XIRO, A XENOPUS HOMOLOG OF THE DROSOPHILA-IROQUOIS COMPLEX GENES, CONTROLS DEVELOPMENT AT THE NEURAL PLATE

The Drosophila homeoproteins Ara and Caup are members of a combination of factors (prepattern) that control the highly localized expression of the proneural genes achaete and scute, We have identified two Xenop us homologs of ara and caup, Xiro1 and Xiro2. Similarly to their Droso phila counterparts, they control the expression of proneural genes and , probably as a consequence, the size of the neural plate. Moreover, X iro1 and Xiro2 are themselves controlled by noggin and retinoic acid a nd, similarly to ara and caup, they are overexpressed by expression in Xenopus embryos of the Drosophila cubitus interruptus gene. These and other findings suggest the conservation of at least part of the genet ic cascade that regulates proneural genes, and the existence in verteb rates of a prepattern of factors important to control the differentiat ion of the neural plate.