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Asynchronous replication, mono-allelic expression, and long range Cis-effects of ASAR6. PLoS Genet 2013; 9:e1003423. [PMID: 23593023 PMCID: PMC3617217 DOI: 10.1371/journal.pgen.1003423] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Accepted: 02/14/2013] [Indexed: 11/19/2022] Open
Abstract
Mammalian chromosomes initiate DNA replication at multiple sites along their length during each S phase following a temporal replication program. The majority of genes on homologous chromosomes replicate synchronously. However, mono-allelically expressed genes such as imprinted genes, allelically excluded genes, and genes on female X chromosomes replicate asynchronously. We have identified a cis-acting locus on human chromosome 6 that controls this replication-timing program. This locus encodes a large intergenic non-coding RNA gene named Asynchronous replication and Autosomal RNA on chromosome 6, or ASAR6. Disruption of ASAR6 results in delayed replication, delayed mitotic chromosome condensation, and activation of the previously silent alleles of mono-allelic genes on chromosome 6. The ASAR6 gene resides within an ∼1.2 megabase domain of asynchronously replicating DNA that is coordinated with other random asynchronously replicating loci along chromosome 6. In contrast to other nearby mono-allelic genes, ASAR6 RNA is expressed from the later-replicating allele. ASAR6 RNA is synthesized by RNA Polymerase II, is not polyadenlyated, is restricted to the nucleus, and is subject to random mono-allelic expression. Disruption of ASAR6 leads to the formation of bridged chromosomes, micronuclei, and structural instability of chromosome 6. Finally, ectopic integration of cloned genomic DNA containing ASAR6 causes delayed replication of entire mouse chromosomes. Mammalian chromosomes are duplicated every cell cycle during a precise temporal DNA replication program. Thus, every chromosome contains regions that are replicated early and other regions that are replicated late during each S phase. Most of the genes, present in two copies on homologous chromosomes, replicate synchronously during each S phase. Exceptions to this rule are genes located on X chromosomes, genetically imprinted genes, and genes subject to allelic exclusion. Thus, all mono-allelically expressed genes are subject to asynchronous replication, where one allele replicates before the other. Perhaps the best-studied example of asynchronous replication in mammals occurs during X inactivation in female cells. A large non-coding RNA gene called XIST, located within the X inactivation center, controls the transcriptional silencing and late replication of the inactive X chromosome. We have identified a locus on human chromosome 6 that shares many characteristics with XIST. This chromosome 6 locus encodes a large intergenic non-coding RNA gene, ASAR6, which displays random mono-allelic expression, asynchronous replication, and controls the mono-allelic expression of other genes on chromosome 6. Our work supports a model in which all mammalian chromosomes contain similar cis-acting loci that function to ensure proper chromosome replication, mitotic condensation, mono-allelic expression, and stability of individual chromosomes.
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Donley N, Thayer MJ. DNA replication timing, genome stability and cancer: late and/or delayed DNA replication timing is associated with increased genomic instability. Semin Cancer Biol 2013; 23:80-9. [PMID: 23327985 DOI: 10.1016/j.semcancer.2013.01.001] [Citation(s) in RCA: 90] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Accepted: 01/04/2013] [Indexed: 11/30/2022]
Abstract
Normal cellular division requires that the genome be faithfully replicated to ensure that unaltered genomic information is passed from one generation to the next. DNA replication initiates from thousands of origins scattered throughout the genome every cell cycle; however, not all origins initiate replication at the same time. A vast amount of work over the years indicates that different origins along each eukaryotic chromosome are activated in early, middle or late S phase. This temporal control of DNA replication is referred to as the replication-timing program. The replication-timing program represents a very stable epigenetic feature of chromosomes. Recent evidence has indicated that the replication-timing program can influence the spatial distribution of mutagenic events such that certain regions of the genome experience increased spontaneous mutagenesis compared to surrounding regions. This influence has helped shape the genomes of humans and other multicellular organisms and can affect the distribution of mutations in somatic cells. It is also becoming clear that the replication-timing program is deregulated in many disease states, including cancer. Aberrant DNA replication timing is associated with changes in gene expression, changes in epigenetic modifications and an increased frequency of structural rearrangements. Furthermore, certain replication timing changes can directly lead to overt genomic instability and may explain unique mutational signatures that are present in cells that have undergone the recently described processes of "chromothripsis" and "kataegis". In this review, we will discuss how the normal replication timing program, as well as how alterations to this program, can contribute to the evolution of the genomic landscape in normal and cancerous cells.
