Biomedical subjects

Baerbel Rohrer

Publications and source records attributed to Baerbel Rohrer.

17 recordsLinked to original sources

PubMed2006

Gene silencing in Xenopus laevis by DNA vector-based RNA interference and transgenesis.

A vector-based RNAi expression system was developed using the Xenopus tropicalis U6 promoter, which transcribes small RNA genes by RNA polymerase III. The system was first validated in a Xenopus laevis cell line, designing a short hairpin DNA specific for the GFP gene. Co-transfection of the vector-based RNAi and the GFP gene into Xenopus XR1 cells significantly decreased the number of GFP-expressing cells and overall GFP fluorescence. Vector-based RNAi was subsequently validated in GFP transgenic Xenopus embryos. Sperm nuclei from GFP transgenic males and RNAi construct-incubated-sperm nuclei were used for fertilization, respectively. GFP mRNA and protein were reduced by approximately 60% by RNAi in these transgenic embryos compared with the control. This transgene-driven RNAi is specific and stable in inhibiting GFP expression in the Xenopus laevis transgenic line. Gene silencing by vector-based RNAi and Xenopus transgenesis may provide an alternative for 'repression of gene function' studies in vertebrate model systems.

Animals↗

PubMed2005

Downregulation of cone-specific gene expression and degeneration of cone photoreceptors in the Rpe65-/- mouse at early ages.

PURPOSE: RPE65 is essential for the generation of 11-cis retinal. Rod photoreceptors in the RPE65-knockout (Rpe65(-/-)) mouse are known to degenerate slowly with age. This study was designed to examine cone photoreceptors and the expression of cone-specific genes in the Rpe65(-/-) mouse. METHODS: Gene expression changes were identified by microarray and confirmed by real-time RT-PCR. Cone photoreceptors were stained by peanut agglutinin (PNA) lectin in the flatmounted retina. The 9- or 11-cis retinal was supplied by intraperitoneal injections. RESULTS: The short-wavelength (SWL) cone opsin mRNA was markedly decreased at 2 weeks of age, whereas the decrease in the middle-wavelength (MWL) cone opsin mRNA occurred relatively later in age. In contrast, the rhodopsin mRNA level did not show any significant change at all the ages analyzed. Consistent with the cone opsin changes, the cone transducin alpha-subunit mRNA decreased at both 4 and 8 weeks of age, whereas again the rod transducin alpha-subunit did not show any significant change. Rpe65(-/-) mice showed significant cone loss in both the central and ventral retina between 2 and 3 weeks of age. Administration of 9- or 11-cis retinal to Rpe65(-/-) mice 2 weeks of age increased cone density by twofold in these areas. CONCLUSIONS: In the Rpe65(-/-) mouse, the expression of cone-specific genes is downregulated and is accompanied by cone degeneration at early ages. Early administration of 9- or 11-cis retinal can partially prevent cone loss, suggesting that the absence of 11-cis chromophore may be responsible for the early cone degeneration.

Animals↗

PubMed2005

Cone opsin mislocalization in Rpe65-/- mice: a defect that can be corrected by 11-cis retinal.

PURPOSE: In retinal degenerative diseases, rod photoreceptors typically deteriorate more rapidly than cone photoreceptors. In the Rpe65(-/-) mouse, a model for Leber's congenital amaurosis, cones degenerate much more rapidly than rods. In this model, the retinoid processing pathway in the retinal pigment epithelium is disrupted, and 11-cis retinal is not generated. This study was designed to investigate the feasibility of restoring functional cones with exogenous 11-cis retinal. METHODS: Rpe65(-/-)::Rho(-/-) mice were used to remove any interference of rods and compared with wild-type (wt) mice. Pups were injected intraperitoneally with 11-cis retinal, starting at postnatal day (P)10, and were maintained in complete darkness. At P25, cone function was assessed with photopic single-flash and flicker ERGs. Cone survival was determined immunohistochemically with cone-specific antibodies, and cone opsin levels were obtained by quantitative RT-PCR. RESULTS: At P25, cone density and transcript levels of cone opsins were drastically reduced, but a minute cone electroretinogram was detected, indicating that the cones were functional. Confocal microscopy revealed that the cone opsins were mislocalized, suggesting that their transport to the outer segments was impaired. Intraperitoneal administrations of 11-cis retinal before P25 led to increased transport of cone opsins to the outer segments and preserved cones anatomically and functionally. CONCLUSIONS: The results suggest that the ligand is required during cone opsin synthesis for successful opsin trafficking and that without 11-cis retinal, cones may degenerate because of opsin mislocalization. These results may have important consequences for the treatment of cone dystrophies.

