The Xenopus Emx genes identify presumptive dorsal telencephalon and are induced by head organizer signals

We have isolated and studied the expression pattern of Xemx1 and Xerox2 genes in Xenopus laevis. Xemx genes are the homologues of mouse Emx genes, related to Drosophila empty spiracles. They are expressed in selected regions of the developing brain, particularly in the telencephalon, and, outside the brain, in the otic vesicles, olfactory placodes, visceral arches and the developing excretory system. We also report on experiments concerning the tissue and molecular signals responsible for their activation in competent ectoderm. Xerox genes are activated in ectoderm conjugated with head organizer tissue, but not with tail organizer tissue. Furthermore, they are not activated in animal caps either by noggin or by Xnr3, thus suggesting that a different inducer or the integration of several signals may be responsible for their activation.