Making a move: EMT holds the key to planarian regeneration

During development and wound healing, progenitor cells are required to migrate to different locations before they can differentiate into terminal tissue types. This cell migration often involves epithelial-to-mesenchymal transition (EMT), a process by which cells delaminate from an epithelium and become motile. On page 3440, Aziz Aboobaker and colleagues investigate how neoblasts, the adult stem cell population present in planarians, are able to migrate to sites of damage in order to regenerate tissue after irradiation. Using a shielded X-ray irradiation assay, they show that neoblasts require β-integrin and the activity of a matrix metalloproteinase to interact with the extracellular matrix and move through the tissue, just as in EMT. In addition, they show that migration requires EMT-associated transcription factor orthologs, such as snail-1, snail-2 and zeb-1. Strikingly, the differentiation status of cells also affects their ability to migrate. Finally the authors report that, even in the absence of wounding, a notum-dependent signal from the brain, which normally lacks resident stem cells, draws in migrating neoblasts to maintain tissue homeostasis. Together, these results suggest that EMT-related mechanisms controlling cell migration are conserved among bilaterians and provide insights into how progenitor populations move to a site of wounding before regeneration begins.