Step-by-step evolution of telomeres: lessons from yeasts

Abstract In virtually every eukaryotic species, the ends of nuclear chromosomes are protected by telomeres, nucleoprotein structures counteracting the end-replication problem and suppressing recombination and undue DNA repair. Although in most cases, the primary structure of telomeric DNA is conserved, there are several exceptions to this rule. One is represented by the telomeric repeats of ascomycetous yeasts, which encompass a great variety of sequences, whose evolutionary origin has been puzzling for several decades. At present, the key questions concerning the driving force behind their rapid evolution and the means of co-evolution of telomeric repeats and telomere-binding proteins remain largely unanswered. Previously published studies addressed mostly the general concepts of the evolutionary origin of telomeres, key properties of telomeric proteins as well as the molecular mechanisms of telomere maintenance, however, the evolutionary process itself has not been analyzed thoroughly. Here, we aimed to inspect the evolution of telomeres in ascomycetous yeasts from the subphyla Saccharomycotina and Taphrinomycotina, with special focus on the evolutionary origin of species-specific telomeric repeats. We analyzed the sequences of telomeric repeats from 204 yeast species classified into 20 families and as a result, we propose a step-by-step model, which integrates the diversity of telomeric repeats, telomerase RNAs, telomere-binding protein complexes and explains a propensity of certain species to generate the repeat heterogeneity within a single telomeric array.

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G-Quadruplexes at Telomeres: Friend or Foe?

Molecules ◽

10.3390/molecules25163686 ◽

2020 ◽

Vol 25 (16) ◽

pp. 3686 ◽

Cited By ~ 3

Author(s):

Tracy M. Bryan

Keyword(s):

Tandem Repeats ◽

Genome Instability ◽

Protein Complexes ◽

Telomere Maintenance ◽

Telomeric Dna ◽

Positive Role ◽

Telomere Biology ◽

Linear Chromosomes

Telomeres are DNA-protein complexes that cap and protect the ends of linear chromosomes. In almost all species, telomeric DNA has a G/C strand bias, and the short tandem repeats of the G-rich strand have the capacity to form into secondary structures in vitro, such as four-stranded G-quadruplexes. This has long prompted speculation that G-quadruplexes play a positive role in telomere biology, resulting in selection for G-rich tandem telomere repeats during evolution. There is some evidence that G-quadruplexes at telomeres may play a protective capping role, at least in yeast, and that they may positively affect telomere maintenance by either the enzyme telomerase or by recombination-based mechanisms. On the other hand, G-quadruplex formation in telomeric DNA, as elsewhere in the genome, can form an impediment to DNA replication and a source of genome instability. This review summarizes recent evidence for the in vivo existence of G-quadruplexes at telomeres, with a focus on human telomeres, and highlights some of the many unanswered questions regarding the location, form, and functions of these structures.

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Mechanism of processive telomerase catalysis revealed by high-resolution optical tweezers

10.1101/700294 ◽

2019 ◽

Author(s):

Eric M. Patrick ◽

Joseph Slivka ◽

Bramyn Payne ◽

Matthew J. Comstock ◽

Jens C. Schmidt

Keyword(s):

High Resolution ◽

Optical Tweezers ◽

Single Molecule ◽

Telomerase Activity ◽

Telomere Maintenance ◽

Telomeric Dna ◽

Telomeric Repeats ◽

G Quadruplex ◽

Stable Substrate ◽

Template Region

Telomere maintenance by telomerase is essential for continuous proliferation of human cells and is vital for the survival of stem cells and 90% of cancer cells. To compensate for telomeric DNA lost during DNA replication, telomerase processively adds GGTTAG repeats to chromosome ends by copying the template region within its RNA subunit. Between repeat additions, the RNA template must be recycled. How telomerase remains associated with substrate DNA during this critical translocation step remains unknown. Using a newly developed single-molecule telomerase activity assay utilizing high-resolution optical tweezers, we demonstrate that stable substrate DNA binding at an anchor site within telomerase facilitates the processive synthesis of telomeric repeats. After release of multiple telomeric repeats from telomerase, we observed folding of product DNA into G-quadruplex structures. Our results provide detailed mechanistic insights into telomerase catalysis, a process of critical importance in aging and cancer.

