Sperm Prions: A Mechanism of Epigenetic Inheritance

描述（由申请人提供）：越来越多的证据表明，父亲的环境暴露会影响其后代的表型，在某些情况下，这些影响可能是适应性的。事实上，雄性大鼠在子宫内暴露于内分泌干扰物vinclozolin会导致几代的生育能力下降和癌症发病率增加。虽然经典的表观遗传机制，如DNA甲基化的变化已经被观察到，但迄今为止还没有明确的机制来解释这些跨代效应是如何通过精子传播的。表观遗传学是研究基因表达或细胞表型的可遗传变化的机制，而不是潜在DNA序列的变化。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遗传方式。我们假设精子朊病毒是哺乳动物跨代遗传的一种新机制。朊病毒是高度有序结构的蛋白质自聚集体，称为淀粉样蛋白，可以将蛋白质的天然形式转化为自聚集体状态，从而自我延续。我们的假设是基于酵母中基于朊病毒的遗传的既定机制。酵母中的许多调节蛋白含有富含Q/N的朊病毒结构域，当暴露于细胞应激时，将蛋白质从其天然折叠转变为自聚集的朊病毒，从而改变蛋白质功能和细胞表型，可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，并形成朊病毒，改变与人类疾病相关的正常蛋白质功能。肿瘤抑制因子p53也被证明可以形成朊病毒。虽然TDP43、AR和p53的朊病毒形式的重要性尚不清楚，但这些哺乳动物蛋白与酵母朊病毒之间的相似性表明，它们具有调节蛋白功能和可能产生新表型的共同机制。我们已经取得了令人兴奋的观察，朊病毒存在于小鼠和大鼠精子中，包括头部和中心体区域，这在胚胎发育中起着关键作用。虽然这些朊病毒的身份尚不清楚，但我们已经确定TDP43定位于精子头部和中心体，并且精子中有一部分TDP43处于朊病毒状态。我们假设精子蛋白，可能是TDP43， AR， p53等，可能在环境胁迫下被诱导形成朊病毒（或更多的朊病毒），并且这些朊病毒参与了新表型的跨代遗传。为了验证我们的假设，我们将利用已建立的跨代遗传模型，在大鼠子宫内暴露于vinclozolin，并进行以下研究：1)鉴定和表征F1-F3雄性精子中包括TDP43在内的朊病毒；2)确定受精卵母细胞中是否存在精子朊病毒。

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.