RESUMO
Human centromeres have been traditionally very difficult to sequence and assemble owing to their repetitive nature and large size1. As a result, patterns of human centromeric variation and models for their evolution and function remain incomplete, despite centromeres being among the most rapidly mutating regions2,3. Here, using long-read sequencing, we completely sequenced and assembled all centromeres from a second human genome and compared it to the finished reference genome4,5. We find that the two sets of centromeres show at least a 4.1-fold increase in single-nucleotide variation when compared with their unique flanks and vary up to 3-fold in size. Moreover, we find that 45.8% of centromeric sequence cannot be reliably aligned using standard methods owing to the emergence of new α-satellite higher-order repeats (HORs). DNA methylation and CENP-A chromatin immunoprecipitation experiments show that 26% of the centromeres differ in their kinetochore position by >500 kb. To understand evolutionary change, we selected six chromosomes and sequenced and assembled 31 orthologous centromeres from the common chimpanzee, orangutan and macaque genomes. Comparative analyses reveal a nearly complete turnover of α-satellite HORs, with characteristic idiosyncratic changes in α-satellite HORs for each species. Phylogenetic reconstruction of human haplotypes supports limited to no recombination between the short (p) and long (q) arms across centromeres and reveals that novel α-satellite HORs share a monophyletic origin, providing a strategy to estimate the rate of saltatory amplification and mutation of human centromeric DNA.
Assuntos
Centrômero , Evolução Molecular , Variação Genética , Animais , Humanos , Centrômero/genética , Centrômero/metabolismo , Proteína Centromérica A/metabolismo , Metilação de DNA/genética , DNA Satélite/genética , Cinetocoros/metabolismo , Macaca/genética , Pan troglodytes/genética , Polimorfismo de Nucleotídeo Único/genética , Pongo/genética , Masculino , Feminino , Padrões de Referência , Imunoprecipitação da Cromatina , Haplótipos , Mutação , Amplificação de Genes , Alinhamento de Sequência , Cromatina/genética , Cromatina/metabolismo , Especificidade da EspécieRESUMO
The human Y chromosome has been notoriously difficult to sequence and assemble because of its complex repeat structure that includes long palindromes, tandem repeats and segmental duplications1-3. As a result, more than half of the Y chromosome is missing from the GRCh38 reference sequence and it remains the last human chromosome to be finished4,5. Here, the Telomere-to-Telomere (T2T) consortium presents the complete 62,460,029-base-pair sequence of a human Y chromosome from the HG002 genome (T2T-Y) that corrects multiple errors in GRCh38-Y and adds over 30 million base pairs of sequence to the reference, showing the complete ampliconic structures of gene families TSPY, DAZ and RBMY; 41 additional protein-coding genes, mostly from the TSPY family; and an alternating pattern of human satellite 1 and 3 blocks in the heterochromatic Yq12 region. We have combined T2T-Y with a previous assembly of the CHM13 genome4 and mapped available population variation, clinical variants and functional genomics data to produce a complete and comprehensive reference sequence for all 24 human chromosomes.
Assuntos
Cromossomos Humanos Y , Genômica , Análise de Sequência de DNA , Humanos , Sequência de Bases , Cromossomos Humanos Y/genética , DNA Satélite/genética , Variação Genética/genética , Genética Populacional , Genômica/métodos , Genômica/normas , Heterocromatina/genética , Família Multigênica/genética , Padrões de Referência , Duplicações Segmentares Genômicas/genética , Análise de Sequência de DNA/normas , Sequências de Repetição em Tandem/genética , Telômero/genéticaRESUMO
Centromeres are critical for cell division, loading CENH3 or CENPA histone variant nucleosomes, directing kinetochore formation and allowing chromosome segregation1,2. Despite their conserved function, centromere size and structure are diverse across species. To understand this centromere paradox3,4, it is necessary to know how centromeric diversity is generated and whether it reflects ancient trans-species variation or, instead, rapid post-speciation divergence. To address these questions, we assembled 346 centromeres from 66 Arabidopsis thaliana and 2 Arabidopsis lyrata accessions, which exhibited a remarkable degree of intra- and inter-species diversity. A. thaliana centromere repeat arrays are embedded in linkage blocks, despite ongoing internal satellite turnover, consistent with roles for unidirectional gene conversion or unequal crossover between sister chromatids in sequence diversification. Additionally, centrophilic ATHILA transposons have recently invaded the satellite arrays. To counter ATHILA invasion, chromosome-specific bursts of satellite homogenization generate higher-order repeats and purge transposons, in line with cycles of repeat evolution. Centromeric sequence changes are even more extreme in comparison between A. thaliana and A. lyrata. Together, our findings identify rapid cycles of transposon invasion and purging through satellite homogenization, which drive centromere evolution and ultimately contribute to speciation.
