Rapid actin filament turnover maintains cortical connectivity while allowing for cell cortex deformation and flow

Cells harness the actomyosin contractility of the cell cortex to drive rapid cellular deformations and intracellular flows during cell polarization, migration, and division. To sustain contractile network architectures while allowing for network deformation and remodeling, the balance of actin filament assembly and disassembly must be finely tuned, but how this is coordinated in the cell remains obscure. Here, we combine quantitative measurements and manipulations of filament assembly and disassembly rates with live imaging of network contractility dynamics in the C. elegans zygote to identify co-dependencies between assembly rates, disassembly rates, and large-scale deformations of the cortical actin network. We find that strong reductions in either filament assembly or disassembly rates both result in actin cortex collapse, but each perturbation has distinct effects on actin cortex and cell membrane dynamics. These findings demonstrate that rapid turnover, involving tightly coordinated assembly and disassembly, allows the cortex to maintain a connected architecture while undergoing rapid deformation and coherent flow.