Coexisting Liquid Phases Underlie Nucleolar Subcompartments

• Published in: Cell Vol. 165; no. 7; pp. 1686 - 1697
• Main Authors: Feric, Marina, Vaidya, Nilesh, Harmon, Tyler S., Mitrea, Diana M., Zhu, Lian, Richardson, Tiffany M., Kriwacki, Richard W., Pappu, Rohit V., Brangwynne, Clifford P.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 16.06.2016
• Subjects: Animals; Caenorhabditis elegans; Cell Nucleolus - chemistry; Cells, Cultured; Chromosomal Proteins, Non-Histone - analysis; Intestines - chemistry; Intestines - cytology; Mammals; Nuclear Proteins - analysis; Oocytes - chemistry; Oocytes - cytology; Ribonucleoproteins - metabolism; RNA Processing, Post-Transcriptional; Xenopus laevis
• ISSN: 0092-8674; 1097-4172
• DOI: 10.1016/j.cell.2016.04.047

The nucleolus and other ribonucleoprotein (RNP) bodies are membrane-less organelles that appear to assemble through phase separation of their molecular components. However, many such RNP bodies contain internal subcompartments, and the mechanism of their formation remains unclear. Here, we combine in vivo and in vitro studies, together with computational modeling, to show that subcompartments within the nucleolus represent distinct, coexisting liquid phases. Consistent with their in vivo immiscibility, purified nucleolar proteins phase separate into droplets containing distinct non-coalescing phases that are remarkably similar to nucleoli in vivo. This layered droplet organization is caused by differences in the biophysical properties of the phases—particularly droplet surface tension—which arises from sequence-encoded features of their macromolecular components. These results suggest that phase separation can give rise to multilayered liquids that may facilitate sequential RNA processing reactions in a variety of RNP bodies. [Display omitted] [Display omitted] •Multiple subcompartments of nucleoli are immiscible liquid phases•Mixing nucleolar proteins in vitro yields similar multiphase behavior•Disordered domains drive phase separation; RNA binding domains confer immiscibility•Differences in droplet surface tensions organize core-shell structure Immiscibility of different liquid-like phases comprised of RNA and protein can recapitulate the subcompartmentalized organization characteristic of nucleoli.