FIGURE 4.

Effects of boundary and initial conditions on morphogen gradients for Pe = 0.25. (A) Cell-secreted protease distribution assuming a constant surface concentration (top row) and corresponding ECM-released morphogen distribution (bottom row) serve as a control for evaluating effects of changing boundary conditions. Dark red, 1 (maximum concentration); dark blue, 0. (B) The constant surface flux protease condition resulted in a slightly altered cell-released protease distribution (top row) when compared to the constant concentration boundary case (A); however, the dimensionless ECM-released morphogen profiles shown on the bottom row appear nearly identical. (C) Protease distribution of A, with the resulting ECM-released morphogen profile calculated assuming that the ECM-bound morphogen was nonuniformly distributed. The ECM-released morphogen gradient (bottom row) shares the same qualitative shape as for the previous two conditions. (D) Dimensionless ECM-released concentration profiles along the bisecting midline of the three cases shown in A–C are similar.