Unlike traditional materials, living cells actively generate forces at the molecular scale that change their structure and mechanical properties. This nonequilibrium activity is essential for cellular function, and drives processes such as cell division. Single molecule studies have uncovered the detailed force kinetics of isolated motor proteins in-vitro , however their behavior in-vivo has been elusivedue to the complex environment inside the cell . Here, we quantify active force generation in living oocytesusing in-vivo optical trapping and laser interferometry of endogenous vesicles. We integrate an experimental and theoretical framework to connect mesoscopic measurements of nonequilibrium properties to the underlying molecular-scale force kinetics . Our results show that force generation by myosin-V drives the cytoplasmic-skeleton out-of-equilibrium (at frequencies below 300 Hz) and actively softens the environment. In vivo myosin-V activity generates a forceof F \sim 0.4 pN, with a power-stroke of length \Delta x \sim 20 nm and duration \tau \sim 300 \mus , that drives vesicle motion at v_v \sim 320 nm/s. This framework is widely applicable to quantify nonequilibrium properties of living cells and other soft active materials .
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 .
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Unlike traditional materials, living cells actively generate forces at the molecular scale that change their structure and mechanical properties. This nonequilibrium activity is essential for cellular function, and drives processes such as cell division. Single molecule studies have uncovered the detailed force kinetics of isolated motor proteins
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
R
, however their behavior
by single molecule approaches, however, their
R
has been elusivedue to the complex environment inside the cell
behavior has remained elusive
R
quantify active force generation in living oocytesusing in-vivo optical trapping and laser interferometry of endogenous vesicles. We integrate
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
R
connect mesoscopic measurements of nonequilibrium properties to the underlying
extract
R
. Our results show that force generation by myosin-V drives the cytoplasmic-skeleton out-of-equilibrium (at frequencies below 300 Hz) and actively softens the environment. In vivo myosin-V activity generates a forceof F \sim 0.4 pN, with a
in-vivo (motor force,
R
of length \Delta x \sim 20 nm and
, and velocity). We find that myosin-V induces rapid kicks of
R
, that drives vesicle motion at v_v \sim 320 nm/s. This framework is widely applicable to quantify nonequilibrium properties of living cells and other soft active materials
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