Biological Consequences of Polyglutamine Repeats in Drosophila Muscle

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Barwell, Taylor
Drosophila , polyglutamine , Huntington's disease , neurodegeneration , muscle , aging , heat-shock protein
Polyglutamine (polyQ) disease occurs by CAG repeat expansion, encoding a glutamine tract in the affected protein. Accumulation of these mutant polyQ proteins leads to formation of insoluble protein aggregates that impair many vital cellular processes. This manifests in neurodegenerative symptoms like progressive loss of motor control, cognitive decline, and neuropsychosis. While polyQ disease is widely recognized as a disease affecting the nervous system, there is much evidence to suggest peripheral or non-neuronal tissues are affected as well. In particular, evidence from other model systems suggests a potential involvement of the muscle. Huntington’s disease (HD) is the most widely recognized polyQ disease. Here, we utilize the UAS/GAL4 system to express a pathogenic HD construct in the muscle of the fly, and characterize the effects. We observe detrimental phenotypes like reduced lifespan, decreased locomotion, and accumulation of protein aggregates. Interestingly, the aggregates were observed to distribute differently in the muscle depending on the GAL4 driver used to express the construct. These different aggregate distributions were found to be dependent on expression level and likely the timing of expression. Therefore we concluded that not only is polyglutamine detrimental to the muscle, but there are alternate modes of pathogenicity as well. Towards understanding the molecular mechanism of toxicity in the muscle, we looked at the effect of expressing Hsp70 and EDTP in an HD background. Hsp70 is well documented to be a suppressor of polyQ toxicity, while EDTP has been described as an enhancer. Interestingly, while both genes were found to suppress the accumulation of aggregates in the eye, neither had any effect in the muscle. These data would imply there is a different molecular mechanism of toxicity in muscle than that which has been described in the nervous system. 

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