title: Post-mitotic dynamics of pre-nucleolar bodies is driven by pre-rRNA processing.
abstract: 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.
authors: Université de Toulouse, UPS, Laboratoire de Biologie Moléculaire Eucaryote, F-31000 Toulouse,  France.
authors: Coralie
authors: C
authors: Carron
authors: Stéphanie
authors: S
authors: Balor
authors: Franck
authors: F
authors: Delavoie
authors: Célia
authors: C
authors: Plisson-Chastang
authors: Marlène
authors: M
authors: Faubladier
authors: Pierre-Emmanuel
authors: PE
authors: Gleizes
authors: Marie-Françoise
authors: MF
authors: O'Donohue
mesh_terms: D002466:Cell Nucleolus / Q000378:metabolism* / Q000648:ultrastructure; D055032:Electron Microscope Tomography; D016193:G1 Phase / Q000235:genetics; D055785:Gene Knockdown Techniques; D006367:HeLa Cells; D006801:Humans; D008938:Mitosis / Q000235:genetics*; D008954:Models, Biological; D012322:RNA Precursors / Q000235:genetics / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional / Q000235:genetics*; D034741:RNA, Small Interfering / Q000378:metabolism; D020537:RNA, Small Nucleolar / Q000235:genetics / Q000378:metabolism; D012269:Ribosomal Proteins / Q000378:metabolism
chemical_list: D012322:RNA Precursors; D034741:RNA, Small Interfering; D020537:RNA, Small Nucleolar; D012269:Ribosomal Proteins