Telomeric Repeat Research Articles

Telomeric repeat evolution in the phylum Nematoda revealed by high-quality genome assemblies and subtelomere structures.

Telomeres are composed of tandem arrays of telomeric-repeat motifs (TRMs) and telomere-binding proteins (TBPs), which are responsible for ensuring end-protection and end-replication of chromosomes. TRMs are highly conserved owing to the sequence specificity of TBPs, although significant alterations in TRM have been observed in several taxa, except Nematoda. We used public whole-genome sequencing data sets to analyze putative TRMs of 100 nematode species and determined that three distinct branches included specific novel TRMs, suggesting that evolutionary alterations in TRMs occurred in Nematoda. We focused on one of the three branches, the Panagrolaimidae family, and performed a de novo assembly of four high-quality draft genomes of the canonical (TTAGGC) and novel TRM (TTAGAC) isolates; the latter genomes revealed densely clustered arrays of the novel TRM. We then comprehensively analyzed the subtelomeric regions of the genomes to infer how the novel TRM evolved. We identified DNA damage-repair signatures in subtelomeric sequences that were representative of consequences of telomere maintenance mechanisms by alternative lengthening of telomeres. We propose a hypothetical scenario in which TTAGAC-containing units are clustered in subtelomeric regions and pre-existing TBPs capable of binding both canonical and novel TRMs aided the evolution of the novel TRM in the Panagrolaimidae family.

Lactoferrin improves symptoms of dextran sulfate sodium-induced colitis in mice through modulation of cellular senescence

The multifaceted effects of lactoferrin (LF) on the digestive and immune systems make it an attractive therapeutic option in inflammatory bowel diseases. In this study, we aimed to explore the anti-inflammatory effects of LF in colitis, particularly in relation to cellular senescence. We hypothesize that LF has the potential to modulate the senescence process. The effects of LF on senescence were tested in vitro using HCT116 and SW480 cell lines, and in vivo, the dextran sulfate sodium–induced mouse model of colitis. LF (500 mg/kg) alleviated symptoms of colitis in mice with a significant decrease in colon damage (P < .0001 vs. control) and microscopic (P < .05 vs. control) scores. Cellular senescence markers p16 and p21 were significantly upregulated in the mouse colon during inflammation (both P < .01 vs. control), and LF at 500 mg/kg decreased these markers (both P < .05 vs. dextran sulfate sodium–treated mice). In vitro, LF significantly affected the expression of p16 and p21 (P < .05–P < .0001 vs. control), senescence associated secretory phenotype (P < .01–P < .0001 vs. control), and telomere-specific proteins: telomeric repeat binding factor 1 and 2 (P < .05–P < .0001 vs. control) in a concentration-dependent manner. LF modulates the expression of cellular senescence markers and shows hallmarks of senolytic and pro-senescent activity, depending on dose. Further studies are needed to fully understand the anti-inflammatory effect of LF in the context of senescence and safe utilization in patients with inflammatory bowel diseases.

A High-Quality Genome Assembly for Cercospora janseana, Causal Agent of Narrow Brown Leaf Spot of Rice.

Cercospora janseana causes narrow brown leaf spot of rice. A nearly complete telomere-to-telomere reference genome was assembled with a combination of Oxford Nanopore and Illumina sequences. The genome assembly has a total length of 39,075,509 bp and consists of 15 chromosomes, 14 of which have telomeric repeats at both ends. The assembly N50 is 2.97 Mb and the L50 is five contigs. RNA-seq-mediated gene annotation identified 10,850 genes, including 955 predicted secreted proteins and 361 predicted effector proteins. This highly contiguous and almost complete C. janseana reference genome will be a vital resource for further investigation of host-pathogen interactions and genome evolution within this pathosystem. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Quantifying telomere transcripts as tool to improve risk assessment for genetic instability and genotoxicity.

