Motility and biomimetics
Self-organized remodeling of the cell membrane shape and the accompanying changes in the cytoskeleton play an important role during cell motility and cell division. Such shape changes often take on the form of protrusions, like lamellipodia, filopodia, blebs. These arise from interplay of the active actin network including myosin motor proteins, the adhesion of the cell membrane to a substrate via specific proteins, and – especially for blebs- of connection or disruption between the actin cortex and the cell membrane. The mechanically active structures contain a dense network of polymerized actin, myosin molecular motors, and an inhomogeneous distribution of regulating and functional proteins together with ATP to fuel the molecular motor activity of myosin and the treadmilling polymerization of actin.
We aim to study actin-driven membrane shape instabilities in the presence of several proteins that regulate actin assembly. As the first step, we have already conducted a preliminary set of experiments on functionalized beads [1] as a control experiment on our motility assay (see figure 1 below). Furthermore, we have developed a theoretical model to describe the interplay of pushing forces exerted by actin polymerization on the membrane, pulling forces of attached actin filaments on the cell edge, contractile forces powered by molecular motors across the actin gel and resisting membrane tension [2]. The actin filament network in the bulk of lamellipodia obeys gel flow equations. We investigated in particular the dependence of wave properties on gel parameters and found that inhibition of myosin motors abolishes waves in some cells but not in others in agreement with experimental observations. The model provides a unifying mechanism explaining the dynamics of actin-based motility in a variety of systems.
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Figure 1: Formation of a symmetric actin gel around functionalized beads (A). After few minutes, symmetry breaking happens (B) and an actin tail forms behind the beads with different diameters: d=2.93 µm (C) and d=0.95 µm (D). Actin filaments polymerize at the bead surface and generate the necessary motile force for the bead movement (see movie). |
Contact: Azam Gholami, Eberhard Bodenschatz
[1] A. Bernheim-Groswasser, S. Wiesner, R.M. Golsteyn, M.F. Carlier and C. Sykes, The dynamics of actin-based motility depend on surface parameters, Nature, 417, 308 (2002)
[2] A. Gholami, M. Enculescu. M. Falcke, New Journal of Physics 14(2012) 115002