Liquid-Liquid Phase Separation inside Giant Vesicles Drives Shape Deformations and Induces Lipid Membrane Phase Separation
Research Square (Research Square)(2021)
摘要
Abstract An astounding variety of cellular contexts converge to the process of liquid-liquid phase separation for the creation of new functional levels of organization. But the kinetic pathways by which intracellular phase separation proceeds – typically in physically confined and macromolecularly crowded volumes of topologically closed cellular and intracellular compartments –remain incompletely understood. Here, we monitor the dynamics of liquid-liquid phase separation of mixtures of phase-separating polymers (i.e., polyethyleneglycol and dextran) inside all-synthetic, cell-sized giant unilamellar vesicles in real-time. We dynamically trigger phase separation by subjecting an initially homogeneous polymer solution inside vesicles to an abrupt osmotic quench. The latter removes water and elevates polymer concentrations in the phase-coexistence regime thereby initiating a segregative phase separation of the polymers. 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 early trajectory of droplet coarsening exhibit significant acceleration, but a competing process of membrane-droplet interactions – one in which the membrane boundary is preferentially wetted by one of the incipient phases – dynamically arrests the progression and deforms the membrane. As a result, a novel multi-bud morphology, reminiscent of cellular blebs, decorate the vesicle surface. Furthermore, when the vesicles are composed of phase-separating mixtures of common lipids, the three-dimensional liquid-liquid phase separation 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 new physical principle by which liquid-liquid phase separation inside living cells might be dynamically regulated and materially communicated inside-out to the cellular boundaries.
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关键词
membrane,liquid-liquid
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