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At least 19 recordsLinked to original sources
PubMed1978

Studies on the biosynthesis of bacterio-opsin. Demonstration of the existence of protein species structurally related to bacterio-opsin.

1. The kinetics of processing newly synthesized bacterio-opsin from the non-crystalline state within the brown membrane to the crystalline state within the purple membrane was followed by pulse-chase experiments. 2. Biosynthesis of bacterio-opsin was found to be highly resistant to RNA-synthesis inhibitors like rifampicin and ethidium bromide. In the presence of ethidium bromide, only five protein species continue to be synthesized in halobacteria, one of them being bacterio-opsin. 3. In spheroplasts, synthesis of bacterio-opsin is found to be selectively disturbed. The purple membrane isolated from spheroplasts contains new, additional protein species with apparent molecular weights of 19 000, 23 000 and 29 000. These proteins share common amino acid sequences with bacterio-opsin. 4. In the halobacterial cell membrane, two membrane proteins with apparent molecular weights of 30 000 and 36 000 were detected which are structurally related to bacterio-opsin. 5. Bacterio-opsin as well as the 30 000 Mr and 36 000-Mr proteins contain covalently bound sulphate.

Amino Acid Sequence↗
PubMed1991

In vitro expression of bovine opsin using recombinant baculovirus: the role of glutamic acid (134) in opsin biosynthesis and glycosylation.

Expression levels of functional bovine opsin in the insect cell line IPLB-Sf9 using recombinant baculovirus were shown not to depend on the use of novel transfer vectors (pAcRP23, pAcDZ1) that were reported to improve biosynthesis levels of other proteins in this system. A production of 5 micrograms opsin per 10(6) cells (approx. 1.5% of total cell protein) was achieved by batch fermentation of infected cells in spinner cultures. Infection of the cells in the presence of the glycosyltransferase inhibitor tunicamycin led to the synthesis of the complete protein, which, however, now migrated with a substantially lower Mr. This demonstrates that opsin in insect cells also undergoes N-linked glycosylation and allowed partial purification (10-fold) of the resulting rhodopsin by affinity chromatography over Concanavalin A-Sepharose. Through site-directed mutagenesis (rhod)opsin mutants have been obtained allowing dissection of functional domains of opsin. Amino acid substitutions that involved Glu-134 and/or Arg-135 affected the normal biosynthetic process leading in part to nonglycosylated, to a small extent even incomplete, protein. A number of mutations, that involve other charged residues within the second and third transmembrane domain of the protein, had no effect on the biosynthetic processing of the protein. We therefore suggest that the charge-pair Glu-134-Arg-135 is part of an important internal signal sequence and that alterations in this region may result in incorrect membrane translocation and/or folding of the protein.

Animals↗
PubMed1990

Opsin gene expression during early and late phases of retinal degeneration in rds mice.

Opsin mRNA levels, opsin synthetic rates and localization of opsin were studied throughout the photoreceptor's life span in the rds mice. Mutant mice 11 days to 11 months old were investigated. Opsin mRNA levels were studied by means of northern blot analysis. Opsin synthesis was measured by incorporation of [35S]methionine into newly synthesized opsin in vitro. Distribution of opsin in the retina was determined by immunoelectron microscopy. Opsin mRNA was detected in young as well as old retinas, and opsin synthesis could be detected at early phases of degeneration but not in late phases. The absence of opsin synthesis in older rds mice might be due to translational down-regulation or some other defect in the capacity to synthesize opsin. In young mice, opsin was detected in the subretinal space in opsin-laden vesicular membranes: such membranes were absent from retinas of older mice. This disappearance parallels the cessation of opsin synthesis and the consequent failure to deliver opsin to the subretinal space in retinas from older mice. Immunochemical analysis revealed the presence of small amounts of opsin in all retinas up to 11 months of age. Immunoelectron microscopy localized the residual opsin, mostly to the plasma membrane which envelops the nuclei and synaptic terminals. These opsin molecules might be a consequence of very low levels of opsin synthesis, too low to be detected by our assays, or may have been synthesized at an earlier age and retained in the plasma membrane of the old mutant photoreceptors.

Animals↗
PubMed1990

Opsin synthesis and mRNA levels in dystrophic retinas devoid of outer segments in retinal degeneration slow (rds) mice.

