scholarly journals Sequencing Micronuclei Reveals the Landscape of Chromosomal Instability

2021 ◽  
Author(s):  
Catalina Pereira ◽  
Ana Rita Rebelo ◽  
Dashiell Massey ◽  
John C. Schimenti ◽  
Robert S Weiss ◽  
...  
Keyword(s):  
Systematic Approach ◽  
Genome Instability ◽  
Chromosome Breakage ◽  
Cell Cycles ◽  
Chromosome Breaks ◽  
Chromosomal Fragility ◽  
Chromosome Fragments ◽  
Nuclear Structures ◽  
Somatic Diseases ◽  
Long Genes

Genome instability (GIN) is a main contributing factor to congenital and somatic diseases, but its sporadic occurrence in individual cell cycles makes it difficult to study mechanistically. One profound manifestation of GIN is the formation of micronuclei (MN), the engulfment of chromosomes or chromosome fragments in their own nuclear structures separate from the main nucleus. Here, we developed MN-seq, an approach for sequencing the DNA contained within micronuclei. We applied MN-seq to mice with mutations in Mcm4 and Rad9a, which disrupt DNA replication, repair, and damage responses. Data analysis and simulations show that centromere presence, fragment length, and a heterogenous landscape of chromosomal fragility all contribute to the patterns of DNA present within MN. In particular, we show that long genes, but also gene-poor regions, are associated with chromosome breaks that lead to the enrichment of particular genomic sequences in MN, in a genetic background-specific manner. Finally, we introduce single-cell micronucleus sequencing (scMN-seq), an approach to sequence the DNA present in MN of individual cells. Together, sequencing micronuclei provides a systematic approach for studying GIN and reveals novel molecular associations with chromosome breakage and segregation.

scholarly journals Gametocidal Genes Induce Chromosome Breakage in the Interphase Prior to the First Mitotic Cell Division of the Male Gametophyte in Wheat

Genetics ◽  
1998 ◽  
Vol 149 (2) ◽  
pp. 1115-1124 ◽  
Author(s):  
Shuhei Nasuda ◽  
Bernd Friebe ◽  
Bikram S Gill
Keyword(s):  
Cell Cycle ◽  
Male Gametophyte ◽  
Chromosomal Rearrangements ◽  
Low Frequency ◽  
Chromosome Breakage ◽  
Mitotic Cell ◽  
Aegilops Speltoides ◽  
Chromosome Breaks ◽  
Chromosome Fragments ◽  
Chromosome Bridges

Abstract Male gametogenesis was cytologically analyzed in wheat lines homozygous or hemizygous for gametocidal (Gc) factors with different modes of action. The first and second meiotic divisions in all lines were cytologically normal. The postmeiotic mitoses were normal in the homozygous lines; however, chromosome fragments and bridges were observed in the mitoses of the hemizygous lines. The morphology of the chromosome fragments suggests that the Gc genes induce chromosome breaks in the G1 phase prior to DNA synthesis of the first postmeiotic mitosis. The age of an anther was correlated with the frequency of aberrant second mitosis. Younger anthers contained a higher number of pollen undergoing normal second mitosis. This observation suggests that the arresting of the cell cycle occurs as the result of chromosome breaks during the first mitosis. Because chromosome bridges were more frequent than fragments in the second mitosis, breakage-fusion-bridge cycles possibly occurred during gametogenesis, which led to further chromosomal rearrangements. The Gc factors located on chromosomes 2S of Aegilops speltoides and 4Ssh of Ae. sharonensis induce severe chromosome breakage in pollen lacking them. However, the Gc factor on telosome 2CcL of Ae. cylindrica only induced chromosome breaks at a low frequency. The observed partial fertility of Gc lines is presumably due to cell cycle arrest and the competition among gametes with and without chromosome breakage.

