Mitotic chromosomes are the structure where DNA is tightly compacted, and they carry genetic information to be passed on to the next generation. These chromosomes are transmitted from the mother cell onto the daughter cell with physical force from microtubes and other factors. In other words, chromosomes should have mechanical resistance to endure such forces.
Recently, Daniel W. Gerlich and his colleagues have shown that chromosomes condense and gain such mechanical resistance by phase transition（Schneider et al. “A chromatin phase transition protects mitotic chromosomes against microtubule perforation” Nature 2022 doi: 10.1038/ s41586-022-05027-y）. In this paper, Schneider et al. have shown that global histone deacetylation cause phase transition in mitotic chromosomes, which makes them condensed and resistant to mechanical forces. The authors have also shown that a protein complex called condensin, which was previously thought to be essential for chromosome condensation, is not involved in the condensation process itself.
Professor Kazuhiro Maeshima at Genome Dynamics Laboratory wrote a commentary on this paper in the News & Views section of Nature. Maeshima discussed how global histone deacetylation causes chromosome condensation and the role of condensin in shaping rod-like chromosomes (chromatin loop formation mechanism).
Figure: When a chromosome is transmitted during cell division, microtubules physically push and pull it. a) When histones are globally acetylated, the chromosome loses its mechanical resistance. It allows microtubules to penetrate the chromosome. b) A condensin-depleted chromosome shows an abnormal shape but retains mechanical resistance. c) When DNA is fragmented by restriction enzyme AluⅠ, chromosomes form “liquid droplets”. Still, chromosomes have similar mechanical resistance.
