Differential amphiplasty and the control of ribosomal RNA synthesis

Wallace, H.; Langridge, William H. R.

doi:10.1038/hdy.1971.66

Cited by 76 publications

(41 citation statements)

References 38 publications

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“…The understanding of NORs as loci composed of many hundreds of rRNA genes explained McClintock's obervation that an NOR can be split and yet retain nucleolus organizer function, which was an early indication that the information at the locus was redundant. Moreover, the molecular understanding of the NOR suggested that Navashin's observations of differential secondary constriction formation might be a visible manifestation of differential rRNA gene transcription at NORs derived from the two progenitors [16], a prediction that was subsequently verified by Honjo and Reeder in studies of Xenopus (frog) hybrids [8].…”

mentioning

confidence: 90%

rRNA gene silencing and nucleolar dominance: Insights into a chromosome-scale epigenetic on/off switch

Preuss

Pikaard

2007

Biochimica et Biophysica Acta (BBA) - Gene Structure and Expres

135

105

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Ribosomal RNA (rRNA) gene transcription accounts for most of the RNA in prokaryotic and eukaryotic cells. In eukaryotes, there are hundreds (to thousands) of rRNA genes tandemly repeated head-to-tail within nucleolus organizer regions (NORs) that span millions of basepairs. These nucleolar rRNA genes are transcribed by RNA Polymerase I (Pol I) and their expression is regulated according to the physiological need for ribosomes. Regulation occurs at several levels, one of which is an epigenetic on/off switch that controls the number of active rRNA genes. Additional mechanisms then fine-tune transcription initiation and elongation rates to dictate the total amount of rRNA produced per gene. In this review, we focus on the DNA and histone modifications that comprise the epigenetic on/off switch. In both plants and animals, this system is important for controlling the dosage of active rRNA genes. The dosage control system is also responsible for the chromatinmediated silencing of one parental set of rRNA genes in genetic hybrids, a large-scale epigenetic phenomenon known as nucleolar dominance.Keywords epigenetic phenomena; RNA polymerase I; DNA methylation; cytosine methylation; histone methylation; histone deacetylation; histone deacetylase; transcription; ribosomal RNA; nucleolus; nucleolus organizer region Large scale cytological effects of rRNA gene regulation: nucleolus and secondary constriction formationThe most prominent feature of a eukaryotic nucleus during interphase is the nucleolus (Figure 1), a region that contains relatively little chromosomal DNA but is rich in RNAs, proteins and ribonucleoprotein particles, including the large and small ribosome subunits as they undergo assembly [1][2][3]. The location of a nucleolus is not determined randomly; instead its formation is determined by the position of a discrete chromosomal locus known as a nucleolus organizer region, or NOR [4]. This fact was discovered based on an intriguing property: upon condensation of chromosomes at metaphase, NORs fail to condense to the same extent as surrounding chromosomal sequences and thus give rise to "secondary constrictions", with "primary constrictions" being defined as the centromeres (see Figure 1). Heitz initially noted that nucleoli form at, or very near, the sites of secondary constrictions [5] and McClintock soon thereafter obtained direct evidence [6]. She identified a maize line in which a chromosome break at or near the secondary constriction on chromosome 9, followed by translocation of one *Author to whom correspondence should be addressed: pikaard@biology2.wustl.edu, phone: Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the conte...

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mentioning

confidence: 90%

rRNA gene silencing and nucleolar dominance: Insights into a chromosome-scale epigenetic on/off switch

Preuss

Pikaard

2007

Biochimica et Biophysica Acta (BBA) - Gene Structure and Expres

135

105

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“…Nucleolar dominance is a phenomenon in plant (Brassica, Arabidopsis, Pikaard, 1999) and animal (Xenopus, Honjo and Reeder, 1973) hybrids in which one parental set of ribosomal 45S RNA genes is transcribed, but the hundreds of rRNA genes inherited from the other parent are transcriptionally silent. Possibly, the same repression mechanisms that control the nucleolar dominance in hybrids may be responsible for the control of the number of active genes within a pure species (Wallace and Langridge, 1971), and they probably reflect a dosage-compensation mechanism (Pikaard, 1999). The absence of 5S RNA polymorphism, up to now, prevented the search for a "5S dominance," but the high number of 5S and 45S rDNA units indicates a dosage compensation mechanism for 5S genes and could explain the noncontribution of some 5S loci to the 5S RNA pool.…”

