Vertebrate endoderm development

Endoderm, one of the three principal germ layers, contributes to all organs of the alimentary tract. For simplicity, this review divides formation of endodermal organs into four fundamental steps: (a) formation of endoderm du ring gastrulation, (b) morphogenesis of a gut tube from a sheet of cells, ( c) budding of organ domains from the tube, and (d) differentiation of organ -specific cell types within the growing buds. We discuss possible mechanism s that regulate how undifferentiated endoderm becomes specified into a myri ad of cell types that populate the respiratory and gastrointestinal tracts.