The retinal pigment epithelial (RPE) layer serves multiple functions in maintaining photoreceptor cell viability. Among these, none is more critical than the phagocytic removal of the shed tips of the rod outer segments (ROS). To study this essential process we will use a genetic model of retinal degeneration, the Royal College of Surgeons (RCS) retinal dystrophic (rdy) rat, in which phagocytosis is 90-95% deficient. The defect in the RCS rat is detected at the RPE cell plasma membrane, where ROS binding occurs but ingestion is impaired. Because any of several steps in phagocytosis may be aberrant, we propose to study the primary defect in dystrophic rat RPE using the methods of molecular genetics. We will employ both nucleic acid probes, which require no prior assumptions regarding the expression site of the rdy mutation, as well as anit-RPE plasma membrane antibodies.
The specific aim of this proposal is to identify cDNA clones which can be used to produce probes for the characterization of differences between normal and dystrophic RPE cells at the level of gene structure, RNA synthesis and processing, and protein systhesis and localization. These clones will be identified by two approaches: (1) the differential screening of an RPE cell cDNA expression library cloned in lambda gtll, with sequences complementary to normal and dystrophic rat RPE mRNA, and (2) immunological screening of the CDNA library with selected monoclonal antibodies to RPE plasma membranes. By these methods we will attempt to isolate sequences whose expression is altered as a result of the rdy mutation. The RPE cDNA library is valuable not only for understanding the RCS rat model; it will also premit further study of changes in RPE function which accompany normal development and aging. Moreover, under appropriate cross-hybridization conditions we can use these clones to analyse human RPE cells for age-related changes and genetic disorders. Thus, our long range goals include applying these techniques to the human system, to ask whether RPE cell involvement is primary or secondary to the etiology of retinal dysfunction.