Animals↗

PubMed2004

Multidestructive pathways triggered in photoreceptor cell death of the rd mouse as determined through gene expression profiling.

In the rd/rd mouse, photoreceptor degeneration is due to a mutation of the rod-specific enzyme cGMP phosphodiesterase, resulting in permanently opened cGMP-gated cation channels in the rod outer segment membrane that allow Na(+) and Ca(2+) ions to enter the cell, resulting in possibly toxic levels of Ca(2+). To identify pathways involved in cell death of the rd/rd rods, we evaluated gene expression in the rd/rd and wild type (wt) mouse retina (U74A oligonucleotide arrays (Affymetrix)) over the known time course of photoreceptor degeneration. 181 genes passed the selection criteria (low standard deviation and high correlation between replicates), falling into six clusters. For any given pair of genes, an expression profile correlation distance and a semantic distance (one for each class of gene ontology terms) were established using newly designed software. Gene expression in rd/rd started to deviate from wt by postnatal day 10. The reduction in photoreceptor-specific genes followed the known time course of photoreceptor degeneration. Likewise the increase in transcription factors and apoptosis- and neuroinflammation-specific genes followed the kinetics of the rise in intracellular cGMP in the rod photoreceptors. In addition, genes coding for calcium-binding proteins and those implicated in tissue and vessel remodeling were increased. These results suggest that photoreceptor degeneration in the rd/rd mouse is a process starting with Ca(2+) toxicity followed by secondary insults involving multidestructive pathways such as apoptosis and neuroinflammation, presumably boosting morphological changes. All of these components need to be addressed if rods are to be successfully protected.

Animals↗

PubMed2004

Calcium-induced calpain mediates apoptosis via caspase-3 in a mouse photoreceptor cell line.

The rd mouse, an accepted animal model for photoreceptor degeneration in retinitis pigmentosa, has a recessive mutation for the gene encoding the beta-subunit of the cGMP phosphodiesterase. This mutation results in high levels of cGMP, which leaves an increased number of the cGMP-gated channels in the open state, thus allowing intracellular calcium (Ca(2+)) to rise to toxic levels, and rapid photoreceptor degeneration follows. To delineate the events in rd photoreceptor degeneration, we demonstrated an increase in calpain and caspase-3 activity, hypothesizing that Ca(2+)-mediated apoptosis in photoreceptors is mediated by calpain, involving mitochondrial depolarization and caspase-3 activation. To examine this hypothesis further, a murine photoreceptor-derived cell line (661W) was treated with the Ca(2+) ionophore A23187, cGMP-gated channel agonist 8-bromo-cGMP, or phosphodiesterase inhibitor isobutylmethylxanthine to mimic the increased Ca(2+) influx seen in the rd photoreceptors. Ca(2+)-induced cell death in 661W cells was found to be mediated by calpain and caspase-3 and could be completely inhibited by the calpain inhibitor SJA6017, implicating both calpain and caspases in the apoptotic process. The apoptotic events correlated in an SJA6017-inhibitable manner with bid cleavage, mitochondrial depolarization, cytochrome c release, and caspase-3 and -9 activation. We concluded that Ca(2+) influx in the rd model of photoreceptor degeneration leads to the activation of the cysteine protease calpain, which executes apoptosis via modulation of caspase-3 activity.

Animals↗

PubMed2004

Neurodegenerative alterations in the nigrostriatal system of trkB hypomorphic mice.

Brain-derived neurotrophic factor (BDNF) acts through the neurotrophin receptor TrkB and promotes survival and differentiation of dopaminergic ventral mesencephalic neurons. To further evaluate the role of TrkB in the nigrostriatal pathway, we studied neurotrophin levels, dopamine metabolism, and morphology of dopaminergic neurons of the substantia nigra (SN-DA) in young adult hypomorphic trkB mice (trkBfbz/fbz), which express only approximately 25% of wild type levels of TrkB. Tyrosine hydroxylase immunostaining revealed altered morphology of SN-DA neurons in trkBfbz/fbz when compared to wild type mice, in particular a significant enlargement of nuclear size. Cell counts revealed a pronounced loss of SN-DA neurons in these mice. Measurement of monoamine levels by high performance liquid chromatography (HPLC) showed that dopamine (DA) levels in the target field (striatum) were significantly elevated in trkBfbz/fbz compared to trkB+/fbz and wild type mice (P < 0.05), without altering DA turnover. Likewise, enzyme-linked immunosorbent assay (ELISA) for neurotrophic factors measurement showed that BDNF levels were increased in the striatum (P < 0.01) and frontal cortex (P < 0.005) of trkBfbz/fbz mice, but not in the SN when compared to trkB+/fbz and wild type mice. These data suggest that elevated neurotransmitter and neurotrophic factor levels might be a compensatory mechanism following dopaminergic cell loss in the SN. Thus, TrkB-activation seems essential for the maintenance of the nigrostriatal dopaminergic system.

