The role of the endogenous retroviral family, IAP, in placentation.

摘要 内源性逆转录病毒（ERV）占所有基因组的10%，但它们仍然是人类基因组的狂野西部。 尽管它们在宿主细胞内以无数关键方式发挥作用，包括作为调节因子， 元件，作为细胞外信使，作为病毒样颗粒（VLP）的来源，重要的是，作为体细胞 诱变剂我们的目标是了解ERV家族，IAP（脑池内A型蛋白）， 在小鼠母胎界面发挥作用。存在数千个由gag组成的基因组IAP实例， pro、pol序列侧翼为LTR。这些实例已经失去了祖先的包膜（env）序列， 形成裸露的VLP，留在细胞内并可以转座。今天，只剩下一个副本，即IAPE-D1， 具有介导其VLP的细胞外释放的保守包膜（env）序列。这种强烈 IAPE-D1中env的进化保守性表明它具有重要的细胞外功能。 因此，IAP在两个不同的细胞结构域中起作用：一个作为细胞外信使，另一个作为细胞外信使。 调节和突变的细胞内来源。 先前研究的严谨性有力地支持了这一假设。50多年前， 在所有物种的胎盘中描述，包括小鼠和人类。小鼠VLP的来源可能是IAP 因为我们发现它是胎盘形成过程中唯一表达的ERV家族。我们的数据表明，这些VLP是 当我们在滋养层干细胞（TSC）或小鼠胚胎中使用shRNA敲低IAP时， 我们观察到分化和胎座形成的缺陷。此外，我们发现IAP结合TSC中的特异性RNA， 包括介导分化和印记的那些，表明IAP VLP含有货物。 重要的是，我们发现IAP蛋白在没有转录本的情况下在母体组织中表达，这表明 它是从邻近的胎盘细胞运输过来的根据我们自己的初步结果和更多 根据50多年来对IAP的研究，我们假设：1）唯一的细胞外IAP，IAPE-D1，正在形成 小鼠胎盘中的VLP，其将特异性RNA转运到母体蜕膜中，以及2）细胞内的VLP， IAP具有多种功能，包括产生致突变的裸VLP和作为序列 作为胎盘基因组中的关键调节元件。虽然人类胎盘没有IAP， 他们确实有HERVK，它形成了可能发挥类似功能的VLP，特别是考虑到 胎盘是趋同进化的热点总体而言，本提案将提供 在怀孕期间未被探索的基因组的主要部分。

ABSTRACT Endogenous retroviruses (ERVs) constitute 10% of all genomes, yet they remain the wild west of biology, even though they function within the host cell in a myriad of critical ways, including as regulatory elements, as extracellular messengers, as sources of viral-like particles (VLPs), and, importantly, as somatic mutagens. Our overreaching goal is to understand how the ERV family, IAP (Intracisternal type A Protein), functions at the mouse maternal-fetal interface. Thousands of genomic IAP instances exist that consist of gag, pro, pol sequences flanked by LTRs. These instances have lost the ancestral envelope (env) sequence and form naked VLPs that remain inside the cell and can transpose. Today, only a single copy, IAPE-D1, remains with a conserved envelope (env) sequence that mediates extracellular release of its VLPs. This strong evolutionary conservation of the env in IAPE-D1 suggests that it serves an important extracellular function. Thus, IAPs function in two distinct cellular domains: one as an extracellular messenger, and the other as an intracellular source of regulation and mutation. The rigor of prior research strongly supports this hypothesis. More than 50 years ago VLPs were described in placentas of all species, including mouse and human. The source of the mouse VLPs is likely IAP as we find that it is the only ERV family expressed during placentation. Our data suggests that these VLPs are functional as, when we knock down IAP using shRNA in trophoblast stem cells (TSCs) or in mouse embryos, we observe defects in differentiation and placentation. Further, we find that IAP binds specific RNAs in TSCs, including those that mediate differentiation and imprinting, suggesting that IAP VLPs contain cargo. Importantly, we find that IAP protein is expressed in maternal tissues in the absence of transcript, suggesting that it was transported from the neighboring placental cells. Based on our own preliminary results and more than 50 years of prior research on IAP, we hypothesize that 1) the only extracellular IAP, IAPE-D1, is forming VLPs in the mouse placenta that transport specific RNAs into the maternal decidua and 2) the intracellular IAPs serve multiple functions including the generation of naked VLPs that are mutagenic and as sequences that serve as critical regulatory elements within the placenta genome. While human placentas do not have IAP, they do have HERVK, which forms VLPs that are likely to serve similar functions especially given that the placenta is a hotspot for convergent evolution. Overall, this proposal will deliver the function and mechanism of a major fraction of the unexplored genome during pregnancy.