The ancient mariner sails again: Transposition of the human Hsmar1 element by a reconstructed transposase and activities of the SETMAR protein on transposon ends
The ancient mariner sails again: Transposition of the human Hsmar1 element by a reconstructed transposase and activities of the SETMAR protein on transposon ends
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DOI：
10.1128/mcb.02027-06
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发表时间：
2007-06-01
影响因子：
5.3
通讯作者：
Ivics, Zoltan
中科院分区：
文献类型：
--
作者：
Miskey, Csaba;Papp, Balazs;Ivics, Zoltan
Hsmar 1是人类mariner转座子的两个亚家族之一，是一种古老的元素，类似于5000万年前进入灵长类基因组谱系。虽然Hsmar 1元件由于突变损伤而失活，但转座酶基因的一个特定拷贝显然已被选择。该转座酶编码区是SETAM基因的一部分，其中组蛋白甲基转移酶SET结构域与Hsmarl转座酶结构域融合。采用系统发育学方法重建了祖先Hsmar 1转座酶基因，我们将其命名为Hsmar 1-Ra。Hsmar 1-Ra转座酶在人类细胞和斑马鱼胚胎中通过剪切和粘贴机制有效地动员Hsmar 1转座子。Hsmar 1-Ra还可以动员与Hsmar 1（MiHsmar 1）相关的短反向重复转座元件（MITE），从而在Hsmar 1转座酶源和这些MITE之间建立功能关系。MiHsmar 1切除比长元件的切除效率高2个数量级，从而为它们的高拷贝数提供了解释。我们表明，SETMAR蛋白结合并在体外引入单链切口到Hsmarl反向重复序列。发现DNA断裂修复的途径选择在体内对Hsmar 1-Ra和SETMAR介导的转座子切割的反应中具有特征性不同。而非同源末端连接在修复由Hsmar 1-Ra转座酶产生的切除位点中起主导作用，DNA修复后由SETMAR切割主要遵循同源依赖性途径。新的转座子系统可以是一个有用的工具，在脊椎动物的基因组操作和调查的转座动力学和灵长类动物基因组进化的贡献。
Hsmar1, one of the two subfamilies of mariner transposons in humans, is an ancient element that entered the primate genome lineage similar to 50 million years ago. Although Hsmar1 elements are inactive due to mutational damage, one particular copy of the transposase gene has apparently been under selection. This transposase coding region is part of the SETAM gene, in which a histone methylatransferase SET domain is fused to an Hsmarl transposase domain. A phylogenetic approach was taken to reconstruct the ancestral Hsmarl transposase gene, which we named Hsmar1-Ra. The Hsmar1-Ra transposase efficiently mobilizes Hsmarl transposons by a cut-and-paste mechanism in human cells and zebra fish embryos. Hsmar1-Ra can also mobilize short inverted-repeat transposable elements (MITEs) related to Hsmarl (MiHsmar1), thereby establishing a functional relationship between an Hsmarl transposase source and these MITEs. MiHsmar1 excision is 2 orders of magnitude more efficient than that of long elements, thus providing an explanation for their high copy numbers. We show that the SETMAR protein binds and introduces single-strand nicks into Hsmarl inverted-repeat sequences in vitro. Pathway choices for DNA break repair were found to be characteristically different in response to transposon cleavage mediated by Hsmar1-Ra and SETMAR in vivo. Whereas nonhomologous end joining plays a dominant role in repairing excision sites generated by the Hsmar1-Ra transposase, DNA repair following cleavage by SETMAR predominantly follows a homology-dependent pathway. The novel transposon system can be a useful tool for genome manipulations in vertebrates and for investigations into the transpositional dynamics and the contributions of these elements to primate genome evolution.