Localization of ribosomal RNA genes on human acrocentric chromosomes

Spadari, Silvio; Lernia, R. Di; Simoni, Giuseppe; Pedrali-Noy, G.; Carli, L. De

doi:10.1007/bf00267783

Cited by 10 publications

(3 citation statements)

References 33 publications

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“…The tandem arrays of ribosomal RNA gene (rDNA) clusters or nucleolar organizing regions (NORs) are present on each acrocentric short arm. After mitosis, numerous mini-nucleoli arise around the NORs, coalescing into one or a few large nucleoli during interphase that bring the acrocentric short arms into close proximity [10], [55]–[58]. To test if dnTRF2 perturbed acrocentric associations, we visualized nucleolar organization in control (HT1080 and uninduced cells) and dnTRF2-expressing cells by immunostaining for two nucleolar proteins, Ki-67 and fibrillarin on three-dimensionally preserved nuclei (Figure 4A and 4B).…”

Section: Resultsmentioning

confidence: 99%

Telomere Disruption Results in Non-Random Formation of De Novo Dicentric Chromosomes Involving Acrocentric Human Chromosomes

et al. 2010

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Genome rearrangement often produces chromosomes with two centromeres (dicentrics) that are inherently unstable because of bridge formation and breakage during cell division. However, mammalian dicentrics, and particularly those in humans, can be quite stable, usually because one centromere is functionally silenced. Molecular mechanisms of centromere inactivation are poorly understood since there are few systems to experimentally create dicentric human chromosomes. Here, we describe a human cell culture model that enriches for de novo dicentrics. We demonstrate that transient disruption of human telomere structure non-randomly produces dicentric fusions involving acrocentric chromosomes. The induced dicentrics vary in structure near fusion breakpoints and like naturally-occurring dicentrics, exhibit various inter-centromeric distances. Many functional dicentrics persist for months after formation. Even those with distantly spaced centromeres remain functionally dicentric for 20 cell generations. Other dicentrics within the population reflect centromere inactivation. In some cases, centromere inactivation occurs by an apparently epigenetic mechanism. In other dicentrics, the size of the α-satellite DNA array associated with CENP-A is reduced compared to the same array before dicentric formation. Extra-chromosomal fragments that contained CENP-A often appear in the same cells as dicentrics. Some of these fragments are derived from the same α-satellite DNA array as inactivated centromeres. Our results indicate that dicentric human chromosomes undergo alternative fates after formation. Many retain two active centromeres and are stable through multiple cell divisions. Others undergo centromere inactivation. This event occurs within a broad temporal window and can involve deletion of chromatin that marks the locus as a site for CENP-A maintenance/replenishment.

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Section: Resultsmentioning

confidence: 99%

Telomere Disruption Results in Non-Random Formation of De Novo Dicentric Chromosomes Involving Acrocentric Human Chromosomes

et al. 2010

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“…To date, there is no connection available between the working draft sequence of the acrocentric chromosomes to the conserved repeat sequence TTAGGG [Moyzis et al, 1988] of the p-telomeres, as done for most autosomes [Riethman et al, 2001], because the region between contains heterochromatin comprising mostly repeated DNA, which is unstable in yeast and bacteria, and therefore difficult to clone and characterize. Nevertheless, there are reports concerning human ribosomal DNA (rDNA) as tandemly arranged multicopy gene family present on the p-arms of the five acrocentric chromosomes [Spadari et al, 1973;Gonzalez and Sylvester, 2001], and two putative genes (ZNF72 and ZNF73) with zinc finger motifs are mapped by FISH to 22pter [Aubry et al, 1992]. Most reported or commercially available subtelomeric probe sets exclude acrocentric FISH-probes from the analysis.…”

Section: Discussionmentioning

confidence: 99%

Rapid detection of subtelomeric deletion/duplication by novel real-time quantitative PCR using SYBR-green dye

Boehm

Herold

Kuechler³

et al. 2004

Hum. Mutat.

