Heterogeneity in telomere length of human chromosomes

Changes in telomere length with aging in human neurons and glial cells revealed by quantitative fluorescence in situ hybridization analysis

AIM

The telomere is a structure present at the ends of chromosomes, and is known to shorten with aging and successive rounds of cell division. However, very little is known about telomere attrition in post-mitotic cells, such as neurons.

METHODS

Using our originally developed quantitative fluorescence in situ hybridization method, we analyzed age-dependent alterations of telomere length in three types of cells in the human cerebrum: neurons and glial cells in both the gray and white matter.

RESULTS

In adults, telomeres were significantly longer in neurons than in glial cells, whereas in infants, telomere lengths did not differ among the three cell types. No aging-related telomere attrition was evident in neurons. However, the telomeres of glial cells were shorter in older individuals than in younger individuals, and attrition was more rapid in the white matter than in the gray matter.

CONCLUSIONS

The present results suggest that the telomeres of neurons remain stable throughout life, whereas telomeres in white matter glial cells become significantly shorter with age. Examination of adults showed no significant correlation between telomere length and age in the three cell types. Although the present study was cross-sectional, the results suggest that telomere shortening before adolescence contributes to the significant decrease of telomere length in white matter glial cells. The present findings in normal cerebral tissues will be informative for future studies of telomere stability in the diseased brain. Geriatr Gerontol Int 2018; 18: 1507-1512.

Telomere Length and Lung Cancer Mortality among Heavy Smokers

Background: Accumulating evidence suggests that short telomere length is associated with increased overall mortality, but the relationship with cancer mortality is less clear. We examined whether telomere length (global, and chromosome arm 5p- and 13q-specific) is associated with lung cancer mortality among cases from the β-Carotene and Retinol Efficacy Trial of heavy smokers.Methods: Telomere length was measured on average 6 years before diagnosis for 788 lung cancer cases. Adjusted Cox proportional hazards models of all-cause and lung cancer-specific mortality were assessed for lung cancer overall and by histotype.Results: Short telomere length was associated with increased mortality for small cell lung cancer (SCLC), particularly stage III/IV SCLC [HR and 95% confidence interval for shortest vs. longest telomere length tertile: 3.32 (1.78-6.21)]. Associations were strongest for those randomized to the active intervention and when telomere length was measured ≤5 years before diagnosis. All-cause mortality patterns were similar. Short chromosome 5p telomere length was suggestively associated with lung cancer mortality, but there was no association with chromosome 13q telomere length.Conclusions: Our large prospective study suggests that among heavy smokers who developed lung cancer, short prediagnosis telomere length is associated with increased risk of death from SCLC.Impact: This is the first study to examine telomere length and mortality in lung cancer cases by histotype. If the association between short telomere length and SCLC mortality is replicated, elucidation of mechanisms through which telomere length influences survival for this highly aggressive cancer may inform more effective use of telomere-targeted therapeutics. Cancer Epidemiol Biomarkers Prev; 27(7); 829-37. ©2018 AACR.

Cytogenetics in Arctica islandica (Bivalvia, Arctidae): the Longest Lived Non-Colonial Metazoan

Due to its extraordinary longevity and wide distribution, the ocean quahog Arctica islandica has become an important species model in both aging and environmental change research. Notwithstanding that, most genetic studies on ocean quahogs have been focused on fishery related, phylogeographic and phylogenetic aspects but nothing is known about their chromosomes. In this work, the chromosomes of the ocean quahog Arctica islandica were analysed by means of 4′,6-diamidino-2-phenylindole (DAPI)/propidium iodide (PI) staining and fluorescent in situ hybridization (FISH) with rDNA, histone gene and telomeric probes. Whilst both 5S rDNA and 45S rDNA were clustered at single subcentromeric locations on the long arms of chromosome pairs 2 and 12, respectively, histone gene clusters located on the short arms of chromosome pairs 7, 10 and 17. As happens with most bivalves, the location of the vertebrate type telomeric sequence clusters was restricted to chromosome ends. The knowledge of the karyotype can facilitate the anchoring of genomic sequences to specific chromosome pairs in this species.

Nested case-control study of telomere length and lung cancer risk among heavy smokers in the β-Carotene and Retinol Efficacy Trial

Background

Telomeres protect cells from genomic instability. We examined telomere length and lung cancer risk prospectively in heavy smokers.

Methods

In a nested case–control study with 709 cases and 1313 controls, conditional logistic regression was used to evaluate associations between telomere length (global, chromosome 5p, and 13q) and lung cancer risk by histotype, controlling for detailed smoking history.

Results

Risks of overall lung cancer and adenocarcinoma were suggestively elevated among individuals with telomere length in the longest tertile. No clear patterns were observed for other histotypes, or for chromosome 5p or 13q telomere length. Associations with adenocarcinoma were strongest among (OR, 95% CI for longest versus shortest tertile): former smokers (2.26, 1.03–4.96), individuals <65 years (2.22, 1.13–4.35), and women (2.21, 0.99–4.93).

Conclusions

Our large study of heavy smokers adds additional evidence that long telomere length prior to diagnosis is associated with risk of lung adenocarcinoma, but not other histotypes.

DNA and chromosome damage induced by bleomycin in mammalian cells: An update

Bleomycin (BLM) is an antibiotic isolated from Streptomyces verticillus. It has radiomimetic actions on DNA thus it has been widely used in clinical chemotherapy for the treatment of different types of cancer, including head and neck tumors, lymphomas, squamous-cell carcinomas and germ-cell tumors. Because of this, the study of BLM genotoxicity is of practical interest. This antibiotic is an S-independent clastogen and an agent that generates free radicals and induces single- and double-strand breaks in DNA. In the present review, we will summarize our current knowledge concerning the DNA and chromosome damage induced by BLM in mammalian cells, with emphasis on new developments published since 1991.

Identification of a New Mullet Species Complex Based on an Integrative Molecular and Cytogenetic Investigation of Mugil hospes (Mugilidae: Mugiliformes)

Mullets are very common fishes included in the family Mugilidae, (Mugiliformes), which are characterized by both a remarkably uniform external morphology and internal anatomy. Recently, within this family, different species complexes were molecularly identified within Mugil, a genus which is characterized by lineages that sometimes show very different karyotypes. Here we report the results of cytogenetic and molecular analyses conducted on Mugil hospes, commonly known as the hospe mullet, from Ecuador. The study aims to verify whether the original described species from the Pacific Ocean corresponds to that identified in the Atlantic Ocean, and to identify species-specific chromosome markers that can add new comparative data about Mugilidae karyotype evolution. The karyotype of M. hospes from Ecuador is composed of 48 acrocentric chromosomes and shows two active nucleolar organizer regions (NORs). In situ hybridization, using different types of repetitive sequences (rDNAs, U1 snDNA, telomeric repeats) as probes, identified species-specific chromosome markers that have been compared with those of other species of the genus Mugil. Cytochrome c oxidase subunit I (COI) sequence analysis shows only 92-93% similarity with sequences previously deposited under this species name in GenBank, all of which were from the Atlantic Ocean. Phylogenetic reconstructions indicate the presence of three well-supported hospe mullet lineages whose molecular divergence is compatible with the presence of distinct species. Indeed, the first lineage includes samples from Ecuador, whereas the other two lineages include the Atlantic samples and correspond to M. brevirostris from Brazil and Mugil sp. R from Belize/Venezuela. Results here provided reiterate the pivotal importance of an integrative molecular and cytogenetic approach in the reconstruction of the relationships within Mugilidae.

