Natural mutagenesis of human genomes by endogenous retrotransposons

描述（由申请人提供）： 转座基因元件（Transposable genetic elements，TE）占人类基因组的44%。人类TE，如L1元件，当它们“跳”到基因中时会导致疾病，并且在人类中已经记录了几十种致病的TE插入。人们普遍认为TE动员主要发生在人类生殖系中。然而，最近的一些证据表明，人类L1元件也转座体细胞。体细胞L1插入已经在至少两种类型的人类肿瘤中观察到，这表明这种插入可能产生疾病状态，包括癌症。在这个提议中，我们将研究人类生殖细胞与体细胞L1动员的相对水平。在目标1中，我们将使用我们最近开发的转座子测序技术来检查从健康美国人获得的组织面板中的L1插入。通过研究来自同一个体的多个组织中的L1动员，我们将建立健康美国人中生殖细胞与体细胞L1插入的相对丰度。我们还将寻找L1动员的RNA携带机制的证据，该机制在小鼠中产生镶嵌体细胞插入，也可能在人类中产生这种插入。在目标2中，我们将检查正常/肿瘤组织对，以确定生殖细胞和体细胞L1插入是否有助于推动人类肿瘤形成。我们的实验室最近发现，L1在人类肺肿瘤中以高频率被动员，我们怀疑一些新的L1插入促进了肿瘤的发生。我们将在目标2中直接检验这一假设。我们还将确定体细胞L1动员是否发生在其他肿瘤类型。在目标3中，我们将研究在人类中产生新的L1插入的源元件。我们将确定源元件拷贝数是否影响L1诱变和人类癌症风险。最后，我们将测试的假设，即在人类肺癌的源元件是由甲基化控制。总之，这些研究将大大扩展我们对人类L1诱变的了解，并将为L1诱变如何影响人类健康提供重要的新见解。

DESCRIPTION (provided by applicant): Project Summary Transposable genetic elements (TEs) occupy 44% of the human genome. Human TEs such as the L1 element can cause diseases when they "jump" into genes, and several dozen disease-causing TE insertions have been documented in humans. It has been widely assumed that TE mobilization occurs primarily in the human germline. However, several recent lines of evidence indicate that the human L1 element also transposes in somatic cells. Somatic L1 insertions have been observed in at least two types of human tumors, suggesting that such insertions may produce disease states, including cancers. In this proposal, we will examine the relative levels of germline vs. somatic L1 mobilization in humans. In Aim 1, we will use our recently developed transposon-seq technologies to examine L1 insertions in a tissue panel obtained from healthy Americans. By studying L1 mobilization in multiple tissues from the same individuals, we will establish the relative abundances of germline vs. somatic L1 insertions in healthy Americans. We also will seek evidence for the RNA carryover mechanism of L1 mobilization, which produces mosaic somatic insertions in mice and may also produce such insertions in humans. In Aim 2, we will examine normal/tumor tissue pairs to determine whether germline and somatic L1 insertions help to drive tumor formation in humans. Our laboratory recently found that L1 is mobilized at high frequencies in human lung tumors, and we suspect that some of the new L1 insertions fuel tumorigenesis. We will directly test this hypothesis in Aim 2. We also will determine whether somatic L1 mobilization occurs in other tumor types. In Aim 3, we will study source elements that produce new L1 insertions in humans. We will determine whether source element copy number influences L1 mutagenesis and cancer risk in humans. Finally, we will test the hypothesis that source elements are controlled by methylation in human lung cancers. Together, these studies will greatly expand our knowledge of L1 mutagenesis in humans and will provide major new insights on how L1 mutagenesis impacts human health.