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Title: Drosophila indirect flight muscles as a model system for the study of human thin filament myopathies
Author: Sevdali, Maria
ISNI:       0000 0004 2677 0943
Awarding Body: University of York
Current Institution: University of York
Date of Award: 2009
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Human thin filament myopathies are a group of skeletal muscle diseases caused by mutations in thin filament protein genes. Over 170 mutations within the human skeletal Cl-actin gene, ACTA1, cause congenital actin myopathies (CAM). These are dominant, often lethal mutations resulting in death at birth or shortly after. Several mutations have been identified in the genes encoding for Troponin I and Troponin T proteins, which cause arthrogryposis. The aim of this work was to see if the Drosophila Indirect Flight Muscles can be used as a genetic model system, with which to study the ACTA1 and arthrogryposis disorders and understand their aetiology. Six different mutations in the Drosophila Act88F gene, GI5R, I136M, DI54N, VI63L, VI63M and D292V, homologous to the human CAM actin mutations were transgenically expressed in Drosophila Indirect Flight Muscles (lFM) as wild type heterozygotes. All the mutants were dominant and with some myofibrillar defects similar to those seen in humans. Certain mutations resulted in intranuclear rods, similar to those found in humans and split Z-discs. The mutations varied in severity and matched that of the human mutations. An extra copy of wild type actin rescued the phenotype of all the heterozygote mutants, suggesting that upregulation of expression of the wild type actin gene might be a future prospect for therapy. Atypically, flies heterozygous for the R372H Act88F mutation complete normal IFM myogenesis and young flies can fly, but later become flightless and by day 7 show the Drosophila equivalent of the human nemaline phenotype. Electron microscopy revealed progressive loss of muscle structure. From the ultrastructure, the phenotypic requirement for muscle usage and the known α-actinin binding sites on the actin monomer, the R372H mutation is proposed to reduce the strength of F-actin/α-actinin binding, leading to muscle damage during use and breakdown of muscle structure. Binding studies confirmed a I3-fold reduction in u-actinin binding for R372H actin. The GAL4/UAS system was employed for the study of arthrogryposis mutations. The wild-type TnT and TnI IFM isoforms were transgenically expressed to rescue the TnT and TnI IFM nulls, respectively. Only the TnI null was rescued. The TnI arthrogryposis mutants were transgenically expressed and resulted in hypercontracted muscles.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available