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Haig D. Paradox lost: Concerted evolution and centromeric instability: Centromeres are hospitable habitats for repeats that evolve adaptations for proliferation within the nucleus sometimes at organismal cost.: Centromeres are hospitable habitats for repeats that evolve adaptations for proliferation within the nucleus sometimes at organismal cost. Bioessays 2022; 44:e2200023. [PMID: 35748194 DOI: 10.1002/bies.202200023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Revised: 06/07/2022] [Accepted: 06/09/2022] [Indexed: 11/11/2022]
Abstract
Homologous centromeres compete for segregation to the secondary oocyte nucleus at female meiosis I. Centromeric repeats also compete with each other to populate centromeres in mitotic cells of the germline and have become adapted to use the recombinational machinery present at centromeres to promote their own propagation. Repeats are not needed at centromeres, rather centromeres appear to be hospitable habitats for the colonization and proliferation of repeats. This is probably an indirect consequence of two distinctive features of centromeric DNA. Centromeres are subject to breakage by the mechanical forces exerted by microtubules and meiotic crossing-over is suppressed. Centromeric proteins acting in trans are under selection to mitigate the costs of centromeric repeats acting in cis. Collateral costs of mitotic competition at centromeres may help to explain the high rates of aneuploidy observed in early human embryos.
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Affiliation(s)
- David Haig
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, USA
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2
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Population Scale Analysis of Centromeric Satellite DNA Reveals Highly Dynamic Evolutionary Patterns and Genomic Organization in Long-Tailed and Rhesus Macaques. Cells 2022; 11:cells11121953. [PMID: 35741082 PMCID: PMC9221937 DOI: 10.3390/cells11121953] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Revised: 06/12/2022] [Accepted: 06/14/2022] [Indexed: 02/04/2023] Open
Abstract
Centromeric satellite DNA (cen-satDNA) consists of highly divergent repeat monomers, each approximately 171 base pairs in length. Here, we investigated the genetic diversity in the centromeric region of two primate species: long-tailed (Macaca fascicularis) and rhesus (Macaca mulatta) macaques. Fluorescence in situ hybridization and bioinformatic analysis showed the chromosome-specific organization and dynamic nature of cen-satDNAsequences, and their substantial diversity, with distinct subfamilies across macaque populations, suggesting increased turnovers. Comparative genomics identified high level polymorphisms spanning a 120 bp deletion region and a remarkable interspecific variability in cen-satDNA size and structure. Population structure analysis detected admixture patterns within populations, indicating their high divergence and rapid evolution. However, differences in cen-satDNA profiles appear to not be involved in hybrid incompatibility between the two species. Our study provides a genomic landscape of centromeric repeats in wild macaques and opens new avenues for exploring their impact on the adaptive evolution and speciation of primates.
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Abstract
We are entering a new era in genomics where entire centromeric regions are accurately represented in human reference assemblies. Access to these high-resolution maps will enable new surveys of sequence and epigenetic variation in the population and offer new insight into satellite array genomics and centromere function. Here, we focus on the sequence organization and evolution of alpha satellites, which are credited as the genetic and genomic definition of human centromeres due to their interaction with inner kinetochore proteins and their importance in the development of human artificial chromosome assays. We provide an overview of alpha satellite repeat structure and array organization in the context of these high-quality reference data sets; discuss the emergence of variation-based surveys; and provide perspective on the role of this new source of genetic and epigenetic variation in the context of chromosome biology, genome instability, and human disease.
