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P. K. Buch, P. Cottrill, S. E. Wilkie, R. A. Pearson, Y. Duran, E. L. West, S. S. Bhattacharya, A. M. Dizhoor, R. R. Ali, D. M. Hunt; A Novel ‘Knock-In’ Mouse Model for Cone Dystrophy: A Point Mutation in Guca1a Causes a Loss of Cone-Mediated Retinal Function and Photoreceptor Degeneration. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4036.
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In order to accurately model cone dystrophy 3 (COD3), caused by an E155G substitution in the guanylate cyclase activating protein 1 (GCAP1), we created knock-in mice that have the same amino acid substitution. Here we present extensive, long-term characterization of the retinal phenotype.
Mutant mice, generated using gene targeting, were genotyped using PCR and sequencing. Visual function was assessed using Ganzfeld electroretinography (ERG), and ocular morphology assessed using paraffin and resin-embedded sections. Immunohistochemistry was carried out on cryosections and retinal flatmounts.
We saw a progressive loss of cone-mediated ERG in heterozygous and homozygous mutant mice; b-wave amplitudes from 12 month-old mice were down to 17 % of wild-type. Mutant mice also lacked a flicker response to 10- and 15-Hz light stimuli, whereas wild-type litter-mates had a normal flicker. Rod-mediated b-wave amplitudes were also reduced in mutant mice, although in 12 month-old homozygous mice the rod dominated ERG was still 44 % of wild-type suggesting the mutation primarily affects cone function. Histological analysis showed significant loss of photoreceptor cells at five months of age, up to 47 % loss in homozygotes. We have also studied the effects of the mutation on rod recovery kinetics, photopigment expression, and retinal morphology.
The analysis performed to date indicates that mice harbouring an E155G mutation in GCAP1 have a phenotype that is consistent with altered cone cell function. Further evaluation of this model using single-cell suction electrode recording, calcium imaging and biochemical analyses is now in progress.
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