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Results for “visual opsins”

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At least 433 records · Page 24Linked to original sources
PubMed1993

Fatty acids in the lipids of Drosophila heads: effects of visual mutants, carotenoid deprivation and dietary fatty acids.

Lipids of Drosophila heads were extracted and separated by high-performance thin-layer chromatography. Fatty acid compositions of major phospholipids as well as of triglycerides were analyzed by gas-liquid chromatography. Proportions of the major fatty acids (14:0, 16:0, 16:1, 18:0, 18:1, 18:2, 18:3) varied depending on the lipid analyzed. Docosahexaenoic acid (22:6), common in vertebrate photoreceptors and brain, and arachidonic acid (20:4), a precursor of eicosanoids, were lacking. A comparison of the fatty acid composition of the diet vs. the head suggested that Drosophila can desaturate but may not be able to elongate fatty acid carbon chains. Fatty acid analyses were carried out after the following visual system alterations: i) the transduction mutant where no receptor potential results from a deficit in phospholipase C; ii) an allele of eyes absent; iii) the mutant outer rhabdomeres absent which lacks visual pigment and rhabdomeres in the predominant type of compound eye receptor, rhabdomeres 1 through 6; and iv) carotenoid deprivation which reduces opsin and rhabdomere size. We also evaluated aging by comparing newly-emerged vs. aged wild-type flies. Alterations in fatty acid composition based on some of these manipulations were found. Based on comparisons between flies reared on media differing in C16 and C18, there is an indication that diet readily affects tissue fatty acid composition.

Age Factors↗
PubMed1979

11-cis-Retinal-binding protein from bovine retina. Isolation and partial characterization.

11-cis-Retinal-binding protein from bovine retina has been purified to apparent homogeneity by gel filtration ion exchange, and hydroxylapatite chromatography. The molecular weight determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis was 33,000. A value of 36,000 was obtained by gel filtration. With 11-cis-retinal bound to the protein a bleachable spectral peak with maximum absorption at 425 nm was observed. When isolated without addition of exogenous retinal the purified binding protein displayed absorbance maxima at 340 and 425 nm, indicating the occurrence of two ligands in addition to the typical protein absorbance. The endogenous ligands responsible for these maxima were tentatively identified as 11-cis-retinol and 11-cis-retinal, respectively. The binding protein did not cross-react with antibodies prepared against bovine opsin, and its amino acid composition was distinct from that of opsin. The amount of retinal-binding protein extracted was approximately 1 nmol/retina or 1 mol of binding protein/20 mol of opsin. Its specificity and relative abundance suggest that the 11-cis-retinal-binding protein may play a major role in the visual cycle.

Amino Acids↗
PubMed1993

Transcription of photoreceptor genes during fetal retinal development. Evidence for positive and negative regulation.

Rod photoreceptor outer segments are elaborated at approximately 6 months gestation in the cow coinciding with a dramatic increase in mRNAs encoding many visual transduction and associated proteins. Nuclear run-on determination of relative transcription rates demonstrates that gene expression follows three distinct patterns. Opsin, S-antigen, and transducin are all minimally detectable at 5.2 months gestation and increase throughout development. Only opsin demonstrates an additional sharp increase in transcriptional activity which resembles a positive gene-specific enhancer that is first effective between 6.3 and 7.4 months gestation. In contrast, interphotoreceptor retinoid binding protein (IRBP) transcription is already at 43% of its adult level at 5.2 months gestation. To further understand these differences, the relative contributions of initiation and elongation to nuclear run-on signals were examined using either Sarkosyl or ammonium sulfate. Transcriptional rates for S-antigen and transducin were not affected, however, opsin was reduced approximately 4-fold and IRBP was increased approximately 2-fold. Opsin is therefore likely to be initiated de novo during the run-on reaction and responds to a gene-specific positive regulator. The increase in IRBP transcription rate suggests the removal of an elongation inhibitory factor and supports the idea that a negative regulatory element may be involved in controlling IRBP expression.

