Rush James S, Fugmann Sebastian D, Schatz David G
Section of Immunobiology, Howard Hughes Medical Institute and Yale School of Medicine, New Haven, CT, USA.
Int Immunol. 2004 Apr;16(4):549-57. doi: 10.1093/intimm/dxh057.
Class switch recombination (CSR) is the process whereby B cells alter the effector properties of their Ig molecules. Whilst much is known about the cellular regulation of this process, many of the molecular details remain elusive. Recent evidence suggests that CSR involves blunt DNA double strand breaks (dsbs), and that formation of these dsbs requires the function of the activation-induced cytidine deaminase (AID). We sought to characterize the structural properties and kinetics of induction of the DNA lesions associated with CSR. Using ligation-mediated PCR, we found that AID-dependent DNA dsbs were specifically induced in the S mu region of murine B cells stimulated to undergo CSR. While blunt dsbs were detected, they were only a minor species, with staggered breaks being more than an order of magnitude more abundant. In addition, these breaks could be detected at equal frequency at upstream and downstream portions of S mu, and were induced prior to expression of newly switched isotypes. Collectively, these results provide direct evidence that staggered, S mu-targeted AID-dependent dsbs are the predominant DNA lesion associated with CSR, with important implications for the mechanisms by which CSR DNA lesions are made and processed.
类别转换重排（CSR）是B细胞改变其Ig分子效应特性的过程。尽管人们对该过程的细胞调节了解很多，但许多分子细节仍不清楚。最近的证据表明，CSR涉及钝性DNA双链断裂（dsb），并且这些dsb的形成需要激活诱导的胞苷脱氨酶（AID）的功能。我们试图表征与CSR相关的DNA损伤诱导的结构特性和动力学。使用连接介导的PCR，我们发现，在刺激进行CSR的小鼠B细胞的Sμ区域中特异性诱导了AID依赖性DNA dsb。虽然检测到钝性dsb，但它们只是少数类型，交错断裂的丰度要高出一个数量级以上。此外，这些断裂在Sμ的上游和下游部分以相同频率被检测到，并且在新转换的同种型表达之前被诱导。总体而言，这些结果提供了直接证据，即交错的、以Sμ为靶点的AID依赖性dsb是与CSR相关的主要DNA损伤，这对CSR DNA损伤的产生和处理机制具有重要意义。
