Description of Research Expertise

Research Interests:

Molecular bases of inherited blindness

Key words: Retinal degeneration, photoreceptor cells, gene therapy.

Description of Research
Our research is directed to identifying the genetic causes of inherited blindness, identifying the mechanisms linking mutation to disease, and developing treatment approaches. Studies are done in the dog model which is affected a large variety of inherited photoreceptor diseases that are now being characterized at the molecular level. For "disease hunting" work, we have used two general approaches. The first, phenotype directed candidate gene analysis, directs selection of a small subset of candidate genes that, when mutated, would be expected to result in the observed phenotype. The second approach utilizes informative pedigree resources we have developed to carry out genome wide scans to identify the disease bearing chromosomal region. Subsequently, positional cloning of the gene and identification of the causative mutation is carried out. Once the genes and mutations are identified, we use molecular and proteomic approaches to examine the disease mechanism. In parallel, gene based therapies are developed with the goal of restoring function and preventing the degeneration of the mutant photoreceptor cells.

Examples of specific projects include:

RPGR: mechanisms of disease and treatment. The RP3 form of X-linked retinitis pigmentosa (XLRP) is caused by mutations in the RP GTPase regulator (RPGR) gene. This is a uniformly severe, early onset retinal disease in man, and mutations in RPGR account for the majority of XLRP, and for ~8-25% of all molecularly diagnosed RP cases. Besides man, the dog is the only other species in which naturally occurring mutations in RPGRORF15 occur. Two different ORF15 microdeletions have been identified that are termed XLPRA1 and XLPRA2 because they are different forms of X linked progressive retinal atrophy, the dog counterpart of human RP. To examine the mechanism of disease, our lab is using microarray analysis to characterize global gene expression profiles, and determine the gene classes that are activated or suppressed at different stages of the disease. In parallel, proteomic analysis examine the different RPGR protein isoforms, and their distribution in retina and other tissues. Therapy studies are starting and will use AAV2/5 vectors carrying a truncated but functional gene, and regulated by promoters that target expression to rods and/or cones.



Rhodopsin and light damage. Mutations in the rhodopsin gene are one of the most common causes of autosomal dominant retinits pigmentosa. Dogs have a mutation in this gene that substitutes arginine for threonine at the first consensus glycosylation site. This renders the mutant rhodopsin exquisitively sensitive to light levels that are within the normal intensity range. Following light exposures, the photoreceptors die and retina degenerates within a brief time period. Using a standard light exposure paradigm, we are examining the signaling pathways that become activated following light exposure to identify those involved in cell survival and cell death.



Bestrophin mutations and disease. Mutations in the Bestrophin gene impair the function of calcium dependent chloride channels in the retinal pigment epithelium (RPE), and cause Best Macular Dystrophy (BMD), a disease of young children and young adults that results in central visual impairment. We have identified 2 different mutations in the Bestrophin gene in dogs that cause a disease similar to BMD although with multifocal distribution. We now aim to use a combination of cell culture, molecular and proteomic approaches to characterize normal and mutant Bestrophin expression, distribution and function in the RPE as an initial approach to examine the functional consequences of these mutations.