The intricacies of chromosome separation during cell division have long fascinated scientists. A recent study by a team at the European Molecular Biology Laboratory in Heidelberg, Germany, led by Sara Cuylen-Haering, has shed new light on this process. The researchers discovered that a protein called Ki-67 plays a crucial role in keeping chromosomes apart and clustering them together during cell division.
The team used live-cell imaging, in vitro experiments, and simulations to reveal the mechanisms underlying Ki-67’s dual function. Initially, Ki-67 is phosphorylated, forming a brush-like layer on the surface of chromosomes that pushes them apart. This process relies on colloidal phenomena such as surface tension.
As cell division progresses, enzymes dephosphorylate Ki-67, rendering it positively charged. The protein then binds with RNA molecules in the nucleus and phase-separates into dense, liquid-like droplets that spread over chromosome surfaces. Fusion of these droplets pulls chromosomes together, facilitated by surface tension.
The study highlights the importance of considering multiple length scales in biological processes. Chromosome separation is not solely a molecular-level process but rather an intricate interplay between molecular changes and large-scale cell processes.
In this context, it’s essential to recognize that biology often employs molecules to achieve specific outcomes, as Nobel laureate François Jacob noted in 1970. However, modern research has revealed a more pluralistic view, where no single length scale is privileged. Instead, distinct principles govern organization at various scales, from the atomic to the organismal.
The study also underscores the significance of biomolecular condensates, which are now recognized as ubiquitous in cell biology. Ki-67 and RNA molecules form liquid-like droplets that facilitate chromosome clustering, demonstrating the complex interplay between molecular and mesoscale processes.
Source: https://www.chemistryworld.com/opinion/a-broader-view-of-condensates/4020153.article