Abstract. Dystrophin, the protein product of the Duchenne muscular dystrophy (DMD) gene locus, is expressed on the muscle fiber surface. One key to further understanding of the cellular function of dystrophin would be extended knowledge about its subcellular organization. We have shown that dystrophin molecules are not uniformly distributed over the humeri, rat, and mouse skeletal muscle fiber surface using three independent methods. Incubation of singleteased muscle fibers with antibodies to dystrophin revealed a network of denser transversal rings (costameres) and finer longitudinal interconnections. Double staining of longitudinal semithin cryosections for dystrophin and oz-actinin showed spatial juxtaposition of the costameres to the Z bands. Where peripheral myonuclei precluded direct contact of dystrophin to the Z bands the organization of dystrophin was altered into lacunae harboring the myonucleus. These lacunae were surrounded by a dystrophin ring and covered by a more uniform dystrophin veil. Mechanical skinning of singleteased fibers revealed tighter mechanical connection of dystrophin to the plasma membrane than to the underlying internal domain of the muscle fiber. The entire dystrophin network remained preserved in its structure on isolated muscle sarcolemma and identical in appearante to the pattern observed on teased fibers. Therefore, connection of defined areas of plasma membrane or its constituents such as ion channels to single sarcomeres might be a potential function exerted by dystrophin alone or in conjunction with other submembrane cytoskeletal proteins. YSTROPHIN, the protein product of the Duchenne muscular dystrophy (DMD) 1 gene locus on chromosome Xp21 is a rod like molecule with a potential capacity of self association (11,18,29). Extensive sequence homologies to its autosomal homologue 6q dystrophin-related protein (DRP) (21) as well as to spectrin and o~-actinin suggested that these molecules may be members of a family of large structural proteins expressed in muscle tissue (18). Individuals suffering from DMD show complete lack or vast reduction of dystrophin in muscle tissue, whereas those with the allellc milder disease form, Becket muscular dystrophy (BMD), express reduced quantities of a semifunctional molecule (1, 10, 12, 27, 37). Lack of dystrophin expression also causes the myopathy in the animal model of the mdr mouse (4, 33). Previous immunohistochemical studies using antibodies to different portions of the dystrophin molecule have indicated that dystrophin is localized at the plasma membrane in normal skeletal muscle (3,40). Immanoelectron microscopic localization revealed that the COOH-terminal end of dystrophin is localized at or within the plasma membrane (7) whereas the NH2 terminus and the rod portion of the molecule are part of the subsarcolemmal cytoskeleton (5,7,8,39). Ultrastructural studies using immunogold sug-1. Abbreviation used in this paper: DMD, Duchenne muscular dystrophy. gested a regular distribution with an average distance of ~120 nm between neighbor...
Palyelanal (DMD) patients and rndjc mice through mutations which disrupt the reading frame of the transcript preventing dystrophin expression in the corresponding skeletal muscles [g-14]. I-Iigh concentrations of dystrophin (or a dyscrophin-like protein) have been observed at the neuromuscular junctions (NMJ) in normal rats, rabbits or mice as well as in the electric organ of Torpedo marmwata recently reported a positive immunofluorescence response at the NMJ of DMD patients and rndx mice, using antibodies raised against the central and distal parts of chicken skeletal muscle dystrophin [20,21].We now observe a protein of Mr 400000 which is present in extracts of mdx muscle from regions which contain NMJs and is absent from those which do not. This NMJ-associated homologue of dystrophin has at least 2 epitopes which are different to the usual Xp21 form of dystrophin expressed along the sarcolcmma of muscle fibres in normal muscles. This protein is also expressed at the NMJ of a DMD patient who lacks the first 52 exons of the Xp21 dystrophin gene.
MATERIALS AND METI-IODS
Biopsy tnarerials and diagnosesThe patient was a g-year-old male who has followed a severe, Duchcnne course and is also mentally retarded.
No hybridization
In our search for genes up-or down-regulated genes in the mdx mouse model for Duchenne muscular dystrophy, we isolated a down-regulated mitochondrial DNA clone. In addition to this clone, all protein-coding mitochondrial genes tested had tissue-specific and age independent down-regulated expression. This implied mechanisms at the RNA level since no change in the mitochondrial DNA contents were detected. Cytocbrome c oxidase activity showed the same range of down-regulated expression. These data provide a molecular basis for energetic metabolism modifications in mdx mice.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.