Generation and Characterization of Knock-in Mouse Models Expressing Versions of Normal (7Q) and Mutant (140Q) Huntington with Deletions of the Proline-rich Region

Neveklovská, Michelle Milena, Department of Neuroscience, University of Virginia
Zeitlin, Scott, Department of Neuroscience, University of Virginia
Lee, Kevin, Department of Neuroscience, University of Virginia
Bloom, George, Department of Biology, University of Virginia
Grant, Patrick, Department of Biochemistry and Molecular Genetics, University of Virginia
Harrison, Madaline, Department of Neurology, University of Virginia
Mandell, Jim, Department of Pathology, University of Virginia

Huntington's disease (HD) is an autosomal dominant disorder that is caused by the expansion of a polyglutamine (polyQ) tract in the huntingtin (htt) protein. HD is one of several neurodegenerative diseases that are caused by an expansion of a polyQ stretch in a ubiquitously expressed protein. The htt polyQ stretch is flanked by two evolutionarily conserved domains–an amino terminal N17 domain, and a proline-rich region (PRR). The overall goal of my research is to understand how the PRR contributes to wild-type htt function, and can modulate mutant htt pathogenesis in vivo. To determine the role of the PRR in normal htt function, I characterized a knock-in mouse line expressing a version of the mouse HD gene that contains a deletion of its PRR in the context of the normal murine 7Q stretch (Hdh ∆P ). I was able to obtain mice homozygous for this deletion (Hdh ∆P/∆P ), suggesting that the PRR is not required for htt's normal essential functions during development. In older Hdh ∆P/∆P mice, I observed only a mild behavioral phenotype, a result suggesting that the deletion of the PRR in the context of a normal polyQ stretch has only a subtle impact on htt function in the adult brain. To determine the role of the PRR in modulating the toxic effects of htt's expanded polyQ stretch, I generated a knock-in mouse model expressing a version of htt with both an expanded stretch of polyQ (140Q) and a deletion of the adjacent PRR (Hdh 140Q-∆P ). I observed a change in the conformation of mutant htt aggregates, an alteration in their subcellular localization, and a reduction in mutant aggregate numbers in Hdh 140Q-∆P/+ mice compared to Hdh 140Q/+ mice. In addition, behavioral deficits in Hdh 140Q-∆P/+ mice were ameliorated in comparison to the Hdh 140Q/+ mice. Taken together, my data suggest III that the deletion of the htt PRR in the context of a normal polyQ stretch has only a minimal effect on htt function, while a PRR deletion in the context of an expanded polyQ stretch can modulate mutant htt toxicity by altering the kinetics of mutant htt aggregate formation and their conformation.

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PHD (Doctor of Philosophy)
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