VEGF directs newly gastrulated mesoderm to the endothelial lineage.

Herein, we investigated the role of VEGF signaling in the earliest events in vasculogenesis and found that it exerts critical effects shortly after mesodermal cells form by gastrulation. We showed that VEGF treatment of embryos caused an increase in the population of newly gastrulated mesodermal (NGM) cells that express the transcription factor TAL1. This increase in TAL1-positive cells was attributed to VEGF induction of VEGF receptor-2 (Flk1)-positive NGM cells that would normally not have been induced due to the limited availability of VEGF in the NGM.