Dr. John C Saari
PositionEmeritus Professor (Retired)
Work in my group is directed towards obtaining a molecular understanding of visual cycle reactions and retinoid transport processes. We employ several approaches to the problem. HPLC analysis of visual cycle intermediates has been useful in identifying the slow steps in the vertebrate rod visual cycle and in understanding the flux of retinoids through the visual cycle after a flash or during constant illumination. The information obtained from these studies allows us to concentrate our efforts on understanding the nature of the enzymes catalyzing slow steps where control may be exerted. Characterization of the phenotypes of mice with targeted disruptions of genes coding putative visual cycle components has also resulted in considerable insight into molecular aspects of the visual cycle. For example, deletion of the gene for cellular retinaldehyde-binding protein (CRALBP) produced mice with a substantial delay in visual pigment regeneration because of an impaired isomerase reaction, suggesting that the binding protein is a functional component of this reaction. Deletion of the gene for interphotoreceptor retinoid-binding protein (IRBP), a protein suggested to function in the intercellular diffusion of retinoids, resulted in mice with normal visual cycle kinetics, suggesting that the role of this protein in visual physiology needs to be re-evaluated. Deletion of the gene for cellular retinol-binding protein type I (CRBPI), thought to deliver vitamin A to an esterification enzyme, resulted in delayed transport of vitamin A between photoreceptors and RPE, providing insight into the mechanism of intercellular diffusion of the vitamin. Thus, early in vitro experiments led to hypotheses for biological functions, which were tested by targeted deletion of specific genes in mice. The results from these in vivo approaches leads us back to in vitro experiments with which we will define more precisely the molecular functions of various components of the visual cycle. The information obtained from our studies will dovetail with medical genetic findings outlining the molecular basis for inherited defects in individuals suffering from inherited night blindnesses.