Telomere length of gallbladder epithelium is shortened in patients with congenital biliary dilatation: measurement by quantitative fluorescence in situ hybridization

BACKGROUND

Congenital biliary dilatation (CBD) is a congenital malformation involving both dilatation of the extrahepatic bile duct and pancreaticobiliary maljunction. Persistent reflux of pancreatic juice injures the biliary tract mucosa, resulting in chronic inflammation and higher rates of carcinogenesis in the biliary tract, including the gallbladder. Telomeres are repetitive DNA sequences located at the ends of chromosomes. Chromosomal instability due to telomere dysfunction plays an important role in the carcinogenesis of many organs. This study was performed to determine whether excessive shortening of telomeres occurs in the gallbladder mucosa of patients with CBD.

METHODS

Resected gallbladders were obtained from 17 patients with CBD, ten patients with cholecystolithiasis without pancreatic juice reflux, and 17 patients with normal gallbladders (controls) (median age of each group of patients: 37, 50, and 53 years, respectively). The telomere lengths of the gallbladder epithelium were measured by quantitative fluorescence in situ hybridization using tissue sections, and the normalized telomere-to-centromere ratio (NTCR) was calculated.

RESULTS

The NTCRs in the CBD, cholecystolithiasis, and control groups were 1.24 [interquartile range (IQR) 1.125-1.52], 1.96 (IQR 1.56-2.295), and 1.77 (IQR 1.48-2.53), respectively. The NTCR in the CBD group was significantly smaller than that in the cholecystolithiasis and control groups (p = 0.003 and 0.004, respectively), even in young patients.

CONCLUSIONS

Our findings indicate that telomere shortening in the gallbladder mucosa plays an important role in the process of carcinogenesis in patients with CBD. These results support the recommendation of established guidelines for prophylactic surgery in patients with CBD because CBD is a premalignant condition with excessive telomere shortening.

Stabilization of Reversed Replication Forks by Telomerase Drives Telomere Catastrophe

Telomere maintenance critically depends on the distinct activities of telomerase, which adds telomeric repeats to solve the end replication problem, and RTEL1, which dismantles DNA secondary structures at telomeres to facilitate replisome progression. Here, we establish that reversed replication forks are a pathological substrate for telomerase and the source of telomere catastrophe in Rtel1-/- cells. Inhibiting telomerase recruitment to telomeres, but not its activity, or blocking replication fork reversal through PARP1 inhibition or depleting UBC13 or ZRANB3 prevents the rapid accumulation of dysfunctional telomeres in RTEL1-deficient cells. In this context, we establish that telomerase binding to reversed replication forks inhibits telomere replication, which can be mimicked by preventing replication fork restart through depletion of RECQ1 or PARG. Our results lead us to propose that telomerase inappropriately binds to and inhibits restart of reversed replication forks within telomeres, which compromises replication and leads to critically short telomeres.

A Distinct Class of Genome Rearrangements Driven by Heterologous Recombination

Erroneous DNA repair by heterologous recombination (Ht-REC) is a potential threat to genome stability, but evidence supporting its prevalence is lacking. Here we demonstrate that recombination is possible between heterologous sequences and that it is a source of chromosomal alterations in mitotic and meiotic cells. Mechanistically, we find that the RTEL1 and HIM-6/BLM helicases and the BRCA1 homolog BRC-1 counteract Ht-REC in Caenorhabditis elegans, whereas mismatch repair does not. Instead, MSH-2/6 drives Ht-REC events in rtel-1 and brc-1 mutants and excessive crossovers in rtel-1 mutant meioses. Loss of vertebrate Rtel1 also causes a variety of unusually large and complex structural variations, including chromothripsis, breakage-fusion-bridge events, and tandem duplications with distant intra-chromosomal insertions, whose structure are consistent with a role for RTEL1 in preventing Ht-REC during break-induced replication. Our data establish Ht-REC as an unappreciated source of genome instability that underpins a novel class of complex genome rearrangements that likely arise during replication stress.

The Detection and Analysis of Chromosome Fragile Sites

A fragile site is a chromosomal locus that is prone to form a gap or constriction visible within a condensed metaphase chromosome, particularly following exposure of cells to DNA replication stress. Based on their frequency, fragile sites are classified as either common (CFSs; present in all individuals) or rare (RFSs; present in only a few individuals). Interest in fragile sites has remained high since their discovery in 1965, because of their association with human disease. CFSs are recognized as drivers of oncogene activation and genome instability in cancer cells, while some RFSs are associated with neurodegenerative diseases. This review summaries our current understanding of the nature and causes of fragile site "expression", including the recently characterized phenomenon of telomere fragility. In particular, we focus on a description of the methodologies and technologies for detection and analysis of chromosome fragile sites.

Study of Telomere Dysfunction in TP53 Mutant LoVo Cell Lines as a Model for Genomic Instability

Telomere restriction fragment, 3D quantitative FISH on nuclei, and quantitative FISH on metaphases are complementary approaches that explore telomere dysfunction genomically, cellularly, and chromosomally, respectively. We used these approaches to study association between telomere dysfunction and degree of genomic instability related to TP53 mutations in LoVo isogenic cell lines. We found a strong correlation between degree of genomic instability, telomere dysfunction, and specific mutations of TP53. The use of complementary approaches to study telomere biology is essential to have a comprehensive understanding of telomere involvement in genomic instability.

Nanoscale Properties of Human Telomeres Measured with a Dual Purpose X-ray Fluorescence and Super Resolution Microscopy Gold Nanoparticle Probe

Techniques to analyze human telomeres are imperative in studying the molecular mechanism of aging and related diseases. Two important aspects of telomeres are their length in DNA base pairs (bps) and their biophysical nanometer dimensions. However, there are currently no techniques that can simultaneously measure these quantities in individual cell nuclei. Here, we develop and evaluate a telomere "dual" gold nanoparticle-fluorescent probe simultaneously compatible with both X-ray fluorescence (XRF) and super resolution microscopy. We used silver enhancement to independently visualize the spatial locations of gold nanoparticles inside the nuclei, comparing to a standard QFISH (quantitative fluorescence in situ hybridization) probe, and showed good specificity at ∼90%. For sensitivity, we calculated telomere length based on a DNA/gold binding ratio using XRF and compared to quantitative polymerase chain reaction (qPCR) measurements. The sensitivity was low (∼10%), probably because of steric interference prohibiting the relatively large 10 nm gold nanoparticles access to DNA space. We then measured the biophysical characteristics of individual telomeres using super resolution microscopy. Telomeres that have an average length of ∼10 kbps, have diameters ranging between ∼60-300 nm. Further, we treated cells with a telomere-shortening drug and showed there was a small but significant difference in telomere diameter in drug-treated vs control cells. We discuss our results in relation to the current debate surrounding telomere compaction.

