Small-scale fluctuations of cytoplasmic vesicles

Intracellular environments are dynamic spaces filled with various particles moving in every direction. Included in this diverse group of particles 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 cytoskeletal proteins such as microtubules, actin filaments, and myosin-II motors. However, it is uncertain exactly how these cytoskeletal proteins affect the mobility of vesicles in the cytoplasm since they could both facilitate and impede motion. Here we show that vesicle motion is significantly affected by cytoskeletal elements. We found that myosin-II has the largest impact on vesicle mobility: when present, it increases the effective diffusivity and decreases the duration that vesicles spend undergoing non-directed motion. We also found evidence that actin filaments act as a barrier to vesicle motion, trapping them in the cytoplasm and blocking potential pathways for directed and non-directed motion. Our study suggests that by modulating myosin-II activity in the cytoplasm cells can tune the mobility of vesicles. This allows a mechanism for cells to dynamically tune the cytoplasmic environment in space and time.