Fig. 1.

Vessel fusion contributes to engaging the vessel diameter. a Vessel fusion in the cultured mouse embryo. Blood enters the vascular plexus through the vitelline artery to the distal capillaries and is ultimately collected by the vitelline vein at E8.5. Vessel fusion (marked with circles) occurs in the proximal vessels that are exposed to high blood flow, resulting in a rapid change in vessel diameter. Vessel hierarchy is established through vessel fusion by E9.0–9.5, resulting in different flow velocity distributions in arteries, capillaries and veins. b Vessel fusion is mediated by the redistribution of ECs. Figure a adapted from Ryan et al. [6]