Endothelial cell-specific chemotaxis receptor (ECSCR) is a cell surface protein expressed by blood endothelial cells with roles in endothelial cell migration and signal transduction. We investigated the function of ecscr in the development of the zebrafish vasculature. Zebrafish ecscr is expressed in angioblasts and in axial vessels during angioblast migration and vasculogenesis. Morpholino-directed ecscr knockdown resulted in defective angioblast migration in the posterior lateral plate mesoderm, a process known to depend on vascular endothelial-derived growth factor (VEGF). In cultured cells, transfected ECSCR localized to actin-rich membrane protrusions, colocalizing with kinase insert domain protein receptor (KDR)/VEGF receptor 2 in these regions. ECSCR-silenced cells show reduced VEGF-induced phosphorylation of KDR but not of FMS-like tyrosine kinase 1 (FLT1)/VEGF receptor 1. Finally, chemical inhibition of VEGF receptor activity in zebrafish resulted in angioblast deficiencies that partially overlap with those seen in ecscr morphants. We propose that ecscr promotes migration of zebrafish angioblasts by enhancing endothelial kdr sensitivity to VEGF.

BackgroundVasculogenesis, the de novo formation of blood vessels from precursor cells is critical for a developing embryo. However, the signals and events that dictate the formation of primary axial vessels remain poorly understood.Methodology/Principal FindingsIn this study, we use ets-related protein-1 (etsrp), which is essential for vascular development, to analyze the early stages of vasculogenesis in zebrafish. We found etsrp + cells of the head, trunk and tail follow distinct developmental sequences. Using a combination of genetic, molecular and chemical approaches, we demonstrate that fli + etsrp + hemato-vascular progenitors (FEVPs) are proliferating at the lateral plate mesoderm (LPM). The Shh-VEGF-Notch-Hey2 signaling pathway controls the proliferation process, and experimental modulation of single components of this pathway alters etsrp + cell numbers at the LPM.Conclusions/SignificanceThis study for the first time defines factors controlling proliferation, and cell numbers of pre-migratory FEVPs in zebrafish.