Complete genomic and epigenetic maps of human centromeres

The telomere-to-telomere genome of Pucai () (Typha angustifolia L.): a distinctive semiaquatic vegetable with lignin and chlorophyll as quality characteristics

Pucai () (Typha angustifolia L.), within the Typha spp., is a distinctive semiaquatic vegetable. Lignin and chlorophyll are two crucial traits and quality indicators for Pucai. In this study, we assembled a 207.00-Mb high-quality gapless genome of Pucai, telomere-to-telomere (T2T) level with a contig N50 length of 13.73 Mb. The most abundant type of repetitive sequence, comprising 16.98% of the genome, is the long terminal repeat retrotransposons (LTR-RT). A total of 30 telomeres and 15 centromeric regions were predicted. Gene families related to lignin, chlorophyll biosynthesis, and disease resistance were greatly expanded, which played important roles in the adaptation of Pucai to wetlands. The slow evolution of Pucai was indicated by the σ whole-genome duplication (WGD)-associated Ks peaks from different Poales and the low activity of recent LTR-RT in Pucai. Meanwhile, we found a unique WGD event in Typhaceae. A statistical analysis and annotation of genomic variations were conducted in interspecies and intraspecies of Typha. Based on the T2T genome, we constructed lignin and chlorophyll metabolic pathways of Pucai. Subsequently, the candidate structural genes and transcription factors that regulate lignin and chlorophyll biosynthesis were identified. The T2T genomic resources will provide molecular information for lignin and chlorophyll accumulation and help to understand genome evolution in Pucai.

Eukaryotic Centromere Remodeling: Plasticity, Dynamics, and Holocentromere Formation

Eukaryotic centromeres highlight the remarkable plasticity of eukaryotic chromosomes through their conserved functionality and sequence divergence. Holocentric chromosomes, where centromere activity is distributed along the entire chromosome length, offer a unique model for investigating the molecular mechanisms underlying adaptive evolution between centromeres and chromosomes. In this review, we summarise and speculate on the multiple changes and prerequisites potentially involved in the evolution of holocentromeres. The interplay between environmental factors, chromosomal rearrangements, and centromere plasticity drives the transition from regional to holocentric characteristics. The centromeric histone H3 (CenH3) protein mediates neocentromere formation by recognising non-centromeric chromosomal regions with appropriate AT content, thereby facilitating chromosome restructuring in the transition from regional to holocentric chromosomes. Dynamic changes in repetitive sequences provide functional sites for centromere assembly, chromosomal recombination and repair and centromere spreading and maturation. Epigenetic modifications maintain functional coordination among multiple centromeric units by modulating chromatin states, CenH3 localisation, and kinetochore assembly. This review provides a comprehensive framework for understanding the evolutionary mechanisms of holocentromeres derived from monocentromere and offers insights into the design of artificial centromeres.

Increased maize chromosome number by engineered chromosome fission

Activation of synthetic centromeres on chromosome 4 in maize leads to its breakage and formation of trisomic fragments called neochromosomes. A limitation of neochromosomes is their low and unpredictable transmission rates due to trisomy. Here, we report that selecting for dicentric recombinants through male crosses uncovers stabilized chromosome 4 fission events, which split it into 4a-4b complementary chromosome pairs, where 4a carries a native centromere and 4b carries a synthetic one. The cells rapidly stabilized chromosome ends by de novo telomere formation, and the new centromeres spread among genes without altering their expression. When both 4a and 4b chromosomes were made homozygous, they segregated through meiosis indistinguishably from wild type and gave rise to healthy plants with normal seed set, indicating that the synthetic centromere was fully functional. This work leverages synthetic centromeres to engineer chromosome fission, raising the diploid chromosome number of maize from 20 to 22.

Nuclear m6A modification regulates satellite transcription and chromosome segregation

The precise location and functions of N6-methyladenosine (m6A) modification on mammalian nuclear noncoding RNA remain largely unknown. Here we developed nuclear-m6A-label-seq to directly map human and mouse cell nuclear RNA m6A methylome at single-base resolution. Specifically, m6A modifications have been identified on abundant human γ satellite DNA II (GSATII) RNA transcripts, a type of repeat RNA, transcribed from SST1-TAR1-GSATII satellite arrays in the pericentromeric region of chromosome 9. GSATII RNA m6A positively regulates the transcription of GSATII-located satellite arrays as well as trans-associated peri/centromeric satellites, typically chromosome 3 centromeric higher-order repeat α satellite. Dysregulation of this circuit renders a phenotype of abnormal chromosome segregation. Mechanistic study reveals that YTHDC1 reads GSATII RNA m6A marks and recruits bromodomain protein 4 (BRD4) to promote transcriptions of the associated satellites via an m6A-YTHDC1-BRD4-H3K27ac axis. These results uncover a mechanism governing the transcription of cis- and trans-associated pericentromeric and centromeric satellites via cross-talk between epitranscriptomic and epigenomic marks.

Revealing long-range heterogeneous organization of nucleoproteins with 6mA footprinting by ipdTrimming

Enabled by long-read sequencing technologies, particularly Single Molecule, Real-Time sequencing, N6-methyladenine (6mA) footprinting is a transformative methodology for revealing the heterogenous and dynamic distribution of nucleosomes and other DNA-binding proteins. Here, we present ipdTrimming, a novel 6mA-calling pipeline that outperforms existing tools in both computational efficiency and accuracy. Utilizing this optimized experimental and computational framework, we are able to map nucleosome positioning and transcription factor occupancy in nuclear DNA and establish high-resolution, long-range binding events in mitochondrial DNA. Our study highlights the potential of 6mA footprinting to capture coordinated nucleoprotein binding and to unravel epigenetic heterogeneity.

Nucleosome dynamics render heterochromatin accessible in living human cells

The eukaryotic genome is packaged into chromatin, which is composed of a nucleosomal filament that coils up to form more compact structures. Chromatin exists in two main forms: euchromatin, which is relatively decondensed and enriched in transcriptionally active genes, and heterochromatin, which is condensed and transcriptionally repressed. It is widely accepted that chromatin architecture modulates DNA accessibility, restricting the access of sequence-specific, gene-regulatory, transcription factors to the genome. However, the evidence for this model derives primarily from experiments with isolated nuclei, in which chromatin remodeling has ceased, resulting in a static chromatin structure. Here, using a DNA methyltransferase to measure accessibility in vivo, we show that both euchromatin and heterochromatin are fully accessible in living human cells, whereas centromeric α-satellite chromatin is partly inaccessible. We conclude that all nucleosomes in euchromatin and heterochromatin are highly dynamic in living cells, except for nucleosomes in centromeric chromatin.

Modeling the Copy Number of HSATII Repeats in Human Pericentromere

Tandemly repeated DNA fragments are major components of centromeres and pericentromeric heterochromatin, which is responsible for chromosomal stability and segregation. Recent evidence suggests that transcripts from these repeats play a key role in heterochromatin maintenance, and these repeats can be highly dynamic with various copy numbers. Here, we developed a mathematical model for human satellite repeats, which tracks the silenced and desilenced repeats, lncRNA, and copy number. Our model shows that chromatin factors for silencing and RNA stability can facilitate copy gain in satellites. Also, the system can be bistable, and cells with different copy numbers, silenced repeats with a small copy number, and desilenced repeats with a large copy number may coexist. To incorporate the cooperative methylation by neighboring repeats and the local chromatin environment, we also developed a spatial model where the local chromatin environment facilitates methylation locally. This model suggests that a local domain of silenced repeats may be an important feature of copy number regulation. Our models suggest that pericentromeric repeats are highly dynamic, and small changes in chromatin regulation can lead to large changes in satellite copy numbers.

