A liquid-like coat mediates chromosome clustering during mitotic exit

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Chromosome individualization and clustering are vital for accurate eukaryotic chromosome segregation during mitosis.
• The protein Ki-67 regulates these processes but its dual function remains unclear.

Purpose of the Study:

• To elucidate the mechanism by which Ki-67 transitions from a chromosome repellent to an attractant.
• To understand how Ki-67 mediates chromosome clustering during mitotic exit.

Main Methods:

• Utilized human cells to observe Ki-67 behavior during mitosis.
• Employed biochemical experiments and coarse-grained simulations.
• Investigated the role of Ki-67 dephosphorylation and RNA in phase condensation.

Main Results:

• Demonstrated that Ki-67 switches function from repellent to attractant during anaphase.
• Showed Ki-67 dephosphorylation and RNA exposure trigger liquid-like phase formation on chromosomes.
• Provided evidence that Ki-67/RNA co-condensation drives chromosome surface coalescence and clustering.

Conclusions:

• The switch in Ki-67's function is mediated by dephosphorylation and RNA interaction, forming a liquid-like phase.
• This phase transition generates mechanical forces crucial for genome segregation and nuclear reformation post-mitosis.