Dynamic distribution of an antigen involved in the differentiation of avian myoblasts: II. Possible association of beta 1 integrin with myofibril organization

Previous studies have shown that a monoclonal antibody, H-145, inhibits myo tube formation of quail myoblasts transformed with a:temperature-sensitive mutant of Rous sarcoma virus (QM-RSV cells) [Hyodo and Kim, 1994: Exp. Cell Res. 212.120-131]. The antigen recognized by H-145 (H-145 antigen), which is a glycoprotein with a molecular mass of about 116 kDa, is related to a s tep immediately before myoblast fusion. To determine the functional signifi cance of H-145 antigen, we examined its dynamic state during myogenic diffe rentiation of QM-RSV cells. H-145 antigen showed a unique and discrete dist ribution. In immature myotubes immediately after myoblast fusion, many ring -like structures of H-145 antigen appeared on the ventral surface of the ce lls, encircling the actin dots detected simultaneously by immunofluorescenc e and interference reflection microscopy. The core of the ring-like structu res was filled with the termini of actin bundles, mainly formed by alpha-ac tin. Other cytoskeletal-associated proteins, such as vinculin and alpha-act inin, were also associated with these structures. The ring-like structures of H-145 antigen were observed only during a restricted period when myoblas ts fused actively, suggesting their relationships to myotube formation and an early stage of myofibril formation. With maturation of the myotubes, mos t of the H-145 antigen became redistributed in linear arrays on the apical cell surface and was probably associated with the termini of actin bundles to organize myofibrils, suggesting that the antigen was also related to mat uration of myotubes. Experiments using monoclonal antibodies against chick beta 1 integrin showed that H-145 antigen is pr integrin or a very closely related derivation. Thus H-145 antigen (pl integrin) is possibly involved i n both myoblast fusion and the myofibril organization in myotubes. Cell Mot il, Cytoskeleton 45.27-41, 2000. (C) 2000 Wiley-Liss, Inc.