scholarly journals Breakage–fusion–bridge cycles and de novo telomere formation on broken chromosomes in maize callus cultures

Genome ◽  
2016 ◽  
Vol 59 (6) ◽  
pp. 367-378 ◽  
Author(s):  
Janay A. Santos-Serejo ◽  
Margarida L.R. Aguiar-Perecin
Keyword(s):  
De Novo ◽  
Chromosomal Evolution ◽  
Callus Cultures ◽  
Chromosome 7 ◽  
Telomeric Sequences ◽  
Chromosome Healing ◽  
Regenerated Plants ◽  
The Stability ◽  
Maize Callus

Breakpoints involved in chromosome alterations associated with heterochromatin have been detected in maize plants regenerated from callus culture. A cytogenetic analysis of plants regenerated from a maize callus was performed aiming to analyze the stability of a chromosome 7 bearing a deficiency-duplication (Df-Dp), which was interpreted as derived from a chromatid type breakage–fusion–bridge (BFB) cycle. The Df-Dp chromosome 7 was stable in mitotic and meiotic cells of the regenerated plants. Fluorescence in situ hybridization showed signals of telomeric sequences on the broken chromosome arm and provided evidence of de novo telomere formation. The stability of two types of altered chromosome 7 was investigated in C-banded metaphases from samples of the original callus that were collected during a period of 30–42 months after culture initiation. New alterations involving heterochromatic knobs of chromosomes 7 and 9 were observed. The aberrant chromosomes were stable in the subcultures, thus providing evidence of broken chromosome healing. The examination of anaphases showed the presence of bridges, which was consistent with the occurrence of BFB cycles. De novo telomere formation occurred in euchromatic and heterochromatic chromosome termini. The results point to events of chromosomal evolution that might occur in plants.

Distribution of telomeric repeats and their role in the healing of broken chromosome ends in wheat

Genome ◽  
1992 ◽  
Vol 35 (5) ◽  
pp. 844-848 ◽  
Author(s):  
Joanna E. Werner ◽  
Rama S. Kota ◽  
Bikram S. Gill ◽  
T. R. Endo
Keyword(s):  
In Situ Hybridization ◽  
De Novo ◽  
Wheat Chromosome ◽  
Variable Number ◽  
Mitotic Chromosomes ◽  
Telomeric Repeats ◽  
Telomeric Sequences ◽  
Chromosome Healing ◽  
Synthetic Probe

The distribution of the telomeric repeats in common wheat and their role in the healing of broken ends of deleted chromosomes was studied. In situ hybridization to mitotic chromosomes was carried out using a synthetic probe that was derived from the sequence of the telomeric repeats of Arabidopsis thaliana. Sites of hybridization were visualized as double dots at both ends of each wheat chromosome. Variation in the strength of the signal that was detected among chromosome arms might be due to the variable number of telomeric repeats of each chromosome end. While signals were absent on normal chromosomes at the pericentric and intercalary regions, hybridization sites were detected at the broken chromosome ends of all deleted chromosomes included in the study. All telocentric chromosomes of multitelocentric lines of 'Chinese Spring' showed a strong signal at the centromeric region. The results suggest that a de novo chromosome healing mechanism exists in wheat involving the addition of the telomeric sequences to the ends of broken chromosome. Further evidence indicated that the healing of broken ends is probably intrinsic to replication during gametogenesis.Key words: in situ hybridization, telomeric sequences, deleted chromosomes, chromosome healing, telosome.

scholarly journals Maize Chromosome Abnormalities and Breakage-Fusion-Bridge Cycles in Callus Cultures

2020 ◽  
Author(s):  
Margarida L.R. Aguiar-Perecin ◽  
Janay A. Santos-Serejo ◽  
José R. Gardingo ◽  
Mateus Mondin
Keyword(s):  
Dna Sequences ◽  
De Novo ◽  
Callus Cultures ◽  
Chromosome Abnormalities ◽  
Anaphase Bridges ◽  
C Banding ◽  
Chromosome Healing ◽  
Bfb Cycle ◽  
Chromosome Alterations

