Blood vessel formation is important during the progression of numerous human diseases, including cancer and diabetes. Recent evidence indicates that proper specification of the endothelial cells that line arteries and veins is required for blood vessel formation. A better understanding of the signals that govern this process will aid in therapeutic manipulation of pathological blood vessel growth in a clinical setting. We have used the zebrafish to identify signals that specifically govern artery development. In this proposal, we will draw on our previous screening experience using transgenic zebrafish with fluorescently labeled blood vessels to perform an F3 screen to identify mutants that affect embryonic artery development. This will be accomplished by identifying mutant vascular morphology phenotypes that we have found associated with loss of artery identity. Subsequently, we will characterize and document visual morphology in mutants that affect artery development. The ability to easily visualize both vascular and non-vascular defects in transgenic embryos will allow documentation of phenotypes and facilitate identification of complementation groups. Finally, we will determine arterial endothelial cell differentiation in artery mutants ana perform preliminary linkage mapping. We will analyze expression of artery and vein specific markers in mutants to distinguish defects in artery morphogenesis and differentiation. The combination of morphologic and molecular characterization will allow us to prioritize mutants of interest and determine which will be analyzed by bulk segregant linkage mapping to identify possible candidate genes. Since these mutants will provide a valuable resource to the zebrafish community, all phenotypic information and the lines themselves will be made available to researchers. Together, these studies will allow identification of genes that are required for proper artery and vein development and will represent putative targets for therapeutic manipulation.