Spatial distributions of progenitor cells in a growing domain. (A) Crypt dynamics of progenitor cell density at three different times. A small amount of progenitor cells (C0 = 0.1) is initially placed in the center of the domain (1/10 of the length of the entire domain). The solution is close to the steady state at T = 100. (B) Comparison of the progenitor cell density along the crypt direction s in the fixed domain (blue dash curve) and the growing domain (red solid curve). (C) Time evolution of the progenitor cells in single crypt starting with three different initial levels of progenitor cells. The progenitor cells are initially placed at the center of the domain with C0 = 0.1, 0.5, and 1.0. Parameters in the simulations are listed in Additional file 1: Table S2.