The Effect of TPX2 on the Mechanical Stability of Microtubules

Microtubules are hollow, filamentous polymers that play key structural and functional roles in eukaryotic cells. They comprise the cytoskeleton, facilitate intracellular transport, and drive chromosome segregation during mitosis via spindle formation. The mechanical stability of microtubules—their ability to withstand and exert forces without sustaining damage—is essential to these functions. TPX2, a microtubule-associated protein involved in branching nucleation during mitotic spindle assembly, undergoes liquid–liquid phase separation to form biomolecular condensates that coat microtubules. We use atomic force microscopy (AFM) to investigate how TPX2 condensates influence microtubule mechanics. Topographic AFM imaging is used to visualize microtubules and condensate coatings, while force spectroscopy is employed to probe local mechanical properties. We radially indent individual microtubules at varying AFM tip velocities and measure the critical force required for buckling, a proxy for mechanical stability. Our results show that TPX2-coated microtubules exhibit increased buckling forces, indicating enhanced mechanical reinforcement. These findings provide insight into how phase-separated TPX2 condensates modulate cytoskeletal mechanics during spindle formation.