Animals↗
PubMed1996

The spatio-temporal pattern of photoreceptor degeneration in the aged rd/rd mouse retina.

Photoreceptor degeneration in the retina of the rd/rd (retinal degeneration) mice has been studied using immunocytochemistry with antisera against cone- and rod-opsin. The rd/rd mice exhibited different regional specific rates of degeneration for rods and cones. As early as postnatal day 25, cells labelled with the rod-opsin and cone-opsin antisera disappeared preferently from the central retina. Whereas in the inferior half of the retina, degeneration subsequently proceeded towards the periphery, this did not occur in the dorsal hemisphere. By the age of 100 days, many cells immunoreactive for the cone-opsin antiserum and a few cells immunoreactive for the rod-opsin antiserum were located in an area of the dorsal retina. The ventral retina lacked labelled elements at this age. Finally, rd/rd mice at one year or 600 days of age contained a similar number of cone-opsin immunopositive cells (approximately 2000-2800 cells), occupying almost the same area in the retina as that found at 100 days of age. A photoreceptor candidate for the entrainment of non-visual photoreception probably remains in the cone population in aged rd/rd mice.

Aging↗
PubMed2004

Constitutive opsin signaling: night blindness or retinal degeneration?

A subset of genetic mutations in photoreceptor-specific genes results in abnormally prolonged activation of transducin-mediated photosignaling in rod cells. In humans and animal models, these mutations cause visual dysfunctions ranging from a mild stationary night blindness to severe, early-onset retinal degeneration. There are mechanistic differences between mutations causing night blindness and those causing retinal degeneration. Here, we hypothesize that mutations causing continuous activation of the visual cascade as the result, for example, of the inability of the photoreceptor to regenerate rhodopsin, lead to retinal degeneration; those mutations that can terminate signaling, even if only partially and intermittently, slow the rate of degeneration sufficiently to give rise to stationary night blindness. Furthermore, we hypothesize that a prolonged decrease in intracellular calcium concentration resulting from persistent activation is responsible for triggering apoptotic rod-cell death.

Animals↗
PubMed2005

Patterns of cell proliferation and cell death in the developing retina and optic tectum of the brown trout.

We have analyzed the patterns of cell proliferation and cell death in the retina and optic tectum of the brown trout (Salmo trutta fario) throughout embryonic and postembryonic stages. Cell proliferation was detected by immunohistochemistry with an antibody against the proliferating cell nuclear antigen (PCNA), and apoptosis by means of the TUNEL method. Haematoxylin and DAPI staining were also used to demonstrate apoptotic cells. Photoreceptor cell differentiation was assessed by immunohistochemistry with antibodies against opsins. Throughout embryonic development, PCNA-immunoreactive (PCNA-ir) cells become progressively restricted to the peripheral growth zone of the retina, which appears to be the principal source of new retinal cells from late embryos to adults. However, some PCNA-ir cells are observed secondarily in the differentiated retina, first in the inner nuclear layer of 15-mm alevins and later in the outer nuclear layer of 16-mm alevins, after differentiation of the first rods in the central retina, as demonstrated with opsin immunocytochemistry. Our observations also support the view that the PCNA-ir cells observed secondarily in the INL of the central retina of alevins are photoreceptor precursors. The number and distribution of apoptotic cells in the retina and optic tectum of the trout change throughout development, allowing distinction of several waves of apoptosis. Cell death is detected in proliferating areas at early stages, then in postmitotic or differentiating areas, and later concurring temporal and spatially with the establishment of visual circuits, thus indicating a relationship between apoptosis and proliferation, differentiation and synaptogenesis.

Animals↗
PubMed2000

Responses of neurones of the rat suprachiasmatic nucleus to retinal illumination under photopic and scotopic conditions.

