Recycling of the actin monomer pool limits the lifetime of network turnover

Intracellular organization is largely mediated by actin turnover. Cellular actin networks continuously assemble and disassemble, while maintaining their overall appearance. This behavior, called dynamic steady state, allows cells to sense and adapt to their environment. However, how structural stability can be maintained during the constant turnover of a limited actin monomer pool is poorly understood. To answer this question, we developed an experimental system where polystyrene beads are propelled by an actin comet in a microwell containing a limited amount of components. We used the speed and the size of the actin comet tails to evaluate the system's monomer consumption and its lifetime. We established the relative contribution of actin assembly, disassembly, and recycling for a bead movement over tens of hours. Recycling mediated by cyclase-associated protein (CAP) is the key step in allowing the reuse of monomers for multiple assembly cycles. ATP supply and protein aging are also factors that limit the lifetime of actin turnover. This work reveals the balancing mechanism for long-term network assembly with a limited amount of building blocks.

Automated summary

Intracellular organization is regulated by actin turnover, where actin networks continuously assemble and disassemble while maintaining overall appearance. This study developed an experimental system to evaluate the consumption and lifetime of actin monomers by observing the speed and size of actin comet tails. The study found that recycling mediated by cyclase-associated protein (CAP) is crucial for the reuse of monomers, while ATP supply and protein aging also limit actin turnover lifetime. This work reveals the balancing mechanism for long-term network assembly with a limited amount of building blocks.