D. Förderung des wissenschaftlichen Nachwuchses

Within an epithelial cell monolayer, cellular division causes the overall cell
density to increase until the monolayer reaches a certain ‘homeostatic’ density;
following which, a Feedback loop balances the rates of cell division and cell death
such that this homeostatic density is maintained and cells stay jammed with very
little movement. Interestingly, the same cells unjam and perform collective migra-
tion to long distances in response to a trauma such as a wound. We acquired phase
contrast images of the epithelial cells as they packed over time (Fig la, left panel)
and used particle image velocimetry to obtain the velocity profile of the cells; this
revealed that movement is much higher at lower density (Fig la, right panel). Since
an effective wound healing response requires collective mobility, at first thought


Figure 1. Would healing performance of cell cultures at different densities. (a) Representative phase contrast Ima-
ges of an epithelial cell monolayer at different time points marking low density (top panel) and homeostatic density
(bottom panel) and corresponding velocity profies obtainedfrom PIV analysis. These show higher movement
velocities at low density. Scale bar = 100 pm. (b) and (c) Velocity correlation length analysis at low density and
homeostatic density dnring migration, showing (b) velocity correlation (scale bar =100 pm), and (c) number
of coordinated cells. (d) Representative phase contrast images dnring wound closure at T3h (top panel) and T8h
(bottom panel) for monolayers wounded at low density (left panel) and at homeostatic density (right panel) (e)
Tracks ofleader cells (orange) andfollower cells (green) at low density (top panel) and at homeostatic density
(bottom panel) showing cells at homeostatic density migrate muchfurther into the wound.

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