Bend, and snap! How flexible actin filaments enable cell division
Date:
Abstract: Contraction of actomyosin networks underpins active movement and division of biological cells. These networks exist in the cell cortex beneath the plasma membrane, and consist of the proteins actin and myosin. Actin molecules form polarised filaments approximately one micron in length, with distinct plus and minus-ends. Myosin forms shorter molecular motors that attach to these filaments and move actively towards their plus-ends. This motion generates either contractile or expansive force. In the cell cortex, filaments have random positions and orientations, and we might expect myosin movement to generate contraction or expansion with equal probability. However, these disordered networks are contractile, and the mechanism of contraction is not immediately clear.
We investigated how filament bending facilitates contraction. We first developed a two-dimensional agent-based model, to simulate network evolution and quantify the stress generated. Comparing simulations of rigid and semi-flexible filaments, we found that bending gives rise to network-scale contraction. We then analysed a simplified system of two filaments to understand the microscopic origin of contraction in more detail. Asymptotic analysis and numerics show that bending induces a geometric asymmetry that inhibits expansion. The net result is contraction — it works every time!