Loss of progenitor cells or a crypt can be regenerated through Wnt signaling. (A) At T = 0, one half of progenitor cells in Crypt I are removed from the wild-type steady crypt (T = 100 in Figure 2A). With the regulation of Wnt signaling, progenitor cells in Crypt I start to repopulate (T = 10). Eventually, the original pattern of progenitor cells in Crypt I is regenerated (T = 100). (B) The maximal density of progenitor cells in Crypt I (blue dash line) and Crypt II (red solid line) as functions of time. Cell velocity, V, (C) and progenitor cell flux, VC0, (D) are plotted at the time T = 0 (blue dash curve), T = 10 (black dot curve), and T = 100 (red solid curve).