Role of Target DNA sequences in mutation and DNA Break Generation

描述（由申请人提供）：在对抗原的反应中，活化的B细胞经历体细胞超突变（SHM）和类开关重组（CSR）以增强抗体多样性。SHM和CSR都需要激活诱导脱氨酶（AID），它能催化dna特异性胞苷脱氨酶的活性。AID靶向免疫球蛋白重链（Igh）位点的高度重复开关(S)区域，诱导DNA双链断裂（dsb），这是CSR的中间产物。当靶向IgH和IgL位点的可变(V)区外显子时，AID主要诱导点突变，称为SHM，导致抗体对抗原的亲和力增加。经过大量的研究，已经确定了可能结合S区DNA或RNA转录本的潜在AID辅助因子。这表明AID靶向与S区转录暂停或RNA加工之间存在联系。与研究相对充分的

DESCRIPTION (provided by applicant): In response to antigens, activated B cells undergo somatic hypermutation (SHM) and class switch recombination (CSR) to enhance antibody diversity. SHM and CSR each require the Activation Induced Deaminase (AID), which catalyses DNA-specific cytidine deaminase activity. AID targets the highly repetitive switch (S) regions of immunoglobulin heavy chain (Igh) loci to induce DNA double strand breaks (DSBs), which are intermediates in CSR. When targeting to variable (V) region exons of IgH and IgL loci, AID predominantly induces point mutations, termed SHM, resulting in the increased affinity of antibody for antigen. Intensive efforts have identified potential AID co-factors, which could bind S region DNA or RNA transcripts of Igh loci. This suggests a link between AID targeting and transcriptional pausing or RNA processing of S regions. In contrast to the relatively well studied targeting mechanisms for CSR, the mechanism of AID targeting to V region locus is much less well understood. Although AID has the ability to deaminate any transcribed substrate in vitro and could potentially access the genome widely to induce genomic instability in B cells, its physiological targets during SHM are almost exclusively restricted to V regions of Ig loci. However, due to the lack of robust experimental systems, it remains largely unknown how AID is specifically targeted to V regions, which is one of the most interesting unresolved questions in the field of AID regulation. Thus, we have established a unique experimental system, and propose to address these fundamental questions. The completion of our proposal will provide novel insights into the regulation of AID-mediated SHM in B cell immune responses and elucidate molecular mechanism of genomic instability in B cell lymphomas.