How to make less webby webs

Forming a web of blood vessels requires both adventurous explorers and stable stay-at-homes. Notch, say two teams of researchers, helps endothelial cells to split up between these two fates. The explorers form new vessels even as the stay-at-homes maintain the integrity of existing vessels.

The explorers are called tip cells. Mats Hellström, Christer Betsholtz (Karolinska Institute, Stockholm, Sweden), Holger Gerhardt (Cancer Research UK, London) and colleagues found that inhibiting the Notch pathway in a mouse retina greatly increased the number of endothelial cells that had both tip cell markers and the tip cell habit of sprouting. The resulting webs of vessels were overly dense and disorganized; similarly Notch-inhibited and disorganized vessels were recently shown to be largely nonfunctional in mouse tumors.

Arndt Siekmann and Nathan Lawson (University of Massachusetts Medical School,...