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PubMed1992

Interphotoreceptor matrix in the human retina: cone-like domains surround a small population of rod photoreceptors.

The interphotoreceptor matrix (IPM) in mammalian retinas is subdivided into rod and cone specific compartments: peanut agglutinin (PNA) binding glycoconjugates are associated with cones, whereas wheat germ agglutinin (WGA) binding glycoconjugates are associated with rods. To establish the identity of a photoreceptor cell type in the human retina with rod dimensions but with a matrix domain which stains with PNA, double label studies, using PNA-ferritin to decorate the extracellular domains and immunocytochemical techniques using a rod specific anti-opsin antibody were conducted. The PNA-binding domains were observed in the cone-associated IPM as well as in the IPM surrounding a small population of rod-shaped photoreceptors. The outer segments of these rod-shaped photoreceptors showed intense labeling with a rod specific anti-opsin antibody as did all other rods which were free of PNA-labeling. A quantitative analysis of all retinal quadrants indicates that this novel rod represents approximately 0.3% of the total rod population in the human retina.

Arachis↗
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↗
PubMed2005

Rhodopsin-iCre transgenic mouse line for Cre-mediated rod-specific gene targeting.

Retinal photoreceptors are highly differentiated postmitotic neurons that transduce photons into electrical signals. While the functions of many photoreceptor-specific genes can be evaluated by direct gene targeting, here we facilitate the studies of nonphotoreceptor-specific genes in these cells by developing an Opsin-iCre transgenic mouse line, iCre-75, in which a 4-kb mouse rod opsin promoter drives the expression of bacteriophage P1 Cre recombinase. Immunohistochemical analysis demonstrated that Cre recombinase is present exclusively in the outer nuclear layer of iCre75 mouse retina. Cre expression is found only in rods and not in cones. The expression level reached 188+/-44 ng per retina at postnatal day (pnd) 11 and increased to 687+/-56 ng at 2 months and older. Cre-mediated excision of floxed genomic DNA was absent at pnd 4, became detectable at pnd 7, and was completed by pnd 18. Retinal morphology and electroretinograms were normal in 8-month-old transgenic animals. The iCre-75 transgenic mice are thus suitable for future genetic studies of essential genes in retinal rod photoreceptors.

Animals↗
PubMed1986

Rod outer segment lipids in vitamin A-adequate and -deficient rats.

Weanling albino rats were fed a vitamin-A-adequate diet or vitamin-A-deficient diet and maintained in a cyclic light or dark environment for up to 14 weeks. One half of the rats were supplemented with additional dietary linolenic acid in the form of linseed oil. The lipid composition and rhodopsin-opsin contents of isolated rod outer segments were determined after 6-7 weeks or 12-14 weeks on diet. This study shows that feeding rats a standard vitamin A-adequate or -deficient diet results in an age-dependent loss of omega three docosahexaenoic acid and a concomitant increase in omega six docosapentanoic acid in the rod outer segments. The loss of docosahexaenoate appears to be caused by insufficient dietary omega three fatty acids. The increase in omega six docosapentanoic acid appears to arise from the high concentration of linoleic acid in standard diets containing either cottonseed, or peanut oil or supplemental corn oil. Feeding rats diets supplemented with linseed oil, however, results in a rod outer-segment lipid profile which is the same as for chow-fed animals. The same effects were seen in the fatty-acid profile of lipids from liver, although the content of polyunsaturates was much lower than in rod outer segments. Vitamin A deficiency, itself, does not lead to changes in the fatty-acid composition of either the rod outer segments or liver. After 6-7 weeks on A+ or A- diet, rhodopsin levels were, as expected, higher in dark-reared rats than in cyclic-light animals. Although the rhodopsin levels in dark-reared vitamin A-adequate rats were significantly higher than in vitamin A-deficient animals, measurements of the lipid to opsin ratio of rod outer segments indicate that the rods of vitamin A-deficient rats are not markedly different than those of vitamin A-adequate rats. It is concluded that these diets may be useful in providing a means for evaluating the role of docosahexaenoic acid in visual cell death from damaging light.