Unraveling architectural RNAs: Structural and functional blueprints of membraneless organelles and strategies for genome-scale identification

Architectural RNAs (arcRNAs) are long noncoding RNAs that serve as structural scaffolds for membraneless organelles (MLOs), facilitating cellular organization and dynamic responses to stimuli. Acting as blueprints for MLO assembly, arcRNAs recruit specific proteins and nucleic acids to establish and maintain the internal structure of MLOs while coordinating their spatial relationships with other organelles. This organized framework enables precise spatiotemporal regulation, allowing for targeted control of transcription, RNA processing, and cellular responses to stress. Notably, arcRNAs exhibit the "semi-extractable" feature, a property derived from their stable binding to cellular structures, making them partially resistant to conventional RNA extraction methods. This unique feature serves as a useful criterion for identifying novel arcRNAs, providing an opportunity to accelerate research in long noncoding RNAs and deepen our understanding of their functional roles in cellular processes.

How repeats rearrange chromosomes: The molecular basis of chromosomal inversions in deer mice

Large genomic rearrangements, such as chromosomal inversions, can play a key role in evolution, but the mechanisms by which these rearrangements arise remain poorly understood. To study the origins of inversions, we generated chromosome-level de novo genome assemblies for four subspecies of the deer mouse (Peromyscus maniculatus) with known inversion polymorphisms. We identified ∼8,000 inversions, including 47 megabase-scale inversions, that together affect ∼30% of the genome. Analysis of inversion breakpoints suggests that while most small (<1 Mb) inversions arose via ectopic recombination between retrotransposons, large (>1 Mb) inversions are primarily associated with segmental duplications (SDs). Large inversion breakpoints frequently occur near centromeres, which may be explained by an accumulation of retrotransposons in pericentromeric regions driving SDs. Additionally, multiple large inversions likely arose from ectopic recombination between near-identical centromeric satellite arrays located megabases apart, suggesting that centromeric repeats may also facilitate inversions. Together, our results illuminate how repeats give rise to massive shifts in chromosome architecture.

Fast sequence alignment for centromeres with RaMA

The release of the first draft of the human pangenome has revolutionized genomic research by enabling access to complex regions like centromeres, composed of extra-long tandem repeats (ETRs). However, a significant gap remains as current methodologies are inadequate for producing sequence alignments that effectively capture genetic events within ETRs, highlighting a pressing need for improved alignment tools. Inspired by UniAligner, we developed a rare match aligner (RaMA), using rare matches as anchors and two-piece affine gap cost to generate complete pairwise alignment that better captures genetic evolution. RaMA also employs parallel computing and the wavefront algorithm to accelerate anchor discovery and sequence alignment, achieving up to 13.66 times faster processing using only 11% of UniAligner's memory. Downstream analysis of simulated data and the CHM13 and CHM1 higher-order repeat (HOR) arrays demonstrates that RaMA achieves more accurate alignments, effectively capturing true HOR structures. RaMA also introduces two methods for defining reliable alignment regions, further refining and enhancing the accuracy of centromeric alignment statistics.

Four near-complete genome assemblies reveal the landscape and evolution of centromeres in Salicaceae

BACKGROUND

Centromeres play a crucial role in maintaining genomic stability during cell division. They are typically composed of large arrays of tandem satellite repeats, which hinder high-quality assembly and complicate our efforts to understand their evolution across species. Here, we use long-read sequencing to generate near-complete genome assemblies for two Populus and two Salix species belonging to the Salicaceae family and characterize the genetic and epigenetic landscapes of their centromeres.

RESULTS

The results show that only limited satellite repeats are present as centromeric components in these species, while most of them are located outside the centromere but exhibit a homogenized structure similar to that of the Arabidopsis centromeres. Instead, the Salicaceae centromeres are mainly composed of abundant transposable elements, including CRM and ATHILA, while LINE elements are exclusively discovered in the poplar centromeres. Comparative analysis reveals that these centromeric repeats are extensively expanded and interspersed with satellite arrays in a species-specific and chromosome-specific manner, driving rapid turnover of centromeres both in sequence compositions and genomic locations in the Salicaceae.

CONCLUSIONS

Our results highlight the dynamic evolution of diverse centromeric landscapes among closely related species mediated by satellite homogenization and widespread invasions of transposable elements and shed further light on the role of centromere in genome evolution and species diversification.

Centrophilic Retrotransposons of Plant Genomes

The centromeres of eukaryotic chromosomes are required to load CENH3/CENP-A variant nucleosomes and the kinetochore complex, which connects to spindle microtubules during cell division. Despite their conserved function, plant centromeres show rapid sequence evolution within and between species and a range of monocentric, holocentric, and polymetacentric architectures, which vary in kinetochore numbers and spacing. Plant centromeres are commonly composed of tandem satellite repeat arrays, which are invaded by specific families of centrophilic retrotransposons, whereas in some species the entire centromere is composed of such retrotransposons. We review the diversity of plant centrophilic retrotransposons and their mechanisms of integration, together with how epigenetic information and small RNAs control their proliferation. We discuss models for rapid centromere sequence evolution and speculate on the roles that centrophilic retrotransposons may play in centromere dynamics. We focus on plants but draw comparisons with animal and fungal centromeric transposons to highlight conserved and divergent themes across the eukaryotes.

Marking dad's centromeres: maintaining CENP-A in sperm

During spermiogenesis, histones are removed from most genomic loci and are replaced by protamines in mature sperm nuclei. Yet, centromeres appear resistant to this process. We review the experimental evidence that the centromeric histone CENP-A is maintained in mature sperm nuclei, comparing human, bovine, mouse and fly species. We also recall how the detection of centromeres in mature sperm nuclei in the 1990's contributed to the isolation of the CENP-A protein and the eventual cloning of the human CENP-A gene. Further, based on more recent genetic studies carried out in flies and in mice, we discuss the inheritance and functional importance of paternal CENP-A and how it is complemented by maternal CENP-A to give rise to a healthy embryo. Finally, we raise some unanswered questions regarding the exclusive maintenance of CENP-A on sperm, the organisation of sperm centromeric chromatin and its importance for fertility and early embryo development.

Human de novo mutation rates from a four-generation pedigree reference

Understanding the human de novo mutation (DNM) rate requires complete sequence information1. Here using five complementary short-read and long-read sequencing technologies, we phased and assembled more than 95% of each diploid human genome in a four-generation, twenty-eight-member family (CEPH 1463). We estimate 98-206 DNMs per transmission, including 74.5 de novo single-nucleotide variants, 7.4 non-tandem repeat indels, 65.3 de novo indels or structural variants originating from tandem repeats, and 4.4 centromeric DNMs. Among male individuals, we find 12.4 de novo Y chromosome events per generation. Short tandem repeats and variable-number tandem repeats are the most mutable, with 32 loci exhibiting recurrent mutation through the generations. We accurately assemble 288 centromeres and six Y chromosomes across the generations and demonstrate that the DNM rate varies by an order of magnitude depending on repeat content, length and sequence identity. We show a strong paternal bias (75-81%) for all forms of germline DNM, yet we estimate that 16% of de novo single-nucleotide variants are postzygotic in origin with no paternal bias, including early germline mosaic mutations. We place all this variation in the context of a high-resolution recombination map (~3.4 kb breakpoint resolution) and find no correlation between meiotic crossover and de novo structural variants. These near-telomere-to-telomere familial genomes provide a truth set to understand the most fundamental processes underlying human genetic variation.

