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Elaine Tan, Quan Wang, Alexander B. Quiambao, Xiaoping Xu, Nasser M. Qtaishat, Neal S. Peachey, Janis Lem, Steven J. Fliesler, David R. Pepperberg, Muna I. Naash, Muayyad R. Al-Ubaidi; The Relationship between Opsin Overexpression and Photoreceptor Degeneration. Invest. Ophthalmol. Vis. Sci. 2001;42(3):589-600.
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purpose. To characterize the process by which overexpression of normal opsin leads
to photoreceptor degeneration.
methods. Three transgenic mouse lines were generated that express different
levels of an opsin with three amino acid modifications at the C
terminus. These modifications created an epitopic site that can be
readily distinguished from the endogenous protein using a bovine
opsin-specific antibody. Evidence of degeneration associated with opsin
overexpression was provided by anatomic studies and electroretinogram
(ERG) recordings. Western blot analysis was used to confirm the
production of the transgenic opsin, and an enzyme-linked immunosorbent
assay (ELISA) was used to determine the amounts of opsin overexpressed
in each line. Immunocytochemistry was used to determine the cellular
localization of transgenic opsin. Amounts of 11-cis retinal
were determined by extraction and high-performance liquid
results. Opsin expression levels in the three lines were found to be 123%,
169%, and 222% of the level measured in nontransgenic
animals, providing direct correlation between the level of transgene
expression and the severity of the degenerative phenotype. In the lower
expressing lines, ERG a-wave amplitudes were reduced to less than
approximately 30% and 15% of normal values, whereas responses of the
highest expressing line were indistinguishable from noise. In the
lowest expressor, a 26% elevation in 11-cis retinal was
observed, whereas in the medium and the high expressors,
11-cis retinal levels were increased by only 30% to 33%,
well below the 69% and 122% increases in opsin levels.
conclusions. The overexpression of normal opsin induces photoreceptor degeneration
that is similar to that seen in many mouse models of retinitis
pigmentosa. This degeneration can be induced by opsin levels that
exceed by only approximately 23% that of the normal mouse retina.
Opsin overexpression has potential implications in retinitis
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