Mitotic chromosome assembly is essential for the faithful segregation of genetic information into daughter cells. Although this process was once considered highly complex, recent studies have revealed that its core mechanisms rely on a limited number of structural components, namely, condensins, topoisomerase II (topo II), and histones. Condensins and topo II cooperate to actively generate and manipulate DNA loops, whereas histones assemble nucleosomes to compact these loops. In this review, I will highlight recent advances in the field, with particular emphasis on the mechanistic aspects of mitotic chromosome assembly.

Male Japanese rhinoceros beetles develop a large, four-branched horn on their head. This horn forms in two distinct steps: first, it appears as a rounded structure during pupation; then, it is remodeled into an angular shape inside the pupa. While these changes are driven by epithelial deformation, their underlying mechanisms remain elusive. Using detailed biological observations and computational simulations based on reconstructed 3D shapes, we found that the pupal horn is generated by “fold formation and unfolding,” and the remodeling is achieved by “adhesion and shrinkage.” These findings provide a mechanical basis for understanding exoskeletal morphogenesis and complement genetic studies.

Kinesin superfamily members have evolved a variety of N- and C-terminal linkers whose conformational changes are thought to generate directional force. It remains unclear whether a conformational change of the linker is the only process contributing directional force. In this review, we report that using our recently developed tether-scanning approach, kinesin motor domains tethered via double-stranded DNAs attached to surface loops were found to drive robust microtubule gliding. In three loop-tethered kinesins, the directionality was reversed. These findings indicate a novel motility mechanism that does not rely on conformational changes in the neck-linker as the primary driving force for motility.

Intracellular droplets formed via liquid-liquid phase separation are essential for maintaining cellular homeostasis, although they can transform into aggregates associated with neurodegenerative diseases. To clarify whether droplets are beneficial or pathological, in situ quantification is crucial. We developed a quantitative Raman imaging method utilizing a Raman band of water as an internal standard. Applying this method, we quantified the concentration of nucleic acids in stress granules. We further assessed the degree of crowding environments inside and outside of stress granules formed under different stress conditions and found that intracellular droplets are not necessarily more crowded than their surrounding environments.