FIGURE 3.

Mitogenic attractants improve the robustness of self-generated gradients to concentration, population and topological effects. (A) Ring-shaped wave of cells emerging from a 1 mm radius well in a 10 μM background of folate at 0 h (LHS) and 4 h (RHS). (B) Simulations of a small spot of cells allowed to freely migrate in an attractant background. With a simple (non-mitogenic) attractant, cells progress for a moderate distance, then stall as the circumference of the wave expands to a point where the influx of attractant requires more cells to degrade it than are present. In contrast, a mitogenic attractant (i.e., an attractant that stimulates population growth at high concentrations) causes population expansion exactly where it is needed, making the migration far more robust to the drawback of the initially small founder population. (C) Radial distance traveled by the leading cells across a range of concentrations for simple and mitogenic attractants. (D) Distance traveled in a 10 μM background by a linear wave of cells for simple (red) and mitogenic (black, dashed) attractants (compare with 2D- the red line is the same data in both panels). (E) Initial populations of 400 and 50 cells with a mitogenic attractant, compared against their counterparts with a simple attractant from Figure 2A.