In vivo measurements of embryonal tissue mechanics

Tissue sheet movements are critical in embryonal development. To understand the machinery driving morphogenesis it is important to quantitate the mechanical properties of the involved tissues. We here study the process of dorsal closure (DC) in Drosophila melanogaster embryos. Time-lapse microscopy of the process provides data on the complex tissue movements occurring during DC. In order to elucidate the force generating processes driving the movements, however, one needs to know the tissue material properties. Measuring those properties has been extremely challenging since the embryo is tightly enclosed in an egg shell. We use peeled embryos that are directly accessible to mechanical probing while continuing DC. We apply calibrated twin glass microneedles to directly probe DC tissue response in the living embryos. In addition, we use finite-element modeling (FEM, Comsol) to estimate Young's moduli of the various tissue types involved in DC. We find a modulus of ~700 Pa for amnioserosa tissue, comparable to soft vertebrate tissues. Our novel approach allows us to directly probe tissue mechanics in the developing embryo and it provides the possibility to study the effect that particular molecular players have on material properties and on the forces that drive morphogenesis in embryonal development.