A novel repeat-associated small interfering RNA-mediated silencing pathway downregulates complementary sense gypsy transcripts in somatic cells of the Drosophila ovary
A novel repeat-associated small interfering RNA-mediated silencing pathway downregulates complementary sense gypsy transcripts in somatic cells of the Drosophila ovary
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DOI：
10.1128/jvi.01980-06
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发表时间：
2007-02-01
影响因子：
5.4
通讯作者：
Bucheton, Alain
中科院分区：
文献类型：
--
作者：
Pelisson, Alain;Sarot, Emeline;Bucheton, Alain
吉普赛内源性逆转录病毒的复制涉及邻近体细胞组织对雌性生殖系的污染。这是防止flam，一个尚未克隆的异染色质pericentromeric位点，在这些体细胞卵巢组织中的转录积累的水平。我们测试了假定的RNA沉默机制对含有各种吉普赛序列的构建体产生的RNA积累的影响，并报告沉默的效率确实与卵巢中长度为25至30个核苷酸的互补RNA的量相关。例如，虽然发现这些RNA显示出3 - 5倍过量的反义链，但只有含有互补正义吉普赛序列的转录物可以被抑制，表明它们靶向RNA而不是DNA水平。它们的大小和链极性的不对称性是典型的新的重复相关的小干扰RNA（rasiRNA）介导的途径，最近怀疑防止有害的表达自私的DNA，特别是在生殖系。与microRNA不同（但与rasiRNA相似，令人惊讶的是，siRNA也是如此），吉普赛rasiRNA在3'端被修饰。吉普赛沉默需要与rasiRNA相关的蛋白Piwi（而不是Aub），而Dicer-2（产生siRNA）则不是。相反，piwi，aub和flam似乎不影响体细胞siRNA介导的沉默。吉普赛rasiRNA的量在遗传上由flam基因座以不依赖于前病毒拷贝数的方式决定，并且在体细胞组织中由一些着丝粒周围前病毒触发，从而能够保护生殖系免受逆转录病毒侵袭。
Replication of the gypsy endogenous retrovirus involves contamination of the female germ line by adjacent somatic tissues. This is prevented by flam, an as-yet-uncloned heterochromatic pericentromeric locus, at the level of transcript accumulation in these somatic ovarian tissues. We tested the effect of a presumptive RNA silencing mechanism on the accumulation of RNAs produced by constructs containing various gypsy sequences and report that the efficiency of silencing is indeed correlated with the amount of complementary RNAs, 25 to 30 nucleotides in length, in the ovary. For instance, while these RNAs were found to display a three- to fivefold excess of the antisense strands, only the transcripts that contain the complementary sense gypsy sequences could be repressed, indicating that they are targeted at the RNA, not DNA, level. Their size and asymmetry in strand polarity are typical of the novel repeat-associated small interfering RNA (rasiRNA)-mediated pathway, recently suspected to prevent the deleterious expression of selfish DNA specifically in the germ line. Unlike microRNAs (but like rasiRNAs and, surprisingly, siRNAs as well), gypsy rasiRNAs are modified at the 3' end. The rasiRNA-associated protein Piwi (but not Aub) is required for gypsy silencing, whereas Dicer-2 (which makes siRNAs) is not. In contrast, piwi, aub, and flam do not appear to affect somatic siRNA-mediated silencing. The amount of gypsy rasiRNAs is genetically determined by the flam locus in a provirus copy number-independent manner and is triggered in the somatic tissues by some pericentromeric provirus(es), which are thereby able to protect the germ line from retroviral invasion.