Characterizing the effect of huntingtin's flanking sequences on polyglutamine aggregation and toxicity in Caenorhabditis elegans.

Polyglutamine (polyQ) diseases are a group of at least nine incurable neurodegenerative diseases characterized by an expanded polyglutamine tract that causes protein misfolding and subsequently protein aggregation and cell death. The causative protein in each of the diseases is flanked by sequences that differ in amino acid sequence, structure, and their contribution to the disease pathology. Additionally, protein chaperones are thought to modulate aggregation and toxicity by assisting in protein folding and unfolding of misfolded protein. One chaperone in particular, heat shock protein 70 has been studied extensively. I aimed to elucidate the relationships involving flanking sequences, chaperone Hsp70, aggregation, and toxicity in one of the polyQ diseases, Huntington’s Disease, using it’s causative gene, htt. Transgenic Caenorhabditis elegans strains were used to compare the degree of aggregation and level of toxicity in polyQ fusion constructs, huntingtin polyQ fragment fusion constructs, and these same constructs with and without chaperone Hsp70. Fluorescently tagged aggregates were imaged using confocal fluorescence microscopy and analyzed using image analysis software. The level of toxicity was measured using a behavioral assay that characterizes motility. Results showed that the flanking sequences of huntingtin significantly increased the degree of aggregation and that overexpression of Hsp70 in strains with huntingtin fragment constructs exacerbates protein aggregation, while overexpression of Hsp70 in polyQ constructs did not affect the degree of aggregation. The presence of flanking sequences and overexpression of Hsp70 did not mitigate toxicity