Initial process of polyglutamine aggregate formation in vivo

Background: Polyglutamine expansion in protein is responsible for several i nherited neuro-degenerative diseases. The expansion has toxic effects on ne ural cells as well as results in forming aggregates. Using yeast, we examin ed the initial process of polyglutamine aggregate formation in vivo. Results: Following expression, polyglutamine tracts were of a soluble form during a lag period, and then formed insoluble complexes. The lag was prolo nged and the formation of insoluble complex became slower by decreasing the number of polyglutamine tracts and by a treatment with guanidine hydrochlo ride. Gel filtration analysis revealed that the soluble polyglutamine exist ed in a small form. Formation of polyglutamine aggregates appeared to follo w similar kinetics reported in the in vitro studies, where polyglutamine tr acts self-aggregate in a length-, concentration- and time-dependent manner. However, in vivo, Hsp104 was required for the conversion from a soluble to an insoluble state. Without Hsp104, polyglutamine tracts tended to remain in a small soluble form, prolonging the lag. Moreover, the dependency on Hs p104 for aggregate formation was strong with the short polyglutamine tract, and decreased with the long polyglutamine tract. Conclusion: For polyglutamine aggregate formation, a balance of parameters including the length of the polyglutamine tract, Hsp104, and level of polyg lutamine expression determined its efficiency.