Opsin gene regulation, as a function of outer segment structure, was studied in normal and mutant retinal degeneration slow (rds) mice. We investigated the level of expression of the opsin gene in the rds mutant to determine if the reduced opsin content observed in this mutation (around 3% of normal) is a consequence of lowered expression of its gene. Normal BALB/c and rds mice were analyzed for levels of opsin mRNA and opsin content by Northern and immunoblot analysis, respectively. The rate of opsin synthesis in isolated retinas was measured by 35S-methionine incorporation in vitro, followed by analysis of the radiolabeled opsin by SDS-gel electrophoresis and autoradiography. Photoreceptor cell loss at various stages of degeneration was determined by quantitation of surviving photoreceptor nuclei. Opsin was localized in the mutant photoreceptors by immunoelectron microscopy of LR gold-embedded retinas using anti-opsin and antibody gold conjugates. The results indicate that 11- and 30-d-old mutant mice have considerable levels of opsin mRNA (60-70% of normal) and opsin synthetic rates (76-92% of normal), after the data from mutant mice are corrected for photoreceptor cell loss. We conclude, therefore, that the very low level of opsin observed in rds mice (approximately 3%) is not a result of greatly reduced expression of the opsin gene. Rather, continuous turnover of newly synthesized opsin as a result of its failure to become sequestered into an intact outer segment appears to account for the low levels of opsin in the rds mutant.

Animals↗
PubMed1989

Immunocytochemical localization of opsin in degenerating photoreceptors of RCS rats and rd and rds mice.

Opsin is normally sequestered predominantly in the outer segment disc and plasma membranes of adult photoreceptors. Absence of opsin from the inner segment plasma membrane in normal photoreceptors is probably not due to the inability of the inner segment plasma membrane to retain opsin. Rather, in the adult mammalian retina, if opsin is inserted at sites in the apical inner segment plasma membrane, in a fashion comparable to the pathway in amphibians, it is rapidly transported predominantly to the outer segment by unknown mechanisms. Dystrophic rds retinas, lacking an outer segment, display newly synthesized opsin throughout the plasma membrane. If opsin is transported to the inner segment plasma membrane as a specific insertional site, diffusion in the plane of the membrane may redistribute opsin throughout the plasma membrane which encloses the nucleus and the synaptic terminal. Alternatively, opsin may be inserted randomly throughout the entire cell's plasmalemma beneath the cilium. Selective transport to the outer segment may preferentially clear the inner segment of most of its opsin and nearly clear the perikaryal and synaptic terminal's plasmalemma in normal cells. In dystrophic retinas, however, as outer segments degenerate or fail to form, opsin is detected readily in the remaining plasma membrane sites. In the rd mouse, some of the opsin molecules in the inner segment plasma membrane might be newly synthesized while others may arise from molecules which reached the inner segment by back-diffusion from the outer segment at least at early stages in the degeneration while outer segments survive. The opsin in the plasma membrane which envelopes the residual rod nuclei and synaptic terminals in dystrophic retinas may account for the persisting light perception in retinas which have lost both the rod outer and inner segments. Dystrophic retinas, such as the rd mouse and RCS rats and possibly human RP retinas, in which cone nuclei survive long after rods disappear, might retain light perception because of cone photo-pigments in the outer nuclear and outer plexiform layers. To explore these questions further, the localization of other components of the transduction cascade and the determination of the efficiency of their coupling in dystrophic cells is necessary. We need to know where the cyclic GMP-sensitive sodium channels lie in these dystrophic cells and the cellular requirements for proximity of these components to generate a signal. Outer segment-free photoreceptors, bearing opsin in their plasma membranes, resemble other cells which have receptor-mediated alterations in membrane permeability to ions.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Opsin distribution and synthesis in degenerating photoreceptors of rd mutant mice.

