Making tubes: step by step.

Branched hollow tubes form the architectural basis of many mammalian organs. The growth factor HGF/SF and its receptor, the Met receptor tyrosine kinase, stimulate epithelial cells to undergo tubulogenesis in vitro. In this issue of Developmental Cell, O'Brien et al. (2004) look at temporal regulation and the role of two HGF/SF effectors, the ERK 1/2 MAP kinases and matrix metalloproteases, in this process.