Active microrheology of actin-vimentin intermediate filaments composite networks

The cytoskeleton--a complex dynamic network of biopolymers comprising actin, microtubules, and intermediate filaments--plays a vital role in several cellular processes ranging from the stability and rigidity of biological cells to cell motility and shape change. Central to this multifunctionality are the inherent stiffness of each filament and the myriad binding proteins that serve to crosslink, bundle, and stabilize these filaments. Exploring the mechanics and dynamics of in vitro reconstituted networks consisting of only one of these cytoskeletal components has been the subject of extensive experimental work. However, the role each cytoskeletal component plays in their composite networks' mechanical properties and structural dynamics is yet to be well understood. Here, we couple optical tweezers microrheology with confocal imaging to measure the nonlinear viscoelastic response and structural dynamics of in vitro reconstituted filamentous actin (F-actin)--vimentin intermediate filaments (VIFs) composite networks by varying the relative concentration of actin and vimentin. Our measurements shed new light on how VIFs and F-actin work synergistically during the various cellular processes.