AMPHIBIAN INTESTINAL TRANSFORMATION RELAT ED TO METAMORPHOSIS AND EVOLUTION

Metamorphosis of anuran amphibians is correlated with a change of feed ing behaviour and intestinal transformations (such as epithelial renew al) involving histolytic and histogenetic phenomena. Epithelium substi tution coincides with biochemical maturation and qualitative and quant itative changes in gene expression, triggered by thyroid hormones. Add itionally, 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 d ifferentiating enterocytes. This intestinal evolution is compared with intestinal transformations in other vertebrates, especially during ag nathans metamorphosis, hatching birds and mammalian birth.