scholarly journals Drosophila TIF-IA is required for ribosome synthesis and cell growth and is regulated by the TOR pathway

2007 ◽  
Vol 179 (6) ◽  
pp. 1105-1113 ◽  
Author(s):  
Savraj S. Grewal ◽  
Justin R. Evans ◽  
Bruce A. Edgar
Keyword(s):  
Cell Growth ◽  
Transcription Initiation ◽  
Ribosomal Proteins ◽  
Ribosome Biogenesis ◽  
Cellular Growth ◽  
Initiation Factor ◽  
Rrna Synthesis ◽  
Messenger Rnas ◽  
Tor Pathway

Synthesis of ribosomal RNA (rRNA) is a key step in ribosome biogenesis and is essential for cell growth. Few studies, however, have investigated rRNA synthesis regulation in vivo in multicellular organisms. Here, we present a genetic analysis of transcription initiation factor IA (TIF-IA), a conserved RNA polymerase I transcription factor. Drosophila melanogaster Tif-IA−/− mutants have reduced levels of rRNA synthesis and sustain a developmental arrest caused by a block in cellular growth. We find that the target of rapamycin (TOR) pathway regulates TIF-IA recruitment to rDNA. Furthermore, we show that the TOR pathway regulates rRNA synthesis in vivo and that TIF-IA overexpression can maintain rRNA transcription when TOR activity is reduced in developing larvae. We propose that TIF-IA acts in vivo as a downstream growth–regulatory target of the TOR pathway. Overexpression of TIF-IA also elevates levels of both 5S RNA and messenger RNAs encoding ribosomal proteins. Stimulation of rRNA synthesis by TIF-IA may therefore provide a feed-forward mechanism to coregulate the levels of other ribosome components.

scholarly journals Control of ribosomal protein synthesis by Microprocessor complex

2020 ◽  
Author(s):  
Xuan Jiang ◽  
Amit Prabhakar ◽  
Stephanie M. Van der Voorn ◽  
Prajakta Ghatpande ◽  
Barbara Celona ◽  
...  
Keyword(s):  
Cell Growth ◽  
Nuclear Export ◽  
Ribosomal Proteins ◽  
Ribosome Biogenesis ◽  
Cellular Growth ◽  
New Paradigm ◽  
Erythroid Progenitors ◽  
Conditional Deletion ◽  
Microprocessor Complex ◽  
Ribosomal Protein Synthesis

AbstractRibosome biogenesis in eukaryotes requires stoichiometric production and assembly of 80 ribosomal proteins (RPs) and 4 ribosomal RNAs, and its rate must be coordinated with cellular growth. The indispensable regulator of RP biosynthesis is the 5’-terminal oligopyrimidine (TOP) motif, spanning the transcription start site of all RP genes. Here we show that the Microprocessor complex, previously linked to the first step of processing microRNAs (miRNAs), coregulates RP expression by binding the TOP motif of nascent RP mRNAs and stimulating transcription elongation via resolution of DNA/RNA hybrids. Cell growth arrest triggers nuclear export and degradation of the Microprocessor protein Drosha by the E3 ubiquitin ligase Nedd4, accumulation of DNA/RNA hybrids at RP gene loci, decreased RP synthesis, and ribosome deficiency, hence synchronizing ribosome production with cell growth. Conditional deletion of Drosha in erythroid progenitors phenocopies human ribosomopathies, in which ribosomal insufficiency leads to anemia. Outlining a miRNA-independent role of the Microprocessor complex at the interphase between cell growth and ribosome biogenesis offers a new paradigm by which cells alter their protein biosynthetic capacity and cellular metabolism.

scholarly journals Highly efficient RNA-synthesizing system that uses isolated human mitochondria: new initiation events and in vivo-like processing patterns.

1984 ◽  
Vol 4 (8) ◽  
pp. 1605-1617 ◽  
Author(s):  
G Gaines ◽  
G Attardi
Keyword(s):  
Transcription Initiation ◽  
Ribosomal Proteins ◽  
High Efficiency ◽  
Rrna Synthesis ◽  
Isolated Mitochondria ◽  
Highly Efficient ◽  
Light Strand

A highly efficient RNA-synthesizing system with isolated HeLa cell mitochondria has been developed and characterized regarding its requirements and its products. In this system, transcription is initiated and the transcripts are processed in a way which closely reproduces the in vivo patterns. Total RNA labeling in isolated mitochondria proceeds at a constant rate for about 30 min at 37 degrees C; the estimated rate of synthesis is at least 10 to 15% of the in vivo rate. Polyadenylation of the mRNAs is less extensive in this system than in vivo. Furthermore, compared with the in vivo situation, rRNA synthesis in vitro is less efficient than mRNA synthesis. This is apparently due to a decreased rate of transcription initiation at the rRNA promoter and probably a tendency also for premature termination of the nascent rRNA chains. The 5'-end processing of rRNA also appears to be slowed down, and it is very sensitive to the incubation conditions, in contrast to mRNA processing. It is suggested that the lower efficiency and the lability of rRNA synthesis and processing in isolated mitochondria may be due to cessation of import from the cytoplasm of ribosomal proteins that play a crucial role in these processes. The formation of the light-strand-coded RNA 18 (7S RNA) is affected by high pH or high ATP concentration differently from the overall light-strand transcription. The dissociation of the two processes may have important implications for the mechanism of formation and the functional role of this unusual RNA species. The high efficiency, initiation capacity, and processing fidelity of the in vitro RNA-synthesizing system described here make it a valuable tool for the analysis of the role of nucleocytoplasmic-mitochondrial interactions in organelle gene expression.

