Confinement induces actin flow in a meiotic cytoplasm

Abstract

In vivo, F-actin flows are observed at different cell life stages and participate in various developmental processes during asymmetric divisions in vertebrate oocytes, cell migration, or wound healing. Here, we show that confinement has a dramatic effect on F-actin spatiotemporal organization. We reconstitute in vitro the spontaneous generation of F-actin flow using Xenopus meiotic extracts artificially confined within a geometry mimicking the cell boundary. Perturbations of actin polymerization kinetics or F-actin nucleation sites strongly modify the network flow dynamics. A combination of quantitative image analysis and biochemical perturbations shows that both spatial localization of F-actin nucleators and actin turnover play a decisive role in generating flow. Interestingly, our in vitro assay recapitulates several symmetry-breaking processes observed in oocytes and early embryonic cells.

A propagating ATPase gradient drives transport of surface-confined cellular cargo

“…Our results strongly implicate the extreme spatial confinement within a bacterial cell as an underappreciated requirement for ParA-type transport, and likely for other forms of intracellular spatial organization (20). In our diffusion-ratchet model, the motive force is not generated by a self-supporting filament, as it is for the actin-like class of partition ATPases (21).…”

Cell-sized liposomes reveal how actomyosin cortical tension drives shape change

“…An alternative approach is to use either cell-free extracts (18,19) or systems reconstituted from a minimal set of purified cellular components (20). These approaches have been successfully used to show that contractility of bulk actomyosin networks depends on the kinetic parameters of the motors (21)(22)(23), as well as on the presence of actin cross-linkers that allow build-up of stress (24,25).…”

Spatiotemporal control of microtubule nucleation and assembly using magnetic nanoparticles

“…Cytostatic-factor-arrested (CSF) Xenopus laevis egg extract, which corresponds to the 'active' cytoplasm of oocytes arrested in metaphase II of meiosis, was prepared as described previously 18,19,45 . Microtubules structures were assembled using metaphase extracts in the presence of rhodamin-X-labelled tubulin and Ran-NPs or RCC1-NPs, as indicated.…”