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J. S. Rowlan, A. E. Cooper, G. M. Acland, G. D. Aguirre, A. M. Komaromy; Distribution of Cone Subclasses and Photoreceptor Specific Gene Expression in the Normal and Achromatopsia-Affected Canine Retina. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4473.
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© ARVO (1962-2015); The Authors (2016-present)
To map the distribution of long/medium- (L/M) and short- (S) wavelength-absorbing cones, and to determine regional variations of photoreceptor-specific gene expression levels in retinas of normal and achromatopsia-affected dogs.
Retinas were obtained from 3 normal and 3 achromatopsia-affected, adult dogs. 4-mm diameter retinal patches were collected from precisely defined locations in each quadrant. For mapping of cone subclasses, the retinal patches were flat-mounted and labeled with S-opsin, L/M-opsin or hCAR antibodies. The density of each cone subclass was determined by manual counts. For determination of relative gene expression levels mRNA was extracted and expression levels of rod- and cone-specific genes were measured by qRT-PCR. The genes analyzed were S- and L/M-opsin, rod opsin as well as cyclic nucleotide-gated channel subunits specific for rods (CNGA1, CNGB1) and cones (CNGA3, CNGB3).
Preliminary results show that the canine cone population consist of ~8% S-cones in the superior and ~14% in the inferior quadrants. Compared to the age-matched control, the density of L/M-cones was significantly decreased by ~32-43% in the 1-year old achromat, while no significant change in S-cone density could be observed. In the same dog, analysis of opsin expression revealed a ~38% decrease in L/M-opsin mRNA, but no change in S-opsin or rod opsin mRNA. As cones deteriorate, they loose their inner and outer segments, and their cell bodies migrate in the subretinal space; their axons projecting into the outer plexiform layer are maintained for an unknown period of time.
In the normal canine retina S-cone density is higher in the inferior than in the superior quadrants. Despite the lack of function, cones are present in canine, achromatopsic retinas, but their density gradually decreases with age. L/M-cones are preferentially lost in the early stages of the disease process.
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