DNA G-Quadruplexes Contribute to CTCF Recruitment

Area of Science:

• Genomics
• Epigenetics
• Molecular Biology

Background:

• CCCTC-binding factor (CTCF) is a key regulator of genome architecture.
• G-quadruplex (G4) structures are prevalent in CpG islands (CGIs) and often colocalize with CTCF-bound sites.

Purpose of the Study:

• To elucidate the role of G4 structures in the recruitment and positioning of CTCF at CGIs.
• To investigate potential direct and indirect mechanisms of G4-CTCF interaction.

Main Methods:

• In vitro binding assays using quadruplex-forming sequences.
• Chromatin immunoprecipitation followed by quantitative PCR (ChIP-qPCR).
• Bioinformatics analysis of existing genomic data.
• Molecular modeling.

Main Results:

• G4 structures bind CTCF in vitro with affinities comparable to duplex DNA; i-motifs show no affinity.
• G4-stabilizing ligands increase CTCF occupancy at G4-prone sites.
• Bioinformatics analysis suggests G4s do not protect CpG sites from methylation to recruit CTCF.
• High mobility group (HMG) proteins, including HMGN3, colocalize with G4s and may mediate indirect G4-CTCF interactions.

Conclusions:

• G4 structures play both direct and indirect roles in facilitating CTCF recruitment to genomic sites.
• These findings reveal a novel layer of regulation involving G4s in CTCF-mediated genome organization.