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Title: Glycyl-tRNA synthetase mutations in neurological disease : mechanisms and models
Author: Motley, William Washburn
ISNI:       0000 0004 2722 9219
Awarding Body: Oxford University
Current Institution: University of Oxford
Date of Award: 2010
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Charcot-Marie- Tooth disease type 2D (CMT2D) is a dominantly inherited axonal neuropathy caused by missense mutations in the glycyl-tRN A synthetase gene (CARS). Dominant mutations in tyrosyl-tRNA synthetase and alanyl-tRNA synthetase also cause CMT, suggesting a shared mechanism for all three diseases. The goal of this thesis was to investigate possible mechanisms and narrow the potential ways that mutations in CARS could lead to axon loss. GARS mutations are distributed throughout the protein in multiple functional domains. The localization, dimerization, and degradation of GARS were examined as in vitro measures of protein function. Dimer function was preserved in most mutants. Similarly, no differences in wild-type and mutant localization or degradation were seen. In vitro experiments did not show evidence of a loss of function in most GARS mutants. Progress has also been made towards the development of a Drosophila model of CMT2D. Overexpression of mutant Aats-gly, the Drosophila ortholog of CARS, was found to cause lethality in fruit flies, while overexpression of the wild-type did not reduce viability. Results suggest that CMT2D can be modeled in fly, that the toxicity of the mutant protein is tissue autonomous, and that mutations in CARS and YARS have similar effects in Drosophila, hinting at a shared mechanism. There are two murine models of CMT2D with different mutations in the Cars gene. While they have very different levels of severity, they are both reliable models of the human disease. Each disease model was crossed to mice ubiquitously overexpressing wild-type GARS in order to determine whether the disease phenotype is caused by a loss of function in GARS. Using behavioral, histological, and electrophysiological measures of nerve function, it was determined that overexpression of wild-type CARS cDNA mitigates, but does not dramatically improve neuromuscular function in either model. The wild-type transgenes were able to rescue compound heterozygous CarsC201RIXM256 mice from embryonic lethality proving that the protein product of the two transgenes is functional. In summary, my work in cells, fruit flies, and mice provides evidence that CARS mutations cause CMT2D primarily by a pathogenic gain of function.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available