganglion cells provide most of the retinal input to the SCN, IGL, and lateral habenula and much of that to the OPN, but that other ganglion cells do contribute at least some retinal input to these targets. Staining patterns after monocular enucleation revealed that the projections of these cells are overwhelmingly crossed except for the projection to the SCN, which is bilaterally symmetrical.

Animals↗
PubMed2006

Quantitative analysis of OCT characteristics in patients with achromatopsia and blue-cone monochromatism.

PURPOSE: To quantify optical coherence tomography (OCT) images of the central retina in patients with blue-cone monochromatism (BCM) and achromatopsia (ACH) compared with healthy control individuals. METHODS: The study included 15 patients with ACH, 6 with BCM, and 20 control subjects. Diagnosis of BCM and ACH was established by visual acuity testing, morphologic examination, color vision testing, and Ganzfeld ERG recording. OCT images were acquired with the Stratus OCT 3 (Carl Zeiss Meditec AG, Oberkochen, Germany). Foveal OCT images were analyzed by calculating longitudinal reflectivity profiles (LRPs) from scan lines. Profiles were analyzed quantitatively to determine foveal thickness and distances between reflectivity layers. RESULTS: Patients with ACH and BCM had a mean visual acuity of 20/200 and 20/60, respectively. Color vision testing results were characteristic of the diseases. The LRPs of control subjects yielded four peaks (P1-P4), presumably representing the RPE (P1), the ovoid region of the photoreceptors (P2), the external limiting membrane (ELM) (P3), and the internal limiting membrane (P4). In patients with ACH, P2 was absent, but foveal thickness (P1-P4) did not differ significantly from that in the control subjects (187 +/- 20 vs. 192 +/- 14 microm, respectively). The distance from P1 to P3 did not differ significantly (78 +/- 10 vs. 82 +/- 5 microm) between ACH and controls subjects. In patients with BCM, P3 was lacking, and P2 advanced toward P1 compared with the control subjects (32 +/- 6 vs. 48 +/- 4 microm). Foveal thickness (153 +/- 16 microm) was significantly reduced compared with that in control subjects and patients with ACH. CONCLUSIONS: Quantitative OCT image analysis reveals distinct patterns for controls subjects and patients with ACH and BCM, respectively. Quantitative analysis of OCT imaging can be useful in differentiating retinal diseases affecting photoreceptors. Foveal thickness is similar in both normal subjects and patients with ACH but is decreased in patients with BCM.

Adult↗
PubMed2000

Development of stable cell lines expressing high levels of point mutants of human opsin for biochemical and biophysical studies.

Stable HEK293S cell lines expressing high levels of normal and mutant human rod opsins were generated. Cellular expression is uniform across a population. Secondary overexpression of the same opsin transgene linked to a different drug selection marker (hygro(R)) yielded expression clones with increased opsin levels compared to the neo(R) parent strain. Wild-type and mutant human opsins regenerate with native chromophore and demonstrate spectroscopic properties consistent with previous reports of bovine opsin mutants. HEK293S cells can be grown in larger scale suspension culture (10(9) cells/liter) or in roller bottles (10(8) cells/bottle) to facilitate milligram-order preparations of purified pigments. These cell lines should be useful in any time-resolved spectroscopic or biophysical experiments that require either uniform cellular levels of opsin protein or regenerable pigment, or large amounts of purified visual pigment. They should also be useful in experiments where uniform constitutive levels of a given mutant human visual pigment are needed in each cell. These and similar types of constitutive or inducible cell lines may also be useful for studying mechanisms of human cell death that occur by mutations in the human rod opsin gene.

Amino Acid Substitution↗
PubMed1996

Two opsins from the compound eye of the crab Hemigrapsus sanguineus

The primary structures of two opsins from the brachyuran crab Hemigrapsus sanguineus were deduced from the cDNA nucleotide sequences. Both deduced proteins were composed of 377 amino acid residues and included residues highly conserved in visual pigments of other species, and the proteins were 75 % identical to each other. The distribution of opsin transcripts in the compound eye, determined by in situ hybridization, suggested that the mRNAs of the two opsins were expressed simultaneously in all of the seven retinular cells (R1-R7) forming the main rhabdom in each ommatidium. Two different visual pigments may be present in one photoreceptor cell in this brachyuran crab. The spectral sensitivity of the compound eye was also determined by recording the electroretinogram. The compound eye was maximally sensitive at about 480 nm. These and previous findings suggest that both opsins of this brachyuran crab produce visual pigments with maximal absorption in the blue-green region of the spectrum. Evidence is presented that crustaceans possess multiple pigment systems for vision.

Journal Article↗
PubMed2005

Opsin activation of transduction in the rods of dark-reared Rpe65 knockout mice.

Rpe65 knockout mice (Rpe65-/-) are unable to synthesize the visual pigment chromophore 11-cis retinal; however, if these animals are reared in complete darkness, the rod photoreceptors accumulate a small amount of 9-cis retinal and its corresponding visual pigment isorhodopsin. Suction-electrode recording of single rods from dark-reared Rpe65-/- mice showed that the rods were about 400 times less sensitive than wild-type control rods and that the maximum responses were much smaller in amplitude. Spectral sensitivity measurements indicated that Rpe65-/- rod responses were generated by isorhodopsin rather than rhodopsin. Sensitivity and pigment concentration were compared in the same mice by measuring light responses from rods of one eye and pigment concentration from the retina of the other eye. Retinas had 11-35% of the normal pigment level, but the rods were of the order of 20-30 times less sensitive than could be accounted for by the loss in quantum catch. This extra desensitization must be caused by opsin-dependent activation of the visual cascade, which leads to a state equivalent to light adaptation in the dark-adapted rod. By comparing the sensitivity of dark-reared Rpe65-/- rods to that produced in normal rods by background light, we estimate that Rpe65-/- opsin is of the order of 2.5x10(-5) as efficient in activating transduction as photoactivated rhodopsin (Rh*) in WT mice. Dark-reared Rpe65-/- rods are less desensitized than rods from cyclic light-reared Rpe65-/- mice, have about 50% more photocurrent and degenerate at a slower rate. Retinas sectioned after 9 months in darkness show a larger number of photoreceptor nuclei in dark-reared animals than in cyclic light-reared animals, though both have fewer nuclei than in cyclic light-reared wild-type retinas. Both also have shorter outer segments and a lower free-Ca2+ concentration. These experiments provide the first quantitative measurement of opsin activation in physiologically responding mammalian rods.

Animals↗