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At least 379 records · Page 21Linked to original sources
PubMed2006

Intraocular injection of kainic acid does not abolish the circadian rhythm of arylalkylamine N-acetyltransferase mRNA in rat photoreceptors.

PURPOSE: Melatonin synthesis in mammalian retinal photoreceptors is under photic and circadian control and regulated by changes in the activity of arylalkylamine N-acetyltransferase (AANAT). Recent studies have suggested that retinal dopaminergic neurons contain a circadian pacemaker, and dopamine is the neurotransmitter that drives circadian rhythmicity in the mammalian retina. METHODS: To investigate the role of inner retinal neurons, including dopamine neurons, in generating the rhythm of melatonin synthesis, rat retinas were lesioned with kainic acid (KA), which was shown previously to induce degeneration of neurons in the inner nuclear layer and to eliminate rhythmicity in the dopaminergic system. Aanat, rhodopsin, medium wavelength (mwl) opsin, short wavelength (swl) opsin, and period1 (Per1), and period2 (Per2) mRNA levels were measured using real-time quantitative RT-PCR in KA injected and control eyes. RESULTS: Our data show that intraocular injections of KA did not abolish the daily and circadian rhythms of Aanat mRNA in the photoreceptors, but it did shift the phase of the Aanat transcript rhythm in constant darkness. Surprisingly, KA injections reduced the levels and eliminated daily rhythms of mwl and swl opsin transcripts, but not of rhodopsin mRNA. Per1 and Per2 mRNA levels were rhythmic in saline injected and in KA-treated retinas, and Per2 mRNA levels were significantly reduced (20-50%) in KA-treated retinas. CONCLUSIONS: These findings demonstrate that the circadian clock generating melatonin rhythmicity is largely KA insensitive and likely to be located in the rod photoreceptors, although KA-sensitive neurons do influence its timing. More important, our data demonstrate that dopamine rhythmicity is not necessary for generating the circadian rhythm of Aanat mRNA in the photoreceptors. Our data also indicate that Per1 and Per2 are rhythmically transcribed in the rat retina and KA treatment has a dramatic effect on the overall levels of Per2 mRNA.

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↗
PubMed1992

Retinal cell and photoreceptor transplantation between adult New Zealand red rabbit retinas.

Adult New Zealand Red (NZR) rabbits were used to determine if the techniques developed in the rat to transplant sheets of photoreceptors could be adapted to larger eyes of the rabbit. Adult donor NZR rabbit retina was cut into small strips, oriented, and drawn up in a small and flat polyethylene tube. By transscleral approach, donor retina was correctly oriented and gently placed into the subretinal space of host retinas that were previously ablated of photoreceptors by intravitreal injection of hemoglobin. Two weeks after surgery, rabbits were terminated and eyes processed for histology. Morphologic evaluation indicated that photoreceptors were transplantable between adult rabbits by adaptation of previously developed methods and that they were well maintained for 2 weeks. Transplanted photoreceptors also appeared to retain nearly normal inner and outer segment (I & OS) morphology and anti-opsin reactivity. Finally, inclusion of the inner retina also appeared to help maintain the correct I & OS apposition to the host retinal pigmented epithelium.

Animals↗
PubMed2005

Constitutive activity of a UV cone opsin.

Vertebrate visual pigment proteins contain a conserved carboxylic acid residue in the third transmembrane helix. In rhodopsin, Glu113 serves as a counterion to the positively charged protonated Schiff base formed by 11-cis retinal attached to Lys296. Activation involves breaking of this ion pair. In UV cone pigments, the retinyl Schiff base is unprotonated, and hence such a salt bridge is not present; yet the pigment is inactive in the dark. Mutation of Glu108, which corresponds to rhodopsin's Glu113, to Gln yields a pigment that remains inactive in the dark. The apoproteins of both the wild-type and mutant, however, are constitutively active with the mutant being of significantly higher activity. Thus, one important role for preserving the negatively charged glutamate in the third helix of UV pigments is to maintain a less active opsin in a manner similar to rhodopsin. Ligand binding itself in the absence of a salt bridge is sufficient for deactivation.

Amino Acid Substitution↗
PubMed2002

Transport to the photoreceptor outer segment by myosin VIIa and kinesin II.

