Establishing Polycomb regulatory landscapes in human early development.

H2Aub-dependent H3K27me3 deposition establishes early Polycomb repression in human embryos, with H2Aub emerging by the two-cell stage and affecting gene regulation.

• Why it matters: Understanding how Polycomb complexes regulate gene repression during human early development is crucial because H3K27me3 undergoes genome-wide erasure and reestablishment, and its regulation remains unclear.
• What they did: The study profiled H2Aub dynamics from human gametes to blastocysts, revealing its early emergence, progressive accumulation at PcG targets, and its role in H3K27me3 reestablishment; loss of H2Aub disrupted H3K27me3 patterns and embryonic development.
• The result: H2Aub is essential for H3K27me3 deposition at PcG targets, moderating gene repression and supporting embryonic development, with H2Aub and DNA methylation jointly maintaining H3K27me3 in human embryonic stem cells.