Defining the mechanism by which Sema-PlxnD1 signaling regulates angiogenesis in the zebrafish segmental artery.

Defining the mechanism by which Sema-PlxnD1 signaling regulates angiogenesis in the zebrafish segmental artery By: Carl Gay Advisor: Jesus Torres-Vazquez The cardiovascular system is responsible for vital processes ranging from providing essential developmental cues for the developing embryo to the delivery of gases and nutrients critical for the survival of the adult. Furthermore, abnormalities in the cardiovascular system are directly or indirectly responsible for some of the most significant causes of human morbidity and mortality, including cancer, heart disease, diabetes and cerebrovascular accident. The vascular system develops and reorganizes by two basic processes, vasculogenesis, wherein new blood vessels develop de novo from precursor cells, and angiogenesis, wherein blood vessels emerge via the sprouting of endothelial cells from pre-existing vessels. Focusing our attention on the process of angiogenesis, we build upon previous reports showing that stimulatory VEGF and inhibitory Notch signals are predominantly responsible for the regulation of this highly stereotypical process in the developing zebrafish trunk. We identify the Sema-PlxnD1 pathway, previously implicated in endothelial cell migration, as a key regulator of angiogenesis prior to and after sprouting of the zebrafish segmental artery. Furthermore, we identify a novel mechanism by which Sema-PlxnD1 opposes pro-angiogenic VEGF signaling by promoting the abundance of the VEGF decoy sFlt1. In doing so, Sema-PlxnD1 signaling is able to spatially regulate levels of VEGF activity and restrict sprouting angiogenesis to reproducible locales. We also identify another known modulator of VEGF signaling, the scaffolding protein GIPC1, as both required for segmental artery angiogenesis and, potentially, as the first physical interactor of PlxnD1's intracellular domain in vivo. Along with our data regarding sFlt1, this provides an additional mechanism by which Sema-PlxnD1 and VEGF signaling may communicate to regulate sprouting angiogenesis.