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Adrihan Janbaz, Fatima Pedrosa Domellof; Intra-sarcomeric Cytoskeleton and M-band Proteins in the Human Extraocular Muscles. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1926.
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To investigate the distribution of the intra-sarcomeric cytoskeletal proteins titin, nebulin and obscuring as well as M-band specific proteins in human extraocular muscles (EOMs).
EOM samples obtained with ethical approval, were serially sectioned and processed for immunohistochemistry, with a battery of antibodies (Abs) specific for four parts of the titin molecule, nebulin and obscuring. Additional antibodies were used against the M-band protein, myomesin and EH-myomesin as well as different myosin heavy chain (MyHC) isoforms. Anterior, middle and posterior part of the EOMs were systematically surveyed in both orbital layer (OL) and global layer (GL).
Titin, nebulin and obscuring were detected in practically all muscle fibers throughout the muscle length. Although some heterogeneity in staining intensity was noticed in both orbital and global layer there were no fiber type specific patterns. The majority of muscle fibers totally lacked or was only very weakly stained with antibody against the M-protein. A subgroup of muscle fibers containing MyHC slow and/or slow-tonic, particularly in the global layer, were strongly labeled with this antibody. These fibers were also heavily stained with antibody against myomesin.
The composition of the intra-sarcomeric cytoskeleton of the human EOMs was similar to that of other striated muscles in the body. The M-band, situated in the center of the sarcomere, is suggested to be crucial for stability of the sarcomeric contractions. The M-band specific proteins play an essential role in interconnecting the thick filament myosin as well as titin filaments in the M-band. The present data indicate that the M-band composition of the human EOMs differs from that of limb muscles with respect to M-protein. The composition of the M-band differs among muscle fibers containing MyHC slow and/or slow-tonic in OL and GL. Additional experiments are under way in order to further analyze the organisation of cytoskeletal proteins in different muscle fiber populations in human EOM.
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