Involvement of M-cadherin in terminal differentiation of skeletal muscle cells

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Abstract
Cadherins are a gene family encoding calcium-dependent cell adhesion proteins which are thought to act in the establishment and maintenance of tissue organization. M-cadherin, one member of the family, has been found in myogenic cells of somitic origin during embryogenesis and in the adult. These findings have suggested that M-cadherin is involved in the regulation of morphogenesis of skeletal muscle cells. Therefore, we investigated the function of M-cadherin in the fusion of myoblasts into myotubes (terminal differentiation) in cell culture. Furthermore, we tested whether M-cadherin might influence (a) the expression of troponin T, a typical marker of biochemical differentiation of skeletal muscle cells, and (b) withdrawal of myoblasts from the cell cycle (called terminal commitment). The studies were performed by using antagonistic peptides which correspond to sequences of the putative M-cadherin binding domain. Analogous peptides of N-cadherin have previously been shown to interfere functionally with the N-cadherin-mediated cell adhesion. In the presence of antagonistic M-cadherin peptides, the fusion of myoblasts into myotubes was inhibited. Analysis of troponin T revealed that it was downregulated at the protein level although its mRNA was still detectable. In addition, withdrawal from the cell cycle typical for terminal commitment of muscle cells was not complete in fusion-blocked myogenic cells. Finally, expression of M-cadherin antisense RNA reducing the expression of the endogenous M-cadherin protein interfered with the fusion process of myoblasts. Our data imply that M-cadherin-mediated myoblast interaction plays an important role in terminal differentiation of skeletal muscle cells.