The S1P effect on blood vessel formation was attributed to it promoting migratory activities of angioblasts and early endothelial cells required for the expansion of vascular networks. ![]() The ability of S1P to promote blood vessel formation was not due to effects on cell survival or on changes in numbers of endothelial cells (Flk1 +/PECAM +), angioblasts (Flk1 +/PECAM -), or undifferentiated mesodermal cells (Flk1 -/PECAM -). These effects could not be reproduced by vascular endothelial growth factor or basic fibroblast growth factor administration. Instead of small poorly reticulated clusters of rounded endothelial cells that formed under serum-free conditions, S1P promoted the formation of elongated endothelial cells that arranged into expansive branched networks of capillary-like vessels. We showed that S1P could replace the ability of serum to promote vasculogenesis in cultured allantois explants. Using the cultured mouse allantois explant model of blood vessel formation, we found that vasculogenesis was dependent on S1P signaling. Additionally, sphingosine kinase-2 (SK2), an enzyme that catalyzes the formation of S1P, is expressed in these tissues throughout periods of vasculogenesis. ![]() ![]() At stages preceding the formation of blood vessels (7.5–8 dpc) in the embryo proper, yolk sac, and allantois, the S1P receptor S1P 2 is expressed in conjunction with S1P 1 and/or S1P 3. Here we have investigated the role of sphingosine-1-phosphate (S1P) signaling in the process of vasculogenesis in the mouse embryo.
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