Age Factors↗
PubMed2002

Mouse cone arrestin expression pattern: light induced translocation in cone photoreceptors.

PURPOSE: Arrestins are a superfamily of regulatory proteins that down-regulate activated and phosphorylated G-protein coupled receptors (GPCRs). Cone arrestin (CAR) is expressed in cone photoreceptors and pinealocytes and may contribute to the shutoff mechanisms associtated with high acuity color vision. To initiate a study of CAR's function in cone phototransduction, the mouse CAR (mCAR) transcript and protein expression patterns are examined and in vitro binding assays are also presented. METHODS: Tissue distribution of mCAR was determined by Northern and immunoblot analyses and its cellular localization identified by In situ hybridization and immunohistochemistry. The protein expression pattern of mCAR in the postnatal developmental and adult mouse retina was analyzed by immunoblotting in normal C57 and rd/rd mouse retinas. In vitro binding assays with in vitro translated arrestins were used to study the interaction of mCAR and mouse S-antigen (mSAG) with embryonic chicken outer segment (OS) membranes containing both rod and cone opsins. RESULTS: MCAR has a high level of amino acid sequence identity with orthologous sequences reported for other species except the C-terminal region, which is highly conserved between mouse and rat but divergent in other species. MCAR is expressed exclusively in the retina and the pineal gland, and unique isoforms are expressed during postnatal development of the retina and the pineal gland. The postnatal developmental expression pattern of mCAR and mSAG in the rd/rd mouse retina parallels the generation and degeneration of the cone and rod photoreceptors in these mice. In situ and immunohistochemistry both reveal cone-specific expression of mCAR in the retina. Immunofluorescent staining of retinal sections from dark-adapted or light-exposed mice suggests a light-dependent translocation of mCAR immunoreactivity from the cone inner segments (CIS) and other parts of the cell body to the cone outer segments (COS), similar to but not as dramatic as rod arrestin. In vitro binding assays show a small yet significant increase in binding of the full-length mCAR (mCARFL) to embryonic chicken OS membranes following light activation and phosphorylation of the opsins in the membranes. CONCLUSIONS: MCAR is expressed in retinal cone photoreceptors and the pineal gland. The light-dependent translocation of mCAR immunoreactivity and the increase of mCAR binding to light-activated, phosphorylated embryonic chicken OS membranes, compared to its binding to dark, unphosphorylated membranes, suggest the possibility that mCAR is involved in shutting off the phototransduction cascade in cone photoreceptors as rod arrestin does in rod photoreceptors. However, prominent differences exist between rod arrestin and CAR, suggesting other functions for CAR.

Animals↗
PubMed2001

Constitutive "light" adaptation in rods from G90D rhodopsin: a mechanism for human congenital nightblindness without rod cell loss.

A dominant form of human congenital nightblindness is caused by a gly90-->asp (G90D) mutation in rhodopsin. G90D has been shown to activate the phototransduction cascade in the absence of light in vitro. Such constitutive activity of G90D rhodopsin in vivo would desensitize rod photoreceptors and lead to nightblindness. In contrast, other rhodopsin mutations typically give rise to nightblindness by causing rod cell death. Thus, the proposed desensitization without rod degeneration would be a novel mechanism for this disorder. To explore this possibility, we induced mice to express G90D opsin in their rods and then examined rod function and morphology, after first crossing the transgenic animals with rhodopsin knock-out mice to obtain appropriate levels of opsin expression. The G90D mouse opsin bound the chromophore and formed a bleachable visual pigment with lambda(max) of 492 nm that supported rod photoresponses. (G+/-, R+/-) retinas, heterozygous for both G90D and wild-type (WT) rhodopsin, possessed normal numbers of photoreceptors and had a normal rhodopsin complement but exhibited considerable loss of rod sensitivity as measured electroretinographically. The rod photoresponses were desensitized, and the response time to peak was faster than in (R+/-) animals. An equivalent desensitization resulted by exposing WT retinas to a background light producing 82 photoisomerizations rod(-1) sec(-1), suggesting that G90D rods in darkness act as if they are partially "light-adapted." Adding a second G90D allele gave (G+/+, R+/-) animals that exhibited a further increase of equivalent background light level but had no rod cell loss by 24 weeks of age. (G+/+, R-/-) retinas that express only the mutant rhodopsin develop normal rod outer segments and show minimal rod cell loss even at 1 year of age. We conclude that G90D is constitutively active in mouse rods in vivo but that it does not cause significant rod degeneration. Instead, G90D desensitizes rods by a process equivalent to light adaptation.