This paper reviews our studies in which we have used mutant mice to investigate the roles of myosin VIIa and kinesin II in the transport of proteins to the photoreceptor outer segment. These studies suggest that both motors participate in moving opsin along the connecting cilium. Given the velocities measured for these motors in vitro, it is predicted that the resulting concentration of opsin in the plasma membrane of the connecting cilium is surprisingly low.

Animals↗
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↗
PubMed1999

Structure and function in rhodopsin: kinetic studies of retinal binding to purified opsin mutants in defined phospholipid-detergent mixtures serve as probes of the retinal binding pocket.

In the current standard procedure for preparation of mammalian rhodopsin mutants, transfected COS-1 cells expressing the mutant opsin genes are treated with 5 microM 11-cis-retinal before detergent solubilization for purification. We found that binding of 11-cis-retinal to opsin mutants with single amino acid changes at Trp-265 (W265F,Y,A) and a retinitis pigmentosa mutant (A164V) was far from complete and required much higher concentrations of 11-cis-retinal. By isolation of the expressed opsins in a stable form, kinetic studies of retinal binding to the opsins in vitro have been carried out by using defined phospholipid-detergent mixtures. The results show wide variation in the rates of 11-cis-retinal binding. Thus, the in vitro reconstitution procedure serves as a probe of the retinal-binding pocket in the opsins. Further, a method is described for purification and characterization of the rhodopsin mutants after retinal binding to the opsins in vitro.

Amino Acid Sequence↗
PubMed1992

Ectopic expression of ultraviolet-rhodopsins in the blue photoreceptor cells of Drosophila: visual physiology and photochemistry of transgenic animals.

We have generated transgenic flies expressing R7 cell-specific opsins in the major class of photoreceptor cells of the Drosophila retina and characterized their spectral properties using high-resolution microspectrophotometry and sensitivity recordings. We show that the Rh3 and Rh4 opsin genes encode UV-sensitive opsins with similar spectral properties (lambda max = 345 nm and 375 nm), and that Rh3 corresponds to the R7p and R7marg class of visual pigments. We have also generated Rh3 and Rh4 isoform-specific antibodies and present an R7 cell map of the Drosophila retina. In a related set of experiments, we show that it is possible to coexpress two different visual pigments functionally in the same cell and produce photoreceptors that display the summed spectral response of the individual pigments. These findings open up the possibility of tuning an animal's visual behavior by targeted expression of combinations of opsin genes to selective types of photoreceptors.

Animals↗
PubMed1998

Frequent gene conversion between human red and green opsin genes.

To study the evolution of human X-linked red and green opsin genes, genomic sequences in large regions of the two genes were compared. The divergences in introns 3, 4, and 5 and the 3' flanking sequence of the two genes are significantly lower than those in exons 4 and 5. The homogenization mechanism of introns and the 3' flanking sequence of human red and green opsin genes is probably gene conversion, which also occurred in exons 1 and 6. At least one gene conversion event occurred in each of three regions (1, 3, and 5) in the sequences compared. In conclusion, gene conversion has occurred frequently between human red and green opsin genes, but exons 2, 3, 4, and 5 have been maintained distinct between the two genes by natural selection.

DNA↗
PubMed2004

Differential expression of duplicated opsin genes in two eyetypes of ostracod crustaceans.

In the first molecular study of ostracod (Crustacea) vision, we present partial cDNA sequences of ostracod visual pigment genes (opsins). We found strong support for differential expression of opsins in ostracod median and compound eyes and suggest that photoreceptor specific expression may be a general phenomenon in organisms with multiple receptors. We infer that eye-specific expression predates the divergence of the two species examined, Skogsbergia lerneri and Vargula hilgendorfii, because eye-specific opsin orthologs are present in both species. We found multiple opsin loci in ostracods, estimating that at least eight are present in Skogsbergia lerneri. All opsins from both ostracod species examined are more closely related to each other than to any other known opsin sequences. Because we find no evidence for gene conversion or alternative splicing, we suggest the occurrence of many recent gene duplications. Why ostracods may have retained multiple recent opsin gene duplicates is unknown, but we discuss several possible hypotheses.

Amino Acid Sequence↗
PubMed1986

Multiple opsin mRNA species in bovine retina.

