The extraocular muscles are highly specialized muscles responsible for the complex movements of the eyeball. They differ from other skeletal muscles in many respects, including fundamental components of the contractile apparatus and the extracellular matrix. Using immunohistochemistry and a battery of well-characterized antibodies, we have investigated the composition of the cytoskeleton of their myofibers with respect to desmin, vimentin, and nestin. In the adult and fetal human extraocular muscles, a subgroup of the slow tonic muscle fibers is lacking desmin. These fibers, which are multiply innervated, show a normal myofibrillar arrangement, maintained mitochondrial distribution, and sarcolemma integrity. Desmin, the most abundant intermediate filament protein in muscle, has been considered a ubiquitous protein in skeletal muscle fibers where it links adjacent myofibrils and the myofibrillar network to the sarcolemma, the mitochondria and the membrane of the nuclei. The functional implications of the lack of desmin remain to be determined, but these findings represent a paradigm shift, as desmin has been regarded a ubiquitous protein of the cytoskeleton of muscle fibers.
Part of the book: Cytoskeleton