MOLECULAR CHARACTERIZATION OF THE RHODOPSIN GENE

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Rhodopsin, the major integral membrane protein of the rod outer segment of photoreceptor cells, initiates the complex cascade of events associated with the process of vision, by the absorption of a photon of light. The relationship of both the structural characteristics of the rhodopsin gene and the molecular mechanisms regulating its expression, to the survival of photoreceptor cells is an important neurobiological problem about which relatively little is known. In the mouse retina, the homozygous presence of the rds (retinal degeneration slow) mutation is associate with a) the absence of 97% of the normal amounts of rhodopsin; b) the failure of rod outer segments to develop; and c) the genetically programmed premature cell death of rod photoreceptor cells. The heterozygote (rds/+) has only half the level of rhodopsin as normal and has morphologically shorter and less well organized rod outer segments. Collectively, these data indicate that the rds mutation is either a "cis acting" regulatory gene adjacent to the rhodopsin gene or it is actually within the structural gene for rhodopsin. Our overall objective is to define and characterize the rhodopsin gene and its expression during development in normal and rds mice. We constructed a mouse retinal cDNA expression library, cloned and partially sequenced mouse rhodopsin cDNA and have obtained monoclonal and monospecific antibodies against rhodopsin. We are now proposing to: a) characterize both qualitatively and quantitatively by Northern and Western alalysis, the rhodopsin gene products (mRNA and opsin) during development of normal, heterozygote and rds mice; b) clone and sequence the rhodopsin gene from genomic libraries of normal and rds mice; and c) determine the chromosomal assignment and the exact locus of the mouse rhodopsin gene using Southern Analysis of restriction fragments from a mouse-Chinese hamster somatic cell hybrid chromosome panel and from recombinant inbred lines of mice. The expression of other retina specific genes will also be monitored in order to characterize the biochemical phenotype of the rds mutation during the development and degeneration of photoreceptor cells. The results obtained from this study will have importance for the study of hereditary blindness (e.g. retinitis pigmentosa) and will provide a mammalian model for studying the exact molecular events associated with genetically controlled degeneration of a unique population of neurons, in the central nervous system.