College of Animal Science & Technology, Yangzhou University, Jiangsu, China.
Genome Biol Evol. 2020 Mar 1;12(3):66-76. doi: 10.1093/gbe/evaa034.
The discovery of new members of the Tc1/mariner superfamily of transposons is expected based on the increasing availability of genome sequencing data. Here, we identified a new DD35E family termed Traveler (TR). Phylogenetic analyses of its DDE domain and full-length transposase showed that, although TR formed a monophyletic clade, it exhibited the highest sequence identity and closest phylogenetic relationship with DD34E/Tc1. This family displayed a very restricted taxonomic distribution in the animal kingdom and was only detected in ray-finned fish, anura, and squamata, including 91 vertebrate species. The structural organization of TRs was highly conserved across different classes of animals. Most intact TR transposons had a length of ∼1.5 kb (range 1,072-2,191 bp) and harbored a single open reading frame encoding a transposase of ∼340 aa (range 304-350 aa) flanked by two short-terminal inverted repeats (13-68 bp). Several conserved motifs, including two helix-turn-helix motifs, a GRPR motif, a nuclear localization sequence, and a DDE domain, were also identified in TR transposases. This study also demonstrated the presence of horizontal transfer events of TRs in vertebrates, whereas the average sequence identities and the evolutionary dynamics of TR elements across species and clusters strongly indicated that the TR family invaded the vertebrate lineage very recently and that some of these elements may be currently active, combining the intact TR copies in multiple lineages of vertebrates. These data will contribute to the understanding of the evolutionary history of Tc1/mariner transposons and that of their hosts.
基于越来越多的基因组测序数据，预计将发现 Tc1/mariner 转座子超家族的新成员。在这里，我们鉴定了一个新的 DD35E 家族，称为旅行者（TR）。对其 DDE 结构域和全长转座酶的系统发育分析表明，尽管 TR 形成了一个单系进化枝，但它与 DD34E/Tc1 具有最高的序列同一性和最接近的系统发育关系。该家族在动物界的分类分布非常有限，仅在有鳍鱼类、两栖类和爬行类中检测到，包括 91 种脊椎动物。TR 的结构组织在不同的动物类群中高度保守。大多数完整的 TR 转座子的长度约为 1.5kb（范围为 1,072-2,191bp），并含有一个单一的开放阅读框，编码一个约 340aa（范围 304-350aa）的转座酶，两侧为两个短末端反向重复（13-68bp）。还在 TR 转座酶中鉴定到几个保守基序，包括两个螺旋-转角-螺旋基序、一个 GRPR 基序、一个核定位序列和一个 DDE 结构域。本研究还证明了 TR 在脊椎动物中存在水平转移事件，而跨物种和聚类的 TR 元件的平均序列同一性和进化动态强烈表明，TR 家族最近入侵了脊椎动物谱系，其中一些元件可能目前处于活跃状态，将完整的 TR 拷贝组合在脊椎动物的多个谱系中。这些数据将有助于理解 Tc1/mariner 转座子及其宿主的进化历史。
