The Cell Cytoskeleton as a Composite: Mechanics and Force Transmission
Living cells sense and respond to mechanical forces in their surroundings. This mechanical response is largely due to the cell cytoskeleton, a "composite" polymeric scaffold made of a variety of stiff biopolymers and crosslinking proteins. In this talk I will discuss theories that can explain the experimentally observed synergistic mechanical interplay between (i) different types of protein filaments and (ii) different types of crosslinkers in the cell cytoskeleton, and its consequences for cell mechanics. Two major filament systems in the cytoskeleton are actin filaments (F-actin) and microtubules (MTs). Actin filaments are semiflexible, while the much stiffer MTs behave as rigid rods. First, I will discuss how the direct coupling to the surrounding cytoskeleton allows intracellular MTs to bear large compressive forces ~ 100 pN, and controls the range of force transmission along the MTs which can be as large as tens of microns. Next, I will describe the collective mechanical properties of actin-microtubule composites. We find that stiff filaments such as MTs and stress fibers can not only enhance the stiffness of the cell cytoskeleton, but can also dramatically endow an initially nearly incompressible F-actin matrix with enhanced compressibility relative to its shear compliance. A second source of compositeness in the cell cytoskeleton is the presence of different types of crosslinking proteins. For example, some crosslinkers allow the crossing filaments to rotate freely, while others constrain the angle between crosslinked filaments. I shall conclude my talk by discussing a theory of rigidity percolation that addresses how the cooperative interaction between different types of crosslinkers leads to a mechanically robust cytoskeleton with tunable elasticity.
Dr. Moumita Das is an Assistant Professor of Physics at the Rochester Institute of Technology. She obtained her doctorate at the Indian Institute of Science Bangalore, India on the physics of liquid crystals and colloids. She then shifted focus to researching the physics of living systems, especially cell mechanics and migration. She did her postdoctoral research at Harvard University, University of California Los Angeles and Vrije Universiteit Amsterdam (Netherlands). Her current research interests lie in the interface between Biology and Physics.