表观遗传修饰剂对重构胚发育的影响

自从"Dolly"绵羊克隆成功后,先后有哺乳动物鼠、猪、牛、狗、马等克隆成功的报道,但目前哺乳动物体细胞核移植成功率仍很低,其主要与卵母细胞对供体核的不完全重编程有关.核重编程主要表现为供体核基因的表观遗传改变并指导重构胚胎的正常发育.在核移植过程中,体细胞(供核细胞)携带着其组织所特有的表观遗传修饰标志,这种标志在核重编程中必须被清除.去除供核细胞先前的表观遗传标志能够提高重构胚的体外发育率[1].在核重编程中假如表观遗传修饰标志清除或重建失败,将导致重构胚全能性消失、从而影响后期分化和发育[2].核移植后供体细胞核的重新程序化是否完全是成功产生克隆动物的先决条件[3].表观遗传修饰主要包括3个方面:DNA甲基化,RNA相关性沉寂和组蛋白翻译后修饰,其中DNA甲基化和组蛋白乙酰化在体细胞核移植中研究较多.DNA甲基化能引起染色质结构、DNA构象、DNA稳定性及DNA与蛋白质相互作用方式的改变,从而控制基因表达;组蛋白乙酰化与基因活化以及DNA复制相关,组蛋白的去乙酰化和基因的失活相关.在体细胞克隆过程中加入适量的表观遗传修饰剂,干预DNA甲基化和组蛋白乙酰化过程,将有可能影响重构胚的体内外发育.     

同型半胱氨酸对小鼠卵母细胞成熟过程中组蛋白表观遗传修饰的影响

目的 探讨卵母细胞发育过程中同型半胱氨酸（HCY）对组蛋白表观遗传修饰的影响。 方法 首先使用10只2周ICR雌性小鼠建立完整卵泡的体外培养体系,在卵母细胞发育早期,利用免疫组织化学方法,观察HCY对甲基化组蛋白H3K4、H3K9以及乙酰化组蛋白H3K9分布的影响;其次使用10只4周ICR雌性小鼠,利用卵母细胞的体外成熟培养体系,观察HCY对卵母细胞成熟过程的影响,同时利用实时定量PCR方法,观察在此成熟过程中HCY对卵母细胞内组蛋白乙酰化水平的调控酶GCN5和HDAC表达的影响。 结果 HCY明显抑制卵母细胞的体外成熟,在HCY作用下,甲基化组蛋白H3K4、H3K9以及乙酰化组蛋白H3K9的分布没有变化,但是表达强度降低,核呈现去浓缩的趋势。成熟过程中HCY并不改变基因GCN5的表达水平,却明显抑制卵母细胞内HDAC基因的表达。 结论 卵母细胞发育过程中高水平的同型半胱氨酸影响组蛋白的表观遗传修饰,HCY对卵母细胞核内组蛋白甲基化和乙酰化修饰的影响有可能是造成核染色体稳定性下降的重要原因。     

肿瘤低氧微环境对DNA及组蛋白甲基化的影响

肿瘤细胞的表观遗传修饰受低氧条件的影响,DNA甲基化和组蛋白甲基化是表观遗传调控肿瘤的两种方式。低氧对DNA甲基化的影响可能通过DNA甲基化供体水平的变化、DNA甲基转移酶的活性的改变以及DNA去甲基化过程来实现。组蛋白去甲基化酶在组蛋白甲基化过程中发挥了重要作用,低氧微环境下组蛋白去甲基化酶表达的改变是影响组蛋白甲基化过程的重要原因。深入研究低氧对表观遗传调控肿瘤的影响的分子机制,为临床治疗肿瘤提供帮助。     

