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PubMed1987

Immunocytochemical markers revealing retinal and pineal but not hypothalamic photoreceptor systems in the Japanese quail.

The retinal proteins opsin, alpha-transducin, S-antigen and interstitial retinol-binding protein (IRBP) are essential for the processes of vision. By use of immunocytochemistry we have employed antibodies directed against these "photoreceptor proteins" in an attempt to identify the photoreceptor systems (retina, pineal and deep brain) of the Japanese quail. Opsin immunostaining was identified within many outer (basal portion) and inner segments of retinal photoreceptor cells and limited numbers of photoreceptor perikarya. Opsin immunostaining was also demonstrated in limited numbers of pinealocytes with all parts of these cells being immunoreactive. These results differ from previous observations. In contrast to the results obtained with the antibody against opsin, S-antigen and alpha-transducin immunostaining was seen throughout the entire outer segments and many photoreceptor perikarya of the retina, in the pineal organ immunostaining was seen in numerous pinealocytes in all follicles. These results conform to previous findings in birds. In addition, IRBP has been demonstrated for the first time in the avian retina and pineal organ. These findings underline the structural and functional similarities between the retina and pineal organ and provide additional support for a photoreceptive role of the avian pineal. No specific staining was detected in any other region of the brain in the Japanese quail; the hypothalamic photoreceptors of birds remain unidentified.

Animals↗
PubMed1993

Primary structure of crayfish visual pigment deduced from cDNA.

The primary structure of opsin of the crayfish Procambarus clarkii has been deduced from the cDNA sequence. The opsin is composed of 376 amino acid residues including all the conservative residues characteristic of other members of the rhodopsin family. Comparison of sequences of all known opsins reveals that the major Drosophila rhodopsin is more similar to the crayfish rhodopsin than to the Drosophila UV-sensitive pigments. The phylogenetic trees of invertebrate opsins are constructed.

Amino Acid Sequence↗
PubMed1984

Photophysiological functions of visual pigments.

In order to gain a fundamental understanding of functions of a visual pigment, i.e., photoreception and phototransduction, it is essential to elucidate the molecular structure of visual pigment, its photochemical behavior and connection of the pigment to the molecular physiological amplification mechanism for excitation of a visual cell. A rhodopsin, a rod visual pigment, is composed of an 11-cis-retinal bound with an apo-protein, opsin, through a protonated Schiff-base. Competitive inhibition of beta-ionone on regeneration of rhodopsin from an 11-cis-retinal and cattle opsin demonstrated the existence of a hydrophobic linkage between the beta-ionone ring of the retinal and the hydrophobic region of opsin. Owing to these two linkages, the 11-cis-retinal is fixed in an opsin cleft. As a result, it is endowed with new physiological functions as a chromophore of rhodopsin; the change of 11-cis-retinal (lambda max = 369 nm, epsilon = 26,400) to rhodopsin (lambda max = about 500 nm, epsilon = 40,600) brings not only a spectral shift from near ultraviolet to visible regions and an intensification of the molecular extinction coefficient, but also an increase of a quantum yield of 11-cis-retinal to all-trans form. High quantum yield of rhodopsin suggests rapid formation of the first photoproduct. Study of the first photoproduct was accelerated by the finding of bathorhodopsin, which was formed by irradiation at liquid nitrogen temperatures. The change of rhodopsin to bathorhodopsin has been inferred to be due to a photoisomerization of the chromophore from 11-cis to a twisted all-trans form. This isomerization hypothesis has been verified by the following experimental results. Irradiation of 7-cis- and 9-cis-rhodopsins at liquid nitrogen temperature produced the same bathorhodopsin as that from 11-cis-rhodopsin, indicating that the chromophore of bathorhodopsin should be in all-trans or transoid form. 7-Membered-rhodopsin, in which the rotation of 11-12 double bond of the retinylidene chromophore is locked, did not form bathorhodopsin by excitation of picosecond laser photolysis. This fact indicates that bathorhodopsin is a product formed by photoisomerization of the chromophore. Rhodopsin showed a positive circular dichroism (CD) in the visible while bathorhodopsin showed a remarkable negative CD. The reversal of the sign of CD indicates that not only large conformational change of the retinylidene chromophore occurs during the conversion of rhodopsin to bathorhodopsin, but also the direction of twist of the chromophore reverses. It is inferred that the chromophore of bathorhodopsin is a twisted trans form.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2001

Distribution of blue-sensitive photoreceptors in amphibian retinas.

