Structural chromosomal rearrangements result from different mechanisms of formation, usually related to certain genomic architectural features that may lead to genetic instability. Most of these rearrangements arise from recombination, repair, or replication mechanisms that occur after a double-strand break or the stalling/breakage of a replication fork. Here, we review the mechanisms of formation of structural rearrangements, highlighting their main features and differences. The most important mechanisms of constitutional chromosomal alterations are discussed, including Non-Allelic Homologous Recombination (NAHR), Non-Homologous End-Joining (NHEJ), Fork Stalling and Template Switching (FoSTeS), and Microhomology-Mediated Break-Induced Replication (MMBIR). Their involvement in chromoanagenesis and in the formation of complex chromosomal rearrangements, inverted duplications associated with terminal deletions, and ring chromosomes is also outlined. We reinforce the importance of high-resolution analysis to determine the DNA sequence at, and near, their breakpoints in order to infer the mechanisms of formation of structural rearrangements and to reveal how cells respond to DNA damage and repair broken ends. 

/pdf/mechanisms-of-structural-chromosomal-rearrangement-formation-f1fyd5z3.pdf

Mechanisms of structural chromosomal rearrangement formation

/pdf/mechanisms-of-structural-chromosomal-rearrangement-formation-2hcisgx9.pdf

The pericentric satellite III (SatIII or Sat3) and II tandem repeats recently appeared to be transcribed under stress conditions, and the transcripts were shown to play an essential role in the universal stress response. In this paper, we review the role of human-specific SatIII copy number variation (CNV) in normal stress response, aging and pathology, with a focus on 1q12 loci. We postulate a close link between transcription of SatII/III repeats and their CNV. The accrued body of data suggests a hypothetical universal mechanism, which provides for SatIII copy gain during the stress response, alongside with another, more hypothetical reverse mechanism that might reduce the mean SatIII copy number, likely via the selection of cells with excessively large 1q12 loci. Both mechanisms, working alternatively like swings of the pendulum, may ensure the balance of SatIII copy numbers and optimum stress resistance. This model is verified on the most recent data on SatIII CNV in pathology and therapy, aging, senescence and response to genotoxic stress in vitro.

The Role of Human Satellite III (1q12) Copy Number Variation in the Adaptive Response during Aging, Stress, and Pathology: A Pendulum Model

Improvements in microarray-based comparative genomic hybridization technology have allowed for high-resolution detection of genome wide copy number alterations, leading to a better definition of rearrangements and supporting the study of pathogenesis mechanisms. In this study, we focused our attention on chromosome 8p. We report 12 cases of 8p rearrangements, analyzed by molecular karyotype, evidencing a continuum of fragility that involves the entire short arm. The breakpoints seem more concentrated in three intervals: one at the telomeric end, the others at 8p23.1, close to the beta-defensin gene cluster and olfactory receptor low-copy repeats. Hypothetical mechanisms for all cases are described. Our data extend the cohort of published patients with 8p aberrations and highlight the need to pay special attention to these sequences due to the risk of formation of new chromosomal aberrations with pathological effects.

/pdf/characterization-of-chromosomal-breakpoints-in-12-cases-with-1s64i38a.pdf

Characterization of Chromosomal Breakpoints in 12 Cases with 8p Rearrangements Defines a Continuum of Fragility of the Region

Chromosome and array comparative genomic hybridization (aCGH) analyses were performed on two cases of well-differentiated liposarcoma (WDLPS) and two cases of dedifferentiated liposarcoma (DDLPS). The results revealed the characteristic giant ring (GR) or giant rod marker (GRM) chromosomes in all four cases and amplification of numerous somatic copy number alterations (SCNAs) involving a core segment of 12q14.1q15 and other chromosomal regions in three cases. The levels of amplification for oncogenes OS9, CDK4, HMGA2, NUP107, MDM2, YEATS4, and FRS2 at the core segment or other SCNAs should be characterized to facilitate pathologic correlation and prognostic prediction. Further studies for the initial cellular crisis event affecting chromosome intermingling regions for cell-type specific gene regulation may reveal the underlying mutagenesis mechanism for GR and GRM in WDLPS and DDLPS.

https://downloads.hindawi.com/journals/crig/2022/6341207.pdf

Cytogenomic Characterization of Giant Ring or Rod Marker Chromosome in Four Cases of Well-Differentiated and Dedifferentiated Liposarcoma

Constitutional ring chromosome 9, r(9), is a rare chromosomal disorder. Cytogenomic analyses by karyotyping, array comparative genomic hybridization (aCGH) and whole genome sequencing (WGS) were performed in a patient of r(9). Karyotyping detected a mosaic pattern of r(9) and monosomy 9 in 83% and 17% of cells, respectively. aCGH detected subtelomeric deletions of 407 kb at 9p24.3 and 884 kb at 9q34.3 and an interstitial duplication of 5.879 Mb at 9q33.2q34.11. WGS revealed double strand breaks (DSBs) at ends of 9p24.3 and 9q34.3, inverted repeats at ends of subtelomeric and 9q33.2q34.11 regions, and microhomology sequences at the junctions of this r(9). This is the first report of r(9) analyzed by WGS to delineate the mechanism of ring chromosome formation from repairing of subtelomeric DSBs. The loss of telomeres by subtelomeric DSBs triggered inverted repeats induced intra-strand foldback and then microhomology mediated synthesis and ligation, which resulted in the formation of this r(9) with distal deletions and an interstitial duplication. Review of literature found seven patients of r(9) with clinical and cytogenomic findings. These patients and the present patient were registered into the Human Ring Chromosome Registry and a map correlating critical regions and candidate genes with relevant phenotypes was constructed. Variable phenotypes of r(9) patients could be explained by critical regions and genes of DOCK8, DMRT, SMARCA2, CD274, IL33, PTPRD, CER1, FREM1 for 9p deletions, and the EHMT1 gene for 9q34 deletion syndrome. This interactive registry of r(9) could provide information for cytogenomic diagnosis, genetics counseling and clinical management.

