Localization of dystrophin and beta-spectrin in vacuolar myopathies

We examined the expression of the cytoskeletal proteins dystrophin and beta-spectrin on vacuolar boundaries in vacuolar myopathies. We also localized utrophin, a dystrophin homologue, and laminin, which served as a marker for the basal lamina. Four types of vacuoles were identified. Type 1 vacuoles, found in all diseases, were lined by laminin, dystrophin, and beta-spectrin and arose from infoldings of the basal lamina and sarcolemma into splitting or branching fibers. Type 2 vacuoles were lined by dystrophin and beta-spectrin and were most common in adult acid maltase deficiency, chloroquine myopathy, and periodic paralysis. Traces of utrophin were also noted on the boundaries of some type 2 vacuoles, but only in those fibers that also expressed utrophin on their surface membrane. Type 3 vacuoles were lined by small patches of dystrophin and beta-spectrin and occurred in any vacuolar myopathy. Type 4 vacuoles were unlined by any of the above antigens and were most common in infantile acid maltase deficiency and in the nonlysosomal glycogenoses. Immunoelectron microscopy confirmed the dystrophin label on vacuolar boundaries but revealed no reaction product on any other membranous component within the muscle fiber. We conclude that dystrophin and beta-spectrin provide cytoskeletal support for a species of membrane-bound vacuoles in diverse myopathies.