The distribution of opsin and the capacity of photoreceptors to synthesize opsin was studied in retinas of mice bearing the rd (retinal degeneration) mutation and compared to control normal mice. Opsin was localized by means of pre-embedding and post-embedding immunocytochemistry and electron microscopy. Cones were identified with anti-cone antibodies and peanut agglutinin lectin which labels cone matrix sheaths. Opsin synthesis was measured by incorporation of [35S]methionine into opsin which was detected by immunoblots. Immunocytochemistry revealed that degeneration of rod outer segments was accompanied by accumulation of opsin in the plasma membrane enveloping the inner segment, nuclei and synaptic terminals. Rod photoreceptors degenerated faster than cones. By post-natal day 19 (P19), 87% of the remaining inner segments were cones. Opsin synthesis in rd mice could no longer be measured after P15. However, opsin molecules could be detected both by immunocytochemistry and immunoblotting up to P30. Between P20 and P30 all detectable opsin was localized in the plasma membrane which envelopes nuclei and synaptic terminals. Unlabeled surviving nuclei after P30 are probably cones. The opsin which is detected in rod inner segment plasma membranes might be derived, by back diffusion, from degenerating outer segments and represent molecules synthesized at an earlier time. Alternatively opsin accumulation might be a result of low levels of opsin synthesis, undetectable by [35S]methionine incorporation, which continues in the absence of outer segments.

Animals↗
PubMed1991

Ultrastructure and opsin immunocytochemistry of the pineal complex of the larval Arctic charr Salvelinus alpinus: a comparison with the retina.

The fine structure and opsin immunocytochemistry of the pineal and parapineal organs of the salmonid fish Salvelinus alpinus, the landlocked Arctic charr, were studied and compared with the retina in various developmental stages, from prehatching to two-month-old. For opsin immunocytochemistry two polyclonal antibovine rhodopsin and the monoclonal antichicken opsin antibodies OS-2 (detecting blue and green pigments) and OS-1 (detecting green and red pigments) were used. Histologically, the pineal organ consists of nervous tissue like that of the retina. It is composed of photoreceptor pinealocytes, which formed axon terminals containing synaptic ribbons, on the dendrites and perikarya of secondary pineal neurons. Already in prehatching embryos, both the pineal and retinal photoreceptors display well-developed outer segments and form synaptic terminals. The distal part of the pineal organ differentiates earlier than its proximal stalk. The differentiation of the retina starts centrally, but the caudal and dorsal retinae are differentiated earlier than the rostral and ventral ones. At the end of the larval period, the lateral retina is still undifferentiated. In all stages studied, (rhod)opsin immunoreactivity was found in the outer segments of the pineal organ and rod-type retinal photoreceptors, a finding speaking in favour of the presence of the opsin of a rhodopsin/porphyropsin. Cone-type retinal photoreceptors identified morphologically in the pre- and posthatching stages were opsin-immunonegative with the four primary antisera used. This result suggests that in the charr the opsins of cone visual pigments differ in their chemical nature from those of rhodopsin/porphyropsin. The parapineal organ was opsin immunonegative. Using the monoclonal antibody OS-2 opsin immunoreactivity was also detected in inner segments, perikarya, and pedicles of rod-type photoreceptors of both retina and pineal organ of embryos and 1- to 4-day-old larvae. This may indicate a high level of opsin gene expression during photoreceptor growth around hatching. The well-developed pineal organ and its opsin content are discussed in connection with the photonegative behaviour of the larval charr.

Animals↗
PubMed1987

Immunological and immunopathological aspects of opsin-induced uveoretinitis.

In an extension of our previous studies, experimental autoimmune uveoretinitis (EAU) was induced in Lewis rats by injection of very high doses of bovine opsin. The induced reaction consisted predominantly of a mild posterior retinitis. Varying the amount of injected opsin between 300 and 1,000 micrograms did not influence this result, provided that the antigen was injected in Freund's complete adjuvant. Pathogenicity of opsin appeared to be lower than that of interphotoreceptor retinoid binding protein (IRBP) or S-antigen, while EAU induced by the latter antigens was much more dose-dependent than EAU induced by opsin. An increase of the dose strongly accelerated the onset and increased the incidence of EAU from low to moderate. However, severe inflammation and high incidence were only obtained by co-injection of Hemophilus pertussis bacteria. This adjuvant especially increased cellular immune responses to opsin as measured by lymphocyte transformation. No marked effects on humoral responses were detected by ELISA, using different types of opsin preparations. Development of opsin-induced EAU was inhibited by ciclosporin, a suppressor of certain specific T cell functions. Ciclosporin injections lowered the antibody response of the rats and eliminated measurable lymphocyte transformation in vitro. Induction of opsin-EAU therefore appears to be T-cell-dependent. The effect of pertussis adjuvant may be explained by enhancement of the T cell responses to opsin and by increasing the permeability of the blood-retina barriers. Other properties of the adjuvant may be of importance as well. A relationship between change in molecular conformation and uveitogenicity of opsin is discussed.

