Figure 6.

Schematic dorsal views of the Xenopus embryo at late gastrula stage. (Upper) Drawing shows the dorsal mesoderm divided into the developing notochord and the prechordal plate (future head mesoderm); these two regions correspond to the head and trunk organizer identified in classical transplantation experiments. The expression domain of Xlim-1 encompasses the entire dorsal mesoderm at this stage whereas Xbra is expressed only in the notochord (Lower). These expression domains may define the head and trunk organizer, as further discussed in the text.