Post-mitotic dynamics of pre-nucleolar bodies is driven by pre-rRNA processing

J Cell Sci. 2012 Oct 1;125(Pt 19):4532-42. doi: 10.1242/jcs.106419. Epub 2012 Jul 5.


Understanding the relationship between the topological dynamics of nuclear subdomains and their molecular function is a central issue in nucleus biology. Pre-nucleolar bodies (PNBs) are transient nuclear subdomains, which form at telophase and contain nucleolar proteins, snoRNPs and pre-ribosomal RNAs (pre-rRNAs). These structures gradually disappear in early G1 phase and are currently regarded as reservoirs of nucleolar factors that participate to post-mitotic reassembly of the nucleolus. Here, we provide evidence from fluorescence in situ hybridization and loss-of-function experiments in HeLa cells that PNBs are in fact active ribosome factories in which maturation of the pre-rRNAs transiting through mitosis resumes at telophase. We show that the pre-rRNA spacers are sequentially removed in PNBs when cells enter G1 phase, indicating regular pre-rRNA processing as in the nucleolus. Accordingly, blocking pre-rRNA maturation induces accumulation in PNBs of stalled pre-ribosomes characterised by specific pre-rRNAs and pre-ribosomal factors. The presence of pre-ribosomal particles in PNBs is corroborated by observation of these domains by correlative electron tomography. Most importantly, blocking pre-rRNA maturation also prevents the gradual disappearance of PNBs, which persist for several hours in the nucleoplasm. In a revised model, we propose that PNBs are autonomous extra-nucleolar ribosome maturation sites, whose orderly disassembly in G1 phase is driven by the maturation and release of their pre-ribosome content.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Nucleolus / metabolism*
  • Cell Nucleolus / ultrastructure
  • Electron Microscope Tomography
  • G1 Phase / genetics
  • Gene Knockdown Techniques
  • HeLa Cells
  • Humans
  • Mitosis / genetics*
  • Models, Biological
  • RNA Precursors / genetics
  • RNA Precursors / metabolism*
  • RNA Processing, Post-Transcriptional / genetics*
  • RNA, Small Interfering / metabolism
  • RNA, Small Nucleolar / genetics
  • RNA, Small Nucleolar / metabolism
  • Ribosomal Proteins / metabolism


  • RNA Precursors
  • RNA, Small Interfering
  • RNA, Small Nucleolar
  • Ribosomal Proteins