The alpha 5 beta 1 integrin associates with a dystrophin-containing lattice during muscle development.
The organization of the alpha 5 beta 1 integrin on skeletal muscle was studied in culture and in sections from adult and embryonic tissue using monoclonal antibodies specific for the alpha 5 subunit. The alpha 5 beta 1 integrin showed changes in organization and in the molecules with which it colocalizes. On early myoblasts, possessing a fibroblast-like morphology, the alpha 5 integrin organization was indistinguishable from that on fibroblasts; it was expressed prominently and localized in numerous focal contacts around the cell periphery. In bipolar myoblasts and early myotubes, the alpha 5 integrin was expressed only weakly and localized in a small number of focal contact-like structures. As myogenesis proceeded there was an apparent increase in integrin expression and a change in organization. In addition to the focal contact-like structures that persist throughout myogenesis in vitro, a dense lattice-like structure of integrin appeared. Fibrillar fibronectin, talin, and non-muscle alpha-actinin did not colocalize with the alpha 5 beta 1 integrin in the lattice structure as they did in the focal contact-like structures. However, dystrophin, which displayed a diffuse distribution earlier, now colocalized with the alpha 5 beta 1 integrin in the punctate lattice. Coincident with the registration of myofibrils into visible sarcomeres, the prominent dense, lattice structure disappeared leaving the focal contact-like structures as the only regions of organized alpha 5 beta 1 integrin. Despite the presence of the beta 1 integrin in neuromuscular or myotendinous junctions in vivo and on myotubes in vitro, the alpha 5 beta 1 integrin was not present in either junction. These observations suggest that the alpha 5 beta 1 integrin is involved in the adhesion of muscle to the extracellular matrix, the organization of the dystrophin-containing lattice, and the organization of nascent myofibrils which emanate from the focal contact- and stress fiber-like structures in muscle. Other integrins appear to anchor myofibrils at the myotendinous and neuromuscular junctions.
Lakonishok
M
M
Department of Cell and Structural Biology, University of Illinois, Urbana 61801.
Muschler
J
J
Horwitz
A F
AF
D000818:Animals; D001665:Binding Sites; D002448:Cell Adhesion; D002454:Cell Differentiation; D002642:Chick Embryo; D002645:Chickens; D016189:Dystrophin / Q000032:analysis / Q000378:metabolism*; D005109:Extracellular Matrix / Q000737:chemistry / Q000378:metabolism*; D016023:Integrins / Q000032:analysis / Q000378:metabolism*; D009132:Muscles / Q000737:chemistry / Q000196:embryology*
D016189:Dystrophin; D016023:Integrins