Autosomal recessive loss-of-function mutations in the parkin gene are the most common cause of familial Parkinson's disease (PD), which is characterized by selective loss of dopaminergic (DA) neurons in the substantia nigra and clinical motor disorders. We hypothesize that parkin protein is required to maintain the survival of DA neurons and that increased expression of parkin may protect DA neurons against insults such as oxidative stress and environmental toxins. To test this hypothesis, we have recently generated mouse embryonic stem (ES) cells and animals with targeted germline deletion of the parkin gene. We engineered these parkin "knockout" ES cells and animals to express enhanced green fluorescent protein (EGFP) in place of the normal parkin protein, thus providing a fluorescent reporter of parkin promoter activity. We propose use this reporter in a high throughput assay to screen libraries of compounds, including thousands of FDA approved drugs, over-the-counter medications, vitamins and herbal supplements already in human use, to identify compounds that increase the expression of parkin in our parkin-EGFP ES cells, neurons differentiated from these ES cells, and primary neurons derived from our parkin knockout animals. We will also utilize DNA microarray technology to identify genes with altered expression in brain tissue and neuronal cultures derived from the ventral mesencephalon of our parkin knockout animals compared to control animals. The significance of our proposed research is that compounds that selectively increase parkin levels in DA neurons could immediately be tested in clinical trials of PD therapeutics and that genes with altered expression in our parkin knockout animals could serve as novel targets for subsequent drug discovery and as tools for elucidating the neurodegenerative pathway of PD.