Riyadh Chromosome Breakage Syndrome: Mental Retardation With Depigmentation of the Skin and Hair

1992 ◽  
Vol 7 (1_suppl) ◽  
pp. S79-S82 ◽  
Author(s):  
Pinar T. Ozand ◽  
Manjula Waghray ◽  
Jay D. Cook ◽  
Kirtikant Sheth ◽  
Generoso G. Gascon
Keyword(s):  
Mental Retardation ◽  
Sister Chromatid ◽  
Chromosome Breakage ◽  
Hair Color ◽  
Γ Irradiation ◽  
Exchange Frequency ◽  
Chromosome Breaks ◽  
Chromosome Breakage Syndrome ◽  
Sister Chromatid Exchange Frequency ◽  
Spontaneous Chromosome

A 20-month-old infant with "silvery-blond" hair color, widespread confettilike depigmentation of the skin, and mental retardation was found to have, in lymphocytes and fibroblast cultures, increased spontaneous chromosome breaks and breaks induced by both mitomycin and γ-irradiation. The sister chromatid exchange frequency was normal. This child probably represents a new chromosome breakage syndrome. (J Child Neurol 1992;7(Suppl):S79-S82.)

scholarly journals Absence of Brca2 causes genome instability by chromosome breakage and loss associated with centrosome amplification

1999 ◽  
Vol 9 (19) ◽  
pp. 1107-S1 ◽  
Author(s):  
Andrew Tutt ◽  
Anastasia Gabriel ◽  
David Bertwistle ◽  
Frances Connor ◽  
Hugh Paterson ◽  
...  
Keyword(s):  
Genome Instability ◽  
Chromosome Breakage ◽  
Centrosome Amplification

scholarly journals Cytokinesis-Block Micronucleus Cytome Assay Evolution into a More Comprehensive Method to Measure Chromosomal Instability

Genes ◽  
2020 ◽  
Vol 11 (10) ◽  
pp. 1203
Author(s):  
Michael Fenech
Keyword(s):  
Chromosomal Instability ◽  
Ex Vivo ◽  
Chromosome Breakage ◽  
Comprehensive Method ◽  
Cbmn Assay ◽  
Dividing Cells ◽  
Chromosome Fragments ◽  
Painting Probes ◽  
Cytome Assay

This review describes the cytokinesis-block micronucleus (CBMN) cytome assay and its evolution into a molecular cytogenetic method of chromosomal instability (CIN). Micronuclei (MNi) originate from whole chromosomes or chromosome fragments that fail to segregate to the poles of the cell during mitosis. These lagging chromosomes are excluded from the daughter nuclei and are enveloped in their own membrane to form MNi. The CBMN assay was developed to allow MNi to be scored exclusively in once-divided binucleated cells, which enables accurate measurement of chromosome breakage or loss without confounding by non-dividing cells that cannot express MNi. The CBMN assay can be applied to cell lines in vitro and cells such as lymphocytes that can be stimulated to divide ex vivo. In the CBMN assay, other CIN biomarkers such as nucleoplasmic bridges (NPBs) and nuclear buds (NBUDs) are also measured. Use of centromere, telomere, and chromosome painting probes provides further insights into the mechanisms through which MNi, NPBs and NBUDs originate. Measurement of MNi is also important because entrapment within a micronucleus may cause chromosomes to shatter and, after nuclear reintegration, become rearranged. Additionally, leakage of DNA from MNi can stimulate inflammation via the cyclic GMP-AMP Synthase—Stimulator of Interferon Genes (cGAS-STING) DNA sensing mechanism of the innate immune system.

scholarly journals Mechanisms of Genome Instability in the Fragile X-Related Disorders

Genes ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 1633
Author(s):  
Bruce E. Hayward ◽  
Karen Usdin
Keyword(s):  
Genome Instability ◽  
Fragile Site ◽  
Fragile X ◽  
Fmr1 Gene ◽  
Cgg Repeat ◽  
Cgg Repeats ◽  
Large Numbers ◽  
Structural Abnormalities ◽  
Chromosomal Fragility ◽  
Ataxia Syndrome

