Molecular Genetics of Nucleolar Dominance

描述（由申请人提供）：在植物或动物种间杂交中，核仁显性描述了一组亲本rRNA基因的转录，而另一组亲本rRNA基因的沉默。最近的证据表明，表观遗传开关涉及DNA甲基化、组蛋白甲基化和组蛋白乙酰化的协同变化，控制着激活/沉默的决定。利用拟南芥（拟南芥和沙南芥的杂交植物），短期目标是验证rRNA基因启动子DNA甲基化、组蛋白去乙酰化和组蛋白H3赖氨酸9 （H3K9）甲基化在维持沉默的自我强化循环中彼此上游的假设。两个组蛋白去乙酰化酶（一个位于核仁），一个DNA甲基转移酶和几个核仁优势所需的甲基胞嘧啶结合蛋白已经掌握。沉默所需的其他染色质修饰蛋白将使用rnai介导的基因敲低来鉴定。这些活性的生化特异性将被确定，它们与沉默基因相互作用的假设将通过染色质免疫沉淀、蛋白质-蛋白质相互作用测定和细胞学定位进行测试。将在开发期间和新形成的混合动力车中测试在建立和维持方面参与静音活动。特定启动子胞嘧啶的甲基化是沉默的关键这一假设也将得到验证。这些努力将有助于实现了解核仁优势是如何建立和实施的长期目标。

DESCRIPTION (provided by applicant): Nucleolar dominance describes the transcription of one parental set of rRNA genes, and the silencing of the other parental set, in a plant or animal inter-species hybrid. Recent evidence shows that an epigenetic switch involving concerted changes in DNA methylation, histone methylation and histone acetylation controls the activation/silencing decision. Using Arabidopsis suecica, the hybrid of A. thaliana and A. arenosa, the shortterm goal is to test the hypothesis that rRNA gene promoter DNA methylation, histone deacetylation and histone H3 lysine 9 (H3K9) methylation are each upstream of one another in a self-reinforcing cycle that maintains silencing. Two histone deacetylases (one localized in the nucleolus), one DNA methyltransferase and several methylcytosine binding proteins required for nucleolar dominance are already in hand. Additional chromatin modifying proteins required for silencing will be identified using RNAi-mediated gene knockdowns. Biochemical specificities of these activities will be determined and the hypothesis that they interact at silenced genes will be tested using chromatin immunoprecipitation, protein-protein interaction assays and cytological localization. Involvement of silencing activities in both establishment and maintenance will be tested during development and in newly formed hybrids. The hypothesis that methylation of specific promoter cytosines is key to silencing will also be tested. These efforts will help achieve the long-term goal of understanding how nucleolar dominance is established and enforced. DNA methylation and chromatin modifications are required for proper development. In knockout mice, DNA methyltransferase and histone H3K9 methylase activities are essential for viability. In humans, mutations in a DNA methyltransferase causes ICF syndrome and mutations in a histone deacetylase associated methylcytosine binding protein causes Rett syndrome. DNA methylation is also frequently elevated in tumors and can silence tumor suppressor genes. By dissecting mechanisms of chromatin-mediated silencing in nucleolar dominance, we hope to contribute to the understanding, and ultimately the treatment, of disorders involving aberrant gene expression.