Senataxin and RNase H2 act redundantly to suppress genome instability during class switch recombination

Class switch recombination generates antibody distinct isotypes critical to a robust adaptive immune system and defects are associated with auto-immune disorders and lymphomagenesis. Transcription is required during class switch recombination for the formation of DNA double-strand breaks by AID, and strongly induces the formation of R loops within the immunoglobulin heavy chain locus. However the impact of R loops on double-strand break formation and repair during class switch recombination remains unclear. Here we report that cells lacking two enzymes involved in R loop removal--Senataxin and RNase H2--exhibit increased R loop formation and genome instability at the immunoglobulin heavy chain locus without impacting class switch recombination efficiency or AID recruitment. We propose that Senataxin acts redundantly with RNase H2 to mediate timely R loop removal, promoting efficient repair and suppressing AID-dependent genome instability.