The α7β1 integrin in muscle development and disease

The alpha 7 beta 1 integrin is a laminin receptor on the surface of skeletal myoblasts and myofibers, Alternative forms of both the alpha 7 and beta 1 chains are expressed in a developmentally regulated fashion during myogenesis. These different alpha 7 beta 1 isoforms localize at specific sites on myofibers and appear to have distinct functions in skeletal muscle. These functions include the migration and proliferation of developing myoblasts, the formation and integrity of neuromuscular and myotendinous junctions, and the "gluing" together of muscle fibers that is essential to the generation of contractile force. The alpha 7 beta 1 integrin appears to be both directly and indirectly causally related to several muscle diseases. Enhanced expression of alpha 7 beta 1-mediated linkage of the extracellular matrix is seen in Duchenne muscular dystrophy and may compensate for the absence of the dystrophin-mediated linkage. Downregulation of expression of the integrin may contribute to the development of pathology in congenital laminin deficiencies. Mutations in the alpha 7 integrin gene underlie additional congenital muscle diseases. The functional roles of this integrin in the formation and stability of the neuromuscular and myotendinous junctions and its localization between fibers suggest that altered expression or function of this integrin may have widespread involvement in other myopathies. The localization of the alpha 7 gene at human chromosome 12q13 is a useful clue for focusing such studies.