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元件的形式存在，占哺乳动物基因组序列的20%。这些元件对基因组稳定性造成了负担，因为它们的动员促进了插入激活/失活，并促进了非同源位点之间的重组，导致染色体缺失和易位。逆转录转位已导致人类遗传病，如乳腺癌、结肠癌和肌肉萎缩症。很明显，逆转录是一种诱变的、持续发生的改变哺乳动物基因组的事件。多细胞生物利用胞嘧啶碱基甲基化、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，并防止转座子的动员。我们已经证明组蛋白是通过维生素生物素的共价结合来修饰的。在这里，我们提供了生物素依赖的逆转录转座子沉默的第一个证据，表明这种机制可能通过降低内源元件的流动性来维持基因组的稳定性。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。具体目的：(1)目的1研究将验证特定物种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的假设。在这里，我们将在人类细胞和豚鼠的ltr和LINEs中鉴定与不同区域相关的染色质中新的组蛋白生物素化标记。(2)目的2研究将验证反转录转座子组蛋白生物素化水平取决于哺乳动物细胞中生物素供应的假设。我们还将验证反转录转座子中的一些区域比其他区域更容易受到生物素消耗的影响，以及组蛋白中的一些生物素化位点比其他位点更容易受到生物素消耗的影响。最后，我们将在一个独特的新型小鼠模型中测试生物素耗竭导致乳腺癌发病率增加的假设，该模型包含三个完整的小鼠乳腺肿瘤病毒拷贝。(3) Aim 3研究将验证生物素缺乏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。这一建议为降低反转录转座子相关疾病在生物素缺乏风险人群（如孕妇及其胎儿）中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.