Probing tissue mechanical properties in Drosophila embryos using magnetic tweezers

The amnioserosa is an single-cell-deep epithelial cell sheet that contracts during dorsal closure in Drosophila melanogaster embryos. Displacement can be easily observed by microscopy and strains can be inferred from UV laser ablation experiments. The material properties of the amnioserosa and surrounding cell layers, however, remain elusive, which challenges a complete understanding of the driving forces in developing tissues. We have constructed an experiment to quantify mechanical properties of the amnioserosa cells during dorsal closure using magnetic tweezers. Complex shear moduli of the tissues are directly measured by exerting calibrated magnetic forces and observing displacements of bound magnetic beads.