scholarly journals Chromatin modifiers and recombination factors promote a telomere fold-back structure, that is lost during replicative senescence

2020 ◽  
Author(s):  
Tina Wagner ◽  
Lara Perez-Martinez ◽  
René Schellhaas ◽  
Marta Barrientos-Moreno ◽  
Merve Öztürk ◽  
...  
Keyword(s):  
Dna Damage ◽  
Homologous Recombination ◽  
Replicative Senescence ◽  
Budding Yeast ◽  
Spatial Arrangement ◽  
Chromosome Conformation ◽  
Protein Levels ◽  
Additional Layer ◽  
Histone Modifiers ◽  
Telomere Structure

AbstractTelomeres adopt a lariat conformation and hence, engage in long and short distance intra-chromosome interactions. Budding yeast telomeres were proposed to fold back into subtelomeric regions, but a robust assay to quantitatively characterize this structure has been lacking. Therefore, it is not well understood how the interactions between telomeres and non-telomeric regions are established and regulated. We employ a telomeric chromosome conformation capture (Telo-3C) approach to directly analyze telomere folding and its maintenance in S. cerevisiae. We identify the histone modifiers Sir2, Sin3 and Set2 as critical regulators for telomere folding, which suggests that a distinct telomeric chromatin environment is a major requirement for the folding of yeast telomeres. We demonstrate that telomeres are not folded when cells enter replicative senescence, which occurs independently of short telomere length. Indeed, Sir2, Sin3 and Set2 protein levels are decreased during senescence and their absence may thereby prevent telomere folding. Additionally, we show that the homologous recombination machinery, including the Rad51 and Rad52 proteins, as well as the checkpoint component Rad53 are essential for establishing the telomere fold-back structure. This study outlines a method to interrogate telomere-subtelomere interactions at a single unmodified yeast telomere. Using this method, we provide insights into how the spatial arrangement of the chromosome end structure is established and demonstrate that telomere folding is compromised throughout replicative senescence.Author summaryTelomeres are the protective caps of chromosome ends and prevent the activation of a local DNA damage response. In many organisms, telomeres engage in a loop-like structure which may provide an additional layer of end protection. As we still lack insight into the regulation of the folded telomere structure, we used budding yeast to establish a method to measure telomere folding and then study the genetic requirements for its establishment. We found that cells require the homologous recombination machinery as well as components of the DNA damage checkpoint to successfully establish a folded telomere. Through the deletion of telomerase in budding yeast, we investigated how telomere folding was regulated during replicative senescence, a process that occurs in the majority of telomerase negative human cells. During senescence, telomeres gradually shorten and erode until cells stop dividing which is a potent tumor suppressor and prevents unscheduled growth of potential cancer cells. We found, that the folded telomere structure is compromised as part of the cellular senescence response, but not due to telomere shortening per se. We think, that an altered telomeric chromatin environment during senescence is important to maintain an open state – which may be important for signaling or for repair.

scholarly journals Chromatin modifiers and recombination factors promote a telomere fold-back structure, that is lost during replicative senescence

PLoS Genetics ◽  
2020 ◽  
Vol 16 (12) ◽  
pp. e1008603
Author(s):  
Tina Wagner ◽  
Lara Pérez-Martínez ◽  
René Schellhaas ◽  
Marta Barrientos-Moreno ◽  
Merve Öztürk ◽  
...  
Keyword(s):  
Homologous Recombination ◽  
Short Distance ◽  
Replicative Senescence ◽  
Spatial Arrangement ◽  
Short Telomere ◽  
Chromosome Conformation ◽  
Protein Levels ◽  
Histone Modifiers ◽  
Yeast Telomere ◽  
Subtelomeric Regions

Telomeres have the ability to adopt a lariat conformation and hence, engage in long and short distance intra-chromosome interactions. Budding yeast telomeres were proposed to fold back into subtelomeric regions, but a robust assay to quantitatively characterize this structure has been lacking. Therefore, it is not well understood how the interactions between telomeres and non-telomeric regions are established and regulated. We employ a telomere chromosome conformation capture (Telo-3C) approach to directly analyze telomere folding and its maintenance in S. cerevisiae. We identify the histone modifiers Sir2, Sin3 and Set2 as critical regulators for telomere folding, which suggests that a distinct telomeric chromatin environment is a major requirement for the folding of yeast telomeres. We demonstrate that telomeres are not folded when cells enter replicative senescence, which occurs independently of short telomere length. Indeed, Sir2, Sin3 and Set2 protein levels are decreased during senescence and their absence may thereby prevent telomere folding. Additionally, we show that the homologous recombination machinery, including the Rad51 and Rad52 proteins, as well as the checkpoint component Rad53 are essential for establishing the telomere fold-back structure. This study outlines a method to interrogate telomere-subtelomere interactions at a single unmodified yeast telomere. Using this method, we provide insights into how the spatial arrangement of the chromosome end structure is established and demonstrate that telomere folding is compromised throughout replicative senescence.

