Cytoskeletal remodelling and slow dynamics in the living cell

The cytoskeleton (CSK) is a crowded network of structural proteins that stabilizes cell shape and drives cell motions. Recent studies on the dynamics of the CSK have established that a wide variety of cell types exhibit rheology in which responses are not tied to any particular relaxation times and are thus scalefree 1–4. Scale-free rheology is oft en found in a class of materials called soft glasses 5, but not all materials expressing scale-free rheology are glassy (see plastics, wood, concrete or some metals for example) 6. As such, the extent to which dynamics of the CSK might be regarded as glassy remained an open question. Here we report both forced and spontaneous motions of microbeads tightly bound to the CSK of human muscle cells. Large oscillatory shear fl uidized the CSK matrix, which was followed by slow scale-free recovery of rheological properties (aging). Spontaneous bead motions were subdiff usive at short times but superdiff usive at longer times; intermittent motion