Genome characterization and CRISPR-Cas9 editing of a human neocentromere.

The maintenance of genome integrity is ensured by proper chromosome inheritance during mitotic and meiotic cell divisions. The chromosomal counterpart responsible for chromosome segregation to daughter cells is the centromere, at which the spindle apparatus attaches through the kinetochore. Although all mammalian centromeres are primarily composed of megabase-long repetitive sequences, satellite-free human neocentromeres have been described. Neocentromeres and evolutionary new centromeres have revolutionized traditional knowledge about centromeres. Over the past 20 years, insights have been gained into their organization, but in spite of these advancements, the mechanisms underlying their formation and evolution are still unclear. Today, through modern and increasingly accessible genome editing and long-read sequencing techniques, research in this area is undergoing a sudden acceleration. In this article, we describe the primary sequence of a previously described human chromosome 3 neocentromere and observe its possible evolution and repair results after a chromosome breakage induced through CRISPR-Cas9 technologies. Our data represent an exciting advancement in the field of centromere/neocentromere evolution and chromosome stability.

Centromere sliding on a mammalian chromosome.

The centromere directs the segregation of chromosomes during mitosis and meiosis. It is a distinct genetic locus whose identity is established through epigenetic mechanisms that depend on the deposition of centromere-specific centromere protein A (CENP-A) nucleosomes. This important chromatin domain has so far escaped comprehensive molecular analysis due to its typical association with highly repetitive satellite DNA. In previous work, we discovered that the centromere of horse chromosome 11 is completely devoid of satellite DNA; this peculiar feature makes it a unique model to dissect the molecular architecture of mammalian centromeres. Here, we exploited this native satellite-free centromere to determine the precise localization of its functional domains in five individuals: We hybridized DNA purified from chromatin immunoprecipitated with an anti CENP-A antibody to a high resolution array (ChIP-on-chip) of the region containing the primary constriction of horse chromosome 11. Strikingly, each individual exhibited a different arrangement of CENP-A binding domains. We then analysed the organization of each domain using a single nucleotide polymorphism (SNP)-based approach and single molecule analysis on chromatin fibres. Examination of the ten instances of chromosome 11 in the five individuals revealed seven distinct 'positional alleles', each one extending for about 80-160 kb, were found across a region of about 500 kb. Our results demonstrate that CENP-A binding domains are autonomous relative to the underlying DNA sequence and are characterized by positional instability causing the sliding of centromere position. We propose that this dynamic behaviour may be common in mammalian centromeres and may determine the establishment of epigenetic alleles.

Ring chromosomes, breakpoint clusters, and neocentromeres in sarcomas.

Gene amplification is relatively common in tumors. In certain subtypes of sarcoma, it often occurs in the form of ring and/or giant rod-shaped marker (RGM) chromosomes whose mitotic stability is frequently rescued by ectopic novel centromeres (neocentromeres). Little is known about the origin and structure of these RGM chromosomes, including how they arise, their internal organization, and which sequences underlie the neocentromeres. To address these questions, 42 sarcomas with RGM chromosomes were investigated to detect regions prone to double strand breaks and possible functional or structural constraints driving the amplification process. We found nine breakpoint cluster regions potentially involved in the genesis of RGM chromosomes, which turned out to be significantly enriched in poly-pyrimidine traits. Some of the clusters were located close to genes already known to be relevant for sarcomas, thus indicating a potential functional constraint, while others mapped to transcriptionally inactive chromatin domains enriched in heterochromatic sites. Of note, five neocentromeres were identified after analyzing 13 of the cases by fluorescent in situ hybridization. ChIP-on-chip analysis with antibodies against the centromeric protein CENP-A showed that they were a patchwork of small genomic segments derived from different chromosomes, likely joint to form a contiguous sequence during the amplification process.

Genome-wide characterization of centromeric satellites from multiple mammalian genomes.

