Biotin Deficiency Impairs Silencing of Repeat Regions & Retrotransposons

描述（由申请人提供）：逆转录转座子，以LTR和非LTR元件的形式，构成哺乳动物基因组中>20%的序列。这些元件对基因组稳定性造成负担，因为它们的移动促进插入激活/失活，并促进非同源基因座之间的重组，导致染色体缺失和易位。逆转录转座导致人类遗传疾病，例如，乳腺癌结肠癌和肌肉萎缩症很明显，逆转录转座是改变哺乳动物基因组的致突变、持续事件。多细胞生物体利用胞嘧啶碱基的甲基化、siRNA和组蛋白的翻译后修饰来稳定反转录转座子和异染色质，沉默基因，并防止转座子的移动。我们已经证明，组蛋白被修饰的共价结合的维生素生物素。在这里，我们提供了第一个证据的生物素依赖性沉默的反转录转座子，这表明，这种机制可能会在基因组稳定性降低内源性元素的流动性。长期目标：确定维生素依赖性染色质重塑维持基因组稳定性的途径。具体目标：（1）目标1研究将检验以下假设：特定种类的生物素化组蛋白是哺乳动物基因组中反转录转座子的标记。在这里，我们将确定新的组蛋白生物素化标记在染色质中与不同区域的LTR和LINE在人类细胞和agglomerated小鼠。(2)目的2研究将验证逆转录转座子上组蛋白生物素化水平依赖于哺乳动物细胞中生物素供应的假设。我们还将测试的假设，反转录转座子中的某些区域比其他地区更容易受到生物素耗尽，和一些生物素化位点组蛋白比其他网站更容易受到生物素耗尽。最后，我们将测试的假设，生物素耗竭导致增加乳腺癌的发病率在一个独特的，新的小鼠模型含有三个完整的拷贝的小鼠乳腺肿瘤病毒。(3)目的：3项研究将验证生物素缺乏会增加逆转录转座子的转录、翻译和动员，降低人类细胞基因组稳定性的假设。公共卫生相关性：生物素缺乏症在美国人中很普遍，例如，在高达50%的孕妇中观察到中度生物素缺乏症。这一提议为降低孕妇及其胎儿等生物素缺乏症风险群体中逆转录转座子相关疾病的发病率奠定了基础。

DESCRIPTION (provided by applicant): Retrotransposons, in the form of LTR and non-LTR elements, constitute >20% of the sequences in mammalian genomes. These elements pose a burden to genome stability, as their mobilization facilitates insertional activation/inactivation, and promotes recombination between non-homologous loci, leading to chromosomal deletions and translocations. Retrotranspositions have resulted in genetic disease in humans, e.g., breast cancer, colon cancer, and muscular dystrophy. It is clear that retrotranspositions are mutagenic, ongoing events that alter mammalian genomes. Multicellular organisms utilize methylation of cytosine bases, siRNA, and posttranslational modifications of histones to stabilize retrotransposons and heterochromatin, to silence genes, and to prevent mobilization of transposons. We have demonstrated that histones are modified by covalent binding of the vitamin biotin. Here we provide the first evidence of biotin-dependent silencing of retrotransposons, suggesting that this mechanism may function in genome stability by decreasing the mobility of endogenous elements. Long-term objective: To identify pathways by which vitamin-dependent chromatin remodeling maintains genome stability. Specific aims: (1) Aim 1 studies will test the hypothesis that particular species of biotinylated histones are marks for retrotransposons in mammalian genomes. Here, we will identify novel histone biotinylation marks in chromatin associated with distinct regions in LTRs and LINEs in human cells and agouti mice. (2) Aim 2 studies will test the hypothesis that the level of histone biotinylation at retrotransposons depends on biotin supply in mammalian cells. We will also test the hypotheses that some regions in retrotransposons are more susceptible to biotin depletion than other regions, and that some biotinylation sites in histones are more susceptible to biotin depletion than other sites. Finally, we will test the hypothesis that biotin depletion causes increased breast cancer incidence in a unique, novel mouse model containing three integrated copies of the mouse mammary tumor virus. (3) Aim 3 studies will test the hypothesis that biotin deficiency increases transcription, translation, and mobilization of retrotransposons, decreasing genome stability in human cells. PUBLIC HEALTH RELEVANCE: Biotin deficiency is prevalent among Americans, e.g., moderate biotin deficiency has been observed in up to 50% of pregnant women. This proposal lays the groundwork for decreasing the incidence of retrotransposon-associated diseases in groups at risk for developing biotin deficiency such as pregnant women and their fetuses.