TRANSCRIPTION AND RNA BINDING IN FRAGILE X SYNDROME

描述：脆性X综合征是最常见的遗传性精神疾病 智力迟缓。这是由于FMR1基因产物功能丧失所致。 几乎所有的病例都是由于FMR1的特异转录沉默所致 --因此，该综合征可被认为是一种转录疾病。静音 是CGG扩展到200多份的间接后果 在FMR1‘S 5’-非翻译区重复(正常模式大小为30)。扩展 导致CG患者胞嘧啶脱氧核糖核酸甲基化异常 重复序列内的二核苷酸，以及邻近的上游CpG岛 在FMR1启动子中。甲基化程度过高被认为是导致 患者中FMR1的转录失活。然而，分子 甲基化导致FMR1转录缺失的机制是 未知。患者FMR1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 FMR1 DNA的甲基化状态导致相对超乙酰化 组蛋白H3和H4位于FMR1，并恢复转录。当前的模型 甲基化介导的基因抑制提示组蛋白的募集 脱乙酰酶通过甲基胞嘧啶结合蛋白使启动子 突变FMR1处封闭的染色质环境。这样做的长期目标是 该项目是为了了解转录沉默的分子机制 患者的FMR1，并最终逆转它。目标1将描述 转录因子，包括组蛋白乙酰转移酶活性， 驱动正常的FMR1启动子功能。目标2将确定抑制复合体 在突变的扩大的FMR1中结合甲基化DNA和去乙酰化组蛋白 等位基因。目标3将验证组蛋白乙酰化对 外源表达组蛋白乙酰转移酶和FMR1转录 将其定向到突变的甲基化FMR1启动子。推广者入住率将 在具有重塑染色质中间状态的患者细胞中进行评估。 从这个实验系统获得的结果将使我们能够识别 一种临床上重要的基因转录过程中涉及的步骤 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.