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PubMed2002

The cellular fate of mutant rhodopsin: quality control, degradation and aggresome formation.

Mutations in the photopigment rhodopsin are the major cause of autosomal dominant retinitis pigmentosa. The majority of mutations in rhodopsin lead to misfolding of the protein. Through the detailed examination of P23H and K296E mutant opsin processing in COS-7 cells, we have shown that the mutant protein does not accumulate in the Golgi, as previously thought, instead it forms aggregates that have many of the characteristic features of an aggresome. The aggregates form close to the centrosome and lead to the dispersal of the Golgi apparatus. Furthermore, these aggregates are ubiquitinated, recruit cellular chaperones and disrupt the intermediate filament network. Mutant opsin expression can disrupt the processing of normal opsin, as co-transfection revealed that the wild-type protein is recruited to mutant opsin aggregates. The degradation of mutant opsin is dependent on the proteasome machinery. Unlike the situation with DeltaF508-CFTR, proteasome inhibition does not lead to a marked increase in aggresome formation but increases the retention of the protein within the ER, suggesting that the proteasome is required for the efficient retrotranslocation of the mutant protein. Inhibition of N-linked glycosylation with tunicamycin leads to the selective retention of the mutant protein within the ER and increases the steady state level of mutant opsin. Glycosylation, however, has no influence on the biogenesis and targeting of wild-type opsin in cultured cells. This demonstrates that N-linked glycosylation is required for ER-associated degradation of the mutant protein but is not essential for the quality control of opsin folding. The addition of 9-cis-retinal to the media increased the amount of P23H, but not K296E, that was soluble and reached the plasma membrane. These data show that rhodopsin autosomal dominant retinitis pigmentosa is similar to many other neurodegenerative diseases in which the formation of intracellular protein aggregates is central to disease pathogenesis, and they suggest a mechanism for disease dominance.

Animals↗
PubMed1987

Immunocytochemical evidence of molecular photoreceptor markers in cerebellar medulloblastomas.

With the use of antisera against bovine retinal S-antigen and bovine opsin the authors demonstrate that in cerebellar medulloblastomas certain tumor cells display immunocytochemical properties characteristic of retinal photoreceptors and pinealocytes. S-antigen-like and opsin-like immunoreactions occur in nine of 28 medulloblastomas investigated. All tumors displaying S-antigen-like immunoreactive neoplastic cells also contain opsin-like immunoreactive cells; however, the opsin-like immunoreactive cells were less frequent than the S-antigen-like immunoreactive cells throughout all positive cases. The immunoreactive cells displayed several long processes. Generally, both S-antigen and opsin-like immunoreactive cells considerably vary in number among individual tumors. The results indicate that certain neoplastic cells of medulloblastoma are capable of expression of photoreceptor-specific proteins and, thus, may be closely related to tumor cells of retinoblastoma and pineocytomas previously shown to bind antisera against retinal S-antigen and opsin. No S-antigen and opsin-like immunoreaction was found in malignant teratomas and germinomas of the pineal gland, oat cell tumors, astrocytomas, ependymomas, oligodendrogliomas, glioblastomas, gangliogliomas, gangliocytoma, ganglioneuroblastomas, neuroblastomas, and esthesioneuroblastoma.

Cerebellar Neoplasms↗
PubMed2006

Photoreceptor layer of salmonid fishes: transformation and loss of single cones in juvenile fish.

