Reversible Changes of Chromosome Structure upon Different Concentrations of Divalent Cations

The structural details of chromosomes have been of interest to researchers for many years, but how the metaphase chromosome is constructed remains unsolved. Divalent cations have been suggested to be required for the organization of chromosomes. However, detailed information about the role of these cations in chromosome organization is still limited. In the current study, we investigated the effects of Ca ²⁺ and Mg ²⁺ depletion and the reversibility upon re-addition of one of the two ions. Human chromosomes were treated with different concentrations of Ca ²⁺ and Mg ²⁺ . Depletion of Ca ²⁺ and both Ca ²⁺ and Mg ²⁺ were carried out using 1, 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid and ethylenediaminetetraacetic acid (EDTA), respectively. Chromosome structure was examined by fluorescence microscopy and scanning electron microscopy. The results indicated that chromosome structures after treatment with a buffer without Mg ²⁺ , after Ca ²⁺ depletion, as well as after depletion of both Mg ²⁺ , and Ca ²⁺ , yielded fewer compact structures with fibrous chromatin than those without cation depletion. Interestingly, the chromatin of EDTA-treated chromosomes reversed to their original granular diameters after re-addition of either Mg ²⁺ or Ca ²⁺ only. These findings signify the importance of divalent cations on the chromosome structure and suggest the interchangeable role of Ca ²⁺ and Mg ²⁺ .