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PubMed2000

The murine cone photoreceptor: a single cone type expresses both S and M opsins with retinal spatial patterning.

Mice express S and M opsins that form visual pigments for the detection of light and visual signaling in cones. Here, we show that S opsin transcription is higher than that of M opsin, which supports ultraviolet (UV) sensitivity greater than midwavelength sensitivity. Surprisingly, most cones coexpress both S and M opsins in a common cone cell type throughout the retina. All cones express M opsin, but the levels are graded from dorsal to ventral. The levels of S opsin are relatively constant. However, in the far dorsal retina, S opsin is repressed stochastically, such that some cones express M opsin only. These observations indicate that two different mechanisms control M and S opsin expression. We suggest that a common cone type is patterned across the retinal surface to produce phenotypic cone subtypes.

Animals↗
PubMed1999

Non-visual photoreception by a variety of vertebrate opsins.

Extraretinal photoreceptors in animals are involved in a variety of physiological functions such as photo-entrainment of circadian rhythm, photoperiodicity and body colour change. We have identified pinopsin in the chicken pineal gland as a typical 'non-visual' photoreceptive molecule. Pinopsin with bound 11-cis-retinal shows a blue-light sensitivity (lambda max = 468 nm), and it may play a role in synchronizing the phase of the endogenous circadian oscillator with an environmental dark-light cycle. Pinopsin is not a unique pineal opsin in animals. In the zebrafish, we have detected expression of two rhodopsin genes, the nucleotide sequences of which are very similar but distinct from each other. One is canonical rhodopsin expressed in the retina, and the other is expressed in the pineal gland. The latter gene is widely distributed among teleosts, and we named it 'exo-rhodopsin' after extraocular rhodopsin. On the other hand, our effort to identify the 'deep brain opsin' responsible for the photoperiodic gonadal response resulted in the identification of two kinds of opsins; pinopsin in the toad anterior preoptic nucleus and rhodopsin in the pigeon lateral septum. Both of these opsins are localized in the cerebrospinal fluid-contacting neurons in the brain of the two animals. We also identified VAL opsin in zebrafish retinal horizontal cells, which have not been considered as photoreceptive cells. It has become evident that animals employ a wide variety of photoreceptive molecules for 'non-visual' purposes.

Amino Acid Sequence↗
PubMed1991

Ultrastructure and opsin immunocytochemistry of the pineal complex of the larval Arctic charr Salvelinus alpinus: a comparison with the retina.

The fine structure and opsin immunocytochemistry of the pineal and parapineal organs of the salmonid fish Salvelinus alpinus, the landlocked Arctic charr, were studied and compared with the retina in various developmental stages, from prehatching to two-month-old. For opsin immunocytochemistry two polyclonal antibovine rhodopsin and the monoclonal antichicken opsin antibodies OS-2 (detecting blue and green pigments) and OS-1 (detecting green and red pigments) were used. Histologically, the pineal organ consists of nervous tissue like that of the retina. It is composed of photoreceptor pinealocytes, which formed axon terminals containing synaptic ribbons, on the dendrites and perikarya of secondary pineal neurons. Already in prehatching embryos, both the pineal and retinal photoreceptors display well-developed outer segments and form synaptic terminals. The distal part of the pineal organ differentiates earlier than its proximal stalk. The differentiation of the retina starts centrally, but the caudal and dorsal retinae are differentiated earlier than the rostral and ventral ones. At the end of the larval period, the lateral retina is still undifferentiated. In all stages studied, (rhod)opsin immunoreactivity was found in the outer segments of the pineal organ and rod-type retinal photoreceptors, a finding speaking in favour of the presence of the opsin of a rhodopsin/porphyropsin. Cone-type retinal photoreceptors identified morphologically in the pre- and posthatching stages were opsin-immunonegative with the four primary antisera used. This result suggests that in the charr the opsins of cone visual pigments differ in their chemical nature from those of rhodopsin/porphyropsin. The parapineal organ was opsin immunonegative. Using the monoclonal antibody OS-2 opsin immunoreactivity was also detected in inner segments, perikarya, and pedicles of rod-type photoreceptors of both retina and pineal organ of embryos and 1- to 4-day-old larvae. This may indicate a high level of opsin gene expression during photoreceptor growth around hatching. The well-developed pineal organ and its opsin content are discussed in connection with the photonegative behaviour of the larval charr.

