Adaptive scans allow 3D-targeted laser-dissection to probe the mechanics of cell sheets

Tissue morphogenesis proceeds through the mechanical actuation of cells by active forces from the cytoskeleton. Multicellular laser dissection has emerged as an essential tool to probe these active forces by severing the tissue locally and inferring the tension born by the severed domain from the recoil of the surrounding structures. Laser dissections are however limited by the 2D steering of the laser in most instrumental configurations, while embryos and developing tissues are intrinsically 3D structures. Here, we present a flexible near-infrared (NIR) fs-pulsed laser dissection system in which dissection trajectories proceed in 3D and adapt to the curved surface of cell sheets, which are prominent structures in embryos. Trajectories are computed through an unsupervised search for the surface of interest. With this technique, we demonstrate sectioning of multicellular domains on curved tissue, which we could not do with regular NIR laser scanning. We apply the developed strategy to the mapping of mechanical stresses in the imaginal disc of the developing Drosophila wing. These targeted, adaptive scans could be applied to other forms of non-linear processes such as two-photon fluorescence imaging or optogenetics.