3,4-Dihydroxyphenylacetic Acid↗

PubMed2004

Identification of RDH10, an All-trans Retinol Dehydrogenase, in Retinal Muller Cells.

PURPOSE: To investigate the expression of RDH10, an all-trans retinol dehydrogenase identified in the retinal pigment epithelium (RPE), in retinal Muller cells. METHODS: The RDH10 protein levels in mouse eyecups and bovine tissues were examined by Western blot analysis using a polyclonal antibody against RDH10. The cellular localization in the retina was determined by immunohistochemistry. Expression of RDH10 in rMC-1, a cell line derived from rat Muller cells, was determined by RT-PCR and Western blot analysis. All-trans retinol dehydrogenase activity assays were performed using lysates from rMC-1 cells. The generation of all-trans retinal from tritiated all-trans retinol was analyzed by HPLC. RESULTS: RDH10, retinal G protein-coupled receptor (RGR), and RPE65 all had higher expression levels in the eyecups of BALB/c than in C57Bl/6 mice. In addition to the RPE, RDH10 was also detected at lower levels in the retina and liver. Immunohistochemistry showed that RDH10 was localized in Muller cells in retinal sections. RDH10 was detected in rMC-1 cells, at both the RNA and protein levels. The rat RDH10 cDNA containing the full-length coding region was cloned from rMC-1 cells. The rat RDH10 cDNA encodes a protein of 341 amino acids and shares 99% sequence identity with human, bovine, and mouse RDH10 at the amino acid level. In rMC-1 cells, all-trans retinol dehydrogenase activity was detected in the microsomal fraction. NADP was shown to be the preferred cofactor, which is identical with the cofactor preference of the recombinant RDH10. CONCLUSIONS: RDH10 was expressed in retinal Muller cells, in addition to the RPE. RDH10 generates all-trans retinal, which is the substrate for the photoisomerase RGR in Muller cells.

Alcohol Oxidoreductases↗

PubMed2003

Isorhodopsin rather than rhodopsin mediates rod function in RPE65 knock-out mice.

The chromophore of visual pigments is 11-cis-retinal and, thus, in its absence, opsin is not photosensitive and no visual function exists. However, in the RPE65 knockout (Rpe65-/-) mouse, where synthesis of 11-cis-retinal does not occur, a minimal visual response from rod photoreceptors is obtained. We have examined if an alternative pathway exists for cis-retinoid generation in the absence of RPE65. Cyclic-light-reared, 2-month-old Rpe65-/- mice were placed in complete darkness. No exogenous retinoids were administered. After 4 weeks, enhanced a- and b-wave amplitudes were obtained, increasing >10-fold for the a-wave and >3-fold for the b-wave as compared with cyclic-light-reared Rpe65-/- mice. Visual-pigment levels increased to approximately 10 pmol per retina, compared with no measurable pigment for cyclic-light-reared Rpe65-/- mice. The lambdamax of the isolated pigment was 487 nm, characteristic for isorhodopsin. Retinoid extractions confirmed the presence of 9-cis-retinal and the absence of 11-cis-retinal. Once the Rpe65-/- mice were returned to cyclic light, within 48 h the electroretinogram function returned to levels found in Rpe65-/- mice maintained in cyclic light. This dark-mediated pathway is also operational in older animals, because 13-month-old Rpe65-/- mice kept in prolonged darkness (12 weeks) had increased isorhodopsin levels and electroretinogram a- and b-wave amplitudes. These studies demonstrate that a pathway exists in the eye for the generation of 9-cis-retinal that is independent of RPE65 and light.

Animals↗

PubMed2003

Retarded outer segment development in TrkB knockout mouse retina organ culture.

