An expanded evolutionary landscape of H3 histones with variants that destabilize nucleosomes and promote chromatin accessibility

H3-a and H3-b histone variants in the acoel Hofstenia miamia form nucleosomes that are less stable with incomplete DNA wrapping, and their depletion lowers genome-wide chromatin accessibility during regeneration.

• Why it matters: It is unclear whether highly divergent animal H3 variants regulate chromatin accessibility like broadly conserved H3.3, especially in regeneration systems that rely on adult pluripotent stem cells.
• What they did: The study characterizes Hofstenia miamia histone repertoires, identifies H3-a and H3-b expressed in aPSCs, tests nucleosome assembly in vitro, and uses cryo-EM to assess H3-b histone-DNA contacts.
• The result: In vivo, H3-a and H3-b are upregulated after injury, and depleting them reduces genome-wide chromatin accessibility, linking divergent H3 sequence features to accessible chromatin maintenance during regeneration.

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