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PubMed2006

Conserved cis-elements in the Xenopus red opsin promoter necessary for cone-specific expression.

The long-wavelength sensitive (red) opsin genes encode proteins which play a central role in daytime and color vision in vertebrates. We used transgenic Xenopus to identify 5' cis-elements in the red cone opsin promoter necessary for cone-specific expression. We found a highly conserved extended region (-725 to -173) that was required for restricting GFP transgene expression to cones. We further identified a short element (5'-CCAATTAAGAGAT-3') highly conserved amongst tetrapods, including humans, necessary to restrict expression to cones in the retina. These results identify novel conserved elements that regulate spatial expression of tetrapod red cone opsin genes.

5' Flanking Region↗
PubMed2003

Co-localization of mesotocin and opsin immunoreactivity in the hypothalamic preoptic nucleus of Xenopus laevis.

The purpose of the present investigation was to provide a detailed description of the encephalic photoreceptors of Xenopus laevis at the light microscopic level and to determine their relationship with the neurosecretory cells of the hypothalamus in order to further our understanding of photoperiodic regulation of seasonal rhythms. Numerous opsin-positive neurons were found in the hypothalamic magnocellular preoptic nucleus and their axonal processes were seen to run laterally towards the basal regions of the brain, reaching the neural lobe of the hypophysis. Analysis of labelling with different antisera in adjacent sections, as well as double-immunolabelling carried out on the same section, revealed that mesotocin immunoreactivity was present in most of the opsin-positive neurons; however, no evidence for opsin and vasotocin coexpression was found in any of the sections analysed. The close localization of LHRH and opsin/mesotocin fibers in some regions of the brain, such as the median eminence, suggests that some interaction between these two systems might exist. In conclusion, in this study we provide the first strong evidence that the hypothalamic mesotocinergic neurons, which have been proved to be connected to the GnRH system in other species, are directly involved in photoreception in Xenopus laevis. These findings represent a novel contribution to our understanding of how light influences the seasonal reproductive cycles in lower vertebrates.

Animals↗
PubMed2000

Molecular cloning of fresh water and deep-sea rod opsin genes from Japanese eel Anguilla japonica and expressional analyses during sexual maturation.

We have determined the complete cDNA sequences of fresh water rod opsin gene (fwo) and deep-sea rod opsin gene (dso) from Japanese eel Anguilla japonica. The cDNA clones of fwo and dso consisted of 1437 and 1497 nucleotides, respectively. The predicted opsins of both genes consisted of 352 amino acid residues. Southern blot and PCR analyses of genomic DNA indicated that the Japanese eel genome contains only one fwo and one dso and they are intronless. Quantitative RT-PCR analyses revealed that the expression of fwo decreases with sexual maturation while that of dso increases.

Anguilla↗
PubMed2002

Opsin gene and photopigment polymorphism in a prosimian primate.

A recent genetic investigation found some species of prosimian to have an opsin gene polymorphism [Nature 402 (1999) 36]. In the present study the functional implications of this finding were explored in a correlated investigation of opsin genes and spectral sensitivity measurements of a diurnal prosimian, Coquerel's sifaka (Propithecus verreauxi coquereli). Spectra recorded using electroretinogram (ERG) flicker photometry reveal a cone photopigment polymorphism paralleling an opsin gene polymorphism detected by molecular methods. This species has two middle-to-long-wavelength cone pigments with peak sensitivities of about 545 and 558 nm and a short-wavelength-sensitive cone with a peak at about 430 nm. The distribution of these pigments among animals predicts the presence of both dichromatic and trichromatic forms of color vision.

Animals↗
PubMed2000

Assays for activation of opsin by all-trans-retinal.

The data collected with the techniques discussed in this chapter suggest significant differences between the active conformation(s) of the opsin/atr complex, which are reversibly formed in the dark, and the active conformation (R*) of the meta-II photoproduct. First, there is good evidence for noncovalent opsin/atr complexes with considerable activity (although covalent binding of atr is found in mutant opsins. Even more intriguing, all-trans-retinal in an amount that saturates the activity of the opsin/atr complex toward Gt does not measurably inhibit the access of 11-cis-retinal to the light-sensitive binding site during regeneration (Fig. 2C). On the other hand, forced protonation at or near Glu-134 appears to be an integral mechanism for both the meta-II and the opsin-like activities (Fig. 4). Thus, it is not inconceivable that these two activities of the receptor arise from two fundamentally different conformations, one meta-II-like and one opsin-like. They would be similar with respect to the Gt (or RK) protein-protein interaction but different in their mode of retinal-protein interaction.