The retinas of many vertebrates have cone photoreceptors that express multiple visual pigments. In many of these animals, including humans, the original cones to appear in the retina (which express UV or blue opsin) may change opsin types, giving rise to new spectral phenotypes. Here we used microspectrophotometry and in situ hybridization with cDNA probes to study the distribution of UV and blue cones in the retinas of four species of Pacific salmon (coho, chum, chinook, and pink salmon), in the Atlantic salmon, and in the rainbow/steelhead trout. In Pacific salmon and in the trout, all single cones express a UV opsin at hatching (lambda(max) of the visual pigment approximately 365 nm), and these cones later transform into blue cones by opsin changeover (lambda(max) of the blue visual pigment approximately 434 nm). Cones undergoing UV opsin downregulation exhibit either of two spectral absorbance profiles. The first is characterized by UV and blue absorbance peaks, with blue absorbance dominating the base of the outer segment. The second shows UV absorbance diminishing from the outer segment tip to the base, with no sign of blue absorbance. The first absorbance profile indicates a transformation from UV to blue phenotype by opsin changeover, while the second type suggests that the cone is undergoing apoptosis. These two events (transformation and loss of corner cones) are closely associated in time and progress from ventral to dorsal retina. Each double cone member contains green (lambda(max) approximately 510 nm) or red (lambda(max) approximately 565 nm) visual pigment (double cones are green/red pairs), and, like the rods (lambda(max) approximately 508 nm), do not exhibit opsin changeover. Unlike Pacific salmonids, the Atlantic salmon shows a mixture of UV and blue cones and a partial loss of corner cones at hatching. This study establishes the UV-to-blue cone transformation as a general feature of retinal growth in Pacific salmonids (genus Oncorhynchus).

Adaptation, Ocular↗
PubMed1995

Chlamyrhodopsin represents a new type of sensory photoreceptor.

In order to find optimal light conditions for photosynthetic growth, the green alga Chlamydomonas uses a visual system. An optical device, a rhodopsin photoreceptor and an electrical signal transduction chain that mediates between photoreceptor and flagella comprise this system. Here we present an improved strategy for the preparation of eyespot membranes. These membranes contain a retinal binding protein, which has been proposed to be the apoprotein of the phototaxis receptor. The retinal binding protein, which we named chlamyopsin, was purified and opsin-specific antibodies were raised. Using these antibodies, the opsin was localized in the eyespot region of whole cells during growth and cell division. The opsin cDNA was purified and sequenced. The sequence reveals that chlamyopsin is not a typical seven helix receptor. It shows some homology to invertebrate opsins but not to opsins from halobacteria. It contains many polar and charged residues and might function as a light-gated ion channel complex. It is likely that this lower plant rhodopsin diverged from animal opsins early in opsin evolution.

Algal Proteins↗
PubMed1994

Timing of interphotoreceptor retinoid-binding protein (IRBP) gene expression and hypomethylation in developing mouse retina.

We determined during photoreceptor development if there is a retina-specific hypomethylation of the mouse gene encoding interphotoreceptor retinoid-binding protein (IRBP) that is associated with its activation. Second, the role of IRBP gene and protein expression in development was assessed by determining if their expression occurs before that of opsin. Retina-specific hypomethylation of the IRBP promoter region started on Embryonic (E) Day 11, at the time of cone formation, increased from E12 to E14, at the time of rod formation, and reached a peak on Postnatal (P) Day 4, which was followed thereafter by a slow decrease. Starting on E11, IRBP and opsin mRNA levels were quantitated relative to that of the beta-actin gene with RNase protection analysis. beta-Actin and IRBP transcripts were readily detected on E11. beta-actin levels remained constant during embryonic and early postnatal stages and decreased slightly afterward. On the other hand, beginning on E13, when the rods are formed, the IRBP level markedly increased. In contrast, the opsin transcript first appeared later on P0 and then increased from P3 onward. After P6, the opsin and IRBP transcript levels became comparable and by P20 their levels reached constancy. The timing of the onset of protein expression for the IRBP and opsin genes was determined during the last proliferative cycle of the rod precursor cells before their differentiation. Mice at P2 or P3 were injected with bromodeoxyuridine (BrdU) and their retinal cells were dissociated and then double-labeled with antibodies against BrdU and either IRBP or opsin. Cells positive for both IRBP and BrdU were always observed as soon as 2 hr after injection but it took at least 40 hr before they became positive for both opsin and BrdU. Taken together, these results indicate that IRBP gene activation is associated with hypomethylation during the last mitosis before photoreceptor cell differentiation.

Animals↗
PubMed1988

Histochemical observations on unique rod-like cells in the developing retina of the normal rat.

