Silencing speaks up

Rivier, David H.; Pillus, Lorraine

doi:10.1016/0092-8674(94)90373-5

Cited by 23 publications

(9 citation statements)

References 22 publications

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“…Modi®cation of gene expression by alteration of chromatin packaging has been described in organisms as diverse as Saccharomyces cerevisiae (Rivier and Pillus 1994;Palladino and Gasser 1994;Roth 1995), Caenorhabditis elegans (Ryner and Swain 1995) and Drosophila melanogaster (Heniko 1990;Paro 1993). In ®lamentous fungi (Selker 1990), mammals Bestor and Tycko 1996) and plants (Matzke and Matzke 1993;Meyer and Saedler 1996), alterations in epigenetic states are frequently accompanied by changes in DNA methylation, which might act as an auxiliary mechanism to preserve and reinforce the heritability of epigenetic changes mediated by chromatin modi®cation.…”

Section: Discussionmentioning

confidence: 98%

Condensation of chromatin in transcriptional regions of an inactivated plant transgene: evidence for an active role of transcription in gene silencing

1997

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The chromatin structures of two epigenetic alleles of a transgene were investigated by measuring the local accessibility of transgene chromatin to endonucleases. The two epialleles represented the active, hypomethylated state of a transgene in line 17-I of Petunia hybrida, and a transcriptionally inactive, hypermethylated derivative of the same transgene in line 17-IV. In nuclear preparations the inactive epiallele was significantly less sensitive to DNasel digestion and nuclease S7 digestion than the transcriptionally active epiallele, whereas no significant differences in accessibility were observed between naked DNA samples of the two epialleles. Our data suggest that a condensed chromatin structure is specifically imposed on transcribed regions of the construct in line 17-IV. In contrast, in both epialleles the plasmid region of the transgene, which is not transcriptionally active in plants, retains the same accessibility to endonucleases as the chromosomal integration site. These data suggest that transcriptional inactivation is linked to the process of transcription, and imply that control of transgene expression via the use of inducible or tissue-specific promoters might prevent transgene silencing and conserve the active state of transgenes during sexual propagation.

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Section: Discussionmentioning

confidence: 98%

Condensation of chromatin in transcriptional regions of an inactivated plant transgene: evidence for an active role of transcription in gene silencing

1997

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“…Although the molecular details remain to be elucidated, it is generally believed that silencing in these systems (i.e. the formation of a transcriptionally inactive domain) is based on the spreading of a heterochromatin-like structure originating from inactivation centers [Rivier and Pillus (1994) and references therein].…”

Section: Discussionmentioning

confidence: 99%

Silencing of Escherichia coli bgl promoter by flanking sequence elements.

Schnetz

1995

The EMBO Journal

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Silencing of a transcriptional unit by flanking sequence elements has so far only been described for eukaryotic systems. Here, a similar system is described in bacteria. The Escherichia coli bgl operon (P-glucoside utilization)is normally cryptic due to very low promoter activity. However, low activity is not attributable to the quality of the promoter itself but is caused by its chromosomal context. The bgl promoter is perfectly active when tested outside of its normal context of a stretch of a few hundred base pairs. In addition, other promoters become inactivated when placed into the bgl region. Both the deletion of an upstream sequence element and the replacement of sequences located downstream result in promoter de-repression, demonstrating that silencing of promoters within this stretch of DNA in vivo is an active process brought about by the combined action of upstream and downstream chromosomal elements.

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“…Ten Lohuis et al (1995) showed that in petunia, repetitive DNA that carries a hot spot for methylation induces variegated expression of adjacent sequences, which was suggested to be due to heterochromatinmediated gene inactivation. Genes in inactive or heterochromatin domains are not considered to be accessible to the regulation, either activation or repression, that is afforded by DNA elements in promoters (Lewin, 1994;Rivier and Pillus, 1994).…”

Section: A Refined Model For Rna-mediated Virus Resistancementioning

confidence: 99%

RNA-Mediated Virus Resistance: Role of Repeated Transgenes and Delineation of Targeted Regions.

Sijen¹,

Wellink²,

Hiriart³

et al. 1996

Plant Cell

173

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Resistance to cowpea mosaic virus (CPMV) in transgenic Nicotiana benthamiana plants is RNA mediated. In resistant CPMV movement protein (MP) gene-transformed lines, transgene steady state mRNA levels were low, whereas nuclear transcription rates were high, implying that a post-transcriptional gene-silencing mechanism is at the base of the resistance. The silencing mechanism can also affect potato virus X (PVX) RNAs when they contain CPMV MP gene sequences.In particular, sequences situated in the 3 ' part of the transcribed region of the MP transgene direct elimination of recombinant PVX genomes. Remarkabty, successive portions of this 3' part, which can be as small as 60 nucleotides; all tag PVX genomes for degradation. These observations suggest that the entire 3' part of the MP transgene mRNA is the initial target of the silencing mechanism. The arrangement of transgenes in the plant genome plays an important role in establishing resistance because the frequency of resistant lines increased from 20 to 60% when transformed with a transgene containing a direct repeat of MP sequences rather than a single MP transgene. Interestingly, we detected strong methylation in all of the plants containing directly repeated MP sequences. In sensitive lines, only the promoter region was found to be heavily methylated, whereas in resistant lines, only the transcribed region was strongly methylated.

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Silencing speaks up

Cited by 23 publications

References 22 publications

Condensation of chromatin in transcriptional regions of an inactivated plant transgene: evidence for an active role of transcription in gene silencing

Condensation of chromatin in transcriptional regions of an inactivated plant transgene: evidence for an active role of transcription in gene silencing

Silencing of Escherichia coli bgl promoter by flanking sequence elements.

RNA-Mediated Virus Resistance: Role of Repeated Transgenes and Delineation of Targeted Regions.

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