VEGF-induced vessel sprouting and macrophage-mediated anastomosis act synergistically to promote vascular network formation. (A-F) Morphology of the SVP (IB4-positive, red) and distribution of tissue macrophages (IB4/F4/80-double positive, yellow) in 11.5 dpc hindbrains of the indicated genotypes; arrows in panel D indicate macrophages interacting with endothelial tip cells in Vegfa120/120 mutants; arrowheads in panels D through F denote examples of bulbous vessel ends, typical of Vegfa120/120 mutants. Scale bar represents 100 μm. (G) Quantitation of the number of vascular intersections in the SZ of the indicated genotypes at 11.5 dpc; n > 3. Error bars represent SD of the mean. (H) Schematic illustration of the role of macrophages during hindbrain vascularization.