A Hitchhiker's Guide to long-read genomic analysis

Over the past decade, long-read sequencing has evolved into a pivotal technology for uncovering the hidden and complex regions of the genome. Significant cost efficiency, scalability, and accuracy advancements have driven this evolution. Concurrently, novel analytical methods have emerged to harness the full potential of long reads. These advancements have enabled milestones such as the first fully completed human genome, enhanced identification and understanding of complex genomic variants, and deeper insights into the interplay between epigenetics and genomic variation. This mini-review provides a comprehensive overview of the latest developments in long-read DNA sequencing analysis, encompassing reference-based and de novo assembly approaches. We explore the entire workflow, from initial data processing to variant calling and annotation, focusing on how these methods improve our ability to interpret a wide array of genomic variants. Additionally, we discuss the current challenges, limitations, and future directions in the field, offering a detailed examination of the state-of-the-art bioinformatics methods for long-read sequencing.

The impact of long-read sequencing on human population-scale genomics

Long-read sequencing technologies, particularly those from Pacific Biosciences and Oxford Nanopore Technologies, are revolutionizing genome research by providing high-resolution insights into complex and repetitive regions of the human genome that were previously inaccessible. These advances have been particularly enabling for the comprehensive detection of genomic structural variants (SVs), which is critical for linking genotype to phenotype in population-scale and rare disease studies, as well as in cancer. Recent developments in sequencing throughput and computational methods, such as pangenome graphs and haplotype-resolved assemblies, are paving the way for the future inclusion of long-read sequencing in clinical cohort studies and disease diagnostics. DNA methylation signals directly obtained from long reads enhance the utility of single-molecule long-read sequencing technologies by enabling molecular phenotypes to be interpreted, and by allowing the identification of the parent of origin of de novo mutations. Despite this recent progress, challenges remain in scaling long-read technologies to large populations due to cost, computational complexity, and the lack of tools to facilitate the efficient interpretation of SVs in graphs. This perspective provides a succinct review on the current state of long-read sequencing in genomics by highlighting its transformative potential and key hurdles, and emphasizing future opportunities for advancing the understanding of human genetic diversity and diseases through population-scale long-read analysis.

RAmbler resolves complex repeats in human Chromosomes 8, 19, and X

Repetitive regions in eukaryotic genomes often contain important functional or regulatory elements. Despite significant algorithmic and technological advancements in genome sequencing and assembly over the past three decades, modern de novo assemblers still struggle to accurately reconstruct highly repetitive regions. In this work, we introduce RAmbler (Repeat Assembler), a reference-guided assembler specialized for the assembly of complex repetitive regions exclusively from Pacific Biosciences (PacBio) HiFi reads. RAmbler (1) identifies repetitive regions by detecting unusually high coverage regions after mapping HiFi reads to the draft genome assembly, (2) finds single-copy k-mers from the HiFi reads, (i.e., k-mers that are expected to occur only once in the genome), (3) uses the relative location of single-copy k-mers to barcode each HiFi read, (4) clusters HiFi reads based on their shared barcodes, (5) generates contigs by assembling the reads in each cluster, and (6) generates a consensus assembly from the overlap graph of the assembled contigs. Here, we show that RAmbler can reconstruct human centromeres and other complex repeats to a quality comparable to the manually curated Telomere-to-Telomere human genome assembly. Across more than 250 synthetic data sets, RAmbler outperforms hifiasm, LJA, HiCANU, and Verkko across various parameters such as repeat lengths, number of repeats, heterozygosity rates, and depth of sequencing.

Decoding G-Quadruplexes Sequence in Vitis vinifera: Regulatory Region Enrichment, Drought Stress Adaptation, and Sugar-Acid Metabolism Modulation

G-quadruplexes play a crucial role in transcription, translation, and DNA replication in plant genomes. Here, we comprehensively examined the prevalence and functions of G-quadruplexes in Vitis vinifera. A total of 467,813 G-quadruplexes were identified in grapevine genome, with enrichment in the promoter (0.54/kbp) and near transcription start sites (TSSs, 1.00/kbp), and showed conservative strand preference. The G-quadruplex density in centromeres exhibited heterogeneity. The differentially expressed genes (DEGs) under two-day drought stress manifested high G-quadruplex density in the promoter and TSS regions. The upregulated DEGs showed template strand-biased G-quadruplex enrichment, while downregulated DEGs displayed coding strand dominance linked to metal ion homeostasis and sugar-acid metabolism pathways, respectively. G-quadruplexes were enriched in key sugar-acid metabolism genes, including pyruvate kinase and sucrose synthase. The number of G-quadruplexes in sucrose transferase VINV genes was higher than that in the CWINV and NINV genes. This study revealed G-quadruplexes as regulatory elements of stress response and berry development, providing abundant genetic targets for precision breeding and the quality improvement of grapevines.

Genome-wide maps of highly-similar intrachromosomal repeats that can mediate ectopic recombination in three human genome assemblies

Repeated sequences spread throughout the genome play important roles in shaping the structure of chromosomes and facilitating the generation of new genomic variation through structural rearrangements. Several mechanisms of structural variation formation use shared nucleotide similarity between repeated sequences as substrate for ectopic recombination. We performed genome-wide analyses of direct and inverted intrachromosomal repeated sequence pairs with 200 bp or more and 80% or greater sequence identity in three human genome assemblies, GRCh37, GRCh38, and T2T-CHM13. Overall, the composition and distribution of direct and inverted repeated sequences identified was similar among the three assemblies involving 13%-15% of the haploid genome, with an increased, albeit not significant, number of repeated sequences in T2T-CHM13. Interestingly, the majority of repeated sequences are below 1 kb in length with a median of 84.2% identity, highlighting the potential relevance of smaller, less identical repeats, such as Alu-Alu pairs, for ectopic recombination. We cross-referenced the identified repeated sequences with protein-coding genes to identify those at risk for being involved in genomic rearrangements. Olfactory receptors and immune response genes were enriched among those impacted.

Non-canonical DNA in human and other ape telomere-to-telomere genomes

Non-canonical (non-B) DNA structures-e.g. bent DNA, hairpins, G-quadruplexes (G4s), Z-DNA, etc.-which form at certain sequence motifs (e.g. A-phased repeats, inverted repeats, etc.), have emerged as important regulators of cellular processes and drivers of genome evolution. Yet, they have been understudied due to their repetitive nature and potentially inaccurate sequences generated with short-read technologies. Here we comprehensively characterize such motifs in the long-read telomere-to-telomere (T2T) genomes of human, bonobo, chimpanzee, gorilla, Bornean orangutan, Sumatran orangutan, and siamang. Non-B DNA motifs are enriched at the genomic regions added to T2T assemblies and occupy 9%-15%, 9%-11%, and 12%-38% of autosomes and chromosomes X and Y, respectively. G4s and Z-DNA are enriched at promoters and enhancers, as well as at origins of replication. Repetitive sequences harbor more non-B DNA motifs than non-repetitive sequences, especially in the short arms of acrocentric chromosomes. Most centromeres and/or their flanking regions are enriched in at least one non-B DNA motif type, consistent with a potential role of non-B structures in determining centromeres. Our results highlight the uneven distribution of predicted non-B DNA structures across ape genomes and suggest their novel functions in previously inaccessible genomic regions.

