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J. Cell Biol.,
Volume 144, Number 6, March 22, 1999 1259-1270
Department of Physiology, School of Medicine, University of Maryland, Baltimore, Maryland 21201
We used immunofluorescence techniques
and confocal imaging to study the organization of the
membrane skeleton of skeletal muscle fibers of mdx
mice, which lack dystrophin. 
-Spectrin is normally
found at the sarcolemma in costameres, a rectilinear array of longitudinal strands and elements overlying Z
and M lines. However, in the skeletal muscle of mdx
mice, -spectrin tends to be absent from the sarcolemma over M lines and the longitudinal strands may
be disrupted or missing. Other proteins of the membrane and associated cytoskeleton, including syntrophin, -dystroglycan, vinculin, and Na,K-ATPase are
also concentrated in costameres, in control myofibers,
and mdx muscle. They also distribute into the same altered sarcolemmal arrays that contain -spectrin. Utrophin, which is expressed in mdx muscle, also codistributes with -spectrin at the mutant sarcolemma. By
contrast, the distribution of structural and intracellular
membrane proteins, including 
-actinin, the Ca-ATPase and dihydropyridine receptors, is not affected, even at sites close to the sarcolemma. Our results suggest
that in myofibers of the mdx mouse, the membrane-
associated cytoskeleton, but not the nearby myoplasm,
undergoes widespread coordinated changes in organization. These changes may contribute to the fragility of
the sarcolemma of dystrophic muscle.
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