J. Phys. IV France 104 (2003) 313
DOI: 10.1051/jp4:200300088

Fine structures of human chromosomes observed by X-ray contact microscopy coupled with atomic force microscopy

Y. Kinjo¹, M. Watanabe², H. Fiedorowicz³, H. Daido⁴, E. Yanase⁴, S. Fujii⁵, E. Sato⁵ and K. Shinohara<sup>6

1</sup>  Tokyo Metropolitan Industrial Technology Research Institute, 2-11-1 Fukazawa, Setagaya-ku, Tokyo 158-0081, Japan
²  Japan Mendel Society, 2-27-2 Hongo, Bunkyou-ku, Tokyo 113-0033, Japan
³  Military University of Technology, Institute of Optoelectronics, 2 Kaliskiego Str. 01-489, Warsaw, Poland
⁴  Advanced Photon Research Center, Japan Atomic Energy Research Institute, 8-1 Umemidai, Kidu-cho, Aira-gun, Kyoto 619-0215, Japan
⁵  Kawasaki Heavy Industries Ltd., 118 Futatsudzuka, Noda-shi, Chiba 278-8585, Japan
⁶  University of Tokyo, 7-3-1 Hongo, Bunkyou-ku, Tokyo 113-0033, Japan

Abstract
Chromosomes from human lymphocytes were observed by X-ray contact microscopy (XRCM) using laser-produced plasma X-rays coupled with atomic force microscopy (AFM). A resist with either dry or hydrated chromosomes was exposed to laser-produced plasma X-rays. The exposed resist was then developed after removing all cell-derived materials including chromosomes and was observed directly by AFM. Clear images of fine structures of chromosomes in various periods of the cell cycle could be obtained. It was shown that AFM is a powerful tool for XRCM for its easiness to locate the X-ray images on a resist once pinpointed by light microscopy in comparison with transmission electron microscopy (TEM) in combination with replica method. In addition, the data suggested that chromatin fiber is composed basically of linearly arranged particles with heterogeneous sizes, which is incompatible with the current textbook model regarding the conformation of chromatin where a nucleosomal fiber coils to generate a chromatin fiber with the homogeneous size of ca. 30 nm in diameter.

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