Fig. 7. Computer modeling demonstrates the mitogen gradient model can robustly pattern growth. (a) Diagram of the computer simulation of the mitogen gradient model. The proliferation rates and differentiation rates of a one-dimensional row of precursors are regulated by their distance from the growth organizer according to a linear function set by the user. Precursors are pushed ventrally away from the growth organizer when they divide. (b) To show the emergence of the growth zone, the state of cells in the model after every 30 iterations for the first 1020 iterations is shown. The squiggly line indicates where additional cells in the simulation are not shown. The growth zone is a robust and dynamically stable region whose size and shape is controlled by the proliferation and differentiation rate gradients and is independent of the starting number of precursors. (c) The mitogen gradient model can pattern cell cycle divisions and exits across a field of cells as seen in a chart of the total number of divisions and exits at each distance from the growth organizer after 1500 iterations of the simulation. The mitogen gradient model can also generate a constant rate of outgrowth and a constant supply of differentiated cells along an outgrowing structure. (d) The total length of the field of cells, including precursors and post-mitotic cells, at the end of every 30 iterations is shown. The total length of the field of cells increase roughly linearly with time.