Dll4 assembles the umbilical cord and placental vasculature.

Proper development of the umbilical cord and placental vasculature is essential for embryonic development. While the allantois is known give rise to endothelial cells (ECs) within the placenta, whether the allantois gives rise to ECs in the umbilical cord is debated. Furthermore, a lack of genetic tools to study placental vascular development independent of the embryo proper has hindered robust investigation into the primary cause of vascular defects from early studies utilizing global KOs. In this study, we delineate the contribution of the allantois to the umbilical vessels and utilize a mouse genetic tool previously developed by our lab to revisit the role of Notch signaling during placental development. We show that the allantois has mosaic contribution to the umbilical endothelium with higher contributions closer to the placenta. Allantoic deletion of Dll4 disrupts umbilical cord and placental vascular formation with secondary defects in the heart. Lastly, we identify Unc5b downstream of Notch signaling that restricts EC migration while promoting chemokine signaling for vascular smooth muscle cell (vSMC) recruitment to arteries. These findings identify a genetic tool for investigating placental vascular development and give insights into the ontogeny and mechanisms of placental vascular and umbilical cord development.