Liver specification and early morphogenesis

The classically defined induction of the liver from the endoderm, elicited by the cardiac mesoderm, has recently been discovered to involve signaling by fibroblast growth factors (FGFs). Multiple FGFs induce hepatic gene expr ession independent of an effect on growth. A subset of these FGFs cooperate s with other factors to promote morphogenesis of the newly specified hepato cytes. Subsequent to the formation of the liver bud, distinct mesenchymal s ignals and hepatic response pathways stimulate further growth and different iation of the hepatic parenchymal cells and prevent apoptosis. The initial stases of hepatogenesis are therefore beginning to be understood, and serve as a paradigm for the development of other tissues from the endoderm. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.