Control of Nucleolar Dominance in Arabidopsis

越来越多的人认识到，在复杂生物体的正常发育所必需的基因的精心策划的表达中，基因沉默可能与激活一样重要。 相关现象包括X染色体失活、配子印记、原病毒失活、共抑制和转座因子失活。 目前尚不清楚这些表观遗传现象中的基因抑制是如何建立的;然而，DNA甲基化和染色质结构的改变与动物和植物的基因沉默密切相关。 核仁优势是一种广泛存在于动植物中的表观遗传现象。 核显性是指在种间杂种或异源多倍体中遗传自一个亲本的染色体上选择性形成核仁的现象。 核仁形成于核仁组织区，即串联排列的rRNA基因被RNA聚合酶I转录的染色体位点。 核仁优势的细胞学表现是只有一个亲本rRNA基因组的转录。 负责核仁优势的分子机制尚不清楚。这项研究将测试两个假设，涉及偏见的基因抑制机制：第一，一组rRNA基因是选择性沉默的DNA甲基化，第二，核仁组织者区域间接控制作为一个单一的基因座或染色体结构域，其染色质状态决定基因活性。 这些模型在机械层面上不一定相互排斥。 该实验室已经开发了必要的生化和遗传工具，以测试模式植物拟南芥中的这些假设。 在异源四倍体拟南芥（Arabidopsis suecica）中，来自Arabidopsis arenosa的rRNA基因是转录活性的，而来自拟南芥（Arabidopsis thaliana）的rRNA基因被抑制。 自从A. arenosa和A. thaliana基因组可以通过遗传杂交，arenosa x thaliana遗传杂交，使用A. DNA低甲基化突变体将用于确定DNA甲基化和核仁优势之间是否存在因果关系。 a.具有稳定整合的rRNA转基因的拟南芥细胞系将用于确定核仁组织者区内的位置是否是核仁优势所需的。 在理解核仁优势机制方面的进展将为染色体控制基因表达提供重要的新见解。 基因沉默可能与基因激活一样重要，基因的表达是复杂生物体正常发育所必需的。目前尚不清楚如何建立有偏见的基因抑制;然而，DNA甲基化和染色质结构的改变强烈涉及在动物和植物中的基因沉默。 核仁优势是指遗传自双亲之一的染色体上核仁的选择性形成。核仁优势的表现是只表达一组亲本rRNA基因。本研究将调查是否发生核显性基因沉默机制涉及选择性DNA甲基化和/或位点特异性染色体结构。 在理解核仁优势机制方面的进展将为染色体控制基因表达提供重要的新见解。

9617471 Pikaard There is growing realization that gene silencing is probably as important as activation in the carefully orchestrated expression of genes essential for proper development of complex organisms. Relevant phenomena include X-chromosome inactivation, gametic imprinting, provirus inactivation, co-supression and transposable element inactivation. It is not yet clear how biased gene repression is first established in any of these epigenetic phenomena; however, DNA methylation and alterations in chromatin structure are strongly implicated in gene silencing in both animals and plants. Nucleolar dominance is an epigenetic phenomenon which is widespread in both plants and animals. Nuclear dominance is the selective formation of nucleoli on chromosomes inherited from only one parent in an interspecific hybrid or allopolyploid. Nucleoli form at nucleolus organizer regions, chromosomal sites where tandemly arrayed rRNA genes are transcribed by RNA polymerase I. The cytological manifestation of nucleolar dominance is the transcription of only one parental set of rRNA genes. The molecular mechanisms responsible for nucleolar dominance are not clear. This research will test two hypotheses involving biased gene repression mechanisms: First, that one set of rRNA genes is selectively silenced by DNA methylation, and second that nucleolar organizer regions are indirectly controlled as a single locus or chromosomal domain whose chromatin state determines gene activity. These models are not necessarily mutually exclusive at a mechanistic level. This laboratory has developed the biochemical and genetic tools necessary to test these hypotheses in the model plant Arabidopsis. In the allotetraploid Arabidopsis suecica, rRNA genes derived from Arabidopsis arenosa are transcriptionally active whereas rRNA genes derived from Arabidopsis thaliana are repressed. Since the A. arenosa and A. thaliana genomes can be combined by a genetic cross, an arenosa x thaliana genetic cross using an A. thalian a DNA hypomethylation mutant will be used to determine if a causal relationship exists between DNA methylation and nucleolar dominance. A. thaliana cell lines with stable integrated rRNA transgenes will be used to determine if location within a nucleolar organizer region is required for nucleolar dominance. Progress in understanding the mechanisms responsible for nucleolar dominance will provide important new insights into chromosomal controls of gene expression. Gene silencing is probably as important as activation in the carefully orchestrated expression of genes essential for proper development of complex organisms. It is not yet clear how biased gene repression is first established; however, DNA methylation and alterations in chromatin structure are strongly implicated in gene silencing in both animals and plants. Nucleolar dominance is the selective formation of nucleoli on chromosomes inherited from one parent. The manifestation of nucleolar dominance is the expression of only one parental set of rRNA genes. This research will investigate whether nuclear dominance occurs by gene silencing mechanisms involving selective DNA methylation and/or locus-specific chromosomal structure. Progress in understanding the mechanisms responsible for nucleolar dominance will provide important new insights into chromosomal controls of gene expression.