THE EVOLUTION OF VERTEBRATE GASTRULATION

The availability of molecular markers now permits the analysis of the common elements of vertebrate gastrulation, While gastrulation appears to be very diverse in the vertebrates, by analyzing a head-organizer marker, goosecoid, and a marker common to all forming mesoderm, Brachy ury, we attempt to identify homologous structures and equivalent stage s in Xenopus, zebrafish, chick and mouse gastrulation, Using a tail-or ganizer marker, Xnot-2, we also discuss how the late stages of gastrul ation lead to the formation of the postanal tail, a structure characte ristic of the chordates.