The cross-regulation of host DNA replication and LTR Retrotransposons

描述(由申请人提供)： Ltr逆转座子是真核生物基因组中可移动的遗传元件和主要成分，参与结构变异和表观遗传调控。它们与逆转录病毒高度相关，与所有寄生成分一样，它们的进化成功依赖于关键细胞过程的开发。它们的活动可能导致染色体改变，从而导致癌症等疾病。我们发现LTR反转录转座子TF1在基因组复制叉障碍附近插入，并在其自身基因组中包括新的复制叉障碍。在这项建议中，我们的目的是描述LTR逆转座子和宿主DNA复制的相互作用，以及它如何影响整合位点选择、基因组完整性和表观遗传转录沉默。有待评估的总体假设是，复制分叉是宿主和LTR逆转录转座子之间的串点，通过结合转座子插入位点和LTR并控制复制的反式作用因子 染色质重塑过程中的分叉进展。这导致了有管理的同源重组和转录沉默。我们将利用裂殖酵母的LTR逆转座子作为DNA复制参与LTR逆转座子生物学的模型。具体目的：1.确定TF1插入位点选择的机制，并确定Sap1在此过程中的作用。Sap1是一种DNA结合因子， 阻止复制分叉的进展，并引导将TF1插入到被阻止的站点。我们将表征复制叉在插入途径中的参与以及Sap1在归巢机制中可能的拴系作用。2.确定逆转座子对DNA复制的影响及其对DNA复制方向性和基因组稳定性的影响。众所周知，LTR是重组基因，但原因尚不清楚。我们将研究LTR中存在的复制分叉障碍在其重组潜力中的参与，以及它们对基因组不稳定性和定向复制现象的影响。3.探讨LTR逆转录转座子转录沉默的机制，以及DNA复制与RNAi之间的相互作用。异色沉默是转座元件的普遍特征。我们已经发现，管理复制分叉进展的相同因素决定了一种新的抑制性异染色质结构，该结构可以使其沉默。我们将研究DNA复制管理因素在LTR逆转录转座子转录沉默机制中的作用。意义：这些研究将提供一个新的和全面的宿主-逆转录元件相互作用的模型，以及它们对基因组调控和稳定性的影响。

DESCRIPTION (provided by applicant): LTR Retrotransposons are mobile genetic elements and major constituents of eukaryotic genomes, where they contribute to structural variation and epigenetic regulation. They are highly related to Retroviruses, and like all parasitic elements their evolutionary success depends on exploitation of critical cellular processes. Their activity can lead to chromosomal alterations that drive diseases like cancer. We have discovered that the LTR Retrotransposon Tf1 inserts near genomic replication fork barriers, and includes new replication fork barriers in its own genome. In this proposal we aim to characterize the interaction of LTR Retrotransposons and host DNA replication, and how it influences integration site selection, genome integrity and epigenetic transcriptional silencing. The overall HYPOTHESIS to be evaluated is that the replication fork is a point of cross-talk between the host and the LTR retrotransposon, by way of trans-acting factors that bind to the transposon insertion site and the LTR and control replication fork progression through chromatin remodeling. This results in managed Homologous Recombination and transcriptional silencing. We will use the LTR Retrotransposons of the fission yeast Schizosaccharomyces pombe as models for the involvement of DNA replication in LTR Retrotransposon biology. Specific aims: 1. To determine the mechanism of Tf1 insertion site selection and to ascertain the role of Sap1 in this process. Sap1 is a DNA binding factor that blocks progression of the replication fork and guides insertion of Tf1 to the blocked sites. We wil characterize the involvement of the replication fork in the insertion pathway and the possible tethering role of Sap1 in the homing mechanism. 2. To determine the influence of Retrotransposons on DNA replication and their consequences on DNA replication directionality and genome stability. The LTR are notoriously recombinogenic but the reasons are unknown. We will investigate the involvement of the replication fork barriers present in LTR in their recombinogenic potential, and their consequences on genome instability and the phenomenon of directional replication. 3. To determine the mechanism of transcriptional silencing of LTR retrotransposons, and the interaction between DNA replication and RNAi. Heterochromatic silencing is a universal feature of Transposable Elements. We have discovered the same factors that manage replication fork progression at the LTR determine a novel repressive heterochromatin structure that silences it. We will investigate the involvement of the DNA replication management factors on the mechanisms of transcriptional silencing of LTR retrotransposons. Significance: These studies will provide a novel and comprehensive model of host-retroelement interactions, and their consequences on genome regulation and stability.