Formation of Multi-Compartment Condensates through Aging of Protein-RNA Condensates

Cells can dynamically organize reactions through the formation of biomolecular condensates. These viscoelastic networks exhibit complex material properties and mesoscale architectures, including the ability to form multi-phase assemblies. Understanding the molecular mechanisms underlying the formation of compartmentalized condensates has implications not only in biology but also in the development of advanced materials. In this study, we demonstrate that the aging of heterotypic protein-RNA condensates can lead to the formation of double-emulsion structures. By combining fluorescence-based techniques with theoretical modeling, we show that, as the condensates age, the strengthening of homotypic protein-protein interactions induces the release of RNA molecules from the dense phase. Notably, when condensates exceed a critical size, the slow diffusion of RNA molecules triggers the nucleation of a dilute phase within the protein-rich condensates, ultimately resulting in the formation of double-emulsion structures. These findings illustrate a new mechanism for a formation of dynamic multi-compartment condensates.