scholarly journals Initiation of Nucleolar Assembly Is Independent of RNA Polymerase I Transcription

2000 ◽  
Vol 11 (8) ◽  
pp. 2705-2717 ◽  
Author(s):  
Thibaut Dousset ◽  
Chen Wang ◽  
Céline Verheggen ◽  
Danyang Chen ◽  
Danièle Hernandez-Verdun ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Rna Polymerase ◽  
Nucleolar Organizer ◽  
Rna Polymerase I ◽  
Nucleolar Organizer Regions ◽  
Rdna Transcription ◽  
M Phase ◽  
Upstream Binding Factor ◽  
Polymerase I ◽  
Processing Factors

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.

A role for upstream binding factor in organizing ribosomal gene chromatin

2006 ◽  
Vol 73 ◽  
pp. 77-84 ◽  
Author(s):  
Jane E. Wright ◽  
Christine Mais ◽  
José-Luis Prieto ◽  
Brian McStay
Keyword(s):  
Nucleolar Organizer ◽  
Ribosomal Gene ◽  
Rna Polymerase I ◽  
Nucleolar Organizer Regions ◽  
Binding Factor ◽  
Upstream Binding Factor ◽  
Acrocentric Chromosomes ◽  
Polymerase I ◽  
Secondary Constrictions ◽  
Active Nors

Human ribosomal genes are located in NORs (nucleolar organizer regions) on the short arms of acrocentric chromosomes. During metaphase, previously active NORs appear as prominent chromosomal features termed secondary constrictions, which are achromatic in chromosome banding and positive in silver staining. The architectural RNA polymerase I transcription factor UBF (upstream binding factor) binds extensively across the ribosomal gene repeat throughout the cell cycle. Evidence that UBF underpins NOR structure is provided by an examination of cell lines in which large arrays of a heterologous UBF binding sequences are integrated at ectopic sites on human chromosomes. These arrays efficiently recruit UBF even to sites outside the nucleolus, and during metaphase form novel silver-stainable secondary constrictions, termed pseudo-NORs, that are morphologically similar to NORs.

scholarly journals Regulation of ribosomal DNA transcription by insulin

1998 ◽  
Vol 275 (1) ◽  
pp. C130-C138 ◽  
Author(s):  
Katherine M. Hannan ◽  
Lawrence I. Rothblum ◽  
Leonard S. Jefferson
Keyword(s):  
Rna Polymerase ◽  
Cell Types ◽  
Rna Polymerase I ◽  
Model Systems ◽  
Serum Starvation ◽  
Swiss Albino Mouse ◽  
Rdna Transcription ◽  
Cellular Content ◽  
Upstream Binding Factor ◽  
Polymerase I

The experiments reported here used 3T6-Swiss albino mouse fibroblasts and H4-II-E-C3 rat hepatoma cells as model systems to examine the mechanism(s) through which insulin regulates rDNA transcription. Serum starvation of 3T6 cells for 72 h resulted in a marked reduction in rDNA transcription. Treatment of serum-deprived cells with insulin was sufficient to restore rDNA transcription to control values. In addition, treatment of exponentially growing H4-II-E-C3 with insulin stimulated rDNA transcription. However, for both cell types, the stimulation of rDNA transcription in response to insulin was not associated with a change in the cellular content of RNA polymerase I. Thus we conclude that insulin must cause alterations in formation of the active RNA polymerase I initiation complex and/or the activities of auxiliary rDNA transcription factors. In support of this conclusion, insulin treatment of both cell types was found to increase the nuclear content of upstream binding factor (UBF) and RNA polymerase I-associated factor 53. Both of these factors are thought to be involved in recruitment of RNA polymerase I to the rDNA promoter. Nuclear run-on experiments demonstrated that the increase in cellular content of UBF was due to elevated transcription of the UBF gene. In addition, overexpression of UBF was sufficient to directly stimulate rDNA transcription from a reporter construct. The results demonstrate that insulin is capable of stimulating rDNA transcription in both 3T6 and H4-II-E-C3 cells, at least in part by increasing the cellular content of components required for assembly of RNA polymerase I into an active complex.