DNA甲基化及其对哺乳动物早期发育的影响

表观遗传修饰（epigenetic reprogramming）是指不改变DNA序列的可逆性修饰，在哺乳动物中其修饰的主要方式为DNA甲基化/去甲基化和组蛋白修饰。DNA甲基化主要发生在两个时期：生殖细胞发育期和植入前胚胎期，如果在此期间发生去甲基化不充分或者是过早的再甲基化，则会导致胚胎的死亡及出生后各种遗传病的发生，也是目前体细胞核移植来源的胚胎受孕率低的重要原因。     

Sirtuins及其在肿瘤发生发展过程中的作用

表观遗传是指DNA序列不发生变化但基因表达却发生了可遗传的改变,主要涉及DNA甲基化、组蛋白修饰和染色质重塑三种机制.组蛋白共价修饰包括甲基化/去甲基化、乙酰化/去乙酰化、磷酸化/去磷酸化、泛素化/去泛素化等等,发生在核心组蛋白N端尾部的这些可逆的共价修饰具有复杂的相互作用,其中,组蛋白的乙酰化/去乙酰化是组蛋白共价修饰最重要的一种机制,这种共价修饰主要由组蛋白乙酰化酶(histone acetylase, HAT)和组蛋白去乙酰化酶(histone deacetylase, HDAC)分别催化乙酰化和去乙酰化过程,这种可逆的乙酰化修饰可使染色质结构发生动态改变,并维持一个可逆而稳定的状态,同时精密调节某些基因的转录和表达,从而不但影响发育、分化和衰老等生理过程,而且与癌变密切相关.     

胚胎(胎儿)发育编程中的表观遗传修饰现象

胚胎(胎儿)发育是遗传信息和环境因素相互作用的编程过程。表观遗传是指由非DNA序列改变引起的、可遗传的基因表达水平的改变,它主要包括DNA甲基化、组蛋白修饰、RNA调控和染色质重塑等现象。表观遗传通过调控基因表达参与发育编程,如早期发育重编程、基因组印记、X染色体失活和组织分化等事件。当胚胎(胎儿)发育编程受到了饮食或环境因素的影响,表观遗传修饰可发生改变,从而影响其表型,甚至增加成年疾病的易感性。     

TET蛋白家族在中枢神经系统中的作用

正表观遗传(epigenetics)的调控机制主要包括DNA甲基化、组蛋白修饰和非编码RNA调控。其中DNA甲基化(DNA methylation)在胚胎发育、遗传印记、X染色体失活等过程中具有重要意义。DNA甲基化是在DNA甲基转移酶(DNA methyltransferases,DNMTs)作用下的一种相对稳定的表观遗传调控机制,可随DNA的复制遗传给下一代,在人类     

肿瘤细胞中的表观遗传编码紊乱

不改变基因的DNA编码,通过改变DNA双链与组蛋白间紧密度来决定基因是否转录表达,这称为表观遗传编码机制。表观遗传编码的生理作用是通过组蛋白修饰和DNA甲基化,调控细胞在适当的时间、空间位置表达适当的基因,从而控制细胞的增殖状况和分化方向。在细胞发育过程中,细胞内DNA甲基化水平增龄性增高,基因转录活性逐渐降低,使细胞从幼稚增殖进入成熟分化。肿瘤细胞中出现表观遗传编码紊乱,致细胞增殖失控,不能进入分化成熟阶段。基因启动子出现甲基化重排,阻碍转录因子与启动子结合,导致基因转录丧失正常调控,合成成熟功能蛋白受阻。利用表观遗传机制(如,RNA干涉)可成为肿瘤治疗的新方法。     

表观遗传调控在肥胖症研究领域中的研究进展

肥胖症被认为是一种由遗传因素和环境因素共同决定的复杂型疾病,已成为严重影响现代人类健康的公共卫生问题.在肥胖症的发生和发展过程中,表观遗传调控发挥了极其重要的作用.表观遗传主要的调控方式包括DNA的甲基化修饰,非编码RNA和组蛋白翻译后修饰,近年来组蛋白修饰方向的研究获得了较大突破.在此基础上,本文对表观遗传领域的肥胖症相关研究现状和进展进行了简要综述.     

