Supracellular organization confers directionality and mechanical potency to migrating pairs of cardiopharyngeal progenitor cells

Physiological and pathological morphogenetic events involve a wide array of collective movements, suggesting that these multicellular arrangements confer biochemical and biomechanical properties that contribute to tissue scale organization. The cardiopharyngeal progenitors of the tunicate Ciona provide the simplest possible model of collective cell migration. They form cohesive bilateral cell pairs, leader-trailer polarized along the migration path as they migrate between the ventral epidermis and trunk endoderm. Here, circumventing difficulties in quantifying cellular mechanics in live embryos, we use the Cellular Potts Model to computationally probe the distributions of forces consistent with the shapes and collective polarity of migrating cell pairs. Combining computational modeling, confocal microscopy, and molecular perturbations, we first determine that cardiopharyngeal progenitors display hallmarks of supracellular organization, with differential distributions of protrusive forces, cell-matrix adhesion, and myosin-based retraction forces along the leader-trailer axis. Combined 4D simulations and experimental observations suggest that cell-cell communication helps establish a hierarchy that contributes to aligning collective polarity with the direction of migration, as observed with three or more cells bothin silicoandin vivo. Our approach reveals emerging properties of the migrating collective. Specifically, cell pairs are more persistent, thus migrating over longer distances, and presumably with higher accuracy. Finally, simulations suggest that polarized cell pairs literally join forces to deform the trunk endoderm, as they migrate through the extracellular space. We thus propose that the polarized supracellular organization of cardiopharyngeal progenitors confers emergent physical properties that determine mechanical interactions with their environment during morphogenesis.