Reconstituting the Dynamic Steady States of Actin

Laurent Blanchoin

Intracellular organization is largely mediated by actin turnover. Cellular actin networks continuously assemble and disassemble while maintaining their overall structure. This behavior, called dynamic steady state, allows cells to sense and adapt to their environment. We developed reconstituted systems in vitro to mimic steady-state conditions with either unlimited or limited amounts of components, establishing feedback mechanisms that perfectly synchronize the rates of assembly and disassembly of the actin network. We demonstrated the necessity of actin turnover to maintain this dynamic steady state over long periods. We propose a balancing mechanism essential for the competitive assembly of a diverse array of actin networks with a limited amount of building blocks. These reconstituted systems were pushed to the limits that are key to cellular life: recycling and energy production to support active assembly/disassembly, as well as component self-renewal to limit aging. Finally, we will discuss how turnover enables biological populations with varying competitive strengths to coexist despite resource constraints.