When cells divide, DNA condenses into chromosomes, which are then equally distributed between the two daughter cells. At metaphase, a specific DNA region called the centromere is pulled by the spindle microtubules to the poles. At telophase, the chromosomes decondense and the cell nucleus is reconstructed. If the distribution of centromeres pulled to the two poles remains unchanged, the cell nucleus becomes Rabl structure, and if the centromeres are no longer unevenly distributed on the inner nuclear membrane, the cell nucleus becomes a centromere-dispersed cell nucleus (non-Rabl structure). For example, the spatial arrangement of centromeres in the nuclei of yeast, Drosophila, and wheat, is Rabl structure, while that in humans, Arabidopsis thaliana, and Caenorhabditis elegans is non-Rabl structure. Imaging and molecular cell biological studies using A. thaliana mutants with non-Rabl-structured nuclei have revealed that there are two molecular processes involved in the establishment of non-Rabl-structured nuclei. The process of dispersion of the centromeres after anaphase involves the CII-LINC complex, which is composed of the condensin II complex and the LINC (linker of nucleoskeleton and cytoskeleton) complex. Subsequently, the nuclear lamina, CRWN, acts to stabilize the dispersed centromeres near the inner nuclear membrane. Mutants of these factors have normal developmental and differentiation phenotypes without the significant alternation of gene transcription. On the other hand, when DNA damage stress is applied by adding a DNA double-strand break inducer, the frequency of DNA double-strand breaks in CII and CRWN mutants increases, resulting in abnormal organogenesis. Thus, the proper arrangement of centromeres may play a role in preventing DNA double-strand breaks in the nucleus.
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