Measurement of Average Telomere Length in Ex Vivo Expanded Natural Killer Cells by Fluorescence In Situ Hybridization (FISH) and Flow Cytometry

Natural killer (NK) cells are a subset of cytotoxic lymphocytes that play a critical role in innate immune surveillance against infections and tumors through cytokine secretion and target cell lysis. NK cells function without any need for prior antigen exposure. Thus, more recently NK cells are considered a promising source of lymphocytes for adoptive tumor therapy. However, because NK cells represent only a small lymphocyte fraction, expand poorly ex vivo, and have limited life spans, clinical scale generation of NK cells for tumor immunotherapy was a challenging issue. To overcome this challenge, numerous expansion platforms have been developed. However, ex vivo expansion of NK cells could lead to proliferation-induced senescence. Telomeres at the end of chromosomes play a crucial role in maintaining the integrity of the chromosome and are lost at each cell division in somatic cells and have emerged as important cellular elements in aging and cancer. Because telomere length is known to decrease in adult human NK cells and is associated with proliferation-induced senescence, it is important to determine the effect of NK cell expansion systems on telomere length. In this chapter, a detailed protocol is provided to analyze the telomere length of expanded NK cells using a commercially available Flow FISH kit.

Telomeres in cancer

Telomere shortening as a consequence of cell divisions during aging and chronic diseases associates with an increased cancer risk. Experimental data revealed that telomere shortening results in telomere dysfunction, which in turn affects tumorigenesis in two ways. First, telomere dysfunction suppresses tumor progression by the activation of DNA damage checkpoints, which induce cell cycle arrest (senescence) or apoptosis, as well as by inducing metabolic compromise and activation of immune responses directed against senescent cells. Second, telomere dysfunction promotes tumorigenesis by inducing chromosomal instability in tumor initiating cells, by inhibiting proliferative competition of non-transformed cells, and possibly, also by influencing tumor cell plasticity. The tumor promoting effects of telomere dysfunction are context dependent and require the loss of p53-dependent DNA damage checkpoints or other genetic modifiers that attenuate DNA damage responses possibly involving complex interactions of different genes. The activation of telomere stabilizing mechanisms appears as a subsequent step, which is required to enable immortal grotwh of emerging cancer cells. Here, we conceptually discuss our current knowledge and new, unpublished experimental data on telomere dependent influences on tumor initiation and progression.

γPNA FRET Pair Miniprobes for Quantitative Fluorescent In Situ Hybridization to Telomeric DNA in Cells and Tissue

Measurement of telomere length by fluorescent in situ hybridization is widely used for biomedical and epidemiological research, but there has been relatively little development of the technology in the 20 years since it was first reported. This report describes the use of dual gammaPNA (γPNA) probes that hybridize at alternating sites along a telomere and give rise to Förster resonance energy transfer (FRET) signals. Bright staining of telomeres is observed in nuclei, chromosome spreads and tissue samples. The use of FRET detection also allows for elimination of wash steps, normally required to remove unhybridized probes that would contribute to background signals. We found that these wash steps can diminish the signal intensity through the removal of bound, as well as unbound probes, so eliminating these steps not only accelerates the process but also enhances the quality of staining. Thus, γPNA FRET pairs allow for brighter and faster staining of telomeres in a wide range of research and clinical formats.

Telomere Shortening in Hematological Malignancies with Tetraploidization-A Mechanism for Chromosomal Instability?

Aneuploidy, the presence of an abnormal number of chromosomes in a cell, is one of the most obvious differences between normal and cancer cells. There is, however, debate on how aneuploid cells arise and whether or not they are a cause or a consequence of tumorigenesis. Further, it is important to distinguish aneuploidy (the “state” of the karyotype) from chromosomal instability (CIN; the “rate” of karyotypic change). Although CIN leads to aneuploidy, not all aneuploid cells exhibit CIN. One proposed route to aneuploid cells is through an unstable tetraploid intermediate because tetraploidy promotes chromosomal aberrations and tumorigenesis. Tetraploidy or near-tetraploidy (T/NT) (81–103 chromosomes) karyotypes with or without additional structural abnormalities have been reported in acute leukemia, T-cell and B-cell lymphomas, and solid tumors. In solid tumors it has been shown that tetraploidization can occur in response to loss of telomere protection in the early stages of tumorigenesis in colon cancer, Barrett’s esophagus, and breast and cervical cancers. In hematological malignancies T/NT karyotypes are rare and the role of telomere dysfunction for the induction of tetraploidization is less well characterized. To further our understanding of possible telomere dysfunction as a mechanism for tetrapolydization in hematological cancers we here characterized the chromosomal complement and measured the telomere content by interphase nuclei quantitative fluorescence in situ hybridization (iQFISH) in seven hematological cancer patients with T/NT karyotypes, and after cytogenetic remission. The patients were identified after a search in our local cytogenetic registry in the 5-year period between June 2012 and May 2017 among more than 12,000 analyzed adult patients in this period. One advantage of measuring telomere content by iQFISH is that it is a single-cell analysis so that the telomere content can be distinguished between normal karyotype cells and cells with T/NT karyotypes. We find that the telomeres are particularly short in cells with T/NT karyotypes as compared with normal cells, and in T/NT karyotypes harboring additional chromosomal aberrations as well. These findings suggest that telomere dysfunction in hematological malignancies may be a mechanism for tetraploidization and CIN.

Telomeres, Aging and Exercise: Guilty by Association?

Telomeres are repetitive tandem DNA sequences that cap chromosomal ends protecting genomic DNA from enzymatic degradation. Telomeres progressively shorten with cellular replication and are therefore assumed to correlate with biological and chronological age. An expanding body of evidence suggests (i) a predictable inverse association between telomere length, aging and age-related diseases and (ii) a positive association between physical activity and telomere length. Both hypotheses have garnered tremendous research attention and broad consensus; however, the evidence for each proposition is inconsistent and equivocal at best. Telomere length does not meet the basic criteria for an aging biomarker and at least 50% of key studies fail to find associations with physical activity. In this review, we address the evidence in support and refutation of the putative associations between telomere length, aging and physical activity. We finish with a brief review of plausible mechanisms and potential future research directions.

PRL-3 promotes telomere deprotection and chromosomal instability

Phosphatase of regenerating liver (PRL-3) promotes cell invasiveness, but its role in genomic integrity remains unknown. We report here that shelterin component RAP1 mediates association between PRL-3 and TRF2. In addition, TRF2 and RAP1 assist recruitment of PRL-3 to telomeric DNA. Silencing of PRL-3 in colon cancer cells does not affect telomere integrity or chromosomal stability, but induces reactive oxygen species-dependent DNA damage response and senescence. However, overexpression of PRL-3 in colon cancer cells and primary fibroblasts promotes structural abnormalities of telomeres, telomere deprotection, DNA damage response, chromosomal instability and senescence. Furthermore, PRL-3 dissociates RAP1 and TRF2 from telomeric DNA in vitro and in cells. PRL-3-promoted telomere deprotection, DNA damage response and senescence are counteracted by disruption of PRL-3–RAP1 complex or expression of ectopic TRF2. Examination of clinical samples showed that PRL-3 status positively correlates with telomere deprotection and senescence. PRL-3 transgenic mice exhibit hallmarks of telomere deprotection and senescence and are susceptible to dextran sodium sulfate-induced colon malignancy. Our results uncover a novel role of PRL-3 in tumor development through its adverse impact on telomere homeostasis.

