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Stress-induced activation of heterochromatic transcription.

Tittel-Elmer M, Bucher E, Broger L, Mathieu O, Paszkowski J, Vaillant I - PLoS Genet. (2010)

Bottom Line: We have found that heterochromatin-associated silencing in Arabidopsis plants subjected to a particular temperature regime is released in a genome-wide manner.This occurs without alteration of repressive epigenetic modifications and does not involve common epigenetic mechanisms.Thus, our results reveal new regulatory aspects of transcriptional repression in constitutive heterochromatin and open up possibilities to identify the molecular mechanisms involved.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Biology, University of Geneva, Geneva, Switzerland.

ABSTRACT
Constitutive heterochromatin comprising the centromeric and telomeric parts of chromosomes includes DNA marked by high levels of methylation associated with histones modified by repressive marks. These epigenetic modifications silence transcription and ensure stable inheritance of this inert state. Although environmental cues can alter epigenetic marks and lead to modulation of the transcription of genes located in euchromatic parts of the chromosomes, there is no evidence that external stimuli can globally destabilize silencing of constitutive heterochromatin. We have found that heterochromatin-associated silencing in Arabidopsis plants subjected to a particular temperature regime is released in a genome-wide manner. This occurs without alteration of repressive epigenetic modifications and does not involve common epigenetic mechanisms. Such induced release of silencing is mostly transient, and rapid restoration of the silent state occurs without the involvement of factors known to be required for silencing initiation. Thus, our results reveal new regulatory aspects of transcriptional repression in constitutive heterochromatin and open up possibilities to identify the molecular mechanisms involved.

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Related in: MedlinePlus

ITS-induced transcriptional activation occurs without detectable changes in the levels of DNA methylation at endogenous loci.(A) Southern blot analysis of DNA methylation at 106B, 5S and 180-bp repeats using the indicated methylation-sensitive restriction endonucleases. (B) Southern blot analysis of DNA methylation at MULE F19G14 was performed by digesting genomic DNAs with SspI (methylation insensitive), followed by digestion with the indicated methylation-sensitive restriction endonucleases.
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pgen-1001175-g004: ITS-induced transcriptional activation occurs without detectable changes in the levels of DNA methylation at endogenous loci.(A) Southern blot analysis of DNA methylation at 106B, 5S and 180-bp repeats using the indicated methylation-sensitive restriction endonucleases. (B) Southern blot analysis of DNA methylation at MULE F19G14 was performed by digesting genomic DNAs with SspI (methylation insensitive), followed by digestion with the indicated methylation-sensitive restriction endonucleases.

Mentions: To determine possible epigenetic mechanisms associated with ITS-induced release of silencing, we first analyzed DNA methylation levels at ITS-sensitive sequences before and after ITS and CTS treatments (Figure 4). Southern blot analyses were performed on genomic DNA digested with MspI (inhibited by methylation of the outer C in the sequence CCGG), HpaII (inhibited by methylation of either C in the sequence CCGG), HaeIII (inhibited by methylation of the inner C in the sequence GGCC), NlaIII (inhibited by methylation of the C in the sequence CATG), NheI (inhibited by methylation of either C in the sequence GCTAGC) and TaiI (reporting on CG methylation). This set of experiments was performed with the Zürich ecotype, which withstands ITS conditions better than the Columbia ecotype (Figure S1). The DNA methylation-deficient mutant ddm1-5 available in this ecotype was used as a control. DNA methylation analyses revealed that ITS had no significant influence on methylation levels of cytosines located in either symmetrical (CG or CHG) or asymmetrical (CHH) contexts at the single-copy MULE-F19G14 (Figure 4B). This is in agreement with a recent finding that a treatment of 48 h at 42°C reactivates transcription of the L5 transgene and of a LINE element without significant changes in DNA methylation [26]. Importantly, DNA methylation status was also maintained at 106B, 5S and 180-bp multicopy targets all residing in constitutive heterochromatin (Figure 4A).