scholarly journals Comparative Analysis of P73 and P53 Regulation and Effector Functions

1999 ◽  
Vol 147 (4) ◽  
pp. 823-830 ◽  
Author(s):  
Li Fang ◽  
Sam W. Lee ◽  
Stuart A. Aaronson
Keyword(s):  
Dna Damage ◽  
Replicative Senescence ◽  
Human Cancer ◽  
Growth Arrest ◽  
Mcf7 Cells ◽  
Effector Functions ◽  
Human Cancer Cells ◽  
Protein Levels ◽  
Selective Pressures ◽  
Dna Damaging Agents

p53 is mutated in ∼50% of human cancers, whereas mutations of the related p73 gene are rare. p73 can activate p53-responsive promoters and induce apoptosis when overexpressed in certain p53-deficient tumor cells. We show that p73 isoforms, p73α and p73β, can each induce permanent growth arrest with markers of replicative senescence when overexpressed in a tetracycline-regulatable manner in human cancer cells lacking functional p53. Human homologue of mouse double minute 2 gene product (hMDM2), but not an NH2-terminal deletion mutant, coimmunoprecipated with p73α or p73β, and inhibited p73 transcriptional activity as with p53. In contrast to p53, ectopically expressed hemagglutinin (HA)-tagged p73 proteins were not stabilized by treatment with several DNA damaging agents. Furthermore, unlike normal p53, which increases in response to DNA damage due to enhanced protein stability in MCF7 cells, endogenous p73 protein levels were not increased in these cells under the same conditions. Thus, although p73 has an ability, comparable to that of p53, to suppress tumor cell growth in p53-deficient cells, p73 induction is regulated differently from p53. These findings suggest that the selective pressures for p53 rather than p73 inactivation in tumors may reflect their differential responses to stresses such as DNA damage, rather than their capacities to induce permanent growth arrest or apoptosis programs.

scholarly journals Genome protection: histone H4 and beyond

2020 ◽  
Vol 66 (5) ◽  
pp. 945-950
Author(s):  
Kundan Kumar ◽  
Romila Moirangthem ◽  
Rupinder Kaur
Keyword(s):  
Dna Damage ◽  
Dna Repair ◽  
Homologous Recombination ◽  
Stress Responses ◽  
Gene Dosage ◽  
Repair Process ◽  
Histone H4 ◽  
Pathogenic Yeast ◽  
Protein Levels ◽  
Genome Protection

Abstract Histone proteins regulate cellular factors’ accessibility to DNA, and histone dosage has previously been linked with DNA damage susceptibility and efficiency of DNA repair pathways. Surplus histones are known to impede the DNA repair process by interfering with the homologous recombination-mediated DNA repair in Saccharomyces cerevisiae. Here, we discuss the recent finding of association of methyl methanesulfonate (MMS) resistance with the reduced histone H4 gene dosage in the pathogenic yeast Candida glabrata. We have earlier shown that while the low histone H3 gene dosage led to MMS susceptibility, the lack of two H4-encoding ORFs, CgHHF1 and CgHHF2, led to resistance to MMS-induced DNA damage. This resistance was linked with a higher rate of homologous recombination (HR). Taking these findings further, we review the interactome analysis of histones H3 and H4 in C. glabrata. We also report that the arginine residue present at the 95th position in the C-terminal tail of histone H4 protein is required for complementation of the MMS resistance in the Cghhf1Δhhf2Δ mutant, thereby pointing out a probable role of this residue in association with HR factors. Additionally, we present evidence that reduction in H4 protein levels may constitute an important part of varied stress responses in C. glabrata. Altogether, we present an overview of histone H4 dosage, HR-mediated repair of damaged DNA and stress resistance in this opportunistic human fungal pathogen.

scholarly journals EXO1 Plays a Role in Generating Type I and Type II Survivors in Budding Yeast

Genetics ◽  
2004 ◽  
Vol 166 (4) ◽  
pp. 1641-1649
Author(s):  
Laura Maringele ◽  
David Lydall
Keyword(s):  
Homologous Recombination ◽  
Budding Yeast ◽  
Human Cells ◽  
Telomere Maintenance ◽  
Recombination Process ◽  
Yeast Cells ◽  
Type I ◽  
Type Ii ◽  
Recombination Proteins

Abstract Telomerase-defective budding yeast cells escape senescence by using homologous recombination to amplify telomeric or subtelomeric structures. Similarly, human cells that enter senescence can use homologous recombination for telomere maintenance, when telomerase cannot be activated. Although recombination proteins required to generate telomerase-independent survivors have been intensively studied, little is known about the nucleases that generate the substrates for recombination. Here we demonstrate that the Exo1 exonuclease is an initiator of the recombination process that allows cells to escape senescence and become immortal in the absence of telomerase. We show that EXO1 is important for generating type I survivors in yku70Δ mre11Δ cells and type II survivors in tlc1Δ cells. Moreover, in tlc1Δ cells, EXO1 seems to contribute to the senescence process itself.

