Xenopus goosecoid: a gene expressed in the prechordal plate that has dorsalizing activity.

gsc is a homeobox gene expressed in the dorsal lip of the blastopore in Xenopus. Its mRNA can mimic many aspects of Spemann's organizer activity when microinjected into the ventral side of the embryo. In the present study we analyze gsc expression in late gastrula and neurula embryos of Xenopus. At these stages gsc is expressed in the prechordal plate, an anterior mesodermal structure underlying the forebrain. Furthermore, we studied the dorsalizing activity of gsc in animal caps and found that UV-sensitive cofactors in the marginal zone are required to induce dorso-anterior mesoderm in concert with gsc. FGF, an inducer of ventral mesoderm, cannot substitute for these factors.