Sale J E, Calandrini D M, Takata M, Takeda S, Neuberger M S
Medical Research Council Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK.
Nature. 2001 Aug 30;412(6850):921-6. doi: 10.1038/35091100.
After gene rearrangement, immunoglobulin V genes are further diversified by either somatic hypermutation or gene conversion. Hypermutation (in man and mouse) occurs by the fixation of individual, non-templated nucleotide substitutions. Gene conversion (in chicken) is templated by a set of upstream V pseudogenes. Here we show that if the RAD51 paralogues XRCC2, XRCC3 or RAD51B are ablated the pattern of diversification of the immunoglobulin V gene in the chicken DT40 B-cell lymphoma line exhibits a marked shift from one of gene conversion to one of somatic hypermutation. Non-templated, single-nucleotide substitutions are incorporated at high frequency specifically into the V domain, largely at G/C and with a marked hotspot preference. These mutant DT40 cell lines provide a tractable model for the genetic dissection of immunoglobulin hypermutation and the results support the idea that gene conversion and somatic hypermutation constitute distinct pathways for processing a common lesion in the immunoglobulin V gene. The marked induction of somatic hypermutation that is achieved by ablating the RAD51 paralogues is probably a consequence of modifying the recombination-mediated repair of such initiating lesions.
基因重排后，免疫球蛋白V基因通过体细胞超突变或基因转换进一步多样化。超突变（在人和小鼠中）通过单个非模板化核苷酸取代的固定而发生。基因转换（在鸡中）由一组上游V假基因作为模板。我们在此表明，如果RAD51旁系同源物XRCC2、XRCC3或RAD51B被敲除，鸡DT40 B细胞淋巴瘤系中免疫球蛋白V基因的多样化模式会呈现出从基因转换向体细胞超突变的显著转变。非模板化的单核苷酸取代以高频率特异性地掺入V结构域，主要在G/C处，且具有明显的热点偏好。这些突变的DT40细胞系为免疫球蛋白超突变的遗传剖析提供了一个易于处理的模型，结果支持了基因转换和体细胞超突变构成处理免疫球蛋白V基因中常见损伤的不同途径这一观点。通过敲除RAD51旁系同源物实现的体细胞超突变的显著诱导可能是修饰此类起始损伤的重组介导修复的结果。