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Affiliation(s)
- Nathan Donley
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Knight Cancer Institute, 3181 S.W. Sam Jackson Park Road, Portland, OR 97239, USA
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Thayer MJ. Mammalian chromosomes contain cis-acting elements that control replication timing, mitotic condensation, and stability of entire chromosomes. Bioessays 2012; 34:760-70. [PMID: 22706734 DOI: 10.1002/bies.201200035] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Recent studies indicate that mammalian chromosomes contain discrete cis-acting loci that control replication timing, mitotic condensation, and stability of entire chromosomes. Disruption of the large non-coding RNA gene ASAR6 results in late replication, an under-condensed appearance during mitosis, and structural instability of human chromosome 6. Similarly, disruption of the mouse Xist gene in adult somatic cells results in a late replication and instability phenotype on the X chromosome. ASAR6 shares many characteristics with Xist, including random mono-allelic expression and asynchronous replication timing. Additional "chromosome engineering" studies indicate that certain chromosome rearrangements affecting many different chromosomes display this abnormal replication and instability phenotype. These observations suggest that all mammalian chromosomes contain "inactivation/stability centers" that control proper replication, condensation, and stability of individual chromosomes. Therefore, mammalian chromosomes contain four types of cis-acting elements, origins, telomeres, centromeres, and "inactivation/stability centers", all functioning to ensure proper replication, condensation, segregation, and stability of individual chromosomes.
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Affiliation(s)
- Mathew J Thayer
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Knight Cancer Institute, Portland, OR, USA.
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Stoffregen EP, Donley N, Stauffer D, Smith L, Thayer MJ. An autosomal locus that controls chromosome-wide replication timing and mono-allelic expression. Hum Mol Genet 2011; 20:2366-78. [PMID: 21459774 DOI: 10.1093/hmg/ddr138] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Mammalian DNA replication initiates at multiple sites along chromosomes at different times, following a temporal replication program. Homologous alleles typically replicate synchronously; however, mono-allelically expressed genes such as imprinted genes, allelically excluded genes and genes on the female X chromosome replicate asynchronously. We have used a chromosome engineering strategy to identify a human autosomal locus that controls this replication timing program in cis. We show that Cre/loxP-mediated rearrangements at a discrete locus at 6q16.1 result in delayed replication of the entire chromosome. This locus displays asynchronous replication timing that is coordinated with other mono-allelically expressed genes on chromosome 6. Characterization of this locus revealed mono-allelic expression of a large intergenic non-coding RNA, which we have named asynchronous replication and autosomal RNA on chromosome 6, ASAR6. Finally, disruption of this locus results in the activation of the previously silent alleles of linked mono-allelically expressed genes. We previously found that chromosome rearrangements involving eight different autosomes display delayed replication timing, and that cells containing chromosomes with delayed replication timing have a 30-80-fold increase in the rate at which new gross chromosomal rearrangements occurred. Taken together, these observations indicate that human autosomes contain discrete cis-acting loci that control chromosome-wide replication timing, mono-allelic expression and the stability of entire chromosomes.
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Affiliation(s)
- Eric P Stoffregen
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, 3181 S W Sam Jackson Park Road, Portland, OR 97239, USA
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Stenman S, Saksela E. The relationship of Sendai virus-induced chromosome pulverization to cell cyclus in HeLa cells. Hereditas 2009; 69:1-14. [PMID: 4376137 DOI: 10.1111/j.1601-5223.1971.tb02412.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
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Breger KS, Smith L, Thayer MJ. Engineering translocations with delayed replication: evidence for cis control of chromosome replication timing. Hum Mol Genet 2005; 14:2813-27. [PMID: 16115817 DOI: 10.1093/hmg/ddi314] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Certain chromosome rearrangements, found in cancer cells or in cells exposed to ionizing radiation, exhibit a chromosome-wide delay in replication timing (DRT) that is associated with a delay in mitotic chromosome condensation (DMC). We have developed a chromosome engineering strategy that allows the generation of chromosomes with this DRT/DMC phenotype. We found that approximately 10% of inter-chromosomal translocations induced by two distinct mechanisms, site-specific recombination mediated by Cre or non-homologous end joining of DNA double-strand breaks induced by I-Sce1, result in DRT/DMC. Furthermore, on certain balanced translocations only one of the derivative chromosomes displays the phenotype. Finally, we show that the engineered DRT/DMC chromosomes acquire gross chromosomal rearrangements at an increased rate when compared with non-DRT/DMC chromosomes. These results indicate that the DRT/DMC phenotype is not the result of a stochastic process that could occur at any translocation breakpoint or as an epigenetic response to chromosome damage. Instead, our data indicate that the replication timing of certain derivative chromosomes is regulated by a cis-acting mechanism that delays both initiation and completion of DNA synthesis along the entire length of the chromosome. Because chromosomes with DRT/DMC are common in tumor cells and in cells exposed to ionizing radiation, we propose that DRT/DMC represents a common mechanism responsible for the genomic instability found in cancer cells and for the persistent chromosomal instability associated with cells exposed to ionizing radiation.
