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Maggie Yoder, MichaelAnne Gratton, Muna I Naash; A knockin mouse model for Usher Syndrome Type IIA mutation in usherin gene leads to an early-onset hearing and a late-onset retinitis pigmentosa. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4641.
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© ARVO (1962-2015); The Authors (2016-present)
Usher syndrome (USH) is the leading cause of combined deafness and blindness; but the mechanisms of sensory loss are unknown. The c.2299delG mutation in usherin is the most common cause for USH type 2A in patients. To study the role of usherin in audiovisual impairment we have generated and characterized a knockin (KI) mouse model expressing the human c.2299delG mutation.
The c.2299delG mutation causes a frame shift and premature stop codon. In addition to introducing the c.2299delG mutation, the KI construct contains an internal ribosomal entry site followed by GFP (to assess promoter activity). RT-PCR and immunoblotting were used to assess message and protein levels. Scanning electron microscopy (SEM) and immunohistochemistry (IHC) were used to evaluate retinal and cochlear structure. Electroretinography (ERG) was used to assess retinal function.
The KI mutation is present in the endogenous locus, truncated message is stable, and the mutant protein is expressed in photoreceptors and hair cells. GFP expression identified new tissues expressing usherin that have not been previously reported and will be explored further for structural and functional abnormalities. SEM evaluation of the cochlea showed outer hair cell abnormalities consistent with hearing loss at postnatal day 180 (P180). Retinal evaluations via IHC and ERG up to P180 appear normal; however there is a delay in transducin and arrestin translocation upon light exposure as early as P30. Furthermore, KI mice at P360 have a significant decline in scotopic and photopic amplitudes.
This mouse is the first USH2A model with a human mutation; it is also the first USH model to show retinal dysfunction without rearing in higher cyclic light. GFP expression evaluations allow for further study of possible systemic effects usherin may have in conjunction with deafness/blindness. Data are consistent with USH patients having a later onset visual impairment compared to hearing loss. Full characterization of this model will lead to a better understanding of the human disease and will be a valuable resource to develop targeted therapies for treatment.
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