The maize karyotype was first characterized by the observation of pachytene chromosomes. The somatic chromosomes were identified by C-banding and FISH with repetitive DNA sequences. C-banding was useful for the identification of chromosome abnormalities in callus cultures. In the present review, we focus on the involvement of heterochromatic knobs on the occurrence of chromosome abnormalities in callus cultures. In a previous work we detected anaphase bridges resulting from delayed chromatid separation at knob regions and typical bridges derived from dicentric chromatids in cultures. The analysis of altered chromosomes showed they were derived from a chromatid-type breakage-fusion-bridge (BFB) cycle. Fluorescent in situ hybridization (FISH) showed signals of telomere sequences in the broken chromosome arm, thus giving evidence of de novo telomere formation on the broken chromosome end. Further observations of long- and short-term cultures have shown the presence of chromosome alterations derived from BFB cycles followed by chromosome healing. Additionally, the occurrence of unequal crossing over in a knob region was observed in callus culture. These results are of interest for studies on the mechanisms of chromosome alterations during evolution.

Characterization of telomeres in Hordeum vulgare chromosomes by in situ hybridization. II. Healed broken chromosomes in telotrisomic 4L and acrotrisomic 4L4S lines

Genome ◽  
1992 ◽  
Vol 35 (6) ◽  
pp. 975-980 ◽  
Author(s):  
Shaoke Wang ◽  
Nora L. V. Lapitan ◽  
Marion Roder ◽  
Takumi Tsuchiya
Keyword(s):  
Arabidopsis Thaliana ◽  
In Situ Hybridization ◽  
Hordeum Vulgare ◽  
Telomeric Sequences ◽  
The Absolute ◽  
The Cross ◽  
The Stability ◽  
Different Parts

The ends of barley chromosomes hybridize in situ to the telomeric sequences of Arabidopsis thaliana. It was confirmed that the cross-hybridizing sequences in barley are found at the absolute ends of the chromosomes by exonuclease Bal31 digestion. The Bal31 experiments also indicated that telomere-like sequences do not occur in high copies at interstitial sites in barley. To determine whether healing of broken chromosomes occurred in aneuploid lines of barley containing extra chromosomes with breakages in different parts, in situ hybridization with the A. thaliana telomere on telotrisomic 4L and acrotrisomic 4L4S lines was conducted. Telosome 4L possesses breaks in the centromere and in an interstitial location in the long arm, while acrosome 4L4S possesses interstitial breaks in both long and short arms. In situ hybridization revealed the presence of telomere sequences on both broken ends of telosome 4L and acrosome 4L4S. In telosome 4L, telomere sequences were present even at the broken site of the centromere. These results show that broken ends of barley chromosomes were healed. Such healing may explain the stability of these chromosomes through many generations.Key words: telomere, centromere, telosome, acrosome, acrotrisomic, telotrisomic.

scholarly journals When the Ends Justify the Means: Regulation of Telomere Addition at Double-Strand Breaks in Yeast

2021 ◽  
Vol 9 ◽  
Author(s):  
Remington E. Hoerr ◽  
Katrina Ngo ◽  
Katherine L. Friedman
Keyword(s):  
De Novo ◽  
Chromosome Rearrangement ◽  
Consensus Sequence ◽  
Repetitive Sequences ◽  
Strand Break ◽  
Chromosome Break ◽  
Telomeric Dna ◽  
Strand Breaks ◽  
Telomeric Sequences ◽  
Chromosome Healing

