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First published online 15 June 2004
doi: 10.1242/jcs.01158
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Research Article |
1 Department of Cell Biology and Anatomy, University of Arizona, Tucson, AZ 85724, USA
2 Department of Molecular and Cellular Biology, University of Arizona, Tucson, AZ 85724, USA
3 Institut für Anästhesiologie und Operative Intensivmedizin, Universitätsklinikum 68135 Mannheim, Germany
* Author for correspondence (e-mail: abigailm{at}email.arizona.edu)
Accepted 13 February 2004
The efficient functioning of striated muscle is dependent upon the structure of several cytoskeletal networks including myofibrils, microtubules, and intermediate filaments. However, little is known about how these networks function together during muscle differentiation and maintenance. In vitro studies suggest that members of the muscle-specific RING finger protein family (MURF-1, 2, and 3) act as cytoskeletal adaptors and signaling molecules by associating with myofibril components (including the giant protein, titin), microtubules and/or nuclear factors. We investigated the role of MURF-2, the least-characterized family member, in primary cultures of embryonic chick skeletal and cardiac myocytes. MURF-2 is detected as two species (
55 kDa and 60 kDa) in embryonic muscle, which are down-regulated in adult muscle. Although predominantly located diffusely in the cytoplasm, MURF-2 also colocalizes with a sub-group of microtubules and the M-line region of titin. Reducing MURF-2 levels in cardiac myocytes using antisense oligonucleotides perturbed the structure of stable microtubule populations, the intermediate filament proteins desmin and vimentin, and the sarcomeric M-line region. In contrast, other sarcomeric regions and dynamic microtubules remained unaffected. MURF-2 knock-down studies in skeletal myoblasts also delayed myoblast fusion and myofibrillogenesis. Furthermore, contractile activity was also affected. We speculate that some of the roles of MURF-2 are modulated via titin-based mechanisms.
Key words: MURF, Titin, Microtubules, Myofibrils, M-line, Myofibrillogenesis
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