Previously, we reported that an opsin (Rc-MS) belonging to the SWS2 group opsins is expressed in bullfrog green rods [Hisatomi, O. et al., FEBS Lett., 1999, 447, 44-48]. An anti-Rc-MS antiserum recognized the cones of the Japanese common newt, Cynops pyrrhogaster, which has no green rods. We isolated a cDNA encoding an SWS2 group opsin (Cp-SWS2) from this newt and found that Cp-SWS2 is expressed in a small population of the cones. Our results suggest that SWS2 opsins can be expressed in either green rods or cones of caudata. It seems reasonable to suppose that green rods arose before amphibia were divided into caudata and anura.

Amino Acid Sequence↗
PubMed2002

Characterization of calbindin-positive cones in primates.

The aim of this study is to characterize calbindin-positive photoreceptors and their opsin content in the retina of nocturnal prosimians (Microcebus murinus), New World monkeys (Callithrix jacchus), Old World monkeys (Macaca fascicularis), and humans. To identify the calbindin and opsin content of cones, combined multiple labeling with different fluorescent probes, antibodies directed against calbindin, short, and mid-long wavelength opsins, and lectin peanut agglutinin cytochemistry were used. With the exception of Microcebus, calbindin is present in the cones of all primates but is absent from rods. The distribution of calbindin is similar in human and macaque cones, with dense label in the inner segment, cell body, axon and cone pedicle. Cones in marmoset also show dense staining in the cell body, axon and pedicle but only light label in the inner segment. Primate cone outer segments do not contain calbindin. In the primates studied, three patterns of calbindin and opsin localization are observed. In macaque and marmoset all short and mid-long wavelength cones contain calbindin. In humans, all mid-long wavelength cones contain calbindin whereas all short wavelength cones are devoid of calbindin as confirmed by confocal microscopy. In the nocturnal prosimian Microcebus none of the mid-long or short wavelength cones contain calbindin. In addition to primates, calbindin is absent in cones of other nocturnal species but is present in cones of diurnal species suggesting a difference in the role of calbindin possibly related to the adaptational states or other photoreceptor properties.

Adult↗
PubMed2001

Rods are rods and cones cones, and (never) the twain shall meet.

More than 100 photopigment G protein-coupled receptors (opsins) have been sequenced and organized into six classes. Rod photoreceptors in various species have been found to express an opsin from one of the two rhodopsin classes, while cones express an opsin from one of the four remaining classes. It has now been discovered that salamander short-wavelength sensitive cones and green rods express the same opsin, while manifesting other features that classically distinguish rods from cones.

Adaptation, Ocular↗
PubMedDate not supplied

Molecular cloning and localization of rhodopsin kinase in the mammalian pineal.

Several retinal photoreceptor proteins involved in phototransduction have also been found in the mammalian pineal. This study demonstrates that rat and human pineals express protein kinases that are identical to the corresponding rod photoreceptor rhodopsin kinases. The deduced amino acid sequence of rat and human rhodopsin kinases have 84% sequence similarity to the earlier reported sequence of the bovine retinal enzyme, with complete conservation of the topological regions containing the position of the catalytic domain and sites of posttranslational modifications. Rat pineal also expresses rod opsin and putative blue cone opsin. Using immunocytochemistry, rod opsin and rhodopsin kinase were found to be co-localized in pinealocytes in the human tissue. These data demonstrate that the mammalian pineal contains light-sensitive opsins and a kinase involved in their inactivation. These findings correlate with an earlier report that neonatal rats show extraretinal light sensitivity, and suggest that a functional photoreceptive system may be present in the adult mammalian pineal.

Adult↗
PubMed1985

Biochemical properties of 9-cis- and all-trans-retinoylopsins.