Adjuvants, Immunologic↗
PubMed1992

Expression of opsin and IRBP genes in mutant RCS rats.

The retinal pigment epithelium of RCS rats bearing the autosomal recessive rdy mutation fails to ingest shed rod outer segment tips. Accumulation of disk debris in the subretinal space of the maturing mutant retina causes a secondary degeneration of photoreceptor cells. Two hypotheses have been offered as possible explanations of the death of photoreceptor cells in this disorder: (1) photoreceptors are starved for amino acids, retinal, oxygen, etc; and (2) that IRBP levels and synthesis may be decreased and interfere with retinal transport and this deficiency is lethal to these cells. To test these hypotheses, we have studied the effect of this mutation on the levels of expression of opsin and IRBP genes, and gene products and on rates of synthesis at various ages in dystrophic RCS p+ rats and compared the results to those obtained with normal Long Evans rats. The mutant rats and normal controls had comparable amounts of opsin and IRBP mRNA transcripts and rates of synthesis up to post-natal day 45 (P45) but opsin transcripts were barely detectable at P60 and thereafter. IRBP mRNA levels were also very low after P62 although somewhat higher than opsin mRNA. Opsin could be detected immunochemically, albeit at lower levels, at all the ages studied up to P310, but IRBP levels fell below detection after P45. We localized opsin and IRBP in the retina by post-embedding EM immunocytochemical procedures and found that opsin is present in the remnants of rod outer segment debris, even at P390, long after detectable opsin synthesis had ceased. These data suggest that expression of opsin and IRBP genes is not influenced by the shape and state of the outer segments, and that the rdy mutation does not influence the expression of the opsin and IRBP in these retinas until the photoreceptor cells are profoundly damaged. Thus, neither hypothesis about the causes of cell death in this disorder is supported.

Aging↗
PubMed1988

A diurnal rhythm in opsin content of Rana pipiens rod inner segments.

Quantitative electron microscope immunocytochemistry, employing an antibody specific to opsin, was used to evaluate the amount and location of opsin in Rana pipiens rod photoreceptors throughout a 24 hr light/dark cycle. We found a distinct diurnal rhythm in the density of anti-opsin labeling of the rough endoplasmic reticulum (RER) and Golgi apparatus in the myoid region of the rod inner segment. Opsin labeling of these organelles was lowest at light onset, increasing thereafter by three- to four-fold, and remained high until 2 hr into the dark phase. A fall in labeling density occurred within the following 4 hr, and remained low for the remainder of the dark phase. Our finding of a diurnal rhythm regulating inner segment opsin transport in Rana pipiens contrasts with published observations on outer segment membrane turnover, since it has been shown that the rates of disc formation and disc shedding are governed by environmental lighting alone in this species. These results imply that there is opsin pooling in the inner segment during the first 14 hr of a 24 hr light/dark cycle; thereafter the loss of inner segment opsin due to mobilization of this protein from the Golgi exceeds the rate of formation of new opsin. There was no evidence of accumulation of opsin-containing vesicles near the cilium or in the ellipsoid just prior to light onset. At light onset, prominent opsin labeling was identified at the proximal portion of the outer segment in regions separate from the disc stack. In two separate experiments, additional groups of frogs were killed around the time of light onset and were examined by conventional transmission electron microscopy. Disordered disc membranes were seen at the base of the outer segment which were not in register with the disc stack. These disordered membranes were observed as early as 2 hr before light onset, and were no longer observed by 1 hr after light onset. We suggest that these disordered membranes reflect a step in the biogenesis of new discs, serving as a pool of membrane that forms during the later part of the dark cycle. It appears that light onset triggers the ordering of neatly registered discs from this new membrane, rather than assembly of new membrane from pooled transport vesicles in the inner segment.

Animals↗
PubMed1988

A specific ELISA using purified opsin, for studying autoimmunity in retinal diseases.