Telomere repeat-containing RNAs (TERRA) are transcribed from telomeres as long non-coding RNAs and are part of the telomere structure with protective function. The genetic stability of cells requires telomeric repeats at the ends of chromosomes. Maintenance of telomere length (TL) is essential for proliferative capacity and chromosomal integrity. In contrast, telomere shortening is a recognized risk factor for carcinogenesis and a biomarker of aging due to the cumulative effects of environmental exposures and life experiences such as trauma or stress. In this context, telomere repeats are lost due to cell proliferation, but are also susceptible to stress factors including reactive oxygen species (ROS) inducing oxidative base damage. Quantitative PCR (qPCR) of genomic DNA is an established method to analyze TL as a tool to detect genotoxic events. That same qPCR method can be applied to RNA converted into cDNA to quantify TERRA as a useful tool to perform high-throughput screenings. This short review summarizes relevant qPCR studies using both TL and TERRA quantification, provides an overall view of the molecular mechanisms of telomere protection against ROS by TERRA, and summarizes the presented studies comparing the results at DNA and RNA levels, which indicate that fluctuations at transcript level might reflect a short-term response. Therefore, we conclude that performing both of these measurements together will improve genotoxicity studies.

Telomere sequence variability in genotypes from natural plant populations: unusual block-organized double-monomer terminal telomeric arrays

BackgroundTelomeres are the nucleoprotein complexes that physically cap the ends of eukaryotic chromosomes. Most plants possess Arabidopsis-type telomere sequences (TSs). In addition to terminal TSs, more diverse interstitial TSs exists in plants. Although telomeres have been sufficiently studied, the actual diversity of TSs in land plants is underestimated.ResultsWe investigate genotypes from seven natural populations with contrasting environments of four Chenopodium species to reveal the variability in TSs by analyzing Oxford Nanopore reads. Fluorescent in situ hybridization was used to localize telomeric repeats on chromosomes. We identified a number of derivative monomers that arise in part of both terminal and interstitial telomeric arrays of a single genotype. The former presents a case of block-organized double-monomer telomers, where blocks of Arabidopsis-type TTTAGGG motifs were interspersed with blocks of derivative TTTAAAA motifs. The latter is an integral part of the satellitome with transformations specific to the inactive genome fraction.ConclusionsWe suggested two alternative models for the possible formation of derivative monomers from telomeric heptamer motifs of Arabidopsis-type. It was assumed that derivatization of TSs is a ubiquitous process in the plant genome but occurrence and frequencies of derivatives may be genotype-specific. We also propose that the formation of non-canonical arrays of TSs, especially at chromosomal termini, may be a source for genomic variability in nature.

Near-gapless genome assemblies of Williams 82 and Lee cultivars for accelerating global soybean research.

Complete, gapless telomere-to-telomere chromosome assemblies are a prerequisite for comprehensively investigating the architecture of complex regions, like centromeres or telomeres and removing uncertainties in the order, spacing, and orientation of genes. Using complementary genomics technologies and assembly algorithms, we developed highly contiguous, nearly gapless, genome assemblies for two economically important soybean [Glycine max (L.) Merr] cultivars (Williams 82 and Lee). The centromeres were distinctly annotated on all the chromosomes of both assemblies. We further found that the canonical telomeric repeats were present at the telomeres of all chromosomes of both Williams 82 and Lee genomes. A total of 10 chromosomes in Williams 82 and eight in Lee were entirely reconstructed in single contigs without any gap. Using the combination of ab initio prediction, protein homology, and transcriptome evidence, we identified 58,287 and 56,725 protein-coding genes in Williams 82 and Lee, respectively. The genome assemblies and annotations will serve as a valuable resource for studying soybean genomics and genetics and accelerating soybean improvement.

Ribosomal, Telomere, and Mitochondrial Repeat Copy Number Variations in Female Genomes during Ovarian Stimulation and the Prediction of In Vitro Fertilization Outcome: A Pilot Study.

