Xenopus tropicalis免疫球蛋白轻链重组多样性的研究

Junctional Diversity in Xenopus tropicalis Immunoglobulin Light Chains

热带爪蟾(Xenopus tropicalis)是两栖类动物免疫球蛋白研究中常用的模式生物之一,其免疫球蛋白轻链的类型和基因结构已经研究清楚,3种轻链类型分别为:ρ、σ和typeⅢ.通过克隆测序,并对3种轻链重组cDNA克隆的VJ基因片段的连接方式进行了分析,发现在表达的3种轻链中,仅有少量的N和P核苷酸的插入.σ轻链基因的体细胞VJ重组主要依靠微同源重组.而在ρ和typeⅢ轻链中这种方式不是主要的,ρ和typeⅢ轻链或是通过VJ基因片段的直接连接或是部分删除后连接.研究结果为研究免疫球蛋白轻链多样性产生的机制提供了重要的线索.

Xenopus tropicalis is an important model animal in immunology.Based on the available genome data,the genomic organization of all three light chain gene（ρ,σand typeⅢ） loci were recently characterized in Xenopus tropicalis.On the basis of similarity of protein sequences,genomic organization and chromosomal location of the light chain genes among frogs and mammals,the data strongly support the previous suggestions that theρgenes belong to theκgene lineage,whereas the typeⅢgenes share a common origin with theλgenes.About 200 cDNA fragments from each ofρ,σand typeⅢgenes,were cloned and sequenced respectively generating 22,25 and 44 clones that have unique VJ junctions（after removal of redundant clones） .Recombined VJ junctions of cloned light chain cDNA were analyzed,which showed a paucity of N and P nucleotides in expressedρ,σand typeⅢgenes.They also show that somatic VJ rearrangements of theσgene seemed to be dependent on short stretches of homologous nucleotides（microhomology） .The microhomology-directed VJ recombination obviously results in very limited diversity.However,most expressedρand typeⅢVJ junctions showed direct ligation or deletions of V and J coding ends.These results help researchers to understand the generation of Ig diversity in X.tropicalis.