Dong Yanying, Wu Caijun, Zhao Xiaohui, Zhang Ping, Zhang Hua, Zheng Mingzhe, Li Shichang, Jiao Junna, Yu Xiaozhuo, Lv Zhuangwei, Ji Yanhong
Department of Pathogenic Biology and Immunology, School of Basic Medical Sciences, Xi'an Jiaotong University Health Science Centre, Xi'an, Shaanxi, China.
Key Laboratory of Environment and Genes Related to Diseases (Xi'an Jiaotong University), Ministry of Education of China, Xi'an, Shaanxi, China.
Immunology. 2017 Oct;152(2):218-231. doi: 10.1111/imm.12758. Epub 2017 Jun 23.
The variable region of murine immunoglobulin heavy chain (Igh) is assembled by sequential D -J and V -DJ recombination. The accessibility of the Igh locus determines the order of rearrangement. Because of the large number of V genes and the lack of a suitable model, the epigenetic modifications of V genes after DJ recombination have not previously been characterized. Here, we employed two v-Abl pro-B cell lines, in which the Igh locus is in germline and DJ -recombined configurations, respectively. The DJ junction displays the characteristics of a recombination centre, such as high levels of activation-associated histone modifications and recombination-activating gene protein (RAG) binding in DJ -rearranged pro-B cells, which extend the recombination centre model proposed for the germline Igh locus. The different domains of the V region have distinct epigenetic characteristics after DJ recombination. Distal V genes have higher levels of active histone modifications, germline transcription and Pax5 binding, and good quality recombination signal sequences. Proximal V genes are relatively close to the DJ recombination centre, which partially compensates for the low levels of the above active epigenetic modifications. DJ recombination centre might serve as a cis-acting element to regulate the accessibility of the V region. Furthermore, we demonstrate that RAG weakly binds to functional V genes, which is the first detailed assessment of RAG dynamic binding to V genes. We provide a way for V -DJ recombination in which the V gene is brought into close proximity with the DJ recombination centre for RAG binding by a Pax5-dependent chromosomal compaction event, and held in this position for subsequent cleavage and V -DJ joining.
小鼠免疫球蛋白重链（Igh）的可变区是通过连续的D-J和V-DJ重组组装而成的。Igh基因座的可及性决定了重排的顺序。由于V基因数量众多且缺乏合适的模型，DJ重组后V基因的表观遗传修饰此前尚未得到表征。在这里，我们使用了两种v-Abl前B细胞系，其中Igh基因座分别处于种系和DJ重组构型。DJ连接处表现出重组中心的特征，例如在DJ重排的前B细胞中高水平的与激活相关的组蛋白修饰和重组激活基因蛋白（RAG）结合，这扩展了针对种系Igh基因座提出的重组中心模型。DJ重组后，V区的不同结构域具有不同的表观遗传特征。远端V基因具有更高水平的活性组蛋白修饰、种系转录和Pax5结合，以及高质量的重组信号序列。近端V基因相对靠近DJ重组中心，这部分补偿了上述活性表观遗传修饰的低水平。DJ重组中心可能作为顺式作用元件来调节V区的可及性。此外，我们证明RAG与功能性V基因弱结合，这是对RAG与V基因动态结合的首次详细评估。我们提供了一种V-DJ重组方式，其中V基因通过依赖Pax5的染色体压缩事件与DJ重组中心紧密靠近以进行RAG结合，并保持在该位置以便后续切割和V-DJ连接。