Telomeres, repetitive sequences located at the ends of most eukaryotic chromosomes, provide a mechanism to replenish terminal sequences lost during DNA replication, limit nucleolytic resection, and protect chromosome ends from engaging in double-strand break (DSB) repair. The ribonucleoprotein telomerase contains an RNA subunit that serves as the template for the synthesis of telomeric DNA. While telomere elongation is typically primed by a 3′ overhang at existing chromosome ends, telomerase can act upon internal non-telomeric sequences. Such de novo telomere addition can be programmed (for example, during chromosome fragmentation in ciliated protozoa) or can occur spontaneously in response to a chromosome break. Telomerase action at a DSB can interfere with conservative mechanisms of DNA repair and results in loss of distal sequences but may prevent additional nucleolytic resection and/or chromosome rearrangement through formation of a functional telomere (termed “chromosome healing”). Here, we review studies of spontaneous and induced DSBs in the yeast Saccharomyces cerevisiae that shed light on mechanisms that negatively regulate de novo telomere addition, in particular how the cell prevents telomerase action at DSBs while facilitating elongation of critically short telomeres. Much of our understanding comes from the use of perfect artificial telomeric tracts to “seed” de novo telomere addition. However, endogenous sequences that are enriched in thymine and guanine nucleotides on one strand (TG-rich) but do not perfectly match the telomere consensus sequence can also stimulate unusually high frequencies of telomere formation following a DSB. These observations suggest that some internal sites may fully or partially escape mechanisms that normally negatively regulate de novo telomere addition.

scholarly journals The frequent and clinically benign anomalies of chromosomes 7 and 20 in Shwachman-diamond syndrome may be subject to further clonal variations

2021 ◽  
Vol 14 (1) ◽  
Author(s):  
Abdul Waheed Khan ◽  
Alyssa Kennedy ◽  
Elissa Furutani ◽  
Kasiani Myers ◽  
Annalisa Frattini ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Fluorescent In Situ Hybridization ◽  
De Novo ◽  
Chromosome 7 ◽  
Comparative Genomic ◽  
Sequential Samples ◽  
Karyotype Instability ◽  
Shwachman Diamond Syndrome ◽  
Single Bone

Abstract Background An isochromosome of the long arm of chromosome 7, i(7)(q10), and an interstitial deletion of the long arm of chromosome 20, del(20)(q), are the most frequent anomalies in the bone marrow of patients with Shwachman-Diamond syndrome, which is caused in most cases by mutations of the SBDS gene. These clonal changes imply milder haematological symptoms and lower risk of myelodysplastic syndromes and acute myeloid leukaemia, thanks to already postulated rescue mechanisms. Results Bone marrow from fourteen patients exhibiting either the i(7)(q10) or the del(20)(q) and coming from two large cohorts of patients, were subjected to chromosome analyses, Fluorescent In Situ Hybridization with informative probes and array-Comparative Genomic Hybridization. One patient with the i(7)(q10) showed a subsequent clonal rearrangement of the normal chromosome 7 across years. Four patients carrying the del(20)(q) evolved further different del(20)(q) independent clones, within a single bone marrow sample, or across sequential samples. One patient with the del(20)(q), developed a parallel different clone with a duplication of chromosome 3 long arm. Eight patients bore the del(20)(q) as the sole chromosomal abnormality. An overall overview of patients with the del(20)(q), also including cases already reported, confirmed that all the deletions were interstitial. The loss of material varied from 1.7 to 26.9 Mb and resulted in the loss of the EIF6 gene in all patients. Conclusions Although the i(7)(q) and the del(20)(q) clones are frequent and clinically benign in Shwachman Diamond-syndrome, in the present work we show that they may rearrange, may be lost and then reconstructed de novo, or may evolve with independent clones across years. These findings unravel a striking selective pressure exerted by SBDS deficiency driving to karyotype instability and to specific clonal abnormalities.