The stoichiometry of the reaction between [14C]-9-cis-retinoyl fluoride, a close isostere of 9-cis-retinal, and bovine opsin and the biochemical and spectral properties of this new pigment were investigated. The stoichiometry of retinoid incorporation is approximately one in dodecyl maltoside, a detergent in which opsin is capable of regeneration with 11-cis-retinal. Interestingly, in Ammonyx LO, a detergent that does not permit rhodopsin regeneration, the stoichiometry of binding is still approximately one. By contrast, heat-denatured opsin does not irreversibly bind substantial [14C]retinoyl fluoride. This result strongly suggests that the nucleophilicity of the active site lysine is retained in Ammonyx LO but that further conformational changes in the protein, required to form rhodopsin, are not possible. These results are all consistent with an active site directed mechanism for the irreversible reaction of 9-cis-retinoyl fluoride with opsin probably at the active site lysine residue. The ultraviolet spectra of 9-cis-retinoylopsin and its all-trans congener show gamma max's at 373 and 380 nm, respectively, somewhat bathochromically shifted from their respective model N-butylretinamides which absorb at 347 and 351 nm. Photolysis of both 9-cis- and all-trans-retinoylopsins leads to the same photostationary state. This shows that, as expected, photoisomerization without bleaching occurs. The photolysis of either 9-cis- or all-trans-retinoylopsin in the presence of the G protein (transducin) does not lead to the activation of the latter. This is consistent with the notion that a protonated Schiff base is critical for the function of rhodopsin.

Animals↗
PubMed2005

Induction of photosensitivity by heterologous expression of melanopsin.

Melanopsin has been proposed to be the photopigment of the intrinsically photosensitive retinal ganglion cells (ipRGCs); these photoreceptors of the mammalian eye drive circadian and pupillary adjustments through direct projections to the brain. Their action spectrum (lambda(max) approximately 480 nm) implicates an opsin and melanopsin is the only opsin known to exist in these cells. Melanopsin is required for ipRGC photosensitivity and for behavioural photoresponses that survive disrupted rod and cone function. Heterologously expressed melanopsin apparently binds retinaldehyde and mediates photic activation of G proteins. However, its amino-acid sequence differs from vertebrate photosensory opsins and some have suggested that melanopsin may be a photoisomerase, providing retinoid chromophore to an unidentified opsin. To determine whether melanopsin is a functional sensory photopigment, here we transiently expressed it in HEK293 cells that stably expressed TRPC3 channels. Light triggered a membrane depolarization in these cells and increased intracellular calcium. The light response resembled that of ipRGCs, with almost identical spectral sensitivity (lambda(max) approximately 479 nm). The phototransduction pathway included Gq or a related G protein, phospholipase C and TRPC3 channels. We conclude that mammalian melanopsin is a functional sensory photopigment, that it is the photopigment of ganglion-cell photoreceptors, and that these photoreceptors may use an invertebrate-like phototransduction cascade.

Animals↗
PubMed1952

The role of sulfhydryl groups in the bleaching and synthesis of rhodopsin.

The condensation of retinene(1) with opsin to form rhodopsin is optimal at pH about 6, a pH which favors the condensation of retinene(1) with sulfhydryl rather than with amino groups. The synthesis of rhodopsin, though unaffected by the less powerful sulfhydryl reagents, monoiodoacetic acid and its amide, is inhibited completely by p-chloromercuribenzoate (PCMB). This inhibition is reversed in part by the addition of glutathione. PCMB does not attack rhodopsin itself, nor does it react with retinene(1). Its action in this system is confined to the -SH groups of opsin. Under some conditions the synthesis of rhodopsin is aided by the presence of such a sulfhydryl compound as glutathione, which helps to keep the -SH groups of opsin free and reduced. By means of the amperometric silver titration of Kolthoff and Harris, it is shown that sulfhydryl groups are liberated in the bleaching of rhodopsin, two such groups for each retinene(1) molecule that appears. This is true equally of rhodopsin from the retinas of cattle, frogs) and squid. The exposure of new sulfhydryl groups adds an important element to the growing evidence that relates the bleaching of rhodopsin to protein denaturation. The place of sulfhydryl groups in the structure of rhodopsin is still uncertain. They may be concerned directly in binding the chromophore to opsin; or alternatively they may furnish hydrogen atoms for some reductive change by which the chromophore is formed from retinene(1). In the amperometric silver titration, the bleaching of rhodopsin yields directly an electrical variation. This phenomenon may have some fundamental connection with the role of rhodopsin in visual excitation, and may provide a model of the excitation process in general.

