β1 integrin mediation of myogenic differentiation: implications for satellite cell differentiation

Abstract

Myoblast-extracellular matrix interactions mediated by integrin receptors have been shown to play a pivotal role in skeletal muscle development. In the current study, the avian genetic muscle weakness, low score normal (LSN), which exhibits modified myotube and sarcomere structure and a reduction in β1 integrin expression during satellite cell differentiation, was used as a model system to further investigate the role of β1 integrins in myogenic differentiation. During normal satellite cell differentiation, the β1 integrin was localized at areas of pseudopodial activity and points of cell contact. In contrast, in LSN satellite cell cultures the β1 integrin was predominantly observed in clusters not associated with points of cell to cell contact. The LSN satellite cells underwent apoptosis at the same time normal satellite cells were fusing to form multinucleated myotubes. During muscle development, the β1 integrin is regulated by alternative splicing from a β1A to β1D form. During both embryonic and posthatch pectoralis major muscle development, regulation of the β1A and β1D variants was altered in the LSN. Normal and LSN myogenic satellite cell cultures did not express the β1D integrin, but the LSN satellite cells expressed higher concentrations of the β1A integrin than did normal satellite cells. Taken together, these data further demonstrate the importance of the β1 integrin subunit in the regulation of cell-extracellular matrix signal transduction pathways during muscle growth and differentiation.