Tissue Fluidity Mediates a Trade-off Between the Speed and Accuracy of Multicellular Patterning by Cell Sorting.

The organization of cells into spatial patterns is a fundamental aspect of multicellularity. One major mechanism underlying tissue patterning is adhesion-based cell sorting, in which a heterogeneous mixture of cell types spontaneously separates into distinct domains based on differences in adhesion protein expression. Here, we identify tissue fluidity-the extent to which cells can move freely within a tissue-as a critical regulator of adhesion-based sorting. First, we describe a physically well-understood minimal tissue model that can integrate both tissue fluidity and adhesion-based sorting, and demonstrate that this model can quantitatively reproduce experimentally measured sorting dynamics in a fibroblast cell culture assay. We go on to show that altering tissue fluidity by any mechanism in the model leads to substantial changes in the rate or accuracy of sorting (or both). We further demonstrate that the balance between cell motility, which acts to fluidize the tissue, and homotypic cell-cell adhesion, which acts to solidify the tissue, sensitively tunes a fundamental trade-off between the rate and accuracy of sorting-such that sorting can only occur when motility and adhesion are tightly coupled. Intriguingly, best fits of the simulations to the experiments across a range of adhesion protein expression conditions suggest that cells may naturally scale their motility strength with their adhesion strength - thereby maintaining a permissive fluidity for sorting. Overall, our results indicate that tissue fluidity must be tightly regulated for sorting to occur, and that cells may have evolved a mechanism to naturally co-regulate their mechanical properties in order to sustain a patterning-competent fluidity.