scholarly journals A possible mechanism for the inhibition of ribosomal RNA gene transcription during mitosis.

1995 ◽  
Vol 129 (3) ◽  
pp. 561-575 ◽  
Author(s):  
D Weisenberger ◽  
U Scheer
Keyword(s):  
Rrna Genes ◽  
Rdna Transcription ◽  
Christmas Trees ◽  
Pol I ◽  
Nucleolus Organizing Region ◽  
Cycle Dependent ◽  
Polymerase I ◽  
Transcriptional Reactivation ◽  
Nucleolar Rna

When cells enter mitosis, RNA synthesis ceases. Yet the RNA polymerase I (pol I) transcription machinery involved in the production of pre-rRNA remains bound to the nucleolus organizing region (NOR), the chromosome site harboring the tandemly repeated rRNA genes. Here we examine whether rDNA transcription units are transiently blocked or "frozen" during mitosis. By using fluorescent in situ hybridization we were unable to detect nascent pre-rRNA chains on the NORs of mouse 3T3 and rat kangaroo PtK2 cells. Appropriate controls showed that our approach was sensitive enough to visualize, at the light microscopic level, individual transcriptionally active rRNA genes both in situ after experimental unfolding of nucleoli and in chromatin spreads ("Miller spreads"). Analysis of the cell cycle-dependent redistribution of transcript-associated components also revealed that most transcripts are released from the rDNA at mitosis. Upon disintegration of the nucleolus during mitosis, U3 small nucleolar RNA (snoRNA) and the nucleolar proteins fibrillarin and nucleolin became dispersed throughout the cytoplasm and were excluded from the NORs. Together, our data rule out the presence of "frozen Christmas-trees" at the mitotic NORs but are compatible with the view that inactive pol I remains on the rDNA. We propose that expression of the rRNA genes is regulated during mitosis at the level of transcription elongation, similarly to what is known for a number of genes transcribed by pol II. Such a mechanism may explain the decondensed state of the NOR chromatin and the immediate transcriptional reactivation of the rRNA genes following mitosis.

scholarly journals Dichotomous Impact of Myc on rRNA Gene Activation and Silencing in B Cell Lymphomagenesis

Cancers ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 3009
Author(s):  
Gaurav Joshi ◽  
Alexander Otto Eberhardt ◽  
Lisa Lange ◽  
René Winkler ◽  
Steve Hoffmann ◽  
...  
Keyword(s):  
B Cell ◽  
Gene Activation ◽  
Cpg Methylation ◽  
Rrna Genes ◽  
Rrna Gene ◽  
Rdna Transcription ◽  
Highly Active ◽  
Pol I ◽  
Polymerase I ◽  
Transcriptional Output

A major transcriptional output of cells is ribosomal RNA (rRNA), synthesized by RNA polymerase I (Pol I) from multicopy rRNA genes (rDNA). Constitutive silencing of an rDNA fraction by promoter CpG methylation contributes to the stabilization of these otherwise highly active loci. In cancers driven by the oncoprotein Myc, excessive Myc directly stimulates rDNA transcription. However, it is not clear when during carcinogenesis this mechanism emerges, and how Myc-driven rDNA activation affects epigenetic silencing. Here, we have used the Eµ-Myc mouse model to investigate rDNA transcription and epigenetic regulation in Myc-driven B cell lymphomagenesis. We have developed a refined cytometric strategy to isolate B cells from the tumor initiation, promotion, and progression phases, and found a substantial increase of both Myc and rRNA gene expression only in established lymphoma. Surprisingly, promoter CpG methylation and the machinery for rDNA silencing were also strongly up-regulated in the tumor progression state. The data indicate a dichotomous role of oncogenic Myc in rDNA regulation, boosting transcription as well as reinforcing repression of silent repeats, which may provide a novel angle on perturbing Myc function in cancer cells.

