A hypomorphic allele of telomerase uncovers the minimal functional length of telomeres in Arabidopsis

Genetics ◽  
2021 ◽  
Author(s):  
J Matthew Watson ◽  
Johanna Trieb ◽  
Martina Troestl ◽  
Kyle Renfrew ◽  
Terezie Mandakova ◽  
...  
Keyword(s):  
Genome Stability ◽  
Telomerase Activity ◽  
Minimal Length ◽  
Proper Function ◽  
Loop Formation ◽  
Telomeric Dna ◽  
Essential Requirement ◽  
Cis Acting ◽  
Hypomorphic Allele ◽  
Necessary And Sufficient

Abstract Despite the essential requirement of telomeric DNA for genome stability, the length of telomere tracts between species substantially differs, raising the question of the minimal length of telomeric DNA necessary for proper function. Here we address this question using a hypomorphic allele of the telomerase catalytic subunit, TERT. We show that although this construct partially restored telomerase activity to a tert mutant, telomeres continued to shorten over several generations, ultimately stabilizing at a bimodal size distribution. Telomeres on two chromosome arms were maintained at a length of 1kb, while the remaining telomeres were maintained at 400 bp. The longest telomeres identified in this background were also significantly longer in wild type populations, suggesting cis-acting elements on these arms either promote telomerase processivity or recruitment. Genetically disrupting telomerase processivity in this background resulted in immediate lethality. Thus, telomeres of 400 bp are both necessary and sufficient for Arabidopsis viability. As this length is the estimated minimal length for t-loop formation, our data suggest that telomeres long enough to form a t-loop constitute the minimal functional length.

scholarly journals A hypomorphic allele of telomerase reverse transcriptase uncovers the minimal functional length of telomeres in Arabidopsis

2019 ◽  
Author(s):  
J. Matthew Watson ◽  
Johanna Trieb ◽  
Martina Troestl ◽  
Kyle Renfrew ◽  
Terezie Mandakova ◽  
...  
Keyword(s):  
Genome Stability ◽  
Telomerase Activity ◽  
Minimal Length ◽  
Proper Function ◽  
Loop Formation ◽  
Telomeric Dna ◽  
Essential Requirement ◽  
Cis Acting ◽  
Hypomorphic Allele ◽  
Necessary And Sufficient

AbstractDespite the essential requirement of telomeric DNA for genome stability, the length of telomere tracts between species differs by up to four orders of magnitude, raising the question of the minimal length of telomeric DNA necessary for proper function. Here we address this question using a hypomorphic allele of the telomerase catalytic subunit, TERT. We show that although this construct partially restored telomerase activity to a tert mutant, telomeres continued to shorten over several generations, ultimately stabilizing at a bimodal size distribution. Telomeres on two chromosome arms were maintained at a length of 1kb, while the remaining telomeres were maintained at 400 bp. The longest telomeres identified in this background were also significantly longer in wild type populations, suggesting cis-acting elements on these arms either promote telomerase processivity or recruitment. Genetically disrupting telomerase processivity in this background resulted in immediate lethality. Thus, telomeres of 400 bp are both necessary and sufficient for Arabidopsis viability. As this length is the estimated minimal length for t-loop formation, our data suggest that telomeres long enough to form a t-loop constitute the minimal functional length.

AMPK blocks chromatin activation and consequent R-loop formation to protect genome stability following acute starvation

2021 ◽  
Author(s):  
Bing Sun ◽  
McLean Sherrin ◽  
Richard Roy
Keyword(s):  
Dna Damage ◽  
Genome Stability ◽  
Germ Line ◽  
Critical Role ◽  
Significant Proportion ◽  
Loop Formation ◽  
C Elegans ◽  
Chromatin Activation ◽  
Acute Starvation

Abstract During periods of starvation organisms must modify both gene expression and metabolic pathways to adjust to the energy stress. We previously reported that C. elegans that lack AMPK have transgenerational reproductive defects that result from abnormally elevated H3K4me3 levels in the germ line following recovery from acute starvation1. Here we show that H3K4me3 is dramatically increased at promoters, driving aberrant transcription elongation that results in the accumulation of R-loops in the starved AMPK mutants. DRIP-seq analysis demonstrated that a significant proportion of the genome was affected by R-loop formation with a dramatic expansion in the number of R-loops at numerous loci, most pronounced at the promoter-TSS regions of genes in the starved AMPK mutants. The R-loops are transmissible into subsequent generations, likely contributing to the transgenerational reproductive defects typical of these mutants following starvation. Strikingly, AMPK null germ lines show considerably more RAD-51 foci at sites of R-loop formation, potentially sequestering it from its critical role at meiotic breaks and/or at sites of induced DNA damage. Our study reveals a previously unforeseen role of AMPK in maintaining genome stability following starvation, where in its absence R-loops accumulate, resulting in reproductive compromise and DNA damage hypersensitivity.

scholarly journals The conserved structure of plant telomerase RNA provides the missing link for an evolutionary pathway from ciliates to humans

