Numerous studies show that various genes in all kinds of organisms are transcribed discontinuously, i.e. in short bursts or pulses with periods of inactivity between them. But it remains unclear whether ribosomal DNA (rDNA), represented by multiple copies in every cell, is also expressed in such manner. In this work, we synchronized the pol I activity in the populations of tumour derived as well as normal human cells by cold block and release. Our experiments with 5-fluorouridine (FU) and BrUTP confirmed that the nucleolar transcription can be efficiently and reversibly arrested at +4°C. Then using special software for analysis of the microscopic images, we measured the intensity of transcription signal (incorporated FU) in the nucleoli at different time points after the release. We found that the ribosomal genes in the human cells are transcribed discontinuously with periods ranging from 45 min to 75 min. Our data indicate that the dynamics of rDNA transcription follows the undulating pattern, in which the bursts are alternated by periods of rare transcription events.

• MeSH
• buněčné jadérko genetika   MeSH
• epitelové buňky metabolismus   MeSH
• genetická transkripce * MeSH
• HeLa buňky MeSH
• kinetika MeSH
• lidé středního věku MeSH
• lidé MeSH
• limbus corneae cytologie   MeSH
• mrtvola MeSH
• nízká teplota MeSH
• ribozomální DNA genetika   MeSH
• ribozomy genetika   MeSH
• RNA ribozomální genetika   MeSH
• senioři MeSH
• software MeSH
• transfekce MeSH
• uridin analogy a deriváty   imunologie   metabolismus   MeSH
• uridintrifosfát analogy a deriváty   imunologie   metabolismus   MeSH
• Check Tag
• lidé středního věku MeSH
• lidé MeSH
• senioři MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• 5-bromouridine triphosphate MeSH Prohlížeč
• 5-fluorouridine MeSH Prohlížeč
• ribozomální DNA MeSH
• RNA ribozomální MeSH
• uridin MeSH
• uridintrifosfát MeSH

Nucleoli are formed on the basis of ribosomal DNA (rDNA) clusters called Nucleolus Organizer Regions (NORs). Each NOR contains multiple genes coding for RNAs of the ribosomal particles. The prominent components of the nucleolar ultrastructure, fibrillar centers (FC) and dense fibrillar components (DFC), together compose FC/DFC units. These units are centers of rDNA transcription by RNA polymerase I (pol I), as well as the early processing events, in which an essential role belongs to fibrillarin. Each FC/DFC unit probably corresponds to a single transcriptionally active gene. In this work, we transfected human-derived cells with GFP-RPA43 (subunit of pol I) and RFP-fibrillarin. Following changes of the fluorescent signals in individual FC/DFC units, we found two kinds of kinetics: 1) the rapid fluctuations with periods of 2-3 min, when the pol I and fibrillarin signals oscillated in anti-phase manner, and the intensities of pol I in the neighboring FC/DFC units did not correlate. 2) fluctuations with periods of 10 to 60 min, in which pol I and fibrillarin signals measured in the same unit did not correlate, but pol I signals in the units belonging to different nucleoli were synchronized. Our data indicate that a complex pulsing activity of transcription as well as early processing is common for ribosomal genes.

• Klíčová slova
• fibrillarin, fluctuation, pol I, rDNA, transcription pulsing,
• MeSH
• buněčné jadérko chemie   enzymologie   MeSH
• chromozomální proteiny, nehistonové chemie   metabolismus   MeSH
• DNA řízené RNA-polymerasy chemie   metabolismus   MeSH
• HeLa buňky MeSH
• imunohistochemie MeSH
• konfokální mikroskopie MeSH
• lidé MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• chromozomální proteiny, nehistonové MeSH
• DNA řízené RNA-polymerasy MeSH
• fibrillarin MeSH Prohlížeč

The essential structural components of the nucleoli, Fibrillar Centers (FC) and Dense Fibrillar Components (DFC), together compose FC/DFC units, loci of rDNA transcription and early RNA processing. In the present study we followed cell cycle related changes of these units in 2 human sarcoma derived cell lines with stable expression of RFP-PCNA (the sliding clamp protein) and GFP-RPA43 (a subunit of RNA polymerase I, pol I) or GFP-fibrillarin. Correlative light and electron microscopy analysis showed that the pol I and fibrillarin positive nucleolar beads correspond to individual FC/DFC units. In vivo observations showed that at early S phase, when transcriptionally active ribosomal genes were replicated, the number of the units in each cell increased by 60-80%. During that period the units transiently lost pol I, but not fibrillarin. Then, until the end of interphase, number of the units did not change, and their duplication was completed only after the cell division, by mid G1 phase. This peculiar mode of reproduction suggests that a considerable subset of ribosomal genes remain transcriptionally silent from mid S phase to mitosis, but become again active in the postmitotic daughter cells.

• Klíčová slova
• FC/DFC units, cell cycle, nucleolus, rDNA, replication,
• MeSH
• buněčné jadérko metabolismus   MeSH
• HeLa buňky MeSH
• lidé MeSH
• S fáze MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

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