| The muscular dystrophies are a genetically heterogeneous group of disorders that share a number of clinical and pathological features, but vary in severity, inheritance pattern and molecular defect. Duchenne Muscular Dystrophy (DMD) is the most common form, affecting 1 in 3500 live male births. DMD is caused by alterations in dystrophin, which is associated with a large complex of proteins that links the extracellular matrix to the intracellular actin cytoskeleton. Many of the components of the dystrophin-associated protein complex (DAPC), including the sarcoglycans, are reduced in the muscles of DMD patients. Mutations in the genes encoding the sarcoglycans cause muscular dystrophy.; Dystrophin is a member of a family of proteins that includes utrophin, dystrophin-related protein 2, α-dystrobrevin and β-dystrobrevin. The dystrobrevins are part of the cytoplasmic portion of the DAPC, and bind directly to dystrophin and utrophin, as well as the syntrophins and various intermediate filament proteins. β-dystrobrevin was cloned and mapped to chromosome 2p22-23 and its genomic organization determined.; The sarcoglycan-sarcospan complex is clearly important, as its loss causes muscular dystrophy. Immunofluorescence analysis of muscle biopsies from DMD and sarcoglycanopathy patients showed that sarcospan is extremely sensitive to the presence of an intact DAPC. These studies also suggested the presence of direct interactions between specific members of the sarcoglycan-sarcospan complex, most notably between γ-sarcoglycan and sarcospan, and β-sarcoglycan and δ-sarcoglycan. Co-immunoprecipitation studies of heterologously expressed sarcospan and sarcoglycan proteins were used to demonstrate that sarcospan interacts directly with both γ- and δ-sarcoglycan, and that β-sarcoglycan interacts with δ-sarcoglycan and γ-sarcoglycan.; Based on the presence of sarcospan within the sarcoglycan-sarcospan complex, it was proposed that mutations in sarcospan would cause muscle abnormalities. Despite being an excellent candidate based on genomic localization, expression and binding characteristics, no alterations were found in the sarcospan open reading frame or staining patterns of patients with Congenital Fibrosis of the Extraocular Muscle, type 1.; With the eventual goal of determining the function of dystrophin and its associated complex, this thesis describes the identification of a dystrophin-related and associated protein and the molecular organization of an important subcomplex of the dystrophin-associated protein complex. |