Despite its importance in cell biology and evolution, the centromere has remained the final frontier in genome assembly and annotation due to its complex repeat structure. However, isolation and characterization of the centromeric repeats from newly sequenced species are necessary for a complete understanding of genome evolution and function. In recent years, various genomes have been sequenced, but the characterization of the corresponding centromeric DNA has lagged behind. Here, we present a computational method (RepeatNet) to systematically identify higher-order repeat structures from unassembled whole-genome shotgun sequence and test whether these sequence elements correspond to functional centromeric sequences. We analyzed genome datasets from six species of mammals representing the diversity of the mammalian lineage, namely, horse, dog, elephant, armadillo, opossum, and platypus. We define candidate monomer satellite repeats and demonstrate centromeric localization for five of the six genomes. Our analysis revealed the greatest diversity of centromeric sequences in horse and dog in contrast to elephant and armadillo, which showed high-centromeric sequence homogeneity. We could not isolate centromeric sequences within the platypus genome, suggesting that centromeres in platypus are not enriched in satellite DNA. Our method can be applied to the characterization of thousands of other vertebrate genomes anticipated for sequencing in the near future, providing an important tool for annotation of centromeres.

Gene amplification as double minutes or homogeneously staining regions in solid tumors: origin and structure.

Double minutes (dmin) and homogeneously staining regions (hsr) are the cytogenetic hallmarks of genomic amplification in cancer. Different mechanisms have been proposed to explain their genesis. Recently, our group showed that the MYC-containing dmin in leukemia cases arise by excision and amplification (episome model). In the present paper we investigated 10 cell lines from solid tumors showing MYCN amplification as dmin or hsr. Particularly revealing results were provided by the two subclones of the neuroblastoma cell line STA-NB-10, one showing dmin-only and the second hsr-only amplification. Both subclones showed a deletion, at 2p24.3, whose extension matched the amplicon extension. Additionally, the amplicon structure of the dmin and hsr forms was identical. This strongly argues that the episome model, already demonstrated in leukemias, applies to solid tumors as well, and that dmin and hsr are two faces of the same coin. The organization of the duplicated segments varied from very simple (no apparent changes from the normal sequence) to very complex. MYCN was always overexpressed (significantly overexpressed in three cases). The fusion junctions, always mediated by nonhomologous end joining, occasionally juxtaposed truncated genes in the same transcriptional orientation. Fusion transcripts involving NBAS (also known as NAG), FAM49A, BC035112 (also known as NCRNA00276), and SMC6 genes were indeed detected, although their role in the context of the tumor is not clear.

Epigallocatechin-3-gallate Delivered in Nanoparticles Increases Cytotoxicity in Three Breast Carcinoma Cell Lines.

The anticancer activity of epigallocatechin-3-gallate (EGCG), orally administrated, is limited by poor bioavailability, absorption, and unpredictable distribution in human tissues. EGCG charged nanoparticles may represent an opportunity to overcome these limitations. We assayed two different kinds of lipid nanoparticles (LNPs and LNPs functionalized with folic acid) charged with EGCG on three breast carcinoma cell lines (MCF-7, MDA-MB-231, and MCF-7TAM) and the human normal MCF10A mammary epithelial cells. Both LNPs loaded with EGCG, at low concentrations, induced a significant cytotoxicity in the three breast carcinoma cells but not in MCF10A cells. In view of a future application, both LNPs and LNPs-FA were found to be very suitable for in vitro studies and useful to improve EGCG administration in vivo. Since they are produced by inexpensive procedures using bioavailable, biocompatible, and biodegradable molecules, they represent an applicable tool for a more rationale use of EGCG as an anti-cancer agent.

Human centromere repositioning activates transcription and opens chromatin fibre structure.

Human centromeres appear as constrictions on mitotic chromosomes and form a platform for kinetochore assembly in mitosis. Biophysical experiments led to a suggestion that repetitive DNA at centromeric regions form a compact scaffold necessary for function, but this was revised when neocentromeres were discovered on non-repetitive DNA. To test whether centromeres have a special chromatin structure we have analysed the architecture of a neocentromere. Centromere repositioning is accompanied by RNA polymerase II recruitment and active transcription to form a decompacted, negatively supercoiled domain enriched in 'open' chromatin fibres. In contrast, centromerisation causes a spreading of repressive epigenetic marks to surrounding regions, delimited by H3K27me3 polycomb boundaries and divergent genes. This flanking domain is transcriptionally silent and partially remodelled to form 'compact' chromatin, similar to satellite-containing DNA sequences, and exhibits genomic instability. We suggest transcription disrupts chromatin to provide a foundation for kinetochore formation whilst compact pericentromeric heterochromatin generates mechanical rigidity.

