Non-canonical structures (NCS) refer to the various forms of DNA that differ from the B-conformation described by Watson and Crick. It has been found that these structures are usual components of the genome, actively participating in its essential functions. The present review is focused on the nine kinds of NCS appearing or likely to appear in human ribosomal DNA (rDNA): supercoiling structures, R-loops, G-quadruplexes, i-motifs, DNA triplexes, cruciform structures, DNA bubbles, and A and Z DNA conformations. We discuss the conditions of their generation, including their sequence specificity, distribution within the locus, dynamics, and beneficial and detrimental role in the cell.

• Klíčová slova
• DNA quadruplexes, Non-canonical DNA, R-loops, rDNA,
• MeSH
• G-kvadruplexy * MeSH
• konformace nukleové kyseliny MeSH
• lidé MeSH
• ribozomální DNA genetika   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH
• Názvy látek
• ribozomální DNA MeSH

In human cells, ribosomal DNA (rDNA) is arranged in ten clusters of multiple tandem repeats. Each repeat is usually described as consisting of two parts: the 13 kb long ribosomal part, containing three genes coding for 18S, 5.8S and 28S RNAs of the ribosomal particles, and the 30 kb long intergenic spacer (IGS). However, this standard scheme is, amazingly, often altered as a result of the peculiar instability of the locus, so that the sequence of each repeat and the number of the repeats in each cluster are highly variable. In the present review, we discuss the causes and types of human rDNA instability, the methods of its detection, its distribution within the locus, the ways in which it is prevented or reversed, and its biological significance. The data of the literature suggest that the variability of the rDNA is not only a potential cause of pathology, but also an important, though still poorly understood, aspect of the normal cell physiology.

• Klíčová slova
• copy number, human rDNA, mutations, sequence variability,
• MeSH
• genetická variace * MeSH
• genetické lokusy MeSH
• lidé MeSH
• promotorové oblasti (genetika) genetika   MeSH
• ribozomální DNA genetika   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Názvy látek
• ribozomální DNA MeSH

Genes encoding 45S ribosomal RNA (rDNA) are known for their abundance within eukaryotic genomes and for their unstable copy numbers in response to changes in various genetic and epigenetic factors. Commonly, we understand as epigenetic factors (affecting gene expression without a change in DNA sequence), namely DNA methylation, histone posttranslational modifications, histone variants, RNA interference, nucleosome remodeling and assembly, and chromosome position effect. All these were actually shown to affect activity and stability of rDNA. Here, we focus on another phenomenon - the potential of DNA containing shortly spaced oligo-guanine tracts to form quadruplex structures (G4). Interestingly, sites with a high propensity to form G4 were described in yeast, animal, and plant rDNAs, in addition to G4 at telomeres, some gene promoters, and transposons, suggesting the evolutionary ancient origin of G4 as a regulatory module. Here, we present examples of rDNA promoter regions with extremely high potential to form G4 in two model plants, Arabidopsis thaliana and Physcomitrella patens. The high G4 potential is balanced by the activity of G4-resolving enzymes. The ability of rDNA to undergo these "structural gymnastics" thus represents another layer of the rich repertoire of epigenetic regulations, which is pronounced in rDNA due to its highly repetitive character.

• Klíčová slova
• G4, quadruplex DNA, rDNA stability, replication, ribosomal RNA genes, transcription,
• Publikační typ
• časopisecké články MeSH

In human cells, the intergenic spacers (IGS), which separate ribosomal genes, are complex approximately 30 kb-long loci. Recent studies indicate that all, or almost all, parts of IGS may be transcribed, and that at least some of them are involved in the regulation of the ribosomal DNA (rDNA) transcription, maintenance of the nucleolar architecture, and response of the cell nucleus to stress. However, since each cell contains hundreds not quite identical copies of IGS, the structure and functions of this locus remain poorly understood, and the dynamics of its products has not been specially studied. In this work, we used quantitative PCR to measure the expression levels of various rDNA regions at different times after inhibition of the transcription by Actinomycin D applied in high doses. This approach allowed us to measure real or extrapolated half-life times of some IGS loci. Our study reveals characteristic dynamic patterns suggestive of various pathways of RNA utilization and decay.