Adaptation, Ocular↗
PubMed1985

Sensory cells of the "rod-" and "cone-type" in the pineal organ of Rana esculenta, as revealed by immunoreaction against opsin and by the presence of an oil (lipid) droplet.

The pineal organ of the frog, Rana esculenta, was studied by use of light- and electron-microscopic methods including immunoreaction against opsin. Most of the morphologically classified cone-type outer segments of the pineal photoreceptors reacted with antisera against opsin of the bovine retina that is dominated by rods. Some of the outer segments of pineal photoreceptor cells remained unstained in accord with the reference tissue, the frog retina, where generally the rods were opsin-positive and most of the cones opsin-negative. The opsin-negative outer segments of pineal photoreceptors were found in continuity with inner segments each containing a large oil (lipid) droplet. These oil droplets stained intensely with osmic acid, Sudan III, Sudan Black B or Scharlach R in cryostat sections, and were soluble in lipid solvents. In ultrathin sections of osmicated material, the oil droplets were homogeneous and of varying electron density. Approximately one tenth of the pineal photoreceptors contained oil droplets and at the same time possessed opsin-immunonegative outer segments. Since in the retina oil droplets and a negative immunoreaction against bovine opsin are characteristic of cones, we suggest that in the pineal organ they also mark "cone-type" photoreceptors scattered among "rod-type" photoreceptors, the latter displaying a positive immunoreaction with the antisera used.

Animals↗
PubMed1986

Immunocytochemical binding of anti-opsin N-terminal-specific antibodies to the extracellular surface of rod outer segment plasma membranes. Fixation induces antibody binding.

We have examined the binding of anti-opsin antibodies to the plasma membrane of frog retinal rod outer segments (ROS) by fluorescence light microscopy and electron microscopy. Polyclonal and monoclonal antibodies specific for the N-terminal domain of opsin were observed to bind to the extracellular surface of ROS plasma membrane of aldehyde-fixed but not of unfixed retinas. This reaction was found regardless of whether purified ROS, rhodopsin, opsin, or an N-terminal peptide of opsin was used as the immunogen. The fixation-induced binding of these antibodies contrasts with the more frequently noted loss of antigenicity upon fixation. Concanavalin A, however, binds to unfixed ROS plasma membranes. Its binding sites in the plasma membrane may be oligosaccharides in the N-terminal region of opsin. These results suggest that the N-terminal domain of opsin is latent in the native membrane and that changes in conformation may account for its detectability in fixed membranes.

Amino Acid Sequence↗
PubMed2002

Opsin expression in adult, developing, and regenerating newt retinas.

Japanese common newts (Cynops pyrrhogaster) have an ability to regenerate their neural retina even as adults. Although extensive research has been carried out attempting to understand this retinal regeneration, the molecules characterized in newt retina are limited. We isolated cDNAs encoding three putative opsins (Cp-Rh, -LWS and -SWS1), in addition to Cp-SWS2 [Takahashi et al., FEBS Lett. 501 (2001) 151-155] from a cDNA library of adult newt retina. Our immunohistochemical and in situ hybridization studies demonstrated that Cp-Rh is selectively expressed in rods, whereas the other opsins are expressed in cones. The distribution of opsin mRNAs in normal and regenerated retinas is very similar. In both developing and regenerating retinas, Cp-Rh and its mRNA first appeared in immature rods at the beginning or just after the formation of plexiform layers. Cp-Rh was initially found isotropically in the plasma membrane, and then translocalized to the apical region along with the maturation of regenerating rods. This suggests that reorganization of the intracellular structure takes place during maturation of the regenerating newt photoreceptors.

