qmotif: determination of telomere content from whole-genome sequence data

HIRA protects telomeres against R-loop-induced instability in ALT cancer cells

Inactivating mutations in chromatin modifiers, like the α-thalassemia/mental retardation, X-linked (ATRX)-death domain-associated protein (DAXX) chromatin remodeling/histone H3.3 deposition complex, drive the cancer-specific alternative lengthening of telomeres (ALT) pathway. Prior studies revealed that HIRA, another histone H3.3 chaperone, compensates for ATRX-DAXX loss at telomeres to sustain ALT cancer cell survival. How HIRA rescues telomeres from the consequences of ATRX-DAXX deficiency remains unclear. Here, using an assay for transposase-accessible chromatin using sequencing (ATAC-seq) and cleavage under targets and release using nuclease (CUT&RUN), we establish that HIRA-mediated deposition of new H3.3 maintains telomeric chromatin accessibility to prevent the detrimental accumulation of nucleosome-free single-stranded DNA (ssDNA) in ATRX-DAXX-deficient ALT cells. We show that the HIRA-UBN1/UBN2 complex deposits new H3.3 to prevent TERRA R-loop buildup and transcription-replication conflicts (TRCs) at telomeres. Furthermore, HIRA-mediated H3.3 incorporation into telomeric chromatin links productive ALT to the phosphorylation of serine 31, an H3.3-specific amino acid, by Chk1. Therefore, we identify a critical role for HIRA-mediated H3.3 deposition that ensures the survival of ATRX-DAXX-deficient ALT cancer cells.

Malaria endemicity linked to shorter telomeres in leukocytes

Leukocyte telomere length is a highly polygenic trait that has been associated with a complex range of lifestyle factors and disease risk. McQuillan et al.'s results comparing telomere length to malaria incidence rates suggest that infections may be another important factor, possibly through permanent shortening of telomeres in hematopoietic progenitor cells.

Blastocyst telomere length predicts successful implantation after frozen-thawed embryo transfer

STUDY QUESTION

Do embryos with longer telomere length (TL) at the blastocyst stage have a higher capacity to survive after frozen-thawed embryo transfer (FET)?

SUMMARY ANSWER

Digitally estimated TL using low-pass whole genome sequencing (WGS) data from the preimplantation genetic testing for aneuploidy (PGT-A) process demonstrates that blastocyst TL is the most essential factor associated with likelihood of implantation.

WHAT IS KNOWN ALREADY

The lifetime TL is established in the early cleavage cycles following fertilization through a recombination-based lengthening mechanism and starts erosion beyond the blastocyst stage. In addition, a telomerase-mediated slow erosion of TL in human fetuses has been observed from a gestational age of 6-11 weeks. Finally, an abnormal shortening of telomeres is likely involved in embryo loss during early development.

STUDY DESIGN SIZE DURATION

Blastocyst samples were obtained from patients who underwent PGT-A and FET in an IVF center from March 2015 to May 2018. Digitally estimated mitochondrial copy number (mtCN) and TL were used to study associations with the implantation potential of each embryo.

PARTICIPANTS/MATERIALS SETTING AND METHODS

In total, 965 blastocysts from 232 cycles (164 patients) were available to investigate the biological and clinical relevance of TL. A WGS-based workflow was applied to determine the ploidy of each embryo. Data from low-pass WGS-PGT-A were used to estimate the mtCN and TL for each embryo. Single-variant and multi-variant logistic regression, decision tree, and random forest models were applied to study various factors in association with the implantation potential of each embryo.

MAIN RESULTS AND THE ROLE OF CHANCE

Of the 965 blastocysts originally available, only 216 underwent FET. While mtCN from the transferred embryos is significantly associated with the ploidy call of each embryo, mtCN has no role in impacting IVF outcomes after an embryo transfer in these women. The results indicate that mtCN is a marker of embryo aneuploidy. On the other hand, digitally estimated TL is the most prominent univariant factor and showed a significant positive association with pregnancy outcomes (P < 0.01, odds ratio 79.1). We combined several maternal and embryo parameters to study the joint effects on successful implantation. The machine learning models, namely decision tree and random forest, were trained and yielded classification accuracy of 0.82 and 0.91, respectively. Taken together, these results support the vital role of TL in governing implantation potential, perhaps through the ability to control embryo survival after transfer.

