Regulation of pepsinogen gene expression in epithelial cells of vertebrate stomach during development

Pepsinogens are zymogens of pepsins, aspartic proteases working as digestive enzymes in the vertebrate stomach, of which biological and molecular properties have been extensively studied. In developmental biology, pepsinogens offer excellent molecular markers of differentiation of stomach epithelial cells, since their expression is strictly limited to those cells and there are some isozymes that are expressed in developmental stage-specific manner. It is now well established that the expression of embryonic chicken pepsinogen (ECPg) gene is regulated by epithelial-mesenchymal interactions: it is mesenchyme that determines the expression pattern of ECPg along the digestive tract, by supporting or inhibiting the intrinsically endowed ability of epithelial cells to express it. In the present review article, I will describe recent molecular biological and experimental embryological consequences of our studies on the regulation of ECPg expression by mesenchymal cells, with special attention to the nature of mesenchymal factors and the molecular mechanisms of reactivity of epithelial cells to the mesenchymal influences.