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Affiliation(s)
- Karen H Miga
- UC Santa Cruz Genomics Institute, University of California, Santa Cruz, California 95064, USA; .,Department of Biomolecular Engineering, University of California, Santa Cruz, California 95064, USA
| | - Ivan A Alexandrov
- Department of Genomics and Human Genetics, Vavilov Institute of General Genetics, Russian Academy of Sciences, Moscow 119991, Russia; .,Center for Algorithmic Biotechnology, Institute of Translational Biomedicine, Saint Petersburg State University, Saint Petersburg 199004, Russia.,Research Center of Biotechnology of the Russian Academy of Sciences, Moscow 119071, Russia
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4
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Ahmad SF, Singchat W, Jehangir M, Suntronpong A, Panthum T, Malaivijitnond S, Srikulnath K. Dark Matter of Primate Genomes: Satellite DNA Repeats and Their Evolutionary Dynamics. Cells 2020; 9:E2714. [PMID: 33352976 PMCID: PMC7767330 DOI: 10.3390/cells9122714] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Revised: 12/15/2020] [Accepted: 12/16/2020] [Indexed: 12/12/2022] Open
Abstract
A substantial portion of the primate genome is composed of non-coding regions, so-called "dark matter", which includes an abundance of tandemly repeated sequences called satellite DNA. Collectively known as the satellitome, this genomic component offers exciting evolutionary insights into aspects of primate genome biology that raise new questions and challenge existing paradigms. A complete human reference genome was recently reported with telomere-to-telomere human X chromosome assembly that resolved hundreds of dark regions, encompassing a 3.1 Mb centromeric satellite array that had not been identified previously. With the recent exponential increase in the availability of primate genomes, and the development of modern genomic and bioinformatics tools, extensive growth in our knowledge concerning the structure, function, and evolution of satellite elements is expected. The current state of knowledge on this topic is summarized, highlighting various types of primate-specific satellite repeats to compare their proportions across diverse lineages. Inter- and intraspecific variation of satellite repeats in the primate genome are reviewed. The functional significance of these sequences is discussed by describing how the transcriptional activity of satellite repeats can affect gene expression during different cellular processes. Sex-linked satellites are outlined, together with their respective genomic organization. Mechanisms are proposed whereby satellite repeats might have emerged as novel sequences during different evolutionary phases. Finally, the main challenges that hinder the detection of satellite DNA are outlined and an overview of the latest methodologies to address technological limitations is presented.
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Affiliation(s)
- Syed Farhan Ahmad
- Laboratory of Animal Cytogenetics and Comparative Genomics (ACCG), Department of Genetics, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand; (S.F.A.); (W.S.); (M.J.); (A.S.); (T.P.)
- Special Research Unit for Wildlife Genomics (SRUWG), Department of Forest Biology, Faculty of Forestry, Kasetsart University, Bangkok 10900, Thailand
| | - Worapong Singchat
- Laboratory of Animal Cytogenetics and Comparative Genomics (ACCG), Department of Genetics, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand; (S.F.A.); (W.S.); (M.J.); (A.S.); (T.P.)
- Special Research Unit for Wildlife Genomics (SRUWG), Department of Forest Biology, Faculty of Forestry, Kasetsart University, Bangkok 10900, Thailand
| | - Maryam Jehangir
- Laboratory of Animal Cytogenetics and Comparative Genomics (ACCG), Department of Genetics, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand; (S.F.A.); (W.S.); (M.J.); (A.S.); (T.P.)
- Department of Structural and Functional Biology, Institute of Bioscience at Botucatu, São Paulo State University (UNESP), Botucatu, São Paulo 18618-689, Brazil
| | - Aorarat Suntronpong
- Laboratory of Animal Cytogenetics and Comparative Genomics (ACCG), Department of Genetics, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand; (S.F.A.); (W.S.); (M.J.); (A.S.); (T.P.)
- Special Research Unit for Wildlife Genomics (SRUWG), Department of Forest Biology, Faculty of Forestry, Kasetsart University, Bangkok 10900, Thailand
| | - Thitipong Panthum
- Laboratory of Animal Cytogenetics and Comparative Genomics (ACCG), Department of Genetics, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand; (S.F.A.); (W.S.); (M.J.); (A.S.); (T.P.)
- Special Research Unit for Wildlife Genomics (SRUWG), Department of Forest Biology, Faculty of Forestry, Kasetsart University, Bangkok 10900, Thailand
| | - Suchinda Malaivijitnond
- National Primate Research Center of Thailand, Chulalongkorn University, Saraburi 18110, Thailand;
- Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
| | - Kornsorn Srikulnath
- Laboratory of Animal Cytogenetics and Comparative Genomics (ACCG), Department of Genetics, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand; (S.F.A.); (W.S.); (M.J.); (A.S.); (T.P.)