scholarly journals TGFβ/Activin signalling is required for ribosome biogenesis and cell growth in Drosophila salivary glands

Open Biology ◽  
2017 ◽  
Vol 7 (1) ◽  
pp. 160258 ◽  
Author(s):  
Torcato Martins ◽  
Nadia Eusebio ◽  
Andreia Correia ◽  
Joana Marinho ◽  
Fernando Casares ◽  
...  
Keyword(s):  
Cell Growth ◽  
Salivary Glands ◽  
Ribosomal Proteins ◽  
Ribosome Biogenesis ◽  
Growth Control ◽  
Tissue Growth ◽  
Cellular Growth ◽  
Nucleolar Structure ◽  
Cell Growth And Proliferation ◽  
Tgfβ Superfamily

Signalling by TGFβ superfamily factors plays an important role in tissue growth and cell proliferation. In Drosophila , the activity of the TGFβ/Activin signalling branch has been linked to the regulation of cell growth and proliferation, but the cellular and molecular basis for these functions are not fully understood. In this study, we show that both the RII receptor Punt (Put) and the R-Smad Smad2 are strongly required for cell and tissue growth. Knocking down the expression of Put or Smad2 in salivary glands causes alterations in nucleolar structure and functions. Cells with decreased TGFβ/Activin signalling accumulate intermediate pre-rRNA transcripts containing internal transcribed spacer 1 regions accompanied by the nucleolar retention of ribosomal proteins. Thus, our results show that TGFβ/Activin signalling is required for ribosomal biogenesis, a key aspect of cellular growth control. Importantly, overexpression of Put enhanced cell growth induced by Drosophila Myc, a well-characterized inducer of nucleolar hypertrophy and ribosome biogenesis.

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 Highly efficient RNA-synthesizing system that uses isolated human mitochondria: new initiation events and in vivo-like processing patterns

1984 ◽  
Vol 4 (8) ◽  
pp. 1605-1617
Author(s):  
G Gaines ◽  
G Attardi
Keyword(s):  
Transcription Initiation ◽  
Ribosomal Proteins ◽  
High Efficiency ◽  
Rrna Synthesis ◽  
Isolated Mitochondria ◽  
Highly Efficient ◽  
Light Strand

A highly efficient RNA-synthesizing system with isolated HeLa cell mitochondria has been developed and characterized regarding its requirements and its products. In this system, transcription is initiated and the transcripts are processed in a way which closely reproduces the in vivo patterns. Total RNA labeling in isolated mitochondria proceeds at a constant rate for about 30 min at 37 degrees C; the estimated rate of synthesis is at least 10 to 15% of the in vivo rate. Polyadenylation of the mRNAs is less extensive in this system than in vivo. Furthermore, compared with the in vivo situation, rRNA synthesis in vitro is less efficient than mRNA synthesis. This is apparently due to a decreased rate of transcription initiation at the rRNA promoter and probably a tendency also for premature termination of the nascent rRNA chains. The 5'-end processing of rRNA also appears to be slowed down, and it is very sensitive to the incubation conditions, in contrast to mRNA processing. It is suggested that the lower efficiency and the lability of rRNA synthesis and processing in isolated mitochondria may be due to cessation of import from the cytoplasm of ribosomal proteins that play a crucial role in these processes. The formation of the light-strand-coded RNA 18 (7S RNA) is affected by high pH or high ATP concentration differently from the overall light-strand transcription. The dissociation of the two processes may have important implications for the mechanism of formation and the functional role of this unusual RNA species. The high efficiency, initiation capacity, and processing fidelity of the in vitro RNA-synthesizing system described here make it a valuable tool for the analysis of the role of nucleocytoplasmic-mitochondrial interactions in organelle gene expression.

scholarly journals Commuting to Work: Nucleolar Long Non-Coding RNA Control Ribosome Biogenesis from Near and Far

2021 ◽  
Vol 7 (3) ◽  
pp. 42
Author(s):  
Victoria Mamontova ◽  
Barbara Trifault ◽  
Lea Boten ◽  
Kaspar Burger
Keyword(s):  
Gene Expression ◽  
Rna Polymerase Ii ◽  
Ribosome Biogenesis ◽  
Intergenic Spacer ◽  
Cellular Growth ◽  
Rrna Synthesis ◽  
Protein Coding ◽  
Non Coding Rna ◽  
And Function ◽  
In Cis

