Evidence for "inter- and intraspecific horizontal genetic transfers" between anciently asexual bdelloid rotifers is explained by cross-contamination
Evidence for "inter- and intraspecific horizontal genetic transfers" between anciently asexual bdelloid rotifers is explained by cross-contamination
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交叉污染解释了古代无性蛭形轮虫之间“种间和种内水平遗传转移”的证据
DOI：
10.1101/150490
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Wilson C
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文献类型：
--
作者：
Wilson C
蛭形轮虫是一类多样化的微观无脊椎动物，据信它们已经进化了数千万年，没有进行有性生殖。它们引起了生物学家的注意，他们对几乎所有其他真核生物中性的维持和重组感到困惑。蛭形基因组显示出高比例的非后生动物基因，这些基因是通过水平转移获得的。这一经过充分证实的发现引发了人们的猜测：轮虫之间也可能发生同源水平转移，其速度或许足以“取代”蛭类的性功能。 2016 年，Debortoli 及其同事声称为这一假设提供了证据 (Current Biology26, 723-32)。他们从自然种群中采集了蛭形虫属的个体，提取了 DNA 并对五个标记位点进行了测序。对于几个样本，物种的单倍型分配在位点之间不一致，作者将其解释为“种间水平遗传转移”的证据。在这里，我们使用作者提供的测序色谱图来证明，作为单个个体处理的样本实际上包含来自两个甚至三个动物的线粒体和核糖体单倍型。我们还表明，假定转移的 DNA 分子仅具有 75% 的序列同一性，这与已知的同源重组机制或蛭形基因组的既定特征不兼容。我们认为，这些和其他模式可以简单地通过动物或样品管之间 DNA 的交叉污染来解释，因此这项研究没有为基因在这些蛭形物种内部或之间转移的假设提供可靠的证据。鉴于这一案例和最近的其他案例，由于存在污染风险，我们建议今后在微观动物中进行水平基因转移时要特别谨慎地进行和评估。
Bdelloid rotifers are a diverse group of microscopic invertebrates that are believed to have evolved for tens of millions of years without sexual reproduction. They have attracted the attention of biologists puzzled by the maintenance of sex and recombination among nearly all other eukaryotes. Bdelloid genomes show a high proportion of non-metazoan genes, acquired by horizontal transfer. This well-substantiated finding has invited speculation that homologous horizontal transfer between rotifers also may occur, perhaps at rates sufficient to “replace” the functions of sex in bdelloids. In 2016, Debortoli and colleagues claimed to supply evidence for this hypothesis (Current Biology26, 723-32). They sampled individuals of the bdelloid genusAdinetafrom natural populations, extracted DNA and sequenced five marker loci. For several samples, the assignment of haplotypes to species was incongruent among loci, which the authors interpreted as evidence of “interspecific horizontal genetic transfers”. Here, we use sequencing chromatograms supplied by the authors to demonstrate that samples treated as single individuals actually contained mitochondrial and ribosomal haplotypes from two or even three animals. We also show that the putatively transferred DNA molecules share only 75% sequence identity, which is not compatible with known mechanisms of homologous recombination, or with established features of bdelloid genomes. We argue that these and other patterns are parsimoniously explained by cross-contamination of animals or DNA between sample tubes, and therefore that the study offers no reliable evidence for the hypothesis that genes are transferred either within or between these bdelloid species. In light of this and other recent cases, we recommend that work considering horizontal gene transfer in microscopic animals be conducted and evaluated with special caution in future, owing to the risk of contamination.