1. We have examined the responses of neurones in the suprachiasmatic nuclei (SCN) of the rat to retinal illumination under photopic and scotopic conditions to identify the types of photoreceptor input to these nuclei. 2. The majority of visually responsive SCN neurones studied under dark adaptation received rod input (48 of 52, 92 %). The action spectrum conformed to the sensitivity of rhodopsin, with maximal sensitivity at around 505 nm. 3. When also studied under light adaptation, most visually responsive SCN neurones (20 out of 26, 77 %) responded to input from cones. The action spectra conformed to the spectrum of green cone opsin, with a main sensitivity peak at 510 nm and a significant secondary peak in the near-ultraviolet region of the spectrum. 4. The frequency of spontaneous activity was typically low under scotopic conditions (range 0.2-17.2 Hz) and higher under photopic conditions (range 0.6-40 Hz) for any given neurone. The most common response under scotopic conditions was an 'on-excitation' (32 of 48, 62.5 %), which changed under photopic conditions to an on-excitation followed by a more prominent off-inhibition. 5. Responses also changed due to endogenous ultradian cycles. Depending on the phase, responses could be altogether absent and even reverted from excitation to inhibition on opposite phases of a cycle. Ultradian cycles had a circadian dependence and were most common at around the light phase:dark phase (L:D) and D:L transition points of the circadian cycle. 6. Under photopic conditions, SCN neurones showed rhythmic electrical activity, with a preferred firing interval that had a value between 18 and 39 ms. This rhythmic activity was probably the result of endogenous subthreshold membrane potential oscillations. 7. In conclusion, light acting either via rod or cone pathways could have powerful, opposing actions on SCN neurones. These actions were state dependent. The presence of these neuronal responses suggests a role for rod and cone photoreceptors in SCN function.

Action Potentials↗
PubMed1994

Is chicken green-sensitive cone visual pigment a rhodopsin-like pigment? A comparative study of the molecular properties between chicken green and rhodopsin.

Chicken green is a visual pigment present in chicken green-sensitive cones and has an amino acid sequence more similar than any other cone visual pigments to the rod visual pigments, rhodopsins. Here we have investigated the molecular properties of chicken green and compared them with those of rhodopsin to elucidate whether or not chicken green is a rhodopsin-like pigment. While chicken green has a molecular extinction coefficient and a photosensitivity very similar to those of rhodopsin, it displays faster regeneration from 11-cis-retinal and opsin and faster formation and decay of the physiologically active meta II intermediate than rhodopsin. These differences correlate with the physiological difference between cones and rods. Thus in spite of the similarity in amino acid sequence, chicken green displays molecular properties required for a cone visual pigment that are clearly different from those of rhodopsin.

Animals↗
PubMed2004

A novel amino acid substitution is responsible for spectral tuning in a rodent violet-sensitive visual pigment.

Cone short-wave (SWS1) visual pigments can be divided into two categories that correlate with spectral sensitivity, violet sensitive above 390 nm and ultraviolet sensitive below that wavelength. The evolution and mechanism of spectral tuning of SWS1 opsins are proving more complex than those of other opsin classes. Violet-sensitive pigments probably evolved from an ancestral ultraviolet-sensitive opsin, although in birds ultraviolet sensitivity has re-evolved from violet-sensitive pigments. In certain mammals, a single substitution involving the gain of a polar residue can switch sensitivity from ultraviolet to violet sensitivity, but where such a change is not involved, several substitutions may be required to effect the switch. The guinea pig, Cavia porcellus, is a hystricognathous rodent, a distinct suborder from the Sciurognathi, such as rats and mice. It has been shown by microspectrophotometry to have two cone visual pigments at 530 and 400 nm. We have ascertained the sequence of the short-wave pigment and confirmed its violet sensitivity by expression and reconstitution of the pigment in vitro. Moreover, we have shown by site-directed mutagenesis that a single residue is responsible for wavelength tuning of spectral sensitivity, a Val86Phe causing a 60 nm short-wave shift into the ultraviolet and a Val86Tyr substitution shifting the pigment 8 nm long wave. The convergent evolution of this mammalian VS pigment provides insight into the mechanism of tuning between the violet and UV.