scholarly journals UBF complexes with phosphatidylinositol 4,5-bisphosphate in nucleolar organizer regions regardless of ongoing RNA polymerase I activity

Nucleus ◽  
2013 ◽  
Vol 4 (6) ◽  
pp. 478-486 ◽  
Author(s):  
Margarita Sobol ◽  
Sukriye Yildirim ◽  
Vlada V Philimonenko ◽  
Pavel Marášek ◽  
Enrique Castaño ◽  
...  
Keyword(s):  
Rna Polymerase ◽  
Nucleolar Organizer ◽  
Rna Polymerase I ◽  
Nucleolar Organizer Regions ◽  
Polymerase I

scholarly journals Inhibition of nucleolar reformation after microinjection of antibodies to RNA polymerase I into mitotic cells.

1987 ◽  
Vol 105 (4) ◽  
pp. 1483-1491 ◽  
Author(s):  
R Benavente ◽  
K M Rose ◽  
G Reimer ◽  
B Hügle-Dörr ◽  
U Scheer
Keyword(s):  
Rna Polymerase ◽  
Cultured Cells ◽  
Active Form ◽  
Nucleolar Organizer ◽  
Rna Polymerase I ◽  
Nucleolar Organizer Regions ◽  
Dense Fibrillar Component ◽  
Nucleolar Material ◽  
Fibrillar Component ◽  
Polymerase I

The formation of daughter nuclei and the reformation of nucleolar structures was studied after microinjection of antibodies to RNA polymerase I into dividing cultured cells (PtK2). The fate of several nucleolar proteins representing the three main structural subcomponents of the nucleolus was examined by immunofluorescence and electron microscopy. The results show that the RNA polymerase I antibodies do not interfere with normal mitotic progression or the early steps of nucleologenesis, i.e., the aggregation of nucleolar material into prenucleolar bodies. However, they inhibit the telophasic coalescence of the prenucleolar bodies into the chromosomal nucleolar organizer regions, thus preventing the formation of new nucleoli. These prenucleolar bodies show a fibrillar organization that also compositionally resembles the dense fibrillar component of interphase nucleoli. We conclude that during normal nucleologenesis the dense fibrillar component forms from preformed entities around nucleolar organizer regions, and that this association seems to be dependent on the presence of an active form of RNA polymerase I.

Localization of the RNA polymerase I transcription factor hUBF during the cell cycle

1993 ◽  
Vol 104 (2) ◽  
pp. 327-337 ◽  
Author(s):  
P. Roussel ◽  
C. Andre ◽  
C. Masson ◽  
G. Geraud ◽  
D. Hernandez-Verdun
Keyword(s):  
Rna Polymerase ◽  
Nucleolar Organizer ◽  
Ribosomal Gene ◽  
Human Cells ◽  
Rna Polymerase I ◽  
Nucleolar Organizer Regions ◽  
3 Dimensional ◽  
Definitive Evidence ◽  
Fibrillar Component ◽  
Polymerase I

Autoantibodies directed against nucleoli that recognized a doublet of 97–94 kDa in HeLa nuclear protein extracts were identified. The two polypeptides bound equal amounts of antibody, and each was recognized by antibodies affinity purified using the other polypeptide. These antigens were localized in the secondary constriction of PtK1 cells, i.e. the nucleolar organizer regions (NORs) where ribosomal genes accumulate. They were observed in human cells in the same sites as the NOR-silver-stained proteins. The molecular mass of the antigens, their characteristics in Western blotting and their localization in nucleoli and NORs during mitosis are consistent with them being RNA polymerase I transcriptional factor, UBF. This identification was confirmed on Western blotted proteins by their identical labelling patterns, using these autoantibodies and an anti-mUBF antibody that had been previously described. We obtained definitive evidence that these autoantibodies recognize UBF by the strong positive labelling of purified hUBF (1 to 4 ng). During interphase, these autoantibodies directed against UBF labelled in a folded filament pattern as small beads that may correspond to individual transcriptional units. In electron microscopy, the antibodies were observed in the dense fibrillar component (DFC) of the nucleoli and at the periphery of the fibrillar centers (FCs). At the end of G2 phase, transcription inactivation was concomitant with the gathering of UBF at mitotic NORs. UBF was not equally distributed between NORs in human cells: some NORs scored negative (2 to 4) and the intensity of labelling of positive NORs (6 to 8) differed. In confocal microscopy, 3-dimensional analysis of mitosis indicated that UBF remained associated with NORs during all mitotic stages and that there was equal partition of UBF between the daughter cells. The relationship between proteins associated with the NORs and ribosomal gene transcription is discussed.

