The effect of magnesium ions on chromosome structure as observed by helium ion microscopy.
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.
Laboratory of Dynamic Cell Biology, Department of Biotechnology, Graduate School of Engineering, Osaka University, Yamadaoka, Suita, Osaka 565-0871, Japan.
Astari
A
Dwiranti
Laboratory of Dynamic Cell Biology, Department of Biotechnology, Graduate School of Engineering, Osaka University, Yamadaoka, Suita, Osaka 565-0871, Japan.
Tohru
T
Hamano
Laboratory of Dynamic Cell Biology, Department of Biotechnology, Graduate School of Engineering, Osaka University, Yamadaoka, Suita, Osaka 565-0871, Japan.
Hideaki
H
Takata
Surface Characterization Group, Nano Characterization Unit, Advanced Key Technologies Division, National Institute for Materials Science, Sengen, Tsukuba, Ibaraki 305-0047, Japan.
Shoko
S
Nagano
Global Research Center for Environment and Energy Based on Nanomaterials Science, National Institute for Materials Science, Sengen, Tsukuba, Ibaraki 305-0047, Japan.
Hongxuan
H
Guo
Surface Characterization Group, Nano Characterization Unit, Advanced Key Technologies Division, National Institute for Materials Science, Sengen, Tsukuba, Ibaraki 305-0047, Japan.
Keiko
K
Onishi
Division of Plant Sciences, National Institute of Agrobiological Sciences, Kannondai, Tsukuba, Ibaraki 305-8602, Japan.
Toshiyuki
T
Wako
Laboratory of Dynamic Cell Biology, Department of Biotechnology, Graduate School of Engineering, Osaka University, Yamadaoka, Suita, Osaka 565-0871, Japan.
Susumu
S
Uchiyama
Laboratory of Dynamic Cell Biology, Department of Biotechnology, Graduate School of Engineering, Osaka University, Yamadaoka, Suita, Osaka 565-0871, Japan.
Kiichi
K
Fukui
D002843:Chromatin / Q000737:chemistry / Q000648:ultrastructure; D002877:Chromosomes, Human / Q000737:chemistry* / Q000648:ultrastructure*; D006371:Helium / Q000737:chemistry; D006801:Humans; D007477:Ions; D008274:Magnesium / Q000737:chemistry*; D008853:Microscopy / Q000379:methods*; D010316:Particle Size
D002843:Chromatin; D007477:Ions; D006371:Helium; D008274:Magnesium