Assuntos
Arabidopsis , Centrômero , Elementos de DNA Transponíveis , DNA Satélite , Evolução Molecular , Arabidopsis/genética , Arabidopsis/metabolismo , Centrômero/genética , Centrômero/metabolismo , Elementos de DNA Transponíveis/genética , Histonas/genética , Histonas/metabolismo , Nucleossomos/genética , Nucleossomos/metabolismo , DNA Satélite/genética , Conversão GênicaRESUMO
Increasing the proportion of locally produced plant protein in currently meat-rich diets could substantially reduce greenhouse gas emissions and loss of biodiversity1. However, plant protein production is hampered by the lack of a cool-season legume equivalent to soybean in agronomic value2. Faba bean (Vicia faba L.) has a high yield potential and is well suited for cultivation in temperate regions, but genomic resources are scarce. Here, we report a high-quality chromosome-scale assembly of the faba bean genome and show that it has expanded to a massive 13 Gb in size through an imbalance between the rates of amplification and elimination of retrotransposons and satellite repeats. Genes and recombination events are evenly dispersed across chromosomes and the gene space is remarkably compact considering the genome size, although with substantial copy number variation driven by tandem duplication. Demonstrating practical application of the genome sequence, we develop a targeted genotyping assay and use high-resolution genome-wide association analysis to dissect the genetic basis of seed size and hilum colour. The resources presented constitute a genomics-based breeding platform for faba bean, enabling breeders and geneticists to accelerate the improvement of sustainable protein production across the Mediterranean, subtropical and northern temperate agroecological zones.
Assuntos
Produtos Agrícolas , Diploide , Variação Genética , Genoma de Planta , Genômica , Melhoramento Vegetal , Proteínas de Plantas , Vicia faba , Cromossomos de Plantas/genética , Produtos Agrícolas/genética , Produtos Agrícolas/metabolismo , Variações do Número de Cópias de DNA/genética , DNA Satélite/genética , Amplificação de Genes/genética , Genes de Plantas/genética , Variação Genética/genética , Genoma de Planta/genética , Estudo de Associação Genômica Ampla , Geografia , Melhoramento Vegetal/métodos , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Recombinação Genética , Retroelementos/genética , Sementes/anatomia & histologia , Sementes/genética , Vicia faba/anatomia & histologia , Vicia faba/genética , Vicia faba/metabolismoRESUMO
Satellite DNA is characterized by long, tandemly repeated sequences mainly found in centromeres and pericentromeric chromosomal regions. The recent advent of telomere-to-telomere sequencing data revealed the complete sequences of satellite regions, including centromeric α-satellites and pericentromeric HSat1-3, which together comprise ~ 5.7% of the human genome. Despite possessing constitutive heterochromatin features, these regions are transcribed to produce long noncoding RNAs with highly repetitive sequences that associate with specific sets of proteins to play various regulatory roles. In certain stress or pathological conditions, satellite RNAs are induced to assemble mesoscopic membraneless organelles. Specifically, under heat stress, nuclear stress bodies (nSBs) are scaffolded by HSat3 lncRNAs, which sequester hundreds of RNA-binding proteins. Upon removal of the stressor, nSBs recruit additional regulatory proteins, including protein kinases and RNA methylases, which modify the previously sequestered nSB components. The sequential recruitment of substrates and enzymes enables nSBs to efficiently regulate the splicing of hundreds of pre-mRNAs under limited temperature conditions. This review discusses the structural features and regulatory roles of satellite RNAs in intracellular architecture and gene regulation.