Individual risk assessment of assisted reproductive technologies is essential for personalized treatment strategies. Genetic and genomic indicators of the response to stress by cells could provide individual prognostic indicators for in vitro fertilization (IVF) success. Such indicators include the copy number of ribosomal genes (rDNA), which modulates the level of protein synthesis, and the abundance of mitochondrial DNA (mtDNA), which provides the cell with energy, while the content of telomere repeats (TRs) indicate the biological age. The contents of the three repeats in DNA isolated from blood leukocytes of 40 women before and after ovarian stimulation were assayed prior to IVF. Then, we divided the women into a successful IVF group, IVF+ (N = 17, 7 cases of twins), and a group of failed cases, IVF- (N = 23). The control group included 17 non-pregnant women with natural childbirth in the past. The nonradioactive quantitative hybridization (NQH) method was applied to assay the genome repeat contents. The number of rDNA copies in the IVF+ group was significantly higher than in the IVF- group (p < 10-8). The number of mtDNA copies in the IVF+ group also exceeded those in the IVF- group (p < 0.001), whereas the TR content in the two groups differed, albeit, non-significantly (p < 0.03). Following the ovarian stimulation, the rDNA copy numbers did not change, while the contents of the mtDNA and TR varied significantly. This pilot study has shown that rDNA abundance in blood leukocytes can be considered a stable and effective predictor. Very low numbers of ribosomal repeat copies (<330) entail a high risk of IVF failure. However, a combination of numerous mtDNA and TRs, provided that rDNA content is not very low, increases the probability of multiple pregnancies.

Conserved satellite DNA motif and lack of interstitial telomeric sites in highly rearranged African Nothobranchius killifish karyotypes.

Using African annual killifishes of the genus Nothobranchius from temporary savannah pools with rapid karyotype and sex chromosome evolution, we analysed the chromosomal distribution of telomeric (TTAGGG)n repeat and Nfu-SatC satellite DNA (satDNA; isolated from Nothobranchius furzeri) in 15 species across the Nothobranchius killifish phylogeny, and with Fundulosoma thierryi as an out-group. Our fluorescence in situ hybridization experiments revealed that all analysed taxa share the presence of Nfu-SatC repeat but with diverse organization and distribution on chromosomes. Nfu-SatC landscape was similar in conspecific populations of Nothobranchius guentheri and Nothobranchius melanospilus but slightly-to-moderately differed between populations of Nothobranchius pienaari, and between closely related Nothobranchius kuhntae and Nothobranchius orthonotus. Inter-individual variability in Nfu-SatC patterns was found in N. orthonotus and Nothobranchius krysanovi. We revealed mostly no sex-linked patterns of studied repetitive DNA distribution. Only in Nothobranchius brieni, possessing multiple sex chromosomes, Nfu-SatC repeat occupied a substantial portion of the neo-Y chromosome, similarly as formerly found in the XY sex chromosome system of turquoise killifish N. furzeri and its sister species Nothobranchius kadleci-representatives not closely related to N. brieni. All studied species further shared patterns of expected telomeric repeats at the ends of all chromosomes and no additional interstitial telomeric sites. In summary, we revealed (i) the presence of conserved satDNA class in Nothobranchius clades (a rare pattern among ray-finned fishes); (ii) independent trajectories of Nothobranchius sex chromosome differentiation, with recurrent and convergent accumulation of Nfu-SatC on the Y chromosome in some species; and (iii) genus-wide shared tendency to loss of telomeric repeats during interchromosomal rearrangements. Collectively, our findings advance our understanding of genome structure, mechanisms of karyotype reshuffling, and sex chromosome differentiation in Nothobranchius killifishes from the genus-wide perspective.

In Vitro Assessment of Gold Nanoparticles on Telomerase Activity and Telomere Length in Human Fibroblasts.

