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M. Glosmann, P. Arbogast, L. Peichl; Patterns of Cone Opsin Expression Are Different in Wildtype and Albino Retinas. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2726.
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To establish whether albinism affects the number and the mosaic distribution of spectral cone photoreceptors.
Wildtype (c+/c+) and albino (c/c) deer mice (Peromyscus maniculatus) and Brown Norway and Wistar rats (Rattus norvegicus) were used as models for different ocular pigmentation. Retinas were dissected and prepared as flatmounts. Cone photoreceptors were identified by opsin immunostaining and their numbers, spectral types, and distribution across the retina determined using epifluorescence microscopy.
In wildtype P. maniculatus and Brown Norway rats, two cone opsins, shortwave sensitive (S) and middlewave sensitive (M), were present and expressed in distinct cone types (S cones: 5-15%, M cones: 85-95% of the cones). In pigmented P. maniculatus, different from house mouse, S and M cone patterns did not form dorsoventral gradients and coexpression of cone opsins in single cones was exceptional (0-2% of the cones). In albino P. maniculatus, total cone numbers, the mosaic distribution of generic cones, and the numbers of cones exclusively expressing S opsin were not significantly different from pigmented P. maniculatus. However, in contrast to pigmented P. maniculatus, in albino animals S opsin was coexpressed with M opsin in 60-90% of the cones and therefore the population of cones expressing only M opsin was significantly reduced (5-25%). Both rat strains showed a mouse-like dorsoventral gradient in the number of S cones. In Wistar rats, S cone densities at any retinal position were 3-4 times higher than in Brown Norway rats and a significant proportion of cones coexpressed both opsins.
Albinism in P. maniculatus and Wistar rats appears not to affect cones in their number or general distribution. The pattern of S cone opsin expression, however, differs between albino and pigmented strains of P. maniculatus and rats. Because in both species mutations at the albino locus result in deficits in tyrosinase function, we hypothesize that tyrosinase activity directly or indirectly affects the regulation of S opsin expression.
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