Notochord patterning of the endoderm

Endodermally derived organs of the gastrointestinal and respiratory system form at distinct anterioposterior and dorsoventral locations along the vert ebrate body axis. This stereotyped program of organ formation depends on th e correct patterning of the endodermal epithelium so that organ differentia tion and morphogenesis occur at appropriate positions along the gut tube. W hereas some initial patterning of the endoderm is known to occur early, dur ing germ-layer formation and gastrulation, later signaling events, originat ing from a number of adjacent tissue layers, are essential for the developm ent of endodermal organs. Previous studies have shown that signals arising from the notochord are important for patterning of the ectodermally derived floor plate of the neural tube and the mesodermally derived somites. This review will discuss recent evidence indicating that signals arising from th e notochord also play a role in regulating endoderm development. (C) 2001 A cademic Press.