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PubMed2000

Apoptotic photoreceptor death in the rhodopsin knockout mouse in the presence and absence of c-fos.

A combined total of approximately 100 mutations have been encountered within the rhodopsin gene in retinitis pigmentosa (RP) and congenital night blindness. Mice carrying a targeted disruption of the rhodopsin gene phenotypically mimic RP, losing their photoreceptors over a period of 3 months and having no recordable rod electroretinogram. These animals will serve as a model for both recessive and dominant disease (in the latter case, the presence of normal and mutant human rod opsin transgenes on the murine Rho(-/-)background). Precise knowledge of apoptotic photoreceptor cell death, together with factors which may influence apoptosis will be required for optimum utility of Rho(-/-)mice as a model for therapeutic genetic intervention. A peak phase of apoptosis of the photoreceptors of Rho(-/-)mice was shown to occur at 24 days post-birth. The extent of apoptosis appeared to be similar, irrespective of whether or not the rod opsin knockout was present on a c-fos(+/+)or c-fos(-/-)genetic background, the latter known to favor survival of photoreceptors following exposure of mouse retinas to excessive light. These data clearly support the existence in animals of distinct apoptotic pathways in light-induced, as opposed to mutation-induced apoptosis, and together with similar observations recently reported in studies of the naturally occurring rd mouse, may assist in focusing future research on precisely defining the distinct molecular pathways giving rise to such dichotomy.

Animals↗
PubMed2001

Retinal anatomy and function of the transthyretin null mouse.

Vitamin A (retinol) is vital for the normal development and function of many tissues in the body including the eye. The purpose of this project was to characterize the retinal anatomy and function of the transthyretin (TTR) null mouse. Mice lacking TTR have been constructed by homologous recombination. Immunocytochemistry was performed to localize short and mid-long wavelength cone opsins as well as morphological examination of the entire retina in wild-type and TTR null mice. Visual function was assessed using the electroretinogram (ERG) and resulting waveforms were analysed in terms of receptoral and postreceptoral components. Retinal morphology of the TTR null mouse was normal. In addition, short and mid-long wavelength cone opsins were localized normally in both TTR null and wild-type retinae. Consistent with these findings, TTR null mice show no anomalies of receptoral (P3) nor post-receptoral (b-wave) ERG components compared with wild-type mice. The results suggest that although circulating plasma levels of retinol and retinol binding protein (RBP) are extremely low, this reduction has little effect on the retinal structure or function of the TTR null mouse. These data are consistent with the existence of mechanisms for the transport of retinol to the retina independent of the classical retinol-RBP-TTR complex.

Analysis of Variance↗
PubMed1999

Heterologous gene expression in a membrane-protein-specific system.

We have constructed an expression system for heterologous proteins which uses the molecular machinery responsible for the high level production of bacteriorhodopsin in Halobacterium salinarum. Cloning vectors were assembled that fused sequences of the bacterio-opsin gene (bop) to coding sequences of heterologous genes and generated DNA fragments with cloning sites that permitted transfer of fused genes into H. salinarum expression vectors. Gene fusions include: (i) carboxyl-terminal-tagged bacterio-opsin; (ii) a carboxyl-terminal fusion with the catalytic subunit of the Escherichia coli aspartate transcarbamylase; (iii) the human muscarinic receptor, subtype M1; (iv) the human serotonin receptor, type 5HT2c; and (v) the yeast alpha mating factor receptor, Ste2. Characterization of the expression of these fusions revealed that the bop gene coding region contains previously undescribed molecular determinants which are critical for high level expression. For example, introduction of immunogenic and purification tag sequences into the C-terminal coding region significantly decreased bop gene mRNA and protein accumulation. The bacteriorhodopsin-aspartate transcarbamylase fusion protein was expressed at 7 mg per liter of culture, demonstrating that E. coli codon usage bias did not limit the system's potential for high level expression. The work presented describes initial efforts in the development of a novel heterologous protein expression system, which may have unique advantages for producing multiple milligram quantities of membrane-associated proteins.

Amino Acid Sequence↗
PubMed1987

Immunocytochemical and electron-microscopic investigations of the pineal organ in adult agamid lizards, Uromastix hardwicki.

