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Published 15 September 2003. doi:10.1083/jcb.200305031
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© The Rockefeller University Press, 0021-9525/2003/9/1057 $5.00
The Journal of Cell Biology, Volume 162, Number 6, 1057-1068

Article

 The interaction of tropomodulin with tropomyosin stabilizes thin filaments in cardiac myocytes

Ryan E. Mudry1, Cynthia N. Perry1, Meredith Richards3, Velia M. Fowler3 and Carol C. Gregorio1,2

1 Department of Cell Biology and Anatomy, University of Arizona, Tucson, AZ 85724
2 Department of Molecular and Cellular Biology, University of Arizona, Tucson, AZ 85724
3 Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037

Address correspondence to Carol C. Gregorio, Dept. of Cell Biology and Anatomy, University of Arizona, 1501 N. Campbell Ave., Tucson, AZ 85724. Tel.: (520) 626-8113. Fax.: (520) 626-2097. email: gregorio{at}email.arizona.edu

Actin (thin) filament length regulation and stability are essential for striated muscle function. To determine the role of the actin filament pointed end capping protein, tropomodulin1 (Tmod1), with tropomyosin, we generated monoclonal antibodies (mAb17 and mAb8) against Tmod1 that specifically disrupted its interaction with tropomyosin in vitro. Microinjection of mAb17 or mAb8 into chick cardiac myocytes caused a dramatic loss of the thin filaments, as revealed by immunofluorescence deconvolution microscopy. Real-time imaging of live myocytes expressing green fluorescent protein–{alpha}-tropomyosin and microinjected with mAb17 revealed that the thin filaments depolymerized from their pointed ends. In a thin filament reconstitution assay, stabilization of the filaments before the addition of mAb17 prevented the loss of thin filaments. These studies indicate that the interaction of Tmod1 with tropomyosin is critical for thin filament stability. These data, together with previous studies, indicate that Tmod1 is a multifunctional protein: its actin filament capping activity prevents thin filament elongation, whereas its interaction with tropomyosin prevents thin filament depolymerization.

Key Words: sarcomere; myofibrillogenesis; cardiac muscle; actin; thin filament

Meredith Richards' present address is Luce, Forward, Hamilton & Scripps, LLP, San Diego, CA 92101.


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