scholarly journals RNA polymerase I transcription in confluent cells: Rb downregulates rDNA transcription during confluence-induced cell cycle arrest

Oncogene ◽  
2000 ◽  
Vol 19 (31) ◽  
pp. 3487-3497 ◽  
Author(s):  
Katherine M Hannan ◽  
Brian K Kennedy ◽  
Alice H Cavanaugh ◽  
Ross D Hannan ◽  
Iwona Hirschler-Laszkiewicz ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Rna Polymerase ◽  
Cell Cycle Arrest ◽  
Rna Polymerase I ◽  
Rdna Transcription ◽  
Cycle Arrest ◽  
Polymerase I

Mitosis-specific phosphorylation of nucleolin by p34cdc2 protein kinase

1990 ◽  
Vol 10 (7) ◽  
pp. 3607-3618
Author(s):  
P Belenguer ◽  
M Caizergues-Ferrer ◽  
J C Labbé ◽  
M Dorée ◽  
F Amalric
Keyword(s):  
Cell Cycle ◽  
Cell Cycle Control ◽  
Nucleolar Organizer ◽  
Serine Phosphorylation ◽  
Nucleolar Organizer Regions ◽  
Rdna Transcription ◽  
Amino Terminal ◽  
Nucleolar Chromatin

Nucleolin is a ubiquitous multifunctional protein involved in preribosome assembly and associated with both nucleolar chromatin in interphase and nucleolar organizer regions on metaphasic chromosomes in mitosis. Extensive nucleolin phosphorylation by a casein kinase (CKII) occurs on serine in growing cells. Here we report that while CKII phosphorylation is achieved in interphase, threonine phosphorylation occurs during mitosis. We provide evidence that this type of in vivo phosphorylation involves a mammalian homolog of the cell cycle control Cdc2 kinase. In vitro M-phase H1 kinase from starfish oocytes phosphorylated threonines in a TPXK motif present nine times in the amino-terminal part of the protein. The same sites which matched the p34cdc2 consensus phosphorylation sequence were used in vivo during mitosis. We propose that successive Cdc2 and CKII phosphorylation could modulate nucleolin function in controlling cell cycle-dependent nucleolar function and organization. Our results, along with previous studies, suggest that while serine phosphorylation is related to nucleolin function in the control of rDNA transcription, threonine phosphorylation is linked to mitotic reorganization of nucleolar chromatin.

scholarly journals Species-specific rDNA transcription is due to promoter-specific binding factors.

1984 ◽  
Vol 4 (2) ◽  
pp. 221-227 ◽  
Author(s):  
R Miesfeld ◽  
N Arnheim
Keyword(s):  
Rna Polymerase ◽  
Transcriptional Control ◽  
Specific Binding ◽  
Rna Polymerase I ◽  
Rdna Transcription ◽  
Nucleolar Dominance ◽  
Cell Extracts ◽  
Species Specific ◽  
Polymerase I

RNA polymerase I transcription factors were purified from HeLa and mouse L cell extracts by phosphocellulose chromatography. Three fractions from each species were found to be required for transcription. One of these fractions, virtually devoid of RNA polymerase I activity, was found to form a stable preinitiation complex with small DNA fragments containing promoter sequences from the homologous but not the heterologous species. These species-specific DNA-binding factors can explain nucleolar dominance in vivo in mouse-human hybrid somatic cells and species specificity in cell-free, RNA polymerase I-dependent transcription systems. The evolution of species-specific transcriptional control signals may be the natural outcome of a special relationship that exists between the RNA polymerase I transcription machinery and the multigene family coding for rRNA.

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