FANCJ coordinates two pathways that maintain epigenetic stability at G-quadruplex DNA

Area of Science:

• Molecular Biology
• Genetics
• Epigenetics

Background:

• REV1 deficiency impairs G-quadruplex (G4) DNA replication, uncoupling DNA synthesis from histone redeposition.
• This uncoupling disrupts transcriptional repression by preventing the recycling of repressive histone modifications.
• Similar processes can deactivate transcriptionally active genes.

Purpose of the Study:

• To investigate the impact of G4 DNA replication defects on active gene transcription.
• To develop a single-cell assay for monitoring G4 DNA-associated epigenetic instability.
• To elucidate the roles of FANCJ, WRN, and BLM helicases in maintaining epigenetic stability near G4 motifs.

Main Methods:

• Utilized DT40 cell lines with deficiencies in DNA replication and repair proteins.
• Developed a cell surface marker assay to quantify epigenetic instability at the single-cell level.
• Performed transcriptional profiling to assess gene expression changes in mutant cell lines.

Main Results:

• Demonstrated G4 DNA motif-associated epigenetic instability in mutants of FANCJ, WRN, and BLM helicases.
• Showed that FANCJ coordinates two distinct mechanisms for maintaining epigenetic stability near G4 DNA.
• Identified REV1 and the WRN/BLM helicase complex as key players in G4 replication-associated epigenetic maintenance.

Conclusions:

• Efficient G4 replication in vivo requires FANCJ's 5'-3'-helicase activity, working with either a specialized polymerase or an opposing helicase.
• The study provides a model for how G4 structures are replicated and how their replication impacts epigenetic stability.
• The developed assay offers a sensitive tool for studying epigenetic instability in various contexts.