Animals↗
PubMed1992

Comparative ultrastructure and opsin immunocytochemistry of the retina and pineal organ in fish.

The pineal organ and retina were compared in developing charr and cisco, further in adult cisco, eel, creek chub, dace, zebrafish and black moli by opsin immunocytochemistry. In prehatching charr embryos, retinal rods and cones and pinealocytes displayed well-developed outer segments and formed synapses. Differentiation of the retina started centrally but was more advanced in the dorso-caudal retina than rostroventrally. The pineal organ differentiated earlier distally than proximally. In the cisco, the pineal organ and retina differentiated around hatching. In charr embryos, further in the larval and adult species studied, opsin immunoreactivity was found in retinal rods, accessory cones and many "rod-like" pinealocytes, a result indicating the presence of rhodopsin and/or porphyropsin. Retinal principle cones, long and short cones and some "cone-like" pinealocytes were opsin-immunonegative; they are thought to represent red- and/or u.v./violet-sensitive elements. The pineal organ may be involved in negative phototaxic behavior. Both the retina and pineal organ appear to be suitably differentiated to detect light in the larval and embryonic charr.

Animals↗
PubMed2002

Molecular identification and developmental expression of UV and green opsin mRNAs in the pineal organ of the Atlantic halibut.

The pineal organ is the only differentiated photoreceptor organ present in embryos and early larvae of the Atlantic halibut (Hippoglossus hippoglossus). We investigated the molecular identity of opsins in the pineal organ, and their expression during different life stages. Using RT-PCR we identified two 681-bp gene sequences, named HPO1 and HPO4, in cDNA from adult pineal and whole embryos. The predicted amino acid sequences showed highest identity to the transmembrane regions of teleostean RH2 green cone opsins (HPO1, 72-91%) and SWS-1 UV cone opsins (HPO4, 71-83%). In situ hybridization revealed expression of HPO1 and HPO4 mRNA transcripts in photoreceptors in the pineal organ of embryos, larvae and adults. HPO1 and HPO4 mRNA transcripts were also expressed in the larval retina. Our study provides molecular evidence for short and middle wavelength light sensitive photoreceptors in the pineal organ of Atlantic halibut throughout life, and suggests that pineal photoreception may play an important role during embryonic and larval life stages, especially at the time when the retina does not possesses corresponding photoreceptor capacity.

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↗
PubMed1997

The rod and green cone opsins of two avian species, the budgerigar, Melopsittacus undulatus, and the mallard duck, Anas platyrhynchus.

The genes for the rod and rod-like green cone opsins in two avian species, the budgerigar, Melopsittacus undulatus, and the mallard duck, Anas platyrhynchus, are identified on the basis of amino acid identity with the equivalent chicken sequences and their placement into a single phylogenetic clade with the rod and rod-like green cone opsin genes from other vertebrate species. Since the two bird species studied are taxonomically quite distinct, this would indicate that this rod-like green cone opsin gene, although absent in mammals, is common in the Aves. The two avian pigments differ consistently at site 122, consistent with the reported role of this site in determining the rate of metarhodopsin II formation and decay in rod and cone pigments. Candidate sites are identified to compensate for the known spectral effects of substitution at this site.

Amino Acid Sequence↗
PubMed1996

Identification of a novel Drosophila opsin reveals specific patterning of the R7 and R8 photoreceptor cells.

The function of the compound eye is dependent upon a developmental program that specifies different cell fates and directs the expression of spectrally distinct opsins in different photoreceptor cells. Rh5 is a novel Drosophila opsin gene that encodes a biologically active visual pigment that is expressed in a subset of R8 photoreceptor cells. Rh5 expression in the R8 cell of an individual ommatidium is strictly coordinated with the expression of Rh3, in the overlying R7 cell. In sevenless mutant files, which lack R7 photoreceptor cells, the expression of the Rh5 protein in R8 cells is disrupted, providing evidence for a specific developmental signal between the R7 and R8 cells that is responsible for the paired expression of opsin genes.

Animals↗
PubMed2001

Role of noncovalent binding of 11-cis-retinal to opsin in dark adaptation of rod and cone photoreceptors.

Regeneration of visual pigments of vertebrate rod and cone photoreceptors occurs by the initial noncovalent binding of 11-cis-retinal to opsin, followed by the formation of a covalent bond between the ligand and the protein. Here, we show that the noncovalent interaction between 11-cis-retinal and opsin affects the rate of dark adaptation. In rods, 11-cis-retinal produces a transient activation of the phototransduction cascade that precedes sensitivity recovery, thus slowing dark adaptation. In cones, 11-cis-retinal immediately deactivates phototransduction. Thus, the initial binding of the same ligand to two very similar G protein receptors, the rod and cone opsins, activates one and deactivates the other, contributing to the remarkable difference in the rates of rod and cone dark adaptation.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed2002

Opsin cDNA sequences of a UV and green rhodopsin of the satyrine butterfly Bicyclus anynana.

