The structure of C-banded human metaphase chromosomes as observed by atomic force microscopy.

The ultrastructure of C-banded human metaphase chromosomes was studied by the combined use of light microscopy and atomic force microscopy (AFM). Light microscopy of the C-banded chromosomes showed that the centromeric regions of all chromosomes except the Y chromosome were positively stained. AFM further revealed that the C-positive region was higher than the C-negative region. The area of the C-positive region was specific depending on each chromosome; it ranged from the centromere to the proximal end of the long arm in chromosome 1, while it was restricted to the centromere in chromosomes 2 and 3. At higher magnification, chromatin fibers about 50 nm thick were clearly shown in the entire length of the chromosomes. In the C-positive region, these chromatin fibers were densely packed, while chromatin fibers were loosely packed with gentle twisting in the C-negative region. These AFM findings suggest that certain factors related to the chromatin fiber compaction remain in the C-positive region even after successive C-banging treatment.