Liu J, Wolf B
University of Pennsylvania, School of Veterinary Medicine, Philadelphia, PA, 19104-6008, USA.
Immunology. 1998 Oct;95(2):291-301. doi: 10.1046/j.1365-2567.1998.00590.x.
In the rabbit, recent investigations have provided evidence that gene conversion leads to the generation of diversity of heavy chain rearranged VH-DH-JH genes. No data have been published on a similar mechanism for rabbit light chains. In our laboratory, we initially infected rabbits with Trypanosoma brucei, which stimulates B-cell hyperplasia and hypergammaglobulinaemia. The heterozygous rabbits exhibited the Ckappa1 b4 and b9 kappa light chain allotypes. After reverse transcription of mRNA, and cloning and sequencing of cDNA, the Vkappa-Jkappa-Ckappa genes provided evidence for both somatic hypermutation and gene conversion. We saw that in each of the b4 and b9 kappa light chain cDNA, CDR1 and CDR3 carried both point mutation and provisional gene conversion traits. In the CDR2 region, point mutation and gene conversion inserts were observed in the b4 genes, with only gene conversion in two b9 genes. In the CDR regions, although some genes exhibited only somatic hypermutation or gene conversion, others showed linkage of both somatic hypermutation and gene conversion in the same sequence. This also marks the first time that somatic hypermutation and gene conversion in the same cloned CDR region has been observed in Vkappa1 genes; however, it has been seen earlier in rabbit heavy chain VH sequences. Furthermore, the addition of several codons to the CDR3 segment by gene conversion may have provided a mechanism for length variation. In addition, we demonstrated that Jkappa and framework region segments contained examples of somatic hypermutation. Confirmation of gene conversion necessitates that donor sequences be identified as providing the templated inserts. Thus after cloning two pseudogenes we found putative CDR3 donor segments for two CDR3 rearranged genes. The results offer additional mechanisms for the generation of diversity among rearranged rabbit kappa light chain genes. Whether there is a relationship or influence of gene conversion upon somatic hypermutation or vice versa is not discernable at present.
在兔子中，最近的研究已提供证据表明基因转换导致重链重排的VH-DH-JH基因产生多样性。关于兔子轻链的类似机制尚未有数据发表。在我们实验室，我们最初用布氏锥虫感染兔子，该寄生虫会刺激B细胞增生和高丙种球蛋白血症。杂合兔子表现出Ckappa1 b4和b9 κ轻链同种异型。在对mRNA进行逆转录、cDNA克隆和测序后，Vkappa-Jkappa-Ckappa基因提供了体细胞超突变和基因转换的证据。我们发现，在b4和b9 κ轻链cDNA的每一个中，互补决定区1（CDR1）和互补决定区3（CDR3）都具有点突变和临时基因转换特征。在互补决定区2（CDR2）区域，在b4基因中观察到点突变和基因转换插入，而在两个b9基因中仅观察到基因转换。在互补决定区（CDR）中，尽管一些基因仅表现出体细胞超突变或基因转换，但其他基因在同一序列中显示出体细胞超突变和基因转换的连锁。这也是首次在Vkappa1基因的同一克隆CDR区域中观察到体细胞超突变和基因转换；然而，在兔子重链VH序列中更早之前就已观察到。此外，通过基因转换向CDR3区段添加几个密码子可能提供了长度变异的机制。此外，我们证明Jkappa和框架区区段包含体细胞超突变的实例。基因转换的确认需要将供体序列鉴定为提供模板插入。因此，在克隆两个假基因后，我们发现了两个CDR3重排基因的推定CDR3供体区段。这些结果为重排的兔子κ轻链基因之间多样性的产生提供了额外的机制。目前尚无法确定基因转换与体细胞超突变之间是否存在关系或影响，反之亦然。