The cDNAs of an ultraviolet (UV) and long-wavelength (LW) (green) absorbing rhodopsin of the bush brown Bicyclus anynana were partially identified. The UV sequence, encoding 377 amino acids, is 76-79% identical to the UV sequences of the papilionids Papilio glaucus and Papilio xuthus and the moth Manduca sexta. A dendrogram derived from aligning the amino acid sequences reveals an equidistant position of Bicyclus between Papilio and Manduca. The sequence of the green opsin cDNA fragment, which encodes 242 amino acids, represents six of the seven transmembrane regions. At the amino acid level, this fragment is more than 80% identical to the corresponding LW opsin sequences of Dryas, Heliconius, Papilio (rhodopsin 2) and Manduca. Whereas three LW absorbing rhodopsins were identified in the papilionid butterflies, only one green opsin was found in B. anynana.

Amino Acid Sequence↗
PubMedDate not supplied

Receptor demise from alteration of glycosylation site in Drosophila opsin: electrophysiology, microspectrophotometry, and electron microscopy.

In the delta Asn20 Drosophila stock, the N-linked glycosylation site of opsin in R1-6 receptors (Rh1) is absent. We used electroretinography (ERG), microspectrophotometry (MSP), and electron microscopy (EM) to quantify visual cell defects. Positive controls, w9, had wild type Rh1. MSP revealed minimal photopigment in delta Asn20 for 6 days posteclosion; w9 had near normal visual pigment. ERG sensitivity and prolonged depolarizing afterpotential (PDA) were compared for delta Asn20 and w9. Delta Asn20's R1-6 function is decreased 100-fold at eclosion and diminishes until only R7/8 functions at 11 days. What little rhodopsin is routed to the rhabdomere functions. Morphometry showed smaller R1-6 rhabdomeres in delta Asn20 for 8 days posteclosion. Rhabdomeres in w9 were normal. A negative control, ninaE(ol17), a deletion of the Rh1 gene, also has small rhabdomeres. Delta Asn20 and ninaE(ol17) lack the extreme rhabdomere elimination of ora (outer rhabdomeres absent), a nonsense mutant interrupting Rh1's coding sequence. Delta Asn20 and ora have surplus membrane while ninaE(ol17) does not. Freeze fracture reveals that delta Asn20's rhabdomeric P-face particle count is as low as for vitamin A deprivation, consistent with an opsin defect. High particle density, organized into rows, is present in adjacent plasmalemma where surplus membrane accumulates. In summary, delta Asn20 interferes with either synthesis, deployment, or maintenance of opsin.

Animals↗
PubMedDate not supplied

Expression of a mutant opsin gene increases the susceptibility of the retina to light damage.

The question of whether the expression of mutant opsin predisposes the retina to light damage was addressed using transgenic mice that express rhodopsin with three point mutations near the N-terminus of the molecule. The mutations involve the substitution of histidine for proline at position 23 (P23H), glycine for valine at position 20 (V20G), and leucine for proline at position 27 (P27L). These mice express equal amounts of mutant and wild-type transcripts, and develop a progressive photoreceptor degeneration that is similar to that seen in human retinitis pigmentosa (RP). The P23H mutation is associated with the most frequently occurring form of human autosomal dominant retinitis pigmentosa (ADRP) in the United States. Transgenic and normal littermates were exposed to illuminance of 300 foot-candles (ft-c) for 24 h, then placed in darkness for either 6 h, 6 days, or 14 days. Histological and biochemical techniques were used to evaluate the outer retina in light-exposed and control animals reared on 12-h light/12-h dark cycle. The results indicate that light exposure accelerates the pathological changes associated with the transgene expression. Compared with transgenic animals reared in ambient cyclic light, retinas from light-exposed mice had a reduced rhodopsin content, fewer photoreceptor cell bodies, and less preservation of retinal structure. Data obtained from normal mice did not differ for the lighting regimens used. These findings suggest that the expression of VPP mutations in the opsin gene predisposes the transgenic photoreceptors to be more susceptible to light damage. The data also suggest that reducing photic exposure may be beneficial to any patient with RP mediated by an opsin mutation.