LIMITATIONS REASONS FOR CAUTION

The small sample size limits our study as only 216 blastocysts were transferred. The number was further reduced to 153 blastocysts, where pregnancy outcomes could be accurately traced. The other limitation of this study is that all data were collected from a single IVF center. The uniform and controlled operation of IVF cycles in a single center may cause selection bias.

WIDER IMPLICATIONS OF THE FINDINGS

We present novel findings to show that digitally estimated TL at the blastocyst stage is a predictor of pregnancy capacity after a FET cycle. As elective single-embryo transfer has become the mainstream direction in reproductive medicine, prioritizing embryos based on their implantation potential is crucial for clinical infertility treatment in order to reduce twin pregnancy rate and the time to pregnancy in an IVF center. The AI-powered, random forest prediction model established in this study thus provides a way to improve clinical practice and optimize the chances for people with fertility problems to achieve parenthood.

STUDY FUNDING/COMPETING INTERESTS

This study was supported by a grant from the National Science and Technology Council, Taiwan (MOST 108-2321-B-006-013 -). There were no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Leveraging whole-genome sequencing to estimate telomere length in plants

Changes in telomere length are increasingly used to indicate species' response to environmental stress across diverse taxa. Despite this broad use, few studies have explored telomere length in plants. Thus, evaluation of new approaches for measuring telomeres in plants is needed. Rapid advances in sequencing approaches and bioinformatic tools now allow estimation of telomere content from whole-genome sequencing (WGS) data, a proxy for telomere length. While telomere content has been quantified extensively using quantitative polymerase chain reaction (qPCR) and WGS in humans, no study to date has compared the effectiveness of WGS in estimating telomere length in plants relative to qPCR approaches. In this study, we use 100 Populus clones re-sequenced using short-read Illumina sequencing to quantify telomere length comparing three different bioinformatic approaches (Computel, K-seek and TRIP) in addition to qPCR. Overall, telomere length estimates varied across different bioinformatic approaches, but were highly correlated across methods for individual genotypes. A positive correlation was observed between WGS estimates and qPCR, however, Computel estimates exhibited the greatest correlation. Computel incorporates genome coverage into telomere length calculations, suggesting that genome coverage is likely important to telomere length quantification when using WGS data. Overall, telomere estimates from WGS provided greater precision and accuracy of telomere length estimates relative to qPCR. The findings suggest WGS is a promising approach for assessing telomere length and, as the field of telomere ecology evolves, may provide added value to assaying response to biotic and abiotic environments for plants needed to accelerate plant breeding and conservation management.

Experimental and Computational Approaches to Measure Telomere Length: Recent Advances and Future Directions

PURPOSE OF REVIEW

The length of telomeres, protective structures at the chromosome ends, is a well-established biomarker for pathological conditions including multisystemic syndromes called telomere biology disorders. Approaches to measure telomere length (TL) differ on whether they estimate average, distribution, or chromosome-specific TL, and each presents their own advantages and limitations.

RECENT FINDINGS

The development of long-read sequencing and publication of the telomere-to-telomere human genome reference has allowed for scalable and high-resolution TL estimation in pre-existing sequencing datasets but is still impractical as a dedicated TL test. As sequencing costs continue to fall and strategies for selectively enriching telomere regions prior to sequencing improve, these approaches may become a promising alternative to classic methods. Measurement methods rely on probe hybridization, qPCR or more recently, computational methods using sequencing data. Refinements of existing techniques and new approaches have been recently developed but a test that is accurate, simple, and scalable is still lacking.

