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At least 19 recordsLinked to original sources
PubMed2025

Tandem Gene Clusters as Phylogenetic Anchors Reveal the Hidden History of Vertebrate Visual Opsins.

The expansion of the visual opsin gene family was a crucial event in the diversification of vertebrate vision in evolution. Additional expansions in phototransduction-related genes facilitated the development of dim-light (rods) and color vision (cones). Sequence-based phylogeny and gene positions from extant jawed vertebrate genomes are insufficient to untangle the visual opsin duplications in early vertebrates. Additionally, jawless vertebrates share a visual opsin gene repertoire with jawed vertebrates which conflicts with recent findings of distinct whole-genome duplications in each lineage. To resolve these questions, we analyzed jawless vertebrate genomes, focusing on visual opsin genes. Our findings, based on chromosomal arrangements and relationships, confirm tandem duplications of visual opsins before the vertebrate radiation.

Animals↗
PubMed1990

The structure of bacteriorhodopsin and its relevance to the visual opsins and other seven-helix G-protein coupled receptors.

Bacteriorhodopsin is a light-driven hydrogen-ion pump whose structure is known to about 6.0 A in three dimensions and 2.8 A in projection. It consists of seven transmembrane helices surrounding the chromophore, retinal. Halorhodopsin is a second member of the same family of membrane proteins, both of them from the cell membrane of halobacteria. Halorhodopsin is a light-driven chloride-ion pump but has very close homology to bacteriorhodopsin, especially around the retinal. In contrast, the visual opsins that are responsible for the primary step in visual transduction in all eukaryotes from Drosophila upwards, form a separate family with no direct sequence homology to the bacteriorhodopsin family. The visual opsin family now includes about 15 other receptor proteins, all of which active G-protein cascades, including the beta-adrenergic receptor as well as several others. Despite the lack of clear relations at the level of amino acid sequence, there are topographical similarities between the bacteriorhodopsin and the visual opsin families in the nature and site of chromophore attachment, the number of transmembrane helices and the positions of the amino and carboxyl termini in the membrane. These suggest that if the two were at one time closely related, they have diverged too far to have sequences that are detectably similar.

Amino Acid Sequence↗
PubMed1988

[Synthesis of visual rhodopsin in a cell-free translation system. I. Influence of the structure of the synthetic bovine visual opsin mRNA on its translational efficiency].

Influence of structural changes in nontranslated regions and translation initiation site of the in vitro synthesized bovine opsin mRNA on its translational efficiency in the wheat germ cell-free system has been studied. It is shown that level of the opsin synthesis up to 30 micrograms per 1 ml of translational mixture can be attained by optimizing structure of 5'-nontranslated region.

Animals↗
PubMed1991

Carotenoid replacement therapy in Drosophila: recovery of membrane, opsin and visual pigment.

Rhabdomeres are substantially smaller and visual pigment is nearly eliminated when Drosophila are carotenoid-deprived from egg to adult. Rhabdomeres enlarge and visual pigment increases with carotenoid replacement in adults using carrot juice. We used a monoclonal antibody to the opsin in R1-6 receptors in the compound eye to further quantify opsin recovery in such carotenoid replacement therapy. Density of immunogold, specific to R1-6 (vs. R7), increases between days 1 and 3 of replacement as visual pigment and rhabdomeres recover. In summary, visual pigment, opsin and the opsin-containing organelle recover during carotenoid replacement therapy in carotenoid-deprived Drosophila.

Animals↗
PubMed1991

Proper cotranslational insertion of visual rhodopsin into the lipid bilayer occurs in the absence of protein translocation machinery.

The insertion of visual opsin into membranes occurred during in vitro translation of opsin mRNA in wheat germ extract in the presence of either microsomes or liposomes. The rhodopsin that integrated into both types of membranes after regeneration with 11-cis-retinal was functionally active (in contrast to the nonincorporated protein). Opsin either cotranslationally translocated into microsomes or inserted into liposomes had equal sensitivity to proteolysis and yielded the same pattern of peptides, which differed substantially from the set of peptides produced during proteolysis of opsin not incorporated into membranes. Thus visual opsin does not require protein translocation machinery for proper insertion into the lipid bilayer.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1991

Turnover of membrane and opsin in visual receptors of normal and mutant Drosophila.