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The TGFβ Family in Human Placental Development at the Fetal-Maternal Interface

Biomolecules ◽

10.3390/biom10030453 ◽

2020 ◽

Vol 10 (3) ◽

pp. 453

Author(s):

Susana M. Chuva de Sousa Lopes ◽

Marta S. Alexdottir ◽

Gudrun Valdimarsdottir

Keyword(s):

Stem Cell ◽

Transforming Growth Factor Beta ◽

Molecular Mechanisms ◽

Transforming Growth Factor ◽

Cell Model ◽

Embryonic Stem ◽

Model Systems ◽

Special Focus ◽

Placental Development

Emerging data suggest that a trophoblast stem cell (TSC) population exists in the early human placenta. However, in vitro stem cell culture models are still in development and it remains under debate how well they reflect primary trophoblast (TB) cells. The absence of robust protocols to generate TSCs from humans has resulted in limited knowledge of the molecular mechanisms that regulate human placental development and TB lineage specification when compared to other human embryonic stem cells (hESCs). As placentation in mouse and human differ considerably, it is only with the development of human-based disease models using TSCs that we will be able to understand the various diseases caused by abnormal placentation in humans, such as preeclampsia. In this review, we summarize the knowledge on normal human placental development, the placental disease preeclampsia, and current stem cell model systems used to mimic TB differentiation. A special focus is given to the transforming growth factor-beta (TGFβ) family as it has been shown that the TGFβ family has an important role in human placental development and disease.

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MicroRNAs and Stem-like Properties: The Complex Regulation Underlying Stemness Maintenance and Cancer Development

Biomolecules ◽

10.3390/biom11081074 ◽

2021 ◽

Vol 11 (8) ◽

pp. 1074

Author(s):

Giuseppina Divisato ◽

Silvia Piscitelli ◽

Mariantonietta Elia ◽

Emanuela Cascone ◽

Silvia Parisi

Keyword(s):

Stem Cells ◽

Molecular Mechanisms ◽

Epithelial Mesenchymal Transition ◽

Embryonic Stem ◽

Cell Types ◽

Cancer Development ◽

Special Focus ◽

Self Renewal ◽

Mesenchymal Transition ◽

Different Cell Types

Embryonic stem cells (ESCs) have the extraordinary properties to indefinitely proliferate and self-renew in culture to produce different cell progeny through differentiation. This latter process recapitulates embryonic development and requires rounds of the epithelial–mesenchymal transition (EMT). EMT is characterized by the loss of the epithelial features and the acquisition of the typical phenotype of the mesenchymal cells. In pathological conditions, EMT can confer stemness or stem-like phenotypes, playing a role in the tumorigenic process. Cancer stem cells (CSCs) represent a subpopulation, found in the tumor tissues, with stem-like properties such as uncontrolled proliferation, self-renewal, and ability to differentiate into different cell types. ESCs and CSCs share numerous features (pluripotency, self-renewal, expression of stemness genes, and acquisition of epithelial–mesenchymal features), and most of them are under the control of microRNAs (miRNAs). These small molecules have relevant roles during both embryogenesis and cancer development. The aim of this review was to recapitulate molecular mechanisms shared by ESCs and CSCs, with a special focus on the recently identified classes of microRNAs (noncanonical miRNAs, mirtrons, isomiRs, and competitive endogenous miRNAs) and their complex functions during embryogenesis and cancer development.

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Transcriptome and proteome analysis suggest enhanced photosynthesis in tetraploid Liriodendron sino-americanum

Tree Physiology ◽

10.1093/treephys/tpab039 ◽

2021 ◽

Author(s):

Tingting Chen ◽

Yu Sheng ◽

Zhaodong Hao ◽

Xiaofei Long ◽

Fangfang Fu ◽

...

