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Neves, Nuno; Silva, M.; Heslop‐Harrison, J.; Viegas, Wanda

doi:10.1023/a:1018470208730

Cited by 58 publications

(23 citation statements)

References 17 publications

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“…Another possibility is that aza-dC and histone deacetylase inhibitors derepress silenced rRNA genes by activating a regulatory locus that controls the transcriptional competence of the NOR. Involvement of other loci is consistent with studies showing loss of nucleolar dominance because of chromosome substitution in wheat and triticale (18,36) or because of chromosome rearrangements in Drosophila (38) and barley (47). Our current study suggests that such hypothetical regulatory loci are unlikely to encode species-specific transcription factors.…”

Section: Discussionsupporting

confidence: 90%

“…An effect of genome dosage on the number of nucleoli visible at interphase in allopolyploid Ribes (gooseberry and black currant) hybrids was reported, suggesting that dominance could be overcome by increasing the number of underdominant NORs (35). Studies in wheat have shown also that NOR activity is variable in different chromosome addition lines, suggesting that genes unlinked to the NORs can affect their activity (18,36). However, the demonstration that normally dominant rRNA genes can be made underdominant is unprecedented.…”

Section: Discussionmentioning

confidence: 99%

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Gene dosage and stochastic effects determine the severity and direction of uniparental ribosomal RNA gene silencing (nucleolar dominance) in Arabidopsis allopolyploids

Chen

Comai

Pikaard

1998

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

209

169

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Nucleolar dominance is an epigenetic phenomenon in which one parental set of ribosomal RNA (rRNA) genes is silenced in an interspecific hybrid. In natural Arabidopsis suecica, an allotetraploid (amphidiploid) hybrid of Arabidopsis thaliana and Cardaminopsis arenosa, the A. thaliana rRNA genes are repressed. Interestingly, A. thaliana rRNA gene silencing is variable in synthetic Arabidopsis suecica F 1 hybrids. Two generations are needed for A. thaliana rRNA genes to be silenced in all lines, revealing a species-biased direction but stochastic onset to nucleolar dominance. Backcrossing synthetic A. suecica to tetraploid A. thaliana yielded progeny with active A. thaliana rRNA genes and, in some cases, silenced C. arenosa rRNA genes, showing that the direction of dominance can be switched. The hypothesis that naturally dominant rRNA genes have a superior binding affinity for a limiting transcription factor is inconsistent with dominance switching. Inactivation of a species-specific transcription factor is argued against by showing that A. thaliana and C. arenosa rRNA genes can be expressed transiently in the other species. Transfected A. thaliana genes are also active in A. suecica protoplasts in which chromosomal A. thaliana genes are repressed. Collectively, these data suggest that nucleolar dominance is a chromosomal phenomenon that results in coordinate or cooperative silencing of rRNA genes.Nucleolar dominance was among the first recognized epigenetic phenomena, discovered in interspecific hybrids in the plant genus Crepis. Navashin noted secondary constrictions at metaphase on D chromosomes inherited from one Crepis species, but not on the D chromosome from the other species (1, 2). Navashin's contemporary, McClintock, showed that these secondary constrictions are sites where nucleoli were organized in the preceding interphase (3). Decades later, nucleolus organizer regions (NORs) were identified as loci where genes encoding the precursor of the 18S, 5.8S, and 25-28S ribosomal RNAs are tandemly arrayed (4-7). Thus, nucleolar dominance was shown ultimately to result from uniparental rRNA gene expression (8).Nucleolar dominance occurs throughout the plant and animal kingdoms (9, 10) via mechanisms that remain unclear. Navashin noted that dominant NOR-bearing chromosomes could be contributed through the pollen or egg (2), ruling out maternal or paternal effects. A dominant D chromosome could also be contributed as part of an incomplete chromosome set. In Drosophila melanogaster ϫ Drosophila simulans hybrids, the D. melanogaster NORs on the X and Y chromosomes are dominant over the single NOR on the D. simulans X (11). In hybrid XO males lacking a D. melanogaster sex chromosome, but containing all autosomes, the D. simulans NOR is active. These results indicate that NOR-bearing chromosomes must be present for nucleolar dominance to occur.

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Section: Discussionsupporting

confidence: 90%

Section: Discussionmentioning

confidence: 99%

Gene dosage and stochastic effects determine the severity and direction of uniparental ribosomal RNA gene silencing (nucleolar dominance) in Arabidopsis allopolyploids

Chen

Comai

Pikaard

1998

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

209

169

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“…The latter studies have also shown that plasmid-borne rRNA genes can be efficiently transcribed in hybrid cells in which their endogenous chromosomal counterparts are repressed, indicating that nucleolar dominance is strictly a chromosomal phenomenon (17). Chromosome rearrangements that move NORs to new chromosomal environments, or that delete sequences adjacent to NORs without altering rRNA gene sequences, can also induce or negate nucleolar dominance (18)(19)(20)(21). Collectively, these data suggest that the chromosomal context of an NOR is an important determinant of nucleolar dominance, for reasons that are currently unknown.…”

mentioning

confidence: 97%

Restricted chromosomal silencing in nucleolar dominance

Lewis

Pikaard

2001

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

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Failure of one parent's chromosomes to organize nucleoli in an interspecific hybrid is an epigenetic phenomenon known as nucleolar dominance. Selective gene silencing on a scale of millions of bp is known to be involved, but the full extent to which nucleolus organizer region (NOR)-bearing chromosomes are inactivated beyond the NORs is unknown. Aided by genome sequence data for Arabidopsis thaliana, we have mapped the extent of nucleolar dominance-induced silencing in Arabidopsis suecica, the allotetraploid hybrid of A. thaliana and Arabidopsis arenosa. Using a sensitive reverse transcription PCR assay, we show that the four A. thaliana NORs, each Ϸ4 Mbp in size, are Ϸ99.5% silenced in A. suecica vegetative leaves, whereas the NORs inherited from A. arenosa remain fully active. The two A. thaliana NORs, NOR2 and NOR4, abut the telomeres on chromosomes 2 and 4, thus there are no genes distal to the NORs. The three protein-coding genes nearest NOR4 on its centromere-proximal side, the closest of which is only 3.1 kb from rRNA gene sequences, are shown to be transcribed in the hybrid despite the silencing of the adjacent Ϸ4-Mbp NOR. These data argue against hypotheses in which NOR inactivation is attributed to the spread of silencing from adjacent chromosomal regions, but favor models in which NORs or rRNA genes are the targets of regulation.epigenetic phenomena ͉ ribosomal RNA gene ͉ nucleolus organizer ͉ polyploidy ͉ genetic hybrid

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“…the changes in chromatin organization are of great importance for the control of rRNA gene repression in inter-specific hybrids (12,16,24). one could expect that the same epigenetic mechanisms may also be involved in differential expression of the noRs in cytologically reconstructed barley karyotypes.…”

Section: Introductionmentioning

confidence: 99%