PURPOSE: To determine the effects of trkB deficiency in the mouse retina on photoreceptor development and retinal organization, in the absence of confounding systemic effects. METHODS: Newborn mice that carried two null trkB alleles (trkB-/-) and their wild type (WT) littermates were used for retinal organ cultures. On Day 21, rod development was assessed histologically in plastic sections (outer segment length) and retinal organization was analyzed using retinal cell-type specific antibodies. Anatomical data obtained from the organ cultures were compared to previously published histological results from in vivo data. RESULTS: (1) Rod outer segment length was significantly shorter in retinas from trkB-/- mice in the presence of normal numbers of rods. (2) No dopaminergic amacrine cells were observed in the knockout retina. (3) Unlike in the in vivo condition, recoverin-positive OFF-cone bipolar cells were present in trkB-/- retinas grown in culture. CONCLUSIONS: (1) These results demonstrate that rod outer segment development is compromised in the absence of trkB in the retina. (2) This study further supports our previous conclusion that the elimination of trkB expression alters rod development, because the presence of trkB receptors within the retina is essential for normal rod maturation and not because of confounding systemic effects. (3) More generally, this study stresses the importance of investigating complex phenotypes in gene knockout mice under conditions that isolate the organ under investigation from unrelated systemic variations.

Animals↗

PubMed2003

Does constitutive phosphorylation protect against photoreceptor degeneration in Rpe65-/- mice?

Despite the presence of this virgin opsin, Rpe65-/- rods are behaving like dark-adapted rods. These results argue that opsin which has not been exposed to 11-cis retinal and is constitutively phosphorylated, does not generate the activity generally associated with the bleached apoprotein. However, increased light-independent activation of transducin (due to bleached opsin) could be demonstrated after the addition of exogenous 11-cis retinal. We hypothesize that free opsin in the Rpe65-/- rods does not cause degeneration of rods by constitutive activation of the phototransduction cascade; but rather rods may die due to other causes such as the impairment of RPE function due to excess unprocessed retinyl-esters in the RPE.

Animals↗

PubMed2003

Correlation of regenerable opsin with rod ERG signal in Rpe65-/- mice during development and aging.

PURPOSE: RPE65 has been shown to be essential for the production of 11-cis retinal by the retinal pigment epithelium. Mutations in RPE65 are known to be associated with severe forms of early-onset retinal dystrophy. This project was designed to determine the amount of regenerable opsin in Rpe65-/- mice during development and aging, and to examine the function of this rhodopsin by electroretinography (ERG). METHODS: Young and aged Rpe65-/- and wild-type (WT) mice were dark adapted. Endogenous rhodopsin and regenerable opsin were measured using absorption-difference spectrophotometry. Photoreceptor function was assessed with scotopic single-flash ERGs and photoreceptors were counted in histologic sections. Opsin's primary structure was analyzed by mass-spectrometric mapping. RESULTS: Unlike WT mice, amounts of regenerable opsin in Rpe65-/- mice decreased significantly with age, which correlated with a decrease in the number of photoreceptors and a decline in ERG amplitudes. Opsin structure, however, did not change. No endogenous levels of rhodopsin were measurable in the Rpe65-/- mice (detection limit: 0.225 pmol). 11-cis Retinal injections resulted in the regeneration of similar amounts of rhodopsin and improved rod function in a comparable way, irrespective of age. CONCLUSIONS: In the aged Rpe65-/- mouse, opsin levels decrease because of the loss of photoreceptors. The remaining opsin is structurally intact, and the components of the phototransduction cascade and the retinal circuitry remain functional, despite the absence of normal photoreceptor activity.

Aging↗

PubMed2002

Synthesis, pharmacokinetics, efficacy, and rat retinal toxicity of a novel mitomycin C-triamcinolone acetonide conjugate.

A novel conjugate of mitomycin C (MMC) and triamcinolone acetonide (TA) was synthesized using glutaric acid as a linker molecule. To determine the rate of hydrolysis, the conjugate was dissolved in aqueous solution and the rate of appearance of free MMC and TA was determined by high-performance liquid chromatography analysis. Antiproliferative activity of the MMC-TA conjugate and parent compounds was assessed using an NIH 3T3 fibroblast cell line. Cell growth was quantified using the MTT assay. Kinetic analysis of the hydrolysis rate demonstrated that the conjugate had a half-life of 23.6 h in aqueous solutions. The antiproliferative activities of the MMC-TA conjugate and MMC were both concentration dependent, with similar IC(50) values of 2.4 and 1.7 microM, respectively. However, individual responses at concentrations above 3 microM showed that the conjugate was less active than MMC alone. TA alone showed only limited inhibition of cell growth. Studies evaluating intravitreal injection of the conjugate demonstrate that this agent produced no measurable toxicity. Our data provide evidence that the MMC-TA conjugate could be used as a slow-release drug delivery system. This could in turn be used to modulate a posttreatment wound healing process or to treat various proliferative diseases.

