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The Effect of Magnesium Ions on Chromosome Structure as Observed by Helium Ion Microscopy

Published online by Cambridge University Press:  14 November 2013

Astari Dwiranti ,
Tohru Hamano ,
Hideaki Takata ,
Shoko Nagano ,
Hongxuan Guo ,
Keiko Onishi ,
Toshiyuki Wako ,
Susumu Uchiyama  and
Kiichi Fukui
Astari Dwiranti
Affiliation:
Laboratory of Dynamic Cell Biology, Department of Biotechnology, Graduate School of Engineering, Osaka University, Yamadaoka, Suita, Osaka 565-0871, Japan
Tohru Hamano
Affiliation:
Laboratory of Dynamic Cell Biology, Department of Biotechnology, Graduate School of Engineering, Osaka University, Yamadaoka, Suita, Osaka 565-0871, Japan
Hideaki Takata
Affiliation:
Laboratory of Dynamic Cell Biology, Department of Biotechnology, Graduate School of Engineering, Osaka University, Yamadaoka, Suita, Osaka 565-0871, Japan Frontier Research Base for Global Young Researchers, Graduate School of Engineering, Osaka University, Yamadaoka, Suita, Osaka 565-0871, Japan
Shoko Nagano
Affiliation:
Surface Characterization Group, Nano Characterization Unit, Advanced Key Technologies Division, National Institute for Materials Science, Sengen, Tsukuba, Ibaraki 305-0047, Japan
Hongxuan Guo
Affiliation:
Global Research Center for Environment and Energy Based on Nanomaterials Science, National Institute for Materials Science, Sengen, Tsukuba, Ibaraki 305-0047, Japan
Keiko Onishi
Affiliation:
Surface Characterization Group, Nano Characterization Unit, Advanced Key Technologies Division, National Institute for Materials Science, Sengen, Tsukuba, Ibaraki 305-0047, Japan
Toshiyuki Wako
Affiliation:
Division of Plant Sciences, National Institute of Agrobiological Sciences, Kannondai, Tsukuba, Ibaraki 305-8602, Japan
Susumu Uchiyama
Affiliation:
Laboratory of Dynamic Cell Biology, Department of Biotechnology, Graduate School of Engineering, Osaka University, Yamadaoka, Suita, Osaka 565-0871, Japan
Kiichi Fukui*
Affiliation:
Laboratory of Dynamic Cell Biology, Department of Biotechnology, Graduate School of Engineering, Osaka University, Yamadaoka, Suita, Osaka 565-0871, Japan
*
*Corresponding author. E-mail: kfukui@bio.eng.osaka-u.ac.jp
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Abstract

One of the few conclusions known about chromosome structure is that Mg2+ is required for the organization of chromosomes. Scanning electron microscopy is a powerful tool for studying chromosome morphology, but being nonconductive, chromosomes require metal/carbon coating that may conceal information about the detailed surface structure of the sample. Helium ion microscopy (HIM), which has recently been developed, does not require sample coating due to its charge compensation system. Here we investigated the structure of isolated human chromosomes under different Mg2+ concentrations by HIM. High-contrast and resolution images from uncoated samples obtained by HIM enabled investigation on the effects of Mg2+ on chromosome structure. Chromatin fiber information was obtained more clearly with uncoated than coated chromosomes. Our results suggest that both overall features and detailed structure of chromatin are significantly affected by different Mg2+ concentrations. Chromosomes were more condensed and a globular structure of chromatin with 30 nm diameter was visualized with 5 mM Mg2+ treatment, while 0 mM Mg2+ resulted in a less compact and more fibrous structure 11 nm in diameter. We conclude that HIM is a powerful tool for investigating chromosomes and other biological samples without requiring metal/carbon coating.

Keywords

human chromosomechromosome structurehelium ion microscopy (HIM)magnesium ion (Mg2+)osmium coating
Type
Biological Applications
Information
Microscopy and Microanalysis , Volume 20 , Issue 1 , February 2014 , pp. 184 - 188
Copyright
Copyright © Microscopy Society of America 2014 

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