- Special Research Unit for Wildlife Genomics (SRUWG), Department of Forest Biology, Faculty of Forestry, Kasetsart University, Bangkok 10900, Thailand
- National Primate Research Center of Thailand, Chulalongkorn University, Saraburi 18110, Thailand;
- Center of Excellence on Agricultural Biotechnology (AG-BIO/PERDO-CHE), Bangkok 10900, Thailand
- Omics Center for Agriculture, Bioresources, Food and Health, Kasetsart University (OmiKU), Bangkok 10900, Thailand
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5
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Puppo IL, Saifitdinova AF, Tonyan ZN. The Role of Satellite DNA in Causing Structural Rearrangements in Human Karyotype. RUSS J GENET+ 2020. [DOI: 10.1134/s1022795419080155] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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6
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Black EM, Giunta S. Repetitive Fragile Sites: Centromere Satellite DNA As a Source of Genome Instability in Human Diseases. Genes (Basel) 2018; 9:E615. [PMID: 30544645 PMCID: PMC6315641 DOI: 10.3390/genes9120615] [Citation(s) in RCA: 57] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2018] [Revised: 12/03/2018] [Accepted: 12/03/2018] [Indexed: 12/31/2022] Open
Abstract
Maintenance of an intact genome is essential for cellular and organismal homeostasis. The centromere is a specialized chromosomal locus required for faithful genome inheritance at each round of cell division. Human centromeres are composed of large tandem arrays of repetitive alpha-satellite DNA, which are often sites of aberrant rearrangements that may lead to chromosome fusions and genetic abnormalities. While the centromere has an essential role in chromosome segregation during mitosis, the long and repetitive nature of the highly identical repeats has greatly hindered in-depth genetic studies, and complete annotation of all human centromeres is still lacking. Here, we review our current understanding of human centromere genetics and epigenetics as well as recent investigations into the role of centromere DNA in disease, with a special focus on cancer, aging, and human immunodeficiency⁻centromeric instability⁻facial anomalies (ICF) syndrome. We also highlight the causes and consequences of genomic instability at these large repetitive arrays and describe the possible sources of centromere fragility. The novel connection between alpha-satellite DNA instability and human pathological conditions emphasizes the importance of obtaining a truly complete human genome assembly and accelerating our understanding of centromere repeats' role in physiology and beyond.
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Affiliation(s)
- Elizabeth M Black
- Laboratory of Chromosome and Cell Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA.
| | - Simona Giunta
- Laboratory of Chromosome and Cell Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA.
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7
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Maheshwari S, Ishii T, Brown CT, Houben A, Comai L. Centromere location in Arabidopsis is unaltered by extreme divergence in CENH3 protein sequence. Genome Res 2017; 27:471-478. [PMID: 28223399 PMCID: PMC5340974 DOI: 10.1101/gr.214619.116] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2016] [Accepted: 12/14/2016] [Indexed: 12/17/2022]
Abstract
During cell division, spindle fibers attach to chromosomes at centromeres. The DNA sequence at regional centromeres is fast evolving with no conserved genetic signature for centromere identity. Instead CENH3, a centromere-specific histone H3 variant, is the epigenetic signature that specifies centromere location across both plant and animal kingdoms. Paradoxically, CENH3 is also adaptively evolving. An ongoing question is whether CENH3 evolution is driven by a functional relationship with the underlying DNA sequence. Here, we demonstrate that despite extensive protein sequence divergence, CENH3 histones from distant species assemble centromeres on the same underlying DNA sequence. We first characterized the organization and diversity of centromere repeats in wild-type Arabidopsis thaliana. We show that A. thaliana CENH3-containing nucleosomes exhibit a strong preference for a unique subset of centromeric repeats. These sequences are largely missing from the genome assemblies and represent the youngest and most homogeneous class of repeats. Next, we tested the evolutionary specificity of this interaction in a background in which the native A. thaliana CENH3 is replaced with CENH3s from distant species. Strikingly, we find that CENH3 from Lepidium oleraceum and Zea mays, although specifying epigenetically weaker centromeres that result in genome elimination upon outcrossing, show a binding pattern on A. thaliana centromere repeats that is indistinguishable from the native CENH3. Our results demonstrate positional stability of a highly diverged CENH3 on independently evolved repeats, suggesting that the sequence specificity of centromeres is determined by a mechanism independent of CENH3.
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Affiliation(s)
- Shamoni Maheshwari
- Plant Biology Department and Genome Center, University of California, Davis, California 95616, USA
| | - Takayoshi Ishii
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK) Gatersleben, 06466 Stadt Seeland, Germany
| | - C Titus Brown
- Department of Population Health and Reproduction, University of California, Davis, California 95616, USA
| | - Andreas Houben
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK) Gatersleben, 06466 Stadt Seeland, Germany
| | - Luca Comai
- Plant Biology Department and Genome Center, University of California, Davis, California 95616, USA
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8
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Catacchio CR, Ragone R, Chiatante G, Ventura M. Organization and evolution of Gorilla centromeric DNA from old strategies to new approaches. Sci Rep 2015; 5:14189. [PMID: 26387916 PMCID: PMC4585704 DOI: 10.1038/srep14189] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Accepted: 08/18/2015] [Indexed: 11/09/2022] Open
Abstract
The centromere/kinetochore interaction is responsible for the pairing and segregation of replicated chromosomes in eukaryotes. Centromere DNA is portrayed as scarcely conserved, repetitive in nature, quickly evolving and protein-binding competent. Among primates, the major class of centromeric DNA is the pancentromeric α-satellite, made of arrays of 171 bp monomers, repeated in a head-to-tail pattern. α-satellite sequences can either form tandem heterogeneous monomeric arrays or assemble in higher-order repeats (HORs). Gorilla centromere DNA has barely been characterized, and data are mainly based on hybridizations of human alphoid sequences. We isolated and finely characterized gorilla α-satellite sequences and revealed relevant structure and chromosomal distribution similarities with other great apes as well as gorilla-specific features, such as the uniquely octameric structure of the suprachromosomal family-2 (SF2). We demonstrated for the first time the orthologous localization of alphoid suprachromosomal families-1 and −2 (SF1 and SF2) between human and gorilla in contrast to chimpanzee centromeres. Finally, the discovery of a new 189 bp monomer type in gorilla centromeres unravels clues to the role of the centromere protein B, paving the way to solve the significance of the centromere DNA’s essential repetitive nature in association with its function and the peculiar evolution of the α-satellite sequence.
