CYTOMECH · Reconstituting Cytoplasm Mechanics

The cytoplasm is not a simple water-like liquid; it is a crowded heterogeneous medium filled with macromolecules, active cytoskeleton networks and endomembranes. This rich rheology must be precisely coordinated to regulate fundamental cellular processes such as molecular diffusion or cell division. However, while the material properties of the cytoplasm have been well studied at the nanoscale relevant to e.g. protein diffusion, its regulation at the scale of larger assemblies, like nuclei or mitotic spindles, remains poorly addressed. Recent results from the host team suggest that cytoplasm fluid mechanics play a key role in the regulation of cell division of large cells that mark the development of early embryos. In this CYTOMECH project, I thus aim to address how cytoplasm mechanics is regulated during early embryo development. I hypothesize that endomembrane vesicles, tubules and sheets form a crowded polydisperse suspension close to jamming that dominate cytoplasm rheology at the scale of large objects like nuclei or mitotic spindle, relevant to early embryo morphogenesis. Using sea urchin embryos as a model, I will first combine advanced imaging of the cytoplasm with active measurements of cytoplasm mechanics using in vivo magnetic tweezers to address how this endomembrane suspension evolves during early embryogenesis to modulate cytoplasm material properties along with embryo development. Then, using an artificial cell approach, I propose to reconstitute cytoplasm mechanics by encapsulating different cytoplasm extract fractions, enriched in various sets of endomembranes, in water-in-oil droplets; and use this assay to perform a mechanical screen of the cytoplasm. CYTOMECH will represent a breakthrough for our current understanding of how spatiotemporal changes of cytoplasm composition, organization and activity support cell division and embryo morphogenesis, as well as a unique training opportunity for the applicant to become an independent researcher.