Mechanisms of transgenerational epigenetic inheritance

摘要 对人类和实验室动物的研究表明，祖先接触环境中的化学物质 导致多种疾病的风险增加，包括乳腺癌、肥胖和自闭症， 从暴露者传给后代。因此，确定潜在的机制 环境诱导的表型的跨代传递对人类健康至关重要， 基础生物学，因为解释了表观遗传改变如何能够抵抗重新编程并在 在没有原始刺激的情况下，后代挑战了我们目前对 表观遗传学我们实验室的工作表明，在重编程过程中，F0妊娠雌性小鼠暴露于BPA， 在F2-F6代中，F1胚胎生殖系的肥胖导致肥胖。跨代传播 肥胖与Fto基因座的近端和远端顺式调节元件（克雷斯）的激活相关， 通过募集CTCF、FOXA 1、雌激素受体（ESR 1）和雄激素受体（AR）来调节配子。这些 在BPA的精子中，克雷斯相互作用，并与Fto，Irx 3和Irx 5基因的启动子相互作用， 对照小鼠。Irx 3和Irx 5负性调节食欲的分化，控制POMC和AgRP/NPY 下丘脑的神经元它们在祖先暴露于BPA的小鼠中的过度表达导致了 的AgRP神经元，瘦素抵抗，增加的食物摄入量，和肥胖。同时删除FOXA 1 和CTCF网站在Fto近端CRE逆转所有这些影响后，BPA暴露，这表明BPA- CTCF/FOXA 1位点的诱导占据在肥胖的跨代遗传中起着因果作用 表型在这里，我们建议获得一个详细的了解的分子过程受到双酚A的影响 在生殖系和早期胚胎中暴露。我们将研究转录因子（TF） 组蛋白修饰和组蛋白变体的占据、沉积、DNA甲基化和基因表达 在E13.5天暴露于BPA后立即观察原始生殖细胞（PGCs）。我们将遵循BPA- 在F1雄性和雌性生殖系发育过程中诱导表观遗传改变，包括 减数分裂，直到成年生物体中成熟配子的形成。我们将分析TF的变化 在受精后，在植入前发育过程中，以及在受精卵的组织中， 上胚层含有最近提交PGCs，以了解F1中诱导变化的机制 PGC在F2 PGC中维持或重建。小鼠品系，其中特异性TF和 将分析已删除的eRNA，以确定其募集及其 在建立增强子反馈回路中的作用，导致跨代遗传。这些结果 将填补一个重要的空白，我们的知识的基本原则，广泛使用的内分泌 干扰性化学物质影响暴露的发育中的胚胎中生殖系的表观遗传内容， 对后代造成不利的健康影响。

ABSTRACT Studies in humans and laboratory animals have shown that ancestral exposure to chemicals in the environment results in increased risk to a variety of diseases, including breast cancer, obesity, and autism, that can be transmitted from the exposed to subsequent generations. Therefore, identifying the mechanisms underlying the transgenerational transmission of environmentally induced epiphenotypes is critical for human health and for basic biology, since explaining how epigenetic alterations can resist reprograming and be restored in subsequent generations in the absence of the original stimulus challenges our current understanding of epigenetics. Work in our lab indicates that exposure of F0 pregnant female mice to BPA during reprograming of the F1 embryo germline results in obesity in the F2-F6 generations. Transgenerational transmission of obesity correlates with activation of proximal and distal cis-regulatory elements (CREs) in the Fto locus of the gametes by recruitment of CTCF, FOXA1, estrogen receptor (ESR1) and androgen receptor (AR). These CREs interact with each other and with the promoters of the Fto, Irx3, and Irx5 genes in sperm of BPA but not control mice. Irx3 and Irx5 negatively regulate the differentiation of appetite controlling POMC and AgRP/NPY neurons in the hypothalamus. Their over-expression in mice ancestrally exposed to BPA leads to an increase of AgRP neurons, leptin resistance, increased food intake, and obesity. Simultaneous deletion of the FOXA1 and CTCF sites in the Fto proximal CRE reverses all these effects after BPA exposure, suggesting that BPA- induced occupancy of the CTCF/FOXA1 sites plays a causal role in transgenerational inheritance of obesity epiphenotypes. Here we propose to gain a detailed understanding of the molecular processes affected by BPA exposure in the germline and early embryo. We will study the interplay between transcription factor (TF) occupancy, deposition of histone modifications and histone variants, DNA methylation, and gene expression immediately after exposure to BPA of the primordial germ cells (PGCs) at day E13.5. We will then follow BPA- induced epigenetic alterations in the F1 male and female germlines during their development, including meiosis, up to the formation of the mature gametes in the adult organism. We will analyze changes in TF occupancy in the F2 zygote after fertilization, during pre-implantation development, and in tissues of the epiblast containing recently committed PGCs to understand the mechanisms by which changes induced in F1 PGCs are maintained or re-established in F2 PGCs. Mouse strains in which binding sites for specific TFs and eRNAs have been deleted will be analyzed to determine the causal relationships in their recruitment and their role in the establishment of enhancer feedback loops resulting in transgenerational inheritance. These results will fill an important gap in our knowledge of the fundamental principles by which widely used endocrine disrupting chemicals affect the epigenetic content of the germline in the exposed developing embryo and in subsequent generations to cause adverse health effects.