Our previous immunohistochemical studies using specific anti-opsin antibodies have shown that in the normal postnatal rat retina, opsin-like immunoreactive materials can be seen not only in photoreceptor cells but also in some cells of the inner nuclear layer (INL). To characterize these ectopic opsin-like immunoreactive cells further, we have now studied developing rat retinae at the light and electron microscopic levels using both opsin immunocytochemistry and 5'-nucleotidase (5'-N) cytochemistry. Since photoreceptor cells are specifically stained in both methods, we investigated whether these methods would also stain some of the cells in the INL. Opsin-like immunoreactive cells in the INL always showed a characteristic nuclear structure, which was clearly distinguished from that of other INL cells and resembled rod cell nucleus because of the presence of conspicuous masses of condensed heterochromatin. Moreover, these opsin-like immunoreactive cells in the INL occasionally also displayed a ciliary process. They could only be seen in the INL until about day 25 of postnatal life. In the INL, 5'-N activity was found exclusively in cells showing rod-like nuclear features, and the timing of appearance and disappearance of 5'-N-positive cells in the INL was similar to that of the opsin-like immunoreactive cells. Numerous degenerating cells were observed in the INL at around day 10, some of which showed 5'-N reaction product at the cell surface. These results indicate that during postnatal development of the rat retina, some cells in the INL express several phenotypic properties characteristic of rod cells. It is suggested that these cells might undergo either cell degeneration or phenotypic conversion during the subsequent maturation of the retina.

5'-Nucleotidase↗
PubMed2005

Targeted effects of retinoic acid signaling upon photoreceptor development in zebrafish.

Retinoic acid (RA) is a signaling molecule important for photoreceptor development in vertebrates. The purpose of this study was to examine the mechanisms of the effects of RA upon developing rod and cone photoreceptors in the embryonic zebrafish. Exposure to exogenous RA increased the number of photoreceptors expressing rod opsin and red cone opsin, and decreased the number of photoreceptors expressing the blue and UV cone opsins, suggesting targeted effects of RA on photoreceptor development. RA exposure also increased opsin expression in individual rods and red cones, but decreased opsin expression in individual blue and UV cones, as indicated by differences in the strength of opsin hybridization in identified photoreceptors. RA exposure did not, however, significantly alter quantitative measures of photoreceptor pattern in a manner expected for changes in photoreceptor fate. These observations collectively indicate that RA treatment does not affect photoreceptor fate, but rather differentially influences opsin transcription in determined photoreceptors. An enzyme involved in RA synthesis, RALDH2, was immunocytochemically localized to retinal progenitor cells and the retinal pigmented epithelium (RPE), suggesting the presence of RA in the vicinity of developing photoreceptors. However, expression of an RA response element-driven transgene was restricted to the RPE, retinal progenitors, and a small population of neurons in ventral retina, suggesting that the endogenous RA signaling system is spatially limited within the eye.

Aldehyde Oxidoreductases↗
PubMed1999

Morphological, physiological, and biochemical changes in rhodopsin knockout mice.

Mutations in rod opsin, the visual pigment protein of rod photoreceptors, account for approximately 15% of all inherited human retinal degenerations. However, the physiological and molecular events underlying the disease process are not well understood. One approach to this question has been to study transgenic mice expressing opsin genes containing defined mutations. A caveat of this approach is that even the overexpression of normal opsin leads to photoreceptor cell degeneration. To overcome the problem, we have reduced or eliminated endogenous rod opsin content by targeted gene disruption. Retinas in mice lacking both opsin alleles initially developed normally, except that rod outer segments failed to form. Within months of birth, photoreceptor cells degenerated completely. Retinas from mice with a single copy of the opsin gene developed normally, and rods elaborated outer segments of normal size but with half the normal complement of rhodopsin. Photoreceptor cells in these retinas also degenerated but did so over a much slower time course. Physiological and biochemical experiments showed that rods from mice with a single opsin gene were approximately 50% less sensitive to light, had accelerated flash-response kinetics, and contained approximately 50% more phosducin than wild-type controls.

Animals↗
PubMed2006

Physiological features of the S- and M-cone photoreceptors of wild-type mice from single-cell recordings.