scholarly journals The Ribosomal Gene Loci—The Power behind the Throne

Genes ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 763
Author(s):  
Konstantin I. Panov ◽  
Katherine Hannan ◽  
Ross D. Hannan ◽  
Nadine Hein
Keyword(s):  
Genome Stability ◽  
Cell Cycle Progression ◽  
Global Gene Expression ◽  
Cell Types ◽  
Ribosomal Gene ◽  
Cellular Growth ◽  
Rrna Genes ◽  
Dynamic Regulation ◽  
Pol I ◽  
Polymerase I

Nucleoli form around actively transcribed ribosomal RNA (rRNA) genes (rDNA), and the morphology and location of nucleolus-associated genomic domains (NADs) are linked to the RNA Polymerase I (Pol I) transcription status. The number of rDNA repeats (and the proportion of actively transcribed rRNA genes) is variable between cell types, individuals and disease state. Substantial changes in nucleolar morphology and size accompanied by concomitant changes in the Pol I transcription rate have long been documented during normal cell cycle progression, development and malignant transformation. This demonstrates how dynamic the nucleolar structure can be. Here, we will discuss how the structure of the rDNA loci, the nucleolus and the rate of Pol I transcription are important for dynamic regulation of global gene expression and genome stability, e.g., through the modulation of long-range genomic interactions with the suppressive NAD environment. These observations support an emerging paradigm whereby the rDNA repeats and the nucleolus play a key regulatory role in cellular homeostasis during normal development as well as disease, independent of their role in determining ribosome capacity and cellular growth rates.

An unusual Y chromosome of Drosophila simulans carrying amplified rDNA spacer without rRNA genes.

Genetics ◽  
1990 ◽  
Vol 125 (2) ◽  
pp. 399-406
Author(s):  
A R Lohe ◽  
P A Roberts
Keyword(s):  
Y Chromosome ◽  
Initiation Site ◽  
Drosophila Simulans ◽  
Rrna Genes ◽  
Rdna Transcription ◽  
Nontranscribed Spacer ◽  
Protein Factor ◽  
Y Chromosomes ◽  
Full Complement ◽  
Polymerase I

Abstract The X and Y chromosomes of Drosophila melanogaster each contain a cluster of several hundred ribosomal RNA genes (rDNA). A nontranscribed spacer region separates adjacent rRNA genes and contains tandem copies of 240 bp repeats that include the initiation site for RNA polymerase I transcription. We show here that Drosophila simulans, a sibling species of D. melanogaster, contains few, if any, rRNA genes on its Y chromosome but carries instead a large block (3,000 kb or 12,500 copies) of 240 bp nontranscribed spacer repeats. The repeats are located at the tip of the long arm of the simulans Y chromosome, in contrast to their location among rRNA genes on the short arm of the Y chromosome of D. melanogaster. The bobbed mutation in homozygous females of D. melanogaster shortens and thins the bristles, owing to a partial deletion of rRNA genes on the X chromosome. The bristles of bobbed/Y males are normal owing to the presence of a full complement of rRNA genes on the Y chromosome. Peculiarly, in bobbed/Y males of D. simulans the short bristle phenotype does not return to normal but is enhanced by the presence of the Y chromosome. We propose that the 12,500 nontranscribed spacer repeats on the Y chromosome are responsible for this biological effect by competition for a protein factor(s) essential for normal levels of rDNA transcription at the X-linked locus.

scholarly journals Structure and function of ribosomal RNA gene chromatin

2008 ◽  
Vol 36 (4) ◽  
pp. 619-624 ◽  
Author(s):  
Joanna L. Birch ◽  
Joost C.B.M. Zomerdijk
Keyword(s):  
Ribosomal Rna ◽  
Ribosome Biogenesis ◽  
Rna Polymerase I ◽  
Rrna Genes ◽  
Rrna Gene ◽  
Pol I ◽  
And Function ◽  
Polymerase I ◽  
Cell Growth And Proliferation ◽  
Cellular Control

Transcription of the major ribosomal RNAs by Pol I (RNA polymerase I) is a key determinant of ribosome biogenesis, driving cell growth and proliferation in eukaryotes. Hundreds of copies of rRNA genes are present in each cell, and there is evidence that the cellular control of Pol I transcription involves adjustments to the number of rRNA genes actively engaged in transcription, as well as to the rate of transcription from each active gene. Chromatin structure is inextricably linked to rRNA gene activity, and the present review highlights recent advances in this area.