Mouse embryonic stem cells have increased capacity for replication fork restart driven by the specific Filia-Floped protein complex

Pluripotent stem cells (PSCs) harbor constitutive DNA replication stress during their rapid proliferation and the consequent genome instability hampers their applications in regenerative medicine. It is therefore important to understand the regulatory mechanisms of replication stress response in PSCs. Here, we report that mouse embryonic stem cells (ESCs) are superior to differentiated cells in resolving replication stress. Specifically, ESCs utilize a unique Filia-Floped protein complex-dependent mechanism to efficiently promote the restart of stalled replication forks, therefore maintaining genomic stability. The ESC-specific Filia-Floped complex resides on replication forks under normal conditions. Replication stress stimulates their recruitment to stalling forks and the serine 151 residue of Filia is phosphorylated in an ATR-dependent manner. This modification enables the Filia-Floped complex to act as a functional scaffold, which then promotes the stalling fork restart through a dual mechanism: both enhancing recruitment of the replication fork restart protein, Blm, and stimulating ATR kinase activation. In the Blm pathway, the scaffolds recruit the E3 ubiquitin ligase, Trim25, to the stalled replication forks, and in turn Trim25 tethers and concentrates Blm at stalled replication forks through ubiquitination. In differentiated cells, the recruitment of the Trim25-Blm complex to replication forks and the activation of ATR signaling are much less robust due to lack of the ESC-specific Filia-Floped scaffold. Thus, our study reveals that ESCs utilize an additional and unique regulatory layer to efficiently promote the stalled fork restart and maintain genomic stability.

A method for measuring the distribution of the shortest telomeres in cells and tissues

Improved methods to measure the shortest (not just average) telomere lengths (TLs) are needed. We developed Telomere Shortest Length Assay (TeSLA), a technique that detects telomeres from all chromosome ends from <1 kb to 18 kb using small amounts of input DNA. TeSLA improves the specificity and efficiency of TL measurements that is facilitated by user friendly image-processing software to automatically detect and annotate band sizes, calculate average TL, as well as the percent of the shortest telomeres. Compared with other TL measurement methods, TeSLA provides more information about the shortest telomeres. The length of telomeres was measured longitudinally in peripheral blood mononuclear cells during human aging, in tissues during colon cancer progression, in telomere-related diseases such as idiopathic pulmonary fibrosis, as well as in mice and other organisms. The results indicate that TeSLA is a robust method that provides a better understanding of the shortest length of telomeres.

Short telomeres are a hallmark of senescence and can result in genomic instability as well as cancer progression. Here, the authors present TeSLA, a technique to accurately detect telomeres under 1 kb in length.

Non-random length distribution of individual telomeres in immunodeficiency, centromeric instability and facial anomalies syndrome, type I

Mutations in the de novo DNA methyltransferase DNMT3B lead to Immunodeficiency, Centromeric Instability and Facial anomalies (ICF) syndrome, type I. This syndrome is characterized, among other hypomethylated genomic loci, by severe subtelomeric hypomethylation that is associated with abnormally short telomere length. While it was demonstrated that the mean telomere length is significantly shorter in ICF type I cells, it is unknown whether all telomeres are equally vulnerable to shortening. To study this question we determined by combined telomere-FISH and spectral karyotyping the relative length of each individual telomere in lymphoblastoid cell lines (LCLs) generated from multiple ICF syndrome patients and control individuals. Here we confirm the short telomere lengths, and demonstrate that telomere length variance in the ICF patient group is much larger than in the control group, suggesting that not all telomeres shorten in a uniform manner. We identified a subgroup of telomeres whose relatively short lengths can distinguish with a high degree of certainty between a control and an ICF metaphase, proposing that in ICF syndrome cells, certain individual telomeres are consistently at greater risk to shorten than others. The majority of these telomeres display high sequence identity at the distal 2 kb of their subtelomeres, suggesting that the attenuation in DNMT3B methylation capacity affects individual telomeres to different degrees based, at least in part, on the adjacent subtelomeric sequence composition.

Telomere length in poor-risk chronic lymphocytic leukemia: associations with disease characteristics and outcome

Telomere length in chronic lymphocytic leukemia (CLL) is described as an independent prognostic factor based largely on previously untreated patients from chemotherapy based trials. Here, we studied telomere length associations in high-risk, relapsed/refractory CLL treated with alemtuzumab in the CLL2O study (n = 110) of German and French CLL study groups. Telomere length (median 3.28 kb, range 2.52-7.24 kb) was relatively short, since 84.4% of patients had 17p- which is generally associated with short telomeres. Median telomere length was used for dichotomization into short and long telomere subgroups. Telomere length was associated with s-TK (p = .025) and TP53 mutations (p = .050) in untreated patients, while no association with clinical/biological characteristics was observed in relapsed/refractory CLL. Short telomeres had significant association with shorter PFS (p = .018) only in refractory CLL. Presence of short telomeres, loss of genes maintaining genomic integrity (SMC5) and increased incidence of chromothripsis, indicated the prevalence of genomic instability in this high-risk cohort (clinicaltrials.gov: NCT01392079).

High-throughput single-molecule telomere characterization

We have developed a novel method that enables global subtelomere and haplotype-resolved analysis of telomere lengths at the single-molecule level. An in vitro CRISPR/Cas9 RNA-directed nickase system directs the specific labeling of human (TTAGGG)n DNA tracts in genomes that have also been barcoded using a separate nickase enzyme that recognizes a 7-bp motif genome-wide. High-throughput imaging and analysis of large DNA single molecules from genomes labeled in this fashion using a nanochannel array system permits mapping through subtelomere repeat element (SRE) regions to unique chromosomal DNA while simultaneously measuring the (TTAGGG)n tract length at the end of each large telomere-terminal DNA segment. The methodology also permits subtelomere and haplotype-resolved analyses of SRE organization and variation, providing a window into the population dynamics and potential functions of these complex and structurally variant telomere-adjacent DNA regions. At its current stage of development, the assay can be used to identify and characterize telomere length distributions of 30–35 discrete telomeres simultaneously and accurately. The assay's utility is demonstrated using early versus late passage and senescent human diploid fibroblasts, documenting the anticipated telomere attrition on a global telomere-by-telomere basis as well as identifying subtelomere-specific biases for critically short telomeres. Similarly, we present the first global single-telomere-resolved analyses of two cancer cell lines.

Human MLH1 suppresses the insertion of telomeric sequences at intra-chromosomal sites in telomerase-expressing cells

Aberrant formation of interstitial telomeric sequences (ITSs) promotes genome instabilities. However, it is unclear how aberrant ITS formation is suppressed in human cells. Here, we report that MLH1, a key protein involved in mismatch repair (MMR), suppresses telomeric sequence insertion (TSI) at intra-chromosomal regions. The frequency of TSI can be elevated by double-strand break (DSB) inducer and abolished by ATM/ATR inhibition. Suppression of TSI requires MLH1 recruitment to DSBs, indicating that MLH1's role in DSB response/repair is important for suppressing TSI. Moreover, TSI requires telomerase activity but is independent of the functional status of p53 and Rb. Lastly, we show that TSI is associated with chromosome instabilities including chromosome loss, micronuclei formation and chromosome breakage that are further elevated by replication stress. Our studies uncover a novel link between MLH1, telomerase, telomere and genome stability.

Telomere Biology of Human Hematopoietic Stem Cells

BACKGROUND

Telomeres are protein DNA structures present at the ends of chromosomes and are essential for genetic stability and cell replication. Telomerase is the enzyme complex that maintains telomere integrity. Hematopoietic stem cells express telomerase and contain long telomeres, which become shorter as cells differentiate and mature. The extent of telomere shortening and the level of telomerase activity often correlate with the presence and severity of some hematopoietic diseases.

