Evolutionary diversification of multigene families: Allelic selection of toxins in predatory cone snails
Evolutionary diversification of multigene families: Allelic selection of toxins in predatory cone snails
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DOI：
10.1093/oxfordjournals.molbev.a026412
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发表时间：
2000-09-01
影响因子：
10.7
通讯作者：
Palumbi, SR
中科院分区：
文献类型：
--
作者：
Duda, TF;Palumbi, SR
为了研究芋螺毒素多基因家族在两个近缘关系密切的食虫圆锥动物中的进化，我们从两个圆锥虫个体中测定了104个四环芋螺毒素mRNAs的序列，并将其与已从短圆锥虫中获得的序列进行了比较。与从短冠螺芋螺毒素序列的多样性相比，只有两个常见的序列变异体被回收。这两个个体变异的分离模式和另外9个个体的四环芋螺毒素扩增产物的限制性内切酶分析表明，常见的变异是来自单个基因座的等位基因。这两个假定的等位基因在九个位置上不同，这些位置非随机地出现在序列的毒素编码区。此外，所有的替换都位于非同义位点，导致了预测的等位基因氨基酸序列中的7个氨基酸差异。这些结果表明，芋螺毒素的多样性是由强大的多样性选择和某种形式的频率依赖性或超显性选择所驱动的，这些结果表明，不同的芋螺毒素多基因家族可能起源于多态基因座的重复。此外，从白蜡虫中回收的序列似乎都不是从短毛锦鸡儿中获得的基因座的同源序列，并且试图用座位特异性引物在这些物种中扩增出同源序列的尝试没有成功。这些模式表明，由于芋螺毒素基因座的不同表达，关系密切的螺属物种的毒液可能会有所不同。
In order to investigate the evolution of conotoxin multigene families among two closely related vermivorous Conus species, we sequenced 104 four-loop conotoxin mRNAs from two individuals of Conus ebraeus and compared these with sequences already obtained from Conus abbreviatus. In contrast to the diversity of conotoxin sequences obtained from C. abbreviatus, only two common sequence variants were recovered from C. ebraeus. Segregation patterns of the variants in these two individuals and restriction digests of four-loop conotoxin amplification products from nine additional individuals suggest that the common variants are alleles from a single locus. These two putative alleles differ at nine positions that occur nonrandomly in the toxin-coding region of the sequences. Moreover, all substitutions are at nonsynonymous sites and are responsible for seven amino acid differences among the predicted amino acid sequences of the alleles. These results imply that conotoxin diversity is driven by strong diversifying selection and some form of frequency-dependent or overdominant selection at conotoxin loci, and they suggest that diverse conotoxin multigene families can originate from duplications at polymorphic loci. Furthermore, none of the sequences recovered from C. ebraeus appeared to be orthologs of loci from C. abbreviatus, and attempts to amplify orthologous sequences with locus-specific primers were unsuccessful among these species. These patterns suggest that venoms of closely related Conus species may differ due to the differential expression of conotoxin loci.