eLife assessment
This study provides important, detailed insights into the early stages of angiogenesis and points towards a novel mechanism that could be used to control the density and location of developing blood vessels. Convincing experimental methods, analysis techniques, and mathematical modeling are used to systematically support the findings. This study of the mechanisms by which paracrine and juxtacrine cues control the formation of new blood vessels will be of broad interest to colleagues studying angiogenesis and blood vessel formation.