Active diffusion of intracellular components is emerging as an important process in cell biology. This process is mediated by complex assemblies of molecular motors and cytoskeletal filaments that drive force generation in the cytoplasm and facilitate enhanced motion. The kinetics of molecular motors have been precisely characterized in-vitro by single molecule approaches, however, their in-vivo behavior has remained elusive. Here, we study the myosin-V driven active diffusion of vesicles in mouse oocytes, where this process plays a key role in nuclear positioning during development, and combine an experimental and theoretical framework to extract molecular-scale force kinetics in-vivo (motor force, power-stroke, and velocity) . We find that myosin-V induces rapid kicks of duration \tau \sim 300 \mus resulting in an average force of F \sim 0.4 pN on vesicles  . Our results reveal that measuring in-vivo active fluctuations allows extraction of the underlying molecular motor activity and demonstrates a widely applicable mesoscopic framework to access molecular-scale force kinetics.
Active diffusion of intracellular components is emerging as an important process in cell biology. This process is mediated by complex assemblies of molecular motors and cytoskeletal filaments that drive force generation in the cytoplasm and facilitate enhanced motion. The kinetics of molecular motors have been precisely characterized in-vitro by single molecule approaches, however, their in-vivo behavior remains elusive. Here, we study the active diffusion of vesicles in mouse oocytes, where this process plays a key role in nuclear positioning during development, and combine an experimental and theoretical framework to extract molecular-scale force kinetics ( force, power-stroke, and velocity) of the in-vivo active process. Assuming a single dominant process, we find that the nonequilibrium activity induces rapid kicks of duration \tau \sim 300 \mus resulting in an average force of F \sim 0.4 pN on vesicles in in-vivo oocytes, remarkably similar to the kinetics of in-vitro myosin-V . Our results reveal that measuring in-vivo active fluctuations allows extraction of the molecular-scale activity in agreement with single-molecule studies and demonstrates a mesoscopic framework to access force kinetics.
R
has remained
remains
D
myosin-V driven
R
in-vivo (motor
(
R
. We find that myosin-V
of the in-vivo active process. Assuming a single dominant process, we find that the nonequilibrium activity
A
in in-vivo oocytes, remarkably similar to the kinetics of in-vitro myosin-V
R
underlying molecular motor activity
molecular-scale activity in agreement with single-molecule studies
D
widely applicable
D
molecular-scale