A free-boundary model of a motile cell explains turning behavior Masoud Nickaeen Igor L. Novak Stephanie Pulford Aaron Rumack Jamie Brandon Boris M. Slepchenko Alex Mogilner 10.1371/journal.pcbi.1005862 https://plos.figshare.com/articles/dataset/A_free-boundary_model_of_a_motile_cell_explains_turning_behavior/5601304 <div><p>To understand shapes and movements of cells undergoing lamellipodial motility, we systematically explore minimal free-boundary models of actin-myosin contractility consisting of the force-balance and myosin transport equations. The models account for isotropic contraction proportional to myosin density, viscous stresses in the actin network, and constant-strength viscous-like adhesion. The contraction generates a spatially graded centripetal actin flow, which in turn reinforces the contraction via myosin redistribution and causes retraction of the lamellipodial boundary. Actin protrusion at the boundary counters the retraction, and the balance of the protrusion and retraction shapes the lamellipodium. The model analysis shows that initiation of motility critically depends on three dimensionless parameter combinations, which represent myosin-dependent contractility, a characteristic viscosity-adhesion length, and a rate of actin protrusion. When the contractility is sufficiently strong, cells break symmetry and move steadily along either straight or circular trajectories, and the motile behavior is sensitive to conditions at the cell boundary. Scanning of a model parameter space shows that the contractile mechanism of motility supports robust cell turning in conditions where short viscosity-adhesion lengths and fast protrusion cause an accumulation of myosin in a small region at the cell rear, destabilizing the axial symmetry of a moving cell.</p></div> 2017-11-14 18:47:26 boundary counters causes retraction constant-strength viscous-like adhesion lamellipodial boundary retraction shapes cell boundary dimensionless parameter combinations viscosity-adhesion length free-boundary model viscosity-adhesion lengths myosin-dependent contractility actin protrusion model analysis lamellipodial motility myosin transport equations myosin density centripetal actin flow model parameter space actin network actin-myosin contractility contraction protrusion cause Actin protrusion myosin redistribution contractile mechanism free-boundary models motile cell models account motile behavior