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Structure of Metaphase Chromosomes: A Role for Effects of Macromolecular Crowding
In metaphase chromosomes, chromatin is compacted to a concentration of several hundred mg/ml by mechanisms which remain elusive. Effects mediated by the ionic environment are considered most frequently because mono- and di-valent cations cause polynucleosome chains to form compact ∼30-nm diameter fi...
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Formato: | Online Artículo Texto |
Lenguaje: | English |
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Public Library of Science
2012
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Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3335069/ https://www.ncbi.nlm.nih.gov/pubmed/22540018 http://dx.doi.org/10.1371/journal.pone.0036045 |
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author | Hancock, Ronald |
author_facet | Hancock, Ronald |
author_sort | Hancock, Ronald |
collection | PubMed |
description | In metaphase chromosomes, chromatin is compacted to a concentration of several hundred mg/ml by mechanisms which remain elusive. Effects mediated by the ionic environment are considered most frequently because mono- and di-valent cations cause polynucleosome chains to form compact ∼30-nm diameter fibres in vitro, but this conformation is not detected in chromosomes in situ. A further unconsidered factor is predicted to influence the compaction of chromosomes, namely the forces which arise from crowding by macromolecules in the surrounding cytoplasm whose measured concentration is 100–200 mg/ml. To mimic these conditions, chromosomes were released from mitotic CHO cells in solutions containing an inert volume-occupying macromolecule (8 kDa polyethylene glycol, 10.5 kDa dextran, or 70 kDa Ficoll) in 100 µM K-Hepes buffer, with contaminating cations at only low micromolar concentrations. Optical and electron microscopy showed that these chromosomes conserved their characteristic structure and compaction, and their volume varied inversely with the concentration of a crowding macromolecule. They showed a canonical nucleosomal structure and contained the characteristic proteins topoisomerase IIα and the condensin subunit SMC2. These observations, together with evidence that the cytoplasm is crowded in vivo, suggest that macromolecular crowding effects should be considered a significant and perhaps major factor in compacting chromosomes. This model may explain why ∼30-nm fibres characteristic of cation-mediated compaction are not seen in chromosomes in situ. Considering that crowding by cytoplasmic macromolecules maintains the compaction of bacterial chromosomes and has been proposed to form the liquid crystalline chromosomes of dinoflagellates, a crowded environment may be an essential characteristic of all genomes. |
format | Online Article Text |
id | pubmed-3335069 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2012 |
publisher | Public Library of Science |
record_format | MEDLINE/PubMed |
spelling | pubmed-33350692012-04-26 Structure of Metaphase Chromosomes: A Role for Effects of Macromolecular Crowding Hancock, Ronald PLoS One Research Article In metaphase chromosomes, chromatin is compacted to a concentration of several hundred mg/ml by mechanisms which remain elusive. Effects mediated by the ionic environment are considered most frequently because mono- and di-valent cations cause polynucleosome chains to form compact ∼30-nm diameter fibres in vitro, but this conformation is not detected in chromosomes in situ. A further unconsidered factor is predicted to influence the compaction of chromosomes, namely the forces which arise from crowding by macromolecules in the surrounding cytoplasm whose measured concentration is 100–200 mg/ml. To mimic these conditions, chromosomes were released from mitotic CHO cells in solutions containing an inert volume-occupying macromolecule (8 kDa polyethylene glycol, 10.5 kDa dextran, or 70 kDa Ficoll) in 100 µM K-Hepes buffer, with contaminating cations at only low micromolar concentrations. Optical and electron microscopy showed that these chromosomes conserved their characteristic structure and compaction, and their volume varied inversely with the concentration of a crowding macromolecule. They showed a canonical nucleosomal structure and contained the characteristic proteins topoisomerase IIα and the condensin subunit SMC2. These observations, together with evidence that the cytoplasm is crowded in vivo, suggest that macromolecular crowding effects should be considered a significant and perhaps major factor in compacting chromosomes. This model may explain why ∼30-nm fibres characteristic of cation-mediated compaction are not seen in chromosomes in situ. Considering that crowding by cytoplasmic macromolecules maintains the compaction of bacterial chromosomes and has been proposed to form the liquid crystalline chromosomes of dinoflagellates, a crowded environment may be an essential characteristic of all genomes. Public Library of Science 2012-04-23 /pmc/articles/PMC3335069/ /pubmed/22540018 http://dx.doi.org/10.1371/journal.pone.0036045 Text en Ronald Hancock. http://creativecommons.org/licenses/by/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited. |
spellingShingle | Research Article Hancock, Ronald Structure of Metaphase Chromosomes: A Role for Effects of Macromolecular Crowding |
title | Structure of Metaphase Chromosomes: A Role for Effects of Macromolecular Crowding |
title_full | Structure of Metaphase Chromosomes: A Role for Effects of Macromolecular Crowding |
title_fullStr | Structure of Metaphase Chromosomes: A Role for Effects of Macromolecular Crowding |
title_full_unstemmed | Structure of Metaphase Chromosomes: A Role for Effects of Macromolecular Crowding |
title_short | Structure of Metaphase Chromosomes: A Role for Effects of Macromolecular Crowding |
title_sort | structure of metaphase chromosomes: a role for effects of macromolecular crowding |
topic | Research Article |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3335069/ https://www.ncbi.nlm.nih.gov/pubmed/22540018 http://dx.doi.org/10.1371/journal.pone.0036045 |
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