Highly dynamic mechanical transitions in embryonic cell populations during Drosophila gastrulation

During animal development, the acquisition of three-dimensional morphology is a direct consequence of the dynamic interaction between cellular forces and the mechanical properties of cells and their environment. While the generation and transmission of cellular forces has been widely explored, less is known about the dynamic changes in cell mechanical properties during morphogenesis. Here, we characterise and spatially map in three dimensions the dynamics of cell mechanical properties during Drosophila gastrulation utilising line-scan Brillouin microscopy. We find that cells in the embryo undergo rapid and spatially varying changes in their mechanical properties and that these differ in cell populations with different fates and behaviours. We identify microtubules as potential effectors of cell mechanics in this system, and corroborate our experimental findings with a physical model that underscores the role of localised and dynamic changes in mechanical properties to facilitate tissue folding. Our work provides the first spatio-temporal description of the evolving mechanical properties of cell populations during morphogenesis, and highlights the potential of Brillouin microscopy in studying the dynamic changes in cell shape behaviours and cell mechanical properties simultaneously in different cell populations in an intact organism.