ALPHA(V) AND ALPHA(3) INTEGRIN SUBUNITS ARE ASSOCIATED WITH MYOFIBRILS DURING MYOFIBRILLOGENESIS (VOL 108, PG 975, 1995)

The development of the myofibrillar apparatus in skeletal muscle is a process in which transmembrane linkages with adhesion molecules are im plicated, Integrins are one class of transmembrane adhesion receptors which appear to mediate these interactions, Two prominent linkages are at the myotendinous junction (MTJ), which resides at the ends of the cell and connects myofibrils to the tendon, and the costameres, which encircle the girth of the cell and connect the Z-disks to the sarcolem ma, In this study we report that the av integrin subunit is a prominen t component of the costamere, The av subunit is present initially on d eveloping myotubes in a diffuse staining pattern with some concentrati on along nascent myofibrils, However, it appears in a striated pattern at the costamere and inconsistently at the M-line following the stria tion of cc-actinin and titin but before that of desmin, Its recruitmen t to preformed striation suggests that it is incorporated into a pre-e xisting structure. The presence of av in the costamere points to a rol e in lateral myofibrillar anchorage, In addition, we find that the alp ha(3) subunit is transiently associated with myofibrils along portions of their lengths and at their ends during myofibrillogenesis, The alp ha(3) subunit staining shows a novel localization and junctional struc ture. As myofibrils become striated the as integrin dissociates from t he localized pattern and becomes diffuse, This suggests a possible rol e in the stabilization of nascent myofibrils prior to striation, Antib ody-induced perturbation of adhesion mediated by the integrin beta(1) subunit in developing myotubes inhibits assembly of the sarcomeric arc hitecture, The observations presented here also contribute to an emerg ing theme, where different integrins occupy unique junctional regions on muscle.