Before a wound can heal, epithelial cells on its edges have to swap their adherens junctions (AJs), Taguchi et al. reveal.
A unique type of AJ, the zonula adherens (ZA), generally connects epithelial cells. ZAs are linear, which allows them to zip adjacent cells together without leaving gaps. During development and wound healing, epithelial layers go through an upheaval. Taguchi et al. investigated what happened to ZAs during such changes.
The researchers found that different types of AJs occur in different parts of an epithelial layer. ZAs predominate in the interior, but cells at the tissue margins carry punctate adherens junctions (pAJs), which aren't linear. Scratching a layer of epithelial cells to simulate a wound spurred the cells at the edges to replace their ZAs with punctate junctions, suggesting that pAJs are necessary to bring the two sides together.
pAJs lack EPLIN, a protein that helps organize ZAs, and the researchers discovered that actin fibers perpendicular to the junction keep EPLIN away. Zapping these cables with a laser caused the junctions to convert to ZAs. By contrast, stretching a cell layer boosted the amount of EPLIN at the intercellular junctions. The researchers think that EPLIN serves as a tension sensor in epithelial layers. When the layer is taut, there's plenty of EPLIN in the ZAs. But when the tension eases, such as when the layer is wounded, EPLIN is lost from ZAs, allowing them to convert into the pAJs that will help knit the wound together.