The Regulation of B Lymphocyte Development

描述（由申请人提供）：B细胞发育产生大量多样的单特异性和自我耐受的B细胞，表达表面免疫球蛋白（Ig）作为其抗原受体的识别成分。Ig多样性依赖于一种被称为V(D)J重组的严格调控的新型位点特异性DNA重组反应，该反应将Ig重链和轻链基因的可变外显子从其组成基因片段中组装起来。一对淋巴细胞特异性蛋白，RAG1和RAG2，彼此形成一个复合体，识别重排的基因片段对并帮助催化它们的连接。这一过程在淋巴细胞发育过程中受到谱系（Ig基因在B细胞中完全重排，而不是T细胞）、谱系内的顺序（重链重排先于轻链重排）和等位基因的使用（单个细胞在其表面只表达一个功能性Ig分子，这种现象被称为等位基因排斥）的调节。先前的研究表明，重组酶的靶向性取决于染色质结构内基因片段的可及性，而未重排基因片段的转录与重组酶的可及性相关。这是对B细胞发育调控的长期研究项目的竞争性更新，旨在通过追求四个特定目标来了解在原代B细胞库生成过程中调节V(D)J重组的机制。1)鉴定RAG1和RAG2基因转录调控所需的顺式作用DNA序列和反式作用因子；2)确定Ig kappa基因座如何在b前细胞中激活转录和重排，从而只有一个等位基因被功能重排；3)确定转录因子NF-kB在调节受体编辑和B细胞库阳性选择中的作用（如果有的话）；4)检验关于IgHC V-to-DJ重排的谱系特异性和等位基因排斥机制的假设。这些研究意义重大，因为有缺陷的V(D)J重组可导致严重的免疫缺陷，因为靶向重组酶的错误与基因组不稳定、染色体易位和恶性肿瘤有关，并且因为重组酶的适当调节是避免自身免疫性疾病所必需的。

DESCRIPTION (provided by applicant): B cell development generates a large and diverse repertoire of mono-specific and self-tolerant B cells expressing surface immunoglobulin (Ig) as the recognition component of their antigen receptor. Ig diversity depends upon a tightly regulated novel site-specific DNA recombination reaction known as V(D)J recombination which assembles the variable exons of the Ig heavy-chain and light-chain genes from their component gene-segments. A pair of lymphoid-specific proteins, RAG1 and RAG2, form a complex with one another that recognizes pairs of rearranging gene segments and helps catalyze their joining. This process is regulated during lymphoid development with respect to lineage (Ig genes fully rearrange in B but not T cells), order within the lineage (heavy-chain rearranges before light-chain), and the use of alleles (an individual cell expresses only one functional Ig molecule on its surface, a phenomenon known as allelic exclusion). Previous work has shown that targeting of the recombinase depends upon the accessibility of gene- segments within chromatin structure and that transcription of unrearranged gene segments correlates with their accessibility to the recombinase. This competing renewal of a long-standing program of research on the regulation of B cell development aims to understand the mechanisms which regulate V(D)J recombination during generation of the primary B cell repertoire through the pursuit of four specific aims. 1) To identify the cis-acting DNA sequences and trans-acting factors which are required for the transcriptional regulation of the RAG1 and RAG2 genes; 2) To determine how the Ig kappa locus is activated for transcription and rearrangement in pre-B cells in such a fashion that only one allele is functionally rearranged; 3) To determine what role if any the transcription factor NF-kB plays in the regulation of receptor editing and positive selection of the B cell repertoire; and 4) to test hypotheses regarding the mechanisms of lineage specificity and allelic exclusion of IgHC V-to-DJ rearrangement. These studies are significant because defective V(D)J recombination can lead to profound immunodeficiency, because mistakes in targeting the recombinase are associated with genomic instability, chromosomal translocations, and malignancy, and because appropriate regulation of the recombinase is necessary to avoid autoimmune disease.