A G316A Polymorphism in the Ornithine Decarboxylase Gene Promoter Modulates MYCN-Driven Childhood Neuroblastoma.

Ornithine decarboxylase (ODC1), a critical regulatory enzyme in polyamine biosynthesis, is a direct transcriptional target of MYCN, amplification of which is a powerful marker of aggressive neuroblastoma. A single nucleotide polymorphism (SNP), G316A, within the first intron of ODC1, results in genotypes wildtype GG, and variants AG/AA. CRISPR-cas9 technology was used to investigate the effects of AG clones from wildtype MYCN-amplified SK-N-BE(2)-C cells and the effect of the SNP on MYCN binding, and promoter activity was investigated using EMSA and luciferase assays. AG clones exhibited decreased ODC1 expression, growth rates, and histone acetylation and increased sensitivity to ODC1 inhibition. MYCN was a stronger transcriptional regulator of the ODC1 promoter containing the G allele, and preferentially bound the G allele over the A. Two neuroblastoma cohorts were used to investigate the clinical impact of the SNP. In the study cohort, the minor AA genotype was associated with improved survival, while poor prognosis was associated with the GG genotype and AG/GG genotypes in MYCN-amplified and non-amplified patients, respectively. These effects were lost in the GWAS cohort. We have demonstrated that the ODC1 G316A polymorphism has functional significance in neuroblastoma and is subject to allele-specific regulation by the MYCN oncoprotein.

Repurposing a psychoactive drug for children with cancer: p27Kip1-dependent inhibition of metastatic neuroblastomas by Prozac.

The MYC family of transcription factors is a major driver of human cancer and potential therapeutic target. However, no clinically viable drugs have been yet developed that are able to directly tackle MYC oncoproteins. In our laboratory, we are exploring alternative approaches aiming to disturb signalling downstream of MYC. MYCN is frequently activated in neuroblastoma, a paediatric solid malignancy that, in its metastatic form, has a very poor prognosis. An important pathway regulated by MYC is the CKS1/SKP2/p27kip1 axis. In this study, we have repurposed the anti-psychotic drug Prozac to disrupt CKS1/SKP2/p27Kip1 signalling and assess its potential as an anti-neuroblastoma agent in vitro and in vivo. Using DNA editing technology, we show that stabilisation of p27Kip1 operated by Prozac in MYC-activated cells is essential for the anti-neuroblastoma activity of the drug. Furthermore, dosing mice with a concentration of Prozac equivalent to that used in long-term clinical trials in children with psychiatric disorders caused a significant reduction of metastatic disease in two models of high-risk neuroblastoma. The favourable toxicity profile of Prozac suggests that long-term treatments might be implemented in children with MYC/CKS1high neuroblastomas.

Inhibition of polyamine synthesis and uptake reduces tumor progression and prolongs survival in mouse models of neuroblastoma.

Amplification of the MYCN oncogene is associated with an aggressive phenotype and poor outcome in childhood neuroblastoma. Polyamines are highly regulated essential cations that are frequently elevated in cancer cells, and the rate-limiting enzyme in polyamine synthesis, ornithine decarboxylase 1 (ODC1), is a direct transcriptional target of MYCN. Treatment of neuroblastoma cells with the ODC1 inhibitor difluoromethylornithine (DFMO), although a promising therapeutic strategy, is only partially effective at impeding neuroblastoma cell growth due to activation of compensatory mechanisms resulting in increased polyamine uptake from the surrounding microenvironment. In this study, we identified solute carrier family 3 member 2 (SLC3A2) as the key transporter involved in polyamine uptake in neuroblastoma. Knockdown of SLC3A2 in neuroblastoma cells reduced the uptake of the radiolabeled polyamine spermidine, and DFMO treatment increased SLC3A2 protein. In addition, MYCN directly increased polyamine synthesis and promoted neuroblastoma cell proliferation by regulating SLC3A2 and other regulatory components of the polyamine pathway. Inhibiting polyamine uptake with the small-molecule drug AMXT 1501, in combination with DFMO, prevented or delayed tumor development in neuroblastoma-prone mice and extended survival in rodent models of established tumors. Our findings suggest that combining AMXT 1501 and DFMO with standard chemotherapy might be an effective strategy for treating neuroblastoma.

MAX to MYCN intracellular ratio drives the aggressive phenotype and clinical outcome of high risk neuroblastoma.

