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Journal of Cell Science 114, 3631-3642 (2001)
© 2001 The Company of Biologists Limited

RESEARCH ARTICLE

Transient expression of phosphatidylserine at cell-cell contact areas is required for myotube formation

Stefan M. van den Eijnde1,*, Maurice J. B. van den Hoff2, Chris P. M. Reutelingsperger3, Waander L. van Heerde3, Mieke E. R. Henfling1, Christl Vermeij-Keers4, Bert Schutte1, Marcel Borgers1 and Frans C. S. Ramaekers1

1 Department of Molecular Cell Biology, Cardiovascular Research Institute Maastricht (CARIM), University of Maastricht, PO Box 616, 6200 MD Maastricht, The Netherlands
2 Department of Anatomy & Embryology, Molecular and Experimental Cardiology Group, Academic Medical Center University of Amsterdam, 1105 AZ Amsterdam, The Netherlands
3 Department of Biochemistry, CARIM, University of Maastricht, PO Box 616, 6200 MD Maastricht, The Netherlands
4 Department of Plastic and Reconstructive Surgery, Erasmus University Medical School, PO Box 1738, 3000 DR Rotterdam, The Netherlands

*Author for correspondence (e-mail: vandeneijnde{at}molcelb.unimaas.nl)

Accepted July 5, 2001

Cell surface exposure of phosphatidylserine (PS) is shown to be part of normal physiology of skeletal muscle development and to mediate myotube formation. A transient exposure of PS was observed on mouse embryonic myotubes at E13, at a stage of development when primary myotubes are formed. The study of this process in cell cultures of differentiating C2C12 and H9C2 myoblasts also reveals a transient expression of PS at the cell surface. This exposure of PS locates mainly at cell-cell contact areas and takes place at a stage when the structural organization of the sarcomeric protein titin is initiated, prior to actual fusion of individual myoblast into multinucleated myotubes. Myotube formation in vitro can be inhibited by the PS binding protein annexin V, in contrast to its mutant M1234, which lacks the ability to bind to PS. Although apoptotic myoblasts also expose PS, differentiating muscle cells show neither loss of mitochondrial membrane potential nor detectable levels of active caspase-3 protein. Moreover, myotube formation and exposure of PS cannot be blocked by the caspase inhibitor zVAD(OMe)-fmk. Our findings indicate that different mechanisms regulate PS exposure during apoptosis and muscle cell differentiation, and that surface exposed PS plays a crucial role in the process of myotube formation.

Key words: Myotube formation, Skeletal muscle development, Heart development, Apoptosis, Mouse embryo






© The Company of Biologists Ltd 2001