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Affiliation(s)
- Kevin S Breger
- Division of Molecular Medicine, Oregon Health and Science University, 3181 S.W.Sam Jackson Park Road, Portland, OR 97239, USA
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Kurvink K, Cervenka J. Acrocentric prophasing in bromodeoxyuridine-incorporated chromosomes. CANCER GENETICS AND CYTOGENETICS 1990; 50:265-71. [PMID: 2265405 DOI: 10.1016/0165-4608(90)90185-d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Chromosomes that appear to be incompletely condensed [pulverized, prematurely condensed chromosomes (PCCs), prophasing] are known to occur in metaphase spreads of cells from normal individuals and more frequently in cells from individuals with malignant disease or in cells exposed in vitro or in vivo to various agents such as viruses, chemicals, and radiation. In this study involving bromodeoxyuridine (BrdU)-treated lymphocytes, a selective prophasing of acrocentrics appeared to be occurring. The acrocentrics involved were generally in interconnected groups.
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Affiliation(s)
- K Kurvink
- Department of Biology, Moravian College, Bethlehem, Pennsylvania 18018
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Kürten S, Obe G. Premature chromosme condensation in the bone marrow of Chinese hamster after application of bleomycin in vivo. Mutat Res 1975; 27:285-94. [PMID: 48189 DOI: 10.1016/0027-5107(75)90089-5] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The Chinese hamster bone marrow was used as a test system in vivo to analyse the chromosome-danaging effect of bleomycin. Both chromosome and chromatid aberrations were found. Mitoses with aberrations (Ma) show a linear dose-effect relationship after a recovery time of 24 h, the same hold true for cells with micronuclei (Cm) and for mitoses with premature chromosome condensation (PCC). The dose-effect relationships for Ma, Cm and PCC run parallel to each other with Ma at the highest and PCC at the lowest level (Ma greater than Cm greater than PCC). The time-effect relationships for Ma, Cm and PCC show that after 12 h recovery time there are no PCCs but the highest frequencies of Ma and Cm indicating that most cells are in their first post-treatment mitoses or Gi-phases at this fixation time. In addition to the frequency determinations autoradiographic analysis were performed to clarigy the nature of the PCCs. The results are interpreted as follows: bleomycin induces chromosomal aberrations that in turn give rise to micronuclei by means of lagging chromatin, main and micronuclei eventually become asynchronous in their cell cycles and mitosing main nuclei induce PCC in the micronuclei.
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Abstract
Chromosome changes in human cancer cells appear to evolve by non-random losses and/or gains of particular homologues or groups. It is probable that some of the apparent losses or gains actually represent formation of new chromosome structures, which are then classified as markers or are misclassified as normal homologues. In many cancers these changes appear to continue at a high rate throughout the life of the cancer (so that in some cancers almost every cell will exhibit a different karyotype). In other cancers the rate of change may be slow or arrested so that all cells will have the same abnormal karyotype. One very common step in karyotype evolution is doubling of the entire chromosome complement (2n → 4n or more commonly, S → 2S where S is the stemline number). The 2S cells tend to replace the original stemline. Homologues which have larger amounts of concentrated blocks of heterochromatin (i.e. late replicating DNA) seem more apt to be lost.
