An antiparallel cell circulation driven by self-alignment induces phase separation
Active tissues exhibit diverse collective dynamics, yet the cell-cell interactions that generate ordered microscopic flows remain poorly understood. Here, we show that antiparallel cell circulation can emerge from self-aligned, polarity-dependent tension gradients. Using a minimal vertex model of confluent tissues, we studied polar cells that align their polarity with their own velocity and impose polarity-dependent tension gradients along cell-cell contacts, without relying on substrate traction. This behavior can be generalized as a minimal interaction in which forces transmitted between cells act with opposite signs, reminiscent of action-reaction forces, organizing cells into stable interlocking antiparallel lanes. In mixtures of motile and nonmotile cells, this circulation drives phase separation, in which motile cells spontaneously form persistent domains. Accordingly, we identified similar antiparallel circulation patterns in two-dimensional aggregates of Dictyostelium discoideum, supporting the biological relevance of the mechanism. Together, these results demonstrate that self-aligned tension gradients provide a robust and underappreciated route to dynamic microscopic pattern formation in multicellular systems.