Abstract:

During the development of an organism, sheets of epithelial cells dynamically expand, contract and bend. These movements generate organismal form in a process known as morphogenesis - a process driven by cell-generated forces. The generation, distribution and regulation of these forces have been explored in multiple mathematical and computational models; however, very few attempts have been made to test the validity of these models in vivo. We present a method for probing morphogenetic forces in vivo through laser microsurgery. Our current focus is quantitative analysis via laser hole-drilling - a method borrowed from the analysis of residual stress in manufactured widgets - in which laser microsurgery is used to ablate a single cell edge or surface. The adjacent cells move away from this wound (i.e. recoil) in accord with their mechanical properties and the post-ablation stress imbalance. We have applied this method to the embryonic epithelia of GFP-labeled fruit fly (Drosophila) embryos. We ablate a single cell edge or surface and measure the subsequent plasma, cavitation and tissue recoil dynamics. We have shown that plasma recombination, cavitation, and mechanical recoil take place on well-separated time scales. Thus, with appropriate inversion, the recoil dynamics are a reporter of the both the mechanical properties and stresses inside a living fly embryo.