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Sperling K, Rao PN. The phenomenon of premature chromosome condensation: its relevance to basic and applied research. HUMANGENETIK 1974; 23:235-58. [PMID: 4138742 DOI: 10.1007/bf00272508] [Citation(s) in RCA: 69] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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12
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O'Neill FJ, Rapp F. Premature chromosome condensation in hamster cells treated with cytochalasin B. Exp Cell Res 1972; 70:226-9. [PMID: 5061786 DOI: 10.1016/0014-4827(72)90202-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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Zakharov AF, Egolina NA. Differential spiralization along mammalian mitotic chromosomes. I. BUdR-revealed differentiation in Chinese hamster chromosomes. Chromosoma 1972; 38:341-65. [PMID: 4672290 DOI: 10.1007/bf00320156] [Citation(s) in RCA: 166] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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Ikeuchi T, Weinfeld H, Sandberg AA. Chromosome pulverization in micronuclei induced by tritiated thymidine. J Cell Biol 1972; 52:97-104. [PMID: 5061680 PMCID: PMC2108688 DOI: 10.1083/jcb.52.1.97] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Cultures of a pseudodiploid cell line (Don) of Chinese hamster origin were exposed to varying doses of tritiated thymidine (TdR-(3)H) for relatively long periods of time. In addition to previously observed chromosomal aberrations) such as breaks and reunions, a substantial number of interphasic cells with micronuclei and of metaphases associated with pulverized chromosomes was found; both phenomena were dependent on exposure time to and concentration of TdR-(3)H. The former phenomenon appeared to result from the effects of the beta-emissions originating in the TdR-(3)H. A possible interpretation for chromosome pulverization induction is presented, emphasizing the derivation of the pulverized material from micronuclei in a common cytoplasm with a metaphase nucleus. These observations further substantiate our previously advanced hypothesis regarding the essential role played by substances present in a mitotic cell in the induction of chromosome pulverization and nuclear membrane dissolution.
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Johnson RT, Rao PN. Nucleo-cytoplasmic interactions in the acheivement of nuclear synchrony in DNA synthesis and mitosis in multinucleate cells. Biol Rev Camb Philos Soc 1971; 46:97-155. [PMID: 4399534 DOI: 10.1111/j.1469-185x.1971.tb01180.x] [Citation(s) in RCA: 95] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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16
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Seed J. DNA synthesis in nuclear protrusions. Exp Cell Res 1971; 64:412-8. [PMID: 5542647 DOI: 10.1016/0014-4827(71)90095-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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17
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Obe G. [Inter- and intrachromosomal distribution of spontaneous achromatic lesions and chromatid breaks]. Chromosoma 1971; 33:403-8. [PMID: 5569602 DOI: 10.1007/bf00326503] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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Johnson RT, Rao PN. Mammalian cell fusion: induction of premature chromosome condensation in interphase nuclei. Nature 1970; 226:717-22. [PMID: 5443247 DOI: 10.1038/226717a0] [Citation(s) in RCA: 451] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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Abstract
(3)H-actinomycin D, a guanine-binding agent, labels fixed human chromosomes nonrandomly. Actinomycin D added in G2 inhibits secondary constrictions and breaks chromosomes. There is some tendency for label to be concentrated at the ends of chromosomes and near the centromere. Labeling with (3)H-thymidine in the late stage of DNA synthesis shows a different pattern and in general lacks the telomeric concentrations. The sites of actinomycin D-induced breaks do not show good correspondence with the sites of actinomycin D label.
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MESH Headings
- Chromosomes/drug effects
- Chromosomes, Human, 1-3/drug effects
- Chromosomes, Human, 13-15/drug effects
- Chromosomes, Human, 16-18/drug effects
- Chromosomes, Human, 19-20/drug effects
- Chromosomes, Human, 21-22 and Y/drug effects
- Chromosomes, Human, 4-5/drug effects
- Chromosomes, Human, 6-12 and X/drug effects
- DNA Replication
- Dactinomycin/pharmacology
- Fibroblasts
- Humans
- Lymphocytes
- Sex Chromosomes/drug effects
- Thymidine
- Tritium
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Bühler EM, Luchsinger U, Bühler UK, Méhes K, Stalder GR. Non-condensation of one segment of a chromosome No. 2 in a male with an otherwise normal karyotype (and severe hypospadias). HUMANGENETIK 1970; 9:97-104. [PMID: 5489000 DOI: 10.1007/bf00696019] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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Wurster D, Pomeroy J, Benirschke K, Hoefnagel D. Mental deficiency and malformations in a boy with a group-C ring chromosome: 46, XY, Cr. JOURNAL OF MENTAL DEFICIENCY RESEARCH 1969; 13:184-190. [PMID: 5823674 DOI: 10.1111/j.1365-2788.1969.tb01078.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
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