Evaluation of a behavioral method for objective vision testing and identification of achromatopsia in dogs

Garcia, Monique M.; Ying, Gui Shuang; Cocores, Christina A.; Tanaka, Jacqueline C.; Komàromy, András M.

doi:10.2460/ajvr.71.1.97

Cited by 31 publications

(30 citation statements)

References 21 publications

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“…Substituting the hB3 for the cB3 is reasonable since an appropriate expression vector containing the cB3 was not available. Further, the hB3 gene was used successfully for retinal gene augmentation therapy to restore cone function in dogs with CNGB3 -achromatopsia confirming proper functioning of cA3+ hB3 channels [41]–[43]. Macroscopic currents were recorded from inside-out patches in the range of 200–800 pA with exposure to bath solutions containing cGMP or cAMP.…”

Section: Resultsmentioning

confidence: 96%

A Cyclic Nucleotide-Gated Channel Mutation Associated with Canine Daylight Blindness Provides Insight into a Role for the S2 Segment Tri-Asp motif in Channel Biogenesis

et al. 2014

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Cone cyclic nucleotide-gated channels are tetramers formed by CNGA3 and CNGB3 subunits; CNGA3 subunits function as homotetrameric channels but CNGB3 exhibits channel function only when co-expressed with CNGA3. An aspartatic acid (Asp) to asparagine (Asn) missense mutation at position 262 in the canine CNGB3 (D262N) subunit results in loss of cone function (daylight blindness), suggesting an important role for this aspartic acid residue in channel biogenesis and/or function. Asp 262 is located in a conserved region of the second transmembrane segment containing three Asp residues designated the Tri-Asp motif. This motif is conserved in all CNG channels. Here we examine mutations in canine CNGA3 homomeric channels using a combination of experimental and computational approaches. Mutations of these conserved Asp residues result in the absence of nucleotide-activated currents in heterologous expression. A fluorescent tag on CNGA3 shows mislocalization of mutant channels. Co-expressing CNGB3 Tri-Asp mutants with wild type CNGA3 results in some functional channels, however, their electrophysiological characterization matches the properties of homomeric CNGA3 channels. This failure to record heteromeric currents suggests that Asp/Asn mutations affect heteromeric subunit assembly. A homology model of S1–S6 of the CNGA3 channel was generated and relaxed in a membrane using molecular dynamics simulations. The model predicts that the Tri-Asp motif is involved in non-specific salt bridge pairings with positive residues of S3/S4. We propose that the D262N mutation in dogs with CNGB3-day blindness results in the loss of these inter-helical interactions altering the electrostatic equilibrium within in the S1–S4 bundle. Because residues analogous to Tri-Asp in the voltage-gated Shaker potassium channel family were implicated in monomer folding, we hypothesize that destabilizing these electrostatic interactions impairs the monomer folding state in D262N mutant CNG channels during biogenesis.

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Section: Resultsmentioning

confidence: 96%

A Cyclic Nucleotide-Gated Channel Mutation Associated with Canine Daylight Blindness Provides Insight into a Role for the S2 Segment Tri-Asp motif in Channel Biogenesis

et al. 2014

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“…(37, 40, 59, 60) These methods have been invaluable to demonstrate both the early visual impairment,(40, 59) and subsequent vision restoration following corrective gene therapy in several canine models of inherited degeneration. (34, 36, 37, 61) However, they lack precision as they test global visual function that do not evaluate visual acuity, nor test specific retinal regions for functional defects.…”

Section: Discussionmentioning

confidence: 99%

“…(40) The 3.6 meter-long obstacle course included 5 panels that could be moved either to the left or to the right side. The panel positions were changed between runs to prevent the dogs from memorizing the position of the obstacle panels.…”

Section: Methodsmentioning

confidence: 99%

“…Instead, transit time results for each of the RHO T4R/T4R dogs were presented with descriptive statistics (Mean ± SD), and compared to the range of normal transit time values of WT dogs. In addition, based on prior experience with this same obstacle course to test dogs affected with either cone or rod visual impairment,(37, 40) we considered a transit time of ≤ 10 seconds to be normal.…”

Section: Methodsmentioning

confidence: 99%

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Assessment of visual function and retinal structure following acute light exposure in the light sensitive T4R rhodopsin mutant dog

