Hsu E, Schwager J, Alt F W
Howard Hughes Medical Institute, New York, NY 10032.
Proc Natl Acad Sci U S A. 1989 Oct;86(20):8010-4. doi: 10.1073/pnas.86.20.8010.
We have isolated multiple independent cDNA clones that represent mRNA sequences of immunoglobulin heavy chains from the spleen of adult Xenopus laevis. These cDNA clones contained constant (C) region sequences that were either Cmu or a separate C region sequence believed to be Cnu. In individual cDNA clones the C region sequences were associated with independent heavy-chain variable region (VH) sequences that were classifiable into five distinct families. Genomic Southern blotting analyses with family-specific probes indicated that the haploid genome contains a minimum of 80 VH gene segments, a number similar to that found in various mammalian species. Multiple JH and putative DH segments were also identified (J, joining; D, diversity). Analyses of 13 independent VHDJH junctions suggest that combinatorial and junctional diversification mechanisms probably arose early in vertebrate evolution. Finally, comparison of Xenopus VH sequences to those from other vertebrates indicated conservation of V region framework residues that are responsible for the tertiary structure of the Fv throughout evolution.
我们从成年非洲爪蟾的脾脏中分离出了多个独立的 cDNA 克隆,这些克隆代表免疫球蛋白重链的 mRNA 序列。这些 cDNA 克隆包含恒定(C)区序列,它们要么是 Cμ,要么是一个被认为是 Cν 的单独 C 区序列。在单个 cDNA 克隆中,C 区序列与独立的重链可变区(VH)序列相关联,这些 VH 序列可分为五个不同的家族。使用家族特异性探针进行的基因组 Southern 印迹分析表明,单倍体基因组至少包含 80 个 VH 基因片段,这一数量与在各种哺乳动物物种中发现的数量相似。还鉴定出了多个 JH 和假定的 DH 片段(J,连接;D,多样性)。对 13 个独立的 VHDJH 连接的分析表明,组合和连接多样化机制可能在脊椎动物进化早期就已出现。最后,将非洲爪蟾的 VH 序列与其他脊椎动物的 VH 序列进行比较,结果表明在整个进化过程中,负责 Fv 三级结构的 V 区框架残基具有保守性。