The Regulation of B Lymphocyte Development

描述(由申请人提供)：B细胞的发展产生了大量和多样化的单一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。免疫球蛋白的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，该重组反应将免疫球蛋白重链和轻链基因的可变外显子从其组成的基因片段组装起来。一对淋巴特异性蛋白RAG1和RAG2相互形成一个复合体，识别一对重排的基因片段，并帮助催化它们的连接。这一过程在淋巴发育过程中受到调节，涉及到谱系(B细胞中的Ig基因完全重排，但不是T细胞中的Ig基因)、谱系内的顺序(重链重排在轻链之前)和等位基因的使用(单个细胞在其表面只表达一个功能性的Ig分子，这一现象称为等位基因排斥)。以往的工作表明，重组酶的靶向性取决于染色质结构中基因片段的可及性，而未重排基因片段的转录与它们对重组酶的可及性相关。这项关于B细胞发育调控的长期研究计划的竞争性更新旨在通过追求四个特定目标来了解在初级B细胞谱系生成过程中调节V(D)J重组的机制。1)确定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基因座如何被激活用于前B细胞的转录和重排，使得只有一个等位基因功能重排；3)确定转录因子NF-kB在调节受体编辑和B细胞谱系的正选择中起什么作用；以及4)测试关于IgHC V-to-DJ重排的谱系特异性和等位基因排斥机制的假说。这些研究具有重要意义，因为V(D)J重组缺陷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，并且因为适当调节重组酶对于避免自身免疫性疾病是必要的。

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.