Animals↗
PubMed2001

Molecular cloning of Bombyx cerebral opsin (Boceropsin) and cellular localization of its expression in the silkworm brain.

We have cloned a cDNA for a novel opsin from the larval brain of the silkworm Bombyx mori in which the photoperiodic photoreceptor had been supposed to reside in the cephalic central nervous system (CNS). Its deduced amino acid sequence was composed of 381 amino acids and included amino acid residues highly conserved in insect visual pigments. This opsin belonged to the long wavelength photoreceptor group of insect opsins and showed the greatest degree of homology (84%) with the green visual photoreceptor in the sphingid moth. We have designated this Bombyx cerebral opsin as Boceropsin. Southern blotting experiments indicated that the Boceropsin gene is present in a single copy, and RT-PCR analysis revealed that Boceropsin mRNA is expressed in the larval brain but not in the subesophageal ganglion (Sg) or thoracic ganglion (Tg). Immunohistochemical analyses demonstrated that Boceropsin protein is present bilaterally in some defined cells localized in the brain of Bombyx larvae. This is the first report of expression of an opsin-based protein in CNS of an insect. The possibility that the Boceropsin functions as the photoperiodic receptive pigment in the silkworm is also discussed.

Amino Acid Sequence↗
PubMed2004

Differential expression of duplicated opsin genes in two eyetypes of ostracod crustaceans.

In the first molecular study of ostracod (Crustacea) vision, we present partial cDNA sequences of ostracod visual pigment genes (opsins). We found strong support for differential expression of opsins in ostracod median and compound eyes and suggest that photoreceptor specific expression may be a general phenomenon in organisms with multiple receptors. We infer that eye-specific expression predates the divergence of the two species examined, Skogsbergia lerneri and Vargula hilgendorfii, because eye-specific opsin orthologs are present in both species. We found multiple opsin loci in ostracods, estimating that at least eight are present in Skogsbergia lerneri. All opsins from both ostracod species examined are more closely related to each other than to any other known opsin sequences. Because we find no evidence for gene conversion or alternative splicing, we suggest the occurrence of many recent gene duplications. Why ostracods may have retained multiple recent opsin gene duplicates is unknown, but we discuss several possible hypotheses.

Amino Acid Sequence↗
PubMed2005

Sexual dimorphism of short-wavelength photoreceptors in the small white butterfly, Pieris rapae crucivora.

The eyes of the female small white butterfly, Pieris rapae crucivora, are furnished with three classes of short-wavelength photoreceptors, with sensitivity peaks in the ultraviolet (UV) (lambda(max) = 360 nm), violet (V) (lambda(max) = 425 nm), and blue (B) (lambda(max) = 453 nm) wavelength range. Analyzing the spectral origin of the photoreceptors, we isolated three novel mRNAs encoding opsins corresponding to short-wavelength-absorbing visual pigments. We localized the opsin mRNAs in the retinal tissue and found that each of the short-wavelength-sensitive photoreceptor classes exclusively expresses one of the opsin mRNAs. We, accordingly, termed the visual pigments PrUV, PrV, and PrB, respectively. The eyes of the male small white butterfly also use three classes of short-wavelength photoreceptors that equally uniquely express PrUV, PrV, and PrB. However, whereas the spectral sensitivities of the male photoreceptors with PrUV and PrB closely correspond to those of the female, the male photoreceptor expressing PrV has a double-peaked blue (dB) spectral sensitivity, strongly deviating from the spectral sensitivity of the female V photoreceptor. The male eyes contain a pigment that distinctly fluoresces under blue-violet as well as UV excitation light. It coexists with the dB photoreceptors and presumably acts as a spectral filter with an absorbance spectrum peaking at 416 nm. The narrow-band spectral sensitivity of the male dB photoreceptors probably evolved to improve the discrimination of the different wing colors of male and female P. rapae crucivora in the short-wavelength region of the spectrum.

