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C. S. Harry, X.-Q. Ding; Impaired Cone Function and Cone Degeneration in Mice Lacking the Cyclic Nucleotide-Gated Channel Subunit CNGB3. Invest. Ophthalmol. Vis. Sci. 2009;50(13):492.
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Central and color vision are attributed to the activation of cyclic nucleotide-gated (CNG) channels in cone photoreceptors. Cone CNG channel is composed of two structurally related subunit types, CNGA3 and CNGB3. Mutations in genes encoding these subunits are linked to achromatopsia and progressive cone dystrophy in humans. Indeed mutations in CNGB3 account for 50% of all known cases of achromatopsia. This study investigates the retinal phenotype of CNGB3-deficient (CNGB3-/-) mice.
The heterozygous CNGB3+/- mouse line was obtained from Deltagen Inc. Cross-mating and genotyping were performed to obtain homozygous mice. Photopic and scotopic electroretinalgrams (ERGs) were recorded to assess retinal function. Histology images were analyzed to evaluate retinal morphology. Immunofluorescence labeling was conducted on retinal sections with anti-CNGB3, anti-CNGA3 and anti-S-opsin antibodies and viewed using confocal microscopy. Cone density was evaluated by counting cones labeled with S-opsin. Quantitative (q) RT-PCR was performed to analyze mRNA levels of CNGA3 and phosphodiesterase (PDE) 6C.
Lack of CNGB3 in the retinas of CNGB3-/- mice was verified by immunolabeling and qRT-PCR. The ERG recordings showed a near 80% reduction of cone function in CNGB3-/- mice at postnatal days 30 and 60, compared to age-matched CNGB3+/+ and CNGB3+/- mice. Rod function was unchanged in CNGB3-/- mice. Histology images showed an uneven development of the outer nuclei layer surface in CNGB3-/- mice. CNGA3 immunostaining was dramatically decreased in CNGB3-/- mice. Unexpectedly, this correlated with a significant decrease of CNGA3 mRNA although PDE6C mRNA levels were unchanged. S-opsin immunostaining was also dramatically decreased consistent with a 60% decrease in S-cone density.
Deletion of CNGB3 leads to the impairment of cone function and cone degeneration, demonstrating the essential role of this channel protein in cone function and survival. The down-regulation of CNGA3 mRNA and protein in cones lacking CNGB3 may contribute to the pathogenic mechanism by which CNGB3 mutations lead to human cone diseases.
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