Interaction dynamics between epithelial cysts captured by tissue rheology

Epithelial cysts are minimal structures involved in morphogenesis. They are fluid-filled cavities surrounded by an epithelial monolayer. Cysts grow during development and their interactions shape organs. While their growth dynamics as single structures are well characterised, the physical mechanisms underlying their interaction remain poorly understood. Here we design a minimal assay of interacting cyst doublets based on microfabrication, quantitative biology, and theory to show that Madin-Darby Canine Kidney (MDCK) cyst interactions are essentially determined by the rheological properties of their epithelial monolayers. We report two phases of interaction between epithelial cysts: coalescence of cellular monolayers and lumen fusion, with similar speeds of 0.3 μm/h. We modulate the distribution of interaction phenotypes by reducing cell-cell adhesion using E-cadherin knock-out MDCK cells and we report that E-cadherin depletion promotes lumen fusion. Remarkably, the dynamics of coalescence and fusion are conserved between both cell lines. To understand the conserved speeds and the effect of cell-cell adhesion, we model the mechanical behavior of cyst doublets as a complex fluid to predict a speed determined by viscosity, a stretch-dependent monolayer tension, and the adhesion energy between cells. We measure these parameters through rheological experiments using micropipette aspiration and lumen drainage, which span the full range of stretch. A key insight from this analysis is that accounting for the tension dependence on stretch is is essential to capture the different dynamics observed during cyst interaction. Using these rheological measurements, we successfully recapitulate the conserved speed. Altogether, our results open new perspectives to understand tissue dynamics during organogenesis through simple physical arguments.