Homeobox genes in vertebrate gastrulation.

The formation and anteroposterior patterning of the three definitive germ layers, ectoderm, or epiblast, is the common theme of vertebrate gastrulation. What changes from system to system is the geometry of these events and the nature of the non-epiblast transient structures implicated. A number of molecular markers, including a few homeobox genes and in particular goosecoid and Otx2, are now available that will hopefully allow us to explore the underlying molecular mechanisms and to establish biologically relevant homologies between the various systems.