Cone cells constitute only 3% of the photoreceptors of the wild-type (WT) mouse. While mouse rods have been thoroughly investigated with suction pipette recordings of their outer segment membrane currents, to date no recordings from WT cones have been published, likely because of the rarity of cones and the fragility of their outer segments. Recently, we characterized the photoreceptors of Nrl(-/-) mice, using suction pipette recordings from their "inner segments" (perinuclear region), and found them to be cones. Here we report the use of this same method to record for the first time the responses of single cones of WT mice, and of mice lacking the alpha-subunit of the G-protein transducin (G(t)alpha(-/-)), a loss that renders them functionally rodless. Most cones were found to functionally co-express both S- (lambda(max) = 360 nm) and M- (lambda(max) = 508 nm) cone opsins and to be maximally sensitive at 360 nm ("S-cones"); nonetheless, all cones from the dorsal retina were found to be maximally sensitive at 508 nm ("M-cones"). The dim-flash response kinetics and absolute sensitivity of S- and M-cones were very similar and not dependent on which of the coexpressed cone opsins drove transduction; the time to peak of the dim-flash response was approximately 70 ms, and approximately 0.2% of the circulating current was suppressed per photoisomerization. Amplification in WT cones (A approximately 4 s(-2)) was found to be about twofold lower than in rods (A approximately 8 s(-2)). Mouse M-cones maintained their circulating current at very nearly the dark adapted level even when >90% of their M-opsin was bleached. S-cones were less tolerant to bleached S-opsin than M-cones to bleached M-opsin, but still far more tolerant than mouse rods to bleached rhodopsin, which exhibit persistent suppression of nearly 50% of their circulating current following a 20% bleach. Thus, the three types of mouse opsin appear distinctive in the degree to which their bleached, unregenerated opsins generate "dark light."

Animals↗
PubMed1995

Ciliary neurotrophic factor promotes chick photoreceptor development in vitro.

Previous in vitro studies have convincingly demonstrated the involvement of diffusible factors in the regulation of photoreceptor development. We now provide evidence that ciliary neurotrophic factor (CNTF) represents one of these regulatory molecules. In low density monolayer cultures prepared from embryonic day 8 chick retina, photoreceptor development was studied using the monoclonal antiopsin antibody rho-4D2 as a differentiation marker. The number of cells acquiring opsin immunoreactivity, determined after 3 days in vitro, was increased up to 4-fold in the presence of CNTF to maximally 10.5% of all cells. Basic fibroblast growth factor or taurine both of which have been reported to stimulate opsin expression in rat retinal cultures and other neurotrophic factors tested (nerve growth factor, brain derived neurotrophic factor) had no effect. The EC50 of the CNTF effect (2.6 pM) was virtually identical to that measured for other CNTF receptor mediated cellular responses. Conditioned medium produced by cultured retinal cells (most likely glial cells) exhibited opsin stimulating activity identical to that of CNTF. Stimulation of opsin expression was specific for morphologically less mature photoreceptors and obviously restricted to rods, since changes in the number of identifiable cone photoreceptors expressing opsin immunoreactivity (10% of all cones) were not detectable. Measurement of the kinetics of the CNTF response revealed that the factor acted on immature opsin-negative progenitors and that CNTF effects were unlikely to reflect enhanced cell survival. Proliferation of photoreceptors was also unaffected, as demonstrated by [3H]thymidine autoradiography. With prolonged culture periods a gradual decrease in the number of opsin-positive cells was observed both in controls and in the continuous presence of CNTF. This decrease could be partly prevented by the addition of 1 mM taurine. Our results suggest that CNTF acted as an inductive signal for uncommitted progenitor cells or during early stages of rod photoreceptor differentiation, whereas other extrinsic stimulatory activities seemed to be required for further maturation.

Animals↗
PubMed2004

Photoreceptor differentiation during retinal development, growth, and regeneration in a metamorphic vertebrate.

