Okano Yosuke, Miki Daisuke, Shimamoto Ko
Laboratory of Plant Molecular Genetics, Nara Institute of Science and Technology (NAIST), 8916-5 Takayama, Ikoma 630-0101, Japan.
Plant J. 2008 Jan;53(1):65-77. doi: 10.1111/j.1365-313X.2007.03313.x. Epub 2007 Oct 30.
Recent evidence indicates that small interfering RNA (siRNA) induces chromatin modifications and inactivation at homologous genomic sequences. A large number of endogenous siRNAs have been discovered that correspond to widely dispersed regions of the genome. We used an experimental system in which transgene-derived siRNAs target promoter regions in rice to determine whether or not siRNAs induce chromatin modifications that result in inactivation. Our results indicate that siRNAs targeted to one transgene and seven endogenous genes induce DNA methylation at all of the target promoters, but do not induce transcriptional suppression. Chromatin immunoprecipitation (ChIP) assays indicate that reduced euchromatic histone modifications were concomitant with the silencing of one endogenous gene, but not of six other endogenous genes that were not silenced. Furthermore, heterchromatic H3K9me2 was higher only in the promoter of the transgene that was completely silenced. These findings lead us to assume that siRNA rarely induces chromatin inactivation or changes in pattern of histone modification, especially H3K9 methylation, within most regions of the genome.
最近的证据表明，小干扰RNA（siRNA）可诱导同源基因组序列的染色质修饰和失活。已发现大量内源性siRNA，它们对应于基因组中广泛分散的区域。我们使用了一个实验系统，其中转基因衍生的siRNA靶向水稻中的启动子区域，以确定siRNA是否诱导导致失活的染色质修饰。我们的结果表明，靶向一个转基因和七个内源性基因的siRNA在所有靶启动子处诱导DNA甲基化，但不诱导转录抑制。染色质免疫沉淀（ChIP）分析表明，常染色质组蛋白修饰的减少与一个内源性基因的沉默相伴，但与其他六个未沉默的内源性基因无关。此外，异染色质H3K9me2仅在完全沉默的转基因启动子中更高。这些发现使我们假设，在基因组的大多数区域内，siRNA很少诱导染色质失活或组蛋白修饰模式的改变，尤其是H3K9甲基化。
