A long form of the skate IgX gene exhibits a striking resemblance to the new shark IgW and IgNARC genes
A long form of the skate IgX gene exhibits a striking resemblance to the new shark IgW and IgNARC genes
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DOI：
10.1007/s002510050463
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发表时间：
1999-01-01
期刊：
影响因子：
3.2
通讯作者：
Litman, GW
中科院分区：
文献类型：
--
作者：
Anderson, MK;Strong, SJ;Litman, GW
差异筛选已被用来鉴定编码长型免疫球蛋白X的cDNA。将IgX长型与先前描述的短型IgX cDNA和基因组IgX基因座进行比较，发现短型和长型IgX的V区和两个5‘C区在核苷酸水平上有90%的同源性。长型和短型IgX基因V序列的差异集中在互补决定区，提示这些形式是通过相同基因组座位的选择性剪接或高度相关座位的转录而产生的。不同cDNA间核苷酸序列(包括第三位密码子)的极端保守性，以及在生殖系IgX、IgX短型不育转录本和IgX长型不育转录本的插入序列中核苷酸序列的接近同源性，表明多个IgX基因座最近彼此背离和/或处于激烈的基因校正之下。对已知的软骨鱼免疫球蛋白基因座的系统发育分析表明，该长型免疫球蛋白基因与IGW/IgNARC(NARC)同源，并与：1)在软骨/骨鱼谱系分化之前，IgX/IGW/NARC和类IgM基因座从一个共同的祖先座位分化；2)NAR基因座与IgX/IGW/NARC基因(S)的分化，大约在2.2亿年前，在软骨/骨鱼分裂之后，但在鲨鱼/冰刀鱼分裂之前。
Differential screening has been used to identify cDNAs encoding a long form of IgX in Raja eglanteria (clearnose skate). Comparisons of the IgX long form with the previously described short-form IgX cDNAs and the genomic IgX locus indicate that the V and two 5' C regions of the short and long forms of IgX are >90% identical at the nucleotide level. Differences between the V sequences of the long- and short-form IgX genes are concentrated in complementarity determining regions, suggesting that these forms are derived through alternative splicing of the same genomic loci or transcription of highly related loci. The extreme conservation of nucleotide sequence, including third position codons, among different cDNAs as well as the near identity of nucleotide sequence in the intervening sequences of germline IgX, IgX short-form sterile transcripts and IgX long-form sterile transcripts indicate that the multiple IgX loci are recently diverged from one another and/or are under intense gene correction. Phylogenetic analyses of the known cartilaginous fish immunoglobulin loci demonstrate that the long form of IgX is orthologous to IgW/IgNARC (NARC) and is most consistent with: 1) the divergence of the IgX/IgW/NARC and IgM-like loci from a common ancestral locus prior to the divergence of the cartilaginous/bony fish lineages and 2) the divergence of the NAR locus from the IgX/IgW/NARC gene(s) after the cartilaginous/bony fish split but prior to the shark/skate split, approximately 220 million years ago.