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20 mars

Anne-Cécile Reyman Compressive cortical flow aligns actin filaments to initiate furrowing

13h à 14h

Le séminaire d’Anne-Cécile Reyman (MPI-CBG, Dresde) aura lieu dans la salle 236 du 29 rue d’Ulm

The actin cytoskeleton is a complex self-organized network that maintains cellular integrity while constantly undergoing rapid turnover and remodeling. Within this thin meshwork of actin and myosin filaments tightly coupled to the membrane, actively driven actomyosin flows can play essential roles for morphogenetic processes. In this study we investigate how myosin induced cortical flows impact actin network organization and filaments alignment and thereby modify cell shape and initiate stable ingression. We perform our analysis in the early C. elegans zygote where cortical flows drive polarization as well as the formation of a pseudocleavage furrow, and at a later state during cytokinesis of the one-cell embryo. By imaging and analyzing actin architecture in this system in relation to myosin induced cortical flow, we observe that actin filaments align in converging and compressive flow. Notably, such cortical dynamics and pattern formation arise in a very similar manner both during polarization and cytokinesis. A quantitative analysis of the dynamics of flows, filaments orientation and cell shape changes, together with a theoretical description of alignment and order in the framework of a thin film of active and nematic fluid allows for a precise characterization of how deformation and shear in cortical flow gives rise to ordering of actin filaments, and how ordered actin filaments generate the forces that are required for forming an ingression. Taken together, our work paints a simple picture of how a furrow ingression arises : An increase of myosin in a central region leads to convergent flows, which in turn results in alignment of filaments, and filament alignment by compressive flow in turn drives asymmetric stress generation and furrow ingression. We thus identify the key physical principles that lead to the generation of an ingression for cytokinesis.