Factors and DNA Motifs in Ig Class Switch

描述（由申请人提供）：体液免疫依赖于免疫球蛋白（Ig）的表达来抵御病原性挑战。体液免疫系统已经进化到产生具有广泛结合特异性的Ig。类开关重组（Class switch recombination， CSR）是实现Ig效应物功能多样性和组织定位的重要手段。小鼠的IgH恒定区位点组织为：5′-V(D)J-C¿-Cd-C?3-C?1-C?2b-C?2a-Ce-Ca-3′。CSR涉及染色体内缺失重排，其重点是位于每个CH基因上游的重复开关(S) DNA区域（Cd除外）。CSR的过程可分为起始、S/S突触和修复三个阶段。AID诱导的DNA S区损伤启动了这一过程。我建议研究导致S/S突触的事件，并辨别与转录和DNA修复相关的染色质修饰。利用染色体构象捕获技术（3C），我的实验室最近研究了位于VH和CH基因之间的5个内含子增强子（E¿）和位于IgH位点3‘端的3’ ea增强子以及各种GLT启动子之间的远程相互作用。我们发现，在B细胞中，E¿和3'Ea增强子在空间上非常接近，形成了独特的染色体环结构。B细胞活化导致种系转录物（GLT）启动子以细胞因子依赖的方式向E¿：3’ea复合体募集。这种结构有利于S/S突触，因为S¿靠近E¿，下游S区域与目标GLT启动子共同招募到E¿：3'Ea复合体。我们提出GLT启动子与E¿：3’ea复合物的结合创造了一个结构支架，在CSR过程中促进S/S突触，这些相互作用依赖于AID的稳定作用。染色质重塑是控制S DNA进入AID的重要调控机制。我们在S区和C区发现了不同的组蛋白修饰。我们的研究表明，染色质可接近性与S区组蛋白乙酰化和H3K4me3的增加有关，而可接近性的降低与S区下游的低ac和H3K36me3标记有关。我们将研究可及性与这些组蛋白修饰之间的因果关系。叙述：体液免疫依赖于免疫球蛋白（Ig）的表达来抵御病原性挑战。体液免疫系统已经进化到产生具有广泛结合特异性的Ig。我们研究了新型Ig的分子表达过程。

DESCRIPTION (provided by applicant): Humoral immunity is dependent on the expression of immunoglobulin (Ig) to fend off pathogenic challenges. The humoral immune system has evolved to produce Ig with a broad repertoire of binding specificities. Class switch recombination (CSR) is used to attain diversity of Ig effector function and tissue localization. The murine IgH constant region locus is organized: 5'-V(D)J-C¿-Cd-C?3-C?1-C?2b-C?2a-Ce-Ca-3'. CSR involves an intra-chromosomal deletional rearrangement that focuses on regions of repetitive switch (S) DNA located upstream of each CH gene (with the exception of Cd). The process of CSR can be thought of as composed of three phases including, initiation, S/S synapsis and resolution and repair. AID induced DNA lesions at S regions initiates the process. I propose to examine events leading to S/S synapsis, and discern chromatin modifications associated with transcription and DNA repair. Using the chromosome conformation capture technique (3C), my laboratory has newly investigated the long- range interactions between the 5 intronic enhancer (E¿) located between the VH and CH genes and the 3'Ea enhancer located at the 3'-end of the IgH locus together with the various GLT promoters. We find that in B cells, the E¿ and 3'Ea enhancers are in close spatial proximity forming a unique chromosomal loop configuration. B cell activation leads to recruitment of the germline transcript (GLT) promoters to the E¿: 3'Ea complex in a cytokine dependent fashion. This structure facilitates S/S synapsis since S¿ is proximal to E¿ and the downstream S region are co-recruited with the targeted GLT promoter to the E¿: 3'Ea complex. We propose that GLT promoter association with the E¿: 3'Ea complex creates an architectural scaffolding that promotes S/S synapsis during CSR and these interactions are dependent on the stabilizing influence of AID. Chromatin remodeling is an important regulatory mechanism controlling the accessibility of S DNA to AID. We have defined histone modifications differentially found in the S and C regions. Our studies indicate chromatin accessibility is correlated with increased histone acetylation and H3K4me3 at the S regions whereas reduced accessibility is associated with hypoAc and the H3K36me3 mark downstream of the S region. We will study the causual relationship between accessibility and these histone modifications. NARRATIVE: Humoral immunity is dependent on the expression of immunoglobulin (Ig) to fend off pathogenic challenges. The humoral immune system has evolved to produce Ig with a broad repertoire of binding specificities. We study the molecular processes by which new types of Ig are expressed.