Mechanism of Class Switch Recombination

描述（由申请人提供）：激活诱导胞嘧啶脱氨酶（AID）通过DNA胞嘧啶脱氨（将胞嘧啶转化为尿嘧啶）在特定基因组位点造成DNA损伤，启动免疫球蛋白基因体细胞超突变、基因转换和类开关重组（CSR）。虽然这些病变对于产生抗感染的优化抗体至关重要，但它们也对基因组的完整性构成威胁。艾滋病相关的致癌突变和染色体易位常见于B细胞源性肿瘤。我们提出了三个具体目标，以解决我们在企业社会责任机制方面的几个重大空白。在目标1中，我们将操纵CH12F3细胞中IgH α位点的转录控制元件（启动子/增强子），以鉴定针对AID开关(S)区域至关重要的顺式作用DNA元件。在目标2中，我们将确定S区域的AID足迹的频率和精确位置，以描述CSR期间体内的AID作用。在目标3中，我们将确定哪种DNA连接酶负责S区断裂的替代末端连接。

DESCRIPTION (provided by applicant): Activation-induced cytidine deaminase (AID) initiates immunoglobulin gene somatic hypermutation, gene conversion and class switch recombination (CSR) by inflicting DNA lesions at specific genomic loci via DNA cytosine deamination (that converts cytosine to uracil). While these lesions are essential for the production of optimized antibodies against infections, they are also threats to the genome integrity. AID-associated oncogenic mutations and chromosomal translocations are frequently seen in tumors of B cell origin. We propose three specific aims to address several significant gaps in our knowledge about the mechanism of CSR. In aim 1, we will manipulate the transcription control elements (promoters/enhancers) at IgH α locus in CH12F3 cells to identify cis-acting DNA elements critical for targeting AID to switch (S) regions. In aim 2, we will determine the frequency and precise positions of AID footprints in S regions to delineate AID actions in vivo during CSR. In aim 3, we will determine which DNA ligase is responsible for alternative end-joining of S region breaks.