Figure 2

A model for T3 actions for the metamorphic transformation of Xenopus laevis intestine. During metamorphosis, T3 acts directly (1) on the larval epithelium as well as (2) on the rest of the intestine (the non-epithelium), mostly the connective tissue. Most of the larval epithelial cells are induced to undergo programmed cell death by either one of the two T3 actions: T3-induced cell autonomous apoptosis vs. apoptosis induced by ECM remodeling and cell-cell interaction due to T3 action in the non-epithelium. On the other hand, a small number of cells within the larval epithelium undergo dedifferentiation upon receiving the T3 signal. However, T3 action in these cells alone cannot induce the formation of adult stem cells, unless T3 action in the non-epithelium is also present. This suggests that T3-induced tissue interactions are required for the establishment of the stem cell niche, via ECM remodeling and cell-cell interaction, to enable the dedifferentiated epithelial cells to become stem cells. See [100] for details.