Emergence of Large-Scale Epithelial Mechanics from Cell-Scale Processes - Shaping a Fly Wing
Matthais Merkel Syracuse University
Host: Mark Bowick
Epithelia are two-dimensional cellular sheets. They are active visco-elastic materials which gain their mechanical properties from the collective behavior of a large number of cells. Nowadays, we are able to image tissues with up to 10 000 cells in vivo where the behavior of each individual cell can be followed in detail. We want to understand how large-scale tissue deformation and stresses emerge from the behavior of individual cells.
Here, we study this question in the developing Drosophila wing epithelium. We first establish a general geometrical framework that exactly decomposes large-scale tissue deformation into contributions by different kinds of cellular processes. These processes comprise cell shape changes, cell neighbor exchanges (T1 transitions), cell divisions, and cell extrusions (T2 transitions). As the key idea, we introduce a tiling of the cellular network into triangles. This allows us to define the precise contribution of each kind of cellular process to large-scale tissue deformation. Additionally, our rigorous approach reveals subtle effects of correlated cellular motion, which constitute a novel source of tissue deformation.
Based on this geometrical framework, we describe Drosophila wing mechanics using a novel continuum mechanical model. Similar to preceding models, we describe the wing epithelium as visco-elastic. However in addition to that, our observations led us to appreciate novel effects.
We found active cell rearrangements that are oriented on large scales and have an axis orthogonal to the shear stress axis. Furthermore, cell rearrangements did not respond immediately to material stresses, but were rather delayed. These findings are further underpinned using mechanical and genetic perturbations.
With our work, we contribute to an understanding of epithelial deformation and mechanics, linking it to cellular mechanical properties and cell-scale events.
Penny Davis, administration questions