Alterations in Heterochromatic Knobs in Maize Callus Culture by Breakage-Fusion-Bridge Cycle and Unequal Crossing Over

2018 ◽  
Vol 154 (2) ◽  
pp. 107-118 ◽  
Author(s):  
Janay A. Santos-Serejo ◽  
José R. Gardingo ◽  
Mateus Mondin ◽  
Margarida L.R. Aguiar-Perecin
Keyword(s):  
Callus Culture ◽  
Low Frequency ◽  
Callus Cultures ◽  
Chromosome 7 ◽  
Crossing Over ◽  
Unequal Crossing Over ◽  
Regenerated Plants ◽  
Sister Chromatid Recombination ◽  
Bfb Cycle

The meiotic and mitotic behavior of regenerated plants derived from a long-term callus culture, designated 12-F, was analyzed. This culture was heterozygous for an amplification of the heterochromatic knob on the long arm of chromosome 7 (K7L). We aimed to investigate if the amplification resulted from a breakage-fusion-bridge (BFB) cycle or from unequal sister chromatid recombination. Therefore, C-banded mitotic metaphases and pachytene, diakinesis, and anaphase I of regenerated plants were analyzed. Additionally, the occurrence of alterations in K7L was investigated in C-banded metaphases from short-term callus cultures derived from lines related to the donor genotype of the 12-F culture. As a result, plants homozygous and heterozygous for the amplification were detected. Meiosis was normal with few abnormalities, such as a low frequency of univalents at diakinesis. In the callus cultures a chromosome 7 with knobs of different sizes in the sister chromatids was detected and interpreted as a result of unequal crossing over. Other chromosomal alterations were consistent with the occurrence of BFB cycles. The finding of unequal crossing over in the cultures supports the conclusion that the amplification in the culture 12-F would be derived from this mechanism. If the amplification was derived from a BFB cycle, the terminal euchromatic segment between knob and the telomere would be deleted, and possibly, homozygous plants would not be viable.

Influence of ion-milling on the T2 phase in Al-2.5%Li-2.5%Cu alloy

1989 ◽  
Vol 47 ◽  
pp. 288-289
Author(s):  
J. R. Reed ◽  
D. J. Michel ◽  
P. R. Howell
Keyword(s):  
Thin Foil ◽  
Icosahedral Symmetry ◽  
Ion Milling ◽  
Cu Alloy ◽  
Thin Foils ◽  
Heat Treated ◽  
Aluminum Solid Solution ◽  
In Situ Heating ◽  
The Stability

The Al6Li3Cu (T2) phase, which exhibits five-fold or icosahedral symmetry, forms through solid state precipitation in dilute Al-Li-Cu alloys. Recent studies have reported that the T2 phase transforms either during TEM examination of thin foils or following ion-milling of thin foil specimens. Related studies have shown that T2 phase transforms to a microcrystalline array of the TB phase and a dilute aluminum solid solution during in-situ heating in the TEM. The purpose of this paper is to report results from an investigation of the influence of ion-milling on the stability of the T2 phase in dilute Al-Li-Cu alloy.The 3-mm diameter TEM disc specimens were prepared from a specially melted Al-2.5%Li-2.5%Cu alloy produced by conventional procedures. The TEM specimens were solution heat treated 1 h at 550°C and aged 1000 h at 190°C in air to develop the microstructure. The disc specimens were electropolished to achieve electron transparency using a 20:80 (vol. percent) nitric acid: methanol solution at -60°C.

scholarly journals HP1 drives de novo 3D genome reorganization in early Drosophila embryos

Nature ◽  
2021 ◽  
Author(s):  
Fides Zenk ◽  
Yinxiu Zhan ◽  
Pavel Kos ◽  
Eva Löser ◽  
Nazerke Atinbayeva ◽  
...  
Keyword(s):  
Genome Organization ◽  
Molecular Mechanisms ◽  
High Throughput Sequencing ◽  
De Novo ◽  
Early Embryo ◽  
Heterochromatin Protein ◽  
Chromosome Conformation ◽  
3D Genome ◽  
Genome Reorganization

