Nucleolus organizer region

Last updated
The location of NORs and the nucleolar cycle in human cells. ExternalImageImagec.jpg
The location of NORs and the nucleolar cycle in human cells.

Nucleolus organizer regions (NORs) are chromosomal regions crucial for the formation of the nucleolus. In humans, the NORs are located on the short arms of the acrocentric chromosomes 13, 14, 15, 21 and 22, the genes RNR1, RNR2, RNR3, RNR4, and RNR5 respectively. [1] These regions code for 5.8S, 18S, and 28S ribosomal RNA. [1] The NORs are "sandwiched" between the repetitive, heterochromatic DNA sequences of the centromeres and telomeres. [1] The exact sequence of these regions is not included in the human reference genome as of 2016 [1] or the GRCh38.p10 released January 6, 2017. [2] On 28 February 2019, GRCh38.p13 was released, which added the NOR sequences for the short arms of chromosomes 13, 14, 15, 21, and 22. [3] However, it is known that NORs contain tandem copies of ribosomal DNA (rDNA) genes. [1] Some sequences of flanking sequences proximal and distal to NORs have been reported. [4] The NORs of a loris have been reported to be highly variable. [5] There are also DNA sequences related to rDNA that are on other chromosomes and may be involved in nucleoli formation. [6]

Contents

Silver-stained nucleolus organizer region (arrow) at the tip of a chromosome of the Gecko Lepidodactylus lugubris NORAgc.jpg
Silver-stained nucleolus organizer region (arrow) at the tip of a chromosome of the Gecko Lepidodactylus lugubris

Visualization

The DJ forms a perinucleolar anchor for rDNA repeats. ExternalImageImagec.jpg
The DJ forms a perinucleolar anchor for rDNA repeats.

Barbara McClintock first described the "nucleolar-organizing body" in Zea mays in 1934. [7] In karyotype analysis, a silver stain can be used to identify the NOR. [8] [9] NORs can also be seen in nucleoli using silver stain, and that is being used to investigate cancerous changes. [10] [11] [12] NORs can also be seen using antibodies directed against the protein UBF, which binds to NOR DNA. [1]

Molecular biology

In addition to UBF, NORs also bind to ATRX protein, treacle, sirtuin-7 and other proteins. [1] UBF has been identified as a mitotic "bookmark" of expressed rDNA, which allows it to resume transcription quickly after mitosis. [1] The distal flanking junction (DJ) of the NORs has been shown to associate with the periphery of nucleoli. [4] rDNA operons in Escherichia coli have been found to cluster near each other, similar to a eukaryotic nucleolus. [13]

See also

Related Research Articles

<span class="mw-page-title-main">Nucleolus</span> Largest structure in the nucleus of eukaryotic cells

The nucleolus is the largest structure in the nucleus of eukaryotic cells. It is best known as the site of ribosome biogenesis, which is the synthesis of ribosomes. The nucleolus also participates in the formation of signal recognition particles and plays a role in the cell's response to stress. Nucleoli are made of proteins, DNA and RNA, and form around specific chromosomal regions called nucleolar organizing regions. Malfunction of nucleoli can be the cause of several human conditions called "nucleolopathies" and the nucleolus is being investigated as a target for cancer chemotherapy.

<span class="mw-page-title-main">Ribosomal DNA</span>

Ribosomal DNA (rDNA) is a DNA sequence that codes for ribosomal RNA. These sequences regulate transcription initiation and amplification, and contain both transcribed and non-transcribed spacer segments.

<span class="mw-page-title-main">Treacle protein</span> Protein-coding gene in the species Homo sapiens

Treacle protein is a protein that in humans is encoded by the TCOF1 gene.

<span class="mw-page-title-main">Satellite chromosome</span> Type of chromosome with a special constriction

Satellite or SAT chromosomes are chromosomes that contain secondary constructs that serve as identification. They are observed in Acrocentric chromosomes. In addition to the centromere, one or more secondary constrictions can be observed in some chromosomes at metaphase. These chromosomes are called satellite chromosomes. In humans it is usually associated with the short arm of an acrocentric chromosome, such as in the chromosomes 13, 14, 15, 21, & 22. The Y chromosome can also contain satellites, although these are thought to be translocations from autosomes. The secondary constriction always keeps its position, so it can be used as markers to identify specific chromosomes.

<span class="mw-page-title-main">UBTF</span> Protein-coding gene in the species Homo sapiens

Upstream binding transcription factor (UBTF), or upstream binding factor (UBF), is a protein that in humans is encoded by the UBTF gene.

<span class="mw-page-title-main">60S ribosomal protein L7a</span> Protein found in humans

60S ribosomal protein L7a is a protein that in humans is encoded by the RPL7A gene.

<span class="mw-page-title-main">PES1</span> Protein-coding gene in the species Homo sapiens

Pescadillo homolog is a protein that in humans is encoded by the PES1 gene.

<span class="mw-page-title-main">IMP3</span> Protein-coding gene in the species Homo sapiens

U3 small nucleolar ribonucleoprotein protein IMP3 is a protein that in humans is encoded by the IMP3 gene.

<span class="mw-page-title-main">NOL5A</span> Protein-coding gene in the species Homo sapiens

Nucleolar protein 56 is a protein that in humans is encoded by the NOP56 gene.

<span class="mw-page-title-main">60S ribosomal protein L10a</span> Protein found in humans

60S ribosomal protein L10a is a protein that in humans is encoded by the RPL10A gene.

<span class="mw-page-title-main">60S ribosomal protein L13a</span> Protein found in humans

60S ribosomal protein L13a is a protein that in humans is encoded by the RPL13A gene.