Chromatin-associated α-satellite RNA maintains chromosome stability by reestablishing SAF-A in the mitotic cell cycle

α-Satellite is the largest class of tandem repeats and is located on all human chromosome centromeres. Non-coding α-satellite RNAs have been observed in various cell types and are known to play crucial roles in maintaining genome stability. In this study, we demonstrated that α-satellite RNAs are dynamically expressed, heterogeneous transcripts that are regulated by Aurora kinases and closely associated with centromere chromatin throughout the mitotic cell cycle. We identified scaffold attachment factor A (SAF-A) as a previously uncharacterized α-satellite RNA binding protein. Depletion of either α-satellite RNA or SAF-A resulted in chromosome missegregation, revealing that their concerted action is essential for preserving genome integrity during the mitotic cell cycle. Our result demonstrated that SAF-A is excluded from the chromatin genome-wide during mitosis, and α-satellite RNAs are required for the recruitment of SAF-A upon mitotic exit. Both α-satellite RNAs and SAF-A are essential in safeguarding the human genome against chromosomal instability during mitosis. Moreover, α-satellite RNAs and SAF-A aid in the reassembly of the nuclear lamina. Our results provide novel insights into the features, regulations, and functional roles of α-satellite RNAs and propose a model for the dismantling and reformation of the SAF-A nuclear scaffold during mitosis.

Conservation of dichromatin organization along regional centromeres

The attachment of the kinetochore to the centromere is essential for genome maintenance, yet the highly repetitive nature of satellite regional centromeres limits our understanding of their chromatin organization. We demonstrate that single-molecule chromatin fiber sequencing (Fiber-seq) can uniquely co-resolve kinetochore and surrounding chromatin architectures along point centromeres, revealing largely homogeneous single-molecule kinetochore occupancy. In contrast, the application of Fiber-seq to regional centromeres exposed marked per-molecule heterogeneity in their chromatin organization. Regional centromere cores uniquely contain a dichotomous chromatin organization (dichromatin) composed of compacted nucleosome arrays punctuated with highly accessible chromatin patches. CENP-B occupancy phases dichromatin to the underlying alpha-satellite repeat within centromere cores but is not necessary for dichromatin formation. Centromere core dichromatin is conserved between humans and primates, including along regional centromeres lacking satellite repeats. Overall, the chromatin organization of regional centromeres is defined by marked per-molecule heterogeneity, buffering kinetochore attachment against sequence and structural variability within regional centromeres.

Centromeric transposable elements and epigenetic status drive karyotypic variation in the eastern hoolock gibbon

Great apes have maintained a stable karyotype with few large-scale rearrangements; in contrast, gibbons have undergone a high rate of chromosomal rearrangements coincident with rapid centromere turnover. Here, we characterize fully assembled centromeres in the eastern hoolock gibbon, Hoolock leuconedys (HLE), finding a diverse group of transposable elements (TEs) that differ from the canonical alpha-satellites found across centromeres of other apes. We find that HLE centromeres contain a CpG methylation centromere dip region, providing evidence that this epigenetic feature is conserved in the absence of satellite arrays. We uncovered a variety of atypical centromeric features, including protein-coding genes and mismatched replication timing. Further, we identify duplications and deletions in HLE centromeres that distinguish them from other gibbons. Finally, we observed differentially methylated TEs, topologically associated domain boundaries, and segmental duplications at chromosomal breakpoints, and thus propose that a combination of multiple genomic attributes with propensities for chromosome instability shaped gibbon centromere evolution.

Evolution and instability of human centromeres are accelerated by heterochromatin boundary loss and CENP-A overexpression

Centromere location is specified by CENP-A, a centromere-specific histone that epigenetically defines centromere identity. How CENP-A is maintained at one location in rapidly evolving centromeric DNA is unknown. Using single-cell-derived clones of human cell lines, we demonstrate single-cell heterogeneity in CENP-A position within cell populations at neocentromeres and a native centromere. CENP-A heterogeneity is accompanied by unique DNA methylation and H3K9me3 patterns, with DNA methylation shifting according to CENP-A position. We further demonstrate centromere epigenetic evolution over prolonged proliferation, with native centromeres maintaining stable heterochromatin boundaries, but neocentromeres exhibiting DNA methylation instability, H3K9me3 gain, boundary loss and fragility. Lastly, prolonged CENP-A and HJURP overexpression leads to centromere and neocentromere expansion, gradual CENP-A depletion, neocentromere destabilization and CENP-A re-localization that is accompanied by local heterochromatin remodeling. This study reveals the naturally evolving epigenetic plasticity of human centromeres and neocentromeres and highlights the importance of repressive chromatin boundaries in maintaining centromere stability.

REPrise: de novo interspersed repeat detection using inexact seeding

BACKGROUND

Interspersed repeats occupy a large part of many eukaryotic genomes, and thus their accurate annotation is essential for various genome analyses. Database-free de novo repeat detection approaches are powerful for annotating genomes that lack well-curated repeat databases. However, existing tools do not yet have sufficient repeat detection performance.

RESULTS

In this study, we developed REPrise, a de novo interspersed repeat detection software program based on a seed-and-extension method. Although the algorithm of REPrise is similar to that of RepeatScout, which is currently the de facto standard tool, we incorporated three unique techniques into REPrise: inexact seeding, affine gap scoring and loose masking. Analyses of rice and simulation genome datasets showed that REPrise outperformed RepeatScout in terms of sensitivity, especially when the repeat sequences contained many mutations. Furthermore, when applied to the complete human genome dataset T2T-CHM13, REPrise demonstrated the potential to detect novel repeat sequence families.

CONCLUSION

REPrise can detect interspersed repeats with high sensitivity even in long genomes. Our software enhances repeat annotation in diverse genomic studies, contributing to a deeper understanding of genomic structures.

A telomere-to-telomere genome assembly of cotton provides insights into centromere evolution and short-season adaptation

Cotton (Gossypium hirsutum L.) is a key allopolyploid crop with global economic importance. Here we present a telomere-to-telomere assembly of the elite variety Zhongmian 113. Leveraging technologies including PacBio HiFi, Oxford Nanopore Technology (ONT) ultralong-read sequencing and Hi-C, our assembly surpasses previous genomes in contiguity and completeness, resolving 26 centromeric and 52 telomeric regions, 5S rDNA clusters and nucleolar organizer regions. A phylogenetically recent centromere repositioning on chromosome D08 was discovered specific to G. hirsutum, involving deactivation of an ancestral centromere and the formation of a unique, satellite repeat-based centromere. Genomic analyses evaluated favorable allele aggregation for key agronomic traits and uncovered an early-maturing haplotype derived from an 11 Mb pericentric inversion that evolved early during G. hirsutum domestication. Our study sheds light on the genomic origins of short-season adaptation, potentially involving introgression of an inversion from primitively domesticated forms, followed by subsequent haplotype differentiation in modern breeding programs.