Telomerase activity coincides with lengthening of the ends of chromosomes known as telomeres. Telomere length is used as a marker for cellular aging. Telomeres shorten over time as cells divide, and certain bioactive compounds such as gold nanoparticles (AuNPs) may slow the shortening of telomeres by increasing telomerase activity. The objective of the present study is to assess the effect of AuNPs on telomerase activity and telomere length in human fibroblasts. Telomerase activity was measured using enzyme-linked immunosorbent assay (ELISA) in primary human lung fibroblasts (IMR90) and using quantitative PCR-based telomeric repeat amplification protocol (Q-TRAP) in primary human dermal fibroblasts, neonatal (HDFn). Telomere length was determined by Telomere Analysis Technology (TAT®)assay in HDFn. In IMR90, all AuNP treatments showed significant increases in telomerase activity when compared to earlier passages. HDFn treated with AuNPs at 0 ppm, 0.05 ppm, 0.5 ppm, or 5 ppm did not show significant differences in telomerase activity compared to the control group. Significant differences in telomere length in HDFn were observed at 2 weeks of 0.05 and 0.5 ppm AuNPs under oxidative culture conditions as compared to the control group. The study showed preliminary evidence that AuNPs may increase telomerase activity and decelerate the shortening of telomeres in human fibroblasts, suggesting its potential anti-aging effects, which warrants further investigation.

A telomere-to-telomere reference genome provides genetic insight into the pentacyclic triterpenoid biosynthesis in Chaenomeles speciosa.

Chaenomeles speciosa (2n = 34), a medicinal and edible plant in the Rosaceae, is commonly used in traditional Chinese medicine. To date, the lack of genomic sequence and genetic studies has impeded efforts to improve its medicinal value. Herein, we report the use of an integrative approach involving PacBio HiFi (third-generation) sequencing and Hi-C scaffolding to assemble a high-quality telomere-to-telomere genome of C. speciosa. The genome comprised 650.4Mb with a contig N50 of 35.5Mb. Of these, 632.3Mb were anchored to 17 pseudo-chromosomes, in which 12, 4, and 1 pseudo-chromosomes were represented by a single contig, two contigs, and four contigs, respectively. Eleven pseudo-chromosomes had telomere repeats at both ends, and four had telomere repeats at a single end. Repetitive sequences accounted for 49.5% of the genome, while a total of 45 515 protein-coding genes have been annotated. The genome size of C. speciosa was relatively similar to that of Malus domestica. Expanded or contracted gene families were identified and investigated for their association with different plant metabolisms or biological processes. In particular, functional annotation characterized gene families that were associated with the biosynthetic pathway of oleanolic and ursolic acids, two abundant pentacyclic triterpenoids in the fruits of C. speciosa. Taken together, this telomere-to-telomere and chromosome-level genome of C. speciosa not only provides a valuable resource to enhance understanding of the biosynthesis of medicinal compounds in tissues, but also promotes understanding of the evolution of the Rosaceae.

A pilot study examining the relationship between chronic heroin use and telomere length among individuals of African ancestry

BackgroundPrior research has suggested a possible link between heroin use and shortened telomere length (TL), a marker of cellular aging and genomic stability. We sought to replicate these findings by examining the relationship between TL and heroin use among individuals of African ancestry. MethodsThis cross-sectional study examined TL among 57 participants [17.5 % female; mean age 48.0 (±6.80) years] of African ancestry with Opioid Use Disorder (OUD) and a mean heroin use duration of 18.2 (±10.7) years. Quantitative polymerase chain reaction (qPCR) was used to calculate TL as the ratio between telomere repeat copy number (T) and a single-copy gene, copy number (S). The primary dependent variable was TL (T/S Ratio) measured in kilobase pairs. Covariates included heroin use years and personality traits. Using a hybrid approach, multiple linear regression and Bayesian linear regression examined the association of chronological age, heroin use years and personality traits with TL. ResultsThe multiple linear regression model fit the data well, R2 = 0.265, F(7,49) = 2.53, p < .026. Chronological age (β = −0.36, p = .017), neuroticism (β = 0.46, p = .044), and conscientiousness (β = 0.52, p = .040) were significant predictors of TL. Bayesian linear regression provided moderate support for the alternate hypothesis that chronological age and TL are associated, BF10 = 5.77, R2 = 0.120. The posterior summary of the coefficient was M = 0.719 (SD = 0.278, 95 % credible interval [−1.28, −0.163]). ConclusionsContrary to prior studies, these findings suggest that heroin use duration may not be significantly associated with TL among individuals of African ancestry, highlighting the need for more rigorous research to elucidate the complexity of this relationship.

