Actin dynamics as a multiscale integrator of cellular guidance cues

Cells are able to integrate multiple, and potentially competing, cues to determine a migration direction. For instance, in wound healing, cells follow chemical signals or electric fields to reach the wound edge, regardless of any local guidance cues. To investigate this integration of guidance cues, we monitor the actin-polymerization dynamics of immune cells in response to cues on a subcellular scale (nanotopography) and on the cellular scale (electric fields, EFs). In the fast, amoeboid-type migration, commonly observed in immune cells, actin polymerization at the cell's leading edge is the driver of motion. The excitable systems character of actin polymerization leads to self-propagating, two-dimensional wavefronts that enable persistent cell motion. We show that EFs guide these wavefronts, leading to turning of cells when the direction of the EF changes. When nanoridges promote one-dimensional (1D) waves of actin polymerization that move along the ridges (esotaxis), EF guidance along that direction is amplified. 1D actin waves cannot turn or change direction, so cells respond to a change in EF direction by generating new 1D actin waves. At the cellular scale, the emergent response is a turning of the cell. For nanoridges perpendicular to the direction of the EF, the 1D actin waves are guided by the nanotopography, but both the average location of new actin waves and the whole cell motion are guided by the EF. Thus, actin waves respond to each cue on its intrinsic length scale, allowing cells to exhibit versatile responses to the physical microenvironment.

The angular distribution of directional changes of guided 3T3 cells.

This paper reports that the angular distribution of directional change of 3T3 cells which followed guiding lines on a substrate and left the guidance at various angles shows a peculiar preference for angles between 30 degrees and 60 degrees. Regarding the phenomenon of cellular guidance itself, 3T3 cells faced with a choice between guiding lines toward different directions seem to explore various options before following one. This observation suggests that the outcome of a probing action and not substrate properties alone can explain the guidance behavior of 3T3 cells.