| dc.description.abstract | Living tissues are active, non-linear viscoelastic materials that move drastically,
often in concert, during embryogenesis. In many cases, the mechanics of this motion
remain unknown. Using a combination of laser microsurgery and finite-element
simulations, I explore the mechanics of Drosophila embryogenesis during two
consecutive stages: germband retraction and dorsal closure. First, I investigate the
interactions between two tissues, the amnioserosa and germband, as they move cohesively
across the surface of the embryo during germband retraction. I find that the amnioserosa
mechanically assists germband retraction but only by pulling on a few germband segments
– specifically those around the curve. Retraction also depends on cell autonomous
elongation in the germband, modeled by a polarization of cell edge tensions that aligns
perpendicular rather than parallel to the principle stress direction. Cell elongation aligns
with this polarization in most germband segments, but in a few, again mostly around the
curve, cell elongation aligns with the direction of greatest anisotropic stress. Second, I
probe the tension distribution within a single contracting tissue, the amnioserosa during
dorsal closure. These tests demonstrate that the amnioserosa acts more like a continuous
sheet than a cellular foam, where tensile stress is carried both by cell-cell interfaces and by
an apical actin network. Together these results further our understanding of the physics of
embryogenesis and provide a framework for future experiments probing how the
mechanics change in mutants that fail to complete germband retraction or dorsal closure. | |
