ELECTRON MICROSCOPY OF SILVER-STAINED CORE-LIKE STRUCTURES IN METAPHASE CHROMOSOMES

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Abstract
Chinese hamster metaphase chromosomes, stained with ammoniacal Ag and examined by EM, were covered with fine Ag grains of variable size. In addition, many chromosomes contained linear aggregates of Ag grains running continuously from one end of each chromatid to the other, forming a core-like structure. Extensive deposits of Ag were observed over the nucleolar organizers and the centromeric regions, and the Ag precipitate in the latter region appeared to be a localized differentiation of the core-like structure. The Ag cores ranged from thin to thick and continuous to discontinuous elements in different chromosomes. This extreme variability suggests that these cores are not true structural components of chromosomes. The amount of Ag deposit over any given chromosome region may simply reflect the concentration of chromatin in that region of the chromosome. The Ag-stained core-like structure probably reflects an underlying difference in the concentration of chromatin in the central and peripheral region of each chromatid. Such differences in chromatin concentration may be induced during the prolonged hypotonic treatment required for the subsequent visualization of cores.