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Jian-hua Xu, Lynsie Morris, Steven J. Fliesler, David M. Sherry, Xi-Qin Ding; Progression of Cone Photoreceptor Dysfunction and Degeneration in CNGB3-Deficient Mice. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1838.
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© ARVO (1962-2015); The Authors (2016-present)
The cone cyclic nucleotide-gated (CNG) channel is essential for central and color vision and for visual acuity. Mutations in CNG subunits CNGA3 and CNGB3 are associated with achromatopsia and cone dystrophies, with mutations in CNGB3 alone accounting for >50% of achromatopsia patients. Previously we showed that CNGB3-/- mice exhibit impaired cone function and cone degeneration, similar to human patients carrying CNGB3 mutations. Here, we studied the progression of cone dysfunction and degeneration in CNGB3-/- mice.
CNGB3-/- and wildtype (WT) mice were generated and their retinas evaluated at different ages by electroretinography (ERG), light and electron microscopy, lectin cytochemistry and immunohistochemistry, and Western blot analysis, as previously described (Ding et al., Hum. Mol. Genet., 18:4770, 2009).
Light-adapted (cone) ERG response amplitudes in CNGB3-/- mice were only ~50% of WT levels by postnatal day 15. By 1 postnatal month, cone ERG responses were only ~30% of WT levels; further loss to ~20% of WT levels was observed by 12 months of age. Dark-adapted (rod) ERG responses in CNGB3-/- and age-matched WT mice were comparable. Cone cell densities in CNGB3-/- mice were ~80% of WT levels at 1 mo, and slowly declined thereafter, with only ~50% of cones remaining at 12 mo. Expression levels of M-opsin, cone transducin α-subunit, and cone arrestin in CNGB3-/- mice were reduced by ~50-60% by 1 mo, compared to age-matched WT levels, and declined to ~35-45% of WT levels by 9 mo. Mislocalization of cone opsin to the outer nuclear and outer plexiform layers also was detected in CNGB3-/- retinas; however, cone and rod synaptic marker expression and synaptic terminal ultrastructure appeared normal.
The retinal phenotype in CNGB3-/- mice involves early-onset, slowly progressing defects in cone structure and function and cell death. Normal cone synaptic terminal structure suggests that cone functional deficits in this model result from disrupted phototransduction and cone cell death, rather than from cone synaptic defects.
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