Membrane proteins connected to the cytoskeleton are essential for maintaining the integrity of the muscle plasma membrane under mechanical stress. The filamentous costamere lattice is particularly important for resisting lateral forces. It contains a variety of proteins, including ankyrin, dystrophin, integrins and spectrin, but critical organizing components have proven elusive. Elizabeth Luna and co-workers now reveal a potential mastermind behind the operation: archvillin (see p. 2261). Archvillin is a novel, muscle-specific isoform of supervillin, an actin-bundling protein that is implicated in actin-membrane linkage and shares some similarity with the microvillar protein villin. The authors show that archvillin is present at costameres in skeletal muscle and cofractionates with the plasma membrane. They also show that it can bind to actin, associates with actin filaments in vivo and localizes to the tips of differentiating myotubes. Perhaps their most important observation, however, is that a dominant negative archvillin mutant containing the insert...

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