Control of Nucleolar Dominance in Arabidopsis

9617471皮卡德：越来越多的人意识到，在精心安排的基因表达中，基因沉默可能与激活一样重要，这些基因对于复杂生物体的正常发育至关重要。相关现象包括X染色体失活、配子印迹、前病毒失活、共抑制和转座元件失活。目前尚不清楚偏向基因抑制是如何在这些表观遗传现象中首次建立的；然而，DNA甲基化和染色质结构的改变与动植物的基因沉默密切相关。核仁优势是一种表观遗传现象，广泛存在于动植物中。核显性是指在种间杂种或异源多倍体中只从一个亲本遗传的染色体上选择性地形成核仁。核仁形成于核仁组织者区域，核仁组织者区域是核仁组织者区域，核仁组织区域是核仁聚合酶I转录rRNA基因的染色体位置。核仁优势的细胞学表现是只转录一组亲本rRNA基因。核仁优势的分子机制尚不清楚。这项研究将检验两个涉及有偏见的基因抑制机制的假设：第一，一组rRNA基因被DNA甲基化选择性沉默，第二，核仁组织者区域被间接控制为单个基因座或染色体区域，其染色质状态决定了基因的活性。这些模式在机械论层面上不一定是相互排斥的。该实验室已经开发出在模式植物拟南芥中检验这些假说所需的生化和遗传工具。在异源四倍体拟南芥中，来自拟南芥的rRNA基因具有转录活性，而来自拟南芥的rRNA基因则受到抑制。由于刺参和刺参的基因组可以通过遗传杂交进行组合，因此利用刺参的DNA低甲基化突变体与刺参杂交将被用来确定DNA甲基化和核仁显性之间是否存在因果关系。具有稳定整合rRNA转基因的拟南芥细胞系将被用来确定核仁优势是否需要位于核仁组织者区域内。了解核仁显性的机制的进展将为染色体控制基因表达提供重要的新见解。在精心安排的基因表达中，基因沉默可能与激活一样重要，这些基因对于复杂生物体的正常发育至关重要。目前尚不清楚偏向的基因抑制最初是如何建立的；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。核仁显性是指从一个亲本遗传来的染色体上核仁的选择性形成。核仁显性的表现是只表达一组亲本rRNA基因。这项研究将调查核显性是否通过基因沉默机制发生，包括选择性DNA甲基化和/或特定于位点的染色体结构。了解核仁显性的机制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.