scholarly journals DHX9-dependent recruitment of BRCA1 to RNA promotes DNA end resection in homologous recombination

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Prasun Chakraborty ◽  
Kevin Hiom
Keyword(s):  
Dna Damage ◽  
Homologous Recombination ◽  
Rna Polymerase Ii ◽  
Critical Role ◽  
Dna Breaks ◽  
Double Stranded Dna ◽  
Recombination Repair ◽  
Dna End Resection ◽  
End Resection ◽  
Rna Polymerase Ii Transcription

AbstractDouble stranded DNA Breaks (DSB) that occur in highly transcribed regions of the genome are preferentially repaired by homologous recombination repair (HR). However, the mechanisms that link transcription with HR are unknown. Here we identify a critical role for DHX9, a RNA helicase involved in the processing of pre-mRNA during transcription, in the initiation of HR. Cells that are deficient in DHX9 are impaired in the recruitment of RPA and RAD51 to sites of DNA damage and fail to repair DSB by HR. Consequently, these cells are hypersensitive to treatment with agents such as camptothecin and Olaparib that block transcription and generate DSB that specifically require HR for their repair. We show that DHX9 plays a critical role in HR by promoting the recruitment of BRCA1 to RNA as part of the RNA Polymerase II transcription complex, where it facilitates the resection of DSB. Moreover, defects in DHX9 also lead to impaired ATR-mediated damage signalling and an inability to restart DNA replication at camptothecin-induced DSB. Together, our data reveal a previously unknown role for DHX9 in the DNA Damage Response that provides a critical link between RNA, RNA Pol II and the repair of DNA damage by homologous recombination.

scholarly journals Telomeres and replicative cellular aging of the human placenta and chorioamniotic membranes

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tsung-Po Lai ◽  
Mark Simpson ◽  
Krunal Patel ◽  
Simon Verhulst ◽  
Jungsik Noh ◽  
...  
Keyword(s):  
Dna Damage ◽  
Preterm Birth ◽  
Telomere Length ◽  
Human Placenta ◽  
Replicative Senescence ◽  
Preterm Births ◽  
Full Term ◽  
Cellular Aging ◽  
Telomere Dysfunction ◽  
Replicative Aging

AbstractRecent hypotheses propose that the human placenta and chorioamniotic membranes (CAMs) experience telomere length (TL)-mediated senescence. These hypotheses are based on mean TL (mTL) measurements, but replicative senescence is triggered by short and dysfunctional telomeres, not mTL. We measured short telomeres by a vanguard method, the Telomere shortest length assay, and telomere-dysfunction-induced DNA damage foci (TIF) in placentas and CAMs between 18-week gestation and at full-term. Both the placenta and CAMs showed a buildup of short telomeres and TIFs, but not shortening of mTL from 18-weeks to full-term. In the placenta, TIFs correlated with short telomeres but not mTL. CAMs of preterm birth pregnancies with intra-amniotic infection showed shorter mTL and increased proportions of short telomeres. We conclude that the placenta and probably the CAMs undergo TL-mediated replicative aging. Further research is warranted whether TL-mediated replicative aging plays a role in all preterm births.

scholarly journals Systems Level Modeling of the Cell Cycle Using Budding Yeast

2007 ◽  
Vol 3 ◽  
pp. 117693510700300 ◽  
Author(s):  
B.P. Ingalls ◽  
B.P. Duncker ◽  
D.R. Kim ◽  
B.J. McConkey
Keyword(s):  
Cell Cycle ◽  
Budding Yeast ◽  
Human Cancer ◽  
Quality Data ◽  
Cell Cycle Gene ◽  
Mathematical Framework ◽  
Gene Transcript ◽  
Proteomics Data ◽  
Yeast Saccharomyces Cerevisiae ◽  
Protein Levels

Proteins involved in the regulation of the cell cycle are highly conserved across all eukaryotes, and so a relatively simple eukaryote such as yeast can provide insight into a variety of cell cycle perturbations including those that occur in human cancer. To date, the budding yeast Saccharomyces cerevisiae has provided the largest amount of experimental and modeling data on the progression of the cell cycle, making it a logical choice for in-depth studies of this process. Moreover, the advent of methods for collection of high-throughput genome, transcriptome, and proteome data has provided a means to collect and precisely quantify simultaneous cell cycle gene transcript and protein levels, permitting modeling of the cell cycle on the systems level. With the appropriate mathematical framework and sufficient and accurate data on cell cycle components, it should be possible to create a model of the cell cycle that not only effectively describes its operation, but can also predict responses to perturbations such as variation in protein levels and responses to external stimuli including targeted inhibition by drugs. In this review, we summarize existing data on the yeast cell cycle, proteomics technologies for quantifying cell cycle proteins, and the mathematical frameworks that can integrate this data into representative and effective models. Systems level modeling of the cell cycle will require the integration of high-quality data with the appropriate mathematical framework, which can currently be attained through the combination of dynamic modeling based on proteomics data and using yeast as a model organism.

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