Mesenchyme-dependent differentiation of epithelial progenitor cells in the gut.

The digestive tract and the gut as a paradigm represents an attractive system for the study of mechanisms involved in the differentiation of two types of progenitor cells: the endodermal cells during embryonic life and the undifferentiated crypt cells during epithelial renewal of the adult intestine. The morphological and functional events that accompany the differentiation processes of progenitor cells into the polarized epithelial cell types characteristic of the intestine appear comparable in both situations (1,2). During organogenesis of the gut, histological observations underlined a close relationship between epithelial cells and their underlying mesenchymal cells (3,4). Developmental biologists have emphasized experimentally the importance of interactions between the endoderm and mesenchyme during organogenesis of the digestive tract. In the adult intestine, gastroenterologists have focused their attention on a specialized mesenchymal cell type (the pericryptal fibroblasts) that displays, like epithelial cells, proliferative activities and migrating properties. The aim of this review is to provide current knowledge on epithelial-mesenchymal interactions during ontogenesis of the digestive tract and also to relate some experiments supporting the view of the perpetuation of epithelial-mesenchymal interactions beyond embryonic life.