METHODS

The fundamentals of telomeres and telomerase are reviewed, and the telomere biology of human hematopoietic cells is discussed.

RESULTS

Telomere length and telomerase activity are important in the self-renewal of hematopoietic stem cells. Changes within these compartments affect both normal hematopoietic cells and the generation of hematopoietic disease. Telomere length provides information pertaining to the proliferative history and potential of a hematopoietic cell.

CONCLUSIONS

The role of telomerase and telomeres within the hematopoietic compartment needs further clarification. Advances in our knowledge in this field may improve clinical outcomes for the treatment of hematologic disease.

Evaluation of telomere length in human cardiac tissues using cardiac quantitative FISH

Telomere length has been correlated with various diseases, including cardiovascular disease and cancer. The use of currently available telomere-length measurement techniques is often restricted by the requirement of a large amount of cells (Southern-based techniques) or the lack of information on individual cells or telomeres (PCR-based methods). Although several methods have been used to measure telomere length in tissues as a whole, the assessment of cell-type-specific telomere length provides valuable information on individual cell types. The development of fluorescence in situ hybridization (FISH) technologies enables the quantification of telomeres in individual chromosomes, but the use of these methods is dependent on the availability of isolated cells, which prevents their use with fixed archival samples. Here we describe an optimized quantitative FISH (Q-FISH) protocol for measuring telomere length that bypasses the previous limitations by avoiding contributions from undesired cell types. We have used this protocol on small paraffin-embedded cardiac-tissue samples. This protocol describes step-by-step procedures for tissue preparation, permeabilization, cardiac-tissue pretreatment and hybridization with a Cy3-labeled telomeric repeat complementing (CCCTAA)₃ peptide nucleic acid (PNA) probe coupled with cardiac-specific antibody staining. We also describe how to quantify telomere length by means of the fluorescence intensity and area of each telomere within individual nuclei. This protocol provides comparative cell-type-specific telomere-length measurements in relatively small human cardiac samples and offers an attractive technique to test hypotheses implicating telomere length in various cardiac pathologies. The current protocol (from tissue collection to image procurement) takes ∼28 h along with three overnight incubations. We anticipate that the protocol could be easily adapted for use on different tissue types.

Human ribonuclease H1 resolves R-loops and thereby enables progression of the DNA replication fork

Faithful DNA replication is essential for genome stability. To ensure accurate replication, numerous complex and redundant replication and repair mechanisms function in tandem with the core replication proteins to ensure DNA replication continues even when replication challenges are present that could impede progression of the replication fork. A unique topological challenge to the replication machinery is posed by RNA-DNA hybrids, commonly referred to as R-loops. Although R-loops play important roles in gene expression and recombination at immunoglobulin sites, their persistence is thought to interfere with DNA replication by slowing or impeding replication fork progression. Therefore, it is of interest to identify DNA-associated enzymes that help resolve replication-impeding R-loops. Here, using DNA fiber analysis, we demonstrate that human ribonuclease H1 (RNH1) plays an important role in replication fork movement in the mammalian nucleus by resolving R-loops. We found that RNH1 depletion results in accumulation of RNA-DNA hybrids, slowing of replication forks, and increased DNA damage. Our data uncovered a role for RNH1 in global DNA replication in the mammalian nucleus. Because accumulation of RNA-DNA hybrids is linked to various human cancers and neurodegenerative disorders, our study raises the possibility that replication fork progression might be impeded, adding to increased genomic instability and contributing to disease.

Characterization of an acquired jumping translocation involving 3q13.31-qter in a patient with de novo acute monocytic leukemia

We studied an adult with de novo acute monocytic leukemia and a dismal outcome where her leukemic cells harbored an acquired rare jumping translocation (JT). We used oligo-based array CGH (oaCGH) analysis, fluorescence in situ hybridization (FISH), and 24-color karyotyping to enhance the characterization of the JT. G-banding detected a JT involving the 3q13.3-qter chromosomal segment and the recipient chromosomal regions 17p, 8q, and 15q. Each clone with JT was associated with trisomy 8. oaCGH analysis revealed an additional submicroscopic deletion in 3q13.31 as well as small subtelomeric duplications on several chromosomes. Locus-specific FISH with BAC-based probes from the 3q13.31-q13.32 region showed great heterogeneity. Telomere FISH revealed significantly reduced telomeric content in the aberrant cells with JT compared with cytogenetically normal cells at diagnosis and in normal cells at complete remission. A literature search revealed two previous de novo AML-M5 cases of JT involving the 3q13.3-qter chromosomal segment and concomitant trisomy 8. In addition, a case with an unbalanced der(Y)t(Y;3)(q12;q13.31) and additional trisomy 8 was previously reported in a patient with de novo AML-M5. All of these cases had a dismal outcome. In the present case, and in the der(Y)t(Y;3) case, a concurrent submicroscopic deletion at 3q13.31 was observed affecting the TUSC7 gene. Duplication of 3q13.31-qter might be a non-random chromosomal abnormality with concomitant submicroscopic deletion at 3q13.31 occurring in rare cases of acute monocytic leukemia, being associated with adverse prognosis. The impact of shortened telomeres in forming the JT is reviewed.

Leukocyte Telomere Length and All-Cause, Cardiovascular Disease, and Cancer Mortality: Results From Individual-Participant-Data Meta-Analysis of 2 Large Prospective Cohort Studies

We studied the associations of leukocyte telomere length (LTL) with all-cause, cardiovascular disease, and cancer mortality in 12,199 adults participating in 2 population-based prospective cohort studies from Europe (ESTHER) and the United States (Nurses' Health Study). Blood samples were collected in 1989-1990 (Nurses' Health Study) and 2000-2002 (ESTHER). LTL was measured by quantitative polymerase chain reaction. We calculated z scores for LTL to standardize LTL measurements across the cohorts. Cox proportional hazards regression models were used to calculate relative mortality according to continuous levels and quintiles of LTL z scores. The hazard ratios obtained from each cohort were subsequently pooled by meta-analysis. Overall, 2,882 deaths were recorded during follow-up (Nurses' Health Study, 1989-2010; ESTHER, 2000-2015). LTL was inversely associated with age in both cohorts. After adjustment for age, a significant inverse trend of LTL with all-cause mortality was observed in both cohorts. In random-effects meta-analysis, age-adjusted hazard ratios for the shortest LTL quintile compared with the longest were 1.23 (95% confidence interval (CI): 1.04, 1.46) for all-cause mortality, 1.29 (95% CI: 0.83, 2.00) for cardiovascular mortality, and 1.10 (95% CI: 0.88, 1.37) for cancer mortality. In this study population with an age range of 43-75 years, we corroborated previous evidence suggesting that LTL predicts all-cause mortality beyond its association with age.

Nucleic Acid-Based Nanodevices in Biological Imaging

The nanoscale engineering of nucleic acids has led to exciting molecular technologies for high-end biological imaging. The predictable base pairing, high programmability, and superior new chemical and biological methods used to access nucleic acids with diverse lengths and in high purity, coupled with computational tools for their design, have allowed the creation of a stunning diversity of nucleic acid-based nanodevices. Given their biological origin, such synthetic devices have a tremendous capacity to interface with the biological world, and this capacity lies at the heart of several nucleic acid-based technologies that are finding applications in biological systems. We discuss these diverse applications and emphasize the advantage, in terms of physicochemical properties, that the nucleic acid scaffold brings to these contexts. As our ability to engineer this versatile scaffold increases, its applications in structural, cellular, and organismal biology are clearly poised to massively expand.