Animals↗
PubMed1987

Electrostatic interaction between retinylidene chromophore and opsin in rhodopsin studied by fluorinated rhodopsin analogues.

Photochemical reactions of fluorinated rhodopsin analogues (F-rhodopsins) prepared from 10- or 12-fluorinated retinals (10- or 12-F-retinals) and cattle opsin were investigated by means of low-temperature spectrophotometry. On irradiation with blue light at liquid nitrogen temperature (-191 degrees C), the F-rhodopsins were converted to their respective batho intermediates. On warming, they decomposed to their respective fluororetinals and cattle opsin through lumi and meta intermediates. There was a difference in photochemical behavior between batho-12-F-rhodopsin and batho-10-F-rhodopsin. Upon irradiation with red light at -191 degrees C, batho-12-F-rhodopsin was converted to a mixture of 12-F-rhodopsin and 9-cis-12-F-rhodopsin like that of the natural bathorhodopsin, whereas batho-10-F-rhodopsin was not converted to 9-cis-10-F-rhodopsin but only to 10-F-rhodopsin. This fact suggests that the fluorine substituent at the C10 position (i.e., 10-fluoro) of the retinylidene chromophore may interact with the protein moiety during the process of isomerization of the chromophore or in the state of the batho intermediate. On irradiation with blue light at -191 degrees C, 9-cis-10-F-rhodopsin was converted to another bathochromic intermediate that was different in absorption spectrum from batho-10-F-rhodopsin. 9-cis-10-F-rhodopsin was practically "photoinsensitive" at liquid helium temperature (-265 degrees C), whereas 10-F-rhodopsin was converted to a photo-steady-state mixture of 10-F-rhodopsin and batho-10-F-rhodopsin. The specific interaction between the fluorine atom at the C10 position of the retinylidene chromophore and the opsin was discussed in terms of electrostatic interactions.

Animals↗
PubMed2003

Spontaneous activity of opsin apoprotein is a cause of Leber congenital amaurosis.

Mutations in Rpe65 disrupt synthesis of the opsin chromophore ligand 11-cis-retinal and cause Leber congenital amaurosis (LCA), a severe, early-onset retinal dystrophy. To test whether light-independent signaling by unliganded opsin causes the degeneration, we used Rpe65-null mice, a model of LCA. Dark-adapted Rpe65-/- mice behaved as if light adapted, exhibiting reduced circulating current, accelerated response turn-off, and diminished intracellular calcium. A genetic block of transducin signaling completely rescued degeneration irrespective of an elevated level of retinyl ester. These studies clearly show that activation of sensory transduction by unliganded opsin, and not the accumulation of retinyl esters, causes light-independent retinal degeneration in LCA. A similar mechanism may also be responsible for degeneration induced by vitamin A deprivation.

Animals↗
PubMed1996

Molecular evolution of retinal and nonretinal opsins.

Vision and the circadian rhythms of various biological functions are triggered by phototransduction. The retinal and nonretinal (pineal gland-specific) opsins are traced back to a single common ancestor. Evolutionary analyses of these opsins identify amino acid changes that are potentially important in the regulation of wavelength absorption of photosensitive molecules-visual pigments. Such theoretical predictions can now be tested experimentally using site-directed mutagenesis; expressing the mutagenized opsins in tissue culture cells, reconstituting with 11-cis retinal, and measuring the absorption spectra of the regenerated visual pigments.

Animals↗
PubMed1996

Ret 1, a cis-acting element of the rat opsin promoter, can direct gene expression in rod photoreceptors.

The Ret 1 element, located at -136 to -110 in the rat opsin promoter, binds developmentally regulated retinal nuclear proteins. A similar sequence is found up-stream of opsin genes, from humans to Drosophila, as well as many other photoreceptor-specific genes. The function of the Ret 1 element was tested both in vitro and in two sets of transgenic mice. A mutated Ret 1 element did not bind retinal nuclear proteins in vitro. The same mutations in an otherwise normal 1.9-kb rat opsin promoter failed to drive expression of a lacZ reporter gene in nine of 12 lines. In the three other lines, expression in photoreceptors was very faint. Four tandem copies of the Ret 1 element maintained the Ret 1 binding specificity in vitro and were able to direct expression of a lacZ transgene in photoreceptors of all nine mouse lines obtained. In two lines, expression was also detected in the ganglion cell layer and the ciliary epithelium. In three lines, a characteristic pattern of expression was found in the nervous system in addition to the normal retinal expression. These results indicate that Ret 1 can and is necessary to drive gene expression in rod photoreceptors. Furthermore, our results suggest that Ret 1-like elements may also be important in the developing nervous system.

Animals↗