Schematic of vascular pruning.

(A) Initial selection of a vessel with low wall shear stress, . (B) The endothelial cells from the pruning branch polarise and migrate up the wall shear stress gradient and against flow towards the neighbouring vessel, as shown by the black arrows. (C) The endothelial cells of the pruning branch are incorporated into the neighbouring vessel, leaving an empty basement sleeve in place of the pruning vessel. The coloured arrows indicate the direction and the intensity of blood flow, with arterial flow shown in red, and venous flow shown in blue. The endothelial cell nuclei and the Golgi apparatus in within each cell are yellow and red, respectively, showing the endothelial cell polarisation against the flow. Figure adapted with permissions from Santamaría and colleagues [12].