Development of software and modification of Q-FISH protocol for estimation of individual telomere length in immunopathology

Telomere length is an important indicator of proliferative cell history and potential. Decreasing telomere length in the cells of an immune system can indicate immune aging in immune-mediated and chronic inflammatory diseases. Quantitative fluorescent in situ hybridization (Q-FISH) of a labeled (C3TA[Formula: see text] peptide nucleic acid probe onto fixed metaphase cells followed by digital image microscopy allows the evaluation of telomere length in the arms of individual chromosomes. Computer-assisted analysis of microscopic images can provide quantitative information on the number of telomeric repeats in individual telomeres. We developed new software to estimate telomere length. The MeTeLen software contains new options that can be used to solve some Q-FISH and microscopy problems, including correction of irregular light effects and elimination of background fluorescence. The identification and description of chromosomes and chromosome regions are essential to the Q-FISH technique. To improve the quality of cytogenetic analysis after Q-FISH, we optimized the temperature and time of DNA-denaturation to get better DAPI-banding of metaphase chromosomes. MeTeLen was tested by comparing telomere length estimations for sister chromatids, background fluorescence estimations, and correction of nonuniform light effects. The application of the developed software for analysis of telomere length in patients with rheumatoid arthritis was demonstrated.

Dysregulation of Telomere Lengths and Telomerase Activity in Myelodysplastic Syndrome

Background

Telomere shortening is thought to be involved in the pathophysiology of myeloid malignancies, but telomere lengths (TL) during interphase and metaphase in hematopoietic malignancies have not been analyzed. We aimed to assess the TLs of interphase and metaphase cells of MDS and telomerase activity (TA) and to find out prognostic significances of TL and TA.

Methods

The prognostic significance of TA by quantitative PCR and TL by quantitative fluorescence in situ hybridization (QFISH) of interphase nuclei and metaphase chromosome arms of bone marrow cells from patients with MDS were evaluated.

Results

MDS patients had shorter interphase TL than normal healthy donors (P<0.001). Average interphase and metaphase TL were inversely correlated (P=0.013, p arm; P=0.029, q arm), but there was no statistically significant correlation between TA and TL (P=0.258). The progression free survival was significantly shorter in patients with high TA, but the overall survival was not different according to average TA or interphase TL groups. Multivariable Cox analysis showed that old age, higher International Prognostic Scoring System (IPSS) subtypes, transformation to AML, no history of hematopoietic stem cell transplantation and short average interphase TL (<433 TL) as independent prognostic factors for poorer survival (P=0.003, 0.001, 0.005, 0.005, and 0.013, respectively).

Conclusions

The lack of correlation between age and TL, TA, and TL, and the inverse relationship between TL and TA in MDS patients reflect the dysregulation of telomere status and proliferation. As a prognostic marker for leukemia progression, TA may be considered, and since interphase TL has the advantage of automated measurement by QFISH, it may be used as a prognostic marker for survival in MDS.

Changes of telomere status with aging: An update

Accumulated data have shown that most human somatic cells or tissues show irreversible telomere shortening with age, and that there are strong associations between telomere attrition and aging-related diseases, including cancers, diabetes and cognitive disorders. Although it has been largely accepted that telomere attrition is one of the major causes of aging-related disorders, critical aspects of telomere biology remain unresolved, especially the lack of standardized methodology for quantification of telomere length. Another frustrating issue is that no potentially promising methods for safe prevention of telomere erosion, or for telomere elongation, have been devised. Here, we review several methods for quantification of telomere length currently utilized worldwide, considering their advantages and drawbacks. We also summarize the results of our recent studies of human cells and tissues, mainly using quantitative fluorescence in situ hybridization and Southern blotting, including those derived from patients with progeria-prone Werner syndrome and trisomy 21, and several strains of induced pluripotent stem cells. We discuss the possible merits of using telomere shortness as an indicator, or a new marker, for diagnosis of precancerous states and aging-related disorders. In addition, we describe newly found factors that are thought to impact telomere dynamics, providing a new avenue for examining the unsolved issues related to telomere restoration and maintenance.

Assessment of Telomere Length, Phenotype, and DNA Content

Telomere sequences at the end of chromosomes control somatic cell division; therefore, telomere length in a given cell population provides information about its replication potential. This unit describes a method for flow cytometric measurement of telomere length in subpopulations using fluorescence in situ hybridization of fluorescently-labeled probes (Flow-FISH) without prior cell separation. After cells are stained for surface immunofluorescence, antigen-antibody complexes are covalently cross-linked onto cell membranes before FISH with a telomere-specific probe. Cells with long telomeres are included as internal standards. Addition of a DNA dye permits exclusion of proliferating cells during data analysis. DNA ploidy measurements of cells of interest and internal standard are performed on separate aliquots in parallel to Flow-FISH. Telomere fluorescence of G0/1 cells of subpopulations and internal standards obtained from Flow-FISH are normalized for DNA ploidy, and telomere length in subsets of interest is expressed as a fraction of the internal standard telomere length. © 2017 by John Wiley & Sons, Inc.

Telomere-associated aging disorders

Telomeres are dynamic nucleoprotein-DNA structures that cap and protect linear chromosome ends. Several monogenic inherited diseases that display features of human premature aging correlate with shortened telomeres, and are referred to collectively as telomeropathies. These disorders have overlapping symptoms and a common underlying mechanism of telomere dysfunction, but also exhibit variable symptoms and age of onset, suggesting they fall along a spectrum of disorders. Primary telomeropathies are caused by defects in the telomere maintenance machinery, whereas secondary telomeropathies have some overlapping symptoms with primary telomeropathies, but are generally caused by mutations in DNA repair proteins that contribute to telomere preservation. Here we review both the primary and secondary telomeropathies, discuss potential mechanisms for tissue specificity and age of onset, and highlight outstanding questions in the field and future directions toward elucidating disease etiology and developing therapeutic strategies.

Telomere Length Analysis by Quantitative Fluorescent in Situ Hybridization (Q-FISH)

Length is a functional parameter of telomeres, the nucleoprotein structures that protect chromosome ends. The availability of highly specific, high affinity probes for telomeric repeat sequences allowed the development of quantitative approaches aimed at measuring telomere length directly on chromosomes or in interphase nuclei. Here, we describe a general method for telomere quantitative FISH on metaphase chromosomes and discuss its most common applications in research.