Animals↗
PubMed1990

Optimization, constraint, and history in the evolution of eyes.

Several features of the evolution of eyes and photoreceptors are examined in an effort to explore the relative roles of adaptation and historical and developmental constraints. Optical design shows clear evidence of adaptation, which in some respects approaches optima predictable from physics. The primate fovea, on the other hand, illustrates how adaptation can be channeled by developmental heritage. The primary structures of opsins reveal multiple evolutionary lineages within both Drosophila and humans. The pigments of vertebrae rods comprise a subset of opsins whose evolutionary relationships map onto the phylogeny of the parent species. The evolutionary reasons for why most rod pigments absorb maximally at 500 +/- 10 nm are obscure, as there is no convincing explanation based on adaptation alone. Rods are appropriately distinguished from cones on the basis of which opsin gene is expressed. This criterion is likely to be in conflict with other definitions in phyletic lines (e.g., geckos, snakes) that have long diurnal or nocturnal histories accompanied by loss of one or more opsin genes, followed by a secondary adaptation to life in a different photic environment. Color vision--a generalizable perception associated with the spectral composition of light--is usefully distinguished from wavelength-specific behaviors. The latter are also based on multiple visual pigments and more than one spectral class of receptors but cannot be altered by learning. The distinction is particularly forceful in bees, which exhibit both kinds of behavior. The evolution of primate color vision has been shaped by historical factors involving an extensive period of early mammalian nocturnality. Birds, by contrast, have more elaborate cones and a richer set of visual pigments. Avian color space can be represented in a tetrahedron.

Amino Acid Sequence↗
PubMed2002

Different transmembrane domains associate with distinct endoplasmic reticulum components during membrane integration of a polytopic protein.

We have been studying the insertion of the seven transmembrane domain (TM) protein opsin to gain insights into how the multiple TMs of polytopic proteins are integrated at the endoplasmic reticulum (ER). We find that the ER components associated with the first and second TMs of the nascent opsin polypeptide chain are clearly distinct. The first TM (TM1) is adjacent to the alpha and beta subunits of the Sec61 complex, and a novel component, a protein associated with the ER translocon of 10 kDa (PAT-10). The most striking characteristic of PAT-10 is that it remains adjacent to TM1 throughout the biogenesis and membrane integration of the full-length opsin polypeptide. TM2 is also found to be adjacent to Sec61alpha and Sec61beta during its membrane integration. However, TM2 does not form any adducts with PAT-10; rather, a transient association with the TRAM protein is observed. We show that the association of PAT-10 with opsin TM1 does not require the N-glycosylation of the nascent chain and occurs irrespective of the amino acid sequence and transmembrane topology of TM1. We conclude that the precise makeup of the ER membrane insertion site can be distinct for the different transmembrane domains of a polytopic protein. We find that the environment of a particular TM can be influenced by both the "stage" of nascent chain biosynthesis reached, and the TM's relative location within the polypeptide.

Animals↗
PubMed1999

Genetic analyses of visual pigments of the pigeon (Columba livia).

We isolated five classes of retinal opsin genes rh1(Cl), rh2(Cl), sws1(Cl), sws2(Cl), and lws(Cl) from the pigeon; these encode RH1(Cl), RH2(Cl), SWS1(Cl), SWS2(Cl), and LWS(Cl) opsins, respectively. Upon binding to 11-cis-retinal, these opsins regenerate the corresponding photosensitive molecules, visual pigments. The absorbance spectra of visual pigments have a broad bell shape with the peak, being called lambdamax. Previously, the SWS1(Cl) opsin cDNA was isolated from the pigeon retinal RNA, expressed in cultured COS1 cells, reconstituted with 11-cis-retinal, and the lambdamax of the resulting SWS1(Cl) pigment was shown to be 393 nm. In this article, using the same methods, the lambdamax values of RH1(Cl), RH2(Cl), SWS2(Cl), and LWS(Cl) pigments were determined to be 502, 503, 448, and 559 nm, respectively. The pigeon is also known for its UV vision, detecting light at 320-380 nm. Being the only pigments that absorb light below 400 nm, the SWS1(Cl) pigments must mediate its UV vision. We also determined that a nonretinal P(Cl) pigment in the pineal gland of the pigeon has a lambdamax value at 481 nm.

