Detection and Characterization of R‐loops at the Murine Immunoglobulin S α Region

Abstract

IgA is the most abundant antibody in mammals. However, the mechanism of its class switching is still not clear. The formation of the R‐loops has been proposed to play a crucial role during mammalian class switch recombination. Hence, we investigate if R‐loops exist at Sα. In addition, the correlation between R‐loops and IgA class switching is also been investigated. Here, we are the first to provide a systematic evaluation of R‐loops at Sα (IgA) in vitro and in situ in CH12F3–2A cells, which is a unique cell model system for class switch recombination for its consistent switching to IgA upon stimulation. R‐loops form at Sα, despite variable G density and relatively few GGGG clusters in Sα. The short distance from the promoter to Sα may compensate for the less robust R‐loop‐forming factors at Sα relative to other switch regions. R‐loops have distinct features specific to Sα. Therefore, R‐loops at the Sα region further support R‐loop formation as a general feature of all stimulated switch regions. Furthermore, the IgA class switching is altered in the deficiency of R‐loops‐related enzymes in CH12F3–2A cells.