Patterning in motion: Cell interfaces guide mesenchymal collective migration and morphogenesis.

Collective cell migration is a fundamental process in development, wound healing, and cancer. The best-characterized modes of collective migration typically involve cells that retain an epithelial architecture. However, in this review, we explore less well-understood modes of migration driven by cells with a more mesenchymal phenotype. To better understand and compare contact-dependent collective cell behaviors, we propose envisioning each cell as a structure made up of smaller dynamic parts and inferring how these parts behave to understand the overall collective behavior. By examining how local cell shapes influence single-cell behaviors, we can gain insight into how swarm-like behaviors emerge through cell-cell contact. Through this lens, we compare key processes such as contact inhibition of locomotion, mesenchymal cell intercalation, and more complex heterotypic swarm behaviors. Finally, we discuss the emerging concept of contact-mediated rules that regulate motility and have the potential to encode blueprints for complex patterns and even organ shapes.