Diversity and developmental regulation of extraocular muscle: progress and prospects

The developmental regulation of skeletal muscle phenotypes has attracted much attention from cell and molecular biologists. Myogenesis serves as an excellent model of the interaction of genetic and epigenetic events in determining definitive adult characteristics. The muscles that are responsible for eye movements are among the most structurally and functionally diverse mammalian skeletal muscles. Despite these unique attributes, the extraocular muscle has been studied less extensively than the traditional limb and diaphragm models. This review explores current concepts regarding the development of these muscles. Proper interocular alignment and coordination of eye movements are essential for normal vision in the adult. Moreover, coordinated oculomotor function during the perinatal period is critical for the normal development of the visual system. Therefore, a thorough understanding of the sequence of events and mechanisms that regulate extraocular muscle development and maldevelopment is vital. Studies related to myoblast origin and differentiation and to the role of genetic versus environmental factors in shaping and maintaining adult extraocular muscle phenotype are reviewed. Prospects for understanding the cellular and molecular mechanisms that regulate the heterogeneity and plasticity of these muscles also are discussed.