Epithelial branching: the power of self-loathing

Branching morphogenesis of epithelia is an important mechanism in mammalian development. The last decade has seen the identification of many signalling pathways and intracellular mechanisms that control epithelial branching. Tissue-level mechanisms that space new branches out have, however, remained an unsolved problem. A recent publication by Nelson et al.1 suggests--if extrapolation from their novel and abstract culture system is valid--that branches may be spaced out by a system of mutual inhibition based on diffusion of TGFbeta. Such a system would allow a developing tree to arrange itself, without detailed genetic specification, by adaptive self-organization.