Animals↗
PubMed1992

Double immunogold localization of opsin and actin in the cilium of developing mouse photoreceptors.

A 9 + 0 cilium represents the only connection between the light-sensitive rod outer segment (ROS) and the visual cell body. Differentiation of a ROS derives from a remodeling of the plasma membrane at the distal end of the cilium. Prior to this event, an actin-rich domain can be demonstrated within the distal cilium using immunocytochemical techniques. This actin is in the filamentous form and is also observed in mature photoreceptors where it has been implicated in ROS disc morphogenesis. In separate studies, the visual pigment protein, opsin, has also been localized to the distal ciliary membrane before disc synthesis begins. For the current report, we have used double label immunoelectron microscopy to investigate the presence of opsin and actin in the cilia of developing mouse photoreceptors during the period preceding ROS differentiation. Initially, we used post-embedding immunolabeling for the localization of both proteins on ultrathin sections of Lowicryl embedded tissues. However, increased sensitivity for the detection of membrane opsin was obtained when the retinas were immersion labeled prior to resin embedment. Although it remains unclear whether the appearance of ciliary opsin and actin are synchronized, the results of this study confirm that opsin and actin are each sequestered within their respective ciliary domains prior to the differentiation of an ROS.

Actins↗
PubMed2001

All-trans-retinal forms a visible-absorbing pigment with human rod opsin.

Rhodopsin activation elicits transmembrane currents due to electrostatic events associated with conformational changes. We employed the sensitive rhodopsin early receptor current approach to reevaluate whether all-trans-retinal can form a visual pigment with rod opsin apoprotein. An opsin shift above 440 nm is induced in the action spectrum of charge motions caused by visible flashes in cells expressing human rod opsin and regenerated with all-trans-retinal, compared to cells without opsin. Near-ultraviolet stimulation of opsin regenerated with all-trans-retinal promotes charge motions similar to those arising from the meta-II signaling state while photochemically regenerating a pigment with ground state charge motion properties. These results indicate that all-trans-retinal can form a visual pigment with opsin, through both protonated and unprotonated Schiff base linkages and likely within the native ligand binding pocket at lysine-296. The agonist effects of all-trans-retinal may relate to its structural accommodation within the core of opsin, similar to other G-protein-coupled receptors.

Apoproteins↗
PubMed2005

Adaptive molecular evolution in the opsin genes of rapidly speciating cichlid species.

Cichlid fish inhabit a diverse range of environments that vary in the spectral content of light available for vision. These differences should result in adaptive selective pressure on the genes involved in visual sensitivity, the opsin genes. This study examines the evidence for differential adaptive molecular evolution in East African cichlid opsin genes due to gross differences in environmental light conditions. First, we characterize the selective regime experienced by cichlid opsin genes using a likelihood ratio test format, comparing likelihood models with different constraints on the relative rates of amino acid substitution, across sites. Second, we compare turbid and clear lineages to determine if there is evidence of differences in relative rates of substitution. Third, we present evidence of functional diversification and its relationship to the photic environment among cichlid opsin genes. We report statistical evidence of positive selection in all cichlid opsin genes, except short wavelength-sensitive 1 and short wavelength-sensitive 2b. In all genes predicted to be under positive selection, except short wavelength-sensitive 2a, we find differences in selective pressure between turbid and clear lineages. Potential spectral tuning sites are variable among all cichlid opsin genes; however, patterns of substitution consistent with photic environment-driven evolution of opsin genes are observed only for short wavelength-sensitive 1 opsin genes. This study identifies a number of promising candidate-tuning sites for future study by site-directed mutagenesis. This work also begins to demonstrate the molecular evolutionary dynamics of cichlid visual sensitivity and its relationship to the photic environment.

Animals↗
PubMed1997

Primary structure of locust opsins: a speculative model which may account for ultraviolet wavelength light detection.

