DNA transposons are generally destroyed by mutations and have short lifespans in hosts, as they are neutral or harmful to the host and therefore not conserved by natural selection. The clawed frog Xenopus harbors many DNA transposons and certain families, such as T2-MITE, have extremely long lives. These have ancient origins, but have shown recent transposition activity. In addition, certain transposase genes may have been “domesticated” by Xenopus and conserved over long time periods by natural selection. The aim of this study was to elucidate the evolutionary interactions between the host and the long-lived DNA transposon family it contains. Here, we investigated the molecular evolution of the Kolobok DNA transposon superfamily. Kolobok is thought to contribute to T2-MITE transposition. In the diploid western clawed frog Xenopus tropicalis and the allotetraploid African clawed frog Xenopus laevis, we searched for transposase genes homologous to those in the Kolobok superfamily. To determine the amplification and domestication of these genes, we used molecular phylogenetics and analyses of copy numbers, conserved motifs, orthologous gene synteny, and coding sequence divergence between the orthologs of X. laevis and X. tropicalis, or between those of two distant X. tropicalis lineages. Among 38 X. tropicalis and 24 X. laevis prospective transposase genes, 10 or more in X. tropicalis and 14 or more in X. laevis were apparently domesticated. These genes may have undergone multiple independent domestications from before the divergence of X. laevis and X. tropicalis. In contrast, certain other transposases may have retained catalytic activity required for transposition and could therefore have been recently amplified. Multiple domestication of certain transposases and prolonged conservation of the catalytic activity in others suggest that Kolobok superfamily transposons were involved in complex, mutually beneficial relationships with their Xenopus hosts. Some transposases may serve to activate long-lived T2-MITE subfamilies.

中文翻译：

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爪蛙爪蟾中 Kolobok 超家族转座子的多次大规模驯化和近期扩增

DNA转座子通常被突变破坏并且在宿主中的寿命很短，因为它们对宿主是中性的或有害的，因此不被自然选择保存。爪蛙 Xenopus 含有许多 DNA 转座子，某些家族，如 T2-MITE，寿命极长。这些具有古老的起源，但显示出最近的转座活动。此外，某些转座酶基因可能已被非洲爪蟾“驯化”，并通过自然选择长期保存。这项研究的目的是阐明宿主与其包含的长寿 DNA 转座子家族之间的进化相互作用。在这里，我们研究了 Kolobok DNA 转座子超家族的分子进化。Kolobok 被认为有助于 T2-MITE 转座。在二倍体西部爪蛙热带爪蟾和异源四倍体非洲爪蛙非洲爪蟾中，我们寻找与 Kolobok 超家族同源的转座酶基因。为了确定这些基因的扩增和驯化，我们使用分子系统发育学和分析拷贝数、保守基序、直系同源基因同源性以及 X. laevis 和 X.tropicalis 直系同源物之间或两个遥远 X. . 热带血统。在38个热带X.和24个X. laevis前瞻性转座酶基因中，有10个或更多的热带X.和14个或更多的X. laevis明显被驯化。在 X. laevis 和 X.tropicalis 分化之前，这些基因可能已经经历了多次独立的驯化。相比之下，某些其他转座酶可能保留了转座所需的催化活性，因此最近可能被扩增。某些转座酶的多重驯化和在其他转座酶中催化活性的延长表明 Kolobok 超家族转座子与其非洲爪蟾宿主之间存在复杂、互利的关系。一些转座酶可能有助于激活长寿的 T2-MITE 亚家族。