Amino Acid Sequence↗
PubMedDate not supplied

Cone and rod inputs to murine retinal ganglion cells: evidence of cone opsin specific channels.

To identify ultraviolet (UV) and middle- (M) wavelength-sensitive cone and rod signals in murine retinal ganglion cells, single ganglion cell responses were studied in anesthetized, light-adapted C57/BL6 mice with tungsten microelectrodes driven through the sclera and vitreous to the neural retina. One hundred fifty-four ganglion cells were examined in 43 retinas of 34 mice. The retina was stimulated with diffuse flashes and/or pulses of ultraviolet (360 nm) or green (520 nm) light in the presence and absence of a strong steady orange adapting light. Twelve ganglion cells were studied in the dark-adapted retina in order to identify the signals of rods. Three functionally different types of ganglion cells were found: (1) phasic responding cells (31%) with no spontaneous activity and large impulse amplitudes; (2) tonic responding cells (60%) with irregular, low frequency (5-10 Hz) spontaneous activity and smaller impulse amplitudes; and (3) metronome-like cells (9%) with regular, relatively high-frequency (20-40 Hz) spontaneous activity. A few cells (1%) had habituating responses. Every cell encountered was affected by diffuse stimulation. The more common two types were excited at either the ON or OFF or at both the ON and OFF phases of stimulation. Type III cells had weaker responses, sometimes only inhibited by turning off a light. In the light-adapted state, most cells received signals of the same polarity from UV- and M-cones but UV-cone inputs were usually more dominant, especially in ventral retina. A fraction of cells received signals from only UV- (18%) or only M- (3%) cones. In rare cases (2%) these cone inputs had an opposite polarity on the same cell. In the dark-adapted state, all cells were at least four or five logarithmic units more sensitive and more to green than ultraviolet light. The results indicate that co-expression of both UV-and M-cone opsins cannot be ubiquitous in murine retina. Some cones, especially UV cones, exist without the presence of any functional M-cone opsin. This must be the case to explain the presence of ganglion cells that receive inputs only from UV-cones and others that receive inputs of opposite polarity from UV- and M-cones. The results support the hypothesis that murine retina has the physiological capacity to relay signals to the brain that allow the sensing of chromatic contrast and color vision.

Adaptation, Physiological↗
PubMed1989

(Na+ + K+)-ATPase and opsin in retinas of RCS dystrophic rats: time course study.

Retinas of Royal College of Surgeons (RCS) dystrophic rats were investigated immunocytochemically for the distribution of the membrane-bound enzyme (Na+ + K+)-ATPase and the photo-pigment opsin prior to and during the retinal disease process. Retinas of 11 day-old dystrophic and control Long Evans rats showed (Na+ + K+)-ATPase immunostain most dense in the outer nuclear layer (ONL) and inner plexiform layer (IPL). Also, in these retinas, immunostaining for opsin was dense along rod inner segments (RIS) and on plasmalemma of ONL cell bodies and several cell bodies in the inner nuclear layer (INL). In retinas of control rats at 30 days and later, less dense (Na+ + K+)-ATPase immunostain was detected in the ONL than at 11 days and opsin-immunostained ROS were also detected. However, (Na+ + K+)-ATPase immunostained RIS were shorter in retinas of 30 day-old dystrophic than in retinas of age-matched control rats and an opsin-immunostained debris zone was also observed in dystrophic retinas. In retinas of 60 day-old dystrophic rats, the opsin-immunostained debris zone was more prominent than at 30 days, while the few ONL cell bodies immunostained for both proteins. Also, the outer IPL of 60 day-old dystrophic rat retinas immunostained more densely for (Na+ + K+)-ATPase than the inner IPL. In 120 day-old dystrophic rat retinas, (Na+ + K+)-ATPase immunostain was detected in the INL and IPL, while opsin staining was demonstrated only in the debris zone. This opsin-immunostained debris disappeared in a central-to-peripheral gradient. (Na+ + K+)-ATPase immunostain was still present in the INL and IPL in retinas and the optic nerve of one year-old RCS dystrophic rats; however, opsin was restricted to a few surviving cell bodies in the peripheral retina.

