  The intracellular environment is a dynamic space filled with various
organelles moving in all directions. Included in this diverse group of
organelles are vesicles, which are involved in transport of molecular cargo
throughout the cell. Vesicles move in either a directed or non-directed
fashion, often depending on interactions with cytoskeletal proteins such as
microtubules, actin filaments, and molecular motors. How these proteins affect
the local fluctuations of vesicles in the cytoplasm is not clear since they
have the potential to both facilitate and impede movement. Here we show that
vesicle mobility is significantly affected by myosin-II, even though it is not
a cargo transport motor. We find that myosin-II activity increases the
effective diffusivity of vesicles and its inhibition facilitates longer states
of non-directed motion. Our study suggests that altering myosin-II activity in
the cytoplasm of cells can modulate the mobility of vesicles, providing a
possible mechanism for cells to dynamically tune the cytoplasmic environment in
space and time.