Amino Acid Sequence↗
PubMed2006

Immunohistochemical evidence of a melanopsin cone in human retina.

PURPOSE: Melanopsin, expressed in a subset of intrinsically photosensitive ganglion cells that project to the suprachiasmatic nucleus (SCN), is involved in the photic entrainment of circadian rhythms and other non-image-forming functions (pupil light reflex, masking, acute heart rate response, and alertness). Melanopsin has recently been shown to be a "bireactive" photopigment that functions as a photosensory opsin using 11-cis retinaldehyde as a chromophore and has intrinsic photoisomerase activity. Melanopsin is widely distributed in the retina of vertebrates and, depending on the species, is expressed in ganglion, amacrine, horizontal, and photoreceptor cells. The present study was conducted to determine the distribution of this opsin in the human retina. METHODS: Human donor eyes were obtained from donors and fixed shortly after death. Immunohistochemistry was used to determine melanopsin expression in the retinas of three donors. The possible coexpression of this photopigment with other opsins was studied by double-labeling immunocytochemistry and confocal analysis. RESULTS: In addition to the expected labeling in ganglion cells of the inner retinal layers, an unexpected finding showed melanopsin-immunopositive label in the outer segments of cones that did not coexpress other known opsins. These melanopsin-expressing cones are extremely sparse (5-25 cones/mm2; 0.1%-0.5% of the entire cone population) and are located in the peripheral retina. CONCLUSIONS: The presence of melanopsin in human cones suggests image and non-image-forming roles in visual responses at both the cone input and ganglion cell output stages and their involvement in a broad spectrum of irradiance detection functions in the visual system.

Adult↗
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↗
PubMed1992

Retinal photoisomerase: role in invertebrate visual cells.

In invertebrate visual cells, the rhodopsin content is maintained at a high level by the fast process of photoregeneration during daylight. Rhodopsin is converted by photoabsorption to metarhodopsin, which is reconverted to rhodopsin by light. In addition, rhodopsin is regenerated by a slow process of renewal which takes days to complete and involves the biosynthesis of opsin. It is well known that rhodopsin can be formed from opsin only when 11-cis-retinal is present; this requires the existence of an isomerizing enzyme which is capable of transforming all-trans-retinal, released from the degradation of metarhodopsin, into the 11-cis-retinal isomer. In some invertebrate visual systems, experiments on rhodopsin regeneration have been interpreted by assuming that the isomerization reaction is a light-dependent process involving a retinal-protein complex. Two retinal photoisomerases which have been well characterized, i.e. bee photoisomerase and cephalopod retinochrome, are reviewed here. Their properties are compared in order to determine their physiological role, which is likely to be in the renewal of visual pigment rhodopsin. To conclude, a visual pigment cycle is proposed in which rhodopsin regeneration follows two light-dependent pathways. This greatly simplifies the rhodopsin regeneration scheme for invertebrate visual systems.

Animals↗
PubMed1993

Effects of hydroxylamine, digitonin and triton X-100 on photoreceptor (paraflagellar swelling) and photoreception of Euglena gracilis.

We present experiments that test the effects of agents commonly used in visual pigment investigations, namely hydroxylamine (NH2OH), digitonin and triton X-100, on the photoreceptor and photoreception of Euglena. Hydroxylamine reacts with free and opsin-bound retinal, in aqueous solution, to form stable oximes, whereas digitonin and triton X-100 are the most common extractants of rhodopsin. Since previous data indicate that the chromophore present in Euglena photoreceptor is retinal, we investigated the influence of these chemicals on this organelle. The effects of these agents were studied by means of phase contrast, fluorescence and transmission electron microscopy and photobehaviour experiments. Hydroxylamine inhibited the formation of the Euglena photoreceptor. Photoaccumulation experiments on hydroxylamine-treated cells showed that they are unable to perceive light. Digitonin solubilized the crystalline structure of the photoreceptor, whereas the triton effect was limited to the membranous structures of the cell, leaving the photoreceptor unimpaired.