Two CENH3 paralogs in the green alga Chlamydomonas reinhardtii have a redundantly essential function and associate with ZeppL-LINE1 elements

Centromeres in eukaryotes are defined by the presence of histone H3 variant CENP-A/CENH3. Chlamydomonas encodes two predicted CENH3 paralogs, CENH3.1 and CENH3.2, that have not been previously characterized. We generated peptide antibodies to unique N-terminal epitopes for each of the two predicted Chlamydomonas CENH3 paralogs as well as an antibody against a shared CENH3 epitope. All three CENH3 antibodies recognized proteins of the expected size on immunoblots and had punctate nuclear immunofluorescence staining patterns. These results are consistent with both paralogs being expressed and localized to centromeres. CRISPR-Cas9-mediated insertional mutagenesis was used to generate predicted null mutations in either CENH3.1 or CENH3.2. Single mutants were viable but cenh3.1 cenh3.2 double mutants were not recovered, confirming that the function of CENH3 is essential. We sequenced and assembled two chromosome-scale Chlamydomonas genomes from strains CC-400 and UL-1690 (a derivative of CC-1690) with complete centromere sequences for 17/17 and 14/17 chromosomes respectively, enabling us to compare centromere evolution across four isolates with near complete assemblies. These data revealed significant changes across isolates between homologous centromeres including mobility and degeneration of ZeppL-LINE1 (ZeppL) transposons that comprise the major centromere repeat sequence in Chlamydomonas. We used cleavage under targets and tagmentation (CUT&Tag) to purify and map CENH3-bound genomic sequences and found enrichment of CENH3-binding almost exclusively at predicted centromere regions. An interesting exception was chromosome 2 in UL-1690, which had enrichment at its genetically mapped centromere repeat region as well as a second, distal location, centered around a single recently acquired ZeppL insertion. The CENH3-bound regions of the 17 Chlamydomonas centromeres ranged from 63.5 kb (average lower estimate) to 175 kb (average upper estimate). The relatively small size of its centromeres suggests that Chlamydomonas may be a useful organism for testing and deploying artificial chromosome technologies.

Integrated analysis of the complete sequence of a macaque genome

The crab-eating macaques (Macaca fascicularis) and rhesus macaques (Macaca mulatta) are pivotal in biomedical and evolutionary research1-3. However, their genomic complexity and interspecies genetic differences remain unclear4. Here, we present a complete genome assembly of a crab-eating macaque, revealing 46% fewer segmental duplications and 3.83 times longer centromeres than those of humans5,6. We also characterize 93 large-scale genomic differences between macaques and humans at a single-base-pair resolution, highlighting their impact on gene regulation in primate evolution. Using ten long-read macaque genomes, hundreds of short-read macaque genomes and full-length transcriptome data, we identified roughly 2 Mbp of fixed-genetic variants, roughly 240 Mbp of complex loci, 16.76 Mbp genetic differentiation regions and 110 alternative splice events, potentially associated with various phenotypic differences between the two macaque species. In summary, the integrated genetic analysis enhances understanding of lineage-specific phenotypes, adaptation and primate evolution, thereby improving their biomedical applications in human disease research.

Post-polyploidization centromere evolution in cotton

Upland cotton (Gossypium hirsutum) accounts for more than 90% of the world's cotton production and, as an allotetraploid, is a model plant for polyploid crop domestication. In the present study, we reported a complete telomere-to-telomere (T2T) genome assembly of Upland cotton accession Texas Marker-1 (T2T-TM-1), which has a total size of 2,299.6 Mb, and annotated 79,642 genes. Based on T2T-TM-1, interspecific centromere divergence was detected between the A- and D-subgenomes and their corresponding diploid progenitors. Centromere-associated repetitive sequences (CRCs) were found to be enriched for Gypsy-like retroelements. Centromere size expansion, repositioning and structure variations occurred post-polyploidization. It is interesting that CRC homologs were transferred from the diploid D-genome progenitor to the D-subgenome, invaded the A-subgenome and then underwent post-tetraploidization proliferation. This suggests an evolutionary advantage for the CRCs of the D-genome progenitor, presents a D-genome-adopted inheritance of centromere repeats after polyploidization and shapes the dynamic centromeric landscape during polyploidization in polyploid species.

Species-specific satellite DNA composition dictates PRC1-mediated pericentric heterochromatin

Pericentromeres are heterochromatic regions adjacent to centromeres that ensure accurate chromosome segregation. Despite their conserved function, they are composed of rapidly evolving A/T-rich satellite DNA. This paradoxical observation is partially resolved by epigenetic mechanisms that maintain H3K9me3-based heterochromatin, independent of specific DNA sequences. However, these mechanisms can function only after H3K9me3 has already been established, and this mark is absent from paternal chromatin in the mouse zygote. It is unknown how variation in satellite DNA sequence impacts alternative forms of heterochromatin at this earliest stage of life. Here we show functional consequences of satellite DNA variation for pericentric heterochromatin formation, recruitment of the Chromosome Passenger Complex (CPC), and interactions with the mitotic spindle. The AT-hook of Polycomb Repressive Complex 1 (PRC1) directly recognizes A/T-rich satellite DNA and packages it in H2AK119ub1 heterochromatin. By fertilizing M. musculus eggs with sperm from other mouse species, we show that divergent satellite sequences differ in their ability to bind PRC1, resulting in differences in H2AK119ub1 heterochromatin formation on mitotic chromosomes. Furthermore, we find that satellites that robustly form H2AK119ub1 inhibit molecular pathways that recruit the CPC to pericentromeres, increasing microtubule forces on kinetochores during mitosis. Our results provide a direct link between satellite DNA composition and pericentromere function and highlight early embryogenesis as a critical point in development that is sensitive to satellite DNA evolution.

Simulation and Quantitative Analysis of Spatial Centromere Distribution Patterns

A prominent feature of eukaryotic chromosomes are centromeres, which are specialized regions of repetitive DNA required for faithful chromosome segregation during cell division. In interphase cells, centromeres are non-randomly positioned in the three-dimensional space of the nucleus in a cell type-specific manner. The functional relevance and the cellular mechanisms underlying this localization are unknown, and quantitative methods to measure distribution patterns of centromeres in 3D space are needed. Here, we developed an analytical framework that combines sensitive clustering metrics and advanced modeling techniques for the quantitative analysis of centromere distributions at the single-cell level. To identify a robust quantitative measure for centromere clustering, we benchmarked six metrics for their ability to sensitively detect changes in centromere distribution patterns from high-throughput imaging data of human cells, both under normal conditions and upon experimental perturbation of centromere distribution. We found that Ripley's K function has the highest accuracy with minimal sensitivity to variations in the number of centromeres, making it the most suitable metric for measuring centromere distributions. As a complementary approach, we also developed and validated spatial models to replicate centromere distribution patterns, and we show that a radially shifted Gaussian distribution best represents the centromere patterns seen in human cells. Our approach creates tools for the quantitative characterization of spatial centromere distributions with applications in both targeted studies of centromere organization and unbiased screening approaches.

