Two Distinct Modes of Signaling by Vascular Endothelial Growth Factor C Guide Blood and Lymphatic Vessel Patterning in Zebrafish: A Dissertation

Vascular Endothelial Growth Factor Receptor-3 (VEGFR3/Flt4) and its ligand Vegfc are necessary for development of both blood and lymphatic vasculature in vertebrates. In zebrafish, Vegfc/Flt4 signaling is essential for formation of arteries, veins, and lymphatic vessels. Interestingly, Flt4 appears to utilize distinct signaling pathways during the development of each of these vessels. To identify components of this pathway, we performed a transgenic haploid genetic screen in zebrafish that express EGFP under the control of a blood vessel specific promoter. As a result, we indentified a mutant allele of vascular endothelial growth factor c (vegfc), vegfcum18. vegfcum18 mutants display defects in vein and lymphatic vessel development but normal segmental artery (SeA) formation. Characterization of this allele led to the finding that the primary defect in vegfcum18 mutants was a general failure in vein and lymphatic vessel sprouting. Further genetic and biochemical analysis of this mutant revealed profound paracrine defects, which likely result in the observed loss of lymphatic and venous structures. Furthermore, double mutant analysis demonstrated that defects during SeA formation in vegfcum18 mutants were masked by inputs from the Vegfa signaling pathway. Endothelial cell autonomous expression of vegfcum18 induced angiogenic effects on blood vessels while endothelial cells lacking vegfc displayed defects in tip cell occupancy, suggesting a cell autonomous-autocrine role for Vegfc during developmental angiogenesis. Finally, we present genetic evidence that links processing of Vegfc by Furin during the formation of lymphatics in zebrafish. Together the data presented here suggest two discrete modes of signaling during blood and lymphatic vessel development, thus implying that regulation of Vegfc secretion and processing may play a pivotal role in the formation of these distinct vessel types in zebrafish