Mechanisms and evolutionary consequences of transposon strategies to counteract host silencing

项目总结 含有活性转座元件(TES)会对宿主基因组造成很大的突变负担。至 减少这一负担，大多数生物已经进化出复杂的，而且往往是多层的机制，用于 识别和停用TES。尽管有这些防御措施，在几乎所有的TES的基因组中都发现了活性的TES 真核生物。对工商业污水附加费进化持久性的一种解释是，它们正在与自己的 宿主基因组：TES是不断进化的小说，当宿主基因组 正在不断演变，以重新建立TE抑制。虽然这一理论很有吸引力，但在 因为TES可以阻止或逃避宿主防御的机制在很大程度上是未知的。 申请人实验室的长期目标是了解TE/宿主共同的进化动力学。 进化论。该项目的总体目标是理解并在功能上验证一种新的TE战略， 在申请人的实验室中发现的，这涉及到TES使用自己的piRNA来靶向宿主沉默因子 为了镇压。申请者实验室产生的初步数据表明，果蝇 黑素胃泌素端粒转座子START-A捕获了宿主TE沉默因子Nxf2的一部分，这使得 Tart-A产生靶向抑制Nxf2的piRNAs。提出这项研究的理由是，它将 提供对主机-TE冲突机制的重要洞察，以及TE反击策略如何 影响宿主基因的表达和适合性。这个项目的目标将通过追求三个具体的目标来实现 目的：1)在果蝇中鉴定端粒TES获得的基因；2)确定非端粒TES是否 转座子也使用piRNA介导的反沉默策略；以及3)使用 CRISPR在黑腹盘藻中的分布。将在28种果蝇中鉴定端粒TES，并对其进行检测 确定他们是否获得了宿主基因片段。申请人的实验室已经鉴定出45 与TE衍生的piRNAs有同源性并已知在其中起作用的候选基因。 在TE抑制中。将对这些基因进行测试，以确定它们是否抑制了与它们相同的TE 同源。候选TE/基因对将使用CRISPR基因组编辑进行验证，以删除它们共享的 同源性，这应该导致有问题的基因上调。建议的研究具有创新性。 因为它代表着与现状的重大背离：而不是以前以东道主为中心的观点 这项研究考察了基因组对TE活动的反应，这个项目将研究方程式中TE的那一边 通过调查TES如何响应和对抗宿主防御。该领域的主要目标之一是 理解为什么参与TE沉默的宿主基因正在快速进化。这项拟议的研究具有重要意义 因为它将通过表征和在功能上验证特定TE反防御来支持这一目标 战略，这将为军备竞赛理论提供经验支持，同时也增加了对 寄主基因组和它们的TE同系物之间的共同进化动力学。

PROJECT SUMMARY Harboring active transposable elements (TEs) imposes a substantial mutational burden on the host genome. To reduce this burden, most organisms have evolved sophisticated, and often multi-layered, mechanisms for identifying and inactivating TEs. In spite of these defenses, active TEs are found in the genomes of almost all eukaryotes. One explanation for the evolutionary persistence of TEs is that they are in an “arms race” with their host genome: TEs are constantly evolving novels ways to block or evade host silencing while the host genome is continuously evolving to re-establish TE suppression. While this theory is appealing, there is a gap in knowledge because the mechanisms by which TEs could block or evade host defenses are largely unknown. The long-term goal of this applicant’s laboratory is to understand the evolutionary dynamics of TE/host co- evolution. The overall objective of this project is to understand and functionally validate a novel TE strategy, discovered in the applicant’s laboratory, that involves TEs using their own piRNAs to target host silencing factors for suppression. Preliminary data produced in the applicant’s laboratory suggests that the Drosophila melanogaster telomeric transposon TART-A captured a portion of the host TE silencing factor nxf2, which allows TART-A to produce piRNAs targeting nxf2 for suppression. The rationale for the proposed research is that it will provide critical insight into the mechanisms of host-TE conflict and how TE counter-defense strategies can impact host gene expression and fitness. The objective of this project will be achieved by pursuing three specific aims: 1) Identify genes acquired by telomeric TEs across Drosophila; 2) Determine whether non-telomeric transposons also use a piRNA-mediated counter-silencing strategy; and 3) Disrupt TE counter-silencing using CRISPR in D. melanogaster. Telomeric TEs will be identified in 28 species of Drosophila and assayed to determine whether they have acquired host gene fragments. The applicant’s laboratory has identified 45 candidate genes in D. melanogaster that share homology with TE-derived piRNAs and are known to play a role in TE suppression. These genes will be tested to determine if they suppress the same TE with which they share homology. Candidate TE/gene pairs will be validated using CRISPR genome editing to erase their shared homology, which should result in upregulation of the gene in question. The proposed research is innovative because it represents a substantial departure from the status quo: instead of the host-centric view of previous studies, which examine how the genome responds to TE activity, this project will study the TE side of the equation by investigating how TEs respond to and counteract host defenses. One of the major goals of the field is to understand why host genes involved in TE silencing are rapidly evolving. The proposed research is significant because it will support this goal by characterizing and functionally validating a specific TE counter-defense strategy, which will provide empirical support for the arms race theory, while also increasing understanding of the co-evolutionary dynamics between host genomes and their TE associates.