Abstract 1034: Opposing Effects of Phosphatidyl Inositol-3 Kinase and ERK/MAP Kinase Signaling Pathways on Artery-Vein Specification.
Angioblasts are multipotent progenitor cells that give rise both arteries and veins. The precise biochemical signals within angioblasts that determine the artery-vein cell fate decision are poorly understood. The zebrafish is readily amenable to chemical genetic analysis, in which small molecules discovered by phenotype-based screens are used as tools for dissecting developmental processes. Genetic disruption of the zebrafish gridlock gene, required for arterial specification, results in generation of insufficient numbers of arterial cells. We have identified by chemical screening two classes of compounds that compensate for a mutation in the gridlock gene. Both target the VEGF signaling pathway and reveal two downstream branches emanating from the VEGF receptor with opposing effects on arterial specification. We show that the activation of ERK (p42/44 MAP kinase) is a specific marker of early arterial progenitors and is among the earliest known determinants of arterial specification. In the early embryo, cells fated to contribute to arteries express high levels of activated ERK, whereas cells fated to contribute to veins do not. Inhibiting the phosphatidylinositol-3 kinase (PI3-K) branch with GS4898 or known PI3-K inhibitors, or with mosaic expression of dominant negative form of AKT, a downstream mediator of PI3-K, promotes arterial specification. Conversely, inhibiting the ERK branch blocks arterial specification. In summary, chemical genetic analysis has uncovered unanticipated opposing roles of PI3-K and ERK in artery-vein specification. Moreover, small molecule suppressors of a genetic vascular defect, such as GS4898, may serve not only as useful tools for study of vascular development, but also as potential leads for treatments of vascular diseases.