The movement of continuous sheets of epithelial cells occurs during embryonic development and tissue repair. It is generally assumed that active movement of the cells at the leading edge of a migrating cell sheet pulls the rest of the sheet along in a somewhat passive manner. Rizwan Farooqui and Gabriel Fenteany overturn this dogma by showing that, by extending lamellipodia beneath the cell sheet, multiple rows of cells behind an epithelial wound edge actively crawl along the substratum (see ). The authors use confocal and two-photon microscopy combined with GFP-actin labelling and transmission electron microscopy to examine the cells behind the margin – submarginal cells – of a wounded epithelial cell monolayer. They report that these cells maintain their apical cell-cell contacts but extend basal lamellipodia that are hidden from conventional microscopy. Further work is now needed to reveal how the migratory behaviour of individual cells is coordinated to achieve collective cell migration.