Section: Genome Research 139mentioning

confidence: 99%

Analysis of the 5S RNA Pool in Arabidopsis thaliana: RNAs Are Heterogeneous and Only Two of the Genomic 5S Loci Produce Mature 5S RNA

Cloix¹,

Tutois²,

Yukawa³

et al. 2001

Genome Res.

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One major 5S RNA, 120 bases long, was revealed by an analysis of mature 5S RNA from tissues, developmental stages, and polysomes in Arabidopsis thaliana. Minor 5S RNA were also found, varying from the major one by one or two base substitutions; 5S rDNA units from each 5S array of the Arabidopsis genome were isolated by PCR using CIC yeast artificial chromosomes (YACs) mapped on the different loci. By using a comparison of the 5S DNA and RNA sequences, we could show that both major and minor 5S transcripts come from only two of the genomic 5S loci: chromosome 4 and chromosome 5 major block. Other 5S loci are either not transcribed or produce rapidly degraded 5S transcripts. Analysis of the 5Ј-and 3Ј-DNA flanking sequence has permitted the definition of specific signatures for each 5S rDNA array.

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“…Nuclear run-on assays later suggested that transcription of only one parental set of rRNA genes is the molecular explanation for nucleolar dominance (11,12). Presumably, transcription of rRNA genes during interphase somehow reduces their condensation at metaphase, thus explaining the appearance of secondary constrictions (13).…”

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confidence: 99%

Natural variation in nucleolar dominance reveals the relationship between nucleolus organizer chromatin topology and rRNA gene transcription in Arabidopsis

Pontes¹,

Lawrence²,

Neves³

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

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In genetic hybrids, nucleolus formation on chromosomes inherited from only one parent is the epigenetic phenomenon, nucleolar dominance. By using Arabidopsis suecica, the allotetraploid hybrid of Arabidopsis thaliana and Arabidopsis arenosa, natural variation in nucleolar dominance was found to occur, providing a unique opportunity to examine homologous nucleolus organizer regions (NORs) in their active and inactive states. In A. suecica strain LC1, NORs derived from A. arenosa are active, whereas A. thalianaderived NORs are silenced. In A. suecica strain 9502, NORs of both parental species are active. When active, NORs are partially, but not fully, decondensed. Both active and inactive LC1 NORs colocalize with the nucleolus, contradicting the long-standing assumption that rRNA gene transcription drives nucleolus association. Collectively, these observations clarify the relationships among NOR chromatin topology, rRNA gene transcription, and NOR-nucleolus associations. A. suecica strains LC1 and 9502 have each lost one pair of A. thaliana NORs during evolution, and amplified fragmentlength polymorphism analysis further indicates that these strains are genetically very similar. These data suggest that nucleolar dominance can result from subtle genetic or epigenetic variation but is not a trait fundamental to a given interspecies hybrid combination.

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Differential amphiplasty and the control of ribosomal RNA synthesis

Cited by 76 publications

References 38 publications

rRNA gene silencing and nucleolar dominance: Insights into a chromosome-scale epigenetic on/off switch

rRNA gene silencing and nucleolar dominance: Insights into a chromosome-scale epigenetic on/off switch

Analysis of the 5S RNA Pool in Arabidopsis thaliana: RNAs Are Heterogeneous and Only Two of the Genomic 5S Loci Produce Mature 5S RNA

Natural variation in nucleolar dominance reveals the relationship between nucleolus organizer chromatin topology and rRNA gene transcription in Arabidopsis

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