Amino Acid Sequence↗
PubMed1997

Color vision of ancestral organisms of higher primates.

The color vision of mammals is controlled by photosensitive proteins called opsins. Most mammals have dichromatic color vision, but hominoids and Old World (OW) monkeys enjoy trichromatic vision, having the blue-, green-, and red-sensitive opsin genes. Most New World (NW) monkeys are either dichromatic or trichromatic, depending on the sex and genotype. Trichromacy in higher primates is believed to have evolved to facilitate the detection of yellow and red fruits against dappled foliage, but the process of evolutionary change from dichromacy to trichromacy is not well understood. Using the parsimony and the newly developed Bayesian methods, we inferred the amino acid sequences of opsins of ancestral organisms of higher primates. The results suggest that the ancestors of OW and NW monkeys lacked the green gene and that the green gene later evolved from the red gene. The fact that the red/green opsin gene has survived the long nocturnal stage of mammalian evolution and that it is under strong purifying selection in organisms that live in dark environments suggests that this gene has another important function in addition to color vision, probably the control of circadian rhythms.

Amino Acid Sequence↗
PubMed1995

The molecular basis for the green-blue sensitivity shift in the rod visual pigments of the European eel.

When the European eel matures sexually and migrates back to deep sea breeding grounds the visual pigments in its rod photoreceptors change from being maximally sensitive to green light to being maximally sensitive to blue light. In part, this change in sensitivity is due to a change in the opsin component of the visual pigment molecule. We used hormone injection to induce these developmental changes in a group of eels and from these animals an opsin coding region was cloned and sequenced using cDNA made from retinal mRNA. From the retinae of hormone-injected eels and those not injected with hormones, distinct opsin mRNAs were isolated. These mRNAs encode two rod opsin proteins that are very similar but have significant amino acid substitutions in key positions that are likely to be involved in spectral tuning of the eel green and blue sensitive rod visual pigment molecules.

Amino Acid Sequence↗
PubMed2006

Polymorphism of visual pigment genes in the muriqui (Primates, Atelidae).

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 lambdamax 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.

Animals↗
PubMed2002

Circadian photoreception in humans and mice.

Circadian rhythms are the endogenous oscillations, occurring with a periodicity of approximately twenty-four hours, in the biochemical and behavioral functions of organisms. In mammals, the phase and period of the rhythm are synchronized to the daily light-dark cycle by light input through the eye. Certain retinal degenerative diseases affecting the photoreceptor cells, both rods and cones, in the outer retina reveal that classical opsins (i.e., rhodopsin and color opsins located in these cells) are essential for vision, but are not required for circadian photoreception. The mammalian cryptochromes and melanopsin (and possibly other opsin family pigments) have been proposed as circadian photoreceptor pigments that exist in the inner retina. Genetic analysis indicates that the cryptochromes, which contain flavin and folate as the light-absorbing cofactors, are the primary circadian photoreceptors. The classical photoreceptors in the outer retina, and melanopsin or other minor opsins in the inner retina, may perform redundant functions in circadian rhythmicity.

Animals↗
PubMed2005

Illumination of the melanopsin signaling pathway.

In mammals, a small population of intrinsically photosensitive retinal ganglion cells (ipRGCs) plays a key role in the regulation of nonvisual photic responses, such as behavioral responses to light, pineal melatonin synthesis, pupillary light reflex, and sleep latency. These ipRGCs also express melanopsin (Opn4), a putative opsin-family photopigment that has been shown to play a role in mediating these nonvisual photic responses. Melanopsin is required for the function of this inner retinal pathway, but its precise role in generating photic responses has not yet been determined. We found that expression of melanopsin in Xenopus oocytes results in light-dependent activation of membrane currents through the Galpha(q)/Galpha(11) G protein pathway, with an action spectrum closely matching that of melanopsin-expressing ipRGCs and of behavioral responses to light in mice lacking rods and cones. When coexpressed with arrestins, melanopsin could use all-trans-retinaldehyde as a chromophore, which suggests that it may function as a bireactive opsin. We also found that melanopsin could activate the cation channel TRPC3, a mammalian homolog of the Drosophila phototransduction channels TRP and TRPL. Melanopsin therefore signals more like an invertebrate opsin than like a classical vertebrate rod-and-cone opsin.

Animals↗