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P. K. Buch, P. Cottrill, S. E. Wilkie, R. A. Pearson, S. S. Bhattacharya, D. J. Wells, D. M. Hunt; Mice Heterozygous for a Glu155Gly Gene Targeted Mutation in GCAP1 Lack Flicker Response and Show Severely Reduced Photopic ERG Amplitudes. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4666.
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Mutations in the gene encoding guanylate cyclase activating protein (GCAP1), also known as GUCA1A, cause the autosomal dominant cone dystrophy COD3. The Tyr99Cys and Glu155Gly mutations result in a GCAP1 protein that shows reduced Ca2+-dependent inactivation of retinal guanylate cyclase activity. Mice expressing a mutant Tyr99Cys Gcap1 transgene expressed only in rod photoreceptors have been shown to suffer photoreceptor degeneration in vivo. The studies presented here have been undertaken with mice harbouring a Glu155Gly knock-in mutation in Gcap1 and therefore represent a more accurate model of the human cone dystrophy.
Mutant mice were generated using gene targeting, and were genotyped using PCR and sequencing. Retinal function was assayed using Ganzfeld ERGs.
The presence of an A→G substitution at position 19 of exon 6 in the Gcap1 gene, resulting in a Glu155→Gly amino acid change, was confirmed using PCR and direct sequencing. Electroretinography performed on mice heterozygous for this mutation showed that photopic b-wave amplitudes are significantly reduced (102.9 µV ± 26.1 µV) when compared to wild-type litter-mates (194.8 µV ± 34.1 µV) at six months of age (p < 0.001); mice harbouring the mutation also lack a flicker response to 10- and 15-Hz flash stimulus, whereas wild-type litter-mates have normal flicker responses. Scotopic b-wave amplitudes at this time point appear normal in knock-in mice.
The analysis performed to date indicates that mice harbouring a Glu155Gly mutation in Gcap1 have a phenotype that is consistent with altered cone cell function. This will be further explored using a range of techniques including histology, single-cell suction electrode recording, and calcium imaging, so as to fully describe the cellular and physiological pathology of this human disease mutation.
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