At the beginning of gastrulation the homeobox-containing gene, XANF-1, is expressed at a low level throughout the animal hemisphere of Xenopus laevis embryos, with a local maximum of expression in the region of the dorsal blastopore lip. By the end of gastrulation expression ceases everywhere except in the most anterior part of the neurectoderm. We have investigated the functions of this gene by microinjecting XANF-1 mRNA in the blastomeres of the 32-cell stage embryo and have observed the following effects. First, microinjections of the mRNA in the animal blastomeres and the blastomeres of the marginal zone elicited massive migration of cells to the interior of the embryo at the early gastrula stage. Second, overexpression of XANF-1 in the ventral marginal zone (VMZ) resulted in the appearance of an additional centre of gastrulation movements and the formation of a secondary axis. In addition we showed that synthetic XANF-1 mRNA was able to cause dorsal-type differentiation in VMZ explants extirpated from the microinjected embryos at the beginning of gastrulation. These results suggest that XANF-1 may control the main functions of cells of the Spemann organizer.

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