Nuclear Body Formation: LLPS Hypothesis

Scientific text and reference appraisal

Scientific text/reference appraisal completed 3 October 2026 for this revised HTML overview. Its scientific paragraphs, evidence table and six references have been checked against the primary sources below. This is an evidence-focused appraisal of those examples, not an exhaustive literature search or a validation of every nuclear body. Associated documents and decorative-asset licensing remain outside this appraisal.

What the phase-separation claim means

Here, liquid-liquid phase separation (LLPS) means demixing into coexisting liquid phases. Li et al. (2012) observed concentration- and valency-dependent demixing in purified modular protein mixtures. Such reconstitution shows that defined binding interactions can generate collective phase behaviour; it does not establish the mechanism of an endogenous nuclear body.

Nucleolar evidence: reconstitution and cellular organization

Mitrea et al. (2016) linked NPM1 multivalency and its protein/RNA interactions to droplet formation in purified mixtures and to nucleolar localization in mammalian models. The localization comparisons support a connection between molecular interactions and localization; they do not isolate phase separation from all ordinary binding effects.

Feric et al. (2016) combined observations of Xenopus oocyte nucleoli with reconstitution of NPM1-rich and fibrillarin-rich condensed phases in an RNA-containing mixture. The reconstituted system contains two distinct protein-rich phases plus the surrounding solution. It does not reproduce all three anatomical nucleolar compartments.

Selective sorting is compatible with phase separation

In the model droplets studied by Banani et al. (2016), client recruitment depended on cognate binding sites, scaffold composition and valency. Clients and scaffolds also had different fluorescence-recovery behaviour. Thus, neither selectivity nor a single uniform exchange rate is a defining requirement of LLPS.

PML assembly is a separate mechanistic question

Sahin et al. (2014) distinguished initial PML mesh assembly from partner recruitment and retention in mouse-fibroblast and human-cell models. Their results support oxidation-mediated PML multimerization and subsequent SUMO/SIM-dependent partner interactions. This study establishes assembly and sorting mechanisms in those systems; it does not measure liquid phase coexistence throughout an entire PML body.

Dynamics and perturbations need context

Feric et al. (2016) found different material behaviour and recovery dynamics for nucleolar components. Lower ATP availability changed fibrillarin dynamics more strongly than NPM1 dynamics in their cellular comparisons. These observations support regulated, component-dependent material behaviour; they do not support a universal solid-core model for nuclear bodies.

Itoh et al. (2021) found altered chromatin motion and compaction in human cell models exposed to 1,6-hexanediol. An interpretation based on this perturbation must therefore consider chromatin changes as well as condensate changes. This is a caution about assay specificity, not evidence that LLPS never occurs.

Fluorescence recovery reports molecular recovery, while phase/composition measurements address coexistence. The complementary observations in Banani et al. (2016) and Feric et al. (2016) illustrate why recovery should be interpreted alongside composition and material-property evidence rather than used as a universal phase diagnosis.

Evidence assessment

The checked examples support phase separation by particular nucleolar components, selective sorting within model phases, and a distinct assembly/sorting account for PML bodies. They do not establish a common mechanism for Cajal bodies, speckles, paraspeckles or every transcriptional compartment. Those bodies require separate, body-specific appraisals.Evidence and interpretation: Li et al. (2012); Mitrea et al. (2016); Feric et al. (2016); Banani et al. (2016); Sahin et al. (2014); Itoh et al. (2021).

What each source establishes

Primary references

1. Li et al. (2012). Phase transitions in the assembly of multivalent signalling proteins. Nature 483, 336–340. DOI: 10.1038/nature10879.
2. Mitrea et al. (2016). Nucleophosmin integrates within the nucleolus via multi-modal interactions with proteins displaying R-rich linear motifs and rRNA. eLife 5, e13571. DOI: 10.7554/eLife.13571.
3. Feric et al. (2016). Coexisting liquid phases underlie nucleolar sub-compartments. Cell 165, 1686–1697. DOI: 10.1016/j.cell.2016.04.047.
4. Banani et al. (2016). Compositional Control of Phase-Separated Cellular Bodies. Cell 166, 651–663. DOI: 10.1016/j.cell.2016.06.010.
5. Sahin et al. (2014). Oxidative stress-induced assembly of PML nuclear bodies controls sumoylation of partner proteins. Journal of Cell Biology 204, 931–945. DOI: 10.1083/jcb.201305148.
6. Itoh et al. (2021). 1,6-hexanediol rapidly immobilizes and condenses chromatin in living human cells. Life Science Alliance 4, e202001005. DOI: 10.26508/lsa.202001005.