XRASGRP2 is essential for blood vessel formation during Xenopus development

Ras guanyl nucleotide-releasing protein 2 (RASGRP2), one of the Ras guanine exchange factors, is implicated as a critical regulator of inside-out integrin activation in human lymphocytes, neutrophils and platelets. However, the activities of this protein in endothelial cells remain unclear. In the current study, we identify a physiological function in blood vessel formation for XRASGRP2, which is the Xenopus ortholog of mammalian RASGRP2. XRASGRP2 overexpression induced ectopic vascular formation, and XRASGRP2-knockdown embryos showed delayed vascular development. We also investigated the upstream signaling of XRASGRP2 in endothelium formation. XRASGRP2 expression was up-regulated in the presence of VEGF-A and down-regulated following VEGF-A depletion. XRASGRP2 knockdown abolished the ectopic induction of endothelial cells by VEGF-A in the posterior ventral blood island. These results suggest that XRASGRP2 is essential for vascular formation during Xenopus development.