Assuntos
RNA Longo não Codificante , RNA Satélite , Humanos , RNA Satélite/genética , Fatores de Transcrição/metabolismo , Regulação da Expressão Gênica , DNA Satélite/genética , Heterocromatina , Centrômero/metabolismoRESUMO
The complete assembly of each human chromosome is essential for understanding human biology and evolution1,2. Here we use complementary long-read sequencing technologies to complete the linear assembly of human chromosome 8. Our assembly resolves the sequence of five previously long-standing gaps, including a 2.08-Mb centromeric α-satellite array, a 644-kb copy number polymorphism in the ß-defensin gene cluster that is important for disease risk, and an 863-kb variable number tandem repeat at chromosome 8q21.2 that can function as a neocentromere. We show that the centromeric α-satellite array is generally methylated except for a 73-kb hypomethylated region of diverse higher-order α-satellites enriched with CENP-A nucleosomes, consistent with the location of the kinetochore. In addition, we confirm the overall organization and methylation pattern of the centromere in a diploid human genome. Using a dual long-read sequencing approach, we complete high-quality draft assemblies of the orthologous centromere from chromosome 8 in chimpanzee, orangutan and macaque to reconstruct its evolutionary history. Comparative and phylogenetic analyses show that the higher-order α-satellite structure evolved in the great ape ancestor with a layered symmetry, in which more ancient higher-order repeats locate peripherally to monomeric α-satellites. We estimate that the mutation rate of centromeric satellite DNA is accelerated by more than 2.2-fold compared to the unique portions of the genome, and this acceleration extends into the flanking sequence.
Assuntos
Cromossomos Humanos Par 8/química , Cromossomos Humanos Par 8/genética , Evolução Molecular , Animais , Linhagem Celular , Centrômero/química , Centrômero/genética , Centrômero/metabolismo , Cromossomos Humanos Par 8/fisiologia , Metilação de DNA , DNA Satélite/genética , Epigênese Genética , Feminino , Humanos , Macaca mulatta/genética , Masculino , Repetições Minissatélites/genética , Pan troglodytes/genética , Filogenia , Pongo abelii/genética , Telômero/química , Telômero/genética , Telômero/metabolismoRESUMO
Abundant tandemly repeated satellite DNA is present in most eukaryotic genomes. Previous limitations including a pervasive view that it was uninteresting junk DNA, combined with challenges in studying it, are starting to dissolve - and recent studies have found important functions for satellite DNAs. The observed rapid evolution and implied instability of satellite DNA now has important significance for their functions and maintenance within the genome. In this review, we discuss the processes that lead to satellite DNA copy number instability, and the importance of mechanisms to manage the potential negative effects of instability. Satellite DNA is vulnerable to challenges during replication and repair, since it forms difficult-to-process secondary structures and its homology within tandem arrays can result in various types of recombination. Satellite DNA instability may be managed by DNA or chromatin-binding proteins ensuring proper nuclear localization and repair, or by proteins that process aberrant structures that satellite DNAs tend to form. We also discuss the pattern of satellite DNA mutations from recent mutation accumulation (MA) studies that have tracked changes in satellite DNA for up to 1000 generations with minimal selection. Finally, we highlight examples of satellite evolution from studies that have characterized satellites across millions of years of Drosophila fruit fly evolution, and discuss possible ways that selection might act on the satellite DNA composition.
Assuntos
DNA Satélite , Drosophila , Animais , DNA Satélite/genética , Drosophila/genética , Mutação , Evolução MolecularRESUMO
Maintenance of genome stability relies on functional centromeres for correct chromosome segregation and faithful inheritance of the genetic information. The human centromere is the primary constriction within mitotic chromosomes made up of repetitive alpha-satellite DNA hierarchically organized in megabase-long arrays of near-identical higher order repeats (HORs). Centromeres are epigenetically specified by the presence of the centromere-specific histone H3 variant, CENP-A, which enables the assembly of the kinetochore for microtubule attachment. Notably, centromeric DNA is faithfully inherited as intact haplotypes from the parents to the offspring without intervening recombination, yet, outside of meiosis, centromeres are akin to common fragile sites (CFSs), manifesting crossing-overs and ongoing sequence instability. Consequences of DNA changes within the centromere are just starting to emerge, with unclear effects on intra- and inter-generational inheritance driven by centromere's essential role in kinetochore assembly. Here, we review evidence of meiotic selection operating to mitigate centromere drive, as well as recent reports on centromere damage, recombination and repair during the mitotic cell division. We propose an antagonistic pleiotropy interpretation to reconcile centromere DNA instability as both driver of aneuploidy that underlies degenerative diseases, while also potentially necessary for the maintenance of homogenized HORs for centromere function. We attempt to provide a framework for this conceptual leap taking into consideration the structural interface of centromere-kinetochore interaction and present case scenarios for its malfunctioning. Finally, we offer an integrated working model to connect DNA instability, chromatin, and structural changes with functional consequences on chromosome integrity.
