“蛭形輪蟲”被認為已經(jīng)以無性方式存在和分化了數(shù)百萬年,,這很奇怪,,因為有性生殖的喪失對后生動物來說被普遍認為是走進了一條演化上的死胡同。此前人們仍懷疑它們也許偶爾會進行有性生殖,。但在這項研究中,,Olivier Jaillon及同事對一種名叫“Adineta vaga”的“蛭形輪蟲”的基因組進行了測序,發(fā)現(xiàn)其結構與傳統(tǒng)減數(shù)分裂(與有性生殖相關的細胞分裂類型)不匹配,。其基因組已經(jīng)歷了豐富的基因轉換,,這可能限制了在沒有減數(shù)分裂時有害突變的積累。多達8%的基因可能來自非后生動物,,可能是通過橫向基因轉移獲得的,。這些發(fā)現(xiàn)為無性演化提供了肯定證據(jù),支持關于“蛭形輪蟲”從古以來進行無性生殖的假說,。(生物谷Bioon.com)
生物谷推薦英文摘要:
Nature doi: 10.1038/nature12326
Genomic evidence for ameiotic evolution in the bdelloid rotifer Adineta vaga
Jean-Francois Flot, Boris Hespeels, Xiang Li, Benjamin Noel, Irina Arkhipova, Etienne G. J. Danchin, Andreas Hejnol, Bernard Henrissat, Romain Koszul, Jean-Marc Aury, Valérie Barbe, Roxane-Marie Barthélémy, Jens Bast, Georgii A. Bazykin, Olivier Chabrol, Arnaud Couloux, Martine Da Rocha, Corinne Da Silva, Eugene Gladyshev, Philippe Gouret, Oskar Hallatschek, Bette Hecox-Lea, Karine Labadie, Benjamin Lejeune, Oliver Piskurek et al.
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. 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. 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), 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.