Keyword(s):

Molecular Mechanisms ◽

Protein Complexes ◽

Proteome Analysis ◽

Tree Height ◽

Photosynthetic Electron Transport ◽

Industrial Applications ◽

Chlorophyll Protein Complexes ◽

Chlorophyll Protein ◽

Photosynthesis Genes ◽

Underlying Mechanisms

Abstract Polyploidy generally provides an advantage in phenotypic variation and growth vigor. However, the underlying mechanisms remain poorly understood. The tetraploid L. sino-americanum exhibits altered morphology compared to its diploid counterpart, including larger, thicker and deeper green leaves, bigger stomata, thicker stems and increased tree height. Such characteristics can be useful in ornamental and industrial applications. To elucidate the molecular mechanisms behind this variation, we performed a comparative transcriptome and proteome analysis. Our transcriptome data indicated that some photosynthesis genes and pathways were differentially altered and enriched in tetraploid L. sino-americanum, mainly related to F-type ATPase, the cytochrome b6/f complex, photosynthetic electron transport, the light harvesting chlorophyll protein complexes, photosystem I and II. Most of the differentially expressed proteins we could identify are also involved in photosynthesis. Our physiological results showed that tetraploids have an enhanced photosynthetic capacity, concomitant with great levels of sugar and starch in leaves. This suggests that tetraploid L. sino-americanum might experience comprehensive transcriptome reprogramming of genes related to photosynthesis. This study has especially emphasized molecular changes involved in photosynthesis that accompany polyploidy, and provides a possible explanation for the altered phenotype of polyploidy plants in comparison to their diploid form.

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Molecular Analysis of SARS-CoV-2 Genetic Lineages in Jordan: Tracking the Introduction and Spread of COVID-19 UK Variant of Concern at a Country Level

Pathogens ◽

10.3390/pathogens10030302 ◽

2021 ◽

Vol 10 (3) ◽

pp. 302

Author(s):

Malik Sallam ◽

Azmi Mahafzah

Keyword(s):

Amino Acid ◽

Amino Acid Substitution ◽

Rapid Evolution ◽

Molecular Signature ◽

Special Focus ◽

Genetic Lineage ◽

Synonymous Mutation ◽

Spike Gene ◽

Genetic Lineages ◽

The Uk

The rapid evolution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is manifested by the emergence of an ever-growing pool of genetic lineages. The aim of this study was to analyze the genetic variability of SARS-CoV-2 in Jordan, with a special focus on the UK variant of concern. A total of 579 SARS-CoV-2 sequences collected in Jordan were subjected to maximum likelihood and Bayesian phylogenetic analysis. Genetic lineage assignment was undertaken using the Pango system. Amino acid substitutions were investigated using the Protein Variation Effect Analyzer (PROVEAN) tool. A total of 19 different SARS-CoV-2 genetic lineages were detected, with the most frequent being the first Jordan lineage (B.1.1.312), first detected in August 2020 (n = 424, 73.2%). This was followed by the second Jordan lineage (B.1.36.10), first detected in September 2020 (n = 62, 10.7%), and the UK variant of concern (B.1.1.7; n = 36, 6.2%). In the spike gene region, the molecular signature for B.1.1.312 was the non-synonymous mutation A24432T resulting in a deleterious amino acid substitution (Q957L), while the molecular signature for B.1.36.10 was the synonymous mutation C22444T. Bayesian analysis revealed that the UK variant of concern (B.1.1.7) was introduced into Jordan in late November 2020 (mean estimate); four weeks earlier than its official reporting in the country. In Jordan, an exponential increase in COVID-19 cases due to B.1.1.7 lineage coincided with the new year 2021. The highest proportion of phylogenetic clustering was detected for the B.1.1.7 lineage. The amino acid substitution D614G in the spike glycoprotein was exclusively present in the country from July 2020 onwards. Two Jordanian lineages dominated infections in the country, with continuous introduction/emergence of new lineages. In Jordan, the rapid spread of the UK variant of concern should be monitored closely. The spread of SARS-CoV-2 mutants appeared to be related to the founder effect; nevertheless, the biological impact of certain mutations should be further investigated.

