A small family of sushi-class retrotransposon-derived genes in mammals and their relation to genomic imprinting
A small family of sushi-class retrotransposon-derived genes in mammals and their relation to genomic imprinting
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DOI：
10.1007/s00239-004-0332-0
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发表时间：
2005-10-01
影响因子：
3.9
通讯作者：
Ferguson-Smith, AC
中科院分区：
文献类型：
--
作者：
Youngson, NA;Kocialkowski, S;Ferguson-Smith, AC
Ty 3/gypsy反转录转座子在哺乳动物基因组中是罕见的，尽管它们在无脊椎动物和其他脊椎动物类中丰富。在这里，我们确定了一个家庭的9个保守的哺乳动物基因同源Ty 3/吉普赛反转录转座子，但已失去了自主反转录转座的能力。其中，5个映射到X染色体，而其余4个是常染色体。比较系统发育分析表明，它们与红鳍东方鲀的sushi-ichi元件具有最强的同源性。已知两个常染色体基因成员Peg 10和Rtl 1是印记的，从父系遗传的染色体同源物表达。这表明，与宿主-寄生虫反应理论的印记机制的演变，父母起源的特定表观遗传控制可能介导的基因组“寄生”的元素，如这些。或者，这些元件可以优先整合到两条同源染色体上差异修饰的区域，如印记结构域和X染色体，并获得单等位基因表达。我们评估了这个家族的其余常染色体成员的印记状态，并显示它们在胚胎和胎盘中双等位基因表达。此外，在整个开发过程中检测了Rtl 1的甲基化状态，发现其类似于活跃的沉默重复元件，而不是印迹序列。这表明，进行基因组印记的能力是不是这个家庭的所有成员的retroelements的固有属性。尽管如此，不同成员之间的保守性，但功能的分歧表明，他们已经经历了积极的选择，并获得了不同的内源性功能在其哺乳动物宿主。
Ty3/gypsy retrotransposons are rare in mammalian genomes despite their abundance in invertebrate and other vertebrate classes. Here we identify a family of nine conserved mammalian genes with homology to Ty3/gypsy retrotransposons but which have lost their ability to autonomously retrotranspose. Of these, five map to the X chromosome while the remaining four are autosomal. Comparative phylogenetic analyses show them to have strongest homology to the sushi-ichi element from Fugu rubripes. Two of the autosomal gene members, Peg10 and Rtl1, are known to be imprinted, being expressed from the paternally inherited chromosome homologue. This suggests, consistent with the host-parasite response theory of the evolution of the imprinting mechanism, that parental-origin specific epigenetic control may be mediated by genomic "parasitic" elements such as these. Alternatively, these elements may preferentially integrate into regions that are differentially modified on the two homologous chromosomes such as imprinted domains and the X chromosome and acquire monoallelic expression. We assess the imprinting status of the remaining autosomal members of this family and show them to be biallelically expressed in embryo and placenta. Furthermore, the methylation status of Rtl1 was assayed throughout development and was found to resemble that of actively, silenced repetitive elements rather than imprinted sequences. This indicates that the ability to undergo genomic imprinting is not an inherent property of all members of this family of retroelements. Nonetheless, the conservation but functional divergence between the different members suggests that they have undergone positive selection and acquired distinct endogenous functions within their mammalian hosts.