RNA transcription modulates phase transition-driven nuclear body assembly.

TitleRNA transcription modulates phase transition-driven nuclear body assembly.
Publication TypeJournal Article
Year of Publication2015
AuthorsBerry, J, Weber, SC, Vaidya, N, Haataja, M, Brangwynne, CP
JournalProc Natl Acad Sci U S A
Date Published2015 Sep 22
KeywordsAnimals, Caenorhabditis elegans, Cell Nucleolus, Cell Nucleus, Cytoplasm, Green Fluorescent Proteins, Intranuclear Inclusion Bodies, Microscopy, Fluorescence, RNA, Ribosomal, Thermodynamics, Transcription, Genetic

<p>Nuclear bodies are RNA and protein-rich, membraneless organelles that play important roles in gene regulation. The largest and most well-known nuclear body is the nucleolus, an organelle whose primary function in ribosome biogenesis makes it key for cell growth and size homeostasis. The nucleolus and other nuclear bodies behave like liquid-phase droplets and appear to condense from the nucleoplasm by concentration-dependent phase separation. However, nucleoli actively consume chemical energy, and it is unclear how such nonequilibrium activity might impact classical liquid-liquid phase separation. Here, we combine in vivo and in vitro experiments with theory and simulation to characterize the assembly and disassembly dynamics of nucleoli in early Caenorhabditis elegans embryos. In addition to classical nucleoli that assemble at the transcriptionally active nucleolar organizing regions, we observe dozens of "extranucleolar droplets" (ENDs) that condense in the nucleoplasm in a transcription-independent manner. We show that growth of nucleoli and ENDs is consistent with a first-order phase transition in which late-stage coarsening dynamics are mediated by Brownian coalescence and, to a lesser degree, Ostwald ripening. By manipulating C. elegans cell size, we change nucleolar component concentration and confirm several key model predictions. Our results show that rRNA transcription and other nonequilibrium biological activity can modulate the effective thermodynamic parameters governing nucleolar and END assembly, but do not appear to fundamentally alter the passive phase separation mechanism.</p>

Alternate JournalProc Natl Acad Sci U S A
PubMed ID26351690
PubMed Central IDPMC4586886
Grant ListDP2 GM105437 / GM / NIGMS NIH HHS / United States
P40 OD010997 / OD / NIH HHS / United States
1DP2GM105437-01 / DP / NCCDPHP CDC HHS / United States