Centromeres are stress-induced fragile sites

Centromeres are unique loci on eukaryotic chromosomes and are complexed with centromere-specific histone H3 molecules (CENP-A in mammals, Cse4 in yeast). The centromere provides the binding site for the kinetochore that captures microtubules and provides the mechanical linkage required for chromosome segregation. Centromeres encounter fluctuations in force as chromosomes jockey for position on the metaphase spindle. We have developed biological assays to examine the response of centromeres to high force. Torsional stress is induced on covalently closed DNA circles from supercoiling. Plasmid-borne centromeres with single-nucleotide inactivating mutations exhibit a high conversion frequency to plasmid dimer species. Conversion to dimers is dependent on the activity of the Rad1 single-strand endonuclease, indicative of unwinding a region of the centromere sequence in the absence of a functional kinetochore. To determine the region of unwinding, we used conditionally functional dicentric chromosomes to exert tension. Centromere DNA is exquisitely sensitive to cleavage following activation of the dicentric chromosome. Cleavage is dependent on the action of Rad1, highlighting the propensity of centromeres to unwind in response to supercoiling or mechanical stress. These studies provide mechanistic insights into the evolution of AT-rich pericentromere DNA throughout phylogeny and suggest a mechanism for stress-induced error correction at the centromere.

Analysis of 30 chromosome-level Drosophila genome assemblies reveals dynamic evolution of centromeric satellite repeats

BACKGROUND

The Drosophila genus is ideal for studying genome evolution due to its relatively simple chromosome structure and small genome size, with rearrangements mainly restricted to within chromosome arms, such as Muller elements. However, work on the rapidly evolving repetitive genomic regions, composed of transposons and tandem repeats, have been hampered by the lack of genus-wide chromosome-level assemblies.

RESULTS

Integrating long-read genomic sequencing and chromosome capture technology, here we produce and annotate 30 chromosome-level genome assemblies within the Drosophila genus. Based on this dataset, we reveal the evolutionary dynamics of genome rearrangements across the Drosophila phylogeny, including the identification of genomic regions that show comparatively high structural stability throughout evolution. Moreover, within the ananassae subgroup, we uncover the emergence of new chromosome conformations and the rapid expansion of novel satellite DNA sequence families, which form large and continuous pericentromeric domains with higher-order repeat structures that are reminiscent of those observed in the human and Arabidopsis genomes.

CONCLUSIONS

These chromosome-level genome assemblies present a valuable resource for future research, the power of which is demonstrated by our analysis of genome rearrangements and chromosome evolution. In addition, based on our findings, we propose the ananassae subgroup as an ideal model system for studying the evolution of centromere structure.

Centromeric chromatin clearings demarcate the site of kinetochore formation

The centromere is the chromosomal locus that recruits the kinetochore, directing faithful propagation of the genome during cell division. Using cryo-ET on human mitotic chromosomes, we reveal a distinctive architecture at the centromere: clustered 20- to 25-nm nucleosome-associated complexes within chromatin clearings that delineate them from surrounding chromatin. Centromere components CENP-C and CENP-N are each required for the integrity of the complexes, while CENP-C is also required to maintain the chromatin clearing. We find that CENP-C is required in mitosis, not just for kinetochore assembly, likely reflecting its role in organizing the inner kinetochore during chromosome segregation. We further visualize the scaffold of the fibrous corona, a structure amplified at unattached kinetochores, revealing crescent-shaped parallel arrays of fibrils extending >1 μm. Thus, we reveal how the organization of centromeric chromatin creates a clearing at the site of kinetochore formation as well as the nature of kinetochore amplification mediated by corona fibrils.

p53 enhances DNA repair and suppresses cytoplasmic chromatin fragments and inflammation in senescent cells

Genomic instability and inflammation are distinct hallmarks of aging, but the connection between them is poorly understood. Here we report a mechanism directly linking genomic instability and inflammation in senescent cells through a mitochondria-regulated molecular circuit involving p53 and cytoplasmic chromatin fragments (CCF) that are enriched for DNA damage signaling marker γH2A.X. We show that p53 suppresses CCF accumulation and its downstream inflammatory phenotype. p53 activation suppresses CCF formation linked to enhanced DNA repair and genome integrity. Activation of p53 in aged mice by pharmacological inhibition of MDM2 reverses transcriptomic signatures of aging and age-associated accumulation of monocytes and macrophages in liver. Mitochondrial ablation in senescent cells suppresses CCF formation and activates p53 in an ATM-dependent manner, suggesting that mitochondria-dependent formation of γH2A.X + CCF dampens nuclear DNA damage signaling and p53 activity. These data provide evidence for a mitochondria-regulated p53 signaling circuit in senescent cells that controls DNA repair, genome integrity, and senescence- and age-associated inflammation, with relevance to therapeutic targeting of age-associated disease.

Nanopore Long-Read Sequencing Unveils Genomic Disruptions in Alzheimer's Disease

Studies in laboratory models and postmortem human brain tissue from patients with Alzheimer's disease have revealed disruption of basic cellular processes such as DNA repair and epigenetic control as drivers of neurodegeneration. While genomic alterations in regions of the genome that are rich in repetitive sequences, often termed "dark regions," are difficult to resolve using traditional sequencing approaches, long-read technologies offer promising new avenues to explore previously inaccessible regions of the genome. In the current study, we leverage nanopore-based long-read whole-genome sequencing of DNA extracted from postmortem human frontal cortex at early and late stages of Alzheimer's disease, as well as age-matched controls, to analyze retrotransposon insertion events, non-allelic homologous recombination (NAHR), structural variants and DNA methylation within retrotransposon loci and other repetitive/dark regions of the human genome. Interestingly, we find that retrotransposon insertion events and repetitive element-associated NAHR are particularly enriched within centromeric and pericentromeric regions of DNA in the aged human brain, and that ribosomal DNA (rDNA) is subject to a high degree of NAHR compared to other regions of the genome. We detect a trending increase in potential somatic retrotransposition events of the small interfering nuclear element (SINE) AluY in late-stage Alzheimer's disease, and differential changes in methylation within repetitive elements and retrotransposons according to disease stage. Taken together, our analysis provides the first long-read DNA sequencing-based analysis of retrotransposon sequences, NAHR, structural variants, and DNA methylation in the aged brain, and points toward transposable elements, centromeric/pericentromeric regions and rDNA as hotspots for genomic variation.

PBRM1 directs PBAF to pericentromeres and protects centromere integrity

The specialised structure of the centromere is critical for effective chromosome segregation, but its repetitive nature makes it vulnerable to rearrangements. Centromere fragility can drive tumorigenesis, but protective mechanisms preventing fragility are still not fully understood. The PBAF chromatin remodelling complex is frequently misregulated in cancer, but its role in cancer is incompletely characterized. Here, we identify PBAF as a protector of centromere and pericentromere structure with profound consequences for genome stability. A conserved feature of isogenic cell lines lacking PBRM1, a subunit of PBAF, is compromised centromere and pericentromere integrity. PBAF is present at these regions, and binding patterns of PBAF and H3K9 methylation change when PBRM1 is absent. PBRM1 loss creates a dependence on the spindle assembly checkpoint, which represents a therapeutic vulnerability. Importantly, we find that even in the absence of any perturbations, PBRM1 loss leads to centromere fragility, thus identifying a key player in centromere protection.

Pericentromeric sequences, where a conservation paradox occurs

Pericentromeric sequences are characterized by their tandem repeat structure, heterochromatinization, and rapid evolution. The rapid evolvement creates highly diversified pericentromeric sequences, which facilitate reproductive isolation, as best exemplified in Drosophila studies. Despite their high variability, pericentromeric sequences ranging from fission yeast to humans are heterochromatinized with the same histone modification, H3K9 methylation. These features present a paradox, how highly variable sequences get recognized by conserved machineries. This Opinion discusses how this paradox is resolved and how diversification and conservation get unified at pericentromeric sequences.

