Active mechanics reveal molecular-scale force kinetics in living oocytes

TL;DR

This study combines experimental and theoretical methods to measure molecular-scale force kinetics of active diffusion in living mouse oocytes, revealing in-vivo force dynamics similar to in-vitro motor behavior.

Contribution

It introduces a mesoscopic framework to extract molecular force kinetics from in-vivo active fluctuations, bridging the gap between in-vitro and in-vivo motor studies.

Findings

Active diffusion involves rapid force kicks of ~300 μs duration.

Average force exerted on vesicles is ~0.4 pN, similar to in-vitro myosin-V.

The framework enables in-vivo measurement of molecular force kinetics.

Abstract

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 $\mu$s 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.