The Fragile X-related disorders (FXDs), which include the intellectual disability fragile X syndrome (FXS), are disorders caused by expansion of a CGG-repeat tract in the 5′ UTR of the X-linked FMR1 gene. These disorders are named for FRAXA, the folate-sensitive fragile site that localizes with the CGG-repeat in individuals with FXS. Two pathological FMR1 allele size classes are distinguished. Premutation (PM) alleles have 54–200 repeats and confer the risk of fragile X-associated tremor/ataxia syndrome (FXTAS) and fragile X-associated primary ovarian insufficiency (FXPOI). PM alleles are prone to both somatic and germline expansion, with female PM carriers being at risk of having a child with >200+ repeats. Inheritance of such full mutation (FM) alleles causes FXS. Contractions of PM and FM alleles can also occur. As a result, many carriers are mosaic for different sized alleles, with the clinical presentation depending on the proportions of these alleles in affected tissues. Furthermore, it has become apparent that the chromosomal fragility of FXS individuals reflects an underlying problem that can lead to chromosomal numerical and structural abnormalities. Thus, large numbers of CGG-repeats in the FMR1 gene predisposes individuals to multiple forms of genome instability. This review will discuss our current understanding of these processes.

scholarly journals Mechanistic basis for microhomology identification and genome scarring by polymerase theta

2020 ◽  
Vol 117 (15) ◽  
pp. 8476-8485 ◽  
Author(s):  
Juan Carvajal-Garcia ◽  
Jang-Eun Cho ◽  
Pablo Carvajal-Garcia ◽  
Wanjuan Feng ◽  
Richard D. Wood ◽  
...  
Keyword(s):  
Dna Polymerase ◽  
De Novo ◽  
Genome Instability ◽  
End Joining ◽  
Complementary Sequence ◽  
Chromosome Breaks ◽  
Complete Repair ◽  
Cancer Genomes ◽  
Mechanistic Basis ◽  
Scanning Mechanism

DNA polymerase theta mediates an end joining pathway (TMEJ) that repairs chromosome breaks. It requires resection of broken ends to generate long, 3′ single-stranded DNA tails, annealing of complementary sequence segments (microhomologies) in these tails, followed by microhomology-primed synthesis sufficient to resolve broken ends. The means by which microhomologies are identified is thus a critical step in this pathway, but is not understood. Here we show microhomologies are identified by a scanning mechanism initiated from the 3′ terminus and favoring bidirectional progression into flanking DNA, typically to a maximum of 15 nucleotides into each flank. Polymerase theta is frequently insufficiently processive to complete repair of breaks in microhomology-poor, AT-rich regions. Aborted synthesis leads to one or more additional rounds of microhomology search, annealing, and synthesis; this promotes complete repair in part because earlier rounds of synthesis generate microhomologies de novo that are sufficiently long that synthesis is more processive. Aborted rounds of synthesis are evident in characteristic genomic scars as insertions of 3 to 30 bp of sequence that is identical to flanking DNA (“templated” insertions). Templated insertions are present at higher levels in breast cancer genomes from patients with germline BRCA1/2 mutations, consistent with an addiction to TMEJ in these cancers. Our work thus describes the mechanism for microhomology identification and shows how it both mitigates limitations implicit in the microhomology requirement and generates distinctive genomic scars associated with pathogenic genome instability.

CHROMOSOME BREAKAGE INDUCED IN VICIA FABA ROOT TIPS BY 2,4,6-TRI(ETHYLENEIMINO)-1,3,5-TRIAZINE

1959 ◽  
Vol 37 (3) ◽  
pp. 403-411 ◽  
Author(s):  
Resa Wakonig ◽  
T. J. Arnason
Keyword(s):  
Vicia Faba ◽  
Heterochromatic Region ◽  
Chromosome Breakage ◽  
Equal Frequency ◽  
Root Tips ◽  
Satellite Chromosome ◽  
Root Cells ◽  
Chromosome Breaks ◽  
Satellite Chromosomes ◽  
Unit Of Length