Assuntos
Centrômero , DNA Satélite , Humanos , DNA Satélite/genética , Centrômero/genética , Cromatina , DNA , Meiose/genéticaRESUMO
There has been tremendous progress in phased genome assembly production by combining long-read data with parental information or linked-read data. Nevertheless, a typical phased genome assembly generated by trio-hifiasm still generates more than 140 gaps. We perform a detailed analysis of gaps, assembly breaks, and misorientations from 182 haploid assemblies obtained from a diversity panel of 77 unique human samples. Although trio-based approaches using HiFi are the current gold standard, chromosome-wide phasing accuracy is comparable when using Strand-seq instead of parental data. Importantly, the majority of assembly gaps cluster near the largest and most identical repeats (including segmental duplications [35.4%], satellite DNA [22.3%], or regions enriched in GA/AT-rich DNA [27.4%]). Consequently, 1513 protein-coding genes overlap assembly gaps in at least one haplotype, and 231 are recurrently disrupted or missing from five or more haplotypes. Furthermore, we estimate that 6-7 Mbp of DNA are misorientated per haplotype irrespective of whether trio-free or trio-based approaches are used. Of these misorientations, 81% correspond to bona fide large inversion polymorphisms in the human species, most of which are flanked by large segmental duplications. We also identify large-scale alignment discontinuities consistent with 11.9 Mbp of deletions and 161.4 Mbp of insertions per haploid genome. Although 99% of this variation corresponds to satellite DNA, we identify 230 regions of euchromatic DNA with frequent expansions and contractions, nearly half of which overlap with 197 protein-coding genes. Such variable and incompletely assembled regions are important targets for future algorithmic development and pangenome representation.
Assuntos
DNA Satélite , Polimorfismo Genético , Humanos , DNA Satélite/genética , Haplótipos , Duplicações Segmentares Genômicas , Análise de Sequência de DNARESUMO
Tandem repeat elements such as the diverse class of satellite repeats occupy large parts of eukaryotic chromosomes, mostly at centromeric, pericentromeric, telomeric and subtelomeric regions1. However, some elements are located in euchromatic regions throughout the genome and have been hypothesized to regulate gene expression in cis by modulating local chromatin structure, or in trans via transcripts derived from the repeats2-4. Here we show that a satellite repeat in the mosquito Aedes aegypti promotes sequence-specific gene silencing via the expression of two PIWI-interacting RNAs (piRNAs). Whereas satellite repeats and piRNA sequences generally evolve extremely quickly5-7, this locus was conserved for approximately 200 million years, suggesting that it has a central function in mosquito biology. piRNA production commenced shortly after egg laying, and inactivation of the more abundant piRNA resulted in failure to degrade maternally deposited transcripts in the zygote and developmental arrest. Our results reveal a mechanism by which satellite repeats regulate global gene expression in trans via piRNA-mediated gene silencing that is essential for embryonic development.
