Figure 3.

Cells rapidly reorient and respond to new light conditions, with no detectable memory of light or movement directionality. t = 0 min denotes the time of the first change in light condition. (A) The direction of light incidence on an inoculation of cells was rotated by 90°, from the y axis to the x axis. (i) Phase-contrast images of cells within the midfinger, before and after the rotation. (ii) After the direction change (dotted line), the cells reequilibrated their movement biases along the directions parallel and perpendicular to the light to their prechange values within minutes. (iii) The distribution of bias values also reequilibrated rapidly. (iv) Step-size distributions were similar pre- and post-light change. (B) Cells were imaged for 20 min with incident light (“On 1”), after which the light source was switched off for 20 min (“Off”), and then switched back on for 20 min (“On 2”). (i) Phase-contrast images of a fingertip at the start of imaging and at the end of the “Off” and “On 2” intervals. (ii) The motility bias parallel to the light quickly dropped to a slightly negative value once the light was turned off, and then reestablished its original value on restoration of incident light with minutes. (iii) The distributions of bias values along each axis were the same before and after the “Off” condition, whereas the distribution in the perpendicular direction was similar to the parallel direction in the “Off” condition. Distributions were computed from every 100 s interval over 20 min of imaging. (iv) Step-size distributions were similar with the light on and off. Distributions were compiled using n = 4 independent inoculations.