Mechanical forces regulate cellular behaviour to guide correct tissue size and shape. Distribution of stress can affect individual cell morphology, but how global forces are balanced across the whole tissue is largely unknown. In this issue, two papers examine how mechanical stress influences cell shape, and how these forces converge to regulate tissue morphogenesis in the developing Drosophila wing.

On p. 4051, Thomas Lecuit and colleagues investigate the global pattern of stress in the developing wing disc. They find that cell shape is governed by stretching at the periphery and compression at the interior, which may arise from increased proliferation at the centre of the wing. Cells at the periphery counteract this stress by polarising Myosin II tangent to the wing pouch, and by switching their cell division axis to align with the direction of stress. To support these findings, the authors inactivate Hippo signalling to mimic the effect of overproliferation. They observe a loss of the directionally dependent stress effect and a reduced apical surface in the mutant clones compared with their wild-type counterparts, which results in distortion of the bordering cells. These results suggest that the pressure exerted by proliferating cells influences global mechanical stress, which in turn regulates tissue morphogenesis at the periphery of the wing.

The role of mechanical stress in regulating cell shape and tissue morphogenesis is further examined by Shuji Ishihara and Kaoru Sugimura (p. 4091), who investigate the formation of hexagonal cell geometry in the phase II pupal wing. The authors use live imaging and Bayesian inference to map global mechanical forces in response to defined perturbations. They show that the direction of stress originates primarily from the attachment site to the wing hinge, and that this results in a redistribution of myosin, which enables greater tension at the cell junction as a means to resist tissue stretch. This in turn provides directional information for the cells, which ultimately results in the hexagonal configuration and a structurally balanced wing.