Intercellular signaling plays a critical role in patterning embryonic development and in the regulation of cell proliferation and survival in embryos and adults. By temporally and spatially combining signals from different signaling pathways, organisms gain the ability to produce complex cellular decisions through the activation of target genes that respond to multiple signaling factors. How these combinatorial signals are used at the molecular and cellular level is for the most part not well understood. The central question of this proposal is: how do Bmps and Wnts work together to establish genetic hierarchies leading to the formation of the posterior mesoderm and neural crest? To examine this, three avenues will be pursued using zebrafish as a model system. (1) Transgenic zebrafish expressing Bmp and Wnt/B-catenin activators and inhibitors under heat shock control will be used to determine when and how these signals are used to regulate the formation of the posterior mesoderm and neural crest throughout development. (2) The promoters of several key target genes responding to Bmp and Wnt/B-catenin signals will be analyzed in order to understand how these signaling pathways are ultimately integrated at the transcriptional level. (3) Microarray and subtractive screens will be used to identify genes that are regulated by both Bmp and Wnt/B-catenin signals using zebrafish mutants that have defects in the Bmp and Wnt signaling pathways. A critically chosen subset of these genes, which are expressed in the posterior mesoderm and neural crest, will be selected for further study using a combination of the transgenic fish expressing inducible Bmp and Wnt activators and inhibitors, overexpression studies and morpholino antisense oligonucleotides. Finally, this analysis will provide a molecular framework for understanding how combinatorial Bmp and Wnt signals lead to the formation of specific tissues within the embryo. Since both Bmp and Wnt signaling are involved in disease processes in humans, and since these signaling pathways are highly conserved, this research will have direct relevance to understanding mechanisms of human disease.
