Much like animals can trace odors, cells also move toward certain chemicals. In fact, cells often do this in groups, which can be up to millions of individuals strong. But how do these cell populations manage to move together as a cohesive unit while following chemical cues? New work from the Center for Systems Biology Dresden and Max Planck Institute for the Physics of Complex Systems shows that the answer lies in limitations in the ability of cells to sense chemicals at high concentrations. Thus, the work of Ricard Alert and collaborators bridges scales by connecting the sensing of tiny molecules by individual cells to the shape and motion of an entire cell population, which can be centimeters or even larger in size. The work is important because it reveals a potentially general principle: Sensing—a distinguishing feature of living systems—governs the ability of cells to migrate in groups. This principle could operate in many other examples of collective migration, as cells and other living creatures can sense and follow a variety of stimuli, such as electric fields, temperature, and light intensity. Finally, the new results open a tantalizing question for future work: Has evolution pushed the sensing limitations of cells to ensure that they can follow chemical cues as a cohesive group? (Image credit: Mariona Esquerda Ciutat.) 

Ricard Alert, Alejandro Martínez-Calvo, and Sujit S. Datta Phys. Rev. Lett. 128, 148101