Mechanisms of transgenerational epigenetic inheritance

摘要 对人类和实验动物的研究表明，祖先接触环境中的化学物质 会增加患各种疾病的风险，包括乳腺癌、肥胖症和自闭症 从接触过的人传给后代。因此，确定潜在的机制 环境诱导表型的跨代传递对人类健康和 对于基础生物学来说，由于解释了表观遗传改变如何抵抗重新编程并在 在没有原始刺激的情况下，后代人挑战了我们目前对 表观遗传学。我们实验室的工作表明，F0孕鼠在重新编程期间暴露于BPA F1胚胎胚系的遗传变异会导致F2-F6世代的肥胖。的跨代传播 肥胖与FTO基因座近端和远端顺式调节元件(Cres)的激活相关 通过募集CTCF、FOXA1、雌激素受体(ESR1)和雄激素受体(AR)的配子。这些 Cre相互作用，并与BPA精子中FTO、IRX3和IRX5基因启动子相互作用，但不相互作用 控制小鼠。IRX3和IRX5负调控食欲分化控制POMC和AgRP/NPY 下丘脑中的神经元。在祖先暴露于双酚A的小鼠中，它们的过度表达导致增加 AgRP神经元、瘦素抵抗、食物摄入量增加和肥胖。同时删除FOXA1 而FTO近端Cre的CTCF位点逆转了BPA暴露后的所有这些效应，表明BPA- CTCF/FOXA1位点的诱导占位在肥胖的跨代遗传中起到因果作用 表型表型。在这里，我们建议对双酚A影响的分子过程有一个详细的了解 在生殖系和早期胚胎中暴露。我们将研究转录因子(Tf)之间的相互作用 占有率、组蛋白修饰和组蛋白变体的沉积、DNA甲基化和基因表达 在E13.5天的原始生殖细胞(PGC)暴露于双酚A后即刻。然后我们将跟踪双酚A- 在F1雄性和雌性生殖系发育过程中诱导的表观遗传变化，包括 减数分裂，直到成熟的配子在成熟的生物体中形成。我们将分析TF的变化 受精后、着床前发育过程中F2受精卵的占有率以及 含有新近承诺的PGCs的表皮母细胞以了解F1诱导变化的机制 PGC在F2 PGC中维护或重新建立。在小鼠品系中，特定的转录因子和 将对已被删除的eRNAs进行分析，以确定其招聘和他们的 在建立增强子反馈环导致跨代遗传方面发挥作用。这些结果 将填补我们对广泛使用内分泌的基本原理的认识上的一个重要空白 干扰性化学物质会影响暴露的发育中胚胎和胚胎中胚系的表观遗传含量。 对后代人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.