Pickering stabilization of a dynamic intracellular emulsion

Biomolecular condensates are cellular compartments that form by phase separation in the absence of limiting membranes. Studying the P granules of C. elegans , we find that condensate dynamics are regulated by protein clusters that adsorb to the condensate interface. Using in vitro reconstitution, live observations and theory, we demonstrate that localized assembly of P granules is controlled by MEG-3, an intrinsically disordered protein that forms low dynamic assemblies on P granules. Following classic Pickering emulsion theory, MEG-3 clusters lower surface tension and slow down coarsening. During zygote polarization, MEG-3 recruits DYRK/MBK-2 kinase to accelerate localized growth of the P granule emulsion. By tuning condensate-cytoplasm exchange, interfacial clusters regulate the structural integrity of biomolecular condensates, reminiscent of the role of lipid bilayers in membrane-bound organelles. One Sentence Summary Biomolecular condensates are stabilized by interfacial nanoscale protein clusters. ### Competing Interest Statement Geraldine Seydoux serves on the Scientific Advisory Board of Dewpoint Therapeutics