Measuring forces and stresses in situ in living tissues

In living tissues, genetics and mechanics interact, especially during morphogenesis. Two main classes of mechanical measurements are already established: live imaging helps quantifying tissue deformation, cell-level dynamics, and protein distributions; cell or tissue rheology yields access to material properties such as elastic stiffness and viscosity. The third one, measuring forces and stresses in situ at scales ranging from molecule to cell and to tissue, involves different challenges. We review several emerging techniques, their fields of applications, their advantages and limitations, their validations. We argue that they will strongly impact our understanding of developmental biology in the near future.