A highly sensitive enzyme-linked immunosorbent assay (ELISA) was developed to measure nanogram quantities of rhodopsin or its apoprotein, opsin, in bovine retinal rod outer segment (ROS) preparations. Anti-opsin anti-sera could detect as little as 4 ng of purified opsin or of opsin in ROS preparations. The purified opsin was prepared by quantitative elution from a preparative polyacrylamide gel, and showed higher immunoreactivity with anti-opsin than did ROS when the same amount (per weight) of protein was allowed to bind in the wells of the ELISA plates. The effect of the ionic detergent SDS (sodium dodecyl sulphate) on the immunoreactivity and antigen binding to the ELISA wells was studied. Concentrations of 0.1% SDS and above reduced the apparent binding of opsin with anti-opsin when examined by ELISA. This may have been because the negatively charged SDS reduced the efficiency of the antigen coating process, or because changes in the epitopes' conformations made them less recognisable by the corresponding antibodies. A similar ELISA system using a specific anti-S-antigen anti-serum allowed the detection of even very small amounts (nanograms) of S-antigen in ROS preparations. The presence of S-antigen in ROS preparations was confirmed by immunoblotting. Thus purified opsin is preferable to ROS for ELISA tests of autoimmunity to rhodopsin in retinal diseases. These sensitive ELISA techniques could be used to examine the presence of minute amounts of rhodopsin, opsin or S-antigen in different retinal preparations.

Animals↗
PubMed1986

Deficiency in light-dependent opsin phosphorylation in Irish setters with rod-cone dysplasia.

A deficiency in light-dependent opsin phosphorylation and a slight reduction in opsin synthesis were observed during photoreceptor cell development (22-26 days) preceding photoreceptor cell loss in Irish setters with rod-cone dysplasia. In addition to opsin, two other phosphoprotein bands were found associated with the photoreceptor cell layer; synthesis and phosphorylation of one of these (band 3; 44-48 Kd) appeared reduced, while synthesis and phosphorylation of the other (band 1; 29-31 Kd) was within the normal range in 25-day-old affected setters. The deficiency in light-dependent opsin phosphorylation in affected setters was not due to a deficiency in opsin kinase, since soluble proteins from affected or normal outer segments catalyzed equally well opsin phosphorylation in partially kinase-depleted outer segment membranes from normal, while both kinase preparations failed to promote light-dependent opsin phosphorylation in those from affected setters. A deficiency in light-dependent opsin phosphorylation was also observed in rd/rd mice at all ages studied. In contrast, in Royal College of Surgeons (RCS) rats, light-dependent opsin phosphorylation was within the normal range prior to photoreceptor loss, and became nondetectable only after 50% or more of the photoreceptors had degenerated.

Animals↗
PubMed1971

Energy transfer in rhodopsin, N-retinyl-opsin, and rod outer segments.

N-retinyl, the chromophore of bleached and reduced rhodopsin, N-retinyl-opsin, was used as a covalently attached fluorescence probe to examine the structure of N-retinyl-opsin and the rod outer segment. The efficiency of energy transfer from the protein part of N-retinyl-opsin to the chromophore is 12 +/- 5%. It is argued that this implies that the N-retinyl-opsin molecule is asymmetrical. Kropf has estimated the efficiency of energy transfer from the protein to the chromophore in native rhodopsin to be about 50%. This difference of efficiencies seems to imply a large movement of the chromophore away from the tryptophans of the opsin after rhodopsin is bleached. From excitation spectrum measurements, it has been found that light absorbed by the protein of the rod outer segments has more action in sensitizing the fluorescence of the chromophore than does light absorbed by the protein part of pure N-retinyl-opsin. Thus, some other tryptophans or tyrosines in either another N-retinyl-opsin molecule or another protein must be close enough (about 28 A) to the chromophore to transfer energy to it. Measurements of the polarization of the fluorescence of the chromophore suggest, however, that the chromophores of neighboring N-retinyl-opsin molecules are more than 20 A apart. Moreover, these neighboring chromophores do not transfer energy to each other, tending to rule out any clustering of chromophores of different N-retinyl-opsin molecules and suggesting that rhodopsin chromophores do not transfer energy to each other.

Energy Transfer↗
PubMed1979

Messenger RNA of opsin from bovine retina: isolation and partial sequence of the in vitro translation product.