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Affiliation(s)
- C R Catacchio
- University of Bari Aldo Moro, Department of Biology, Via Orabona 4, Bari, 70125, Italy
| | - R Ragone
- University of Bari Aldo Moro, Department of Biology, Via Orabona 4, Bari, 70125, Italy
| | - G Chiatante
- University of Bari Aldo Moro, Department of Biology, Via Orabona 4, Bari, 70125, Italy
| | - M Ventura
- University of Bari Aldo Moro, Department of Biology, Via Orabona 4, Bari, 70125, Italy
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9
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Sujiwattanarat P, Thapana W, Srikulnath K, Hirai Y, Hirai H, Koga A. Higher-order repeat structure in alpha satellite DNA occurs in New World monkeys and is not confined to hominoids. Sci Rep 2015; 5:10315. [PMID: 25974220 PMCID: PMC4431391 DOI: 10.1038/srep10315] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2014] [Accepted: 03/25/2015] [Indexed: 11/17/2022] Open
Abstract
Centromeres usually contain large amounts of tandem repeat DNA. Alpha satellite DNA (AS) is the most abundant tandem repeat DNA found in the centromeres of simian primates. The AS of humans contains sequences organized into higher-order repeat (HOR) structures, which are tandem arrays of larger repeat units consisting of multiple basic repeat units. HOR-carrying AS also occurs in other hominoids, but results reported to date for phylogenetically more remote taxa have been negative. Here we show direct evidence for clear HOR structures in AS of the owl monkey and common marmoset. These monkeys are New World monkey species that are located phylogenetically outside of hominoids. It is currently postulated that the presence of HOR structures in AS is unique to hominoids. Our results suggest that this view must be modified. A plausible explanation is that generation of HOR structures is a general event that occurs occasionally or frequently in primate centromeres, and that, in humans, HOR-carrying AS became predominant in the central region of the centromere. It is often difficult to assemble sequence reads of tandem repeat DNAs into accurate contig sequences; our careful sequencing strategy allowed us to overcome this problem.
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Affiliation(s)
- Penporn Sujiwattanarat
- 1] Primate Research Institute, Kyoto University, Inuyama City 484-8506, Japan [2] Faculty of Science, Kasetsart University, Bangkok 10900, Thailand
| | - Watcharaporn Thapana
- 1] Primate Research Institute, Kyoto University, Inuyama City 484-8506, Japan [2] Faculty of Science, Kasetsart University, Bangkok 10900, Thailand
| | | | - Yuriko Hirai
- Primate Research Institute, Kyoto University, Inuyama City 484-8506, Japan
| | - Hirohisa Hirai
- Primate Research Institute, Kyoto University, Inuyama City 484-8506, Japan
| | - Akihiko Koga
- Primate Research Institute, Kyoto University, Inuyama City 484-8506, Japan
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Sequence variability of the MspI satellite DNA family of the pinewood nematode Bursaphelenchus xylophilus at different geographic scales. Mol Phylogenet Evol 2013; 70:120-9. [PMID: 24076248 DOI: 10.1016/j.ympev.2013.09.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Revised: 09/16/2013] [Accepted: 09/18/2013] [Indexed: 12/22/2022]
Abstract
Tandemly repeated sequences known as satellite DNA (satDNA) generally exhibit complex evolutionary patterns of concerted evolution in which mutations are homogenized and fixed in a stochastic process of molecular drive. Here, the nucleotidic variability of the MspI satDNA family of the pinewood nematode Bursaphelenchus xylophilus is analyzed in order to understand the evolutionary dynamics of satDNA at the intraspecific level. A total of 425 MspI monomer units, either PCR-amplified from isolates of local (Peninsula of Setúbal, Portugal) or worldwide origin, or retrieved from the B. xylophilus genome sequence, were characterized and compared. Whatever their origin, sliding window analysis of sequence variability patterns among monomers revealed low, moderate and highly variant domains, indicating that variable levels of evolutionary constraint may act upon the entire monomers. The phylogenetic inference based on the different sets of MspI satDNA family for this species shows a broad polymorphism of the individual monomers, which were distributed into four main clusters. However, such clustering appeared independent from the geographic origin of the nematodes, and could not discriminate isolates or groups of geographically close isolates. Rather, the formation of different phylogenetic groups within this satDNA family suggests an a priori embodying of a set of diverging repeats from a common ancestor satDNA library, which have been differently amplified along the evolutionary pathway of this species. The present work improves knowledge on the evolutionary dynamics of satDNA at the intraspecific level, and provides new information on satDNA sequence variability among natural populations sampled at a local geographic scale.
