Orientation- independent- DIC imaging reveals that a transient rise in depletion attraction contributes to mitotic chromosome condensation

• 成果类型: Article
• 署名作者: Iida, Shiori; Ide, Satoru; Tamura, Sachiko; Sasai, Masaki; Tani, Tomomi; Goto, Tatsuhiko; Shribak, Michael; Maeshima, Kazuhiro
• 署名单位: Research Organization of Information & Systems (ROIS); National Institute of Genetics (NIG) - Japan; Graduate University for Advanced Studies - Japan; Kyoto University; Nagoya University; National Institute of Advanced Industrial Science & Technology (AIST); Obihiro University of Agriculture & Veterinary Medicine; Obihiro University of Agriculture & Veterinary Medicine; Marine Biological Laboratory - Woods Hole
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-12070
• DOI: 10.1073/pnas.2403153121
• 发表日期: 2024-09-03
• 关键词: mass measurements show; cells swell; chromatin; Visualization; ORGANIZATION; architecture; metaphase; DYNAMICS; genome; principles

摘要

Genomic information must be faithfully transmitted into two daughter cells during mitosis. To ensure the transmission process, interphase chromatin is further condensed into mitotic chromosomes. Although protein factors like condensins and topoisomerase II alpha are involved in the assembly of mitotic chromosomes, the physical bases of the condensation process remain unclear. Depletion attraction/macromolecular crowding, an effective attractive force that arises between large structures in crowded environments around chromosomes, may contribute to the condensation process. To approach this issue, we investigated the chromosome milieu during mitosis of living human cells using an orientation- independent- differential interference contrast module combined with a confocal laser scanning microscope, which is capable of precisely mapping optical path differences and estimating molecular densities. We found that the molecular density surrounding chromosomes increased with the progression from prophase to anaphase, concurring with chromosome condensation. However, the molecular density went down in telophase, when chromosome decondensation began. Changes in the molecular density around chromosomes by hypotonic or hypertonic treatment consistently altered the condensation levels of chromosomes. In vitro, native chromatin was converted into liquid droplets of chromatin in the presence of cations and a macromolecular crowder. Additional crowder made the chromatin droplets stiffer and more solid- like. These results suggest that a transient rise in depletion attraction, likely triggered by the relocation of macromolecules (proteins, RNAs, and others) via nuclear envelope breakdown and by a subsequent decrease in cell volumes, contributes to mitotic chromosome condensation, shedding light on a different aspect of the condensation mechanism in living human cells.