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Title page for ETD etd-11302012-113505

Type of Document Dissertation
Author Lynch, Holley Ellen
URN etd-11302012-113505
Title Investigating Cell and Tissue Mechanics during Drosophila Embryogenesis using Laser Microsurgery
Degree PhD
Department Physics
Advisory Committee
Advisor Name Title
M. Shane Hutson Committee Chair
Chris J. Janetopoulos Committee Member
John P. Wikswo Jr. Committee Member
Kalman Varga Committee Member
Volker E. Oberacker Committee Member
  • finite-element model
  • tissue mechanics
  • drosophila
  • laser microsurgery
  • dorsal closure
  • germband retraction
Date of Defense 2012-11-20
Availability unrestricted
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.

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