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J. J. Lentz, W. C. Gordon, H. Farris, S. Sampath, P. D. Deininger, N. G. Bazan, B. J. Keats; A Knock-In Mouse Model of Usher Type IC. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1341.
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Usher syndrome is the leading cause of combined deaf-blindness. All Usher patients suffer progressive retinitis pigmentosa, with the degree of hearing impairment and the presence or absence of vestibular function differing among subtypes. A cryptic splice site mutation (216G→A) in exon 3 of the USH1C gene, encoding the protein harmonin, was found in Acadian Usher type IC families in south Louisiana. In vitro analysis with mutant 216A constructs and subsequent analysis of patient cell lines revealed a 35 base deletion. Mouse models exist for seven of the known Usher-related genes; however they all lack retinitis pigmentosa. The purpose of this study is to characterize hearing and vision in a knock-in mouse model containing the human 216G→A mutation cloned from an Acadian patient.
Auditory brain stem response (ABR) was used to determine hearing thresholds of 30 day old mutant mice compared with their wild type and heterozygous litter mates. Scotopic electroretinograms (ERG) were performed on six month old mutant, heterozygous and wildtype mice. To confirm the 35 base pair deletion, total RNA was isolated from the retina and cochlea followed by RT-PCR using Ush1c specific primers.
All homozygous Ush1c216A (216AA) mice are hyperactive, display circling and head tossing behavior, and do not exhibit an acoustic startle (Preyer reflex) response at 21-25 days old. The behavior of heterozygous and wildtype mice are identical, showing no mutant behavior. RT-PCR analyses of the retina and cochlea from 216AA mice show the same 35 base deletion characteristic of Usher IC patients. No ABR was evoked from mutant mice at 30 days. Compared with wild type and heterozygous litter mates, 216AA mutant mice show reduced electroretinogram (ERG) amplitudes by six months of age.
We have successfully designed and created a mouse model of Acadian Usher syndrome type IC. These mice are deaf and have the same 35 bp deletion that is found in patients. The reduced ERG amplitudes in our Ush1c 216AA mice at six months of age provide evidence that this mouse has progressive retinal degeneration and is a precise model for Usher syndrome type IC.
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