Two retina specific cDNAs have been isolated by differential colony hybridization to retina and brain, and one of them, pCR-394, was identified as an opsin cDNA. By Northern hybridization experiment, the opsin cDNA hybridized to two species of bovine mRNA, one approximately 18 S (1800 bp) and the other 22 S (2600 bp). Using pCR-394 as a probe two opsin clones, R-5 (about 1200 bp) and LR-8 (about 2500 bp), were isolated from a cDNA library which was prepared by the method of Okayama-Berg. Each had a different length of 3'-untranslated DNA. The nucleotide sequences of R-5 and LR-8, as well as Northern and Southern hybridization experiments suggest that at least two species of opsin mRNA are expressed from a single gene. When the effects of illumination were examined by Northern hybridization and translation assays, the ratio of the two opsin mRNA species was changed between light- and dark-adapted eyes.

Animals↗
PubMed1996

Blue and ultraviolet light-absorbing opsin from the retinal pigment epithelium.

The retinal pigment epithelium (RPE) contains an abundant opsin that is distinct from rhodopsin and cone visual pigments and is able to bind the retinaldehyde chromophore. The putative retinal G protein-coupled receptor (RGR) was isolated in digitonin solution from bovine RPE microsomes and copurified consistently with a minor 34-kDa protein. The absorption spectrum of RGR revealed endogenous pH-sensitive absorbance in the blue and near-ultraviolet regions of light. Membrane-bound RGR was incubated with exogenously added all-trans-retinal and formed two long-lived pH-dependent photopigments with absorption maxima of 469 +/- 2.4 and 370 +/- 7.3 nm. The effects of hydrogen ion concentration suggest that the blue and near-UV photopigments are tautomeric forms of RGR, in which an all-trans-retinal Schiff base is protonated or unprotonated, respectively. The RPE pigment was also demonstrable by its reactivity to hydroxylamine in the dark. The retinaldehyde-RGR conjugate at neutral pH favors the near-UV pigment and is a novel light-absorbing opsin in the vertebrate eye.

Animals↗
PubMed1992

Variable rates of evolution among Drosophila opsin genes.

DNA sequences and chromosomal locations of four Drosophila pseudoobscura opsin genes were compared with those from Drosophila melanogaster, to determine factors that influence the evolution of multigene families. Although the opsin proteins perform the same primary functions, the comparisons reveal a wide range of evolutionary rates. Amino acid identities for the opsins range from 90% for Rh2 to more than 95% for Rh1 and Rh4. Variation in the rate of synonymous site substitution is especially striking: the major opsin, encoded by the Rh1 locus, differs at only 26.1% of synonymous sites between D. pseudoobscura and D. melanogaster, while the other opsin loci differ by as much as 39.2% at synonymous sites. Rh3 and Rh4 have similar levels of synonymous nucleotide substitution but significantly different amounts of amino acid replacement. This decoupling of nucleotide substitution and amino acid replacement suggests that different selective pressures are acting on these similar genes. There is significant heterogeneity in base composition and codon usage bias among the opsin genes in both species, but there are no consistent relationships between these factors and the rate of evolution of the opsins. In addition to exhibiting variation in evolutionary rates, the opsin loci in these species reveal rearrangements of chromosome elements.

Amino Acid Sequence↗
PubMed1999

Myosin VIIa participates in opsin transport through the photoreceptor cilium.

Two types of Usher syndrome, a blindness-deafness disorder, result from mutations in the myosin VIIa gene. As for most other unconventional myosins, little is known about the function or functions of myosin VIIa. Here, we studied the photoreceptor cells of mice with mutant myosin VIIa by electron immunomicroscopy and microscopic autoradiography. We found evidence that myosin VIIa functions in the connecting cilium of each photoreceptor cell and participates in the transport of opsin through this structure. These findings provide the first direct evidence that opsin travels along the connecting cilium en route to the outer segment. They demonstrate that a myosin may function in a cilium and suggest that abnormal opsin transport might contribute to blindness in Usher syndrome.

Animals↗
PubMedDate not supplied

Photoreceptors in a primitive mammal, the South American opossum, Didelphis marsupialis aurita: characterization with anti-opsin immunolabeling.

