In Vivo Release of Mitotic Silencing of Ribosomal Gene Transcription Does Not Give Rise to Precursor Ribosomal RNA Processing

Sirri, Valentina; Roussel, Pascal; Hernandez‐Verdun, Danièle

doi:10.1083/jcb.148.2.259

Cited by 83 publications

(87 citation statements)

References 45 publications

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“…For example, there is ®rm evidence that the rDNA genes are not inactivated or remodeled into inert, mature chromatin concomitant with mitotic chromosome condensation, and that much of the transcriptional machinery, including RNA polymerase I, actually remains on the chromosome (Scheer and Rose, 1984;Weisenberger and Scheer, 1995)! As a consequence, inhibition of mitotic cyclin activity rapidly releases the rDNAs transcriptional quiescence (Sirri et al, 2000). Thus, it is very likely that much fewer chromatin remodeling steps are required for this promoter to become active, because the`inactive' state in this case is one where the gene is poised for activity.…”

Section: No Conclusionmentioning

confidence: 99%

Chromatin remodeling and transcriptional activation: the cast (in order of appearance)

2001

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The number of chromatin modifying and remodeling complexes implicated in genome control is growing faster than our understanding of the functional roles they play. We discuss recent in vitro experiments with biochemically de®ned chromatin templates that illuminate new aspects of action by histone acetyltransferases and ATPdependent chromatin remodeling engines in facilitating transcription. We review a number of studies that present an`ordered recruitment' view of transcriptional activation, according to which various complexes enter and exit their target promoter in a set sequence, and at speci®c times, such that action by one complex sets the stage for the arrival of the next one. A consensus emerging from all these experiments is that the joint action by several types of chromatin remodeling machines can lead to a more profound alteration of the infrastructure of chromatin over a target promoter than could be obtained by these enzymes acting independently. In addition, it appears that in speci®c cases one type of chromatin structure alteration (e.g., histone hyperacetylation) is contingent upon prior alterations of a di erent sort (i.e., ATP-dependent remodeling of histone-DNA contacts). The striking di erences between the precise sequence of action by various cofactors observed in these studies may be ± at least in part ± due to di erences between the speci®c promoters studied, and distinct requirements exhibited by speci®c loci for chromatin remodeling based on their pre-existing nucleoprotein architecture. Oncogene (2001) 20, 2991 ± 3006.

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Section: No Conclusionmentioning

confidence: 99%

Chromatin remodeling and transcriptional activation: the cast (in order of appearance)

2001

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“…Because the cell cycle progresses despite Pol I transcription inhibition, our findings suggest that the initial events could be regulated by means other than activation of Pol I transcription. Recently, it was demonstrated that the activation of Pol I transcription is dependent on the level of cdc2-cyclin B activity when cells enter G1 (Sirri et al, 2000). We speculate that the initial recruitment of pre-rRNA processing factors might be regulated by kinases and/or phosphatases involved in the transition from mitosis to interphase.…”

Section: Direct Recruitment Of Nucleolar Factors To Nors Is Independementioning

confidence: 99%

Initiation of Nucleolar Assembly Is Independent of RNA Polymerase I Transcription

Dousset

Wang

Verheggen

et al. 2000

MBoC

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This report examines the distribution of an RNA polymerase I transcription factor (upstream binding factor; UBF), pre-rRNA processing factors (nucleolin and fibrillarin), and pre-rRNAs throughout mitosis and postmitotic nucleologenesis in HeLa cells. The results demonstrate that nucleolin, fibrillarin, and pre-rRNAs synthesized at G2/M phase of the previous cell cycle are directly recruited to UBF-associated nucleolar organizer regions (NORs) early in telophase before chromosome decondensation. Unlike the fusion of prenucleolar bodies to the nucleoli, this early recruitment of processing factors and pre-rRNAs is independent of RNA polymerase I transcription. In the absence of polymerase I transcription, the initial localization of nucleolin, fibrillarin, and pre-rRNAs to UBF-associated NORs generates segregated mininucleoli that are similar to the larger ones observed in interphase cells grown under the same conditions. Pre-rRNAs are juxtaposed to UBF-nucleolin-fibrillarin caps that may represent the segregated nucleoli observed by electron microscopy. These findings lead to a revised model of nucleologenesis. We propose that nucleolar formation at the end of mitosis results from direct recruitment of processing factors and pre-rRNAs to UBF-associated NORs before or at the onset of rDNA transcription. This is followed by fusion of prepackaged prenucleolar bodies into the nucleolus. Pre-ribosomal ribonucleoproteins synthesized in the previous cell cycle may contribute to postmitotic nucleologenesis. INTRODUCTIONThe nucleus is a complex structure within which various functions and components are spatially and temporally organized and interregulated (reviewed by Lamond and Earnshaw, 1998;Dreyfuss and Struhl, 1999). Nucleoli represent the most prominent example of this organization. The major function of the nucleolus is ribosome biogenesis (reviewed by Busch and Smetana, 1970). rRNAs are synthesized, processed, cleaved, and assembled with ribosomal proteins in the nucleolus before export to the cytoplasm. The nucleolus is composed of three structurally distinguishable constituents: fibrillar centers, dense fibrillar components, and granular components, as observed by electron microscopy (reviewed by Busch and Smetana, 1970;Hadjiolov, 1985). Although the spatial and temporal relationship between rRNA synthesis and the three structural constituents remains to be clarified, it is generally thought that transcription of rDNA takes place in a transient area between the fibrillar centers and the dense fibrillar components and that rRNA processing and preribosomal particle assembly progress from the dense fibrillar components to the surrounding granular components (reviewed by Spector et al., 1993;Shaw and Jordan, 1995;Scheer and Hock, 1999). More recent evidence (reviewed by Pederson, 1998;Garcia and Pillus, 1999) suggests that nucleoli have additional functions related to the cell cycle Visintin et al., 1999), cellular aging (Straight et al., 1999), signal recognition particle biosynthesis (Jacobson and Pederson, 1998),...