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Structural genomics approach to investigate deleterious impact of nsSNPs in conserved telomere maintenance component 1

Scientific Reports ◽

10.1038/s41598-021-89450-7 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Arunabh Choudhury ◽

Taj Mohammad ◽

Nikhil Samarth ◽

Afzal Hussain ◽

Md. Tabish Rehman ◽

...

Keyword(s):

Noncovalent Interactions ◽

Md Simulations ◽

Telomere Maintenance ◽

Nucleotide Polymorphisms ◽

Telomeric Dna ◽

Congenital Diseases ◽

Ob Fold ◽

Significant Conformational Change ◽

The Stability ◽

The Impact

AbstractConserved telomere maintenance component 1 (CTC1) is an important component of the CST (CTC1-STN1-TEN1) complex, involved in maintaining the stability of telomeric DNA. Several non-synonymous single-nucleotide polymorphisms (nsSNPs) in CTC1 have been reported to cause Coats plus syndrome and Dyskeratosis congenital diseases. Here, we have performed sequence and structure analyses of nsSNPs of CTC1 using state-of-the-art computational methods. The structure-based study focuses on the C-terminal OB-fold region of CTC1. There are 11 pathogenic mutations identified, and detailed structural analyses were performed. These mutations cause a significant disruption of noncovalent interactions, which may be a possible reason for CTC1 instability and consequent diseases. To see the impact of such mutations on the protein conformation, all-atom molecular dynamics (MD) simulations of CTC1-wild-type (WT) and two of the selected mutations, R806C and R806L for 200 ns, were carried out. A significant conformational change in the structure of the R806C mutant was observed. This study provides a valuable direction to understand the molecular basis of CTC1 dysfunction in disease progression, including Coats plus syndrome.

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Molecular Mechanisms Underlying the Anti-Breast Cancer Stem Cell Activity of Pterocladia capillacea and Corallina officinalis Polysaccharides

Anti-Cancer Agents in Medicinal Chemistry ◽

10.2174/1871520621666210727122756 ◽

2021 ◽

Vol 21 ◽

Author(s):

Hebatallah G. Hafez ◽

Rafat M. Mohareb ◽

Sohair M. Salem ◽

Azza A. Matloub ◽

Emad F. Eskander ◽

...

Keyword(s):

Breast Cancer ◽

Gene Expression ◽

Signaling Pathways ◽

Molecular Mechanisms ◽

Protein Complexes ◽

Cell Activity ◽

Sulfated Polysaccharide ◽

Corallina Officinalis ◽

Stem Cell Activity ◽

Mcf 7

Objective: This study aimed to appraise the activity of Pterocladia capillacea and Corallina officinalis polysaccharides against breast cancer stem cells (BCSCs). P. capillacea and C. officinalis polysaccharides were characterized to be sulfated polysaccharide-protein complexes. Methods: Cytotoxicity of the polysaccharides against MDA-MB-231 and MCF-7 cell lines along with their impact on CD44+/CD24− and aldehyde dehydrogenase 1(ALDH1) positive BCSC population were determined. Their effect on gene expression of CSC markers, Wnt/β-catenin and Notch signaling pathways was evaluated. Results: P. capillacea and C. officinalis polysaccharides inhibited the growth of breast cancer cells and reduced BCSC subpopulation. P. capillacea polysaccharides significantly down-regulated OCT4, SOX2, ALDH1A3 and vimentin in MDA-MB-231 as well as in MCF-7 cells except for vimentin that was up-regulated in MCF-7 cells. C. officinalis polysaccharides exhibited similar effects except for OCT4 that was up-regulated in MDA-MB-231 cells. Significant suppression of Cyclin D1 gene expression was noted in MDA-MB-231 and MCF-7 cells treated with P. capillacea or C. officinalis polysaccharides. β-catenin and c-Myc genes were significantly down-regulated in MDA-MB-231 cells treated with C. officinalis and P. capillacea polysaccharides, respectively, while being up-regulated in MCF-7 cells treated with either of them. Additionally, P. capillacea and C. officinalis polysaccharides significantly down-regulated Hes1 gene in MCF-7 cells despite increasing Notch1 gene expression level. However, significant down-regulation of Notch1 gene was observed in MDA-MB-231 cells treated with P. capillacea polysaccharides. Conclusion: Collectively, this study provides evidence for the effectiveness of P. capillacea and C. officinalis polysaccharides in targeting BCSCs through interfering with substantial signaling pathways contributing to their functionality.