Lacertilian species display a remarkable diversity in the organization of the neural apparatus of their pineal organ (epiphysis cerebri). The occurrence of immunoreactive S-antigen and opsin was investigated in the retina and pineal organ of adult lizards, Uromastix hardwicki. In this species, numerous retinal photoreceptors displayed S-antigen-like immunoreactivity, whereas only very few pinealocytes were labeled. Immunoreactive opsin was found neither in retinal photoreceptors nor in pinealocytes. Electron microscopy showed that all pinealocytes of Uromastix hardwicki resemble modified pineal photoreceptors. A peculiar observation is the existence of a previously undescribed membrane system in the inner segments of these cells. It is evidently derived from the rough endoplasmic reticulum but consists of smooth membranes. The modified pineal photoreceptor cells of Uromastix hardwicki were never seen to establish synaptic contacts with somata or dendrites of intrapineal neurons, which are extremely rare. Vesicle-crowned ribbons are prominent in the basal processes of the receptor cells, facing the basal lamina or establishing receptor-receptor and receptor-interstitial type synaptoid contacts. Dense-core granules (60-250 nm in diameter) speak in favor of a secretory activity of the pinealocytes. Attention is drawn to the existence of receptor-receptor and receptor-interstitial cell contacts indicating intramural cellular relationships that deserve further study.

Animals↗
PubMed1977

Dark adaptaion processes in the amphibian rod.

Rod dark adaptation in the amphibian retina appears to be due to three processes: 1. background adaptation, occurring immediately after the extinction of an adapting or bleaching light, 2. intermediate adaptation, that frequently lasts 30 min or more and 3. opsin adaptation, which in the isolated retina where regeneration of rhodopsin is insignificant, is observed a a permanent loss of sensitivity after the completion of intermediate adaptation. Intermediate adaptation is characterized by a linear relation between log threshold and the amount of "retinal" present, a similar relation is obtained between log threshold and the amount of rhodopsin bleached in opsin adaptation. These adaptation processes are discussed in terms of a model of the rod outer segment.

Amphibians↗
PubMed2005

Spectral heterogeneity of honeybee ommatidia.

The honeybee compound eye is equipped with ultraviolet, blue, and green receptors, which form the physiological basis of a trichromatic color vision system. We studied the distribution of the spectral receptors by localizing the three mRNAs encoding the opsins of the ultraviolet-, blue- and green-absorbing visual pigments. The expression patterns of the three opsin mRNAs demonstrated that three distinct types ommatidia exist, refuting the common assumption that the ommatidia composing the bee compound eye contain identical sets of spectral receptors. We found that type I ommatidia contain one ultraviolet and one blue receptor, type II ommatidia contain two ultraviolet receptors, and type III ommatidia have two blue receptors. All the three ommatidial types contain six green receptors. The ommatidia appear to be distributed rather randomly over the retina. The ratio of type I, II, and III ommatidia was about 44:46:10. Type III ommatidia appeared to be slightly more frequent (18%) in the anterior part of the ventral region of the eye. Retinal heterogeneity and ommatidial randomness, first clearly demonstrated in butterflies, seems to be a common design principle of the eyes of insects.

Animals↗
PubMed2004

Photoreceptors and photopigments in a subterranean rodent, the pocket gopher (Thomomys bottae).

Pocket gophers (Thomomys bottae) are rodents that spend much of their lives in near-lightless subterranean burrows. The visual adaptations associated with this extreme environment were investigated by making anatomical observations of retinal organization and by recording retinal responses to photic stimulation. The size of the eye is within the normal range for rodents, the lens transmits light well down into the ultraviolet, and the retina conforms to the normal mammalian plan. Electroretinogram recording revealed the presence of three types of photopigments, a rod pigment with a spectral peak of about 495 nm and two types of cone pigment with respective peak values of about 367 nm (UV) and 505 nm (medium-wavelength sensitive). Both in terms of responsivity to lights varying in temporal frequency and in response recovery following intense light adaptation, the cone responses of the pocket gopher are similar to those of other rodents. Labeling experiments indicate an abundance of cones that reach densities in excess of 30,000 mm-2. Cones containing UV opsin are found throughout the retina, but those containing medium-wavelength sensitive opsin are mostly restricted to the dorsal retina where coexpression of the two photopigments is apparently the rule. Rod densities are lower than those typical for nocturnal mammals.

Adaptation, Ocular↗
PubMed2006

Visual pigments of marine carnivores: pinnipeds, polar bear, and sea otter.

