Dynamic Heterogeneity and Stretched Exponential Distributions in Cargo Transport within Living Cells.

Stretched exponential distributions of nonequilibrium steady-state fluctuations are ubiquitous in living and nonliving systems alike, yet their microscopic origins have remained elusive. In this Letter, we track the motion of three types of vesicles across different cell types and find that their trajectories undergo random transitions between directed runs (on state) and diffusionlike jiggling (off state) in the highly dynamic, heterogeneous cytoplasm. The dwell times in these two states follow a stretched exponential distribution, which arises from a continuous weighted sum of simple exponential distributions that align with the unbinding kinetics of motor proteins traversing the cytoskeletal filaments in vitro. Our findings illuminate the profound connection between stretched exponential statistics and dynamic heterogeneity, shedding new light on the complex spatiotemporal landscape of cargo transport within cells.