TRANSCRIPTION AND RNA BINDING IN FRAGILE X SYNDROME

描述：脆性X综合征是遗传性精神分裂症最常见的形式。 迟钝它是由FMR 1基因产物功能丧失引起的。 几乎所有的病例都是由于FMR 1的特异性转录沉默 因此，该综合征可以被认为是一种转录疾病。沉默 是CGG扩展到200多个拷贝的间接结果， 在FMR 1的5 '-非翻译区重复（正常模式大小为30）。膨胀 结果在CG中胞嘧啶的异常从头甲基化， 重复序列内和相邻上游CpG岛中的二核苷酸 FMR 1启动子超甲基化被认为是一个近端的原因， FMR 1在患者中的转录失活。然而，分子 甲基化导致FMR 1转录丢失的机制是 未知患者FMR 1被包装在低乙酰化组蛋白H3和H4中， 转录沉默基因座的另一个特征。逆转的药物 FMR 1 DNA甲基化状态导致 组蛋白H3和H4在FMR 1处并恢复转录。的当前模型 甲基化介导的基因抑制表明， 脱乙酰酶通过甲基胞嘧啶结合蛋白与启动子结合， 在突变FMR 1的封闭染色质环境。长期目标是 该项目旨在了解转录沉默的分子机制 患者FMR 1，并最终逆转它。目标1将表征 转录因子，包括组蛋白乙酰转移酶活性， 驱动正常的FMR 1启动子功能。目标2将确定阻遏复合物 其结合突变、扩增FMR 1中甲基化DNA和脱乙酰化组蛋白 等位基因目标3将测试组蛋白乙酰化对于 通过外源表达组蛋白乙酰转移酶的FMR 1转录， 将其导向突变的甲基化FMR 1启动子。促销员占用率将 在具有重塑染色质的中间状态的患者细胞中进行评价。 从该实验系统获得的结果将允许识别 参与临床重要基因转录的步骤， 它的自然染色体背景。

Description: Fragile X syndrome is the most common form of inherited mental retardation. It results from loss of function of the FMR1 gene product. Virtually all cases are due to the specific transcriptional silencing of FMR1 -- hence, the syndrome can be considered a transcriptional disease. Silencing is an indirect consequence of the expansion to more than 200 copies, of a CGG repeat (normal modal size of 30) in FMR1's 5'-untranslated region. Expansion results in the aberrant de novo methylation of cytosines both in CG dinucleotides within the repeat, and in the neighboring upstream CpG islands in the FMR1 promoter. Hypermethylation is thought to be a proximal cause of the transcriptional inactivity of FMR1 in patients. However the molecular mechanism by which methylation leads to loss of transcription of FMR1 is unknown. Patient FMR1 is packaged in hypoacetylated histones H3 and H4, another characteristic of transcriptionally silent loci. Drugs that reverse the methylation state of FMR1 DNA result in a relative hyperacetylation of histones H3 and H4 at FMR1 and restore transcription. A current model of methylation-mediated gene repression suggests that recruitment of histone deacetylases to the promoter via methyl cytosine binding proteins establish a closed chromatin environment at mutant FMR1. The long range objective of this project is to understand the molecular mechanism of transcriptional silencing of patient FMR1, and to ultimately reverse it. Aim 1 will characterize transcription factors, including histone acetyltransferase activities, that drive normal FMR1 promoter function. Aim 2 will identify repression complexes that bind methylated DNA and deacetylate histones in mutant, expanded FMR1 alleles. Aim 3 will test the idea that histone acetylation is important for FMR1 transcription by exogenously expressing histone acetyltransferase and directing it to the mutant, methylated FMR1 promoter. Promoter occupancy will be evaluated in patient cells with intermediate states of remodeled chromatin. Results obtained from this experimental system will allow identification of the steps involved in transcription of a clinically important gene residing in its natural chromosomal context.