Assuntos
Aedes/embriologia , Aedes/genética , DNA Satélite/genética , RNA Interferente Pequeno/genética , Animais , Sequência de Bases , Feminino , Inativação GênicaRESUMO
After two decades of improvements, the current human reference genome (GRCh38) is the most accurate and complete vertebrate genome ever produced. However, no single chromosome has been finished end to end, and hundreds of unresolved gaps persist1,2. Here we present a human genome assembly that surpasses the continuity of GRCh382, along with a gapless, telomere-to-telomere assembly of a human chromosome. This was enabled by high-coverage, ultra-long-read nanopore sequencing of the complete hydatidiform mole CHM13 genome, combined with complementary technologies for quality improvement and validation. Focusing our efforts on the human X chromosome3, we reconstructed the centromeric satellite DNA array (approximately 3.1 Mb) and closed the 29 remaining gaps in the current reference, including new sequences from the human pseudoautosomal regions and from cancer-testis ampliconic gene families (CT-X and GAGE). These sequences will be integrated into future human reference genome releases. In addition, the complete chromosome X, combined with the ultra-long nanopore data, allowed us to map methylation patterns across complex tandem repeats and satellite arrays. Our results demonstrate that finishing the entire human genome is now within reach, and the data presented here will facilitate ongoing efforts to complete the other human chromosomes.
Assuntos
Cromossomos Humanos X/genética , Genoma Humano/genética , Telômero/genética , Centrômero/genética , Ilhas de CpG/genética , Metilação de DNA , DNA Satélite/genética , Feminino , Humanos , Mola Hidatiforme/genética , Masculino , Gravidez , Reprodutibilidade dos Testes , Testículo/metabolismoRESUMO
Sustained, drug-free control of HIV-1 replication is naturally achieved in less than 0.5% of infected individuals (here termed 'elite controllers'), despite the presence of a replication-competent viral reservoir1. Inducing such an ability to spontaneously maintain undetectable plasma viraemia is a major objective of HIV-1 cure research, but the characteristics of proviral reservoirs in elite controllers remain to be determined. Here, using next-generation sequencing of near-full-length single HIV-1 genomes and corresponding chromosomal integration sites, we show that the proviral reservoirs of elite controllers frequently consist of oligoclonal to near-monoclonal clusters of intact proviral sequences. In contrast to individuals treated with long-term antiretroviral therapy, intact proviral sequences from elite controllers were integrated at highly distinct sites in the human genome and were preferentially located in centromeric satellite DNA or in Krüppel-associated box domain-containing zinc finger genes on chromosome 19, both of which are associated with heterochromatin features. Moreover, the integration sites of intact proviral sequences from elite controllers showed an increased distance to transcriptional start sites and accessible chromatin of the host genome and were enriched in repressive chromatin marks. These data suggest that a distinct configuration of the proviral reservoir represents a structural correlate of natural viral control, and that the quality, rather than the quantity, of viral reservoirs can be an important distinguishing feature for a functional cure of HIV-1 infection. Moreover, in one elite controller, we were unable to detect intact proviral sequences despite analysing more than 1.5 billion peripheral blood mononuclear cells, which raises the possibility that a sterilizing cure of HIV-1 infection, which has previously been observed only following allogeneic haematopoietic stem cell transplantation2,3, may be feasible in rare instances.
Assuntos
Inativação Gênica , Infecções por HIV/genética , Infecções por HIV/virologia , HIV-1/genética , Heterocromatina/genética , Provírus/genética , Integração Viral/genética , Latência Viral/genética , Adulto , Idoso , Centrômero/genética , Cromossomos Humanos Par 19/genética , DNA Satélite/genética , Feminino , Genoma Viral/genética , Infecções por HIV/sangue , HIV-1/isolamento & purificação , Heterocromatina/metabolismo , Humanos , Masculino , Pessoa de Meia-Idade , Provírus/isolamento & purificação , Proteínas Repressoras/genética , Sítio de Iniciação de TranscriçãoRESUMO
In addition to monocentric eukaryotes, which have a single localized centromere on each chromosome, there are holocentric species, with extended repeat-based or repeat-less centromeres distributed over the entire chromosome length. At least two types of repeat-based holocentromeres exist, one composed of many small repeat-based centromere units (small unit-type), and another one characterized by a few large centromere units (large unit-type). We hypothesize that the transposable element-mediated dispersal of hundreds of short satellite arrays formed the small centromere unit-type holocentromere in Rhynchospora pubera. The large centromere unit-type of the plant Chionographis japonica is likely a product of simultaneous DNA double-strand breaks (DSBs), which initiated the de novo formation of repeat-based holocentromeres via insertion of satellite DNA, derived from extra-chromosomal circular DNAs (eccDNAs). The number of initial DSBs along the chromosomes must be higher than the number of centromere units since only a portion of the breaks will have incorporated eccDNA at an appropriate position to serve as future centromere unit sites. Subsequently, preferential incorporation of the centromeric histone H3 variant at these positions is assumed. The identification of repeat-based holocentromeres across lineages will unveil the centromere plasticity and elucidate the mechanisms underlying the diverse formation of holocentromeres.
