Mediator contributes to IgH locus VDJ rearrangements by promoting usage of most distal V segments

INTRODUCTION The immunoglobulin heavy(IgH)chain locus includes a large cluster of V,D and J segments spanning thousands of kilobases in mammals and its expression implies long-range 3D-regulation of various gene modifications.1 V(D)J recombination occurs during early B-cell ontogeny.2 It is regulated by multiple transcription factors and cis-regulatory elements,and most notably by the intronic 5′Eμelement located in the JH to Cμintron.3 The intergenic control region 1(IGCR1)located between the VH and D gene clusters inhibits rearrangement of the most DH-proximal VH gene segments,while promoting usage of distal VH gene segments.4 Other downstream elements of the locus,flanking its 3′end might have more subtle roles:while the large 3′regulatory region(3′RR)shows strong internal synergies2 and behaves as a superenhancer in mature B cells.Its deletion showed no influence on the VDJ repertoire and rather increased transcription of unrearranged V segments.3–5 Insulators binding CTCF farther downstream of the 3′RR were shown,however,to promote usage of distal VH segments.6 Altogether,there are strong indications that elements involved in long-distance regulation of transcription might also influence VDJ recombination.In-frame splicing of VDJ exons is also needed for full Ig expression.7 Given the functional importance of gene architecture and long-range interactions for the IgH locus physiology,we explored the dependence of the VDJ repertoire on Med1,a known actor of long-range enhancer interactions.

哺乳动物免疫球蛋白基因及其表达机制研究进展

动物免疫球蛋白的基因序列、结构类型、功能以及其多样性的机制一直国内外学者关注焦点。目前对于免疫球蛋白基因及其多样性表达机制的研究多数是以人类或者小鼠为对象,该文将论述猪、牛、羊、骆驼和家兔的免疫球蛋白基因结构及其表达机制,探究不同哺乳动物免疫球蛋白基因表达的特点,以期为动物免疫方面和抗病育种的研究提供参考。

重组激活基因研究进展

重组激活基因 (RAGs)的编码产物Rag1和Rag2组成最重要的重组酶 ,能特异地识别Ig和TCR的V、DH、J基因片段两侧的RSS ,并催化DNA双链断裂 ,引起V(D)J重排 ,是Ig和TCR库多样性的主要原因。RAGs在体内和体外激活的成熟B细胞中也能被诱导表达 ,在斑马鱼的嗅觉神经元中检测到第一例非淋巴组织中的RAGs共表达。

重组激活基因与临床疾病

ragl或rag2基因的错义突变可使其编码的重组酶活性部分受损,导致V(D)J重组发生倾向于产生单克隆的活化Th2的改变,结果引起一类严重的联合免疫缺陷综合征(SCID),称为Omenn syndrome(OS)。OS的准确诊断有赖于RAGs基因的直接测序分析,它也是目前在SCID和OS家族中调查胎儿是否受其遗传影响的最有效方法。RAGs基因编码的重组酶催化V(D)J基因重排时,发生的错误识别可导致抗原受体基因和癌基因染色体易位,是淋巴系统恶性肿瘤发生的重要因素。RAGs还可能与自身免疫性疾病等有关。

Human colorectal cancer cells frequently express IgG and display unique Ig repertoire

