Greenberg A S, Steiner L, Kasahara M, Flajnik M F
Department of Microbiology and Immunology, University of Miami School of Medicine, FL 33101.
Proc Natl Acad Sci U S A. 1993 Nov 15;90(22):10603-7. doi: 10.1073/pnas.90.22.10603.
The time of emergence of immunoglobulin kappa and lambda light (L) chains in evolution is unknown. An L chain cDNA clone was isolated from the nurse shark (Ginglymostoma cirratum), a cartilaginous fish, whose predicted variable (V) region amino acid sequence has up to 60% sequence identity to mammalian V kappa domains. Genomic analyses suggest a cluster-type gene organization for this L chain locus, similar to the shark lambda-like immunoglobulin L chain loci rather than mammalian kappa loci. We propose that divergence of the ancestral L chain into isotypes likely occurred before the emergence of elasmobranchs 400-450 million years ago. Similarities in gene organization between the two isotypes in sharks may reflect the gene organization utilized by the ancestral L chain.
免疫球蛋白κ和λ轻链（L链）在进化过程中出现的时间尚不清楚。从一种软骨鱼护士鲨（Ginglymostoma cirratum）中分离出一个L链cDNA克隆，其预测的可变（V）区氨基酸序列与哺乳动物Vκ结构域的序列同一性高达60%。基因组分析表明，该L链基因座具有簇状基因组织，类似于鲨鱼λ样免疫球蛋白L链基因座，而不是哺乳动物κ基因座。我们提出，祖先L链分化为不同的同种型可能发生在4亿至4.5亿年前板鳃亚纲动物出现之前。鲨鱼中两种同种型之间基因组织的相似性可能反映了祖先L链所采用的基因组织。
