The folding and maintenance of proteins in their native conformation is an essential cellular process. Disruption of protein folding homeostasis, leading to protein aggregation, is associated with a variety of human diseases. A prototypical class of these disorders, comprised of eight neurodegenerative diseases including Huntington's Disease, is associated with genes encoding polyglutamine (polyQ) tracts in otherwise unrelated proteins. To investigate the principles underlying aggregation-related cellular dysfunction, we have used C. elegans expressing different lengths of polyQ as chimeric fusions to yellow fluorescent proteins. As C. elegans are transparent, this allows concurrent assessment of aggregate formation and toxicity in the same living animal. We have used this system to demonstrate protein aggregation and cellular toxicity, observed as a motility defect, upon expression of expanded polyQ. Further, we have used intermediate polyQ length (Q40) to demonstrate a direct role of aggregate formation in cellular dysfunction. In the proposed work we will use fluorescence recovery after photobleaching as a tool to investigate the biophysical properties of polyQ proteins in vivo and how this relates to the role of aggregate formation in cellular toxicity. We will use C. elegans lifespan mutants to investigate the relationship between aggregation, toxicity, and aging. Further using both forward and reverse genetic strategies, we will identify modifiers of the aggregation and toxicity phenotypes to expand the list of potential therapeutic targets for human proteinopathies and to further our understanding of how cells sense and adapt to the appearance of misfolded proteins.