Animals↗
PubMed1985

Monoclonal antibodies to crayfish rhodopsin. I. Biochemical characterization and cross-reactivity.

Five antibody secreting cell lines were selected on the basis of specific binding to photoreceptive structures from a fusion of myeloma cells with spleen cells from BALB/c mice immunized with photoreceptor membrane from crayfish compound eyes. On Western blots derived from one- and two-dimensional polyacrylamide gels of purified photoreceptor membrane the antibodies bound strongly to the major 35 kDa peptide and are therefore specific for the visual pigment, rhodopsin. Four antibodies also recognized a minor 24 kDa peptide probably representing a breakdown product generated in vivo by the action of lysosomal hydrolases. Epitope characterization of the antibodies using peptide maps of opsin after protease treatment revealed three grossly different specificities. Three antibodies recognize a major antigenic site located within the large proteolytic fragment of about 24 kDa, possibly derived from the aminoterminus of the molecule. Antibodies applied to lightly fixed frozen sections or semi-thin sections of crayfish retina embedded in Lowicryl or polyethyleneglycol specifically bound to the rhabdomeral structure formed by receptor cells R1-R7, but failed to show significant cross-reaction with R8, the blue receptor, proving significant differences in the primary structure of the apoproteins of visual pigments involved in crayfish colour vision. None of the antibodies revealed any cross-reactivity with Drosophila or squid rhodopsin, corroborating this finding. The antibodies also recognized granular material in the vicinity of the rhabdoms at sites occupied by secondary lysosomes containing degraded rhabdomeral membrane. No significant binding was observed to the outer plasma membrane of the retinula cells, or in any other part of the retina.

Animals↗
PubMed1996

Localization of the human RGR opsin gene to chromosome 10q23.

The human RGR gene encodes an opsin protein (retinal G protein-coupled receptor), which is expressed in Müller cells and the retinal pigment epithelium and is thought to play a role in the visual process. To investigate a possible linkage of the RGR gene to retinal dystrophies, the locus of the gene was mapped on human metaphase chromosomes. Genomic and cDNA fragments of the human RGR gene were used as probes for fluorescence in situ hybridization. Analysis of the fluorescence signals on high-resolution banded chromosomes showed that the RGR gene is localized to human chromosome 10q23. This result now provides for the rapid analysis of this gene with respect to inherited diseases of the retina.

Chromosome Banding↗
PubMed1992

Molecular mechanisms in visual pigment regeneration.

The photochemical bleaching of vertebrate rhodopsin results in the cis to trans isomerization of the 11-cis-retinal protonated Schiff base. Hydrolysis of the Schiff base leads to the formation of opsin and all-trans-retinal. In order for vision to proceed, the enzymatic trans to cis isomerization of a retinoid must occur. Since retinoids exist as alcohols, aldehydes, or esters in the eye, there are potentially nine different routes for isomerization. Moreover, 11-cis-retinoids are approximately 4 kcal/mol higher in energy than their all-trans isomers. Thus, not only must the isomerization route be defined, but an energy source must be identified to power this process. It was discovered that the energy is provided for in a minimally two-step process involving membrane phospholipids as the energy source. First, all-trans-retinol (vitamin A) is esterified in the retinal pigment epithelium by lecithin retinol acyl transferase to produce an all-trans-retinyl ester. Second, this ester is directly transformed into 11-cis-retinol by an isomerohydrolase enzyme, in a process that couples the negative free energy of hydrolysis of the acyl ester to the formation of the strained 11-cis-retinoid.

Acyltransferases↗