Figure 1

Correlation between mouse intestinal maturation (upper panel) and Xenopus laevis metamorphic intestinal remodeling (lower panel). In both species, the adult stem cells are formed from the preexisting epithelial cells when the plasma thyroid hormone (TH) levels become high. In mouse, all epithelial cells in the fetal intestine express Blimp1 (yellow cells) and during postnatal maturation, some Blimp1 positive embryonic/fetal intestinal stem cells (yellow cells with irregular-shaped dark nuclei) in the intervillus pockets loose their Blimp1 expression and develop into adult stem cells expressing PRMT1 and hedgehog (hh) (green cells with irregular-shaped dark nuclei). In Xenopus, there are no identifiable stem cells for the tadpole intestinal epithelium (yellow cells) and the differentiated larval epithelial cells are mitotically active for self-renewal. During metamorphosis, most of the larval epithelial cells undergo apoptosis, whereas some undergo dedifferentiation to become the adult stem cells/progenitors that express high levels of PRMT1 and Shh (green cells with irregular-shaped dark nuclei). Subsequently, the descendants of these adult stem cells in both mouse and Xenopus replace the suckling-type or larval-type epithelial cells via active proliferation and differentiation to generate the adult epithelium possessing a cell-renewal system (green cells). These similarities between the both models predict evolutionary conserved TH-dependent mechanisms underlying development of the adult stem cells.