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S.F. Geller, J.G. Flannery; Ush3A mRNA is Expressed at Wild–Type Levels in Degenerating Rat Retina . Invest. Ophthalmol. Vis. Sci. 2005;46(13):545.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To examine Ush3A mRNA expression levels in wild–type and degenerating rat retina. Methods: Rats (Sprague–Dawley (SD), P23H and S334ter transgenic rhodopsin mutants) were sacrificed at time points where their photoreceptor numbers were greatly reduced. Eyes were removed and fixed for histology or dissected for retinal RNA extraction. Electroretinograms (ERG) were performed on animals prior to sacrifice. Reverse transcriptase–polymerase chain reaction (RT–PCR) was used to qualitatively and quantitatively assess Ush3A expression. Several eyes from each strain were collected for histological analysis. Results: Using RT–PCR, we found little or no change in Ush3A expression in degenerating P23H or S334ter transgenic rat retinas. Histological analyses show a variable but significant loss of photoreceptors in each degenerating strain, and ERGs demonstrate severely attenuated retinal responses. These data indicate that retinas undergoing photoreceptor–initiated degeneration express wild–type levels of Ush3A mRNA. Discussion: In humans, mutations (truncations and point mutations) in USH3 leads to a retinitis pigmentosa (RP)–like disease, most commonly diagnosed in the second decade of life. Normal levels of Ush3A are present in retinas that have lost a majority of their photoreceptors, indicating that Ush3A expression is restricted to the inner retina. This agrees well with previous experimental findings in the mouse. Together, these data suggest that loss of photoreceptors in Usher syndrome type III is likely due to mutant Ush3A expression in second order neurons; which in turn leads to a gradual loss of photoreceptors and an RP–like disease phenotype.
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