Muscle Fibers Lacking Desmin in the Extraocular Muscles: A Paradigm Shift

Abstract

The extraocular muscles are highly specialized muscles responsible for the complex movements of the eyeball. They difer from other skeletal muscles in many respects, including fundamental components of the contractile apparatus and the extracellular matrix. Using immunohistochemistry and a batery of well-characterized antibodies, we have investigated the composition of the cytoskeleton of their myoibers with respect to desmin, vimentin, and nestin. In the adult and fetal human extraocular muscles, a subgroup of the slow tonic muscle ibers is lacking desmin. These ibers, which are multiply innervated, show a normal myoibrillar arrangement, maintained mitochondrial distribution, and sarcolemma integrity. Desmin, the most abundant intermediate ilament protein in muscle, has been considered a ubiquitous protein in skeletal muscle ibers where it links adjacent myoibrils and the myoibrillar 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 indings represent a paradigm shift, as desmin has been regarded a ubiquitous protein of the cytoskeleton of muscle ibers.