INDUCTION OF ECTOPIC ENGRAILED EXPRESSION AND FATE CHANGE IN AVIAN RHOMBOMERES - INTERSEGMENTAL BOUNDARIES AS BARRIERS

We tested the possibility of inducing ectopic expression of the gene E ngrailed-2 (En-2) in the rhombomeres of the 2-days-old chick embryo. T he experimental procedure consisted of grafting En-2-expressing neuroe pithelium (prospective isthmocerebellum) from a quail or a mouse embry o into different rostrocaudal levels in the hindbrain of a host chick embryo. The graft replaced a given excised host rhombomere, the rostra l and caudal limits of which were either also excised or left intact i n different experiments. Induction of En-2 occurred in the host hindbr ain, but only when the graft did not contact with host interrhombomeri c boundaries and only in the alar plate of the rhombomeres immediately contacting the graft. Long survival experimental embryos showed that induced rhombomeres give rise to a cerebellar phenotype in their trans formed alar plates. We thus demonstrate here a pluripotential state of the early rhombomeres as well as a possible role of the interrhombome ric limits as barriers to morphogenetic influences.