Cell-to-cell variability, tissue rheology, and collective measurements*

When cells cooperate to sense a signal, such as a cluster of cells performing collective chemotaxis, they must deal with cell-to-cell variability: even genetically identical cells can have differing responses to chemical signals. We show theoretically and computationally that variability in signaling can limit collective chemotaxis. This occurs because when a strongly responding cell is at one end of a cell cluster, cluster motion is biased toward that cell. These errors can be mitigated if clusters average measurements over times long enough for cells to rearrange - fluid clusters are better able to sense gradients: We develop a bound controlling cluster accuracy as a function of cell-to-cell variation and cluster rheology. We also discuss methods to more accurately measure cell-to-cell variability in both motility and signaling properties, as well as applying our theory to experimental measurements of cluster rearrangement.