Kinetic control of shape deformations and membrane phase separation inside giant vesicles

A variety of cellular processes use liquid–liquid phase separation (LLPS) to create functional levels of organization, but the kinetic pathways by which it proceeds remain incompletely understood. Here in real time, we monitor the dynamics of LLPS of mixtures of segregatively phase-separating polymers inside all-synthetic, giant unilamellar vesicles. After dynamically triggering phase separation, we find that the ensuing relaxation—en route to the new equilibrium—is non-trivially modulated by a dynamic interplay between the coarsening of the evolving droplet phase and the interactive membrane boundary. The membrane boundary is preferentially wetted by one of the incipient phases, dynamically arresting the progression of coarsening and deforming the membrane. When the vesicles are composed of phase-separating mixtures of common lipids, LLPS within the vesicular interior becomes coupled to the membrane’s compositional degrees of freedom, producing microphase-separated membrane textures. This coupling of bulk and surface phase-separation processes suggests a physical principle by which LLPS inside living cells might be dynamically regulated and communicated to the cellular boundaries. The kinetics of liquid–liquid phase separation (LLPS) in cell-like confinements remains poorly understood. Now it has been shown that it involves complex interplay between the incipient phases and the membrane boundary, which arrests phase coarsening, deforms the membrane and couples LLPS with lipid phase separation.