Sperm Prions: A Mechanism of Epigenetic Inheritance

描述(由申请人提供)：越来越多的证据表明，父亲暴露在环境中会影响其后代的表型，在某些情况下，这些影响可以是适应性的。事实上，雄性大鼠在子宫内暴露于内分泌干扰物长春花碱会导致生育力下降，并在几代人中增加癌症发病率。虽然已经观察到了经典的表观遗传学机制，如DNA甲基化的变化，但到目前为止，这些跨代效应是如何通过精子传递的还没有明确的机制。表观遗传学是研究由潜在DNA序列改变以外的机制引起的基因表达或细胞表型的可遗传变化。虽然在哺乳动物中，表观遗传学目前指的是基因组的修饰，如DNA甲基化或组蛋白修饰，但也可能发生非基因组的遗传方式。我们假设精子蛋白是哺乳动物跨代遗传的一种新机制。Prion是蛋白质在高度有序的结构中的自我聚集，被称为淀粉样蛋白，可以将蛋白质的自然形式转化为自我聚集状态，因此是自我永续的。我们的假设是基于酵母菌中已建立的基于普里恩基因的遗传机制。酵母中的许多调节蛋白含有Q/N丰富的普恩结构域，当暴露在细胞压力下时，该蛋白将蛋白质从其天然折叠转换为自聚集的普恩，从而导致蛋白质功能和细胞表型的改变，这些变化可以遗传并传递给子细胞。值得注意的是，包括DNA结合蛋白TDP43和雄激素受体(AR)在内的几种哺乳动物调节蛋白含有Q/N结构域，并形成Prion，改变与人类疾病有关的正常蛋白质功能。肿瘤抑制基因P53也被证明可以形成普恩病毒。虽然目前尚不清楚TDP43、AR和P53蛋白的意义，但这些哺乳动物蛋白与酵母蛋白之间的相似性提示了一种共同的机制来调节蛋白质的功能，并可能产生新的表型。我们已经做出了令人兴奋的观察，即在小鼠和大鼠的精子中存在病毒，包括头部和中心体区域，这在胚胎发育中起着关键作用。虽然目前还不清楚这些蛋白的性质，但我们已经确定TDP43定位于精子头部和中心体，并且在精子中有一定比例的TDP43处于蛋白状态。我们假设，精子蛋白，可能是TDP43、AR、P53等，在环境应激后可能被诱导形成(或更多)Prion，这些Prion参与了新表型的跨代遗传。为了验证我们的假设，我们将使用一个已建立的跨代遗传模型，并在子宫内将大鼠暴露于长春新灵，并进行以下研究：1)鉴定和鉴定F1-F3雄性精子中包括TDP43在内的普恩病毒；2)确定受精卵母细胞中是否存在精子普恩病毒。

DESCRIPTION (provided by applicant): There is growing evidence that environmental exposures to the father can affect the phenotype of his offspring and in some cases these effects can be adaptive. Indeed, in utero exposure of male rats to the endocrine disruptor vinclozolin resulted in decreased fertility and increased rates of cancer over several generations. Although classic epigenetic mechanisms such as changes in DNA methylation have been observed, to date no clear mechanism has been established for how these transgenerational effects were transmitted by spermatozoa. Epigenetics is the study of heritable changes in gene expression or cellular phenotype caused by mechanisms other than changes in the underlying DNA sequence. While in mammals epigenetics currently refers to modifications of the genome such as DNA methylation or histone modifications, it is possible that nongenomic means of inheritance may also occur. We hypothesize that sperm prions are a novel mechanism for transgenerational inheritance in mammals. Prions are self-aggregates of proteins in highly ordered structures known as amyloids that can convert native forms of the protein to the self-aggregated state and thus are self-perpetuating. Our hypothesis is based on an established mechanism for prion-based inheritance in yeast. Many regulatory proteins in yeast contain Q/N rich prion domains that, when exposed to cell stress, switch the protein from its native fold into a self-aggregated prion resulting in changed protein function and cell phenotype that can be heritable and passed on to daughter cells. Remarkably, several mammalian regulatory proteins including the DNA binding proteins TDP43 and androgen receptor (AR) contain Q/N domains and form prions that alter normal protein function that is linked to human disease. The tumor suppressor p53 has also been shown to form prions. While the significance of the prion forms of TDP43, AR and p53 is not known, the similarities between these mammalian proteins and the yeast prions suggest a common mechanism for regulation of protein function and possibly generation of new phenotypes. We have made the exciting observation that prions are present in mouse and rat spermatozoa including the head and the centrosomal region which plays critical roles in embryonic development. Although the identity of these prions is not known, we have determined that TDP43 localizes to the sperm head and centrosome and that a proportion of TDP43 in sperm is in a prion state. We hypothesize that sperm proteins, possibly TDP43, AR, p53 and others, may be induced to form prions (or more prions) following environmental stress and that these prions are involved in the transgenerational inheritance of new phenotypes. To test our hypothesis, we will use an established model for transgenerational inheritance and expose rats in utero to vinclozolin and carry out the following studies: 1) Identify and characterize prions including TDP43 in spermatozoa from F1-F3 males; 2) Determine if sperm prions are present in fertilized oocytes.