The development of animals is accompanied by frequent changes in shape, which result from continuous morphological alterations in the epithelia that surround the animal or its internal organs. A key determinant of epithelial shape changes is the mechanical properties of the tissue, such as tissue tension. Two new studies from Christian Dahmann's lab now reveal how tissue mechanics influence epithelia in Drosophila. In their first paper, they investigate the replacement of larval epithelial cells by adult histoblasts at the dorsal midline of the pupal abdomen (Michel and Dahmann, 2020). At this site, they find that cell extrusion, the process by which old, apoptotic cells are removed from an epithelium, occurs by a novel mechanism that involves pulsatile contractions of a medial actomyosin network. In a second paper (Sui and Dahmann, 2020), the authors address how mechanical tension in tissues may be regulated. Using the wing disc as a model, they show that the presence of the signalling molecule Wingless leads to an increase in mechanical tension at basal cell edges. This, in turn, leads to the basal constriction of cells and prevents the basal widening of cells that is typically required to form epithelial folds. Together, these studies provide new insight into the mechanical control of tissue shape, and identify the Wnt/Wingless signalling pathway as a key regulator of tissue tension.