To test the hypothesis that growth and regeneration of the adult retina involves a mechanistic recapitulation of retinal development, the patterns of photoreceptor differentiation were investigated in the developing retina, as well as growing and regenerating adult retina, of a metamorphic vertebrate, the winter flounder. Only one opsin, of type RH2 (a "green" cone opsin), was expressed in premetamorphic (developing) retina, and a corresponding middle-wavelength visual pigment was observed. In premetamorphic retinas there was no evidence for any other cone opsins or pigments, rods, rod opsin expression, or rod visual pigment. In contrast, a rod opsin (RH1) and three cone opsins (SWS2, RH2, and LWS) were expressed in postmetamorphic (adult) retina, and these opsins were consistent with the observed repertoire of visual pigments. During postmetamorphic retinal growth and regeneration, cones were always produced before rods, but the different cone types were apparently produced simultaneously, suggesting that cone differentiation mechanisms might change after metamorphosis. The results support the hypothesis that photoreceptor differentiation during growth and regeneration of the adult retina involves a recapitulation of mechanisms that control the sequence of photoreceptor production during retinal development.

Amino Acid Sequence↗
PubMed2002

Visual pigment coexpression in all cones of two rodents, the Siberian hamster, and the pouched mouse.

PURPOSE: To decide whether the identical topography of short- and middle-wavelength cone photoreceptors in two species of rodents reflects the presence of both opsins in all cone cells. METHODS: Double-label immunocytochemistry using antibodies directed against short-wavelength (S)-and middle- to long-wavelength (M/L)-sensitive opsin were used to determine the presence of visual pigments in cones of two species of rodents, the Siberian hamster (Phodopus sungorus) and the pouched mouse (Saccostomus campestris) from South Africa. Topographical distribution was determined from retinal whole-mounts, and the colocalization of visual pigments was examined using confocal laser scanning microscopy. Opsin colocalization was also confirmed in consecutive semithin tangential sections. RESULTS: The immunocytochemical results demonstrate that in both the Siberian hamster and the pouched mouse all retinal cones contain two visual pigments. No dorsoventral gradient in the differential expression of the two opsins is observed. CONCLUSIONS: The retina of the Siberian hamster and the pouched mouse is the first example to show a uniform coexpression of M and S cone opsins in all cones, without any topographical gradient in opsin expression. This finding makes these two species good models for the study of molecular control mechanisms in opsin coexpression in rodents, and renders them suitable as sources of dual cones for future investigations on the role and neural connections of this cone type.

Animals↗
PubMed2002

Distinct functions of photoreceptor cell-specific nuclear receptor, thyroid hormone receptor beta2 and CRX in one photoreceptor development.

PURPOSE: To clarify the functions of a specific subtype of thyroid hormone receptor (TR), TRbeta2, and photoreceptor cell-specific nuclear receptor (PNR) in the development of cone photoreceptors. METHODS: The expression of short (S)- and medium (M)-wavelength cone opsins was analyzed by reverse transcription polymerase chain reaction (RT-PCR) and Northern blot analysis in mice without a functional PNR (rd7/rd7 mice), and levels of plasma thyroid hormones and expression of TRbeta2 were also examined. Concomitantly, by means of reporter assays, the roles of PNR and TRbeta2 in the S- and M-cone opsin expression were explored at the transcriptional level. RESULTS: In rd7/rd7 mice, an abnormal increase in cone photoreceptors was observed immediately before retinal maturation normally occurs. Although an increase in S-cone opsin in the retina was observed during and after retinal development, the expression of M-cone opsin expression was not perturbed during retinal maturation. Plasma concentrations of thyroid hormone and levels of TRbeta2 expression in the rd7/rd7 mouse retina over the developmental period were normal. Transcriptional studies demonstrated that TRbeta2, but not PNR, activated the M-cone opsin gene promoter function, while suppressing the S-cone opsin promoter function enhanced by CRX in a thyroid hormone-dependent manner. CONCLUSIONS: The results indicate that PNR may suppress proliferation of cone photoreceptor progenitor cells and that the regulation of S- and M-cone opsin gene expression is mediated by TRbeta2 and CRX, but not by PNR. Thus, our results partly disclosed the molecular mechanism of cone photoreceptor development, highlighting the distinct functions of PNR and TRbeta2.

