2016 年 19 巻 1-4 号 p. 19-23
The structural details of chromosomes have been of interest for many years; however, the enigma of how the metaphase chromosome is constructed has remained unsolved. Divalent cations, especially Mg2+, are known to be required for chromatin condensation. However, details about the effect of Mg2+ at the nanoscale are still limited. In this study, the effect of Mg2+ on chromosome structure was investigated by means of scanning electron microscopy (SEM), because of its high magnification and resolution, as well as by scanning transmission electron microscope (STEM) tomography, because of its advantages in three-dimensionally imaging chromosomes without sectioning. We herewith report the reversibility between 11 and 30 nm chromosome structures according to the concentration of Mg2+ as observed by SEM, and how three-dimensional chromosome structure is affected by Mg2+ concentration by STEM tomography. Treatment with a buffer lacking Mg2+ yields a less compact chromosome structure, with smaller fiber diameters, than for chromosomes treated with a buffer containing 5 mM Mg2+. The changes of chromatin diameter are reversible after re-addition of Mg2+. These findings signify the importance of an adequate concentration of Mg2+ to chromosome structure. The advantages of SEM and STEM for chromosomal research were highlighted in the current study.