表观遗传分子机制及其在肿瘤发生中的作用

表观遗传指不改变DNA序列的基因表达改变,是多细胞真核生物的重要生物学现象.在个体发生过程中,干细胞一旦分化为某种分化细胞,该分化细胞的特征就会维持.肿瘤发生中基因组相同的细胞一旦成为肿瘤细胞,就会维持肿瘤的特征,一旦成为非肿瘤细胞多数也会维持非肿瘤特性.表观遗传关系到细胞分化、分化状态维持、肿瘤发生、衰老等过程.DNA甲基化、组蛋白乙酰化、小RNA与表观遗传的分子机制有关.DNA的CpG甲基化影响基因表达,甲基化状态可以传递给子链DNA,小RNA通过改变DNA甲基化参与表观遗传;组蛋白乙酰化改变染色质构象影响基因表达.基因组的广泛低甲基化和抑癌基因高甲基化在肿瘤细胞中普遍存在,改变表观遗传的药物已试用于肿瘤治疗.     

Znaczenie modyfikacji epigenetycznych w patogenezie białaczek

Relations between genetic alterations and different types of leukemia lead to understanding that leukemogenesis is a mainly genetic-based phenomenon. However recently role of factors of epigenetic nature is highlighted in research on oncogenic transformation. Epigenetic regulation is defined as heritable patterns that are not related to DNA sequence. There are three major forms of epigenetic regulation: DNA methylation, histone modifications – methylation and acetylation – and regulation through small non-coding RNAs. Epigenetic regulation is important in development of different types of leukemia. Changes in DNA methylation patterns as well as in histone methylation and acetylation were detected in samples from patients with leukemia. In addition different profiles of miRNA, one subtype of noncoding RNAs, were associated with this disease. What is more, alteration in activity of enzymes involved in regulation of DNA and histone modification can also be detected in leukemic cells. Current knowledge of epigenetic regulation allows for better diagnostic of leukemia and better understanding of mechanism involved in its therapy. It also allowed for development of new forms of therapies targeted specifically on mechanisms involved in epigenetic regulation.     

The epigenetics of (hereditary) colorectal cancer

In the last decade, it has become apparent that not only DNA sequence variations but also epigenetic modifications may contribute to disease, including cancer. These epigenetic modifications involve histone modification including acetylation and methylation, DNA methylation, and chromatin remodeling. One of the best-characterized epigenetic changes is aberrant methylation of cytosines that occur in so-called CpG islands. DNA hypomethylation, prevalent as a genome-wide event, usually occurs in more advanced stages of tumor development. In contrast, DNA hypermethylation is often observed as a discrete, targeted event within tumor cells, resulting in specific loss of gene expression. Interestingly, it was found that sporadic and inherited cancers may exhibit similar DNA methylation patterns, and many genes that are mutated in familial cancers have also been found to be hypermethylated, mutated, or deleted in sporadic cancers. In this review, we will focus on DNA methylation events as heritable epimutations predisposing to colorectal cancer development.     

RET codon 804 mutations in multiple endocrine neoplasia 2: genotype–phenotype correlations and implications in clinical management

The risk of developing neurodegenerative disorders such as Alzheimer's disease or Parkinson's disease is influenced by genetic and environmental factors. Environmental events occurring during development or later in life can be related to disease susceptibility. One way by which the environment may exert its effect is through epigenetic modifications, which might affect the functioning of genes. These include nucleosome positioning, post-translational histone modifications, and DNA methylation. In this review we will focus in the potential role of DNA methylation in neurodegenerative disorders and in the approaches to explore such epigenetic changes. Advances in deciphering the role of epigenetic modifications in phenotype are being uncovered for a variety of diseases, including cancer, autoimmune, neurodevelopmental and cognitive disorders. Epigenetic modifications are now being also associated with cardiovascular and metabolic traits, and they are expected to be especially involved in learning and memory processes, as well as in neurodegenerative disease. The study of the role of methylation and other epigenetic modifications in disease development will provide new insights in the etiopathogenesis of neurodegenerative disorders, and should hopefully shape new avenues in the development of therapeutic strategies.     

