Paolo Maiuri, Jean-Francois Rupprecht, Stefan Wieser, Verena Ruprecht, Olivier Benichou, Nicolas Carpi, Mathieu Coppey, Simon De Beco, Nir Gov, Carl-Philipp Heisenberg, Carolina Lage Crespo, Franziska Lautenschlaeger, Mael Le Berre, Ana-Maria Lennon-Dumenil, Matthew Raab, Hawa-Racine Thiam, Matthieu Piel, Michael Sixt and Raphael Voituriez.  Cell(2015), in press. Available online at:

Eukaryotic cell migration is essential for a large set of biological processes, from development to immunity or  cancer. Assessing quantitatively the exploratory efficiency of cell trajectories is therefore crucial. In the absence of external guidance, cell movement can be described as a random motion, and proposed models have ranged from simple Brownian motion to persistent random walks, Levy walks, or composite processes such as intermittent random walks. Such models differ in the cell persistence, which quantifies the ability of a cell to maintain its direction of motion. The variety of behaviors, observed even along a single cell trajectory, stems from the fact that, as opposed to a passive tracer in a medium at thermal equilibrium, which performs a classical Brownian motion, a cell is self-propelled, and as such, belongs to the class of active Brownian particles. This class of processes is extremely vast and needs to be restricted to have some predicting power.

 In this work, we show on the basis of experimental data in vitro and in vivo that cell persistence is robustly coupled to cell migration speed. We suggest that this universal coupling constitutes a generic law of cell migration, which originates in the advection of polarity cues by an actin cytoskeleton undergoing flows at the cellular scale. Our analysis relies on a theoretical model that we validate by measuring the persistence of cells upon modulation of actin flow speeds. Beyond the quantitative prediction of the coupling, the model yields a generic phase diagram of cellular trajectories, which recapitulates the full range of observed migration patterns.