AbstractFundamental features of 3D genome organization are established de novo in the early embryo, including clustering of pericentromeric regions, the folding of chromosome arms and the segregation of chromosomes into active (A-) and inactive (B-) compartments. However, the molecular mechanisms that drive de novo organization remain unknown1,2. Here, by combining chromosome conformation capture (Hi-C), chromatin immunoprecipitation with high-throughput sequencing (ChIP–seq), 3D DNA fluorescence in situ hybridization (3D DNA FISH) and polymer simulations, we show that heterochromatin protein 1a (HP1a) is essential for de novo 3D genome organization during Drosophila early development. The binding of HP1a at pericentromeric heterochromatin is required to establish clustering of pericentromeric regions. Moreover, HP1a binding within chromosome arms is responsible for overall chromosome folding and has an important role in the formation of B-compartment regions. However, depletion of HP1a does not affect the A-compartment, which suggests that a different molecular mechanism segregates active chromosome regions. Our work identifies HP1a as an epigenetic regulator that is involved in establishing the global structure of the genome in the early embryo.

scholarly journals Underground Microseismic Event Monitoring and Localization within Sensor Networks

Sensors ◽  
2021 ◽  
Vol 21 (8) ◽  
pp. 2830
Author(s):  
Sili Wang ◽  
Mark P. Panning ◽  
Steven D. Vance ◽  
Wenzhan Song
Keyword(s):  
Sensor Networks ◽  
Real Time ◽  
Information Needs ◽  
Localization Algorithm ◽  
Distributed Sensors ◽  
Distributed Sensor ◽  
Microseismic Events ◽  
The Stability ◽  
Stability And Accuracy

Locating underground microseismic events is important for monitoring subsurface activity and understanding the planetary subsurface evolution. Due to bandwidth limitations, especially in applications involving planetarily-distributed sensor networks, networks should be designed to perform the localization algorithm in-situ, so that only the source location information needs to be sent out, not the raw data. In this paper, we propose a decentralized Gaussian beam time-reverse imaging (GB-TRI) algorithm that can be incorporated to the distributed sensors to detect and locate underground microseismic events with reduced usage of computational resources and communication bandwidth of the network. After the in-situ distributed computation, the final real-time location result is generated and delivered. We used a real-time simulation platform to test the performance of the system. We also evaluated the stability and accuracy of our proposed GB-TRI localization algorithm using extensive experiments and tests.

scholarly journals Jacobsen syndrome and neonatal bleeding: report on two unrelated patients

2021 ◽  
Vol 47 (1) ◽  
Author(s):  
Gregorio Serra ◽  
Luigi Memo ◽  
Vincenzo Antona ◽  
Giovanni Corsello ◽  
Valentina Favero ◽  
...  
Keyword(s):  
Developmental Delay ◽  
De Novo ◽  
Comparative Genomic ◽  
Fish Analysis ◽  
Variable Degree ◽  
Jacobsen Syndrome ◽  
Contiguous Gene ◽  
Clinical Consequences ◽  
11Q Deletion

Abstract Introduction In 1973, Petrea Jacobsen described the first patient showing dysmorphic features, developmental delay and congenital heart disease (atrial and ventricular septal defect) associated to a 11q deletion, inherited from the father. Since then, more than 200 patients have been reported, and the chromosomal critical region responsible for this contiguous gene disorder has been identified. Patients’ presentation We report on two unrelated newborns observed in Italy affected by Jacobsen syndrome (JBS, also known as 11q23 deletion). Both patients presented prenatal and postnatal bleeding, growth and developmental delay, craniofacial dysmorphisms, multiple congenital anomalies, and pancytopenia of variable degree. Array comparative genomic hybridization (aCGH) identified a terminal deletion at 11q24.1-q25 of 12.5 Mb and 11 Mb, in Patient 1 and 2, respectively. Fluorescent in situ hybridization (FISH) analysis of the parents documented a de novo origin of the deletion for Patient 1; parents of Patient 2 refused further genetic investigations. Conclusions Present newborns show the full phenotype of JBS including thrombocytopenia, according to their wide 11q deletion size. Bleeding was particularly severe in one of them, leading to a cerebral hemorrhage. Our report highlights the relevance of early diagnosis, genetic counselling and careful management and follow-up of JBS patients, which may avoid severe clinical consequences and lower the mortality risk. It may provide further insights and a better characterization of JBS, suggesting new elements of the genotype-phenotype correlations.

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