Dansyl chloride-stained nucleolar organizers and core-like structures in Chinese hamster metaphase chromosomes

Abstract

When chromosomes containing both BrdU-substituted and unsubstituted regions were treated with hot NaH 2PO 4 at high or low pH and then stained with dansyl chloride, brightly fluorescent nucleolar organizer regions (NORs) and core-like structures were apparent in the chromosomes. These structures closely parallel the appearance of the same structures in silver-stained chromosomes. Since dansyl chloride is a protein-specific fluorochrome, the distribution of fluorescence suggests that the NORs and central zone of each chromatid contain higher concentrations of protein relative to other chromosome regions. The fluorescent core structures are interpreted to be artefacts of the NaH 2PO 4 pretreatment induced by changes in the concentration of chromatin (including protein) between the chromatin-dense center and more dispersed peripheral region of each chromatid.