The sequences of two locust opsins have been determined by dideoxy nucleotide sequencing of PCR products from cDNA derived from eyecup tissue. The opsins (Lo1 and Lo2) are encoded by 381 and 380 amino acid residues, respectively, with hydropathy profiles and placement of key amino acid residues suggestive of a typical seven-transmembrane rhodopsin structure. The sequence alignment of Lo1 reveals significant homology to mantid opsin. These opsins contain retinal as their visual chromophore and have similarity to the Rh1 type sequences from Drosophila and Calliphora which use 3-hydroxy retinal. Lo2 is most closely related to the Rh3/4 type of visual pigments from Drosophila. The retinal-based opsins show reduced numbers of charged amino acids in the loop region connecting transmembrane segments V and VI compared to the 3-hydroxy retinal opsins. Sequence alignment of all the known insect visual pigments has shown that only those with maximal sensitivity in the blue/UV spectral range, Lo2 and the Rh3/4 opsins of Drosophila, have three charged amino acids in transmembrane segments II, IV and VII. The charged residue in transmembrane VII is two helical turns away from the positively charged Schiff base and could act directly as a counterion to it. From the secondary structure analysis of opsin, the two charged residues in transmembrane II and IV would be in close proximity to form a dipole. These polar motifs in Lo2 and Rh3/Rh4 could act in wavelength modulation of short wavelength sensitive pigments and substantiate the proposed external two-point charge model which accounts for the spectral sensitivity of visual pigments [Honig, B., Dinur, U., Nakanishi, K., Balogh-Nair, V., Gawinowicz, M.A. and Motto, M. (1979). Journal of the American Chemical Society, 101, 7084-7086].

Amino Acid Sequence↗
PubMed2004

Opsin expression: new mechanism for modulating colour vision.

Each cone photoreceptor in the retina responds to light in a limited range of wavelengths, giving it a spectral phenotype. This phenotype is determined by the most prevalent of the photoreceptor's visual-pigment proteins (opsins) and is assumed to remain unchanged during an animal's lifetime. Here we show that in the Pacific pink salmon, Oncorhynchus gorbuscha, single cones can switch their spectral phenotype from ultraviolet to blue by regulating the production of the appropriate opsins as the fish grow older. This photoreceptor plasticity may operate to modulate colour vision as the salmon's lifestyle changes.

Animals↗
PubMed1979

Renewal of opsin in the photoreceptor cells of the mosquito.

Mosquito rhodopsin is a digitonin-soluble membrane protein of molecular weight 39,000 daltons, as determined by sodium dodecyl sulfate gel electrophoresis. The rhodopsin undergoes a spectral transition from R515-520 to M480 after orange illumination. The visual pigment apoprotein, opsin, is the major membrane protein in the eye. Protein synthesis in the photoreceptor cells occurs in the perinuclear cytoplasm and the newly made protein is transported to the rhabdom. Light adaptation increases the rate of turnover of this rhabdomal protein. The turnover of electrophoretically isolated opsin is also stimulated by light adaptation. The changes observed in protein metabolism biochemically, are consistent with previous morphological observations of photoreceptor membrane turnover. The results agree with the hypothesis that the newly synthesized rhabdomal protein is opsin.

Adaptation, Physiological↗
PubMed1998

Switch in rod opsin gene expression in the European eel, Anguilla anguilla (L.).

The rod photoreceptors of the European eel, Anguilla anguilla (L.), alter their wavelength of maximum sensitivity (lambda max) from c.a. 523 nm to c.a. 482 nm at maturation, a switch involving the synthesis of a new visual pigment protein (opsin) that is inserted into the outer segments of existing rods. We artificially induced the switch in rod opsin production by the administration of hormones, and monitored the switch at the level of mRNA accumulation using radiolabelled oligonuleotides that hybridized differently to the two forms of eel rod opsin. The production of the deep-sea form of rod opsin was detected 6 h after the first hormone injection, and the switch in rod opsin expression was complete within four weeks, at which time only the mRNA for the deep-sea opsin was detectable in the retinal cells. It is suggested that this system could be used as a tractable model for studying the regulatory control of opsin gene expression.

