Analysis of dystrophin structure and function in transgenicmdx mice.

Duchenne muscular dystrophy (DMD) is a lethal X-linked recessive muscle wasting disease caused by the altered expression or absence of dystrophin, a 427kDa sarcolemma-associated protein. The expression of dystrophin is initiated by at least five separate promoters, two of which are internal to the gene and express short isoforms of dystrophin (Dp116 and Dp71) in nonmuscle tissues. The mdx mouse is an animal model for DMD that contains a point mutation which prevents expression of the full-length isoforms of dystrophin. This dissertation addresses the structure and function of dystrophin in an in vivo mouse model system of DMD. First, the characterization of a new mdx mutant mouse ($mdx\sp\rm{3Cv}$) was described in which all known isoforms of dystrophin in muscle and nonmuscle tissues were affected. The mutation was identified as a point mutation in intron 65 that affects normal splicing of both the full-length and shorter nonmuscle dystrophin mRNAs. Second, expression of full-length isoform of dystrophin was achieved in transgenic mdx mice. Dystrophin was expressed in muscles at levels 50-fold higher than in control mice. This level of expression prevented completely the appearance of muscular dystrophy symptoms. In addition, no signs of toxicity were observed due to this high level of overexpression. These experiments demonstrated direct in vivo evidence for the feasibility of gene therapy for the treatment of muscular dystrophy. Last, the ectopic expression of the nonmuscle Dp71 isoform of dystrophin in transgenic mdx muscles was examined. The Dp71 protein was localized to the sarcolemma and restored dystrophin-associated proteins to control levels. In spite of these results, no correction of dystrophic symptoms was observed. These results along with patient mutation data indicate that the C-terminal domain of dystrophin is necessary but not sufficient for prevention of muscular dystrophy and demonstrate a structural role for dystrophin in skeletal muscle.PhDHuman GeneticsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/104285/1/9513335.pdfDescription of 9513335.pdf : Restricted to UM users only