Tissue morphogenesis is a complex process that emerges from spatially controlled patterns of cell shape changes. Dedicated genetic programmes regulate cell behaviours, exemplified in animals by the specification of apical constriction in invaginating epithelial tissues, or the orientation of cell intercalation during tissue extension. This genetic control is constrained by physical properties of cells that dictate how they can modify their shape. A major challenge is to understand how biochemical pathways control subcellular mechanics in epithelia, such as how forces are produced by interactions between actin filaments and myosin motors, and how these forces are transmitted at cell junctions. The major objective of our project is to investigate the fundamental principles of epithelial mechanics and to understand how intercellular signals and mechanical coupling between cells coordinate individual behaviours at the tissue level.We will study early Drosophila embryogenesis and combine quantitative cell biological studies of cell dynamics, biophysical characterization of cell mechanics and genetic control of cell signalling to answer the following questions: i) how are forces generated, in particular what underlies deformation and stabilization of cell shape by actomyosin networks, and pulsatile contractility; ii) how are forces transmitted at junctions, what are the feedback interactions between tension generation and transmission; iii) how are individual cell mechanics orchestrated at the tissue level to yield collective tissue morphogenesis?We expect to encapsulate the information-based, cell biological and physical descriptions of morphogenesis in a single, coherent framework. The project should impact more broadly on morphogenesis in other organisms and shed light on the mechanisms underlying robustness and plasticity in epithelia.