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 Xemx2 genes in Xenopus laevis. Xemx genes are the homologues of mouse Emr g enes, related to Drosophila empty spiracles. They are expressed in sel ected regions of the developing brain, particularly in the telencephal on, 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 f or their activation in competent ectoderm. Xemx genes are activated in ectoderm conjugated with head organizer tissue, but not with tail org anizer tissue. Furthermore, they are not activated in animal caps eith er by noggin or by Xnr3, thus suggesting that a different inducer or t he integration of several signals may be responsible for their activat ion. (C) 1998 Elsevier Science Ireland Ltd.