The Role Of Vascular Endothelial Growth Factor - C In Developmental Hematopoiesis

Hematopoietic stem and progenitor cells (HSPCs) are multipotent cells that self-renew or differentiate to establish and replenish the entire blood hierarchy. HSPCs arise from the hemogenic endothelium of the dorsal aorta (DA) in the embryo. We use zebrafish to study endothelial-to-hematopoietic transition (EHT) because the embryos are transparent and develop externally, allowing direct observation of in vivo cellular events. My long-term goal is to identify factors that impact HSPC differentiation during EHT. One candidate, VEGFC, is expressed in the DA and specifically in long-term HSPCs of both mouse and zebrafish. VEGFC has been shown to play a role in fetal liver erythropoiesis, but its developmental role in definitive hematopoiesis has not been explored. I hypothesize that VEGFC maintains HSPC identity by negatively regulating alternative hemogenic endothelium fates. Preliminarily, we have shown in zebrafish that morpholino knock-down of vegfc results in decreased HSPC emergence and altered cell behavior during EHT. During the peak of HSPC emergence from the DA, vegfc knock-down embryos show decreased HSPC emergence, this lack of HSPCs persists into lymphoid development in the thymus. HSPCs in vegfc knock-down embryos also display altered cell behavior, they crawl similar to myeloid cells, instead of the typical and well described budding from the DA. vegfc knock-down embryos and genetic mutants also show an increase in myeloid cells in the caudal hematopoietic tissue (CHT), the zebrafish equivalent of the mammalian fetal liver. We plan to further investigate the role of VEGFC in a mammalian system using human pluripotent stem cell differentiation protocols and aorta-gonad mesonephros explants. We hope to use the results of this research to improve our ability to create HSPCs in vitro to be used in clinical stem cell transplants.