3T3 Cells↗

PubMed2002

Cloning and characterization of a novel all-trans retinol short-chain dehydrogenase/reductase from the RPE.

PURPOSE: In the photic visual cycle, retinal G protein-coupled receptor (RGR) isomerizes all-trans retinal to 11-cis retinal in the retinal pigment epithelium (RPE) after illumination. It is unclear, however, how all-trans retinal, the substrate for RGR, is generated in the RPE, because no all-trans retinol dehydrogenase (atRDH) has been identified in the RPE. This study was conducted to identify the atRDH that generates all-trans retinal in the RPE. METHODS: The full-length cDNA encoding a novel atRDH, RDH10, was cloned by PCR based on an expressed sequence tag (EST). Cellular localization was determined at the mRNA level by Northern blot analysis, RT-PCR, and in situ hybridization and at the protein level by immunohistochemistry with an antibody specific to RDH10. The activity was measured by an RDH activity assay with recombinant RDH10 expressed in COS cells. RESULTS: The full-length RDH10 was cloned from the human, cow, and mouse. These cDNAs encode a protein of 341 amino acids and have significant sequence homology with other short-chain dehydrogenases/reductases (SDRs). The human RDH10 shares 100% and 98.6% amino acid sequence identity with the bovine and mouse proteins, respectively, suggesting a highly conserved sequence during evolution. RDH10 is predominantly expressed in the microsomal fraction of the RPE. Human RDH10 expressed in COS cells oxidized all-trans retinol to all-trans retinal. RDH10 displayed substrate specificity for all-trans retinol and preferred nicotinamide adenine dinucleotide phosphate (NADP) as the cofactor. CONCLUSIONS: RDH10 is a novel retinol oxidase expressed in the RPE. This enzyme can generate all-trans retinal from all-trans retinol and may play an important role in the photic visual cycle.

Alcohol Oxidoreductases↗

PubMedDate not supplied

Structure-function analysis of rods and cones in juvenile, adult, and aged C57bl/6 and Balb/c mice.

To determine whether the photoreceptors change structurally and functionally during aging, and to analyze whether pigmentation in the retinal pigment epithelium might be a contributing factor. Young, adult, and aged C57BL/6 and Balb/c mice (1, 4, and 17 months of age) were housed under a 12-h light/12-h dark cycle, with an ambient light intensity at the eye level of the mice of 85 +/- 18 lux. Scotopic single-flash and photopic-flicker electroretinograms (ERGs) after complete dark adaptation were used to assess rod and cone function, respectively. Numbers of rod photoreceptors were counted in plastic sections, and rhodopsin levels were measured using absorption difference spectrophotometry. Numbers and types of cones were determined using lectin staining in retinal flatmounts and cone-specific antibodies in radial frozen sections. Young pigmented C57BL/6 and nonpigmented Balb/c mice had similar numbers of rods. In both mouse strains, there was an overall decline in rod photoreceptor number during aging, which was more pronounced in albino mice. Rod cell numbers correlated with a drop in the overall amount of rhodopsin and a reduction in the maximum a-wave of the rod ERG. The number of short-wavelength cones was unaffected by age and pigmentation, whereas an age-related decline was observed in mid-wavelength (MWL) cones in albino, but not in pigmented mice. In contrast, MWL cone function was reduced during aging in both strains. Flicker-fusion frequency was determined to be approximately 10 Hz lower in albino animals, which is due to prolonged b-waves in these ERGs. Age-related changes were found in both photoreceptor systems, rods and cones, and in both pigmented and nonpigmented mice. However, rod photoreceptors appear to be more susceptible to both aging and the lack of pigmentation, when compared to cones. These results may help as we begin to understand certain age-related retinal diseases.

Aging↗

PubMedDate not supplied

Functionally intact glutamate-mediated signaling in bipolar cells of the TRKB knockout mouse retina.