After a 12-hour treatment in 10−5 M solution of 2,4,6-tri(ethyleneimino)-1,3,5-triazine (TEM), up to 29% of Vicia and 31% of Allium root cells in anaphase had bridges or fragments. The most abundant metaphase aberrations were chromosome breaks and chromatid interchanges. Aberrations were more numerous after 6-hour treatment with 2 × 10−5 M than after 12-hour treatment with 10−5 M solution. The peak aberration frequencies were reached at 36 hours after 2 × 10−5 M treatments and slightly earlier with weaker solutions. Many chromosomes had incomplete breaks. Sister reunions of chromatids occurred with equal frequency in centric and acentric fragments. Sister reunion was 1.5 times as frequent as chromatid exchange. Along the length of the satellite chromosome, breaks occurred at random except for a slight favoring of the heterochromatic region. Per unit of length the short chromosomes were about 3 times as susceptible to breakage and exchange as satellite chromosomes. TEM introduced through cut stems had no discernible effects on Tradescantia microspore chromosomes even after 3 to 5 days of treatment.

XXV.—Chemically Induced Mosaicism in Drosophila melanogaster

1946 ◽  
Vol 62 (2) ◽  
pp. 211-222 ◽  
Author(s):  
Charlotte Auerbach
Keyword(s):  
Chemical Treatment ◽  
Chromosome Breakage ◽  
Point Of View ◽  
Mutagenic Action ◽  
Similar Data ◽  
X Rays ◽  
Chemical Substances ◽  
Chromosome Breaks ◽  
Chemically Induced ◽  
The Many

Muller's classical discovery in 1927 of the mutagenic action of X-rays has provided an extremely useful tool for studying the nature of gene mutation and chromosome breakage. It has always been realized that if, in addition, chemical substances were found capable of producing mutations and/or chromosome breaks a further important step forward in the analysis of the mutation process would follow. The search for such mutagenic substances has therefore been going on in various laboratories for some ten years, until recently, however, without definitely positive results. Only during the last few years has it been shown that certain chemical substances, such as mustard gas (ββ′-dichlordiethylsulphide, (ClCH2 · CH2)2S), may be as effective as X-rays in producing mutations and chromosome breaks (Auerbach, 1943; Auerbach and Robson, 1944; Auerbach, 1945; Auerbach and Robson, 1946). Indeed, the similarities between the results of these two types of treatment are impressive. In the course of more than four years during which work of this kind has been carried out by the author, only few differences between the genetical results of chemical treatment and of irradiation have come to light. Particular interest attaches to these dissimilarities, because they, rather than the many similarities, may throw some new light on the process of mutation and through this on the nature of the gene. One of the few striking dissimilarities is the high frequency of certain types of mosaics which can be produced by chemical treatment. It is the object of the present paper to summarize the data on chemically induced mosaicism, contrast them with similar data from X-ray experiments, and discuss the similarities and differences from the point of view of the mechanism of induced mutation.

scholarly journals Unscheduled DNA replication in G1 causes genome instability through head-to-tail replication fork collisions

2021 ◽  
Author(s):  
Karl-Uwe Reusswig ◽  
Julia Bittmann ◽  
Martina Peritore ◽  
Michael Wierer ◽  
Matthias Mann ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Dna Replication ◽  
Replication Fork ◽  
Genome Instability ◽  
S Phase ◽  
Replication Initiation ◽  
Dna Replication Initiation ◽  
Chromosome Breaks ◽  
Naturally Occurring ◽  
Identical Response

DNA replicates once per cell cycle. Interfering with the regulation of DNA replication initiation generates genome instability through over-replication and has been linked to early stages of cancer development. Here, we engineered genetic systems in budding yeast to induce unscheduled replication in the G1-phase of the cell cycle. Unscheduled G1 replication initiated at canonical S-phase origins across the genome. We quantified differences in replisomes in G1- and S-phase and identified firing factors, polymerase α, and histone supply as factors that limit replication outside S-phase. G1 replication per se did not trigger cellular checkpoints. Subsequent replication during S-phase, however, resulted in over-replication and led to chromosome breaks via head-to-tail replication fork collisions that are marked by chromosome-wide, strand-biased occurrence of RPA-bound single-stranded DNA. Low-level, sporadic induction of G1 replication induced an identical response, indicating findings from synthetic systems are applicable to naturally occurring scenarios of unscheduled replication initiation by G1/S deregulation.

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