Assessing the impact of endogenous retroviruses on trophoblast gene regulation

在整个进化过程中，逆转录病毒入侵了几乎所有的哺乳动物，并融入了它们的基因组。虽然这些所谓的内源性逆转录病毒（erv）失去了产生病毒颗粒的能力，但在一段时间内，它们仍然可以在基因组内自我复制并传递给下一代。最终，大多数变得不活跃，不能进一步扩大。目前在人类中没有已知的活跃的erv，只有相对少量的erv在小鼠中保持活跃。然而，erv占小鼠和人类基因组的8%左右。一般认为，大多数erv没有特别的用途。然而，一小部分已经被宿主物种“驯化”以执行基本功能。有些已经转化为基因，产生与免疫和胎盘发育等有关的蛋白质。另一些则成为现有基因的重要调节者。这意味着某些erv可以确定给定基因是“开启”还是“关闭”。然而，到目前为止，这方面的例子只知道很少，而且还不清楚erv对基因活性的调节有多重要。erv似乎很重要的一个地方是胎盘。胎盘的形状和结构在不同的哺乳动物之间差异很大，据认为，这些差异可能来自于，至少部分来自于erv对基因活动的影响。在本提案中，我们旨在通过比较erv如何影响小鼠，大鼠和人类胎盘中的基因活性来验证这一假设。首先，我们将寻找这些物种之间erv位置的差异，以及它如何与胎盘中的基因活性相关。这将告诉我们哪些erv可能是重要的。接下来，我们将通过使用分子工具操纵选定的erv来测试erv与基因活性之间的因果关系。我们将采取几种方法，首先同时灭活多个erv，然后从基因组中去除单个erv。我们将测试这些实验是否导致基因“开启”或“关闭”，并最终改变胎盘细胞的行为。这一建议将为erv是否可能在胎盘进化中发挥作用以及对生殖成功的潜在影响提供线索。

Throughout evolution, retroviruses invaded virtually all mammals and became integrated within their genomes. Although these so-called endogenous retroviruses (ERVs) lost their ability to produce viral particles, for a while they could still self-replicate within genomes and be passed on to the next generation. Eventually, most became inactive and could not expand further. Currently there are no known active ERVs in humans and only a relatively small number remain active in mice. Nevertheless, ERVs make up ~8% of the mouse and human genomes.It is thought that most ERVs serve no particular purpose. However, a small subset has been 'domesticated' by the species that host them to perform essential functions. Some have turned into genes, which produce proteins involved in, e.g., immunity and placental development. Others became important regulators of existing genes. That means that certain ERVs can determine whether a given gene is 'on' or 'off'. However, only few examples of this are known to date, and it remains unclear how important ERVs are for the regulation of gene activity.One particular place where ERVs seem to be important is in the placenta. Placental shape and structure varies extensively between different mammals, and it is thought that these differences might come, at least in part, from the influence that ERVs have on gene activity. In this proposal we aim to test this hypothesis by comparing how ERVs affect gene activity in the placenta of mice, rats and humans. First, we will look for differences in the location of ERVs between these species and how it correlates with gene activity in the placenta. This will tell us which ERVs are likely to be important. Next, we will test for causal relationships between ERVs and gene activity by manipulating selected ERVs with molecular tools. We will take several approaches, first inactivating multiple ERVs simultaneously, then removing individual ERVs from the genome. We will test whether these experiments resulted in genes turning 'on' or 'off' and ultimately, any change in the behaviour of placental cells. This proposal will provide clues as to whether ERVs may have played a role in placental evolution, and potentially impact on reproductive success.