<span class="mw-page-title-main">40S ribosomal protein S20</span> Protein-coding gene in the species Homo sapiens

40S ribosomal protein S20 is a protein that in humans is encoded by the RPS20 gene.

<span class="mw-page-title-main">NOLA2</span> Protein-coding gene in the species Homo sapiens

H/ACA ribonucleoprotein complex subunit 2 is a protein that in humans is encoded by the NHP2 gene.

<span class="mw-page-title-main">40S ribosomal protein S8</span> Protein-coding gene in the species Homo sapiens

40S ribosomal protein S8 is a protein that in humans is encoded by the RPS8 gene.

<span class="mw-page-title-main">RRP1</span> Protein-coding gene in the species Homo sapiens

Ribosomal RNA processing protein 1 homolog A is a protein that in humans is encoded by the RRP1 gene.

<span class="mw-page-title-main">60S ribosomal protein L15</span> Protein found in humans

60S ribosomal protein L15 is a protein that in humans is encoded by the RPL15 gene.

<span class="mw-page-title-main">60S ribosomal protein L9</span> Protein found in humans

60S ribosomal protein L9 is a protein that in humans is encoded by the RPL9 gene.

<span class="mw-page-title-main">Probable ribosome biogenesis protein RLP24</span> Protein-coding gene in the species Homo sapiens

Probable ribosome biogenesis protein RLP24 is a protein that in humans is encoded by the RSL24D1 gene.

<span class="mw-page-title-main">IMP4</span> Protein-coding gene in the species Homo sapiens

U3 small nucleolar ribonucleoprotein protein IMP4 is a protein that in humans is encoded by the IMP4 gene.

References

  1. 1 2 3 4 5 6 7 8 McStay B (2016). "Nucleolar organizer regions: genomic 'dark matter' requiring illumination". Genes & Development. 30 (14): 1598–610. doi:10.1101/gad.283838.116. PMC   4973289 . PMID   27474438.
  2. ↑ anon. "Human Genome Overview". ncbi.nlm.nih.gov/. Genome Reference Consortium. Retrieved 17 June 2017.
  3. ↑ The Genome Reference Consortium. "GRCh38.p13 has been released". GenomeRef. Retrieved 16 August 2019.
  4. 1 2 Floutsakou I, Agrawal S, Nguyen TT, Seoighe C, Ganley AR, McStay B (2013). "The shared genomic architecture of human nucleolar organizer regions". Genome Research. 23 (12): 2003–12. doi:10.1101/gr.157941.113. PMC   3847771 . PMID   23990606.
  5. ↑ Baicharoen S, Hirai Y, Srikulnath K, Kongprom U, Hirai H (2016). "Hypervariability of Nucleolus Organizer Regions in Bengal Slow Lorises, Nycticebus bengalensis (Primates, Lorisidae)". Cytogenetic and Genome Research. 149 (4): 267–273. doi:10.1159/000449145. PMID   27648559.
  6. ↑ Kupriyanova NS, Netchvolodov KK, Sadova AA, Cherepanova MD, Ryskov AP (2015). "Non-canonical ribosomal DNA segments in the human genome, and nucleoli functioning". Gene. 572 (2): 237–42. doi:10.1016/j.gene.2015.07.019. PMID   26164756.
  7. ↑ McClintock B (1934). "The relation of a particular chromosomal element to the development of the nucleoli in Zea mays". Zeitschrift für Zellforschung und Mikroskopische Anatomie. 21 (2): 294–328. doi:10.1007/BF00374060.
  8. ↑ Bloom SE, Goodpasture C (October 1976). "An improved technique for selective silver staining of nucleolar organizer regions in human chromosomes". Human Genetics. 34 (2): 199–206. doi:10.1007/bf00278889. PMID   63440.
  9. ↑ Lau YF, Pfeiffer RA, Arrighi FE, Hsu TC (January 1978). "Combination of silver and fluorescent staining for metaphase chromosomes". American Journal of Human Genetics. 30 (1): 76–9. PMC   1685453 . PMID   74950.
  10. ↑ Stepan A, Simionescu C, Pirici D, Ciurea R, Margaritescu C (2015). "Fractal analysis and the diagnostic usefulness of silver staining nucleolar organizer regions in prostate adenocarcinoma". Analytical Cellular Pathology. 2015: 250265. doi: 10.1155/2015/250265 . PMC   4558419 . PMID   26366372.
  11. ↑ Gundog M, Yildiz OG, Imamoglu N, Aslan D, Aytekin A, Soyuer I, Soyuer S (2015). "Prognostic Significance of Two Dimensional AgNOR Evaluation in Local Advanced Rectal Cancer Treated with Chemoradiotherapy". Asian Pacific Journal of Cancer Prevention. 16 (18): 8155–61. doi: 10.7314/apjcp.2015.16.18.8155 . PMID   26745054.
  12. ↑ Sowmya GV, Nahar P, Astekar M, Agarwal H, Singh MP (2017). "Analysis of silver binding nucleolar organizer regions in exfoliative cytology smears of potentially malignant and malignant oral lesions". Biotechnic & Histochemistry. 92 (2): 115–121. doi:10.1080/10520295.2017.1283055. PMID   28296547.
  13. ↑ Gaal T, Bratton BP, Sanchez-Vazquez P, Sliwicki A, Sliwicki K, Vegel A, Pannu R, Gourse RL (2016). "Colocalization of distant chromosomal loci in space in E. coli: a bacterial nucleolus". Genes & Development. 30 (20): 2272–2285. doi:10.1101/gad.290312.116. PMC   5110994 . PMID   27898392.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.