The objective of this project is to determine the mechanism(s) and temporal sequence involved in the commitment of cardiac neural crest cells to mesenchymal, neuronal and non-neuronal cell lines which are essential for normal development of the heart. It is proposed that the decisions made by the cardiac neural crest cells are analogous to those made in the neurogenic region of invertebrate embryos where specific sets of proneural genes are expressed to control the determination of cell lineage. One of the proneural genes of the achaete-scute complex (T3), will be investigated. This gene has been well-characterized in Drosophila and a potential homologues have been identified in chick (CASH-1, C-Notch). The present experiments will characterize the avian homologue of this genes and determine whether it has a role in establishing cell lineage in the cardiac neural crest. Avian cDNA clones will be obtained and characterized. The chick clones and monoclonal antibodies, generated to various regions of the protein products will be used to determine when these genes are expressed in the cardiac neural crest using Northern analysis, in situ hybridization, and immunohistochemistry. Expression of the genes in the cardiac neural crest will be altered in vitro and in vivo. The defects caused by modified expression of the genes will be correlated with a quantitative assessment of cardiac neural crest derivatives. Understanding these molecular events will provide a rationale for testing possible genetic and environmental causes of congenital cardiovascular diseases.