Animals↗
PubMed1985

Membrane assembly in retinal photoreceptors. III. Distinct membrane domains of the connecting cilium of developing rods.

To investigate the putative role of the photoreceptor connecting cilium in the delivery of opsin to forming discs and in the maintenance of membrane domains (Besharse, J. C., and K. H. Pfenninger (1980) J. Cell Biol. 87: 451-463), we have studied developing photoreceptors of neonatal rats during the period of initial disc formation using conventional freeze-fracture, immunocytochemistry, and lectin cytochemistry. Specific anti-opsin-binding sites were localized in the distal cilium, the developing outer segment plasma membrane, and at focal sites on the inner segment plasma membrane at all developmental stages examined, including the period prior to the onset of disc morphogenesis. The proximal ciliary shaft generally lacked anti-opsin-binding sites or exhibited them in extremely low density. The distribution of anti-opsin-binding sites corresponded in a general way to the distribution of large intramembranous particles (IMPs) in freeze-fracture replicas like those seen in the rod outer segment (ROS). The proximal zone corresponded in freeze-fracture images to a zone of consecutive horizontal rows of intramembrane particles (ciliary necklaces) and axoneme-membrane cross-linkers. Although protoplasmic face leaflet IMPs similar to those of the distal cilium and outer segment were less abundant in the inner segment and proximal cilium than in the distal cilium and ROS, they were detected in these zones at low frequency. Cytochemistry with concanavalin A and wheatgerm agglutinin revealed the presence of a well developed glycocalyx in the proximal zone. Although opsin binds both lectins, the results suggest heterogeneity among the glycoconjugates of the three membrane domains. Our data define distinct membrane domains of the developing photoreceptor cilium that have important implications for the mechanisms for delivering and sequestering opsin in the outer segment. They also establish that the mechanism of opsin delivery to the distal zone occurs well in advance of the period of disc morphogenesis.

Animals↗
PubMed1997

Structure and function in rhodopsin: packing of the helices in the transmembrane domain and folding to a tertiary structure in the intradiscal domain are coupled.

A previous study of the retinitis pigmentosa mutation L125R and two designed mutations at this site, L125A and L125F, showed that these mutations cause partial or total misfolding of the opsins expressed in COS cells from the corresponding mutant opsin genes. We now report on expression and characterization of the opsins from the following retinitis pigmentosa mutants in the transmembrane domain of rhodopsin that correspond to six of the seven helices: G51A and G51V (helix A), G89D (helix B), A164V (helix D), H211P (helix E), P267L and P267R (helix F), and T297R (helix G). All the mutations caused partial misfolding of the opsins as observed by the UV/visible absorption characteristics and by separation of the expressed opsins into fractions that bound 11-cis-retinal to form the corresponding mutant rhodopsins and those that did not bind 11-cis-retinal. Further, all the mutant rhodopsins prepared from the above mutants, except for G51A, showed strikingly abnormal bleaching behavior with abnormal metarhodopsin II photointermediates. The results show that retinitis pigmentosa mutations in every one of the transmembrane helices can cause misfolding of the opsin. Therefore, on the basis of these and previous results, we conclude that defects in the packing of the transmembrane helices resulting from these mutations are relayed to the intradiscal domain, where they cause misfolding of the opsin by inducing the formation of a disulfide bond other than the native Cys-110---Cys-187 disulfide bond. Thus, there is coupling between packing of the helices in the transmembrane domain and folding to a tertiary structure in the intradiscal domain.

Amino Acid Sequence↗
PubMed2001

The ability of hyperoxia to limit the effects of experimental detachment in cone-dominated retina.

