Local dynamics and viscoelastic properties of cell biological systems

How the cytoskeleton, a heterogeneous network of dynamic filamentous proteins, provides the cell with structural support is not well understood. Particle-tracking methods, which probe local mechanical properties, are well suited to test existing hypotheses derived from in vitro models of reconstituted cytoskeleton networks. This paper reviews recent applications of single- and multiple-particle tracking microrheology, with an emphasis on the semiflexible polymer F-actin and the flexible polymer keratin, two ubiquitous proteins of the cytoskeleton. Extensive knowledge of the properties of these polymers allows a rigorous comparison between theory and experiments to a level rarely matched by synthetic polymers.