GADD45A binds R-loops and recruits TET1 to CpG island promoters

Area of Science:

• Epigenetics
• Molecular Biology
• Genomics

Background:

• R-loops, DNA-RNA hybrids, are found at CpG islands and influence chromatin.
• The recognition and function of R-loops by epigenetic readers remain unclear.

Purpose of the Study:

• To identify the protein that reads R-loops and mediates their epigenetic effects.
• To elucidate the mechanism by which R-loops regulate gene expression, specifically TCF21.

Main Methods:

• In vitro binding assays to confirm GADD45A interaction with R-loops.
• Analysis of TARID lncRNA, R-loop formation, and TCF21 expression dynamics.
• Genomic profiling using techniques like ChIP-seq and RNA-seq in embryonic stem cells.
• Assessment of DNA demethylation intermediates and TET1 recruitment.

Main Results:

• GADD45A directly binds to R-loops and recruits TET1, initiating DNA demethylation.
• The TARID lncRNA forms an R-loop at the TCF21 promoter, leading to GADD45A binding and TCF21 expression.
• A sequential process of transcription, R-loop formation, demethylation, and gene expression was observed.
• Genomic studies revealed numerous R-loop-dependent TET1 binding sites at CpG islands.

Conclusions:

• GADD45A acts as an epigenetic reader of R-loops.
• GADD45A recruits the DNA demethylation machinery (TET1) to R-loop sites, particularly at promoter CpG islands.
• This mechanism links R-loop formation to gene expression regulation.