  A broad range of membrane proteins display anomalous diffusion on the cell
surface. Different methods provide evidence for obstructed subdiffusion and
diffusion on a fractal space, but the underlying structure inducing anomalous
diffusion has never been visualized due to experimental challenges. We
addressed this problem by imaging the cortical actin at high resolution while
simultaneously tracking individual membrane proteins in live mammalian cells.
Our data confirm that actin introduces barriers leading to compartmentalization
of the plasma membrane and that membrane proteins are transiently confined
within actin fences. Furthermore, superresolution imaging shows that the
cortical actin is organized into a self-similar meshwork. These results present
a hierarchical nanoscale picture of the plasma membrane.
