Amphibian intestinal transformation related to metamorphosis and evolution

Metamorphosis of anuran amphibians is correlated with a change of feeding behaviour and intestinal transformations (such as epithelial renewal) involving histolytic and histogenetic phenomena. Epithelium substitution coincides with biochemical maturation and qualitative and quantitative changes in gene expression, triggered by thyroid hormones. Additionally, specific activities of several hydrolytic enzymes increase. The assembly of a new brush border also takes place, after synthesis of microvillar core proteins such as villin, a precocious marker for differentiating enterocytes. This intestinal evolution is compared with intestinal transformations in other vertebrates, especially during agnathans metamorphosis, hatching birds and mammalian birth.