Assuntos
Centrômero , DNA Satélite , Centrômero/genética , DNA Satélite/genética , Quebras de DNA de Cadeia Dupla , Evolução Molecular , Sequências Repetitivas de Ácido Nucleico/genética , Elementos de DNA Transponíveis/genética , Cromossomos de Plantas/genéticaRESUMO
Centromeres in the legume genera Pisum and Lathyrus exhibit unique morphological characteristics, including extended primary constrictions and multiple separate domains of centromeric chromatin. These so-called metapolycentromeres resemble an intermediate form between monocentric and holocentric types, and therefore provide a great opportunity for studying the transitions between different types of centromere organizations. However, because of the exceedingly large and highly repetitive nature of metapolycentromeres, highly contiguous assemblies needed for these studies are lacking. Here, we report on the assembly and analysis of a 177.6 Mb region of pea (Pisum sativum) chromosome 6, including the 81.6 Mb centromere region (CEN6) and adjacent chromosome arms. Genes, DNA methylation profiles, and most of the repeats were uniformly distributed within the centromere, and their densities in CEN6 and chromosome arms were similar. The exception was an accumulation of satellite DNA in CEN6, where it formed multiple arrays up to 2 Mb in length. Centromeric chromatin, characterized by the presence of the CENH3 protein, was predominantly associated with arrays of three different satellite repeats; however, five other satellites present in CEN6 lacked CENH3. The presence of CENH3 chromatin was found to determine the spatial distribution of the respective satellites during the cell cycle. Finally, oligo-FISH painting experiments, performed using probes specifically designed to label the genomic regions corresponding to CEN6 in Pisum, Lathyrus, and Vicia species, revealed that metapolycentromeres evolved via the expansion of centromeric chromatin into neighboring chromosomal regions and the accumulation of novel satellite repeats. However, in some of these species, centromere evolution also involved chromosomal translocations and centromere repositioning.
Assuntos
Cromossomos Humanos Par 6 , Pisum sativum , Humanos , Pisum sativum/genética , Centrômero/genética , Cromatina/genética , DNA Satélite/genéticaRESUMO
Human satellite II (HSATII), composed of tandem repeats in pericentromeric regions, is aberrantly transcribed in epithelial cancers, particularly pancreatic cancer. Dysregulation of repetitive elements in cancer tissues can facilitate incidental dsRNA formation; however, it remains controversial whether dsRNAs play tumor-promoting or tumor-suppressing roles during cancer progression. Therefore, we focused on the double-stranded formation of HSATII RNA and explored its molecular function. The overexpression of double-stranded HSATII (dsHSATII) RNA promoted mesenchymal-like morphological changes and enhanced the invasiveness of pancreatic cancer cells. We identified an RNA-binding protein, spermatid perinuclear RNA-binding protein (STRBP), which preferentially binds to dsHSATII RNA rather than single-stranded HSATII RNA. The mesenchymal transition of dsHSATII-expressing cells was rescued by STRBP overexpression. Mechanistically, STRBP is involved in the alternative splicing of genes associated with epithelial-mesenchymal transition (EMT). We also confirmed that isoform switching of CLSTN1, driven by dsHSATII overexpression or STRBP depletion, induced EMT-like morphological changes. These findings reveal a novel tumor-promoting function of dsHSATII RNA, inducing EMT-like changes and cell invasiveness, thus enhancing our understanding of the biological significance of aberrant expression of satellite arrays in malignant tumors.
