  Contractile actomyosin network flows are crucial for many cellular processes
including cell division and motility, morphogenesis and transport. How local
remodeling of actin architecture tunes stress production and dissipation and
regulates large-scale network flow remains poorly understood. Here, we generate
contractile actomyosin networks with rapid turnover in vitro, by encapsulating
cytoplasmic Xenopus egg extracts into cell-sized 'water-in-oil' droplets.
Within minutes, the networks reach a dynamic steady-state with continuous
inward flow. The networks exhibit homogenous, density-independent contraction
for a wide range of physiological conditions, indicating that the
myosin-generated stress driving contraction is proportional to the effective
network viscosity. We further find that the contraction rate approximately
scales with the network turnover rate, but this relation breaks down in the
presence of excessive crosslinking or branching. Our findings suggest that
cells use diverse biochemical mechanisms to generate robust, yet tunable, actin
flows by regulating two parameters: turnover rate and network geometry.
