Lecturer: Diego Krapf, Department of Electrical and Computer Engineering and School of Biomedical Engineering, Colorado State University, Fort Collins, CO, USA
Abstract:
Tracking individual proteins on the surface of live mammalian cells reveals complex dynamics
involving anomalous diffusion and clustering into nanoscale domains. Theoretical models
indicate that anomalous diffusion can be caused by vastly different processes. By performing
time series and ensemble analysis of extensive single-molecule tracking in combination with
stochastic modeling, we show that most trajectories violate the ergodic hypothesis, one of the
cornerstones of statistical physics. In particular, ergodicity breaking manifests as substantial
differences between the time-averaged and the ensemble-averaged observables. We find that
ergodicity breaking is caused by the transient localization of membrane proteins within
nanoscale domains, such as endocytic pits. Furthermore, using a combination of dynamic
super-resolution imaging and single-particle tracking, we observe that the actin cytoskeleton
introduces barriers leading to the compartmentalization of the plasma membrane and that
proteins are transiently confined within actin-delimited domains. Our results show that the actin-
induced compartments are scale free and that the actin cortex forms a self-similar fractal
structure.