Experimental Haematology, Leeds Institute of Molecular Medicine, University of Leeds, St James's University Hospital, Leeds LS9 7TF, UK.
Epigenetics Chromatin. 2010 Jan 19;3(1):3. doi: 10.1186/1756-8935-3-3.
Silencing of transgenes in mice is a common phenomenon typically associated with short multi-copy transgenes. We have investigated the regulation of the highly inducible human granulocyte-macrophage colony-stimulating-factor gene (Csf2) in transgenic mice.
In the absence of any previous history of transcriptional activation, this transgene was expressed in T lineage cells at the correct inducible level in all lines of mice tested. In contrast, the transgene was silenced in a specific subset of lines in T cells that had encountered a previous episode of activation. Transgene silencing appeared to be both transcription-dependent and mediated by epigenetic mechanisms. Silencing was accompanied by loss of DNase I hypersensitive sites and inability to recruit RNA polymerase II upon stimulation. This pattern of silencing was reflected by increased methylation and decreased acetylation of histone H3 K9 in the transgene. We found that silenced lines were specifically associated with a single pair of tail-to-tail inverted repeated copies of the transgene embedded within a multi-copy array.
Our study suggests that epigenetic transgene silencing can result from convergent transcription of inverted repeats which can lead to silencing of an entire multi-copy transgene array. This mechanism may account for a significant proportion of the reported cases of transgene inactivation in mice.
在小鼠中，转基因沉默是一种常见现象，通常与短的多拷贝转基因有关。我们研究了高度可诱导的人粒细胞-巨噬细胞集落刺激因子基因（Csf2）在转基因小鼠中的调控。
在没有任何先前转录激活史的情况下，该转基因在所有测试的小鼠品系中以正确的可诱导水平在 T 细胞谱系中表达。相比之下，在遇到先前激活事件的特定 T 细胞亚群中，转基因被沉默。转基因沉默似乎既依赖于转录，也依赖于表观遗传机制。沉默伴随着 DNA 酶 I 超敏位点的丧失和刺激时不能募集 RNA 聚合酶 II。这种沉默模式反映在转基因中组蛋白 H3 K9 的甲基化增加和乙酰化减少。我们发现，沉默的品系与嵌入多拷贝阵列中的转基因的一对首尾倒置重复拷贝特异性相关。
我们的研究表明，表观遗传转基因沉默可能是由反向重复的收敛转录引起的，这可能导致整个多拷贝转基因阵列的沉默。这种机制可能解释了报道的小鼠中转基因失活的很大一部分原因。
