The structure of human metaphase chromosomes: its histological perspective and new horizons by atomic force microscopy.

Studies on the structure of the human chromosome were reviewed from the histological perspective and discussed in connection with our recent findings obtained mainly by atomic force microscopy (AFM). In this paper, we introduce several hitherto known models of the high-order structure of the metaphase chromosome and discuss the actual structure of chromosomes in relation to such structures as spiral chromatids, chromosome bands, and chromosome scaffolds. In chromosomes treated with Ohnuki's hypotonic solution, the chromosome arms were elongated and showed a characteristic spiral pattern of chromatid fibers. On the other hand, alternating transverse ridges and grooves were clearly observed on the surface of chromosomes treated with 0.025% trypsin for G-banding, and these ridges and grooves corresponded to the dark and pale bands of G-banded chromosomes. Similar findings were also found in chromosomes treated with quinacrine mastards for Q-banding. Fibers bridging the gap between the sister chromatids were often observed in G/Q-banded chromosomes; these fibers tended to be restricted within the G/Q-positive portions, suggesting the presence of chromatin fibers bridging these regions. Based on these findings in conjunction with previous studies, we outlined the high-order structure of the human chromosome. Recent advances in nanotechnology have provided new AFM techniques for the imaging and handling of materials at nano-scale resolution. Application of these techniques to chromosome research is expected to provide valuable information on the chromosome structure in relation to its function.