Genomic evidence for ameiotic evolution in the bdelloid rotifer Adineta vaga
Genomic evidence for ameiotic evolution in the bdelloid rotifer Adineta vaga
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DOI：
10.1038/nature12326
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发表时间：
2013-08-22
期刊：
影响因子：
64.8
通讯作者：
Van Doninck, Karine
中科院分区：
文献类型：
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作者：
Flot, Jean-Francois;Hespeels, Boris;Van Doninck, Karine
有性繁殖的丧失被认为是后生动物进化的死胡同，但蜈蚣轮虫挑战这一观点，因为它们似乎已经无性存在了数百万年(1)。在这些显微动物中，既没有观察到男性性器官，也没有观察到减数分裂：卵母细胞是通过有丝分裂形成的，没有染色体数量的减少，也没有染色体配对的迹象。然而，目前的证据并不排除他们可能在罕见的、神秘的场合发生性行为。在这里，我们报道了一种蛭形轮虫Adineta van a(Davis，1873)(3)的基因组，并表明它的结构与传统的减数分裂不相容。在基因水平上，迷走草的基因组是四倍体，既有古老的重复片段，也有较少分歧的等位基因区域。然而，与有性物种相反，等位基因区域被重新排列，有时甚至在同一条染色体上发现。这种结构不允许减数分裂配对；相反，我们发现了大量的基因转换证据，这可能会限制在没有减数分裂的情况下有害突变的积累。参与抗氧化、碳水化合物代谢和防御转座子的基因家族显著扩大，这可能解释了为什么转座元件只覆盖组装序列的3%。此外，8%的基因可能来自非后生动物，可能是水平获得的。蜈蚣类和原核生物之间的这种明显的趋同，为性别的进化意义提供了新的线索。
Loss of sexual reproduction is considered an evolutionary dead end for metazoans, but bdelloid rotifers challenge this view as they appear to have persisted asexually for millions of years(1). Neither male sex organs nor meiosis have ever been observed in these microscopic animals: oocytes are formed through mitotic divisions, with no reduction of chromosome number and no indication of chromosome pairing(2). However, current evidence does not exclude that they may engage in sex on rare, cryptic occasions. Here we report the genome of a bdelloid rotifer, Adineta vaga (Davis, 1873)(3), and show that its structure is incompatible with conventional meiosis. At gene scale, the genome of A. vaga is tetraploid and comprises both anciently duplicated segments and less divergent allelic regions. However, in contrast to sexual species, the allelic regions are rearranged and sometimes even found on the same chromosome. Such structure does not allow meiotic pairing; instead, we find abundant evidence of gene conversion, which may limit the accumulation of deleterious mutations in the absence of meiosis. Gene families involved in resistance to oxidation, carbohydrate metabolism and defence against transposons are significantly expanded, which may explain why transposable elements cover only 3% of the assembled sequence. Furthermore, 8% of the genes are likely to be of non-metazoan origin and were probably acquired horizontally. This apparent convergence between bdelloids and prokaryotes sheds new light on the evolutionary significance of sex.