BACKGROUND There is growing evidence proving that many human carcinomas, including colon cancer, can overexpress immunoglobulin(Ig); the non B cancer cell-derived Ig usually displayed unique V(D)J rearrangement pattern that are distinct from B cell-derived Ig. Especially, the cancer-derived Ig plays important roles in cancer initiation, progression, and metastasis. However, it still remains unclear if the colon cancer-derived Ig can display unique V(D)J pattern and sequencing, which can be used as novel target for colon cancer therapy.AIM To investigate the Ig repertoire features expressed in human colon cancer cells.METHODS Seven cancerous tissue samples of colon adenocarcinoma and corresponding noncancerous tissue samples were sorted by fluorescence-activated cell sorting using epithelial cell adhesion molecule as a marker for epithelial cells. Ig repertoire sequencing was used to analyze the expression profiles of all 5 classes of Ig heavy chains(IgH) and the Ig repertoire in colon cancer cells and corresponding normal epithelial cells.RESULTS We found that all 5 IgH classes can be expressed in both colon cancer cells and normal epithelial cells. Surprisingly, unlike the normal colonic epithelial cells that expressed 5 Ig classes, our results suggested that cancer cells most prominently express IgG. Next, we found that the usage of Ig in cancer cells caused the expression of some unique Ig repertoires compared to normal cells. Some VH segments, such as VH3-7, have been used in cancer cells, and VH3-74 was frequently present in normal epithelial cells. Moreover, compared to the normal cell-derived Ig, most cancer cell-derived Ig showed unique VHDJH patterns.Importantly, even if the same VHDJH pattern was seen in cancer cells and normal cells, cancer cell-derived IgH always displayed distinct hypermutation hot points.CONCLUSION We found that colon cancer cells could frequently express IgG and unique IgH repertoires, which may be involved in carcinogenesis of colon cancer. The unique IgH repertoire has the potential to be used as a novel target in immune therapy for colon cancer.

重组激活基因

本文概述了能诱导可变、多样与连接片段重组（ｒｅｃｏｍｂｉｎａｔｉｏｎｏｆｖａｒｉａｂｌｅ，ｄｉｖｅｒｓｉｔｙａｎｄｊｏｉｎｉｎｇｇｅｎｅｓｅｇｍｅｎｔｓ）又称ＶＤＪ重组的两个重组激活基因（ｒｅｃｏｍｂｉｎａｔｉｏｎａｃｔｉｖａｔｉｎｇｇｅｎｅｓ，ＲＡＧｓ）──ＲＡＧ－１和ＲＡＧ－２的研究现状，主要介绍了ＲＡＧｓ的发现过程、结构特征、功能以及激活ＶＤＪ重组的可能机制。

NHEJ通路缺陷与原发性免疫缺陷病

非同源末端连接（nonhomologous DNA end joining，NHEJ）是人和哺乳动物细胞DNA双链断裂（DSBs）修复的主要通路，如该通路蛋白因子缺陷使DNA损伤不能得到及时修复，将导致VDJ重组障碍和（或）免疫球蛋白类别转换重组缺陷，致联合免疫缺陷、染色体不稳定、细胞死亡及肿瘤等疾病发生。

Characterization of human IgM and IgG repertoires in individuals with chronic HIV-1 infection

Advancements in high-throughput sequencing(HTS)of antibody repertoires(Ig-Seq)have unprecedentedly improved our ability to characterize the antibody repertoires on a large scale.However,currently,only a few studies explored the influence of chronic HIV-1 infection on human antibody repertoires and many of them reached contradictory conclusions,possibly limited by inadequate sequencing depth and throughput.To better understand how HIV-1 infection would impact humoral immune system,in this study,we systematically analyzed the differences between the IgM(HIV-IgM)and IgG(HIV-IgG)heavy chain repertoires of HIV-1 infected patients,as well as between antibody repertoires of HIV-1 patients and healthy donors(HH).Notably,the public unique clones accounted for only a negligible proportion between the HIV-IgM and HIV-IgG repertoires libraries,and the diversity of unique clones in HIV-IgG remarkably reduced.In aspect of somatic mutation rates of CDR1 and CDR2,the HIV-IgG repertoire was higher than HIV-IgM.Besides,the average length of CDR3 region in HIV-IgM was significant longer than that in the HH repertoire,presumably caused by the great number of novel VDJ rearrangement patterns,especially a massive use of IGHJ6.Moreover,some of the B cell clonotypes had numerous clones,and somatic variants were detected within the clonotype lineage in HIV-IgG,indicating HIV-1 neutralizing activities.The in-depth characterization of HIV-IgG and HIV-IgM repertoires enriches our knowledge in the profound effect of HIV-1 infection on human antibody repertoires and may have practical value for the discovery of therapeutic antibodies.