Gene expression is an essential process for cellular growth, proliferation, and differentiation. The transcription of protein-coding genes and non-coding loci depends on RNA polymerases. Interestingly, numerous loci encode long non-coding (lnc)RNA transcripts that are transcribed by RNA polymerase II (RNAPII) and fine-tune the RNA metabolism. The nucleolus is a prime example of how different lncRNA species concomitantly regulate gene expression by facilitating the production and processing of ribosomal (r)RNA for ribosome biogenesis. Here, we summarise the current findings on how RNAPII influences nucleolar structure and function. We describe how RNAPII-dependent lncRNA can both promote nucleolar integrity and inhibit ribosomal (r)RNA synthesis by modulating the availability of rRNA synthesis factors in trans. Surprisingly, some lncRNA transcripts can directly originate from nucleolar loci and function in cis. The nucleolar intergenic spacer (IGS), for example, encodes nucleolar transcripts that counteract spurious rRNA synthesis in unperturbed cells. In response to DNA damage, RNAPII-dependent lncRNA originates directly at broken ribosomal (r)DNA loci and is processed into small ncRNA, possibly to modulate DNA repair. Thus, lncRNA-mediated regulation of nucleolar biology occurs by several modes of action and is more direct than anticipated, pointing to an intimate crosstalk of RNA metabolic events.

scholarly journals Genome-Wide Analysis of mRNA Stability Using Transcription Inhibitors and Microarrays Reveals Posttranscriptional Control of Ribosome Biogenesis Factors

2004 ◽  
Vol 24 (12) ◽  
pp. 5534-5547 ◽  
Author(s):  
Jörg Grigull ◽  
Sanie Mnaimneh ◽  
Jeffrey Pootoolal ◽  
Mark D. Robinson ◽  
Timothy R. Hughes
Keyword(s):  
Heat Stress ◽  
Microarray Data ◽  
Mrna Stability ◽  
Ribosomal Proteins ◽  
Ribosome Biogenesis ◽  
Transcriptional Response ◽  
Rrna Synthesis ◽  
Ribosome Assembly ◽  
Genome Wide ◽  
Genes Encoding

ABSTRACT Using DNA microarrays, we compared global transcript stability profiles following chemical inhibition of transcription to rpb1-1 (a temperature-sensitive allele of yeast RNA polymerase II). Among the five inhibitors tested, the effects of thiolutin and 1,10-phenanthroline were most similar to rpb1-1. A comparison to various microarray data already in the literature revealed similarity between mRNA stability profiles and the transcriptional response to stresses such as heat shock, consistent with the fact that the general stress response includes a transient shutoff of general mRNA transcription. Genes encoding factors involved in rRNA synthesis and ribosome assembly, which are often observed to be coordinately down-regulated in yeast microarray data, were among the least stable transcripts. We examined the effects of deletions of genes encoding deadenylase components Ccr4p and Pan2p and putative RNA-binding proteins Pub1p and Puf4p on the genome-wide pattern of mRNA stability after inhibition of transcription by chemicals and/or heat stress. This examination showed that Ccr4p, the major yeast mRNA deadenylase, contributes to the degradation of transcripts encoding both ribosomal proteins and rRNA synthesis and ribosome assembly factors and mediates a large part of the transcriptional response to heat stress. Pan2p and Puf4p also contributed to the degradation rate of these mRNAs following transcriptional shutoff, while Pub1p preferentially stabilized transcripts encoding ribosomal proteins. Our results indicate that the abundance of ribosome biogenesis factors is controlled at the level of mRNA stability.

scholarly journals Spt6 Is Essential for rRNA Synthesis by RNA Polymerase I

2015 ◽  
Vol 35 (13) ◽  
pp. 2321-2331 ◽  
Author(s):  
Krysta L. Engel ◽  
Sarah L. French ◽  
Olga V. Viktorovskaya ◽  
Ann L. Beyer ◽  
David A. Schneider
Keyword(s):  
Rna Polymerase ◽  
Transcription Initiation ◽  
Initiation Factor ◽  
Rrna Synthesis ◽  
Temperature Sensitive ◽  
Protein Levels ◽  
Pol I ◽  
Low Levels ◽  
Sensitive Allele ◽  
Polymerase I

Spt6 (suppressor ofTy6) has many roles in transcription initiation and elongation by RNA polymerase (Pol) II. These effects are mediated through interactions with histones, transcription factors, and the RNA polymerase. Two lines of evidence suggest that Spt6 also plays a role in rRNA synthesis. First, Spt6 physically associates with a Pol I subunit (Rpa43). Second, Spt6 interacts physically and genetically with Spt4/5, which directly affects Pol I transcription. Utilizing a temperature-sensitive allele,spt6-1004, we show that Spt6 is essential for Pol I occupancy of the ribosomal DNA (rDNA) and rRNA synthesis. Our data demonstrate that protein levels of an essential Pol I initiation factor, Rrn3, are reduced when Spt6 is inactivated, leading to low levels of Pol I-Rrn3 complex. Overexpression ofRRN3rescues Pol I-Rrn3 complex formation; however, rRNA synthesis is not restored. These data suggest that Spt6 is involved in either recruiting the Pol I-Rrn3 complex to the rDNA or stabilizing the preinitiation complex. The findings presented here identify an unexpected, essential role for Spt6 in synthesis of rRNA.

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