Science｜真核染色体是一种带电水凝胶，通过体积相变实现凝缩

TL;DR - A Science study proposes that eukaryotic chromosomes behave as charged hydrogels, condensing through a reversible volume phase transition. This separates physical chromatin compaction from SMC-driven organization of chromosomes into rod-like shapes.

• Isolated mitotic chromosomes expanded nearly tenfold after multivalent cations were removed and recon­densed when spermidine was restored, with isotropic and repeatable volume changes.
• A polyelectrolyte-gel model attributes chromosome volume to competing network elasticity, polymer–water mixing, Donnan osmotic pressure, and cation–chromatin binding.
• Hysteresis and coexistence of condensed and swollen regions support a first-order transition between two stable or metastable states.
• Macromolecular crowding, proteins, ions, and polyamines favor condensation, suggesting compact chromatin may be the cellular default while modifications such as histone acetylation maintain local openness.