Rod and cone visual pigments of 11 marine carnivores were evaluated. Rod, middle/long-wavelength sensitive (M/L) cone, and short-wavelength sensitive (S) cone opsin (if present) sequences were obtained from retinal mRNA. Spectral sensitivity was inferred through evaluation of known spectral tuning residues. The rod pigments of all but one of the pinnipeds were similar to those of the sea otter, polar bear, and most other terrestrial carnivores with spectral peak sensitivities (lambda(max)) of 499 or 501 nm. Similarly, the M/L cone pigments of the pinnipeds, polar bear, and otter had inferred lambda(max) of 545 to 560 nm. Only the rod opsin sequence of the elephant seal had sensitivity characteristic of adaptation for vision in the marine environment, with an inferred lambda(max) of 487 nm. No evidence of S cones was found for any of the pinnipeds. The polar bear and otter had S cones with inferred lambda(max) of approximately 440 nm. Flicker-photometric ERG was additionally used to examine the in situ sensitivities of three species of pinniped. Despite the use of conditions previously shown to evoke cone responses in other mammals, no cone responses could be elicited from any of these pinnipeds. Rod photoreceptor responses for all three species were as predicted by the genetic data.

Amino Acid Sequence↗
PubMed1988

Spectral evidence for cytochrome o in the brown membrane of Halobacterium halobium.

The brown membrane domain of Halobacterium halobium is a developmental precursor of the purple membrane and it contains a b-type cytochrome in addition to bacterio-opsin. In this report we provide spectroscopic evidence that the majority of the cytochrome content is a halobacterial cytochrome o. This cytochrome has absorption spectral properties in the oxidized, reduced, and CO liganded states which are characteristic of cytochrome o. The CD spectra show a complex bilobed pattern in the Soret spectral region which reflects the similarity of the heme environment to those of other b-type cytochromes involved in electron transport. We have also demonstrated a positive cooperativity of CO binding which, combined with CD spectral results, suggests two interacting heme moieties per cytochrome o. Size exclusion HPLC of solubilized brown membrane preparations shows a heme b containing protein with an Mr 42,000-46,000. The cytochrome may be easily separated from bacterio-opsin using a hydroxyapatite elution method on Triton X-100 solubilized preparations. The relative ease with which brown membrane disks may be oriented in high optical quality films should make the brown membrane a valuable model system for future spectroscopic investigations of cytochrome o.

Cell Membrane↗
PubMed1978

Kinetic study of photoregeneration process of digitonin-solubilized squid rhodopsin.

In the photoregeneration process of squid rhodopsin, an intermediate has been found at neutral pH values (phosphate buffer) with a flash light (lambda greater than 540 nm). An intermediate R430, with the 11-cis retinal as chromophore, is produced from metarhodopsin in light and is converted to rhodopsin through the processes R430 leads to P380 and P380 leads to rhodopsin. The pH dependence of the velocity of the conversions suggests that processes R430 leads to P380 and P380 leads to rhodopsin involve a protolytic reaction and that the ionized group is a histidine residue of opsin. Kinetic parameters show that the largest conformational change in opsin occurs in the conversion of R430 leads to P380.

Animals↗
PubMed1984

Photochemical reaction of 7,8-dihydrorhodopsin at low temperatures.

The photoreaction of 9-cis-7,8-dihydrorhodopsin was examined at liquid nitrogen temperatures (-180 degrees C) in order to elucidate the photochemical events in visual pigments. This rhodopsin analog was prepared by incubating 9-cis-7,8-dihydroretinal with bovine opsin in the dark. 9-cis-7,8-Dihydrorhodopsin (lambda max = 427 nm) was cooled to -180 degrees C, and then irradiated at -180 degrees C with a 390 nm light, resulting in formation of its bathochromic product (lambda max = 465 nm). This result indicates that the presence of four double-bonds adjacent to the Schiff base nitrogen is sufficient to allow formation of a bathochromic product. Thus, the mechanism of formation of bathorhodopsin (in bovine rhodopsin system) may be considered as some change of the interaction between the conjugated double-bond system from C-9 to the Schiff base nitrogen and its surrounding charges in opsin, caused by rotation of 11-12 double-bond.

Animals↗
PubMed1977

Reversible changes in circular dichroism spectra of cattle rhodopsin and isorhodopsin.

