Nucleolar dynamics are determined by the ordered assembly of the ribosome.

Ribosomal precursor assembly states dictate nucleolar material properties by modulating NPM1 dynamics, with early intermediates slowing and abortive precursors speeding up the process.

• Why it matters: Understanding nucleolar dynamics is crucial because they influence ribosome biogenesis, a fundamental cellular process, yet the molecular mechanisms governing these dynamics are not fully known.
• What they did: Using a high-throughput FRAP platform called HiT-FRAP, the study screened hundreds of genes to assess their effects on NPM1 dynamics and nucleolar morphology, revealing how different pre-ribosomal intermediates impact condensate behavior.
• The result: The findings show that the assembly state of ribosomal precursors controls nucleolar properties through scaffold-pre-ribosome interactions, and mutations in NPM1 can directly tune these dynamics, enabling targeted manipulation of nucleolar function.