The retinas of placental mammals appear to lack the large number and morphological diversity of cone subtypes found in diurnal reptiles. We have now studied the photoreceptor layer of a South American marsupial (Didelphis marsupialis aurita) by peanut agglutinin labeling of the cone sheath and by labeling of cone outer segments with monoclonal anti-visual pigment antibodies that have been proven to consistently label middle-to-long wavelength (COS-1) and short-wavelength (OS-2) cone subpopulations in placental mammals. Besides a dominant rod population (max. = 400,000/mm2) four subtypes of cones (max. = 3000/mm2) were identified. The outer segments of three cone subtypes were labeled by COS-1: a double cone with a principal cone containing a colorless oil droplet, a single cone with oil droplet, and another single cone. A second group of single cones lacking oil droplets was labeled by OS-2 antibody. The topography of these cone subtypes showed striking anisotropies. The COS-1 labeled single cones without oil droplets were found all over the retina and constituted the dominant population in the area centralis located in the temporal quadrant of the upper, tapetal hemisphere. The population of OS-2 labeled cones was also ubiquitous although slightly higher in the upper hemisphere (200/mm2). The COS-1 labeled cones bearing an oil droplet, including the principal member of double cones, were concentrated (800/mm2) in the inferior, non-tapetal half of the retina. The two spectral types of single cones resemble those of dichromatic photopic systems in most placental mammals. The additional set of COS-1 labeled cones is a distinct marsupial feature. The presence of oil droplets in this cone subpopulation, its absence in the area centralis, and the correlation with the non-tapetal inferior hemisphere suggest a functional specialization, possibly for mesopic conditions. Thus, sauropsid features have been retained but probably with a modified function.

Animals↗
PubMed2005

Retinal regional differences in photoreceptor cell death and regeneration in light-lesioned albino zebrafish.

Teleost fish regenerate retinal cells from a population of inner nuclear layer (INL) stem cells. To characterize photoreceptor regeneration in zebrafish (Danio rerio), adult albino fish were subjected to constant intense light to cause photoreceptor cell death. Retinal morphometry was performed on histological sections of control and light-lesioned albino retinas to compare the extent of light damage in the ventral, central and dorsal retinal regions. In addition, opsin immunohistochemistry and TUNEL were used to compare photoreceptor cell death in these different retinal areas, while PCNA immunolabeling quantified the cell proliferation that precedes the photoreceptor regeneration. Transgenic albino; Tg(alpha1-tubulin:egfp) zebrafish were also exposed to the intense light in order to examine regeneration-related gene expression changes. The light-lesioned retinas are characterized by extensive rod and cone photoreceptor cell death in the central and dorsal regions. In contrast, many of the rods and cones survive in the ventral retina. The highest levels of INL cell proliferation, which occurs subsequent to photoreceptor death, correspond to the retinal regions that suffer the greatest levels of photoreceptor damage. In the ventral retina, where photoreceptor cell death is minimal, cell proliferation is confined to the ONL. In addition, EGFP expression from the alpha1-tubulin promoter is increased in Müller glial cells in the light-damaged central and dorsal retina, while transgene expression in the ventral retina is restricted to small, round INL cells. Furthermore, expression of the HuC/D neuronal antigen is detected in a subpopulation of the Müller cells in the light-damaged superior retinal region. These data demonstrate that adult albino zebrafish display retinal regional differences in photoreceptor cell death and in the regeneration-related INL cell proliferation response. The high levels of INL cell proliferation and alpha1-tubulin:egfp transgene expression in the Müller cells may be graded in response to the degree of photoreceptor cell death. This suggests that the levels of photoreceptor damage may directly influence cell responses in the underlying retinal layers.

Animals↗
PubMed1997

Sequences and evolution of human and squirrel monkey blue opsin genes.

The sequences of the entire blue opsin gene in the squirrel monkey (Saimiri boliviensis) and the five introns of the human blue opsin gene were obtained. Intron 3 of these genes contains an Alu sequence and intron 4 contains a partial mer13 sequence. A comparison of the squirrel monkey opsin sequence with published mammalian opsin sequences shows that features believed to be functionally critical are all conserved. However, the blue opsin has evolved twice as fast as rhodopsin and is only as conservative as the beta globin, which has evolved at the average rate of mammalian proteins. Interestingly, the interhelical loops are, on average, actually more conservative than the transmembrane alpha helical regions. The introns of the blue opsin gene have evolved at the average rate of introns in primate genes.

Amino Acid Sequence↗