Strong associations of telomere length and mitochondrial copy number with suicidality and abuse history in adolescent depressed individuals

Major depressive disorder (MDD) is highly prevalent in adolescents and is a major risk factor for suicidality. Recent evidence shows that accelerated cellular senescence/aging is associated with psychiatric illness, including depression, in adults. The present study examined if the relationships of telomere length (TL) and mitochondrial DNA copy number (mtDNAcn), two critical indicators of cellular senescence/aging, are altered in depressed adolescents and whether these alterations are associated with suicidality, early-life adversities, and other co-occuring factors. In genomic DNA isolated from 53 adolescents (ages 16–19, 19 MDD with suicide attempt/suicidal ideation [MDD + SI/SA], 14 MDD without SA/SI [MDD-SI/SA], and 20 healthy controls [HC]), TL and mtDNAcn were measured as the ratio between the number of telomere repeats and that of a single-copy nuclear-hemoglobin [HBG] gene or the amount of mtDNA (NADH dehydrogenase, subunit 1) relative to HBG. Our data show that TL was significantly lower, and mtDNAcn was significantly higher in the total MDD group than HC. TL was significantly lower and mtDNAcn was significantly higher in the MDD + SA/SI group than in the HC, whereas there were no differences in the MDD-SI/SA group. TL was positively correlated with mtDNAcn in both HC and MDD-SA/SI groups; however, TL was negatively correlated with mtDNAcn in MDD + SA/SI. Furthermore, TL was negatively correlated with the severity of both depression and anxiety, while mtDNAcn was positively correlated with the severity of prior emotional abuse. Our study indicates that cellular senescence is more advanced in depressed adolescents with suicidal ideation and that childhood emotional abuse may participate in such a process.

Satellite III (1q12) Copy Number Variation in Cultured Human Skin Fibroblasts from Schizophrenic Patients and Healthy Controls.

The chromosome 1q12 region harbors the genome's largest pericentromeric heterochromatin domain that includes tandemly repeated satellite III DNA [SatIII (1)]. Increased SatIII (1) copy numbers have been found in cultured human skin fibroblasts (HSFs) during replicative senescence. The aim of this study was to analyze the variation in SatIII (1) abundance in cultured HSFs at early passages depending on the levels of endogenous and exogenous stress. We studied 10 HSF cell lines with either high (HSFs from schizophrenic cases, n = 5) or low (HSFs from healthy controls, n = 5) levels of oxidative stress. The levels of endogenous stress were estimated by the amounts of reactive oxygen species, DNA damage markers (8-hydroxy-2'-deoxyguanosine, gamma-H2A histone family member X), pro- and antioxidant proteins (NADPH oxidase 4, superoxide dismutase 1, nuclear factor erythroid 2-related factor 2), and proteins that regulate apoptosis and autophagy (B-cell lymphoma 2 [Bcl-2], Bcl-2-associated X protein, light chain 3). SatIII (1) copy numbers were measured using the nonradioactive quantitative hybridization technique. For comparison, the contents of telomeric and ribosomal RNA gene repeats were determined. RNASATIII (1 and 9) were quantified using quantitative Polymerase Chain Reaction (PCR). Increased SatIII (1) contents in DNA from confluent HSFs were positively correlated with increased oxidative stress. Confluent cell cultivation without medium replacement and heat shock induced a decrease of SatIII (1) in DNA in parallel with a decrease in RNASATIII (1) and an increase in RNASATIII (9). During HSF cultivation, cells with increased SatIII (1) content accumulated in the cell pool under conditions of exaggerated oxidative stress. This fraction of cells decreased after the additional impact of exogenous stress. The process seems to be oscillatory.

Telomerase mRNA Enhances Human Skin Engraftment for Wound Healing.