Mutant IDH impairs chromatin binding by PDGFB to promote chromosome instability

Non-canonical roles for growth factors in the nucleus have been previously described, but their mechanism of action and biological roles remain enigmatic. Platelet-derived growth factor B (PDGFB) can drive formation of low-grade glioma and here we show that it localizes to the nucleus of human glioma cells where it binds chromatin to preserve genome stability and cell lineage. Failure of PDGFB to localize to the nucleus leads to chromosomal abnormalities, aberrant heterochromatin architecture and accelerated tumorigenesis. Furthermore, nuclear localization of PDGFB is reliant upon the expression levels and mutation status of isocitrate dehydrogenase (IDH). Unexpectedly, we identified macrophages as the predominant source of PDGFB in human, finding that immune-derived PDGFB can localize to the nucleus of glioma cells. Collectively, these studies show that immune derived PDGFB enters the nucleus of glioma cells to maintain genomic stability, while identifying a new mechanism by which IDH mutations promote gliomagenesis.

A refined analysis of Neanderthal-introgressed sequences in modern humans with a complete reference genome

BACKGROUND

Leveraging long-read sequencing technologies, the first complete human reference genome, T2T-CHM13, corrects assembly errors in previous references and resolves the remaining 8% of the genome. While studies on archaic admixture in modern humans have so far relied on the GRCh37 reference due to the availability of archaic genome data, the impact of T2T-CHM13 in this field remains unexplored.

RESULTS

We remap the sequencing reads of the high-quality Altai Neanderthal and Denisovan genomes onto GRCh38 and T2T-CHM13. Compared to GRCh37, we find that T2T-CHM13 significantly improves read mapping quality in archaic samples. We then apply IBDmix to identify Neanderthal-introgressed sequences in 2504 individuals from 26 geographically diverse populations using different reference genomes. We observe that commonly used pre-phasing filtering strategies in public datasets substantially influence archaic ancestry determination, underscoring the need for careful filter selection. Our analysis identifies approximately 51 Mb of Neanderthal sequences unique to T2T-CHM13, predominantly in genomic regions where GRCh38 and T2T-CHM13 assemblies diverge. Additionally, we uncover novel instances of population-specific archaic introgression in diverse populations, spanning genes involved in metabolism, olfaction, and ion-channel function. Finally, to facilitate the exploration of archaic alleles and adaptive signals in human genomics and evolutionary research, we integrate these introgressed sequences and adaptive signals across all reference genomes into a visualization database, ASH ( www.arcseqhub.com ).

CONCLUSIONS

Our study enhances the detection of archaic variations in modern humans, highlights the importance of utilizing the T2T-CHM13 reference, and provides novel insights into the functional consequences of archaic hominin admixture.

Benchmarking, detection, and genotyping of structural variants in a population of whole-genome assemblies using the SVGAP pipeline

Comparisons of complete genome assemblies offer a direct procedure for characterizing all genetic differences among them. However, existing tools are often limited to specific aligners or optimized for specific organisms, narrowing their applicability, particularly for large and repetitive plant genomes. Here, we introduce SVGAP, a pipeline for structural variant (SV) discovery, genotyping, and annotation from high-quality genome assemblies at the population level. Through extensive benchmarks using simulated SV datasets at individual, population, and phylogenetic contexts, we demonstrate that SVGAP performs favorably relative to existing tools in SV discovery. Additionally, SVGAP is one of the few tools to address the challenge of genotyping SVs within large assembled genome samples, and it generates fully genotyped VCF files. Applying SVGAP to 26 maize genomes revealed hidden genomic diversity in centromeres, driven by abundant insertions of centromere-specific LTR-retrotransposons. The output of SVGAP is well-suited for pan-genome construction and facilitates the interpretation of previously unexplored genomic regions.

Bridging scales in chromatin organization: Computational models of loop formation and their implications for genome function

Chromatin loop formation plays a crucial role in 3D genome interactions, with misfolding potentially leading to irregular gene expression and various diseases. While experimental tools such as Hi-C have advanced our understanding of genome interactions, the biophysical principles underlying chromatin loop formation remain elusive. This review examines computational approaches to chromatin folding, focusing on polymer models that elucidate chromatin loop mechanics. We discuss three key models: (1) the multi-loop-subcompartment model, which investigates the structural effects of loops on chromatin conformation; (2) the strings and binders switch model, capturing thermodynamic chromatin aggregation; and (3) the loop extrusion model, revealing the role of structural maintenance of chromosome complexes. In addition, we explore advanced models that address chromatin clustering heterogeneity in biological processes and disease progression. The review concludes with an outlook on open questions and current trends in chromatin loop formation and genome interactions, emphasizing the physical and computational challenges in the field.

CENP-A/CENP-B uncoupling in the evolutionary reshuffling of centromeres in equids

BACKGROUND

While CENP-A is the epigenetic determinant of the centromeric function, the role of CENP-B, a centromeric protein binding a specific DNA sequence, the CENP-B-box, remains elusive. In the few mammalian species analyzed so far, the CENP-B box is contained in the major satellite repeat that is present at all centromeres, with the exception of the Y chromosome. We previously demonstrated that, in the genus Equus, numerous centromeres lack any satellite repeat.

RESULTS

In four Equus species, CENP-B is expressed but does not bind the majority of satellite-based centromeres, or the satellite-free ones, while it is localized at several ancestral, now-inactive, centromeres. Centromeres lacking CENP-B are functional and recruit normal amounts of CENP-A and CENP-C. The absence of CENP-B is related to the lack of CENP-B boxes rather than to peculiar features of the protein itself. CENP-B boxes are present in a previously undescribed repeat which is not the major satellite bound by CENP-A. Comparative sequence analysis suggests that this satellite was centromeric in the equid ancestor, lost centromeric function during evolution, and gave rise to a shorter CENP-A bound repeat not containing the CENP-B box but enriched in dyad symmetries.

CONCLUSIONS

We propose that the uncoupling between CENP-B and CENP-A may have played a role in the extensive evolutionary reshuffling of equid centromeres. This study provides new insights into the complexity of centromere organization in a largely biodiverse world where the majority of mammalian species still have to be studied.

CiFi: Accurate long-read chromatin conformation capture with low-input requirements

By coupling chromatin conformation capture (3C) with PacBio HiFi long-read sequencing, we have developed a new method (CiFi) that enables analysis of genome interactions across repetitive genomic regions with low-input requirements. CiFi produces multiple interacting concatemer segments per read, facilitating genome assembly and scaffolding. Together, the approach enables genomic analysis of previously recalcitrant low-complexity loci, and of small organisms such as single insect individuals.

Multifunctional histone variants in genome function

Histones are integral components of eukaryotic chromatin that have a pivotal role in the organization and function of the genome. The dynamic regulation of chromatin involves the incorporation of histone variants, which can dramatically alter its structural and functional properties. Contrary to an earlier view that limited individual histone variants to specific genomic functions, new insights have revealed that histone variants exert multifaceted roles involving all aspects of genome function, from governing patterns of gene expression at precise genomic loci to participating in genome replication, repair and maintenance. This conceptual change has led to a new understanding of the intricate interplay between chromatin and DNA-dependent processes and how this connection translates into normal and abnormal cellular functions.

