Direct application of tissue-scale tension to epithelia reveals mechanical coupling of germ layers and multi-scale mechanical properties in the developing chick embryo

As cross-disciplinary approaches drawing from physics and mechanics have increasingly influenced our understanding of morphogenesis, the tools available to measure and perturb physical aspects of embryonic development have expanded as well. However, it remains a challenge to measure mechanical properties and apply exogenous forces on the tissue scale in vivo, particularly for epithelial tissues. Exploiting the size and accessibility of the developing chick embryo, here we describe a simple technique to quantitatively apply exogenous forces on the order of microNewtons to the endoderm. With this capability, we performed a series of proof-of-concept experiments that reveal fundamental and unexpected mechanical behaviors in the early chick embryo such as mechanical coupling between the germ layers. This approach enables the investigation of mechanical heterogeneity within the endoderm and links between macroscopic and cell-scale deformations in vivo. Moreover, we show that the method can be adapted to other epithelia in the embryo, conducting preliminary experiments on the quantification of interfacial mechanics during zippering of the neural tube.