Ye An, He Hongzhi, Kim Joomyeong
Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, United States of America.
PLoS One. 2014 Sep 29;9(9):e108596. doi: 10.1371/journal.pone.0108596. eCollection 2014.
The expression of two adjacent imprinted genes, Peg3 and Zim1, is inversely correlated: down-regulation of Peg3 coinciding with up-regulation of Zim1. The current study characterized this inverse correlation using a mutant allele targeting Peg3. According to the results, the mutation on the paternal allele of Peg3 resulted in a dramatic increase in the transcription levels of the maternal allele of Zim1, suggesting the involvement of unknown trans factors in this trans-allelic event. Subsequent ChIP experiments revealed that the protein encoded by Peg3 itself binds to the zinc finger exon of Zim1, which is modified with the repression mark H3K9me3. Interestingly, the levels of H3K9me3 on Zim1 are also reduced in the mutant cells lacking the protein PEG3, suggesting potential roles for PEG3 in establishing H3K9me3 on Zim1. Reintroducing PEG3 into the mutant cell restored down-regulation of Zim1, confirming the predicted repressor role for Peg3 on Zim1. Overall, these results demonstrated that paternally expressed Peg3 controls maternally expressed Zim1 as a trans factor. The current study also provides the first case for the trans-allelic interaction of two oppositely imprinted genes through their gene products.
两个相邻的印记基因Peg3和Zim1的表达呈负相关：Peg3的下调与Zim1的上调同时发生。当前的研究使用靶向Peg3的突变等位基因对这种负相关进行了表征。根据结果，Peg3父本等位基因上的突变导致Zim1母本等位基因的转录水平显著增加，这表明未知的反式作用因子参与了这一反式等位基因事件。随后的染色质免疫沉淀实验表明，Peg3自身编码的蛋白与Zim1的锌指外显子结合，该外显子被抑制标记H3K9me3修饰。有趣的是，在缺乏蛋白PEG3的突变细胞中，Zim1上的H3K9me3水平也降低了，这表明PEG3在Zim1上建立H3K9me3中具有潜在作用。将PEG3重新引入突变细胞中恢复了Zim1的下调，证实了Peg3对Zim1的预测抑制作用。总体而言，这些结果表明，父本表达的Peg3作为反式作用因子控制母本表达的Zim1。当前的研究还提供了两个反向印记基因通过其基因产物进行反式等位基因相互作用的首个案例。
