Hartig Julia Verena, Esslinger Stephanie, Böttcher Romy, Saito Kuniaki, Förstemann Klaus
Department of Chemistry and Biochemistry, Gene Center, Ludwig-Maximilians-Universität München, Munich, Germany.
EMBO J. 2009 Oct 7;28(19):2932-44. doi: 10.1038/emboj.2009.220. Epub 2009 Jul 30.
Colonization of genomes by a new selfish genetic element is detrimental to the host species and must lead to an efficient, repressive response. In vertebrates as well as in Drosophila, piRNAs repress transposons in the germ line, whereas endogenous siRNAs take on this role in somatic cells. We show that their biogenesis depends on a new isoform of the Drosophila TRBP homologue loquacious, which arises by alternative polyadenylation and is distinct from the one that functions during the biogenesis of miRNAs. For endo-siRNAs and piRNAs, it is unclear how an efficient response can be initiated de novo. Our experiments establish that the endo-siRNA pathway will target artificially introduced sequences without the need for a pre-existing template in the genome. This response is also triggered in transiently transfected cells, thus genomic integration is not essential. Deep sequencing showed that corresponding endo-siRNAs are generated throughout the sequence, but preferentially from transcribed regions. One strand of the dsRNA precursor can come from spliced mRNA, whereas the opposite strand derives from independent transcripts in antisense orientation.
新的自私遗传元件对基因组的定殖对宿主物种有害，必然会引发高效的抑制反应。在脊椎动物和果蝇中，piRNA在生殖系中抑制转座子，而内源性siRNA在体细胞中发挥这一作用。我们发现它们的生物合成依赖于果蝇TRBP同源物loquacious的一种新异构体，该异构体通过可变聚腺苷酸化产生，与在miRNA生物合成过程中起作用的异构体不同。对于内源性siRNA和piRNA，尚不清楚如何从头启动高效反应。我们的实验表明，内源性siRNA途径将靶向人工引入的序列，而无需基因组中预先存在的模板。这种反应在瞬时转染的细胞中也会触发，因此基因组整合并非必不可少。深度测序表明，相应的内源性siRNA在整个序列中产生，但优先来自转录区域。dsRNA前体的一条链可以来自剪接后的mRNA，而相反的链则来自反义方向的独立转录本。
