H2A.Z facilitates licensing and activation of early replication origins

Area of Science:

• Epigenetics
• Molecular Biology
• Genomics

Background:

• DNA replication is essential for cell division and genome integrity.
• Replication origin licensing and activation in eukaryotes involve DNA sequences and chromatin features.
• Chromatin-based regulatory mechanisms controlling replication remain poorly understood.

Purpose of the Study:

• To investigate the role of histone variant H2A.Z in regulating DNA replication origins.
• To elucidate the molecular mechanisms by which H2A.Z influences replication timing.

Main Methods:

• Used HeLa cells for experiments.
• Performed in vitro binding assays with nucleosomes, H2A.Z, SUV420H1, and ORC.
• Conducted genome-wide studies to analyze H4K20me2, ORC1, and nascent DNA strand localization.
• Assessed the impact of H2A.Z depletion on these factors and replication timing.

Main Results:

• Nucleosomes with H2A.Z are enriched with H4K20me2 and origin-recognition complex (ORC).
• H2A.Z-containing nucleosomes bind SUV420H1, promoting H4K20me2 deposition required for ORC1 binding.
• Genome-wide data show co-localization of H4K20me2, ORC1, and nascent DNA with H2A.Z.
• H2A.Z depletion reduces H4K20me2, ORC1, and nascent DNA signals, impacting replication origin efficiency and timing.

Conclusions:

• Histone variant H2A.Z epigenetically regulates the licensing and activation of early replication origins.
• H2A.Z maintains replication timing via the SUV420H1-H4K20me2-ORC1 pathway.