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First published online 4 November 2008
doi: 10.1242/jcs.040477

Journal of Cell Science 121, 3867-3877 (2008)
Published by The Company of Biologists 2008
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Research Article

Sarcomeric actin organization is synergistically promoted by tropomodulin, ADF/cofilin, AIP1 and profilin in C. elegans

Sawako Yamashiro1,*, Elisabeth A. Cox2,{ddagger}, David L. Baillie3, Jeff D. Hardin2 and Shoichiro Ono1,§

1 Department of Pathology and Department of Cell Biology, Emory University, Atlanta, GA 30322, USA
2 Department of Zoology, University of Wisconsin, Madison, WI 53706, USA
3 Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6

§ Author for correspondence (e-mail: sono{at}emory.edu)

Accepted 1 September 2008

Sarcomeric organization of thin and thick filaments in striated muscle is important for the efficient generation of contractile forces. Sarcomeric actin filaments are uniform in their lengths and regularly arranged in a striated pattern. Tropomodulin caps the pointed end of actin filaments and is a crucial regulator of sarcomere assembly. Here, we report unexpected synergistic functions of tropomodulin with enhancers of actin filament dynamics in Caenorhabditis elegans striated muscle. Pointed-end capping by tropomodulin inhibited actin filament depolymerization by ADF/cofilin in vitro. However, in vivo, the depletion of tropomodulin strongly enhanced the disorganization of sarcomeric actin filaments in ADF/cofilin mutants, rather than antagonistically suppressing the phenotype. Similar phenotypic enhancements by tropomodulin depletion were also observed in mutant backgrounds for AIP1 and profilin. These in vivo effects cannot be simply explained by antagonistic effects of tropomodulin and ADF/cofilin in vitro. Thus, we propose a model in which tropomodulin and enhancers of actin dynamics synergistically regulate elongation and shortening of actin filaments at the pointed end.

Key words: Actin dynamics, Myofibrils, Striated muscle, Pointed end


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