• Klíčová slova
• Intergenic spacer, Processing, RNA decay, lncRNAs, rDNA,
• MeSH
• HeLa buňky MeSH
• lidé MeSH
• mezerníky ribozomální DNA chemie   genetika   metabolismus   MeSH
• RNA analýza   biosyntéza   genetika   izolace a purifikace   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• mezerníky ribozomální DNA MeSH
• RNA MeSH

BACKGROUND: Ribosomal RNA (rRNA) accounts for the majority of the RNA in eukaryotic cells, and is encoded by hundreds to thousands of nearly identical gene copies, only a subset of which are active at any given time. In Arabidopsis thaliana, 45S rRNA genes are found in two large ribosomal DNA (rDNA) clusters and little is known about the contribution of each to the overall transcription pattern in the species. RESULTS: By taking advantage of genome sequencing data from the 1001 Genomes Consortium, we characterize rRNA gene sequence variation within and among accessions. Notably, variation is not restricted to the pre-rRNA sequences removed during processing, but it is also present within the highly conserved ribosomal subunits. Through linkage mapping we assign these variants to a particular rDNA cluster unambiguously and use them as reporters of rDNA cluster-specific expression. We demonstrate that rDNA cluster-usage varies greatly among accessions and that rDNA cluster-specific expression and silencing is controlled via genetic interactions between entire rDNA cluster haplotypes (alleles). CONCLUSIONS: We show that rRNA gene cluster expression is controlled via complex epistatic and allelic interactions between rDNA haplotypes that apparently regulate the entire rRNA gene cluster. Furthermore, the sequence polymorphism we discovered implies that the pool of rRNA in a cell may be heterogeneous, which could have functional consequences.

• Klíčová slova
• Dominance, Epistasis, Ribosomes, Transcription, rRNA genes,
• MeSH
• alely MeSH
• Arabidopsis genetika   MeSH
• genetická epistáze * MeSH
• haplotypy MeSH
• multigenová rodina * MeSH
• regulace genové exprese u rostlin * MeSH
• RNA ribozomální genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, N.I.H., Extramural MeSH
• Názvy látek
• RNA ribozomální MeSH
• RNA, ribosomal, 45S MeSH Prohlížeč

Nucleoli are formed on the basis of ribosomal genes coding for RNAs of ribosomal particles, but also include a great variety of other DNA regions. In this article, we discuss the characteristics of ribosomal DNA: the structure of the rDNA locus, complex organization and functions of the intergenic spacer, multiplicity of gene copies in one cell, selective silencing of genes and whole gene clusters, relation to components of nucleolar ultrastructure, specific problems associated with replication. We also review current data on the role of non-ribosomal DNA in the organization and function of nucleoli. Finally, we discuss probable causes preventing efficient visualization of DNA in nucleoli.

• Klíčová slova
• DNA staining, NADs, Nucleolus, Replication, Transcription activity, rDNA,
• MeSH
• buněčné jadérko genetika   metabolismus   MeSH
• lidé MeSH
• ribozomální DNA genetika   metabolismus   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Názvy látek
• ribozomální DNA MeSH

We analyzed nuclear ribosomal DNA (rDNA) transcription and chromatin condensation in individuals from several populations of Tragopogon mirus and T. miscellus, allotetraploids that have formed repeatedly within only the last 80 years from T. dubius and T. porrifolius and T. dubius and T. pratensis, respectively. We identified populations with no (2), partial (2), and complete (4) nucleolar dominance. It is probable that epigenetic regulation following allopolyploidization varies between populations, with a tendency toward nucleolar dominance by one parental homeologue. Dominant rDNA loci are largely decondensed at interphase while silent loci formed condensed heterochromatic regions excluded from nucleoli. Those populations where nucleolar dominance is fixed are epigenetically more stable than those with partial or incomplete dominance. Previous studies indicated that concerted evolution has partially homogenized thousands of parental rDNA units typically reducing the copy numbers of those derived from the T. dubius diploid parent. Paradoxically, despite their low copy number, repeats of T. dubius origin dominate rDNA transcription in most populations studied, i.e., rDNA units that are genetic losers (copy numbers) are epigenetic winners (high expression).

• MeSH
• chromatin genetika   MeSH
• diploidie MeSH
• DNA primery genetika   MeSH
• DNA rostlinná genetika   MeSH
• exprese genu MeSH
• genová dávka MeSH
• molekulární evoluce MeSH
• molekulární sekvence - údaje MeSH
• organizátor jadérka genetika   MeSH
• polymorfismus konformace jednovláknové DNA MeSH
• polyploidie MeSH
• populační genetika MeSH
• ribozomální DNA genetika   MeSH
• rostlinné geny MeSH
• sekvence nukleotidů MeSH
• Tragopogon genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Geografické názvy
• Idaho MeSH
• Washington MeSH
• Názvy látek
• chromatin MeSH
• DNA primery MeSH
• DNA rostlinná MeSH
• ribozomální DNA MeSH