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

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2024-08-27
Authors
Iida, Shiori
Ide, Satoru
Tamura, Sachiko
Sasai, Masaki
Tani, Tomomi
Goto, Tatsuhiko
Shribak, Michael
Maeshima, Kazuhiro
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10.1073/pnas.2403153121
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OI-DIC
Mitotic chromosome condensation
Depletion attraction
Chromatin
Liquid droplets
Abstract
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 IIα 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.
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© The Author(s), 2024. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Iida, S., Ide, S., Tamura, S., Sasai, M., Tani, T., Goto, T., Shribak, M., & Maeshima, K. (2024). Orientation-independent-DIC imaging reveals that a transient rise in depletion attraction contributes to mitotic chromosome condensation. Proceedings of the National Academy of Sciences of the United States of America, 121(36), e2403153121, https://doi.org/10.1073/pnas.2403153121.
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Iida, S., Ide, S., Tamura, S., Sasai, M., Tani, T., Goto, T., Shribak, M., & Maeshima, K. (2024). Orientation-independent-DIC imaging reveals that a transient rise in depletion attraction contributes to mitotic chromosome condensation. Proceedings of the National Academy of Sciences of the United States of America, 121(36), e2403153121.
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