An improved method for detecting telomere size differences in T-lymphocyte interphases from older people with Down syndrome with and without mild cognitive impairment

Telomere size (quantified by fluorescence intensity and physical lengths) in short-term T-lymphocyte cultures from adults with Down syndrome (DS) with and without mild cognitive impairment (MCI-DS) or dementia was compared. For these studies, dementia status was determined based on longitudinal assessments employing a battery of cognitive and functional assessments developed to distinguish adult-onset impairment from preexisting developmental disability. In the course of our studies using a MetaSystems Image Analyzer in combination with ISIS software and a Zeiss Axioskop 2, we found that Fluorescein isothiocyanate (FITC) telomere fluorescence referenced to chromosome 2-identified FITC probe fluorescence as a nontelomere standard (telomere/cen2 ratio) showed great promise as a biomarker of early decline associated with Alzheimer's disease (AD) in this high-risk population. We have now obtained a cen (2) CY3 probe that can clearly be distinguished from the blue-green FITC interphase telomere probe, providing a clear distinction between telomere and centromere fluorescence in both interphase and metaphase. We used FITC/CY3 light intensity ratios to compare telomere length in interphases in adults with DS with and without MCI-DS or dementia. Five age-matched female and five age-matched male pairs (n = 10) all showed clear evidence of telomere shortening associated with clinical progression of AD (P < 0.002 - P < 0.000001), with distributions of mean values for cases and controls showing no overlap. We also examined the time needed for microscopy using interphase versus metaphase fluorescence preparations. With interphase preparations, examination time was reduced by an order of magnitude compared with metaphase preparations, indicating that the methods employed herein have considerable practical promise for translation into broad diagnostic practice.

Telomere length reflects reproductive effort indicated by corticosterone levels in a long-lived seabird

Telomere length (TL) is a candidate biomarker of ageing and phenotypic quality, but little is known of the (physiological) causes of TL variation. We previously showed that individual common terns Sterna hirundo with high reproductive success had short telomeres independent of age, and this pattern was particularly strong in the longer telomeres of the within-individual TL distribution. To test whether this relation can be attributed to effects of reproductive effort, we investigated baseline corticosterone in relation to reproductive success (number of fledglings) and TL. In this context, we assume that variation in baseline corticosterone can be interpreted as index of energy expenditure and allostatic load. Males with higher corticosterone levels during incubation, compared between and within individuals, achieved higher reproductive success and had shorter telomeres. The effect on telomeres was more pronounced in corticosterone measured later in incubation and in the longer telomeres of the within-individual TL distribution. Female corticosterone level during incubation was neither related to reproductive success nor to TL. That we observed these effects only in males mirrors different parental roles during reproduction in the common tern, where males do most of the chick provisioning. The negative association between reproductive success and TL suggests individual differences in reproductive effort as reflected in, or mediated by, baseline corticosterone. We see this result as a promising step towards unravelling the physiological causes of variation in TL and the costs of reproduction.

Replication Timing of Human Telomeres is Conserved during Immortalization and Influenced by Respective Subtelomeres

Telomeres are specific structures that protect chromosome ends and act as a biological clock, preventing normal cells from replicating indefinitely. Mammalian telomeres are replicated throughout S-phase in a predetermined order. However, the mechanism of this regulation is still unknown. We wished to investigate this phenomenon under physiological conditions in a changing environment, such as the immortalization process to better understand the mechanism for its control. We thus examined the timing of human telomere replication in normal and SV40 immortalized cells, which are cytogenetically very similar to cancer cells. We found that the timing of telomere replication was globally conserved under different conditions during the immortalization process. The timing of telomere replication was conserved despite changes in telomere length due to endogenous telomerase reactivation, in duplicated homologous chromosomes, and in rearranged chromosomes. Importantly, translocated telomeres, possessing their initial subtelomere, retained the replication timing of their homolog, independently of the proportion of the translocated arm, even when the remaining flanking DNA is restricted to its subtelomere, the closest chromosome-specific sequences (inferior to 500 kb). Our observations support the notion that subtelomere regions strongly influence the replication timing of the associated telomere.

Short telomere length and its correlation with gene mutations in myelodysplastic syndrome

Background

Telomere erosion can lead to genomic instability and cancer progression. It has been suggested that the shortest telomere, not the average telomere length (TL), is critical for cell viability. Some studies have shown shorter TL in myelodysplastic syndrome (MDS) patients but the critically short telomeres, the variability of TL within individual patient has not been evaluated. Thus, we aimed to investigate the TL of MDS patients and assessed the association of TL with recurrent genetic mutations in MDS.

Methods

We measured the TL of bone marrow nucleated cells for diagnostic samples at a single-cell level by quantitative fluorescence in situ hybridization (Q-FISH) for 58 MDS patients and analyzed the minimum, median, average, standard deviation, average of the 0th to 10th percentile TL within a patient, and the proportion of cells with TL that is shorter than the lowest 10th percentile of the normal control (NC). The correlations of TL to clinical parameters, cytogenetic results, and genetic mutations were assessed.

Results

MDS patients showed eroded telomeres and narrow distribution compared to the NC (P < 0.001, P = 0.018, respectively). Patients with mutation showed significantly lesser cells with short TL, below the lowest 10th percentile of the NC (P = 0.017), but no differences in TL were found according to mutations/cytogenetic abnormalities except for CSF3R mutation. However, those patients with a high percentage (≥80 %) of cells with short TL showed poorer overall survival (P = 0.021), and this was an independent prognostic factor, along with TP53, U2AF1 mutation, and high BM blast count (P = 0.044, 0.001, 0.004, 0.012, respectively).

Conclusions

The shortest TL, which determines the fate of the cell, was significantly shorter, and higher burden of cells with short TL were found in MDS, which correlated with poor survival, suggesting the need to measure TL in single cells by Q-FISH.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-016-0287-9) contains supplementary material, which is available to authorized users.

Telomere Visualization in Tissue Sections using Pyrrole-Imidazole Polyamide Probes

Pyrrole–Imidazole (PI) polyamides bind to specific DNA sequences in the minor groove with high affinity. Specific DNA labeling by PI polyamides does not require DNA denaturation with harsh treatments of heat and formamide and has the advantages of rapid and less disruptive processing. Previously, we developed tandem hairpin PI polyamide probes (TH59 series), which label telomeres in cultured cell lines more efficiently than conventional methods, such as fluorescence in situ hybridization (FISH). Here, we demonstrate that a TH59 derivative, HPTH59-b, along with immunostaining for specifying cell types in the tissues, visualizes telomeres in mouse and human tissue sections. Quantitative measurements of telomere length with single-cell resolution suggested shorter telomeres in the proliferating cell fractions of tumor than in non-tumor tissues. Thus, PI polyamides are a promising alternative for telomere labeling in clinical research, as well as in cell biology.

Postnatal telomere dysfunction induces cardiomyocyte cell-cycle arrest through p21 activation

The molecular mechanisms that drive mammalian cardiomyocytes out of the cell cycle soon after birth remain largely unknown. Here, we identify telomere dysfunction as a critical physiological signal for cardiomyocyte cell-cycle arrest. We show that telomerase activity and cardiomyocyte telomere length decrease sharply in wild-type mouse hearts after birth, resulting in cardiomyocytes with dysfunctional telomeres and anaphase bridges and positive for the cell-cycle arrest protein p21. We further show that premature telomere dysfunction pushes cardiomyocytes out of the cell cycle. Cardiomyocytes from telomerase-deficient mice with dysfunctional telomeres (G3 Terc(-/-)) show precocious development of anaphase-bridge formation, p21 up-regulation, and binucleation. In line with these findings, the cardiomyocyte proliferative response after cardiac injury was lost in G3 Terc(-/-) newborns but rescued in G3 Terc(-/-)/p21(-/-) mice. These results reveal telomere dysfunction as a crucial signal for cardiomyocyte cell-cycle arrest after birth and suggest interventions to augment the regeneration capacity of mammalian hearts.