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Kumar A, Kamaraj B, Sethumadhavan R, Purohit R. Evolution driven structural changes in CENP-E motor domain. Interdiscip Sci 2013; 5:102-11. [DOI: 10.1007/s12539-013-0137-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2012] [Revised: 10/19/2012] [Accepted: 10/29/2012] [Indexed: 12/13/2022]
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12
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Melters DP, Bradnam KR, Young HA, Telis N, May MR, Ruby JG, Sebra R, Peluso P, Eid J, Rank D, Garcia JF, DeRisi JL, Smith T, Tobias C, Ross-Ibarra J, Korf I, Chan SWL. Comparative analysis of tandem repeats from hundreds of species reveals unique insights into centromere evolution. Genome Biol 2013; 14:R10. [PMID: 23363705 PMCID: PMC4053949 DOI: 10.1186/gb-2013-14-1-r10] [Citation(s) in RCA: 302] [Impact Index Per Article: 27.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2012] [Accepted: 01/30/2013] [Indexed: 01/01/2023] Open
Abstract
Background Centromeres are essential for chromosome segregation, yet their DNA sequences evolve rapidly. In most animals and plants that have been studied, centromeres contain megabase-scale arrays of tandem repeats. Despite their importance, very little is known about the degree to which centromere tandem repeats share common properties between different species across different phyla. We used bioinformatic methods to identify high-copy tandem repeats from 282 species using publicly available genomic sequence and our own data. Results Our methods are compatible with all current sequencing technologies. Long Pacific Biosciences sequence reads allowed us to find tandem repeat monomers up to 1,419 bp. We assumed that the most abundant tandem repeat is the centromere DNA, which was true for most species whose centromeres have been previously characterized, suggesting this is a general property of genomes. High-copy centromere tandem repeats were found in almost all animal and plant genomes, but repeat monomers were highly variable in sequence composition and length. Furthermore, phylogenetic analysis of sequence homology showed little evidence of sequence conservation beyond approximately 50 million years of divergence. We find that despite an overall lack of sequence conservation, centromere tandem repeats from diverse species showed similar modes of evolution. Conclusions While centromere position in most eukaryotes is epigenetically determined, our results indicate that tandem repeats are highly prevalent at centromeres of both animal and plant genomes. This suggests a functional role for such repeats, perhaps in promoting concerted evolution of centromere DNA across chromosomes.
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Repetitive sequences originating from the centromere constitute large-scale heterochromatin in the telomere region in the siamang, a small ape. Heredity (Edinb) 2012; 109:180-7. [PMID: 22669075 DOI: 10.1038/hdy.2012.28] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Chromosomes of the siamang Symphalangus syndactylus (a small ape) carry large-scale heterochromatic structures at their ends. These structures look similar, by chromosome C-banding, to chromosome-end heterochromatin found in chimpanzee, bonobo and gorilla (African great apes), of which a major component is tandem repeats of 32-bp-long, AT-rich units. In the present study, we identified repetitive sequences that are a major component of the siamang heterochromatin. Their repeat units are 171 bp in length, and exhibit sequence similarity to alpha satellite DNA, a major component of the centromeres in primates. Thus, the large-scale heterochromatic structures have different origins between the great apes and the small ape. The presence of alpha satellite DNA in the telomere region has previously been reported in the white-cheeked gibbon Nomascus leucogenys, another small ape species. There is, however, a difference in the size of the telomere-region alpha satellite DNA, which is far larger in the siamang. It is not known whether the sequences of these two species (of different genera) have a common origin because the phylogenetic relationship of genera within the small ape family is still not clear. Possible evolutionary scenarios are discussed.
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