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Updating the NLRC4 Inflammasome: from Bacterial Infections to Autoimmunity and Cancer

Frontiers in Immunology ◽

10.3389/fimmu.2021.702527 ◽

2021 ◽

Vol 12 ◽

Author(s):

Jiexia Wen ◽

Bin Xuan ◽

Yang Liu ◽

Liwei Wang ◽

Li He ◽

...

Keyword(s):

Bacterial Infections ◽

Molecular Mechanisms ◽

Protein Complexes ◽

Immune Defense ◽

Innate Immune ◽

Sensor Protein ◽

Different Types ◽

Microbial Infections ◽

Activation Mechanisms ◽

Specific Protease

Inflammasomes comprise a family of cytosolic multi-protein complexes that modulate the activation of cysteine-aspartate-specific protease 1 (caspase-1) and promote the maturation and secretion of interleukin (IL)-1β and IL-18, leading to an inflammatory response. Different types of inflammasomes are defined by their sensor protein which recognizes pathogenic ligands and then directs inflammasome assembly. Although the specific molecular mechanisms underlying the activation of most inflammasomes are still unclear, NLRC4 inflammasomes have emerged as multifaceted agents of the innate immune response, playing important roles in immune defense against a variety of pathogens. Other studies have also expanded the scope of NLRC4 inflammasomes to include a range of inherited human autoimmune diseases as well as proposed roles in cancer. In this review article, we provide an updated overview of NLRC4 inflammasomes, describing their composition, activation mechanisms and roles in both microbial infections and other disease conditions.

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Why Do Centromeres Evolve So Fast: BIR Replication, Hypermutation, Transposition, and Molecular-Drive

10.20944/preprints202012.0669.v1 ◽

2020 ◽

Author(s):

William Rice

Keyword(s):

Rapid Evolution ◽

Evolutionary Process ◽

Epigenetic Mark ◽

Replication Forks ◽

Nucleotide Substitutions ◽

Molecular Drive ◽

Repeat Structure ◽

Repeat Units ◽

Initiation Of Replication ◽

Genomic Regions

Centromeres are among the fastest evolving genomic regions in a diverse array of organisms. The evolutionary process driving this rapid evolution has not been unambiguously established. Here I integrate diverse information to motivate a model in which centromeres evolve rapidly because of their intrinsic molecular phenotype: they tightly bind centromeric proteins throughout the cell cycle. DNA-bound proteins have been shown to cause stalling and collapse of DNA replication forks in many genomic regions, including centromeres. Collapsed replication forks generate one-sided double strand breaks (DSBs) that are repaired by the Break-Induced Repair (BIR) pathway. Here I show why this repair is expected to generate tandem repeat structure and three key features at centromeres: i) increased nucleotide substitution mutation rates, ii) out-of- register re-initiation of replication that leads to indels spanning one or more repeat units, and iii) elevated rates of large and small transpositions within centromeres and between genomic regions. These phenotypes lead to: i) a rapid rate of nucleotide substitutions within a clade of centromeric sequences, ii) continual turnover of monomers within centromeres that fosters molecular-drift and molecular-drive, and iii) recurrent quantum leaps in centromere sequence due to the formation of mosaic monomers and new sequences transposed into non-homologous centromeres. These features are plausibly the major reason centromeres evolve so rapidly. I also speculate on how the DNA sequence of centromeres might perpetually coevolve with the protein sequence of histone CENH3 –the major epigenetic mark of centromeres.

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