Stress-induced activation of heterochromatic transcription.

Tittel-Elmer M, Bucher E, Broger L, Mathieu O, Paszkowski J, Vaillant I - PLoS Genet. (2010)

ITS-induced transcriptional activation occurs without detectable changes in the levels of DNA methylation at endogenous loci.(A) Southern blot analysis of DNA methylation at 106B, 5S and 180-bp repeats using the indicated methylation-sensitive restriction endonucleases. (B) Southern blot analysis of DNA methylation at MULE F19G14 was performed by digesting genomic DNAs with SspI (methylation insensitive), followed by digestion with the indicated methylation-sensitive restriction endonucleases.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2965753&req=5

pgen-1001175-g004: ITS-induced transcriptional activation occurs without detectable changes in the levels of DNA methylation at endogenous loci.(A) Southern blot analysis of DNA methylation at 106B, 5S and 180-bp repeats using the indicated methylation-sensitive restriction endonucleases. (B) Southern blot analysis of DNA methylation at MULE F19G14 was performed by digesting genomic DNAs with SspI (methylation insensitive), followed by digestion with the indicated methylation-sensitive restriction endonucleases.
Mentions: To determine possible epigenetic mechanisms associated with ITS-induced release of silencing, we first analyzed DNA methylation levels at ITS-sensitive sequences before and after ITS and CTS treatments (Figure 4). Southern blot analyses were performed on genomic DNA digested with MspI (inhibited by methylation of the outer C in the sequence CCGG), HpaII (inhibited by methylation of either C in the sequence CCGG), HaeIII (inhibited by methylation of the inner C in the sequence GGCC), NlaIII (inhibited by methylation of the C in the sequence CATG), NheI (inhibited by methylation of either C in the sequence GCTAGC) and TaiI (reporting on CG methylation). This set of experiments was performed with the Zürich ecotype, which withstands ITS conditions better than the Columbia ecotype (Figure S1). The DNA methylation-deficient mutant ddm1-5 available in this ecotype was used as a control. DNA methylation analyses revealed that ITS had no significant influence on methylation levels of cytosines located in either symmetrical (CG or CHG) or asymmetrical (CHH) contexts at the single-copy MULE-F19G14 (Figure 4B). This is in agreement with a recent finding that a treatment of 48 h at 42°C reactivates transcription of the L5 transgene and of a LINE element without significant changes in DNA methylation [26]. Importantly, DNA methylation status was also maintained at 106B, 5S and 180-bp multicopy targets all residing in constitutive heterochromatin (Figure 4A).

Bottom Line: We have found that heterochromatin-associated silencing in Arabidopsis plants subjected to a particular temperature regime is released in a genome-wide manner.This occurs without alteration of repressive epigenetic modifications and does not involve common epigenetic mechanisms.Thus, our results reveal new regulatory aspects of transcriptional repression in constitutive heterochromatin and open up possibilities to identify the molecular mechanisms involved.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Biology, University of Geneva, Geneva, Switzerland.

ABSTRACT
Constitutive heterochromatin comprising the centromeric and telomeric parts of chromosomes includes DNA marked by high levels of methylation associated with histones modified by repressive marks. These epigenetic modifications silence transcription and ensure stable inheritance of this inert state. Although environmental cues can alter epigenetic marks and lead to modulation of the transcription of genes located in euchromatic parts of the chromosomes, there is no evidence that external stimuli can globally destabilize silencing of constitutive heterochromatin. We have found that heterochromatin-associated silencing in Arabidopsis plants subjected to a particular temperature regime is released in a genome-wide manner. This occurs without alteration of repressive epigenetic modifications and does not involve common epigenetic mechanisms. Such induced release of silencing is mostly transient, and rapid restoration of the silent state occurs without the involvement of factors known to be required for silencing initiation. Thus, our results reveal new regulatory aspects of transcriptional repression in constitutive heterochromatin and open up possibilities to identify the molecular mechanisms involved.

Show MeSH
Related in: MedlinePlus