Cone photoreceptor cells are the predominant source of visual information for human beings in modern society, and the exclusive retinal cell type underlying the high acuity vision of the fovea. The mouse is the principal mammal used for the investigation of organ function and disease mechanisms, due to its genomic proximity to humans and to the wealth of molecular biological tools for manipulating its genes. In mice, 3% of the photoreceptors are cones, as compared to 5% in humans, but mouse cone function and molecular mechanisms have been little investigated due to the predominance of rod photoreceptors, and to difficulties associated with identifying cones in situ and purifying them for biochemical assays. Recently this lab established that the Neural Leucine Zipper knockout (Nrl -/-) mouse has an """"""""all-cone"""""""" retina and that its cones have ultrastructural, histochemical and functional properties comparable to those of WT, and used the knowledge obtained from Nrl -/-cones to develop methods for recording electrically from WT cones. Here we propose a comprehensive series of experiments aimed at characterizing distinctive molecular mechanisms and function of mouse cones, using single-cell recordings, molecular biological manipulations of key cone phototransduction genes [including cone S-opsin, G-protein receptor kinase (Grk1), cone arrestin (mCarr)], and visual retinoid cycle genes in the all-cone Nrl -/- mouse [including those of the retinoid binding proteins, Rlbp1, Irbp, Rpe65]. Preliminary evidence shows that the functioning of the protein products of these genes can be investigated and hypotheses are presented about their distinctive roles in cones. Of particular importance to the understanding of cone function are the roles of Grk1 and mCarr in rapidly inactivating S-opsin, and the relatively rapid regeneration of cone visual pigment (S-opsin): these distinctive mechanisms are critical for enabling cones (unlike rods) to function in daylight. As a consequence of their rapid retinoid cycling, cones may possess distinct mechanisms for coping with a high flux of potentially toxic aldehyde byproducts of the cycle, and we will investigate the hypothesis that healthy cones possess a novel activity that enables them to detoxify such products. ? ? ?
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