Animals↗
PubMed1958

The thermal stability of rhodopsin and opsin.

Rhodopsin, the red photosensitive pigment of rod vision, is composed of a specific cis isomer of retinene, neo-b (11-cis), joined as chromophore to a colorless protein, opsin. We have investigated the thermal denaturation of cattle rhodopsin and opsin in aqueous digitonin solution, and in isolated rod outer limbs. Both rhodopsin and opsin are more stable in rods than in solution. In solution as well as in rods, moreover, rhodopsin is considerably more stable than opsin. The chromophore therefore protects opsin against denaturation. This is true whether rhodopsin is extracted from dark-adapted retinas, or synthesized in vitro from neo-b retinene and opsin. Excess neo-b retinene does not protect rhodopsin against denaturation. The protection involves the specific relationship between the chromophore and opsin. Similar, though somewhat less, protection is afforded opsin by the stereoisomeric iso-a (9-cis) chromophore in isorhodopsin. The Arrhenius activation energies (E(a)) and entropies of activation (DeltaSdouble dagger) are much greater for thermal denaturation of rhodopsin and isorhodopsin than of opsin. Furthermore, these values differ considerably for rhodopsins from different species -frog, squid, cattle-presumably due to species differences in the opsins. Heat or light bleaches rhodopsin by different mechanisms, yielding different products. Light stereoisomerizes the retinene chromophore; heat denatures the opsin. Photochemical bleaching therefore yields all-trans retinene and native opsin; thermal bleaching, neo-b retinene and denatured opsin.

Animals↗
PubMed1987

Two types of lamprey retina photoreceptors immunoreactive to rod- or cone-specific antibodies.

The localization of structures immunoreactive to antisera against opsin (OPS; a specific marker for rods) and against visinin (VIS; a specific marker for cones in the vertebrate retina) was investigated in the retina of the river lamprey (Lampetra japonica) by means of fluorescence microscopy. Different immunoreactive structures were found with the two antisera. A vitreadly located structure in the outer nuclear layer displayed OPS-like immunoreactivity, while a scleradly located one exhibited VIS-like reactivity. Thus, the two antisera applied to the retina of the river lamprey permit the distinguishing of rod and cone immunoreactive photoreceptors such as occurs typically in all vertebrate classes. The former appears in the outer segments of a type of rod cells, and the latter in the cell bodies and axons of cones.

Animals↗
PubMed1995

Transducin activation by the bovine opsin apoprotein.

The interaction of the bovine opsin apoprotein with transducin in rod outer segment membranes was investigated using a guanyl nucleotide exchange assay. In exhaustive binding experiments, opsin activates transducin, with half-maximal exchange activity occurring at 0.8 mol of opsin/mol of transducin. The opsin activity was light-insensitive, hydroxylamine-resistant, unaffected by stoichiometric concentrations of retinaloxime, and more heat-labile than rhodopsin. The t1/2 of transducin activation in the presence of excess opsin was 8.5 min, compared with 0.7 min for metarhodopsin (II). The second-order rate constants were determined to be 0.012 pmol of guanosine 5'-(gamma-thio)triphosphate (GTP gamma S) bound per min/nM opsin and 0.35 pmol of GTP gamma S bound per min/nM metarhodopsin (II). Opsin was able to activate more than one transducin, although there appeared to be a turnover-dependent inactivation of the apoprotein. Opsin showed a broad pH range (5.8-7.4) for optimal activity, with no activity in buffers of pH > 9, whereas metarhodopsin (II) exhibited activity at pH > 9. Regulation of opsin activity by stoichiometric amounts of retinal was observed, with inhibition by 11-cis-retinal and stimulation by all-trans-retinal. A model for opsin activity is proposed.

Animals↗
PubMed2005

Recombination reaction of rhodopsin in situ studied by photoconversion of "indicator yellow".