When the disk membrane of rod outer segment is treated with detergents, the alpha-band CD of rhodopsin decreases and the gamma-band CD increases. This tendency of CD change is most prominent in the purified rhodopsin in cholic acid obtained by the ammonium sulfate fractionation of disk membranes, and the gamma-band CD is three times larger than the alpha-band CD. The beta-band CD of rhodopsin is only slightly influenced by detergents. The gamma-band of isorhodopsin shows two CD bands, one negative and one positive. Both in rhodopsin and isorhodopsin the gamma-band CD is lost by light irradiation. It is supposed that both chromophore retinal and aromatic amino acid residues of opsin are responsible for the gamma-band CD. When ammonium sulfate is added to the sonicated disk membranes suspended in cholic acid solution, the alpha-band CD of rhodopsin decreases to about a third and the gamma-band CD increases remarkably. The CD spectrum goes back to the original one on eliminating ammonium sulfate from the solution with dialysis. However, the purified rhodopsin recovers native CD spectrum on addition of lipids extracted from disk membranes. The retinal-opsin interaction that induces optical activity depends upon the property of a local environment formed by lipid and detergent.

Animals↗
PubMed1980

Effect of phospholipid and detergent on the Schiff base of cephalopod rhodopsin and metarhodopsin.

In the visual pigment, the chromophore retinal is bound through a Schiff base linkage with the protein moiety, opsin. The secondary interaction of retinal with opsin was studied in cephalopod rhodopsin and its photoproduct, metarhodopsin. The pK of the protonation of the Schiff base in metarhodopsin was affected by the phospholipids and detergents surrounding the protein, and varied between 9.2 and 6.9. Among nonionic detergents, the fatty acid ester of sucrose behaved like phospholipids but other detergents changed the protein conformation so that the pK of the Schiff base in metarhodopsin became nearly equal to the pK of N-retinylidene butylamine. This tendency was manifested in rhodopsin as the formation of a 380 nm pigment.

Animals↗
PubMed1995

Circadian rhythms in mice can be regulated by photoreceptors with cone-like characteristics.

In this report we have characterized the photopigments mediating circadian phase shifts in retinal degenerate (rd) mice. In aged rd/rd mice, which lack detectable opsin, high performance liquid chromatography (HPLC) was used to quantify the photopigment chromophore 11-cis-retinaldehyde. This chromophore was photoisomerized in whole eyes, suggesting the presence of a functional opsin-based photopigment system. We also analyzed the spectral sensitivity of phase shifting circadian locomotor rhythms. Our data implicate a photopigment that is consistent with the involvement of the middle wavelength-sensitive cone photoreceptors (M-cones; lambda(max) = 511 nm) found in the mouse retina. In addition, discrete near-ultraviolet (UV-A) pulses were capable of eliciting large phase shifts in circadian locomotor activity rhythms. This result is consistent with the involvement of the short wavelength-sensitive cone photoreceptors (UV-cones; lambda(max) = 359 nm) in photoentrainment. Collectively, these data suggest that both cone classes of the mouse may mediate the photic regulation of circadian rhythms. If this is the case, circadian sensitivity can be maintained by very few degenerate cones. Alternatively, an unknown class of ocular photoreceptor may fulfill this function.

Animals↗
PubMed1996

Differential effects of bFGF on development of the rat retina.

A variety of growth factors can influence the expression of differentiated properties by cell types of the developing retina. One unresolved question has been whether these factors can direct the differentiation pathway of uncommitted precursors or whether they act to help the expression of properties by already committed cells. To address this question we have studied the effects of basic fibroblast growth factor (bFGF) on the differentiation of ganglion cells and rod photoreceptors in explant cultures of embryonic rat retinas. Incubation of retinas in the presence of bFGF accelerated the appearance of differentiated ganglion cells and incubation in the presence of anti-bFGF antibodies delayed the appearance. bFGF had no effect on the appearance of differentiated rod photoreceptors as judged by expression of opsin, although all-trans-retinoic acid did increase the number of cells expressing opsin. bFGF inhibited the formation of rod photoreceptor rosettes suggesting that it does influence some properties of rods or the adjacent Müller glial cells. The results suggest that bFGF can alter the timing of differentiation of retinal ganglion cells but not direct their production from retinal precursors.

Animals↗
PubMed1984

Glycoprotein synthesis in the human retina: localization of the lipid intermediate pathway.