Deep skin wounds represent a serious condition and frequently require split-thickness skin grafts (STSG) to heal. The application of autologous human-skin-cell-suspension (hSCS) requires less donor skin than STSG without compromising the healing capacity. Impaired function and replicative ability of senescent cutaneous cells in the aging skin affects healing with autologous hSCS. Major determinants of senescence are telomere erosion and DNA damage. Human telomerase reverse transcriptase (hTERT) adds telomeric repeats to the DNA and can protect against DNA damage. Herein, hTERT mRNA lipid nanoparticles (LNP) are proposed and evaluated for enhancing cellular engraftment and proliferation of hSCS. Transfection with optimized hTERT mRNA LNP system enables delivery and expression of mRNA in vitro in keratinocytes, fibroblasts, and in hSCS prepared from donors' skin. Telomerase activity in hSCS is significantly increased. hTERT mRNA LNP enhance the generation of a partial-thickness human skin equivalent in the mouse model, increasing hSCS engraftment (Lamin) and proliferation (Ki67), while reducing cellular senescence (p21) and DNA damage (53BP1).

Bioinformatic analysis of the effect of SNPs in the pig TERT gene on the structural and functional characteristics of the enzyme to develop new genetic markers of productivity traits

BackgroundTelomerase reverse transcriptase (TERT) plays a crucial role in synthesizing telomeric repeats that safeguard chromosomes from damage and fusion, thereby maintaining genome stability. Mutations in the TERT gene can lead to a deviation in gene expression, impaired enzyme activity, and, as a result, abnormal telomere shortening. Genetic markers of productivity traits in livestock can be developed based on the TERT gene polymorphism for use in marker-associated selection (MAS). In this study, a bioinformatic-based approach is proposed to evaluate the effect of missense single-nucleotide polymorphisms (SNPs) in the pig TERT gene on enzyme function and structure, with the prospect of developing genetic markers.ResultsA comparative analysis of the coding and amino acid sequences of the pig TERT was performed with corresponding sequences of other species. The distribution of polymorphisms in the pig TERT gene, with respect to the enzyme’s structural-functional domains, was established. A three-dimensional model of the pig TERT structure was obtained through homological modeling. The potential impact of each of the 23 missense SNPs in the pig TERT gene on telomerase function and stability was assessed using predictive bioinformatic tools utilizing data on the amino acid sequence and structure of pig TERT.ConclusionsAccording to bioinformatic analysis of 23 missense SNPs of the pig TERT gene, a predictive effect of rs789641834 (TEN domain), rs706045634 (TEN domain), rs325294961 (TRBD domain) and rs705602819 (RTD domain) on the structural and functional parameters of the enzyme was established. These SNPs hold the potential to serve as genetic markers of productivity traits. Therefore, the possibility of their application in MAS should be further evaluated in associative analysis studies.

PinX1-Promoted Autophagy Inhibits Cell Proliferation and Induces Cell Apoptosis by Inhibiting the NF-κB/p65 Signaling Pathway in Nasopharyngeal Carcinoma.

The role of Pin2 telomeric repeat factor 1-interacting telomerase inhibitor 1 (PinX1) in tumorigenesis and development has been extensively studied. As we previously demonstrated, PinX1 plays an important role in modulating epithelial-mesenchymal transition (EMT), stemness, cell proliferation, and apoptosis in nasopharyngeal carcinoma (NPC). However, the relationship between PinX1, autophagy, and cell function in NPC remains unclear. This study aimed to investigate the mechanisms by which PinX1 regulates autophagy in NPC, and to explore its biological role and clinical significance in disease progression. The proliferative capacity of NPC cells was assessed by MTT and xenograft tumorigenicity assays. Autophagic flux was monitored using a tandem monomeric DAPI-FITC-LC3 reporter assay. The rates of apoptosis and the cell cycle in NPC cells were analyzed using flow cytometry. The activation of autophagy and the signaling status of the AKT/mTOR and NF-κB/p65 pathways were evaluated by Western blot analysis. In addition to promoting autophagy and apoptosis, PinX1 overexpression suppressed proliferation, migration, invasion, and decelerated cell-cycle progression in NPC cells. These effects were reversed by inhibiting autophagy with 3-methyladenine. Mechanistic investigations clarified that PinX1 overexpression significantly reduced the expression of p-AKT, p-mTOR, p65, and p-p65. Chloroquine treatment in PinX1-overexpressing cells did not significantly alter p-AKT and p-mTOR levels, whereas 3-MA treatment in PinX1-overexpressing cells resulted in increased p65 and p-p65 expression, relative to untreated PinX1-overexpressing cells. It appears that PinX1 promotes autophagy by inhibiting the AKT/mTOR signaling pathway, which then inhibits NF-κB/p65 pathways, and consequently inhibiting cell proliferation and causing cell apoptosis in NPC cells.