Childhood neuroblastoma, a disease of the sympathetic nervous system, is the most common solid tumour of infancy, remarkably refractory to therapeutic treatments. One of the most powerful independent prognostic indicators for this disease is the amplification of the MYCN oncogene, which occurs at high levels in approximately 25% of neuroblastomas. Interestingly, amplification and not just expression of MYCN has a strong prognostic value, although this fact appears quite surprising as MYCN is a transcription factor that requires dimerising with its partner MAX, to exert its function. This observation greatly suggests that the role of MYCN in neuroblastoma should be examined in the context of MAX expression. In this report, we show that, in contrast to what is found in normal cells, MAX expression is significantly different among primary NBs, and that its level appears to correlate with the clinical outcome of the disease. Importantly, controlled modulation of MAX expression in neuroblastoma cells with different extents of MYCN amplification, demonstrates that MAX can instruct gene transcription programs that either reinforce or weaken the oncogenic process enacted by MYCN. In general, our work illustrates that it is the MAX to MYCN ratio that can account for tumour progression and clinical outcome in neuroblastoma and proposes that such a ratio should be considered as an important criterion to the design and development of anti-MYCN therapies.

The Hidden Genomic and Transcriptomic Plasticity of Giant Marker Chromosomes in Cancer.

Genome amplification in the form of rings or giant rod-shaped marker chromosomes (RGMs) is a common genetic alteration in soft tissue tumors. The mitotic stability of these structures is often rescued by perfectly functioning analphoid neocentromeres, which therefore significantly contribute to cancer progression. Here, we disentangled the genomic architecture of many neocentromeres stabilizing marker chromosomes in well-differentiated liposarcoma and lung sarcomatoid carcinoma samples. In cells carrying heavily rearranged RGMs, these structures were assembled as patchworks of multiple short amplified sequences, disclosing an extremely high level of complexity and definitely ruling out the existence of regions prone to neocentromere seeding. Moreover, by studying two well-differentiated liposarcoma samples derived from the onset and the recurrence of the same tumor, we documented an expansion of the neocentromeric domain that occurred during tumor progression, which reflects a strong selective pressure acting toward the improvement of the neocentromeric functionality in cancer. In lung sarcomatoid carcinoma cells we documented, extensive "centromere sliding" phenomena giving rise to multiple, closely mapping neocentromeric epialleles on separate coexisting markers occur, likely due to the instability of neocentromeres arising in cancer cells. Finally, by investigating the transcriptional activity of neocentromeres, we came across a burst of chimeric transcripts, both by extremely complex genomic rearrangements, and cis/trans-splicing events. Post-transcriptional editing events have been reported to expand and variegate the genetic repertoire of higher eukaryotes, so they might have a determining role in cancer. The increased incidence of fusion transcripts, might act as a driving force for the genomic amplification process, together with the increased transcription of oncogenes.

Epigenetic origin of evolutionary novel centromeres.

Most evolutionary new centromeres (ENC) are composed of large arrays of satellite DNA and surrounded by segmental duplications. However, the hypothesis is that ENCs are seeded in an anonymous sequence and only over time have acquired the complexity of "normal" centromeres. Up to now evidence to test this hypothesis was lacking. We recently discovered that the well-known polymorphism of orangutan chromosome 12 was due to the presence of an ENC. We sequenced the genome of an orangutan homozygous for the ENC, and we focused our analysis on the comparison of the ENC domain with respect to its wild type counterpart. No significant variations were found. This finding is the first clear evidence that ENC seedings are epigenetic in nature. The compaction of the ENC domain was found significantly higher than the corresponding WT region and, interestingly, the expression of the only gene embedded in the region was significantly repressed.

Anti-gene peptide nucleic acid specifically inhibits MYCN expression in human neuroblastoma cells leading to cell growth inhibition and apoptosis.

