Mitotic chromosome condensation is an essential process to transmit replicated chromosomes into two daughter cells during cell division. To study the underlying physical principles of this process, we focused on depletion attraction/macromolecular crowding, which is a force that attracts large structures in crowded cell environments. Using special light microscopy, which can image the molecular density of cellular environments, we found that crowding around chromosomes increases during cell division. In vitro, higher concentrations of macromolecules condense chromatin and make it stiffer and more solid-like. Our results suggest that the rise in depletion attraction renders chromosomes more rigid, ensuring accurate chromosome transmission during cell division.
Figure: (Left) Schematic of depletion attraction in interphase live cells with soluble macromolecules in the cytoplasm (light blue), nucleoplasm (gray), and nucleolus (dark gray). The cytoplasm, nucleus, and nucleolus are compartmentalized and do not mix during interphase. Molecular densities of the nucleoplasm are lower than the cytoplasm and nucleolus. (Right) After NEBD, soluble macromolecules that were localized to the cytoplasm, nucleus, and nucleolus at interphase are now mixed. Molecular density of chromosome environment increases, making the depletion attraction stronger, and contributes to local condensation of chromosomes. These schematics are highly simplified models, and depletion attraction also works in interphase chromatin (smaller navy arrows).
Press release (In Japanese only)
