Nuclear RNA forms an interconnected network of transcription-dependent and tunable microgels

Conflicting models have proposed either a fluid-like or solid-like nature for the intranuclear microenvironment. To reconcile this discrepancy, we investigated the 3D structure and properties of the nuclear interior using experiments and computer simulations.

We reveal a novel mechanism where newly synthesized RNA interacts with SAF-A (scaffold attachment factor A, or HNRNPU), forming interconnected microgels degraded by the exonuclease XRN2, leading to dynamic cycles of gelation and fluidization. This emergent microgel network depends on transcription, and is disrupted by SAF-A depletion. It also decreases protein mobility and regulates chromatin compaction by modulating micro-phase separation, thereby opening transcriptionally active regions.