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Intrinsic Toxicity of Unchecked Heterochromatin Spread Is Suppressed by Redundant Chromatin Boundary Functions in Schizosacchromyces pombe

Effective boundary mechanisms halt the spread of repressive histone methylation. In the fission yeast Schizosacchromyces pombe, two factors/elements required for boundary function have been described, the jmjC protein Epe1 and binding sites for the RNA polymerase III transcription factor TFIIIC. Per...

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Autores principales: Garcia, Jennifer F., Al-Sady, Bassem, Madhani, Hiten D.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Genetics Society of America 2015
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4502379/
https://www.ncbi.nlm.nih.gov/pubmed/25957277
http://dx.doi.org/10.1534/g3.115.018663
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author Garcia, Jennifer F.
Al-Sady, Bassem
Madhani, Hiten D.
author_facet Garcia, Jennifer F.
Al-Sady, Bassem
Madhani, Hiten D.
author_sort Garcia, Jennifer F.
collection PubMed
description Effective boundary mechanisms halt the spread of repressive histone methylation. In the fission yeast Schizosacchromyces pombe, two factors/elements required for boundary function have been described, the jmjC protein Epe1 and binding sites for the RNA polymerase III transcription factor TFIIIC. Perplexingly, individual mutation of Epe1 or TFIIIC sites produces only mild boundary defects, and no other boundary factors have been identified. To approach these issues, we developed a synthetic reporter gene tool that uses a tethered Clr4 histone H3K9 methyltransferase and monitors the ability of a DNA element to block heterochromatin spread. The inverted repeat (IR) that flanks the mat2/3 silent mating-type cassette region demonstrates strong boundary activity compared to sequences that flank pericentromeric heterochromatic repeats. Rather than acting in the same inhibitory pathway, Epe1 and TFIIIC sites mediate boundary function of the IR via the two parallel and largely redundant pathways. We also use the system to demonstrate that HP1/Swi6 promotes boundary activity in addition to promoting silencing and acts in the same pathway as Epe1. Inhibition of heterochromatin spread at the endogenous IR element also requires either Epe1 or TFIIIC sites. Strikingly, mutation of both mechanisms results in growth inhibition that is associated with the spread of heterochromatin over many kilobases to the nearest essential gene and the near-complete silencing of several intervening euchromatic genes. The growth defect is reversed by deletion of clr4+, indicating that the redundant boundary mechanisms protect cells from intrinsic toxicity caused by the spread of heterochromatin.
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spelling pubmed-45023792015-07-17 Intrinsic Toxicity of Unchecked Heterochromatin Spread Is Suppressed by Redundant Chromatin Boundary Functions in Schizosacchromyces pombe Garcia, Jennifer F. Al-Sady, Bassem Madhani, Hiten D. G3 (Bethesda) Investigations Effective boundary mechanisms halt the spread of repressive histone methylation. In the fission yeast Schizosacchromyces pombe, two factors/elements required for boundary function have been described, the jmjC protein Epe1 and binding sites for the RNA polymerase III transcription factor TFIIIC. Perplexingly, individual mutation of Epe1 or TFIIIC sites produces only mild boundary defects, and no other boundary factors have been identified. To approach these issues, we developed a synthetic reporter gene tool that uses a tethered Clr4 histone H3K9 methyltransferase and monitors the ability of a DNA element to block heterochromatin spread. The inverted repeat (IR) that flanks the mat2/3 silent mating-type cassette region demonstrates strong boundary activity compared to sequences that flank pericentromeric heterochromatic repeats. Rather than acting in the same inhibitory pathway, Epe1 and TFIIIC sites mediate boundary function of the IR via the two parallel and largely redundant pathways. We also use the system to demonstrate that HP1/Swi6 promotes boundary activity in addition to promoting silencing and acts in the same pathway as Epe1. Inhibition of heterochromatin spread at the endogenous IR element also requires either Epe1 or TFIIIC sites. Strikingly, mutation of both mechanisms results in growth inhibition that is associated with the spread of heterochromatin over many kilobases to the nearest essential gene and the near-complete silencing of several intervening euchromatic genes. The growth defect is reversed by deletion of clr4+, indicating that the redundant boundary mechanisms protect cells from intrinsic toxicity caused by the spread of heterochromatin. Genetics Society of America 2015-05-08 /pmc/articles/PMC4502379/ /pubmed/25957277 http://dx.doi.org/10.1534/g3.115.018663 Text en Copyright © 2015 Garcia et al. http://creativecommons.org/licenses/by/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
spellingShingle Investigations
Garcia, Jennifer F.
Al-Sady, Bassem
Madhani, Hiten D.
Intrinsic Toxicity of Unchecked Heterochromatin Spread Is Suppressed by Redundant Chromatin Boundary Functions in Schizosacchromyces pombe
title Intrinsic Toxicity of Unchecked Heterochromatin Spread Is Suppressed by Redundant Chromatin Boundary Functions in Schizosacchromyces pombe
title_full Intrinsic Toxicity of Unchecked Heterochromatin Spread Is Suppressed by Redundant Chromatin Boundary Functions in Schizosacchromyces pombe
title_fullStr Intrinsic Toxicity of Unchecked Heterochromatin Spread Is Suppressed by Redundant Chromatin Boundary Functions in Schizosacchromyces pombe
title_full_unstemmed Intrinsic Toxicity of Unchecked Heterochromatin Spread Is Suppressed by Redundant Chromatin Boundary Functions in Schizosacchromyces pombe
title_short Intrinsic Toxicity of Unchecked Heterochromatin Spread Is Suppressed by Redundant Chromatin Boundary Functions in Schizosacchromyces pombe
title_sort intrinsic toxicity of unchecked heterochromatin spread is suppressed by redundant chromatin boundary functions in schizosacchromyces pombe
topic Investigations
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4502379/
https://www.ncbi.nlm.nih.gov/pubmed/25957277
http://dx.doi.org/10.1534/g3.115.018663
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