Electron microscopy was used to investigate membrane turnover in the photoreceptors of Drosophila. Coated pits and vesicles, multivesicular bodies, primary lysosomes, multilamellate bodies, residual bodies and Golgi complexes are present throughout a light/dark cycle. Serial sections reveal that the membrane bounding of multivesicular bodies is only seen at an optimal plane of section. The temperature-sensitive shibire (shi(ts)) mutant has a defect in conversion of coated pits into vesicles which may also affect visual receptors. We used monoclonal antibodies to Rh1 in R1-6 receptors in the compound eye (also to Rh2 in ocellar receptors in the simple eyes) ro relate turnover processes at the visual pigment compared with membrane levels. Compound eye rhabdomeres but not rhabdomere caps stained selectively. Immunogold labelling was equivocal in multivesicular bodies. Further, early in the process of carotenoid replacement therapy, labelling is high in the rough endoplasmic reticulum, demonstrating de novo opsin synthesis.

Animals↗
PubMed1985

Immunoassay of rod visual pigment (opsin) in the eyes of rds mutant mice lacking receptor outer segments.

In 020/A mice, homozygous for the retinal degeneration slow (rds) gene, the photoreceptor cells fail to develop outer segments, and in the absorption spectra of retinal extracts the rhodopsin peak is lacking. Application of an enzyme-linked immunoassay using antisera against bovine opsin shows, however, that opsin is present in the homozygous mutant retina (0.010 nmol/eye) at 3% of the level of the normal retina (0.38 nmol/eye) of Balb/c mice. In the retina of heterozygous mice the opsin level (0.19 nmol/eye) is about half of the normal. Detection of opsin in the rds mutant retina demonstrates the functional basis for the reported electroretinographic response and light-mediated reduction in cyclic nucleotide levels in this mutant.

Animals↗
PubMed1989

Genetic regulation of beta-adrenergic receptors.

Several members of the family of receptors coupled to G proteins have been cloned in recent years. From the primary sequence information furnished by these clones, a characteristic seven-membrane spanning topography has emerged as the prototype for this class of receptors, in analogy with the opsin visual pigments. Cloned genes for the various receptors provide important tools for probing the regulation of their expression. For example, the underlying genetic basis for the expression of adrenergic receptor subtypes can now be explored. The physiological regulation of receptors by heterologous hormones, such as steroids and thyroid hormones, has long been suspected to involve changes in the expression of the relevant adrenergic receptor genes. At least for the glucocorticoids, beta 2AR expression is controlled at the level of transcription. The hormonal regulation of other adrenergic receptor subtypes is currently being explored.

Animals↗
PubMed1988

Experimental autoimmune uveoretinitis in rats induced by rod visual pigment: rhodopsin is more pathogenic than opsin.

The rod visual pigment, rhodopsin, and its illuminated form, opsin, were used to induce experimental autoimmune uveoretinitis in rats. Rhodopsin appears to be more pathogenic than opsin. A dose of 250 micrograms rhodopsin injected in Freund's complete adjuvant and pertussis adjuvant induces nongranulomatous inflammation with higher frequency, which starts earlier and is more severe than that induced by opsin. Two weeks postinjection, the mean score of rhodopsin-injected animals is more than twice as high as that of opsin-injected animals. The high pathogenicity of rhodopsin appears to be related to the biochemical integrity of the protein and depends on its state of illumination. The levels of the immune responses (both cellular and humoral) measured at day 10 postinjection do not account for the pronounced difference in pathogenicity between rhodopsin and opsin. The developmental patterns of severe uveoretinitis induced by rhodopsin or opsin were histologically evaluated and appear to be similar. In both cases we observed dense mononuclear and polymorphonuclear cell infiltrations in the retina and anterior uvea. Only in the severe stages does the choroid become involved. However, rhodopsin causes more pronounced involvement of the ciliary body, pars plana, and anterior chamber. The inflammation finally results in total elimination of the photoreceptor cell layer.

Animals↗
PubMed1985

Competition between retinal and 3-dehydroretinal for opsin in the regeneration of visual pigment.

Rhodopsin regenerated faster than porphyropsin in all preparations of bullfrog opsin, bullfrog rod outer segment membrane and cattle opsin. When opsin was incubated with excess amount of an equimolar mixture of 11-cis-retinal and 11-cis-3-dehydroretinal, the composition of the regenerated pigment was simply dependent on the ratio of regeneration rates of rhodopsin and porphyropsin. This result can provide a mechanism to account for the discrepancy in vitamin A1/A2 composition between the retina and the pigment epithelium. The property of opsin preferring retinal to 3-dehydroretinal may be one of the basic factors affecting vitamin A1/A2 visual pigment systems.

Animals↗
PubMed1990

Solid-state NMR studies of the mechanism of the opsin shift in the visual pigment rhodopsin.