We developed an anti-gene peptide nucleic acid (PNA) for selective inhibition of MYCN transcription in neuroblastoma cells, targeted against a unique sequence in the antisense DNA strand of exon 2 of MYCN and linked at its NH(2) terminus to a nuclear localization signal peptide. Fluorescence microscopy showed specific nuclear delivery of the PNA in six human neuroblastoma cell lines: GI-LI-N and IMR-32 (MYCN-amplified/overexpressed); SJ-N-KP and NB-100 (MYCN-unamplified/low-expressed); and GI-CA-N and GI-ME-N (MYCN-unamplified/unexpressed). Antiproliferative effects were observable at 24 hours (GI-LI-N, 60%; IMR-32, 70%) and peaked at 72 hours (GI-LI-N, 80%; IMR-32, 90%; SK-N-KP, 60%; NB-100, 50%); no reduction was recorded for GI-CA-N and GI-ME-N (controls). In MYCN-amplified/overexpressed IMR-32 cells and MYCN-unamplified/low-expressed SJ-N-KP cells, inhibition was recorded of MYCN mRNA (by real-time PCR) and N-Myc (Western blotting); these inhibitory effects increased over 3 days after single treatment in IMR-32. Anti-gene PNA induced G(1)-phase accumulation (39-53%) in IMR-32 and apoptosis (56% annexin V-positive cells at 24 hours in IMR-32 and 22% annexin V-positive cells at 48 hours in SJ-N-KP). Selective activity of the PNA was shown by altering three point mutations, and by the observation that an anti-gene PNA targeted against the noncoding DNA strand did not exert any effect. These findings could encourage research into development of an anti-gene PNA-based tumor-specific agent for neuroblastoma (and other neoplasms) with MYCN expression.

MYC-Driven Neuroblastomas Are Addicted to a Telomerase-Independent Function of Dyskerin.

The RNA-binding protein dyskerin, encoded by the DKC1 gene, functions as a core component of the telomerase holoenzyme as well as ribonuclear protein complexes involved in RNA processing and ribosome biogenesis. The diverse roles of dyskerin across many facets of RNA biology implicate its potential contribution to malignancy. In this study, we examined the expression and function of dyskerin in neuroblastoma. We show that DKC1 mRNA levels were elevated relative to normal cells across a panel of 15 neuroblastoma cell lines, where both N-Myc and c-Myc directly targeted the DKC1 promoter. Upregulation of MYCN was shown to dramatically increase DKC1 expression. In two independent neuroblastoma patient cohorts, high DKC1 expression correlated strongly with poor event-free and overall survival (P < 0.0001), independently of established prognostic factors. RNAi-mediated depletion of dyskerin inhibited neuroblastoma cell proliferation, including cells immortalized via the telomerase-independent ALT mechanism. Furthermore, dyskerin attenuation impaired anchorage-independent proliferation and tumor growth. Overexpression of the telomerase RNA component, hTR, demonstrated that this proliferative impairment was not a consequence of telomerase suppression. Instead, ribosomal stress, evidenced by depletion of small nucleolar RNAs and nuclear dispersal of ribosomal proteins, was the likely cause of the proliferative impairment in dyskerin-depleted cells. Accordingly, dyskerin suppression caused p53-dependent G1 cell-cycle arrest in p53 wild-type cells, and a p53-independent pathway impaired proliferation in cells with p53 dysfunction. Together, our findings highlight dyskerin as a new therapeutic target in neuroblastoma with crucial telomerase-independent functions and broader implications for the spectrum of malignancies driven by MYC family oncogenes. Cancer Res; 76(12); 3604-17. ©2016 AACR.

p21Waf1/Cip1 is a common target induced by short-chain fatty acid HDAC inhibitors (valproic acid, tributyrin and sodium butyrate) in neuroblastoma cells.

Histone acetyltransferase and histone deacetylase (HDAC) determine the acetylation status of histones, and thereby control the regulation of gene expression. HDAC inhibitors have been found to inhibit the growth of a variety of tumor cells in vitro and in vivo. We demonstrated previously that the short-chain fatty acid compound butyrate and its derivative tributyrin (both HDAC inhibitors) arrest cell growth and induce differentiation in human neuroblastoma (NB) cells. In the current study we investigated the effect of the HDAC inhibitor valproic acid (VPA) on proliferation and differentiation in human NB cells (SJ-N-KP, AF8). Treatment with VPA resulted in a strong inhibition of cell proliferation and induction of cell differentiation, as revealed by neurite outgrowth and increase of acetylcholinesterase specific activity. Moreover, we addressed the question of whether the cyclin-dependent kinase inhibitors p21(Cip1) and p27(Kip1) are involved in the mechanism of action of members of the short-chain fatty acids class (VPA, sodium butyrate and tributyrin) of HDAC inhibitors, in human NB cells. We demonstrated that p21(Cip1) is a common target of induction of transcription and protein expression for all the three compounds, while only VPA induced a concomitant increase of p27(Kip1) gene expression. These results suggest that p21(Cip1) could be involved in the inhibition of proliferation and induction of differentiation in human NB cells induced by treatment with VPA or tributyrin or sodium butyrate. Moreover, p21(Cip1) could be applied in the molecular monitoring of drug action in the possible therapeutic application of these short-chain fatty acid members of HDAC inhibitors for human NB treatment.

