Rainbow Nucleus Charts Dynamic Interactome of Membrane-less Organelles
Membrane-less organelles (MLOs) perform diverse cellular functions, but how they interact to coordinate these processes remains poorly understood. Here we constructed a "Rainbow Nucleus" cell line to simultaneously visualize five nuclear MLOs using multi-spectral live-cell imaging. We find that MLO interactions are not random: nuclear speckles serve as hubs, and functionally related MLOs interact more frequently than unrelated MLOs. While some interactions are stable, such as those between the histone locus bodies and Cajal bodies, others are transient, such as those between PML nuclear bodies and Cajal bodies. Single particle tracking revealed that stable contacts between Cajal bodies and nuclear speckles are functional, promoting the outward trafficking of small nuclear ribonucleoproteins from Cajal bodies. Finally, RNA Polymerase II-mediated transcription is required to organize the MLO interactome. Our study reveals a structured, transcription-dependent contact network among nuclear MLOs, laying the foundation for future cellular engineering efforts to modulate the MLO interactome.