Retinal tissue from human eye donors was incubated with [3H]-labeled mannose, glucosamine, fucose, and leucine in the presence and absence of tunicamycin, a selective inhibitor of dolichol-dependent glycoprotein biosynthesis. The incorporation of labeled substrates was examined by quantitative light microscopic autoradiography and biochemical methods. [3H]-Mannose and [3H]-fucose were predominantly incorporated into the photoreceptor layer, while [3H]-glucosamine and [3H]-leucine labeled the entire retinal expanse. Tunicamycin caused a marked and selective reduction in the incorporation of [3H]-mannose and [3H]-glucosamine in the photoreceptor layer (especially the inner segments) without affecting the relative distribution of labeled products derived from [3H]-fucose or [3H]-leucine. All three [3H]-labeled sugars were incorporated preferentially into rod inner segments, relative to cones. Dual-label experiments with [3H]-sugars and [14C]-leucine revealed that tunicamycin selectively inhibited the incorporation of [3H]-mannose, but not the other substrates, into total retinal TCA-precipitable material. This inhibition was not due to decreased mannose uptake by retinal cells. Detergent-solubilized retinas were analyzed by polyacrylamide gel electrophoresis and fluorography. The results indicated that each labeled substrate was incorporated into a variety of glyoproteins, including a component having the electrophoretic mobility of opsin. These results suggest that the lipid intermediate pathway of glycoprotein synthesis is localized preferentially to the photoreceptor layer of the retina, and may subserve the biosynthesis of rod cell glycoproteins (e.g. opsin).

Adolescent↗
PubMed1989

The Gecko visual pigment: the dark exchange reaction and the effects of anions.

A dark reaction is known to occur in retinal extracts of the gecko (Gekko gekko), in which the natural 11-cis-chromophore of the 521-pigment is apparently replaced by adding 9-cis-retinal to form the 9-cis-photopigment. With chloride-deficient extracts the reaction involves some 70% of the 521-pigment. Anions like nitrate, azide, thiocyanate and cyanate that shift the spectrum toward the blue do not affect this 70% exchange. Anions like fluoride, iodide and sulfate likewise do not alter this magnitude of reaction. In contrast, chloride and bromide that induce a bathochromic spectral shift lead to a decrease in this dark replacement of the 11-cis chromophore. This protection is similar to the action of these two anions in antagonizing the pigment loss by NH2OH and by temperature, both occurring in the dark. Apparently, chloride and bromide alter the opsin conformation so as to stabilize and/or protect the Schiff's base linkage but nitrate, azide, thiocyanate and cyanate act at a different opsin site or by a different mechanism.

Animals↗
PubMed1991

Experimental autoimmune retinitis in the rat induced by immunization with rhodopsin: an ultrastructural study.

Experimental autoimmune retinitis induced by immunization with rhodopsin was investigated in the Lewis rat using transmission electron microscopy and light microscopy. The first signs of retinitis consisted of scattered infiltrations of lymphocytes and other mononuclear cells, predominantly in the inner nuclear layer and outer plexiform layer. Occasionally, some macrophages were detected in the photoreceptor cell layer. Eyes exhibiting a clinically moderate or severe inflammation contained areas of normal retina coexistent with mildly to severely inflamed foci. The central retina was more frequently affected than the peripheral area. In moderately inflamed foci, macrophages infiltrated the photoreceptor cell layer, damaging and eliminating its structures. Inflammatory cells penetrated the photoreceptor outer segment layer which remained unaltered so far in spite of a high serum anti-(rhod)opsin antibody titer. In stages of severe inflammation, massive infiltrations of macrophages and polymorphonuclear cells destroyed the photoreceptor cells focally, leaving the retinal pigment epithelium virtually unaffected. Adjacent to these foci the pigment epithelial cells sometimes exhibited increased numbers of phagosomes and swelling. The locations of the cell infiltrations and lesions in progressive stages of development suggest that the rod outer segments are the target for the autoimmune damage. The described patterns of inflammation were compared with those of previous studies using other animal species and inciting antigens. Especially in rhodopsin-induced retinitis, the blood-retina barrier at the level of the Bruch's membrane/pigment epithelium appears to be highly resistant to cytotoxic cells. The present observations are in agreement with the concept that the cellular immune response plays a major role in the pathogenesis of (rhod)opsin-induced retinitis.

Animals↗