We measured the kinetics of recombination of 11-cis-retinal with opsin in intact frog rod outer segment (ROS). The rhodopsin in ROS was bleached and allowed to decay to "indicator yellow," a photoproduct where all-trans-retinal is partly free, and partly bound to non-specific amino groups of disk membranes. By briefly illuminating the "indicator yellow" by an intense 465 or 380-nm flash, we then photoconverted all-trans-retinal to (mostly) the 11-cis- form thus introducing into ROS a certain amount of cis-chromophore. The recombination of cis-retinal with opsin and the formation of rhodopsin were followed by fast single-cell microspectrophotometry. Regeneration proceeded with a time constant of approximately 3.5 min; up to 27% of bleached visual pigment was restored. The regenerated pigment consisted of 91% rhodopsin (11-cis-chromophore) and 9% of presumably isorhodopsin (9-cis-chromophore). The recombination of 11-cis-retinal with opsin inside the ROS proceeds substantially faster than rhodopsin regeneration in the intact eye and, hence, is not the rate-limiting step in the visual cycle.

Animals↗
PubMed2005

Lipid differences in rod outer segment membranes of rats with P23H and S334ter opsin mutations.

PURPOSE: Retinal degenerations and diets low in n-3 fatty acids are associated with decreased docosahexaenoic acid (22:6n-3) in retina and plasma and with sterol abnormalities in retina and sperm. Using wild type (WT) and transgenic rats with P23H and S334ter opsin mutations, we evaluated retinal cholesterol levels, cholesterol synthesis, and fatty acid compositions of phospholipid classes in animals fed diets enriched in n-3 or n-6 polyunsaturated fatty acids. METHODS: Pregnant WT and heterozygous P23H and S334ter transgenic (TG) rats were fed safflower (safflower oil [SO], high n-6, trace n-3 fatty acids) or flaxseed oil (flaxseed oil [FO], high n-3, moderate n-6 fatty acids) diets beginning at E15, and pups were continued on the diets after weaning. Rod outer segment (ROS) membranes were prepared from 55-day-old rats, and the ratios of total fatty acid to cholesterol and the fatty acid compositions of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS) in ROS were determined. Intravitreal injections of [3H]acetate were given to 35-day-old WT and TG rats fed standard chow-diets. Endogenous cholesterol mass and de novo [3H]cholesterol synthesis were measured and normalized to total ROS fatty acid content. Multivariate analysis of variance (ANOVA) with post hoc Newman-Keuls tests were used to determine statistical differences. RESULTS: The relative levels of PC, PE, and PS were similar in all three rat strains independent of diet. Total lipids, PC, PS, and PE of ROS FO fed rats had higher levels of 22:6n-3 and lower levels of 22:5n-6 than those fed SO. Rats fed SO had higher levels of 22:5n-6 than those fed FO. Significant increases in 18:1n-9 were seen in PC and PS of P23H and S334ter rats; arachidonate (20:4n-6) increased only in PE. These changes were independent of diet. ROS membranes of transgenic rats were cholesterol enriched, relative to WT ROS, yet retinal cholesterol synthesis was not altered. Plasma cholesterol levels of transgenic rats were not different from those of WT rats. CONCLUSIONS: Endogenous levels of cholesterol, 18:1n-9, 20:4n-6, 22:5n-6, and 22:6n-3 were altered in ROS membranes of P23H and S334ter compared to WT rats. There appear to be two pools of 22:6n-3 in rat ROS, one that is sensitive to retinal degenerations and one that is not. The stress induced reduction in 22:6n-3 was not specific to any phospholipid class and was not caused by alteration of relative amounts of PC, PS, or PE in the membrane. Elevated retinal cholesterol may be a result of either an increased half life or an increased uptake of cholesterol from the blood.

Animals↗
PubMed2005

DISCO! Dissociation of cone opsins: the fast and noisy life of cones explained.

Vertebrate retinas contain two types of photoreceptors. Rods are for vision in dim light, while cones provide high-speed color vision in bright light. In this issue of Neuron, Kefalov et al. present data to explain the reduced sensitivity and faster response kinetics of cones. They show that the chromophore dissociates from cone but not rod visual pigment, yielding apo-opsin. This apo-opsin activates the signaling cascade to desensitize cones and speed the photoresponse.

Ambystoma↗