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乙烯唑啉导致生育能力下降，并在几代人中增加癌症发病率。虽然已经观察到经典的表观遗传机制，如DNA甲基化的变化，但迄今为止还没有明确的机制来解释这些跨代效应如何通过精子传递。表观遗传学是研究基因表达或细胞表型的遗传变化，这些变化是由潜在DNA序列变化以外的机制引起的。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的自聚集体，称为淀粉样蛋白，其可以将蛋白质的天然形式转化为自聚集状态，从而自我永存。我们的假设是基于一个既定的机制，朊病毒为基础的遗传在酵母。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，所述朊病毒结构域将蛋白质从其天然折叠转换成自聚集朊病毒，导致蛋白质功能和细胞表型改变，所述蛋白质功能和细胞表型可以是可遗传的并传递到子细胞。值得注意的是，包括DNA结合蛋白TDP 43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，其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TDP 43、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质与酵母朊病毒之间的相似性提示了调节蛋白质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，包括头部和中心体区域，在胚胎发育中起着关键作用。虽然这些朊病毒的身份还不清楚，但我们已经确定TDP 43定位于精子头部和中心体，并且精子中的一部分TDP 43处于朊病毒状态。我们假设，精子蛋白，可能TDP 43，AR，p53和其他，可能会被诱导形成朊病毒（或更多的朊病毒）后，环境压力，这些朊病毒参与了新的表型的跨代遗传。为了验证我们的假设，我们将使用已建立的跨代遗传模型，并将大鼠在子宫内暴露于乙烯唑啉，并进行以下研究：1）鉴定和表征F1-F3雄性精子中的朊病毒，包括TDP 43; 2）确定精子朊病毒是否存在于受精卵母细胞中。

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.