Figure 1.

(A) Geometry of the model domain. A source of VEGF (e.g., a tumor) is situated at x = 1. VEGF diffuses toward a parent vessel located at x = 0, and is taken up by endothelial cells lining it. The activated cells migrate up gradients of VEGF, elongating behind them capillaries. (B–D) Motion of a cell on a 2-d lattice in response to VEGF stimulus. The cell begins at position (n, m) in (B). VEGF molecules are shown in red. The number of activated VEGF-receptors is greatest on the cell surface at lattice site (n + 1/2, m), and the probability of motion in this direction is the greatest. Consequently, the cell is likely to move from site (n, m) to (n + 2, m), as shown in (C,D).