Department of Biochemical Science and Technology, College of Life Science, National Taiwan University, Taipei, Taiwan.
Mol Immunol. 2013 Jun;54(2):208-16. doi: 10.1016/j.molimm.2012.11.009. Epub 2012 Dec 31.
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, as the target for AID, has been proposed to play a crucial role during mammalian class switch recombination. Here, we provide a systematic evaluation of R-loops at Sα (IgA) in CH12F3-2A cells, which is a unique cell model system for class switch recombination because of its consistent switching to IgA upon stimulation. The results of R-loop analysis demonstrate distinct features specific to Sα. Some R-loops may initiate from the end of Iα, but all terminate exclusively within Sα. Time-course analysis also indicates that the percentage of R-loops peaks prior to the occurrence of class switch recombination. This is the first demonstration that R-loops form at Sαin vitro and in situ, 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. In conclusion, R-loops at the Sα region further support R-loop formation as a general feature of all stimulated switch regions.
IgA 是哺乳动物中含量最丰富的抗体。然而，其类别转换的机制仍不清楚。作为 AID 的靶标，R 环的形成被认为在哺乳动物类别转换重组中起着至关重要的作用。在这里，我们对 CH12F3-2A 细胞中的 Sα（IgA）处的 R 环进行了系统评估，该细胞是一种独特的类别转换重组细胞模型系统，因为其受到刺激后会持续转换为 IgA。R 环分析的结果表明了 Sα 特有的独特特征。一些 R 环可能从 Iα 的末端开始，但都仅在 Sα 内终止。时程分析还表明，R 环的百分比在类别转换重组发生之前达到峰值。这是首次证明 R 环在体外和体内形成 Sα，尽管 Sα 中的 G 密度和相对较少的 GGGG 簇存在差异。启动子与 Sα 的短距离可能弥补了 Sα 相对于其他转换区的 R 环形成因子的不足。总之，Sα 区的 R 环进一步支持 R 环形成是所有受刺激的转换区的普遍特征。