Ring chromosome formation by intra-strand repairing of subtelomeric double stand breaks and clinico-cytogenomic correlations for ring chromosome 9

Background Oligonucleotide array comparative genomic hybridization (aCGH) analysis has been used for detecting somatic copy number alterations (CNAs) in various types of tumors. This study aimed to assess the clinical utility of aCGH for cases of hepatocellular carcinoma (HCC) and to evaluate the correlation between CNAs and clinicopathologic findings. Methods aCGH was performed on 75 HCC cases with paired DNA samples from tumor and adjacent nontumor tissues. Survival outcomes from these cases were analyzed based on Barcelona-Clinic Liver Cancer Stage (BCLC), Edmondson-Steiner grade (E-S), and recurrence status. Correlation of CNAs with clinicopathologic findings was analyzed by Wilcoxon rank test and clustering vs. K means. Results The survival outcomes indicated that BCLC stages and recurrence status could be predictors and E-S grades could be a modifier for HCC. The most common CNAs involved gains of 1q and 8q and a loss of 16q (50%), losses of 4q and 17p and a gain of 5p (40%), and losses of 8p and 13q (30%). Analyses of genomic profiles and clusters identified that losses of 4q13.2q35.2 and 10q22.3q26.13 seen in cases of stage A, grade III and nonrecurrence were likely correlated with good survival, while loss of 1p36.31p22.1 and gains of 2q11.2q21.2 and 20p13p11.1 seen in cases of stage C, grade III and recurrence were possibly correlated with worst prognosis. Conclusions These results indicated that aCGH analysis could be used to detect recurrent CNAs and involved key genes and pathways in patients with HCC. Further analysis on a large case series to validate the correlation of CNAs with clinicopathologic findings of HCC could provide information to interpret CNAs and predict prognosis.

/pdf/correlating-genomic-copy-number-alterations-with-1prf56gan8.pdf

Correlating genomic copy number alterations with clinicopathologic findings in 75 cases of hepatocellular carcinoma.

Background: Hepatocellular carcinoma (HCC) is one of the deadliest cancers worldwide Metallothioneins (MTs) are metal-binding proteins involved in multiple biological processes such as metal homeostasis and detoxification, as well as in oncogenesis Copy number variation (CNV) plays a vital role in pathogenesis and carcinogenesis Nevertheless, there is no study on the role of MT1 CNV in HCC Methods: Array-based Comparative Genomic Hybridization (aCGH) analysis was performed to obtain the CNV data of 79 Guangxi HCC patients The prognostic effect of MT1-deletion was analyzed by univariate and multivariate Cox regression analysis The differentially expressed genes (DEGs) were screened based on The Gene Expression Omnibus database (GEO) and the Liver Hepatocellular Carcinoma of The Cancer Genome Atlas (TCGA-LIHC) Then function and pathway enrichment analysis, protein-protein interaction (PPI) and hub gene selection were applied on the DEGs Lastly, the hub genes were validated by immunohistochemistry, tissue expression and prognostic analysis Results: The MT1-deletion was demonstrated to affect the prognosis of HCC and can act as an independent prognostic factor 147 common DEGs were screened The most significant cluster of DEGs identified by Molecular Complex Detection (MCODE) indicated that the expression of four MT1s were down-regulated MT1X and other five hub genes (TTK, BUB1, CYP3A4, NR1I2, CYP8B1) were associated with the prognosis of HCC TTK, could affect the prognosis of HCC with MT1-deletion and non-deletion NR1I2, CYP8B1, and BUB1 were associated with the prognosis of HCC with MT1-deletion Conclusions: In the current study, we demonstrated that MT1-deletion can be an independent prognostic factor in HCC We identified TTK, BUB1, NR1I2, CYP8B1 by processing microarray data, for the first time revealed the underlying function of MT1 deletion in HCC, MT1-deletion may influence the gene expression in HCC, which may be the potential biomarkers for HCC with MT1 deletion

/pdf/identification-of-potential-biomarkers-from-hepatocellular-mtmd5w91p0.pdf

Qiping Hu

Papers

Ring chromosome formation by intra-strand repairing of subtelomeric double stand breaks and clinico-cytogenomic correlations for ring chromosome 9

Correlating genomic copy number alterations with clinicopathologic findings in 75 cases of hepatocellular carcinoma.

Identification of Potential Biomarkers From Hepatocellular Carcinoma With MT1 Deletion.