Emergent mechanical properties in zebrafish embryonic tissues: theory and experiment

M. Lisa Manning
Assistant Professor
Department of Physics
Syracuse University
Presented in the Embryo Physics Course, March 7, 2012


Biological tissues often behave like elastic solids on short time scales and fluids on long time scales. Different tissue types exhibit different characteristic macroscopic mechanical properties such as surface tension and viscosity, and cell rearrangements in developing animal tissues closely resemble the behavior of immiscible liquids governed by their surface tensions. But individual cells are not equivalent to molecules in a fluid; cells resist shape changes, modulate adhesive contacts, and exert active tension on their neighbors in tightly packed, disordered structures. By exploiting analogies with foams and supercooled fluids, we develop two models for the emergent mechanical behavior in zebrafish tissues. The first “dynamic” model treats cells as individual units and introduces interactions between cells to capture intracellular degrees of freedom. We show that this minimal model, which contains only three parameters and is carefully calibrated using experimental data, makes predictions for bulk structural and dynamical properties of tissues which we have quantitatively verified. A second “thermodynamic” model studies ensembles of mechanically stable cell packings, and makes predictions for cell shapes that we have also verified experimentally. It also specifies how the collective property of surface tension emerges from properties of individual cells such as cell-cell adhesion and “cortical tension”. Taken together, these models provide a surprising answer to a long-standing paradox, which is the observation that the magnitude of tissue surface tension is orders of magnitude larger that one would expect if it was generated by adhesive molecules alone. Our results suggest that embryonic tissues are a strange viscoelastic “material”: the surface properties are very different than one might expect because individual cells at the surface polarize and change their shapes.




Dr. Lisa Manning is an assistant professor of Physics at Syracuse University. Her research has focused on understanding the collective mechanical properties of disordered, non-equilibrium materials including glasses, granular matter, and biological tissues using theoretical and computational tools. In particular, she is interested in understanding how interactions between single cells give rise to the observed mechanical properties of embryonic tissues. Before arriving at Syracuse, she was a Postdoctoral Fellow at the Princeton Center for Theoretical Science at Princeton University. She earned her Ph. D. in Soft Condensed Matter Physics working with Jean Carlson and James Langer at the University of California Santa Barbara in 2008, and received undergraduate degrees in Mathematics and Physics from the University of Virginia in 2002.



Movie links:

slide 3: zebrafish gastrulation
slide 4: shield stage
slide 8: KV morphogenesis
slide 11: cell sorting
slide 37: 2D slice over time
slide 48: tissue fusion experimental
slide 48: tissue fusion simulation

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