2019 ◽  
Vol 116 (49) ◽  
pp. 24542-24550 ◽  
Author(s):  
Jiarui Song ◽  
Dhenugen Logeswaran ◽  
Claudia Castillo-González ◽  
Yang Li ◽  
Sreyashree Bose ◽  
...  
Keyword(s):  
Telomerase Activity ◽  
Telomere Maintenance ◽  
Telomerase Rna ◽  
Telomeric Dna ◽  
Structural Element ◽  
Stem Loop ◽  
Evolutionary Pathway ◽  
Pol Iii

Telomerase is essential for maintaining telomere integrity. Although telomerase function is widely conserved, the integral telomerase RNA (TR) that provides a template for telomeric DNA synthesis has diverged dramatically. Nevertheless, TR molecules retain 2 highly conserved structural domains critical for catalysis: a template-proximal pseudoknot (PK) structure and a downstream stem-loop structure. Here we introduce the authentic TR from the plant Arabidopsis thaliana, called AtTR, identified through next-generation sequencing of RNAs copurifying with Arabidopsis TERT. This RNA is distinct from the RNA previously described as the templating telomerase RNA, AtTER1. AtTR is a 268-nt Pol III transcript necessary for telomere maintenance in vivo and sufficient with TERT to reconstitute telomerase activity in vitro. Bioinformatics analysis identified 85 AtTR orthologs from 3 major clades of plants: angiosperms, gymnosperms, and lycophytes. Through phylogenetic comparisons, a secondary structure model conserved among plant TRs was inferred and verified using in vitro and in vivo chemical probing. The conserved plant TR structure contains a template-PK core domain enclosed by a P1 stem and a 3′ long-stem P4/5/6, both of which resemble a corresponding structural element in ciliate and vertebrate TRs. However, the plant TR contains additional stems and linkers within the template-PK core, allowing for expansion of PK structure from the simple PK in the smaller ciliate TR during evolution. Thus, the plant TR provides an evolutionary bridge that unites the disparate structures of previously characterized TRs from ciliates and vertebrates.

Telomeres, telomerase, and apoptosis

2004 ◽  
Vol 82 (4) ◽  
pp. 498-507 ◽  
Author(s):  
Chiara Mondello ◽  
A Ivana Scovassi
Keyword(s):  
Cancer Cells ◽  
Telomerase Activity ◽  
Telomeric Dna ◽  
Apoptotic Response ◽  
Reverse Transcriptase Enzyme ◽  
Limited Life ◽  
Specific Proteins ◽  
Telomere Capping ◽  
The Impact ◽  
High Order Chromatin

Telomeres are specialized high-order chromatin structures that cap the ends of eukaryotic chromosomes. In vertebrates, telomeric DNA is composed of repetitions of the TTAGGG hexanucleotide, is bound to a set of specific proteins, and is elongated by the reverse transcriptase enzyme telomerase. Telomerase activity is promptly detected in cells with an indefinite replicative potential, such as cancer cells, while is almost undetectable in normal cells, which are characterized by a limited life span. Mounting evidence indicates that the maintenance of telomere integrity and telomerase protect cells from apoptosis. Disruption of the telomere capping function and (or) telomerase inhibition elicit an apoptotic response in cancer cells, while restoration of telomerase activity in somatic cells confers resistance to apoptosis. The possible mechanisms linking telomeres, telomerase and apoptosis are discussed in this review, together with the impact of this field in anticancer research.Key words: telomeres, telomerase, telomeric proteins, apoptosis, tumorigenesis.

scholarly journals Infinite Paths of Minimal Length on Suborbital Graphs for Some Fuchsian Groups

2019 ◽  
Vol 2019 ◽  
pp. 1-8
Author(s):  
Khuanchanok Chaichana ◽  
Pradthana Jaipong
Keyword(s):  
Prime Number ◽  
Fuchsian Group ◽  
Continued Fraction ◽  
Sufficient Conditions ◽  
Minimal Length ◽  
Necessary And Sufficient Conditions ◽  
Fuchsian Groups ◽  
Suborbital Graphs ◽  
Necessary And Sufficient ◽  
Recursive Representation

In this study, we work on the Fuchsian group Hm where m is a prime number acting on mℚ^ transitively. We give necessary and sufficient conditions for two vertices to be adjacent in suborbital graphs induced by these groups. Moreover, we investigate infinite paths of minimal length in graphs and give the recursive representation of continued fraction of such vertex.

scholarly journals Dissecting Molecular Steps in Chromatin Domain Activation during Hematopoietic Differentiation

2007 ◽  
Vol 27 (12) ◽  
pp. 4551-4565 ◽  
Author(s):  
Shin-Il Kim ◽  
Scott J. Bultman ◽  
Huie Jing ◽  
Gerd A. Blobel ◽  
Emery H. Bresnick
Keyword(s):  
Rna Polymerase Ii ◽  
Transcriptional Activation ◽  
Chromatin Domain ◽  
Loop Formation ◽  
Pol Ii ◽  
Gata Factors ◽  
Hypomorphic Allele ◽  
Promoter Complex ◽  
Complex Locus ◽  
Carboxy Terminal

