Yazaki Euki, Ishikawa Sohta A, Kume Keitaro, Kumagai Akira, Kamaishi Takashi, Tanifuji Goro, Hashimoto Tetsuo, Inagaki Yuji
Graduate School of Life and Environmental Sciences, University of Tsukuba.
Department of Biological Sciences, Graduate School of Sciences, University of Tokyo.
Genes Genet Syst. 2017 Sep 12;92(1):35-42. doi: 10.1266/ggs.16-00056. Epub 2017 Feb 20.
All members of the order Trypanosomatida known to date are parasites that are most likely descendants of a free-living ancestor. Trypanosomatids are an excellent model to assess the transition from a free-living to a parasitic lifestyle, because a large amount of experimental data has been accumulated for well-studied members that are harmful to humans and livestock (Trypanosoma spp. and Leishmania spp.). However, recent advances in our understanding of the diversity of trypanosomatids and their close relatives (i.e., members of the class Kinetoplastea) have suggested that the change in lifestyle took place multiple times independently from that which gave rise to the extant trypanosomatid parasites. In the current study, transcriptomic data of two parasitic kinetoplastids belonging to orders other than Trypanosomatida, namely Azumiobodo hoyamushi (Neobodonida) and Trypanoplasma borreli (Parabodonida), were generated. We re-examined the transition from a free-living to a parasitic lifestyle in the evolution of kinetoplastids by combining (i) the relationship among the five orders in Kinetoplastea and (ii) that among free-living and parasitic species within the individual orders. The former relationship was inferred from a large-scale multigene alignment including the newly generated data from Azumiobodo and Trypanoplasma, as well as the data from another parasitic kinetoplastid, Perkinsela sp., deposited in GenBank; and the latter was inferred from a taxon-rich small subunit ribosomal DNA alignment. Finally, we discuss the potential value of parasitic kinetoplastids identified in Parabodonida and Neobodonida for studying the evolutionary process that turned a free-living species into a parasite.
迄今为止所知的所有动基体目成员都是寄生虫，它们很可能是自由生活祖先的后代。动基体寄生虫是评估从自由生活向寄生生活方式转变的绝佳模型，因为对于已充分研究的、对人类和牲畜有害的成员（锥虫属和利什曼原虫属）已经积累了大量实验数据。然而，我们对动基体寄生虫及其近亲（即动质体纲成员）多样性的最新认识表明，生活方式的改变是多次独立发生的，与导致现存动基体寄生虫的改变不同。在本研究中，我们生成了属于动基体目以外其他目（即阿苏螨动基体虫（新波多虫目）和博氏锥虫（副波多虫目））的两种寄生性动基体的转录组数据。我们通过结合（i）动质体纲五个目的关系和（ii）各目内自由生活和寄生物种的关系，重新审视了动基体在进化过程中从自由生活向寄生生活方式的转变。前一种关系是从大规模多基因比对中推断出来的，该比对包括来自阿苏螨动基体虫和博氏锥虫的新生成数据，以及来自另一种寄生性动基体珀金斯动基体（Perkinsela sp.）并保存在GenBank中的数据；后一种关系是从一个分类丰富的小亚基核糖体DNA比对中推断出来的。最后，我们讨论了在副波多虫目和新波多虫目中鉴定出的寄生性动基体对于研究将自由生活物种转变为寄生虫的进化过程的潜在价值。
