Identification of a CSR specific checkpoint

摘要 体液免疫反应需要通过抗原使免疫球蛋白谱系多样化 受体重排。小鼠免疫球蛋白基因座大小为2.9Mb，其中~100个为功能性基因 参与V(D)J重组的VH基因片段和使用的8个CH基因 在类切换重组(CSR)期间。激活诱导脱氨酶(AID)是 成熟B细胞免疫球蛋白体细胞高突变与CSR企业社会责任要求 必须长时间突触的DNA双链断裂的转录和诱导 基因组距离有助于染色体内重排。IgH轨迹假定为特定的 促进CSR的染色质拓扑结构在B细胞的不同阶段可能会有所不同 发展。在新的研究中，我们研究了发育过程中 调控高阶染色质结构、基因表达和重组 结合功能评估的基于染色体构象捕获的方法 企业社会责任。我们发现了出人意料的高频率染色质相互作用 下游的CH基因。这让我们假设，S下游地区可能会与 彼此之间。我们的研究证实了这一假设，并导致了对企业社会责任模型的修订。 这些研究促使我们寻找积极参与CSR的B细胞亚群。 出乎意料的是，参与CSR的B细胞变成了bcr阴性，并停留在G1期 提示存在DNA双链断裂检查点。 此外，bcr-细胞动态地转变为IgM，然后再循环为bcr-。在这里我们 建议绘制参与CSR的B细胞亚群的转录组并确定其细胞 命运分支点。这些研究非常重要，因为bcr阴性的B细胞将 对外源性抗原无反应，这对B细胞的激活有重要意义。

ABSTRACT Humoral immune responses require the diversification of the Ig repertoire by means of antigen receptor rearrangements. The mouse Igh locus spans 2.9 Mb within which are ~100 functional VH gene segments that participate in V(D)J recombination and eight CH genes that are used during class switch recombination (CSR). Activation induced deaminase (AID) is essential for both immunoglobulin somatic hypermutation and CSR in mature B cells. CSR requires transcription and induction of DNA double strand breaks (DSBs) that must synapse over long genomic distances to facilitate intra-chromosomal rearrangement. The Igh locus assumes specific chromatin topologies that facilitate CSR and these may vary at different stages of B cell development. In new studies we have examined the relationship between developmentally regulated higher-order chromatin structure, gene expression and recombination using chromosome conformation capture based approaches in combination with functional assessment of CSR. We discovered an unexpectedly high frequency of chromatin interactions among downstream CH genes. This led us to postulate that downstream S regions could recombine with each other. Our studies confirmed this hypothesis and led to a revision of the model for CSR. These studies stimulated us to search for B cell subsets that are actively engaged in CSR. Unexpectedly, B cells that are engaged in CSR become BCR negative and reside in the G1 phase of the cell cycle suggesting the presence of a DNA double strand break checkpoint. Furthermore, BCR- cells dynamically transition to IgM+ and then re-cycle to BCR-. Here we propose to profile the transcriptome of B cell subsets engaged in CSR and determine their cell fate branch point. These studies are very important since BCR negative B cells will be unresponsive to exogenous antigen and this has important implications for B cell activation.