PURPOSE: To determine the ability of oxygen supplementation to ameliorate the effects of retinal detachment in a cone-dominated retina. METHODS: Retinal detachments were created in the right eyes of ground squirrels and the animals immediately placed in normoxic (room air) or hyperoxic (70% oxygen) conditions for 3 days. The retinas were sampled from different regions and investigated morphologically or immunocytochemically by light or confocal microscopy. Agarose embedded sections were immunostained with antibody probes to cytochrome oxidase, synaptophysin, medium-to-long wavelength-sensitive (M/L) cone opsin, rod opsin, excitatory amino acid transporter 1 (EAAT1), glutamate synthetase (GS), cellular retinaldehyde-binding protein (CRALBP), and peanut agglutinin (PNA) lectin. Retinal wholemounts were labeled with PNA and antibodies to short (S)-wavelength-sensitive cone opsin and rod opsin. Cell death was examined using a TUNEL assay on agarose sections or using toluidine blue staining on semithin sections. RESULTS: The percentage of dying cells relative to the total nuclei in the photoreceptor layer was significantly reduced, and the total number of nuclei was greater in hyperoxic animals. Triple labeling using TUNEL, anti-M/L cone opsin and anti-rod opsin showed that hyperoxia had a remarkable effect both on the reduction of cone cell death and the maintenance of the overall structure of cone photoreceptors. Analysis of the retinal wholemounts demonstrated the preservation of PNA, S-cone, and rod opsin antibody labeling in the detachments maintained in hyperoxic conditions. Although the disruption of cytochrome oxidase and synaptophysin was seen in normoxic animals, there was minimal disruption in hyperoxic animals. Labeling with anti-EAAT1, anti-GS, and anti-CRALBP was increased in the Müller cells of normoxic animals with detachments, but was decreased in the hyperoxic animals. CONCLUSIONS: Hyperoxia prevents the degeneration of both rods and cones in retinas heavily dominated by cones and mitigates the effect of detachment on Müller cell reactivity. The current results suggest that the rescue of cones is not secondary to that of rods.

Animals↗
PubMed1996

Development of the pattern of photoreceptors in the chick retina.

The various classes of photoreceptor cells found in vertebrate retinae are organized in specific patterns, which are important for visual function. It is not known how these patterns are achieved during development. The chick retina provides an excellent model system in which to investigate this issue, containing cone opsins red, green, blue, and violet, as well as the rod-specific opsin rhodopsin. In this study, whole-mount in situ hybridization has revealed striking differences among opsins in both spatial and temporal aspects of expression. The long-wavelength cone opsins, red and green, were first detected in a small spot within the area centralis at embryonic day 14 (E14). In contrast, the short-wavelength cone opsins, blue and violet, were not detected until 2 d later and showed domains of expression both within the area centralis and in temporal retina. The first rhodopsin transcripts were seen at E15 in inferior retina. When opsin expression was first detected, there were differences in the localization of RNA within the inner segment of cone photoreceptors, suggesting that morphological differentiation preceded the expression of photopigment molecules. Marked differences in the distribution of rods and cones were also found. Within the area centralis, a circular rod-free zone bisected by a narrow rod-sparse region along the nasal-temporal axis was evident as soon as rhodopsin RNA could be detected. Such specialized regions appear to be set aside soon after photoreceptor cells become postmitotic, as evidenced by a spatially restricted pattern of visinin RNA observed at E7. The onset of particular opsins in restricted regions of the retina suggest an underlying pattern related to visual function in the chick.

Animals↗
PubMed2002

Visualization of rod photoreceptor development using GFP-transgenic zebrafish.

Zebrafish retina contains five morphologically distinct classes of photoreceptors, each expressing a distinct type of opsin gene. Molecular mechanisms underlying specification of opsin expression and differentiation among the cell types are largely unknown. This is partly because mutants affected with expression of a particular class of opsin gene are difficult to find. In this study we established the transgenic lines of zebrafish carrying green fluorescent protein (GFP) gene under the 1.1-kb and 3.7-kb upstream regions of the rod-opsin gene. In transgenic fish, GFP expression initiated and proceeded in the same spatiotemporal pattern with rod-opsin gene. The retinal section from adult transgenic fish showed GFP expression throughout the rod cell layer. These results indicate that the proximal 1.1-kb region is sufficient to drive gene expression in all rod photoreceptor cells. These transgenic fish should facilitate screening of mutants affected specifically with rod-opsin expression or rod cell development by visualization of rod cells by GFP.

5' Untranslated Regions↗