Forces shaping the Drosophila wing

- Epithelial topology emerges from the balance between contractility and adhesion
- Increased apical contractility or compression induces apoptosis
- Increased apical stretching induces proliferation
- Planar polarised apical contractility across a tissue induces tissue elongation
- Global stretching forces across a tissue induce tissue elongation

How genes encode the three-dimensional shape of tissues is a fascinating problem in biology. Pioneering genetic studies in the fruit fly Drosophila have identified key genes that control the generation of force patterns in the developing wing. Shortrange force patterns generated by planar polarised myosins can promote boundary formation and tissue elongation during the larval wing disc stage. Long-range force patterns are also crucial to shaping the wing during the pupal stage. We review the different ways in which both local and global force patterns can be generated, such as: patterned acto-myosin contractility, patterned anchorage to the extracellular matrix, and patterned tissue growth. In all cases, the balance between force, mass, and resistance explains how the resulting mechanical response produces particular tissue forms-a point underscored by the ability of computer simulations of tissue mechanics to reproduce such morphogenetic events.