Abstract
A quantitative analysis of photoreceptor properties was performed in the retina of the nocturnal deer mouse, Peromyscus maniculatus, using pigmented (wildtype) and albino animals. The aim was to establish whether the deer mouse is a more suitable model species than the house mouse for photoreceptor studies, and whether oculocutaneous albinism affects its photoreceptor properties. In retinal flatmounts, cone photoreceptors were identified by opsin immunostaining, and their numbers, spectral types, and distributions across the retina were determined. Rod photoreceptors were counted using differential interference contrast microscopy. Pigmented P. maniculatus have a rod-dominated retina with rod densities of about 450.000/mm2 and cone densities of 3000 - 6500/mm2. Two cone opsins, shortwave sensitive (S) and middle-to-longwave sensitive (M), are present and expressed in distinct cone types. Partial sequencing of the S opsin gene strongly supports UV sensitivity of the S cone visual pigment. The S cones constitute a 5-15% minority of the cones. Different from house mouse, S and M cone distributions do not have dorsoventral gradients, and coexpression of both opsins in single cones is exceptional (<2% of the cones). In albino P. maniculatus, rod densities are reduced by approximately 40% (270.000/mm2). Overall, cone density and the density of cones exclusively expressing S opsin are not significantly different from pigmented P. maniculatus. However, in albino retinas S opsin is coexpressed with M opsin in 60-90% of the cones and therefore the population of cones expressing only M opsin is significantly reduced to 5-25%. In conclusion, deer mouse cone properties largely conform to the general mammalian pattern, hence the deer mouse may be better suited than the house mouse for the study of certain basic cone properties, including the effects of albinism on cone opsin expression.
Highlights
The New World deer mice (Genus Permomyscus with more than 50 species) belong to the rodent family Cricetidae, subfamily Neotominae
Given the low cone densities of P. maniculatus, the above values can be taken as the rod density range
Our quantitative photoreceptor analysis shows that the nocturnal deer mouse Peromyscus maniculatus has a roddominated retina with a low but consistent population of cones
Summary
The New World deer mice (Genus Permomyscus with more than 50 species) belong to the rodent family Cricetidae, subfamily Neotominae. Peromyscus maniculatus is the most common deer mouse species in the continental United States and has ecological relevance. Since 1916, P. maniculatus has been used as a laboratory rodent, in toxicological and epidemiological research, as well as in ecological, behavioral, and genetic studies [1]. Peromyscus maniculatus may be a useful additional model to the house mouse Mus musculus for retinal and for photoreceptor studies [2]. The house mouse with its plethora of genetically modified lines has gained unsurpassed importance for research, but with respect to retinal research it has a drawback. We have analyzed the cone properties in the deer mouse retina to see whether they are closer to what is considered the basic mammalian blueprint
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