Widespread distribution and evolutionary patterns of mariner-like elements among various spiders and insects
Widespread distribution and evolutionary patterns of mariner-like elements among various spiders and insects
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DOI：
10.11416/jibs.84.2_029
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发表时间：
2015-06
影响因子：
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通讯作者：
Kaori Yamada;Akinori Yamada;Y. Kawanishi;R. Gurung;Takeshi Sasaki;G. Tokuda;H. Maekawa
中科院分区：
文献类型：
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作者：
Kaori Yamada;Akinori Yamada;Y. Kawanishi;R. Gurung;Takeshi Sasaki;G. Tokuda;H. Maekawa
转座子存在于几乎所有生物体的基因组中。TES根据其移动机制被归类为I类或II类。I类TES是反转录转座子，它通过复制粘贴机制与RNA中间体一起移动，而II类TES是DNA转座子，它作为DNA片段通过剪切粘贴机制移动。Mariner，也被称为Mos1，是一种DNA转座子，首次在果蝇中报道(Jacobson等人，1986；Medhora等人，1991)。它携带一种编码转座酶的基因，这种转座酶可以促进自身转座。水手基因也存在于关系密切的果蝇物种中，但在黑腹果蝇中明显缺失。一个与Mariner(Hcmar1)同源的序列是从天牛夜蛾(Hyalophora Cecropia)中分离出来的，命名为Mariner-like Element(MLE)(Lidholm等人，1991)。目前，已从广泛的系统发育相距遥远的生物中分离出MLEs，例如原生动物(Silva等人，2005年)、昆虫(Robertson，1993)、海洋无脊椎动物(Halaimia-Toumi等人，2004年)和哺乳动物(Auge-Gouillou等人，1995年)。根据目前的分类，MLEs属于Tc1-mariner家族，是更大的IS630-Tc1-mariner超家族的成员(Shao和Tu，2001)。MLEs又可进一步分为五个亚科：毛壳亚科、盲顶亚科、西洋参亚科/头状亚科、刺激亚科和Elegans/briggsae亚科(Robertson和MacLeod，1993)，或分为15个亚科(Rouault等人，2009年)。MLE的全长约为1300个碱基对(Bp)。该转座子含有一个编码约340个氨基酸的转座酶的无内含子开放读框(ORF)，其两侧有约30bp的末端反向重复(TIR)(Jacobson等人，1986；Hartl，1989)。催化转座反应的MLE转座酶包括一个带有螺旋-转角螺旋(HTH)基序的N-末端TIR结合结构域和一个具有独特的DD(34)D催化基序的C-末端催化结构域(Shao和Tu，2001；Plasterk和van Luenen，2002)。此外，水手家族中存在两个高度保守的氨基酸基序，WVPHEL和YSPDLAP(Robertson，1993；Robertson和MacLeod，1993)。特别是，WVPHEL可能参与Mariner转座酶二聚体界面的形成(Auge-Gouillou等人，2005年；Liu和Chalmers，2013年)。MLEs的高度序列相似性及其在基因组内和分类群之间的不均匀分布有力地表明，物种之间发生了水平转移(HT)(Robertson，1993；Lohe等人，1995；Lampe等人，2003；Rouleux-Bonnin等人，2005；Casse等人，2006)。MLE和其他DNA转座子生命周期的一般模型认为，单个拷贝最初侵入基因组，通过复制转座产生多个拷贝，或非水手样元件(MLEs)是广泛存在于真核生物基因组中的DNA转座子，被认为通过水平转移插入到宿主基因组中。在这项研究中，我们进行了系统发育分析，比较了来自蜘蛛目、膜翅目和鳞翅目三个目18种的MLE与以前报道的属于意大利蜂亚科的MLE。这些MLE具有很高的序列相似性(92.78%)。此外，从四个不同物种获得的MLE含有一个完整或几乎完整的开放阅读框架，该框架编码一个假定的转座酶。这些MLE与其各自寄主物种之间的系统发育差异以及MLE的高度序列相似性清楚地表明，最近发生了物种间的水平转移，而不是以前报道的MLE。在对本研究分析的基础上，我们讨论了它们可能的水平转移模式。
Transposable elements (TEs) are present in the genomes of almost all organisms. TEs are classified as either class I or II depending on their mobility mechanism. Class I TEs are retrotransposons that move via a copy– paste mechanism with an RNA intermediate, whereas class II TEs are DNA transposons that move via a cut– paste mechanism as a DNA fragment. Mariner, also referred to as Mos1, is a DNA transposon that was first reported in Drosophila mauritiana (Jacobson et al., 1986; Medhora et al., 1991). It carries a gene encoding a transposase that facilitates self-transposition. Mariner is also present in closely related Drosophila species but is clearly absent from D. melanogaster. A sequence homologous to mariner (Hcmar1) was isolated from the moth Hyalophora cecropia and designated as a mariner-like element (MLE) (Lidholm et al., 1991). At present, MLEs have been isolated from a vast range of phylogenetically distant organisms, such as protozoa (Silva et al., 2005), insects (Robertson, 1993), marine invertebrates (Halaimia-Toumi et al., 2004), and mammals (Auge-Gouillou et al., 1995). According to the current classification, MLEs belong to the Tc1-mariner family, which is a member of the larger IS630-Tc1-mariner superfamily (Shao and Tu, 2001). MLEs can be divided further into five subfamilies: mauritiana, cecropia, mellifera/capitata, irritans, and elegans/briggsae (Robertson and MacLeod, 1993) or into 15 subfamilies (Rouault et al., 2009). The full length of an MLE is approximately 1300 base pairs (bp). This transposon contains one intronless open reading frame (ORF) that encodes a transposase of approximately 340 amino acids, and it is flanked by terminal inverted repeats (TIRs) of approximately 30 bp (Jacobson et al., 1986; Hartl, 1989). MLE transposases that catalyze the transpositional reaction comprise an N-terminal TIR-binding domain with a helix– turn–helix (HTH) motif and a C-terminal catalytic domain with a unique DD(34)D catalytic motif (Shao and Tu, 2001; Plasterk and van Luenen, 2002). In addition, two highly conserved amino acid motifs, WVPHEL and YSPDLAP, are present in the mariner family (Robertson, 1993; Robertson and MacLeod, 1993). In particular, WVPHEL may participate in the formation of the mariner transposase dimer interface (Auge-Gouillou et al., 2005; Liu and Chalmers, 2013). The high sequence similarity of MLEs and their nonuniform distribution, both within genomes and among taxa, strongly suggest that horizontal transfer (HT) has occurred among species (Robertson, 1993; Lohe et al., 1995; Lampe et al., 2003; Rouleux-Bonnin et al., 2005; Casse et al., 2006). The general model of the MLE lifecycle and that of other DNA transposons suggests that a single copy initially invades a genome, which produces multiple copies via duplicative transposition or an unMariner-like elements (MLEs) are DNA transposons that are prevalent in a wide range of eukaryotic genomes and are considered to be inserted into their host genomes via horizontal transfer. In this study, we performed a phylogenetic analysis to compare MLEs obtained from 18 species of three orders, Araneae, Hymenoptera, and Lepidoptera, with previously reported MLEs, which were classified into the mellifera subfamily. These MLEs shared high sequence similarity (92.78%). Furthermore, MLEs obtained from four distinct species contained an intact or almost intact open reading frame that encoded a putative transposase. The phylogenetic differences between these MLEs and their respective host species as well as the high sequence similarity of MLEs clearly suggests that horizontal transfer has recently occurred among species than previously reported MLEs. We discuss their possible modes of horizontal transfer based on the analysis of this study.