RING1 missense variants reveal sensitivity of DNA damage repair to H2A monoubiquitination dosage during neurogenesis

Area of Science:

• Epigenetics and chromatin modification
• Molecular biology
• Neuroscience

Background:

• Polycomb repressive complex 1 (PRC1) catalyzes histone H2A lysine 119 monoubiquitination (H2AK119ub1).
• RING1 and RNF2 are interchangeable catalytic subunits of PRC1.
• Pathogenic variants reveal functions obscured in knockout models, particularly for RING1.

Purpose of the Study:

• Investigate the distinct roles of RING1 and RNF2 in PRC1 function during neurodevelopment.
• Determine the impact of hypomorphic variants on H2AK119ub1 deposition and downstream cellular processes.
• Clarify the sensitivity of DNA damage response versus gene expression to H2AK119ub1 dosage.

Main Methods:

• In vitro neurodevelopment model.
• Analysis of PRC1 complex activity with hypomorphic RING1 and RNF2 variants.
• Assessment of H2AK119ub1 levels, DNA damage repair, cell cycle progression, and gene expression in neural progenitor cells (NPCs).

Main Results:

• RING1 contributes to broad H2AK119ub1 placement, with overlapping targets to RNF2.
• Hypomorphic RING1 reduces H2AK119ub1, delaying DNA repair and cell cycle progression in NPCs without impacting differentiation.
• Hypomorphic RNF2 causes a greater H2AK119ub1 reduction, leading to delayed DNA repair and widespread transcriptional changes.

Conclusions:

• The DNA damage response is more sensitive to H2AK119ub1 dosage changes than gene expression regulation.
• RING1 and RNF2 exhibit differential impacts on cellular processes based on the extent of H2AK119ub1 reduction.
• PRC1 subunit function is critical for maintaining genomic stability and proper cell cycle control in neural progenitors.