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Telomeric chromosome rearrangements may cause mental retardation, congenital anomalies, miscarriages, and hematological malignancies. Automated detection of subtle deletions and duplications involving telomeres is essential for high-throughput screening procedures, but impractical when conventional cytogenetic methods are used. Novel real-time PCR quantitative genotyping of subtelomeric amplicons using SYBR-green dye allows high-resolution screening of single copy number gains and losses by their relative quantification against a diploid genome. To assess the applicability of the technique in the screening and diagnosis of subtelomeric imbalances, we describe here a blinded study in which DNA from 20 negative controls and 20 patients with known unbalanced cytogenetic abnormalities involving at least one or more telomeres were analyzed using a novel human subtelomere-specific primer set, producing altogether 86 amplicons, in the SYBR-green I-based real-time quantitative PCR screening approach. Screening of the DNA samples from 20 unrelated controls for copy number polymorphism do not detect any polymorphism in the set of amplicons, but single-copy-number gains and losses were accurately detected by quantitative PCR in all patients, except the copy number alterations of the subtelomeric p-arms of the acrocentric chromosomes in two cases. Furthermore, a detailed mapping of the deletion/translocation breakpoint was demonstrated in two cases by novel real-time PCR "primer-jumping." Because of the simplicity and flexibility of the SYBR-green I-based real-time detection, the primer-set can easily be extended, either to perform further detailed molecular characterization of breakpoints or to include amplicons for the detection and/or analysis of syndromes that are associated with genomic copy number alterations, e.g., deletion/duplication-syndromes and malignant cancers.

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“…Its main function is to produce ribosome subunits. After exit from mitosis, numerous mini-nucleoli are formed around actively transcribing NORs [14]–[16]. The mini-nucleoli fuse to form larger nucleoli [17]–[19], thereby bringing the NORs of multiple acrocentrics into close proximity [20]–[22].…”

Section: Introductionmentioning

confidence: 99%

Nucleolar Organization, Ribosomal DNA Array Stability, and Acrocentric Chromosome Integrity Are Linked to Telomere Function

et al. 2014

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The short arms of the ten acrocentric human chromosomes share several repetitive DNAs, including ribosomal RNA genes (rDNA). The rDNA arrays correspond to nucleolar organizing regions that coalesce each cell cycle to form the nucleolus. Telomere disruption by expressing a mutant version of telomere binding protein TRF2 (dnTRF2) causes non-random acrocentric fusions, as well as large-scale nucleolar defects. The mechanisms responsible for acrocentric chromosome sensitivity to dysfunctional telomeres are unclear. In this study, we show that TRF2 normally associates with the nucleolus and rDNA. However, when telomeres are crippled by dnTRF2 or RNAi knockdown of TRF2, gross nucleolar and chromosomal changes occur. We used the controllable dnTRF2 system to precisely dissect the timing and progression of nucleolar and chromosomal instability induced by telomere dysfunction, demonstrating that nucleolar changes precede the DNA damage and morphological changes that occur at acrocentric short arms. The rDNA repeat arrays on the short arms decondense, and are coated by RNA polymerase I transcription binding factor UBF, physically linking acrocentrics to one another as they become fusogenic. These results highlight the importance of telomere function in nucleolar stability and structural integrity of acrocentric chromosomes, particularly the rDNA arrays. Telomeric stress is widely accepted to cause DNA damage at chromosome ends, but our findings suggest that it also disrupts chromosome structure beyond the telomere region, specifically within the rDNA arrays located on acrocentric chromosomes. These results have relevance for Robertsonian translocation formation in humans and mechanisms by which acrocentric-acrocentric fusions are promoted by DNA damage and repair.

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Localization of ribosomal RNA genes on human acrocentric chromosomes

Cited by 10 publications

References 33 publications

Telomere Disruption Results in Non-Random Formation of De Novo Dicentric Chromosomes Involving Acrocentric Human Chromosomes

Telomere Disruption Results in Non-Random Formation of De Novo Dicentric Chromosomes Involving Acrocentric Human Chromosomes

Rapid detection of subtelomeric deletion/duplication by novel real-time quantitative PCR using SYBR-green dye

Nucleolar Organization, Ribosomal DNA Array Stability, and Acrocentric Chromosome Integrity Are Linked to Telomere Function

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