Assuntos
Processamento Alternativo , DNA Satélite , Transição Epitelial-Mesenquimal , Regulação Neoplásica da Expressão Gênica , Neoplasias Pancreáticas , RNA de Cadeia Dupla , Humanos , Processamento Alternativo/genética , Linhagem Celular Tumoral , Transição Epitelial-Mesenquimal/genética , Neoplasias Pancreáticas/genética , Neoplasias Pancreáticas/metabolismo , Neoplasias Pancreáticas/patologia , RNA de Cadeia Dupla/genética , Proteínas de Ligação a RNA/genética , Proteínas de Ligação a RNA/metabolismo , Proteínas Associadas aos Microtúbulos/deficiência , Proteínas Associadas aos Microtúbulos/genética , Proteínas Associadas aos Microtúbulos/metabolismo , Proteínas de Ligação ao Cálcio/química , Proteínas de Ligação ao Cálcio/genética , Proteínas de Ligação ao Cálcio/metabolismo , Progressão da Doença , Invasividade Neoplásica/genética , DNA Satélite/genéticaRESUMO
Juncus is the largest genus of Juncaceae and was considered holocentric for a long time. Recent findings, however, indicated that 11 species from different clades of the genus have monocentric chromosomes. Thus, the Juncus centromere organization and evolution need to be reassessed. We aimed to investigate the major repetitive DNA sequences of two accessions of Juncus effusus and its centromeric structure by employing whole-genome analyses, fluorescent in situ hybridization, CENH3 immunodetection, and chromatin immunoprecipitation sequencing. We showed that the repetitive fraction of the small J. effusus genome (~270 Mbp/1C) is mainly composed of Class I and Class II transposable elements (TEs) and satellite DNAs. Three identified satellite DNA families were mainly (peri)centromeric, with two being associated with the centromeric protein CENH3, but not strictly centromeric. Two types of centromere organization were discerned in J. effusus: type 1 was characterized by a single CENH3 domain enriched with JefSAT1-155 or JefSAT2-180, whereas type 2 showed multiple CENH3 domains interrupted by other satellites, TEs or genes. Furthermore, while type 1 centromeres showed a higher degree of satellite identity along the array, type 2 centromeres had less homogenized arrays along the multiple CENH3 domains per chromosome. Although the analyses confirmed the monocentric organization of J. effusus chromosomes, our data indicate a more dynamic arrangement of J. effusus centromeres than observed for other plant species, suggesting it may constitute a transient state between mono- and holocentricity.
Assuntos
Centrômero , Cromossomos de Plantas , DNA Satélite , Hibridização in Situ Fluorescente , Centrômero/genética , Cromossomos de Plantas/genética , DNA Satélite/genética , Genoma de Planta/genética , Elementos de DNA Transponíveis/genética , DNA de Plantas/genética , Sequências Repetitivas de Ácido Nucleico/genética , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismoRESUMO
Among the repetitive elements, satellite DNA (SatDNA) emerges as extensive arrays of highly similar tandemly repeated units, spanning megabases in length. Given that the satDNA PboSat01-176, previously characterized in P. boiei, prompted our interest for having a high abundance in P. boiei and potential for centromeric satellite, here, we employed various approaches, including low coverage genome sequencing, followed by computational analysis and chromosomal localization techniques in four Proceratophrys species and, investigating the genomic presence and sharing, as well as its potential for chromosomal centromere marker in Proceratophrys frog species. Our findings demonstrate that PboSat01-176 exhibits high abundance across all four Proceratophrys species, displaying distinct characteristics that establish it as the predominant repetitive DNA element in these species. The satellite DNA is prominently clustered in the peri/centromeric region of the chromosomes, particularly in the heterochromatic regions. The widespread presence of PboSat01-176 in closely related Proceratophrys species reinforces the validity of the library hypothesis for repetitive sequences. Thus, this study highlighted the utility of the satDNA family PboSat01-176 as a reliable centromeric marker in Proceratophrys species, with potential to be applied in other species of anuran amphibians. The observed sharing and maintenance of this sequence within the genus suggest possibilities for future research, particularly through expanded sampling to elucidate parameters that underlie the library hypothesis and the evolutionary dynamics of satDNA sequences.