In the juvenile trkB knockout (trkB-/-) mouse, retina synaptic communication from rods to bipolar cells is severely compromised as evidenced by a complete absence of electroretinogram (ERG) b-wave, even though the inner retina appears anatomically normal (Rohrer et al., 1999). Since it is well known that the b-wave reflects light-dependent synaptic activation of ON bipolar cells via their metabotropic glutamate receptor, mGluR6, we sought to analyze the anatomical and functional integrity of the glutamatergic synapses at these and other bipolar cells in the trkB(-/-) mouse. Although rod bipolar cells from wild-type juvenile mice were determined to be immunopositive for trkB, postsynaptic metabotropic and ionotropic glutamate receptor-mediated pathways in ON and OFF bipolar cells were found to be functionally intact, based on patch electrode recordings, using brief applications ("puffs") of glutamate or its analog, 2-amino-4-phosphonobutyric acid (APB), a selective agonist for mGluR6 receptors. Ionotropic glutamate receptor function was assayed in OFF-cone bipolar and horizontal cells by applying exogenous glutamatergic agonists in the presence of the channel-permeant guanidinium analogue, 1-amino-4-guanidobutane (AGB). Electron-microscopic analysis revealed that the ribbon synapses between rods and postsynaptic rod bipolar and horizontal cells were formed at the appropriate age and appear to be structurally intact, and immunohistochemical analysis did not detect profound defects in the expression of excitatory amino acid transporters involved in glutamate clearance from the synaptic cleft. These data indicate that there does not appear to be evidence for postsynaptic deficits in glutamatergic signaling in the ON and OFF bipolar cells of mice lacking trkB.

Agmatine↗

PubMedDate not supplied

Long-term ERG analysis in the partially light-damaged mouse retina reveals regressive and compensatory changes.

Most of the blinding retinopathies are due to progressive photoreceptor degeneration. Treatment paradigms that are currently being investigated include strategies to either halt or slow down photoreceptor cell loss, or to replace useful vision with retinal prosthesis. However, more information is required on the pathophysiological changes of the diseased retina, in particular the inner retina, that occur as a consequence of photoreceptor cell loss. Here we wished to use light damage as a stoppable insult to determine the structural and functional consequences on inner and outer retina, with the overall goal of determining whether survival of a functional inner retina is possible even if the outer retina is damaged. Mice were exposed to a 20-day light-damage period. Electroretinograms (ERG) and morphology were used to assess subsequent recovery. Outer retina was monitored analyzing a-waves, which represent photoreceptor cell responses, and histology. Integrity of the inner retina was monitored, analyzing b-waves and oscillatory potentials (OP1-OP4) and immunohistochemical markers for known proteins of the inner retina. All six ERG components were significantly suppressed with respect to amplitudes and kinetics, but stabilized in a wave-dependent manner within 40-70 days after the end of light exposure. As expected, damage of the outer retina was permanent. However, function of the inner retina was found to recover significantly. While b-wave amplitudes remained suppressed to 60% of their baseline values, OP amplitudes recovered completely, and implicit times of all components of the inner retina (b-wave and OP1-OP4) recovered to a level close to baseline values. Histological analyses confirmed the lack of permanent damage to the inner retina. In summary, these data suggests that the inner retina has the potential for significant recovery as well as plasticity if treatment is available to stop the deterioration of the outer retina.

Animals↗

PubMedDate not supplied

9-cis Retinal increased in retina of RPE65 knockout mice with decrease in coat pigmentation.

The protein RPE65 is essential for the generation of the native chromophore, 11-cis retinal, of visual pigments. However, the Rpe65 knockout (Rpe65-/-) mouse shows a minimal visual response due to the presence of a pigment, isorhodopsin, formed with 9-cis retinal. Isorhodopsin accumulates linearly with prolonged dark-rearing of the animals. The majority of Rpe65-/- mice have an agouti coat color. A tan coat color subset of Rpe65-/- mice was found to have an enhanced visual response as measured by electroretinograms. The enhanced response was found to be due to increased levels of 9-cis retinal and isorhodopsin pigment levels. Animals of both coat colors reared in cyclic light have minimal levels of regenerated pigment and show photoreceptor degeneration. On dark-rearing, pigment accumulates and photoreceptor degeneration is decreased. In the tan Rpe65-/- mice, the level of photoreceptor degeneration is less than in the agouti animals, which have an increased pigment and decreased free opsin level. Therefore, photoreceptor damage correlates with the amount of the apoprotein present, supporting findings that the activity from unregenerated opsin can lead to photoreceptor degeneration.

Animals↗