ABSTRACT GATA factors orchestrate hematopoiesis via multistep transcriptional mechanisms, but the interrelationships and importance of individual steps are poorly understood. Using complementation analysis with GATA-1-null cells and mice containing a hypomorphic allele of the chromatin remodeler BRG1, we dissected the pathway from GATA-1 binding to cofactor recruitment, chromatin loop formation, and transcriptional activation. Analysis of GATA-1-mediated activation of the β-globin locus, in which GATA-1 assembles dispersed complexes at the promoters and the distal locus control region (LCR), revealed molecular intermediates, including GATA-1-independent and GATA-1-containing LCR subcomplexes, both defective in promoting loop formation. An additional intermediate consisted of an apparently normal LCR complex and a promoter complex with reduced levels of total RNA polymerase II (Pol II) and Pol II phosphorylated at serine 5 of the carboxy-terminal domain. Reduced BRG1 activity solely compromised Pol II and serine 5-phosphorylated Pol II occupancy at the promoter, phenocopying the LCR-deleted mouse. These studies defined a hierarchical order of GATA-1-triggered events at a complex locus and establish a novel mechanism of long-range gene regulation.

scholarly journals Yeast Est2p Affects Telomere Length by Influencing Association of Rap1p with Telomeric Chromatin

2008 ◽  
Vol 28 (7) ◽  
pp. 2380-2390 ◽  
Author(s):  
Hong Ji ◽  
Christopher J. Adkins ◽  
Bethany R. Cartwright ◽  
Katherine L. Friedman
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Telomere Length ◽  
Specific Binding ◽  
Telomerase Activity ◽  
Negative Regulator ◽  
Wild Type ◽  
Telomeric Dna ◽  
Telomere Length Homeostasis

ABSTRACT In Saccharomyces cerevisiae, the sequence-specific binding of the negative regulator Rap1p provides a mechanism to measure telomere length: as the telomere length increases, the binding of additional Rap1p inhibits telomerase activity in cis. We provide evidence that the association of Rap1p with telomeric DNA in vivo occurs in part by sequence-independent mechanisms. Specific mutations in EST2 (est2-LT) reduce the association of Rap1p with telomeric DNA in vivo. As a result, telomeres are abnormally long yet bind an amount of Rap1p equivalent to that observed at wild-type telomeres. This behavior contrasts with that of a second mutation in EST2 (est2-up34) that increases bound Rap1p as expected for a strain with long telomeres. Telomere sequences are subtly altered in est2-LT strains, but similar changes in est2-up34 telomeres suggest that sequence abnormalities are a consequence, not a cause, of overelongation. Indeed, est2-LT telomeres bind Rap1p indistinguishably from the wild type in vitro. Taken together, these results suggest that Est2p can directly or indirectly influence the binding of Rap1p to telomeric DNA, implicating telomerase in roles both upstream and downstream of Rap1p in telomere length homeostasis.

scholarly journals Towards structural characterization of H. polymorpha telomerase components

2014 ◽  
Vol 70 (a1) ◽  
pp. C816-C816
Author(s):  
Johanna Kallio ◽  
Elena Rodina ◽  
Maria Zvereva ◽  
Olga Petrova ◽  
Alexandr Malyavko ◽  
...  
Keyword(s):  
Cell Division ◽  
Structural Information ◽  
Hansenula Polymorpha ◽  
Embryonic Stem ◽  
Telomerase Activity ◽  
Premature Aging ◽  
Telomeric Dna ◽  
Terminal Domain ◽  
Protein Components

Telomeres are regions of non-coding DNA that cap the chromosomes, preventing the loss of coding DNA during cell division and contributing to chromosomal stability. In actively dividing cells, such as embryonic stem cells, the telomeres need to elongated by telomerase. The telomerase complex consist of the enzyme telomerase reverse transcriptase (TERT), telomerase RNA (TR) and additional proteins. TERT and TR are required for the telomerase activity in vitro. Telomerase is active in vast majority of the cancer cells ensuring continuous cell division and tumor growth. Syndromes leading to premature aging are often associated with short telomeres. Finding ways to regulate the telomerase activity would help to advance therapies for these conditions. However, the structural information available of the telomerase complex is very limited. We have chosen thermophilic yeast Hansenula polymorpha as a model system due to the stability of its proteins. The N-terminal domain of the TERT is essential for telomerase activity and possibly is involved in binding of TR, telomeric DNA and additional protein components of the telomerase complex. We have crystallised the N-terminal domain of H. polymorpha TERT and, in lack of a homologious structure, produced a seleno-methionine derivative of the protein. MAD data on N-terminal domain has been collected to resolution of 2.0 Å at the PETRA-III beamline P13 (EMBL/DESY) in Hamburg. We will discuss the structure-function relationship of the N-domain and the whole TERT component.

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