<B>Biological Physics/Complex Systems Seminar</B><br><i>How Does a Fly Make Itself? Dissecting Morphogenesis with Laser-Microsurgery</i>

Speaker: M. Shane Hutson, (Vanderbilt University)

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, few attempts have been made to test the validity of these models in vivo. I will present a method for probing morphogenetic forces in vivo through laser microsurgery. My group’s current focus is quantitative analysis via laser hole-drilling – a method borrowed from the engineer’s toolbox for residual stress analysis – in which a single laser pulse is used to rapidly ablate a subcellular hole clean through a one-cell thick epithelium. The surrounding cells recoil away from this hole, relaxing the pre-ablation, morphogenetic stresses. By carefully tracking the recoils (on ms time scales, with sub-µm precision and for dozens of embryos), one can estimate how stress is distributed. By staging the embryos, one can infer how this stress distribution changes during development. I will present results from fruit fly (Drosophila) embryos during two stages of embryonic development – germband retraction and dorsal closure. I will also discuss finite-element models that reproduce the observed recoil behavior and their implications for the microscopic construction and dynamic maintenance of an embryonic epithelium.