Telomere Length Changes in Cancer: Insights on Carcinogenesis and Potential for Non-Invasive Diagnostic Strategies

Telomere dynamics play a crucial role in the maintenance of chromosome integrity; changes in telomere length may thus contribute to the development of various diseases including cancer. Understanding the role of telomeric DNA in carcinogenesis and detecting the presence of cell-free telomeric DNA (cf-telDNA) in body fluids offer a potential biomarker for novel cancer screening and diagnostic strategies. Liquid biopsy is becoming increasingly popular due to its undeniable benefits over conventional invasive methods. However, the organization and function of cf-telDNA in the extracellular milieu are understudied. This paper provides a review based on 3,398,017 cancer patients, patients with other conditions, and control individuals with the aim to shed more light on the inconsistent nature of telomere lengthening/shortening in oncological contexts. To gain a better understanding of biological factors (e.g., telomerase activation, alternative lengthening of telomeres) affecting telomere homeostasis across different types of cancer, we summarize mechanisms responsible for telomere length maintenance. In conclusion, we compare tissue- and liquid biopsy-based approaches in cancer assessment and provide a brief outlook on the methodology used for telomere length evaluation, highlighting the advances of state-of-the-art approaches in the field.

Leukocyte telomere length in children born following blastocyst-stage embryo transfer

Perinatal and childhood adverse outcomes associated with assisted reproductive technology (ART) has been reported, but it remains unknown whether the initial leukocyte telomere length (LTL), which is an indicator of age-related phenotypes in later life, is affected. Here, we estimated the LTLs of 1,137 individuals from 365 families, including 202 children conceived by ART and 205 children conceived spontaneously from two centers of the China National Birth Cohort, using whole-genome sequencing (WGS) data. One-year-old children conceived by ART had shorter LTLs than those conceived spontaneously (beta, -0.36; P = 1.29 × 10^-3) after adjusting for plurality, sex and other potential confounding factors. In particular, blastocyst-stage embryo transfer was associated with shorter LTL (beta, -0.54, P = 2.69 × 10^-3) in children conceived by ART. The association was validated in 586 children conceived by ART from five centers using different LTL quantification methods (that is, WGS or qPCR). Blastocyst-stage embryo transfer resulted in shorter telomere lengths in mice at postnatal day 1 (P = 2.10 × 10^-4) and mice at 6 months (P = 0.042). In vitro culturing of mice embryos did not result in shorter telomere lengths in the late cleavage stage, but it did suppress telomerase activity in the early blastocyst stage. Our findings demonstrate the need to evaluate the long-term consequences of ART, particularly for aging-related phenotypes, in children conceived by ART.

Comprehensive genomic and tumour immune profiling reveals potential therapeutic targets in malignant pleural mesothelioma

Background

Malignant pleural mesothelioma (MPM) has a poor overall survival with few treatment options. Whole genome sequencing (WGS) combined with the immune features of MPM offers the prospect of identifying changes that could inform future clinical trials.

Methods

We analysed somatic mutations from 229 MPM samples, including previously published data and 58 samples that had undergone WGS within this study. This was combined with RNA-seq analysis to characterize the tumour immune environment.

Results

The comprehensive genome analysis identified 12 driver genes, including new candidate genes. Whole genome doubling was a frequent event that correlated with shorter survival. Mutational signature analysis revealed SBS5/40 were dominant in 93% of samples, and defects in homologous recombination repair were infrequent in our cohort. The tumour immune environment contained high M2 macrophage infiltrate linked with MMP2, MMP14, TGFB1 and CCL2 expression, representing an immune suppressive environment. The expression of TGFB1 was associated with overall survival. A small subset of samples (less than 10%) had a higher proportion of CD8 T cells and a high cytolytic score, suggesting a ‘hot’ immune environment independent of the somatic mutations.

Conclusions

We propose accounting for genomic and immune microenvironment status may influence therapeutic planning in the future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13073-022-01060-8.