Opsin, the apoprotein of the visual pigment rhodopsin, is synthesized on membranes of the rough endoplasmic reticulum and subsequently passes through the Golgi apparatus to the rod outer segment. This pathway parallels the early stages of biosynthesis of some secretory proteins and viral membrane glycoproteins. Most of these proteins are initially synthesized as precursor molecules with a short-lived hydrophobic extra peptide segment at the NH(2) terminus. Therefore we investigated whether or not the immediate translation product of opsin mRNA contains a similar short-lived NH(2)-terminal extra peptide. The mRNA coding for opsin was isolated from bovine retina polysomes precipitated by antibodies to opsin. The mRNA directed the cell-free synthesis of a protein comparable in size to opsin that was specifically precipitated by anti-opsin antibodies. Sequence analyses of the immunoprecipitated protein labeled with six radioactive amino acids (Met, Asn, Pro, Phe, Tyr, Val) provided the following result: [Formula: see text] (X is unknown). This partial sequence of the cell-free product corresponds exactly to the published NH(2)-terminal segment of native opsin (21 residues long) and extends beyond this region. Met-1 was shown to be the initiator methionine residue, because only the initiator [(35)S]Met-tRNA(1) (Met)-not the internal [(35)S]Met-tRNA(2) (Met)-donated the NH(2)-terminal methionine. This finding essentially rules out the possibility that Met-1 was preceded by a peptide that was rapidly cleaved. Thus opsin, and not a precursor, is the immediate product of opsin mRNA translation.

Amino Acid Sequence↗
PubMed1987

Development and degeneration of retina in rds mutant mice: ultraimmunohistochemical localization of opsin.

In normal retina the developing photoreceptor cells first show presence of opsin over the distal ends of the ciliary protrusions. In a fully differentiated cell intense activity is seen over the rod outer-segment discs; some activity is also seen over the Golgi zone and near the distal ends of the inner segments but the other parts of the receptor cell appear negative. In the pigment epithelium opsin is seen only over phagosomes containing rod outer segment debris. In the homozygous rds mutant retina, developing receptor cells show opsin activity over the ciliary protrusions as in the normal. These ciliary protrusions grow in size and show increased opsin activity and presumably constitute the site of phototransduction in the mutant retina. Although typical disc structures remain lacking, variable amounts of immunopositive, irregular, membranous structures are occasionally observed. The inner segments in the mutant cells show very little immunoreactivity but the perikarya and the spherule terminals show increased immunoreactivity in comparison with the normal. At the onset of degeneration, some of the receptor cells in the mutant retina show extrusion of small, membrane-bound vesicles which are immunopositive for opsin. Some receptor cells undergoing lysis disintegrate and also add to the opsin-positive vesicular structures in the interphotoreceptor space. The vesicles are phagocytized by pigment epithelial cells. In older mutant mice at an advanced stage of degeneration, the receptor cells show reduced opsin activity. In heterozygous mutant mice the outer segments are reduced in length and the discs are abnormal in form. However, the intensity and the pattern of opsin localization in the outer segments and at other sites are similar to normal.

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↗
PubMed1988

Opsin expression in the rat retina is developmentally regulated by transcriptional activation.

The gene for rhodopsin, the primary light sensor of the visual system, is specifically expressed in the rod photoreceptor cells of the retina. We show here that in the rat, opsin RNA first accumulates to detectable levels at postnatal day 2 (PN2) and that nascent transcripts can be detected at PN1; this is the time when peak numbers of photoreceptor cells are generated by the final division of their neuroepithelial precursors. Accumulated opsin RNA then increases to reach the adult level, 0.06% of total retinal RNA, at about PN10. The transcription rate of the opsin gene increases to a similar extent over the same time course between PN3 and adulthood, suggesting that transcriptional activation is responsible for the increase in opsin expression. We used the antibody RET-P1 to show that rhodopsin protein is also detectable at PN2 and that the number of cells expressing the protein increases with time in a central-to-peripheral gradient in the retina. This increase in the number of differentiating photoreceptors in the tissue appears to account for much of the increase in opsin gene transcription and RNA accumulation. In situ hybridization to opsin RNA shows that it is restricted to the photoreceptor layer from the time it can first be detected, at PN7. Later in development, when RET-P1 staining shifts to the photoreceptor outer segments, opsin RNA becomes localized to the inner segments, suggesting that the distributions of opsin protein and RNA are related.

Aging↗