Intestinal epithelium during homeostasis and regeneration. Homeostatic renewal of the intestinal epithelium is maintained by the actively cycling crypt base-resident Lgr5 ISCs. These cells first generate transit amplifying (TA) cells, which continue moving up and differentiate into all cell types. Tissue injury results in the loss of Lgr5 cells and triggers the regeneration process to repair the epithelium. The differentiating progenitor cells in the crypt middle region gain Ascl2 expression, dedifferentiate and move to the base niche where they revert back to the Lgr5 stem cell state
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