9th Annual Symposium
Physics of Cancer
Leipzig, Germany
September 24-26, 2018
Invited Talk
Different modes of fluidization in Human Bronchial Epithelial Cells -- the Unjamming Transition vs. the Epithelial-Mesenchymal Transition
Dapeng Bi
Northeastern University, Dept. of Physics, College of Science, Dana Research Center 110 Forsyth St. Boston, MA 02115
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Epithelial tissues form the lining of every organ surface and cavity in our body. In these tissues the cells are largely confluent with strong apico-basal polarity. They remain non-migratory under homeostatic conditions which has been compared with a jammed system in recent literature. Using a culture of human lung epithelial tissue we compare a newly discovered mode of fluidization of jammed cells – the unjamming transition (UJT) – with the canonical epithelial-mesenchymal transition (EMT). We show that in the UJT, the cells exhibit large-scale dynamic collective motion when subjected to compressive stress from apical to basal side. To induce EMT, on the other hand, we treat the cells with TGF-beta1 which makes them lose the epithelial character, disrupt the cell-cell junctions and express a host of mesenchymal markers. We show that not only the UJT proceeds without expression of any of these markers, the cell-cell junctions remain intact and the cells preserve their confluent epithelial nature with only some elongation of the apical surfaces. In addition, measurements of cell shapes and cellular dynamics reveal the emergence of large and fast moving nematic swirls accompanying the UJT which are not observed during EMT. We use a dynamic vertex model (DVM) to capture the essential ingredients of these two dynamical behaviors and propose how the UJT could be an alternative route to fluidization of jammed epithelial tissues, independent of EMT. The DVM differs from previous vertex models in that edges can now become curved, tortuous and ruffled, thus reflecting the effects of forces acting on the edge locally, and their competition. These forces include cortical tension, intracellular-pressure differences, and polarized motility forces.
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