The goals of this new project are to examine the mechanism by which the primary mouth of deuterostomes forms at the extreme anterior of the embryo. A particular emphasis is on evolutionary conservation, or lack of it, in determining this organ. The primary mouth is the initial opening from the gut of the embryo to the outside, allowing ingestion of food. In most deuterostome species, the primary mouth remains the mouth opening. In vertebrates, the neural crest grows around the primary mouth to form the face and a secondary mouth opening must therefore form. The primary mouth then becomes the pharyngeal opening. The region from which the primary mouth develops is unusual as here ectodermal and endodermal germ layers are directly juxtaposed. Both ectoderm and endoderm are required for primary mouth formation. The broad hypothesis of this proposal is that the mechanisms by which the primary mouth is determined are evolutionarily conserved. There are three specific aims. 1. Markers of the primary mouth region in Xenopus will be isolated. 2. Mechanisms of primary mouth determination in Xenopus will be examined, focusing on candidate transcription factors and signaling systems involved. 3. Comparison of the expression of selected Xenopus markers will be made with expression of homologs in another deuterostome, the zebrafish, Danio. The intellectual merit of this proposal will be the increased understanding of the mechanisms and evolution of primary mouth formation. This region is important and its development poorly understood. Part of the broad impact of the proposal is that it spans the fields of Developmental and Evolutionary Biology. It will allow investigators involved to work with more than one species, which is an unusual training opportunity. Further, this study is a wonderful teaching tool, that will allow graduate, undergraduate and high school students a hands-on opportunity to think about evolution, and to compare formation of distinct animals.
