THE EFFECT OF PERIPHERIN RDS HAPLOINSUFFICIENCY ON ROD AND CONE PHOTORECEPTORS/

Haploinsufficiency because of a null mutation in the gene encoding per ipherin/rds has been thought to be the primary defect associated with the photoreceptor degeneration seen in the retinal degeneration slow ( rds) mouse. We have compared the effects of this haploinsufficiency on rod and cone photoreceptors by measuring the levels of rod- and cone- specific gene expression, by determining the relative rates of rod and cone degeneration, and by electroretinography. These analyses were pe rformed at ages before and after the onset of degeneration of the phot oreceptor cells. The data were consistent in demonstrating that measur es for cone photoreceptors are relatively spared in comparison to comp arable measures for rod photoreceptors. Blue cones were retained in hi gher number than red/green cones for the first 3 months of the degener ation. Our results indicate that the haploinsufficiency present in rds /+ mice has a greater impact on the rod than on the cone photoreceptor , a finding that likely reflects the tight regulation of peripherin/rd s and the need for two functional alleles to assemble the structure of the rod outer segment and/or differences between the ultrastructure o f the rod and cone outer segments.