A liquid +TIP-network regulates microtubule dynamics through tubulin condensation

Abstract

SUMMARYRegulation of microtubule dynamics is required for many biological processes. Here we uncovered a novel mechanism to regulate microtubule dynamics: local tubulin condensation. We show that two microtubule tip-binding proteins, CLIP-170 and EB3, undergo phase separation and form a liquid-like network at growing microtubule tips. In vitro and in cells this liquid network can condense tubulin. This process of tubulin co-condensation is spatially initiated at the microtubule tip and temporally regulated to occur only when microtubules grow. Tubulin condensation at the growing microtubule tip increases growth speeds up to four-fold and strongly reduces depolymerization events. Since tubulin concentration determines microtubule growth, our discovery shows a regulatory mechanism for enriching tubulin availability at strategically important locations: the growing microtubule tips.