Actin Filament Patterning by Myosin Motors

Abstract

We have studied the bulk alignment of actin filament sliding movement, driven by randomly oriented myosin molecules. We performed conventional, actin filament gliding assays, but using micromolar concentrations of actin which are roughly 100,000,000 times greater than normally used in such assays, but close to the concentration of actin found in living cells. Under these conditions, actin filament movement takes up a preferred orientation. The oriented patterns of movement extend over a length scale of ∼100 micrometres, similar to the size of a mammalian cell. We studied the process of filament alignment and found that it depends critically upon filament length and density. Fluorescence video microscopy and image analysis allowed the time course of filament alignment and the formation and disappearance of oriented domains to be measured. Domains of oriented filaments formed spontaneously and were separated by distinct boundaries. The pattern of the domain structures changed on the time scale of several seconds and the collision of neighboring domains led to emergence of new patterns. Our results indicate that actin filament crowding may play an important role in structuring the leading edge of migrating cells. We propose that self-alignment of actin filaments may make an important contribution to cell polarity and provide a mechanism by which the cell migration might respond to chemical cues.