Anguilla↗
PubMed1975

Isorhodopsin II: artificial photosensitive pigment formed from 9,13-dicis retinal.

We have found that in addition to the 11-cis and 9-cis isomers of retinal which are known to couple with the visual pigment apoprotein opsin to form pigments, a third isomer 9,13-dicis retinal also will form a pigment. That this isomer is indeed bound to opsin has been shown unequivocally by removing the chromophore without isomerization and subsequent identification by high-speed liquid chromatography. Using similar techniques, we have shown that the product of bleaching by light of all three pigments in Trition X-100 is the all-trans isomer. This specificity in the product of bleaching, as with many other properties of visual pigments, is not shared by the free chromophore. Of particular interest is that when 9,13-dicis retinal is combined with opsin to form a pigment, a single photon can isomerize it about two double bonds, to the all-trans isomer.

Binding Sites↗
PubMed1985

Tunicamycin blocks the incorporation of opsin into retinal rod outer segment membranes.

Isolated frog retinas were incubated with radiolabeled glycoprotein precursors in the presence or absence of tunicamycin (TM), a selective inhibitor of protein N-glycosylation. In dual-label incubations, TM inhibited the incorporation of [3H]mannose into total retina Cl3CCOOH-precipitable material by 85% relative to controls, whereas incorporation of [14C]leucine was not significantly affected. In a companion single-label incubation, TM blocked the incorporation of [3H]leucine into rod outer segment (ROS) membrane Cl3CCOOH-precipitable material by 95% relative to controls. When retinas were labeled with [35S]methionine, fluorograms of NaDodSO4/polyacrylamide gels from control retinas and ROS membranes exhibited a heavily labeled component (apparent Mr approximately 37,000) which had the electrophoretic and antigenic properties of opsin, the rod visual pigment apoglycoprotein. TM-treated retinas exhibited a substantially reduced labeling of the Mr 37,000 component and incorporation of label into a component (apparent Mr approximately 32,000) not found in control retinas, which exhibited the electrophoretic and antigenic behavior of nonglycosylated opsin. ROS membranes isolated from TM-treated retinas contained neither the Mr 37,000 nor the Mr 32,000 radiolabeled species. Light-microscope autoradiograms of retinas incubated with [3H]leucine in the absence of TM exhibited bands of silver grains at the base of ROS, indicative of new membrane assembly. However, no such bands were observed in autoradiograms of TM-treated retinas. These results suggest that glycosylation of opsin is required for its incorporation into ROS membranes.

Animals↗
PubMed1992

Introduction of hydroxyl-bearing amino acids causes bathochromic spectral shifts in rhodopsin. Amino acid substitutions responsible for red-green color pigment spectral tuning.

Comparisons of the deduced amino acid sequences of eight primate photopigment genes led to the proposal that three amino acid substitutions produce the approximately 1,000 cm-1 difference in the absorption maxima of human red and green pigments (Neitz, M., Neitz, J., and Jacobs, G.H. (1991) Science 252, 971-974). We tested this proposal by mutating these three residues in rhodopsin and evaluating the effects on spectral properties. Nonpolar residues normally present in rhodopsin and in the green pigment were substituted by hydroxyl-bearing residues normally present in the red pigment. Two of these substitutions (Phe-261 to Tyr or Ala-269 to Thr) caused significant red shifts in the absorption maxima of the resulting mutant pigments. A third substitution (Ala-164 to Ser) caused only a slight effect. Combinations of substitutions caused additive shifts in absorption maxima. A double mutant (Phe-261 to Tyr/Ala-269 to Thr) displayed an absorption maximum that was red-shifted by 775 cm-1. Wavelength modulation in the visual pigments responsible for red-green color vision is likely to be governed by retinal-protein interactions involving primarily these two amino acid residues. Furthermore, interactions of hydroxyl-bearing amino acids with the chromophore may be a general mechanism of the opsin shift in visual pigments.

Amino Acid Sequence↗