DNA METHYLATION AND GENE SILENCING IN ARABIDOPSIS

胞嘧啶甲基化是在包括哺乳动物在内的真核生物基因组中发现的一种DNA修饰。植物和丝状真菌。甲基化与基因表达丧失(沉默)和抑制同源重组有关。维持正确的甲基化模式对发育至关重要。例如，在人类中，某些基因组区域甲基化模式的改变会导致许多遗传性疾病，包括智力低下综合征和易患恶性肿瘤。在小鼠中，胞嘧啶甲基转移酶基因敲除突变会导致胚胎死亡。在高等植物模式生物拟南芥中，甲基化缺陷突变体表现出一些异常的形态，但仍然是活的和可育的。因此，拟南芥为用分子和遗传学方法研究甲基化和沉默的机制提供了一个非常容易处理的系统。我们的研究集中在拟南芥中一个甲基化的内源基因家族，该家族由两个单一基因和一个尾到尾的反向重复基因在三个不连锁的基因组位置上组成。以前的工作表明，反向重复基因会触发基因组其他地方相同序列的甲基化。矛盾的是，虽然甲基化导致单个基因座沉默，但甲基化的反向重复序列中的一个基因得到了表达。这项建议的目的是了解反向重复基因座逃避甲基化的正常抑制效应的机制。这个问题将通过描述染色质结构、顺式作用的DNA序列和控制沉默的单线态位点甲基化和表达与表达的反向重复序列的反式作用因子来探索。

Cytosine methylation is a DNA modification found in the genomes of eukaryotes including mammals, higher. plants, and filamentous fungi. Methylation is associated with loss of gene expression (silencing) and suppression of homologous recombination. Maintenance of correct methylation patterns is critically important for development. For example, in humans, alteration of methylation patterns in certain genomic regions leads to a number of genetic diseases including mental retardation syndromes and pre-disposition to malignancies. In mice, a cytosine methyltransferase knock-out mutation results in embryo-lethality. In the higher plant model organism Arabidopsis thaliana, methylation-deficient mutants display a number of aberrant morphologies but are nonetheless viable and fertile. Therefore, Arabidopsis provides an extremely tractable system to study the mechanisms of methylation and silencing with molecular and genetic approaches. Our research focuses on a family of methylated endogenous genes in Arabidopsis that consists of two singlet genes plus a tail-to-tail inverted repeat gene duplication at three unlinked genomic positions. Previous work showed that the inverted repeat locus triggers methylation of the identical sequences elsewhere in the genome. Paradoxically, although methylation causes silencing of a singlet locus, a gene in the methylated inverted repeat is expressed. The goal of this proposal is to understand the mechanisms by which the inverted repeat locus escapes the normally repressive effects of methylation. This question will be explored by characterizing the chromatin structure, cis-acting DNA sequences, and trans-acting factors that control methylation and expression of the silenced singlet locus versus the expressed inverted repeat locus.