Solid-state 13C NMR spectra have been obtained of bovine rhodopsin and isorhodopsin regenerated with retinal selectively 13C labeled along the polyene chain. In rhodopsin, the chemical shifts for 13C-5, 13C-6, 13C-7, 13C-14, and 13C-15 correspond closely to the chemical shifts observed in the 11-cis protonated Schiff base (PSB) model compound. Differences in chemical shift relative to the 11-cis PSB chloride salt are observed for positions 8 through 13, with the largest deshielding (6.2 ppm) localized at position 13. The localized deshielding at C-13 supports previous models of the opsin shift in rhodopsin that place a protein perturbation in the vicinity of position 13. Spectra obtained of isorhodopsin regenerated with 13C-labeled 9-cis-retinals reveal large perturbations at 13C-7 and 13C-13. The similar deshielding of the 13C-13 resonance in both pigments supports the presence of a protein perturbation near position 13. However, the chemical shifts at positions 7 and 12 in isorhodopsin are not analogous to those observed in rhodopsin and suggest that the binding site interactions near these positions are different for the two pigments. The implications of these results for the mechanism of the opsin shift in these proteins are discussed.

Animals↗
PubMed1988

Transcript localization of four opsin genes in the three visual organs of Drosophila; RH2 is ocellus specific.

Drosophila and other Dipteran flies have three different kinds of visual organs; in the adult a pair of compound eyes and three dorsal ocelli; and in the larva a pair of internal photoreceptor organs. They develop in distinct ways, yet have certain features in common. All three organs use retinal-derived chromophores, coupled to distinct opsins, to provide a diversity of spectral sensitivities. Four opsin genes have been identified thus far in Drosophila; Rh1, Rh2, Rh3 and Rh4 (refs 6-11). We have used in situ hybridization to study the messenger RNAs expressed by these four opsin genes in all three visual organs. Rh1, Rh3 and Rh4 are already known to be expressed in different subsets of cells in the compound eye. We found that, in contrast, opsin Rh2 is the predominant opsin expressed in the ocelli. Opsin Rh1 is known to be expressed in the larval photoreceptor. We found that Rh3 and Rh4 are as well, but not Rh2. The ocellar-specific gene expression of Rh2 is of particular interest for its possible bearing on the function of the ocellus.

Animals↗
PubMed1979

The gecko visual pigments. The behavior of opsin.

The 521-pigment extracted out of the retina of the Tokay gecko has the typical stereospecificity of the vertebrate visual pigments. This is true for the pigment in the chloride-depleted, "blue-shifted" state as well as for the normal pigment with added chloride. While in the chloride-deficient state, pigment regeneration occurred with both 11-cis- and 9-cis-retinals and the regenerated photopigments were also in the blue-shifted, chloride-depleted state. As with the native pigment, these regenerated pigments were bathochromically shifted to their normal positions by the addition of chloride. Chloride-deficient opsin by itself also responded to chloride for the pigment regenerated with 11-cis-retinal from such chloride-treated opsin was in the normal 521-position. Regeneration was always rapid, reaching completion in less than 5 min, and was significantly faster than for cow rhodopsin regenerating under the same conditions. This rapid rate was found with or without chloride, with both 11-cis- and 9-cis-retinals and in the presence of the sulfhydryl poison, p-hydroxymercuribenzoate (PMB). Like the native chloride-deficient pigment, the regenerated chloride-depleted photopigments responded to PMB by a blue shift beyond the position of the chloride-deficient state. The addition of chloride to these "poisoned" regenerated pigments caused a bathochromic shift of such magnitude as to indicate a repair of both the PMB and chloride-deficient blue shift. In this discussion the possible implications of these results to phylogenetic considerations are considered as well as to some molecular properties of the 521-pigment.

Animals↗
PubMed1992

Abnormal dark adaptation kinetics in autosomal dominant sector retinitis pigmentosa due to rod opsin mutation.

The time course of dark adaptation was measured in 10 subjects from three families with autosomal dominant sector retinitis pigmentosa (RP) due to mutations in the first exon of the rod opsin gene. In each subject cone adaptation and the early part of the recovery of rod sensitivity followed the normal time course, but the later phase of rod adaptation was markedly prolonged. The recovery of rod sensitivity is much slower than that reported in any other outer retinal dystrophy. Using a model based upon primate data of rod outer segment length and turnover, we have calculated that the delayed phase of the recovery of rod sensitivity in the RP patients tested following strong light adaptation could be due in part to formation of new disc membrane with its normal concentration of rhodopsin rather than in situ regeneration of photopigment.

Adolescent↗