Tuning the dynamics of active cytoskeleton composites via microtubule stabilization

The cytoskeleton is a dynamic network of protein filaments, including rigid microtubules and semiflexible actin filaments, along with force generating motor proteins. In-vitro active cytoskeleton composites (ACCs) comprising microtubules, actin and motor proteins, have been shown to display rich emergent dynamics that can be tuned by the ACC composition. An essential, yet often ignored, component of ACCs is the stabilizers that prevent microtubules from undergoing continuous growth and catastrophe. The two most common stabilization methods are to polymerize microtubules using the nonhydrolizable analog of GTP, GMPCPP or to polymerize with GTP and use the drug paclitaxel (taxol) to stabilize the microtubules against catastrophe. Despite being essential for in vitro reconstitution of microtubules, the effects of the different stabilization approaches on the dynamics and structure of ACCs remains largely unexplored. Here, we investigate the role of microtubule stabilization on the dynamics and structure of co-entangled composites of actin and microtubules driven by microtubule-associated kinesin motor clusters that can crosslink and pull on anti-aligned microtubules. Using multispectral confocal microscopy and custom image analysis algorithms, we characterize the time-varying structure of ACCs prepared with varying concentrations of GMP-CPP or taxol and with varying filament concentrations. We show that taxol-stabilization leads to more contractility and de-mixing of actin and microtubules, while GMP-CPP-stabilization promotes more extensile and flow-like dynamics that are sustained for longer times. These results identify microtubule stabilization chemistry as a key design parameter that tunes emergent dynamics and activity lifetime in active cytoskeletal materials.