RNA 2'-O-methylation promotes persistent R-loop formation and AID-mediated IgH class switch recombination

Area of Science:

• Molecular Biology
• Immunology
• Genetics

Background:

• RNA-DNA hybrids (R-loops) have dual roles in genomic instability and immunoglobulin class switch recombination (CSR).
• The mechanisms governing R-loop functions and their protection during CSR are not fully understood.
• The persistence of CSR-associated R-loops, resistant to RNase H, remains elusive.

Purpose of the Study:

• To investigate the regulatory mechanisms of R-loop stability during immunoglobulin class switch recombination (CSR).
• To elucidate how R-loops contribute to both genomic instability and protective CSR.
• To identify factors involved in the modification and persistence of R-loops at the immunoglobulin heavy chain locus.

Main Methods:

• Analysis of R-loop modification during CSR.
• Investigation of protein-RNA interactions involving fibrillarin (FBL), activation-induced cytidine deaminase (AID), and snoRNA aSNORD1C.
• Gene expression disruption studies (FBL, AID, aSNORD1C) and assessment of R-loop stability and CSR.
• Assessment of AID targeting to the immunoglobulin heavy chain locus.

Main Results:

• R-loops at the immunoglobulin heavy (IgH) chain locus are modified by ribose 2 -O-methylation (2 -OMe) during CSR.
• Fibrillarin (FBL) interacts with activation-induced cytidine deaminase (AID) and snoRNA aSNORD1C to mediate 2 -OMe.
• Disruption of FBL, AID, or aSNORD1C impairs 2 -OMe, R-loop stability, and CSR.
• FBL, AID, and aSNORD1C promote AID targeting to the IgH locus.

Conclusions:

• Ribose 2 -O-methylation (2 -OMe) stabilizes IgH-associated R-loops, enabling productive CSR.
• This study reveals a novel mechanism for regulating R-loop stability during CSR.
• Findings shed light on AID-mediated CSR and the dual role of R-loops in genomic stability.