Iwabe

Ying

Aguirre

et al. 2016

Experimental Eye Research

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The effect of acute exposure to various intensities of white light on visual behavior and retinal structure was evaluated in the T4R RHO dog, a naturally-occurring model of autosomal dominant retinitis pigmentosa due to a mutation in the Rhodopsin gene. A total of 14 dogs (ages: 4–5.5 months) were used in this study: 3 homozygous mutant RHOT4R/T4R, 8 heterozygous mutant RHOT4R/+, and 3 normal wild-type (WT) dogs. Following overnight dark adaptation, the left eyes were acutely exposed to bright white light with a monocular Ganzfeld dome, while the contralateral right eye was shielded. Each of the 3 homozygous (RHOT4R/T4R) mutant dogs had a single unilateral light exposure (LE) to a different (low, moderate, and high) dose of white light (corneal irradiance/illuminance: 0.1 mW/cm2, 170 lux; 0.5 mW/cm2, 820 lux; or 1 mW/cm2, 1590 lux) for 1min. All 8 heterozygous (RHOT4R/+) mutant dogs were exposed once to the same moderate dose of light. The 3 WT dogs had their left eyes exposed 1, 2, or 3 times to the same highest dose of light. Visual function prior to LE and at 2 weeks and 33 weeks after exposure was objectively assessed in the RHOT4R/T4R and WT dogs by using an obstacle-avoidance course. Transit time through the obstacle course was measured under different scotopic to photopic ambient illuminations. Morphological retinal changes were evaluated by non-invasive in vivo cSLO/sdOCT imaging and histology before and at several time-points (2–36 weeks) after light exposure. The analysis of the transit time through the obstacle course showed that no differences were observed in any of mutant or WT dogs at 2 weeks and 33 weeks post LE. The RHOT4R/T4R retina exposed to the lowest dose of white light showed no obvious changes in ONL thickness at 2 weeks, but mild decrease was noted 36 weeks after LE. The RHOT4R/T4R retina that received a moderate dose (showed an obvious decrease in ONL thickness along the superior and temporal meridians at 2 weeks post LE with more severe damage at 36 weeks post LE in all four meridians. The RHOT4R/T4R retina exposed to the high dose showed at 2 weeks after LE extensive ONL damage in all four meridians. This light intensity did not cause any retinal damage in WT dogs even after repeated (up to 3) LE. Analysis of ONL thickness in heterozygous mutant dogs exposed to the moderate dose of light confirmed the increased sensitivity to light damage of the superior/tapetal retina, and the occurrence of an ongoing cell death process several weeks after the acute LE. In conclusion, a short single exposure to a dose of white light that is not retinotoxic in WT dogs causes in the T4R RHO retina an acute loss of ONL in the central to mid peripheral region that keeps progressing over the course of several weeks. However, this severe retinal damage does not affect visual behavior presumably because of islands of surviving photoreceptors found in the area centralis including the newly discovered canine fovea-like area, and the lack of damage to peripheral photoreceptors.

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“…In colony dogs, the visual performance under different light conditions was evaluated by use of an obstacle-avoidance test as previously described [45]. For the privately owned MAS behavioral vision testing was performed by observing the dog maneuver around objects and its ability to find toys under different light conditions.…”

Section: Methodsmentioning

confidence: 99%

Genomic deletion of CNGB3 is identical by descent in multiple canine breeds and causes achromatopsia

et al. 2013

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BackgroundAchromatopsia is an autosomal recessive disease characterized by the loss of cone photoreceptor function that results in day-blindness, total colorblindness, and decreased central visual acuity. The most common causes for the disease are mutations in the CNGB3 gene, coding for the beta subunit of the cyclic nucleotide-gated channels in cones. CNGB3-achromatopsia, or cone degeneration (cd), is also known to occur in two canine breeds, the Alaskan malamute (AM) and the German shorthaired pointer.ResultsHere we report an in-depth characterization of the achromatopsia phenotype in a new canine breed, the miniature Australian shepherd (MAS). Genotyping revealed that the dog was homozygous for a complete genomic deletion of the CNGB3 gene, as has been previously observed in the AM. Identical breakpoints on chromosome 29 were identified in both the affected AM and MAS with a resulting deletion of 404,820 bp. Pooled DNA samples of unrelated purebred Australian shepherd, MAS, Siberian husky, Samoyed and Alaskan sled dogs were screened for the presence of the affected allele; one Siberian husky and three Alaskan sled dogs were identified as carriers. The affected chromosomes from the AM, MAS, and Siberian husky were genotyped for 147 SNPs in a 3.93 Mb interval within the cd locus. An identical shared affected haplotype, 0.5 Mb long, was observed in all three breeds and defined the minimal linkage disequilibrium (LD) across breeds. This supports the idea that the mutated allele was identical by descent (IBD).ConclusionWe report the occurrence of CNGB3-achromatopsia in a new canine breed, the MAS. The CNGB3-deletion allele previously described in the AM was also observed in a homozygous state in the affected MAS, as well as in a heterozygous carrier state in a Siberian husky and Alaskan sled dogs. All affected alleles were shown to be IBD, strongly suggesting an affected founder effect. Since the MAS is not known to be genetically related to the AM, other breeds may potentially carry the same cd-allele and be affected by achromatopsia.

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Evaluation of a behavioral method for objective vision testing and identification of achromatopsia in dogs

Cited by 31 publications

References 21 publications

A Cyclic Nucleotide-Gated Channel Mutation Associated with Canine Daylight Blindness Provides Insight into a Role for the S2 Segment Tri-Asp motif in Channel Biogenesis

A Cyclic Nucleotide-Gated Channel Mutation Associated with Canine Daylight Blindness Provides Insight into a Role for the S2 Segment Tri-Asp motif in Channel Biogenesis

Assessment of visual function and retinal structure following acute light exposure in the light sensitive T4R rhodopsin mutant dog

Genomic deletion of CNGB3 is identical by descent in multiple canine breeds and causes achromatopsia

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