Antitumor activity of sustained N-myc reduction in rhabdomyosarcomas and transcriptional block by antigene therapy.

PURPOSE: Rhabdomyosarcomas are a major cause of cancer death in children, described with MYCN amplification and, in the alveolar subtype, transcription driven by the PAX3-FOXO1 fusion protein. Our aim was to determine the prevalence of N-Myc protein expression and the potential therapeutic effects of reducing expression in rhabdomyosarcomas, including use of an antigene strategy that inhibits transcription. EXPERIMENTAL DESIGN: Protein expression was assessed by immunohistochemistry. MYCN expression was reduced in representative cell lines by RNA interference and an antigene peptide nucleic acid (PNA) oligonucleotide conjugated to a nuclear localization signal peptide. Associated gene expression changes, cell viability, and apoptosis were analyzed in vitro. As a paradigm for antigene therapy, the effects of systemic treatment of mice with rhabdomyosarcoma cell line xenografts were determined. RESULTS: High N-Myc levels were significantly associated with genomic amplification, presence of the PAX3/7-FOXO1 fusion genes, and proliferative capacity. Sustained reduction of N-Myc levels in all rhabdomyosarcoma cell lines that express the protein decreased cell proliferation and increased apoptosis. Positive feedback was shown to regulate PAX3-FOXO1 and N-Myc levels in the alveolar subtype that critically decrease PAX3-FOXO1 levels on reducing N-Myc. Pharmacologic systemic administration of the antigene PNA can eliminate alveolar rhabdomyosarcoma xenografts in mice, without relapse or toxicity. CONCLUSION: N-Myc, with its restricted expression in non-fetal tissues, is a therapeutic target to treat rhabdomyosarcomas, and blocking gene transcription using antigene oligonucleotide strategies has therapeutic potential in the treatment of cancer and other diseases that has not been previously realized in vivo.

Evolutionary descent of a human chromosome 6 neocentromere: a jump back to 17 million years ago.

Molecular cytogenetics provides a visual, pictorial record of the tree of life, and in this respect the fusion origin of human chromosome 2 is a well-known paradigmatic example. Here we report on a variant chromosome 6 in which the centromere jumped to 6p22.1. ChIP-chip experiments with antibodies against the centromeric proteins CENP-A and CENP-C exactly defined the neocentromere as lying at chr6:26,407-26,491 kb. We investigated in detail the evolutionary history of chromosome 6 in primates and found that the primate ancestor had a homologous chromosome with the same marker order, but with the centromere located at 6p22.1. Sometime between 17 and 23 million years ago (Mya), in the common ancestor of humans and apes, the centromere of chromosome 6 moved from 6p22.1 to its current location. The neocentromere we discovered, consequently, has jumped back to the ancestral position, where a latent centromere-forming potentiality persisted for at least 17 Myr. Because all living organisms form a tree of life, as first conceived by Darwin, evolutionary perspectives can provide compelling underlying explicative grounds for contemporary genomic phenomena.

Evolutionary and clinical neocentromeres: two faces of the same coin?

It has been hypothesized that human clinical neocentromeres and evolutionary novel centromeres (ENC) represent two faces of the same phenomenon. However, there are only two reports of loci harboring both a novel centromere and a clinical neocentromere. We suggest that only the tip of the iceberg has been scratched because most neocentromerization events have a very low chance of being observed. In support of this view, we report here on a neocentromere at 9q33.1 that emerged in a ring chromosome of about 12 Mb. The ring was produced by a balanced rearrangement that was fortuitously discovered because of its malsegregation in the propositus. Chromatin-immunoprecipitation-on-chip experiments using anti-centromere protein (CENP)-A and anti-CENP-C antibodies strongly indicated that a novel centromeric domain was present in the ring, in a chromosomal domain where an ENC emerged in the ancestor to Old World monkeys.