The epithelium, a tissue made up of closely juxtaposed cells, forms the glands and covers the outer surface of the human body as well as its internal cavities, such as the lungs or intestines. There are different types of epithelia, depending on the surfaces they cover and the functions they carry out. These tissues are subjected to multiple types of mechanical stretch, such as those caused by passing food or filling a bladder. The mechanical input strongly influences the proliferation and differentiation of epithelial cells, whether healthy or cancerous, but the underlying processes remain poorly understood. Researchers at the University of Geneva (UNIGE), Switzerland, have discovered that the proteins Zonula Occludens-1 and -2 (ZO-1 and ZO-2), which contribute to the tightness of the epithelium, perceive these physical signals and activate different cellular responses accordingly.