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“…Pol I transcription assays were performed on GFP-B23-S125A transitorily transfected cells using Br-UTP as described (Sirri et al, 2000). Br-UTP incorporation was detected by mouse anti-BrdU antibodies (Sigma); the second antibodies were Texas red conjugated.…”

Section: Run-on Transcription Assay and Quantificationmentioning

confidence: 99%

Compartmentation of the Nucleolar Processing Proteins in the Granular Component Is a CK2-driven Process

Louvet

Junera

Berthuy

et al. 2006

MBoC

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To analyze the compartmentation of nucleolar protein complexes, the mechanisms controlling targeting of nucleolar processing proteins onto rRNA transcription sites has been investigated. We studied the reversible disconnection of transcripts and processing proteins using digitonin-permeabilized cells in assays capable of promoting nucleolar reorganization. The assays show that the dynamics of nucleolar reformation is ATP/GTP-dependent, sensitive to temperature, and CK2-driven. We further demonstrate the role of CK2 on the rRNA-processing protein B23. Mutation of the major CK2 site on B23 induces reorganization of nucleolar components that separate from each other. This was confirmed in assays using extracts containing B23 mutated in the CK2-binding sites. We propose that phosphorylation controls the compartmentation of the rRNA-processing proteins and that CK2 is involved in this process. INTRODUCTIONThe nucleolus is a model organelle to study nuclear compartmentation (Strouboulis and Wolffe, 1996). In the nucleolus ribosomal RNAs (rRNAs) are synthesized, processed, and assembled with ribosomal proteins to form the small 40S and large 60S preribosome subunits (for a review, see Shaw and Jordan, 1995). The dynamic integration of these different processes generates a typical nucleolar organization. Three main specific components are observed by electron microscopy (Scheer and Hock, 1999): the fibrillar centers (FCs) that are light areas surrounded by a highly contrasted region, the dense fibrillar component (DFC), and the granular component (GC) in which the FCs and DFC are embedded. In the active nucleolus, the early rRNA-processing proteins associated with transcripts during elongation are localized in the central part of the nucleolus, i.e., in the DFC. The processing proteins associated with late steps of rRNA processing are localized in the external part of the nucleolus, i.e., in the GC.The organization of active nucleoli illustrates the coordination that exists between transcription and processing mechanisms and the recruitment of the nucleolar protein complexes at specific steps of ribosome biogenesis. However the mechanisms that control the compartmentation of nucleolar protein complexes are poorly understood. With this in mind, we undertook to determine whether phosphorylation drives the connection of the processing proteins on rRNAs.It has been established that nucleolar disorganization can be induced by DRB (5,6 dichloro-1-␤-d-ribofuranosylbenzimidazole; Granick, 1975aGranick, , 1975bHaaf et al., 1991;Le Panse et al., 1999). Typically the ribosomal genes extend into the nucleoplasm forming the nucleolar necklace, each of the beads of the necklace corresponding to individual transcription sites in association with early rRNA-processing proteins (Granick, 1975a;Haaf and Ward, 1996). More recently it was demonstrated that DRB also induces the formation of masses containing late rRNA-processing proteins at a distance from the transcription sites (DavidPfeuty et al., 2001;Louvet et al., 2005). Thus, there r...

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In Vivo Release of Mitotic Silencing of Ribosomal Gene Transcription Does Not Give Rise to Precursor Ribosomal RNA Processing

Cited by 83 publications

References 45 publications

Chromatin remodeling and transcriptional activation: the cast (in order of appearance)

Chromatin remodeling and transcriptional activation: the cast (in order of appearance)

Initiation of Nucleolar Assembly Is Independent of RNA Polymerase I Transcription

Compartmentation of the Nucleolar Processing Proteins in the Granular Component Is a CK2-driven Process

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