Mechanical loading induces the expression of a Pol I regulon at the onset of skeletal muscle hypertrophy

2012 ◽  
Vol 302 (10) ◽  
pp. C1523-C1530 ◽  
Author(s):  
Ferdinand von Walden ◽  
Vandre Casagrande ◽  
Ann-Kristin Östlund Farrants ◽  
Gustavo A. Nader
Keyword(s):  
Skeletal Muscle ◽  
Mechanical Loading ◽  
Muscle Hypertrophy ◽  
Rrna Synthesis ◽  
Rdna Transcription ◽  
Hypertrophic Response ◽  
Skeletal Muscle Hypertrophy ◽  
Pol I ◽  
Upstream Binding Factor ◽  
Polymerase I

The main goal of the present study was to investigate the regulation of ribosomal DNA (rDNA) gene transcription at the onset of skeletal muscle hypertrophy. Mice were subjected to functional overload of the plantaris by bilateral removal of the synergist muscles. Mechanical loading resulted in muscle hypertrophy with an increase in rRNA content. rDNA transcription, as determined by 45S pre-rRNA abundance, paralleled the increase in rRNA content and was consistent with the onset of the hypertrophic response. Increased transcription and protein expression of c-Myc and its downstream polymerase I (Pol I) regulon (POL1RB, TIF-1A, PAF53, TTF1, TAF1C) was also consistent with the increase in rRNA. Similarly, factors involved in rDNA transcription, such as the upstream binding factor and the Williams syndrome transcription factor, were induced by mechanical loading in a corresponding temporal fashion. Chromatin immunoprecipitation revealed that these factors, together with Pol I, were enriched at the rDNA promoter. This, in addition to an increase in histone H3 lysine 9 acetylation, demonstrates that mechanical loading regulates rRNA synthesis by inducing a gene expression program consisting of a Pol I regulon, together with accessory factors involved in transcription and chromatin remodeling at the rDNA promoter. Altogether, these data indicate that transcriptional and epigenetic mechanisms take place in the regulation of ribosome production at the onset of muscle hypertrophy.

scholarly journals RNA Polymerase I-Specific Subunit CAST/hPAF49 Has aRole in the Activation of Transcription by UpstreamBinding Factor

2006 ◽  
Vol 26 (14) ◽  
pp. 5436-5448 ◽  
Author(s):  
Kostya I. Panov ◽  
Tatiana B. Panova ◽  
Olivier Gadal ◽  
Kaori Nishiyama ◽  
Takashi Saito ◽  
...  
Keyword(s):  
Rna Polymerase ◽  
T Cell Activation ◽  
Conformational Changes ◽  
Cell Activation ◽  
Rna Polymerase I ◽  
Rrna Genes ◽  
28S Rrna ◽  
Pol I ◽  
Activation Of Transcription ◽  
Polymerase I

