Somatic variation precedes extensive diversification of germline sequences and combinatorial joining in the evolution of immunoglobulin heavy chain diversity.
Somatic variation precedes extensive diversification of germline sequences and combinatorial joining in the evolution of immunoglobulin heavy chain diversity.
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体细胞变异先于种系序列的广泛多样化和免疫球蛋白重链多样性进化中的组合连接。
DOI：
10.1084/jem.178.3.815
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发表时间：
1993-09-01
影响因子：
15.3
通讯作者：
Litman, G W
中科院分区：
文献类型：
--
作者：
Hinds-Frey, K R;Nishikata, H;Litman, R T;Litman, G W
在扁头哈那鲨（一种在系统发育上较为原始的鲨鱼物种）中，可变（VH）、多样（DH）、连接（JH）区段以及恒定（CH）外显子被组织在单个约18 - 20kb的“簇”中。通过对基因组DNA文库的广泛筛选，鉴定出一个具有>90%核酸同源性的单一大型VH家族以及一个单型的第二基因家族。来自不同种系基因簇的DH区段的核苷酸序列几乎没有差异，这表明DH的早期作用是促进连接多样性，而非贡献独特的编码特异性。一种基因特异性寡脱氧核苷酸筛选方法被用于将特定转录产物（cDNA）与单个基因簇相关联，结果表明基因重排是在簇内而非簇间进行的。这为扁头哈那鲨免疫球蛋白重链的有限多样性提供了进一步的证据，由此推断组合多样性是一种较新获得的产生多样性的方式。所选cDNA序列与从常规基因组文库以及通过对基因组DNA直接PCR扩增产生的VH区段特异性文库中获得的区段元件序列之间观察到的差异表明，VH库是通过连接多样性和体细胞突变两种方式实现多样化的。综上所述，这些发现表明了一种此前未被认识的体细胞变异的贡献，它先于种系库的广泛多样化以及体液免疫进化过程中的组合连接过程。
In Heterodontus, a phylogenetically primitive shark species, the variable (VH), diversity (DH), joining (JH) segments, and constant (CH) exons are organized in individual approximately 18-20-kb "clusters." A single large VH family with > 90% nucleic acid homology and a monotypic second gene family are identified by extensive screening of a genomic DNA library. Little variation in the nucleotide sequences of DH segments from different germline gene clusters is evident, suggesting that the early role for DH was in promoting junctional diversity rather than contributing unique coding specificities. A gene-specific oligodeoxynucleotide screening method was used to relate specific transcription products (cDNAs) to individual gene clusters and showed that gene rearrangements are intra- rather than intercluster. This provides further evidence for restricted diversity in the immunoglobulin heavy chain of Heterodontus, from which it is inferred that combinatorial diversity is a more recently acquired means for generating diversity. The observed differences between cDNA sequences selected and the sequences of segmental elements derived from conventional genomic libraries as well as from VH segment-specific libraries generated by direct PCR amplification of genomic DNA indicate that the VH repertoire is diversified by both junctional diversity and somatic mutation. Taken together, these findings suggest a heretofore unrecognized contribution of somatic variation that preceded both extensive diversification of the germline repertoire and the combinatorial joining process in the evolution of humoral immunity.