Assuntos
Anuros , Centrômero , DNA Satélite , Animais , Centrômero/genética , DNA Satélite/genética , Anuros/genética , Marcadores Genéticos , Hibridização in Situ Fluorescente , Sequências Repetitivas de Ácido Nucleico , Especificidade da EspécieRESUMO
Maintaining genome integrity is vital for organismal survival and reproduction. Essential, broadly conserved DNA repair pathways actively preserve genome integrity. However, many DNA repair proteins evolve adaptively. Ecological forces like UV exposure are classically cited drivers of DNA repair evolution. Intrinsic forces like repetitive DNA, which also imperil genome integrity, have received less attention. We recently reported that a Drosophila melanogaster-specific DNA satellite array triggered species-specific, adaptive evolution of a DNA repair protein called Spartan/MH. The Spartan family of proteases cleave hazardous, covalent crosslinks that form between DNA and proteins ("DNA-protein crosslink repair"). Appreciating that DNA satellites are both ubiquitous and universally fast-evolving, we hypothesized that satellite DNA turnover spurs adaptive evolution of DNA-protein crosslink repair beyond a single gene and beyond the D. melanogaster lineage. This hypothesis predicts pervasive Spartan gene family diversification across Drosophila species. To study the evolutionary history of the Drosophila Spartan gene family, we conducted population genetic, molecular evolution, phylogenomic, and tissue-specific expression analyses. We uncovered widespread signals of positive selection across multiple Spartan family genes and across multiple evolutionary timescales. We also detected recurrent Spartan family gene duplication, divergence, and gene loss. Finally, we found that ovary-enriched parent genes consistently birthed functionally diverged, testis-enriched daughter genes. To account for Spartan family diversification, we introduce a novel mechanistic model of antagonistic coevolution that links DNA satellite evolution and adaptive regulation of Spartan protease activity. This framework promises to accelerate our understanding of how DNA repeats drive recurrent evolutionary innovation to preserve genome integrity.
Assuntos
Reparo do DNA , Proteínas de Drosophila , Evolução Molecular , Duplicação Gênica , Animais , Proteínas de Drosophila/genética , Filogenia , Drosophila melanogaster/genética , Drosophila/genética , Família Multigênica , Seleção Genética , DNA Satélite/genéticaRESUMO
Artemisia is a large genus encompassing about 400 diverse species, many of which have considerable medicinal and ecological value. However, complex morphological information and variation in ploidy level and nuclear DNA content have presented challenges for evolution studies of this genus. Consequently, taxonomic inconsistencies within the genus persist, hindering the utilization of such large plant resources. Researchers have utilized satellite DNAs to aid in chromosome identification, species classification, and evolutionary studies due to their significant sequence and copy number variation between species and close relatives. In the present study, the RepeatExplorer2 pipeline was utilized to identify 10 satellite DNAs from three species (Artemisia annua, Artemisia vulgaris, Artemisia viridisquama), and fluorescence in situ hybridization confirmed their distribution on chromosomes in 24 species, including 19 Artemisia species with 5 outgroup species from Ajania and Chrysanthemum. Signals of satellite DNAs exhibited substantial differences between species. We obtained one genus-specific satellite from the sequences. Additionally, molecular cytogenetic maps were constructed for Artemisia vulgaris, Artemisia leucophylla, and Artemisia viridisquama. One species (Artemisia verbenacea) showed a FISH distribution pattern suggestive of an allotriploid origin. Heteromorphic FISH signals between homologous chromosomes in Artemisia plants were observed at a high level. Additionally, the relative relationships between species were discussed by comparing ideograms. The results of the present study provide new insights into the accurate identification and taxonomy of the Artemisia genus using molecular cytological methods.
Assuntos
Artemisia , Artemisia/genética , Hibridização in Situ Fluorescente , Filogenia , DNA Satélite/genética , Variações do Número de Cópias de DNARESUMO
Holocentric species are characterized by the presence of centromeres throughout the length of the chromosomes. We confirmed the holocentricity of the dioecious, small chromosome-size species Myristica fragrans based on the chromosome-wide distribution of the centromere-specific protein KNL1, α-tubulin fibers, and the cell cycle-dependent histone H3 serine 28 phosphorylation (H3S28ph) mark. Each holocentromere is likely composed of, on average, ten centromere units, but none of the identified and in situ hybridized high-copy satellite repeats is centromere-specific. No sex-specific major repeats are present in the high-copy repeat composition of male or female plants, or a significant difference in genome size was detected. Therefore, it is unlikely that M. fragrans possesses heteromorphic sex chromosomes.