ABSTRACT Eukaryotic RNA polymerases are large complexes, 12 subunits of which are structurally or functionally homologous across the three polymerase classes. Each class has a set of specific subunits, likely targets of their cognate transcription factors. We have identified and characterized a human RNA polymerase I (Pol I)-specific subunit, previously identified as ASE-1 (antisense of ERCC1) and as CD3ε-associated signal transducer (CAST), and here termed CAST or human Pol I-associated factor of 49 kDa (hPAF49), after mouse orthologue PAF49. We provide evidence for growth-regulated Tyr phosphorylation of CAST/hPAF49, specifically in initiation-competent Pol Iβ complexes in HeLa cells, at a conserved residue also known to be important for signaling during T-cell activation. CAST/hPAF49 can interact with activator upstream binding factor (UBF) and, weakly, with selectivity factor 1 (SL1) at the rDNA (ribosomal DNA repeat sequence encoding the 18S, 5.8S, and 28S rRNA genes) promoter. CAST/hPAF49-specific antibodies and excess CAST/hPAF49 protein, which have no effect on basal Pol I transcription, inhibit UBF-activated transcription following functional SL1-Pol I-rDNA complex assembly and disrupt the interaction of UBF with CAST/hPAF49, suggesting that interaction of this Pol I-specific subunit with UBF is crucial for activation. Drawing on parallels between mammalian and Saccharomyces cerevisiae Pol I transcription machineries, we advance one model for CAST/hPAF49 function in which the network of interactions of Pol I-specific subunits with UBF facilitates conformational changes of the polymerase, leading to stabilization of the Pol I-template complex and, thereby, activation of transcription.

scholarly journals In vivo regulation of rRNA transcription occurs rapidly in nondividing and dividing Drosophila cells in response to a phorbol ester and serum.

1993 ◽  
Vol 13 (2) ◽  
pp. 928-933 ◽  
Author(s):  
S M Vallett ◽  
M Brudnak ◽  
M Pellegrini ◽  
H W Weber
Keyword(s):  
Phorbol Ester ◽  
Growth Regulation ◽  
Rrna Genes ◽  
Rrna Synthesis ◽  
Rrna Gene ◽  
Rdna Transcription ◽  
Transcription System ◽  
Pol I ◽  
Drosophila Cells

The synthesis of ribosomes is an essential cellular process which requires the transcription of the rRNA genes by RNA polymerase I (Pol I). The regulation of rRNA synthesis is known to be coupled to growth regulation. In nongrowing, slowly growing, and rapidly growing Drosophila cells, exposure to the tumor-promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) increases the synthesis of precursor and mature rRNAs. Using nuclear run-on assays, we show that TPA enhances transcription of the rRNA genes. These results suggest that TPA regulates expression of RNA genes transcribed by Pol I, irrespective of the growth state of the cells. In slowly dividing Drosophila cells, increasing the serum concentration rapidly alters the accumulation of rRNA by enhancing rDNA transcription within 1 h. Thus, TPA and serum are each able to rapidly regulate rRNA gene expression in Drosophila cells. These results indicate that the RNA Pol I transcription system can be regulated by agents which have previously been shown to effect specific genes transcribed by the RNA Pol II system.

scholarly journals The dynamic assembly of distinct RNA polymerase I complexes modulates rDNA transcription

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Eva Torreira ◽  
Jaime Alegrio Louro ◽  
Irene Pazos ◽  
Noelia González-Polo ◽  
David Gil-Carton ◽  
...  
Keyword(s):  
Cell Growth ◽  
Rna Polymerase ◽  
Ribosome Biogenesis ◽  
Mutational Analysis ◽  
Rna Polymerase I ◽  
Initiation Factor ◽  
Rdna Transcription ◽  
Pol I ◽  
Polymerase I

Cell growth requires synthesis of ribosomal RNA by RNA polymerase I (Pol I). Binding of initiation factor Rrn3 activates Pol I, fostering recruitment to ribosomal DNA promoters. This fundamental process must be precisely regulated to satisfy cell needs at any time. We present in vivo evidence that, when growth is arrested by nutrient deprivation, cells induce rapid clearance of Pol I–Rrn3 complexes, followed by the assembly of inactive Pol I homodimers. This dual repressive mechanism reverts upon nutrient addition, thus restoring cell growth. Moreover, Pol I dimers also form after inhibition of either ribosome biogenesis or protein synthesis. Our mutational analysis, based on the electron cryomicroscopy structures of monomeric Pol I alone and in complex with Rrn3, underscores the central role of subunits A43 and A14 in the regulation of differential Pol I complexes assembly and subsequent promoter association.

scholarly journals Organization of small nucleolar ribonucleoproteins (snoRNPs) by fluorescence in situ hybridization and immunocytochemistry.