Telomerase inhibitors: a patent review (2010-2015)

INTRODUCTION

Telomerase is a ribonucleoprotein that catalyses the addition of telomeric repeat sequences (having the sequence 5'-TTAGGG-3' in humans) to the ends of chromosomes. Telomerase activity is detected in most types of human tumours, but it is almost undetectable in normal somatic cells. Therefore, telomerase is a promising therapeutic target. To date, the known inhibitors of telomerase include nucleoside analogues, oligonucleotides and G-quadruplex stabilizers. This review highlights recent advances in our understanding of telomerase inhibitors, the relationships between telomerase inhibitors, cancer, and fields such as inflammation.

AREAS COVERED

This review summarizes new patents published on telomerase inhibitors from 2010 to 2015.

EXPERT OPINION

The review provides a brief account of the background, development, and on-going issues involving telomerase inhibitors. In particular, this review emphasizes imetelstat (GRN163L) and some typical G-quadruplex stabilizers that participate in telomerase inhibition. Overall, the research scope of antineoplastic is becoming broader and telomerase inhibitors have been shown to be a promising therapeutic target. Therefore, novel antineoplastic agents with greater activity and higher specificity must be developed.

Distribution of Telomeric Sequences (TTAGGG)n in Rearranged Chromosomes of Phyllotine Rodents (Cricetidae, Sigmodontinae)

Phyllotines are sigmodontine rodents endemic to South America with broad genetic variability, Robertsonian polymorphisms being the most frequent. Moreover, this taxon includes a species with multiple sex chromosomes, which is infrequent in mammals. However, molecular cytogenetic techniques have never been applied to phyllotines to elucidate their karyotypic evolution. We studied the chromosomes of 4 phyllotine species using FISH with a pantelomeric probe (TTAGGG)n. Graomys griseoflavus, Eligmodontia puerulus, and E. morgani are polymorphic for Robertsonian translocations, whereas Salinomys delicatus possesses XX/ XY1Y2 sex chromosomes. Telomeric signals were detected at both ends of all chromosomes of the studied species. In S. delicatus interstitial telomeric sequences (ITS) were observed in the 3 major chromosome pairs, which are equidistant from one of the telomeres in these chromosomes. These results suggest that ITS are important in the reshuffling of the highly derived karyotype of S. delicatus. Considering the phylogeny of phyllotines, the Robertsonian rearrangements of G. griseoflavus, E. puerulus, and E. morgani possibly represent chromosome fusions which have occurred independently. The pericentromeric regions of the biarmed chromosomes of these species do not contain telomeric sequences characteristic for strict fusions of recent origin, suggesting a common pattern of telomeric repeat loss during chromosomal evolution of these rodents.

Zscan4 Is Activated after Telomere Shortening in Mouse Embryonic Stem Cells

ZSCAN4 is a DNA-binding protein that functions for telomere elongation and genomic stability. In vivo, it is specifically expressed at the two-cell stage during mouse development. In vitro, it is transiently expressed in mouse embryonic stem cells (ESCs), only in 5% of the population at one time. Here we attempted to elucidate when, under what circumstances, Zscan4 is activated in ESCs. Using live cell imaging, we monitored the activity of Zscan4 together with the pluripotency marker Rex1. The lengths of the cell cycles in ESCs were diverse. Longer cell cycles were accompanied by shorter telomeres and higher activation of Zscan4. Since activation of Zscan4 is involved in telomere elongation, we speculate that the extended cell cycles accompanied by Zscan4 activation reflect the time for telomere recovery. Rex1 and Zscan4 did not show any correlation. Taken together, we propose that Zscan4 is activated to recover shortened telomeres during extended cell cycles, irrespective of the pluripotent status.

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At longer cell cycles, telomeres are shorter

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Zscan4 is activated when the cell cycles become long

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After the activation of Zscan4, the next cell cycle becomes short

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We propose Zscan4 is activated for telomere maintenance irrespective of pluripotency

Probing of miniPEGγ-PNA-DNA Hybrid Duplex Stability with AFM Force Spectroscopy

Peptide nucleic acids (PNA) are synthetic polymers, the neutral peptide backbone of which provides elevated stability to PNA-PNA and PNA-DNA hybrid duplexes. It was demonstrated that incorporation of diethylene glycol (miniPEG) at the γ position of the peptide backbone increased the thermal stability of the hybrid duplexes (Sahu, B. et al. J. Org. Chem. 2011, 76, 5614-5627). Here, we applied atomic force microscopy (AFM) based single molecule force spectroscopy and dynamic force spectroscopy (DFS) to test the strength and stability of the hybrid 10 bp duplex. This hybrid duplex consisted of miniPEGγ-PNA and DNA of the same length (γ(MP)PNA-DNA), which we compared to a DNA duplex with a homologous sequence. AFM force spectroscopy data obtained at the same conditions showed that the γ(MP)PNA-DNA hybrid is more stable than the DNA counterpart, 65 ± 15 pN vs 47 ± 15 pN, respectively. The DFS measurements performed in a range of pulling speeds analyzed in the framework of the Bell-Evans approach yielded a dissociation constant, koff ≈ 0.030 ± 0.01 s⁻¹ for γ(MP)PNA-DNA hybrid duplex vs 0.375 ± 0.18 s⁻¹ for the DNA-DNA duplex suggesting that the hybrid duplex is much more stable. Correlating the high affinity of γ(MP)PNA-DNA to slow dissociation kinetics is consistent with prior bulk characterization by surface plasmon resonance. Given the growing interest in γ(MP)PNA as well as other synthetic DNA analogues, the use of single molecule experiments along with computational analysis of force spectroscopy data will provide direct characterization of various modifications as well as higher order structures such as triplexes and quadruplexes.

Telomere longitudinal shortening as a biomarker for dementia status of adults with Down syndrome

Previous studies have suggested that Alzheimer's disease (AD) causes an accelerated shortening of telomeres, the ends of chromosomes consisting of highly conserved TTAGGG repeats that, because of unidirectional 5'-3' DNA synthesis, lose end point material with each cell division. Our own previous work suggested that telomere length of T-lymphocytes might be a remarkably accurate biomarker for "mild cognitive impairment" in adults with Down syndrome (MCI-DS), a population at dramatically high risk for AD. To verify that the progression of cognitive and functional losses due to AD produced this observed telomere shortening, we have now examined sequential changes in telomere length in five individuals with Down syndrome (3F, 2M) as they transitioned from preclinical AD to MCI-DS (N = 4) or dementia (N = 1). As in our previous studies, we used PNA (peptide nucleic acid) probes for telomeres and the chromosome 2 centromere (as an "internal standard" expected to be unaffected by aging or dementia status), with samples from the same individuals now collected prior to and following development of MCI-DS or dementia. Consistent shortening of telomere length was observed over time. Further comparisons with our previous cross-sectional findings indicated that telomere lengths prior to clinical decline were similar to those of other adults with Down syndrome (DS) who have not experienced clinical decline while telomere lengths following transition to MCI-DS or dementia in the current study were comparable to those of other adults with DS who have developed MCI-DS or dementia. Taken together, findings indicate that telomere length has significant promise as a biomarker of clinical progression of AD for adults with DS, and further longitudinal studies of a larger sample of individuals with DS are clearly warranted to validate these findings and determine if and how factors affecting AD risk also influence these measures of telomere length.