Recruitment and the role of nuclear localization in polyglutamine-mediatedaggregation

The inherited neurodegenerative diseases caused by an expanded glutamine re peat share the pathologic feature of intranuclear aggregates or inclusions (NI). Here in cell-based studies of the spinocerebellar ataxia type-3 disea se protein, ataxin-3, we address two issues central to aggregation: the rol e of polyglutamine in recruiting proteins into NI and the role of nuclear l ocalization in promoting aggregation. We demonstrate that full-length ataxi n-3 is readily recruited from the cytoplasm into NI seeded either by a path ologic ataxin-3 fragment or by a second unrelated glutamine-repeat disease protein, ataxin-3. Experiments with green fluorescence protein/polyglutamin e fusion proteins show that a glutamine repeat is sufficient to recruit an otherwise irrelevant protein into NI, and studies of human disease tissue a nd a Drosophila transgenic model provide evidence that specific glutamine-r epeat-containing proteins, including TATA-binding protein and Eyes Absent p rotein, are recruited into NI in vivo. Finally, we show that nuclear locali zation promotes aggregation: an ataxin-3 fragment containing a nonpathologi c repeat of 27 glutamines forms inclusions only when targeted to the nucleu s. Our findings establish the importance of the polyglutamine domain in med iating recruitment and suggest that pathogenesis may be linked in part to t he sequestering of glutamine-containing cellular proteins. In addition, we demonstrate that the nuclear environment may be critical for seeding polygl utamine aggregates.