In vivo measurement of tissue mechanical properties in Drosophila embryos

Material properties determine how tissues respond to forces during embryo morphogenesis. The regulation of both material properties and force generation are key to directing the complex tissue movements required in embryonic development. Quantitative measurements of tissue material properties are challenging because it is usually difficult to access tissues inside a living embryo for mechanical probing. Here, we introduce two experimental approaches, magnetic tweezers and glass microneedles, to probe tissue mechanical properties in Drosophila embryos peeled out of their vitelline egg shells. We image tissue deformations during the process of dorsal closure in a microscope when we exert mechanical stresses by either a magnetic bead or a pair of calibrated glass microneedles. These measurements allow us to calculate viscoelastic material response properties of the tissue probed.