1994 ◽  
Vol 5 (12) ◽  
pp. 1289-1299 ◽  
Author(s):  
A G Matera ◽  
K T Tycowski ◽  
J A Steitz ◽  
D C Ward
Keyword(s):  
In Situ Hybridization ◽  
Fluorescence In Situ Hybridization ◽  
Rnase H ◽  
Rrna Processing ◽  
Pol I ◽  
Rrna Maturation ◽  
Polymerase I ◽  
Processing Factors

The organization of the U3, U8, and U13 small nucleolar ribonucleoproteins (snoRNPs) has been investigated in HeLa cells using antisense DNA and 2'-OMe RNA oligonucleotides. Oligomers corresponding to deoxynucleotides that target RNase H degradation of intact RNP particles were synthesized and used for fluorescence in situ hybridization. U3 and U13 are distributed throughout the nucleolus and colocalize with anti-fibrillarin antibodies. U8, however, is organized in discrete ring-like structures near the center of the nucleolus and surround bright punctate regions visualized with anti-RNA polymerase I and anti-UBF/NOR-90 antibodies. In decondensed nucleoli, a necklace of smaller ring-like structures of U8 RNA appear. A model for the recruitment of U8 (and presumably other processing factors) to the sites of rRNA transcription is discussed. Hybridization to mitotic cells showed that unlike pol I and NOR-90, U8 is dispersed into the cytoplasm during mitosis. The subnucleolar organization of U8 is consistent with its demonstrated participation in early intermediate steps in pre-rRNA processing. In contrast, the more dispersed intranucleolar distribution of U3 agrees with its putative involvement in both early and late steps of rRNA maturation. These studies illustrate the feasibility of mapping functional domains within the nucleolus by correlating the in vitro activities of small nuclear RNPs with their in situ locations.

scholarly journals Transcription of Multiple Yeast Ribosomal DNA Genes Requires Targeting of UAF to the Promoter by Uaf30

2008 ◽  
Vol 28 (21) ◽  
pp. 6709-6719 ◽  
Author(s):  
Robert D. Hontz ◽  
Sarah L. French ◽  
Melanie L. Oakes ◽  
Prasad Tongaonkar ◽  
Masayasu Nomura ◽  
...  
Keyword(s):  
Ribosomal Dna ◽  
Rrna Synthesis ◽  
Synthesis Rate ◽  
Wild Type ◽  
Rdna Transcription ◽  
Rdna Genes ◽  
Pol I ◽  
Polymerase I ◽  
I Cells

ABSTRACT Upstream activating factor (UAF) is a multisubunit complex that functions in the activation of ribosomal DNA (rDNA) transcription by RNA polymerase I (Pol I). Cells lacking the Uaf30 subunit of UAF reduce the rRNA synthesis rate by ∼70% compared to wild-type cells and produce rRNA using both Pol I and Pol II. Miller chromatin spreads demonstrated that even though there is an overall reduction in rRNA synthesis in uaf30 mutants, the active rDNA genes in such strains are overloaded with polymerases. This phenotype was specific to defects in Uaf30, as mutations in other UAF subunits resulted in a complete absence of rDNA genes with high or even modest Pol densities. The lack of Uaf30 prevented UAF from efficiently binding to the rDNA promoter in vivo, leading to an inability to activate a large number of rDNA genes. The relatively few genes that did become activated were highly transcribed, apparently to compensate for the reduced rRNA synthesis capacity. The results show that Uaf30p is a key targeting factor for the UAF complex that facilitates activation of a large proportion of rDNA genes in the tandem array.

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