Association of variants of the relative length of telomeric repeats with coronary heart disease with old myocardial infarction

Association of variants of the relative length of telomeric repeats with coronary heart disease with old myocardial infarction

Histone H1 protects telomeric repeats from H3K27me3 invasion in Arabidopsis

While the pivotal role of linker histone H1 in shaping nucleosome organization is well established, its functional interplays with chromatin factors along the epigenome are just starting to emerge. Here we show that, in Arabidopsis, as in mammals, H1 occupies Polycomb Repressive Complex 2 (PRC2) target genes where it favors chromatin condensation and H3K27me3 deposition. We further show that, contrasting with its conserved function in PRC2 activation at genes, H1 selectively prevents H3K27me3 accumulation at telomeres and large pericentromeric interstitial telomeric repeat (ITR) domains by restricting DNA accessibility to Telomere Repeat Binding (TRB) proteins, a group of H1-related Myb factors mediating PRC2 cis recruitment. This study provides a mechanistic framework by which H1 avoids the formation of gigantic H3K27me3-rich domains at telomeric sequences and contributes to safeguard nucleus architecture.

Digital CRISPR/Cas12a-based platform for precise quantification of telomerase activity

Precise quantification of telomerase activity is of great significance for telomerase-based early cancer diagnosis, as well as the screening of prodrugs. Telomeric repeat amplification protocol (TRAP) has been most widely used for assessing telomerase activity, which is limited by false-positive results, complicated operations, and long detection time. Herein, we develop a droplet digital hyperbranched amplification enhanced CRISPR/Cas12a-based telomerase detection platform (ddHECTelo) for precise quantitative detection of telomerase activity. By combining with the droplet digital platform and hyperbranched amplification, the ddHECTelo allows precise quantification of telomerase activity with single-molecule sensitivity. A polydisperse droplets digital system was employed, so that the reaction mixtures could be partitioned into picoliter-scale polydisperse droplets in several seconds to avoid the pre-amplification, without the need for a sophisticated microfluidic chip. This is the first digital isothermal platform for sensitive and precise quantification of telomerase activity, which shows great potential in telomerase-based early cancer diagnosis. It could also be used to analyze the telomerase activity in fundamental biomedical research.

Distinct characteristics of two types of alternative lengthening of telomeres in mouse embryonic stem cells.

Telomere length must be maintained in actively dividing cells to avoid cellular arrest or death. In the absence of telomerase activity, activation of alternative lengthening of telomeres (ALT) allows the maintenance of telomeric length and prolongs the cellular lifespan. Our previous studies have established two types of ALT survivors from mouse embryonic stem cells. The key differences between these ALT survivors are telomere-constituting sequences: non-telomeric sequences and canonical telomeric repeats, with each type of ALT survivors being referred to as type I and type II, respectively. We explored how the characteristics of the two types of ALT lines reflect their fates using multi-omics approaches. The most notable gene expression signatures of type I and type II ALT cell lines were chromatin remodelling and DNA repair, respectively. Compared with type II cells, type I ALT cells accumulated more mutations and demonstrated persistent telomere instability. These findings indicate that cells of the same origin have separate routes for survival, thus providing insights into the plasticity of crisis-suffering cells and cancers.