Fig. 5: Schematic representation of the movement model.
a The extended motion model used in the simulator builds on the original three component model, contained in the dashed box, to simulate the influence of internal and external factors on cell movement. dtot is the maximum displacement for a defined time interval and is derived from dref, assumed to be the maximum potential displacement obtained for the same cell type under an “optimal” set of conditions; r, p and b indicate how much of dtot is necessary to produce the corresponding random, persistent and bias components. By modifying these parameters, a wide range of factors can influence cell displacement and its final position; examples are cell cycle phase, attachment state, level of vitality and of local confluence, the presence of physical constraints and “local” bias, like repulsion from neighbouring cell or attraction due to the presence of an attractant gradient in the plate. b Cell-cell repulsion gradient represented as colour shades corresponding to cell influence on the surrounding environment. For each cell, the repulsion vector is reported as a white arrow along the straight line between two neighbouring cells and whose module depends on gradient. The time interval between the first three images was 20’ intervals, while the others were taken at 10’ interval. c Effect of a relatively sharp attractant gradient on cell movement. For each cell, the bias vector is reported as an arrow whose module depends on the difference in attractant level over a distance corresponding to the size of the cell body. d Effect of dynamic self-generated local gradients on cell movement. The bias vector is reported as an arrow with a module which, as in c, depends on attractants level, which, in this case, is locally modified by the presence of cells able to degrade the attractant molecule in its immediately vicinity: higher cell concentration produces greater gradient than sparse cells. In both panels, a more intense blue indicates higher attractant level.
