Abstract
Enclosed by two membranes, the nucleus itself is comprised of various membraneless compartments, including nuclear bodies and chromatin domains. These compartments play an important though still poorly understood role in gene regulation. Significant progress has been made in characterizing the dynamic behavior of nuclear compartments and liquid-liquid phase separation (LLPS) has emerged as a prominent mechanism governing their assembly. However, recent work reveals that certain nuclear structures violate key predictions of LLPS, suggesting that alternative mechanisms likely contribute to nuclear organization. Here, we review the evidence for and against LLPS for several nuclear compartments and discuss experimental strategies to identify the mechanism(s) underlying their assembly. We propose that LLPS, together with multiple modes of protein-nucleic acid binding, drive spatiotemporal organization of the nucleus and facilitate functional diversity among nuclear compartments.
Highlights
The cell nucleus is a highly organized yet dynamic organelle
The mutant phenotypes and fluorescence correlation spectroscopy (FCS) results suggest that both bridging and liquid-liquid phase separation (LLPS) contribute to the formation of heterochromatin compartments
Paraspeckles are nuclear bodies that assemble around a long noncoding RNA in mammalian cells
Summary
The cell nucleus is a highly organized yet dynamic organelle It contains a variety of membrane-less compartments, including nuclear bodies and hierarchically folded chromosomes. Compartments contain topologically associated domains (TADs) and chromatin loops that bring distant genomic loci together in space [10,12,13]. This hierarchical organization is thought to contribute to the spatiotemporal control of gene expression and the epigenetic status of a cell [14]. TThhee nnuucclleeuuss ccoonnttaaiinnss mmaannyy ddiiffffeerreenntt mmeemmbbrraanneelleessss ssttrruuccttuurreess,, iinncclluuddiinngg tthhee nnuucclleeoolluuss ((oorraannggee)),,concostnitsutittiuvteivheterhoectheroomchartoinmcaotminparctommepnatsrt(myeelnlotws ),(pyaerlalospwe)c,klepsa(rgarsepeenc)kalnesd tr(agnrsecernip) tioannadl ctroanndsecnrispatieosn(abllucoe)n,dwehniscahtehsa(vbeluaell),bweehnicphrohpaovseedalltobaesesnemprbolpeotsherdoutgohalsisqeumidb-lleiqtuhirdoupghhasleiqsueipda-rliaqtiuoind (pLhLaPsSe).sRepeparliactaiotinon(LcoLmPSp)a. rRtmepelnictsat(ipounrpcloem) fpoarrmtmfoenlltosw(ipnugripnlfee)ctfioornmbyfohlleorwpeins gsiminpfelecxtiovnirubsy. herpes simplex virus
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