Satellite DNA shapes dictate pericentromere packaging in female meiosis

The abundance and sequence of satellite DNA at and around centromeres is evolving rapidly despite the highly conserved and essential process through which the centromere directs chromosome inheritance1-3. The impact of such rapid evolution is unclear. Here we find that sequence-dependent DNA shape dictates packaging of pericentromeric satellites in female meiosis through a conserved DNA-shape-recognizing chromatin architectural protein, high mobility group AT-hook 1 (HMGA1)4,5. Pericentromeric heterochromatin in two closely related mouse species, M. musculus and M. spretus, forms on divergent satellites that differ by both density of narrow DNA minor grooves and HMGA1 recruitment. HMGA1 binds preferentially to M. musculus satellites, and depletion in M. musculus oocytes causes massive stretching of pericentromeric satellites, disruption of kinetochore organization and delays in bipolar spindle assembly. In M. musculus × spretus hybrid oocytes, HMGA1 depletion disproportionately impairs M. musculus pericentromeres and microtubule attachment to their kinetochores. Thus, DNA shape affects both pericentromere packaging and the segregation machinery. We propose that rapid evolution of centromere and pericentromere DNA does not disrupt these essential processes when the satellites adopt DNA shapes recognized by conserved architectural proteins (such as HMGA1). By packaging these satellites, architectural proteins become part of the centromeric and pericentromeric chromatin, suggesting an evolutionary strategy that lowers the cost of megabase-scale satellite expansion.

Identifying Safeguards Disabled by Epstein-Barr Virus Infections in Genomes From Patients With Breast Cancer: Chromosomal Bioinformatics Analysis

Background

The causes of breast cancer are poorly understood. A potential risk factor is Epstein-Barr virus (EBV), a lifelong infection nearly everyone acquires. EBV-transformed human mammary cells accelerate breast cancer when transplanted into immunosuppressed mice, but the virus can disappear as malignant cells reproduce. If this model applies to human breast cancers, then they should have genome damage characteristic of EBV infection.

Objective

This study tests the hypothesis that EBV infection predisposes one to breast cancer by causing permanent genome damage that compromises cancer safeguards.

Methods

Publicly available genome data from approximately 2100 breast cancers and 25 ovarian cancers were compared to cancers with proven associations to EBV, including 70 nasopharyngeal cancers, 90 Burkitt lymphomas, 88 diffuse large B-cell lymphomas, and 34 gastric cancers. Calculation algorithms to make these comparisons were developed.

Results

Chromosome breakpoints in breast and ovarian cancer clustered around breakpoints in EBV-associated cancers. Breakpoint distributions in breast and EBV-associated cancers on some chromosomes were not confidently distinguished (P>.05), but differed from controls unrelated to EBV infection. Viral breakpoint clusters occurred in high-risk, sporadic, and other breast cancer subgroups. Breakpoint clusters disrupted gene functions essential for cancer protection, which remain compromised even if EBV infection disappears. As CRISPR (clustered regularly interspaced short palindromic repeats)-like reminders of past infection during evolution, EBV genome fragments were found regularly interspaced between Piwi-interacting RNA (piRNA) genes on chromosome 6. Both breast and EBV-associated cancers had inactivated genes that guard piRNA defenses and the major histocompatibility complex (MHC) locus. Breast and EBV-associated cancer breakpoints and other variations converged around the highly polymorphic MHC. Not everyone develops cancer because MHC differences produce differing responses to EBV infection. Chromosome shattering and mutation hot spots in breast cancers preferentially occurred at incorporated viral sequences. On chromosome 17, breast cancer breakpoints that clustered around those in EBV-mediated cancers were linked to estrogen effects. Other breast cancer breaks affected sites where EBV inhibits JAK-STAT and SWI-SNF signaling pathways. A characteristic EBV-cancer gene deletion that shifts metabolism to favor tumors was also found in breast cancers. These changes push breast cancer into metastasis and then favor survival of metastatic cells.

Conclusions

EBV infection predisposes one to breast cancer and metastasis, even if the virus disappears. Identifying this pathogenic viral damage may improve screening, treatment, and prevention. Immunizing children against EBV may protect against breast, ovarian, other cancers, and potentially even chronic unexplained diseases.

Simulation and quantitative analysis of spatial centromere distribution patterns

A prominent feature of eukaryotic chromosomes are centromeres, which are specialized regions of repetitive DNA required for faithful chromosome segregation during cell division. In interphase cells centromeres are non-randomly positioned in the three-dimensional space of the nucleus in a cell-type specific manner. The functional relevance and the cellular mechanisms underlying this observation are unknown, and quantitative methods to measure distribution patterns of centromeres in 3D space are needed. Here we have developed an analytical framework that combines robust clustering metrics and advanced modeling techniques for the quantitative analysis of centromere distributions at the single cell level. To identify a robust quantitative measure for centromere clustering, we benchmarked six metrics for their ability to sensitively detect changes in centromere distribution patterns from high-throughput imaging data of human cells, both under normal conditions and upon experimental perturbation of centromere distribution. We find that Ripley's K Score has the highest accuracy with minimal sensitivity to variations in centromeres number, making it the most suitable metric for measuring centromere distributions. As a complementary approach, we also developed and validated spatial models to replicate centromere distribution patterns, and we show that a radially shifted Gaussian distribution best represents the centromere patterns seen in human cells. Our approach creates tools for the quantitative characterization of spatial centromere distributions with applications in both targeted studies of centromere organization as well as in unbiased screening approaches.

YHSeqY3000 panel captures all founding lineages in the Chinese paternal genomic diversity database

BACKGROUND

The advancements in second-/third-generation sequencing technologies, alongside computational innovations, have significantly enhanced our understanding of the genomic structure of Y-chromosomes and their unique phylogenetic characteristics. These researches, despite the challenges posed by the lack of population-scale genomic databases, have the potential to revolutionize our approach to high-resolution, population-specific Y-chromosome panels and databases for anthropological and forensic applications.

OBJECTIVES

This study aimed to develop the highest-resolution Y-targeted sequencing panel, utilizing time-stamped, core phylogenetic informative mutations identified from high-coverage sequences in the YanHuang cohort. This panel is intended to provide a new tool for forensic complex pedigree search and paternal biogeographical ancestry inference, as well as explore the general patterns of the fine-scale paternal evolutionary history of ethnolinguistically diverse Chinese populations.

RESULTS

The sequencing performance of the East Asian-specific Y-chromosomal panel, including 2999-core SNP variants, was found to be robust and reliable. The YHSeqY3000 panel was designed to capture the genetic diversity of Chinese paternal lineages from 3500 years ago, identifying 408 terminal lineages in 2097 individuals across 41 genetically and geographically distinct populations. We identified a fine-scale paternal substructure that was correlating with ancient population migrations and expansions. New evidence was provided for extensive gene flow events between minority ethnic groups and Han Chinese people, based on the integrative Chinese Paternal Genomic Diversity Database.

CONCLUSIONS

This work successfully integrated Y-chromosome-related basic genomic science with forensic and anthropological translational applications, emphasizing the necessity of comprehensively characterizing Y-chromosome genomic diversity from genomically under-representative populations. This is particularly important in the second phase of our population-specific medical or anthropological genomic cohorts, where dense sampling strategies are employed.