表遗传学修饰研究方法新进展

表遗传学修饰重新编程通过DNA甲基化和组蛋白乙酰化等多种修饰方式,有序地改变染色质构形、调整基因表达,在哺乳动物的生殖发育等过程中作用重要。近年来随着有关研究深入,各种新技术、新思路不断涌现,研究方法得以不断改进和完善,该文就表遗传学修饰研究方法学的最新进展作一综述。     

Epigenetic regulation of nervous system development by DNA methylation and histone deacetylation

Alterations in the epigenetic modulation of gene expression have been implicated in several developmental disorders, cancer, and recently, in a variety of mental retardation and complex psychiatric disorders. A great deal of effort is now being focused on why the nervous system may be susceptible to shifts in activity of epigenetic modifiers. The answer may simply be that the mammalian nervous system must first produce the most complex degree of developmental patterning in biology and hardwire cells functionally in place postnatally, while still allowing for significant plasticity in order for the brain to respond to a rapidly changing environment. DNA methylation and histone deacetylation are two major epigenetic modifications that contribute to the stability of gene expression states. Perturbing DNA methylation, or disrupting the downstream response to DNA methylation – methyl-CpG-binding domain proteins (MBDs) and histone deacetylases (HDACs) – by genetic or pharmacological means, has revealed a critical requirement for epigenetic regulation in brain development, learning, and mature nervous system stability, and has identified the first distinct gene sets that are epigenetically regulated within the nervous system. Epigenetically modifying chromatin structure in response to different stimuli appears to be an ideal mechanism to generate continuous cellular diversity and coordinate shifts in gene expression at successive stages of brain development – all the way from deciding which kind of a neuron to generate, through to how many synapses a neuron can support. Here, we review the evidence supporting a role for DNA methylation and histone deacetylation in nervous system development and mature function, and present a basis from which to understand how the clinical use of HDAC inhibitors may impact nervous system function.     

Sequential ChIP-bisulfite sequencing enables direct genome-scale investigation of chromatin and DNA methylation cross-talk

Cross-talk between DNA methylation and histone modifications drives the establishment of composite epigenetic signatures and is traditionally studied using correlative rather than direct approaches. Here, we present sequential ChIP-bisulfite-sequencing (ChIP-BS-seq) as an approach to quantitatively assess DNA methylation patterns associated with chromatin modifications or chromatin-associated factors directly. A chromatin-immunoprecipitation (ChIP)-capturing step is used to obtain a restricted representation of the genome occupied by the epigenetic feature of interest, for which a single-base resolution DNA methylation map is then generated. When applied to H3 lysine 27 trimethylation (H3K27me3), we found that H3K27me3 and DNA methylation are compatible throughout most of the genome, except for CpG islands, where these two marks are mutually exclusive. Further ChIP-BS-seq-based analysis in Dnmt triple-knockout (TKO) embryonic stem cells revealed that total loss of CpG methylation is associated with alteration of H3K27me3 levels throughout the genome: H3K27me3 in localized peaks is decreased while broad local enrichments (BLOCs) of H3K27me3 are formed. At an even broader scale, these BLOCs correspond to regions of high DNA methylation in wild-type ES cells, suggesting that DNA methylation prevents H3K27me3 deposition locally and at a megabase scale. Our strategy provides a unique way of investigating global interdependencies between DNA methylation and other chromatin features.     

Dynamic DNA methylation reprogramming: active demethylation and immediate remethylation in the male pronucleus of bovine zygotes.

DNA methylation reprogramming (DMR) is believed to be a key process by which mammalian zygotes gain nuclear totipotency through erasing epigenetic modifications acquired during gametogenesis. Nonetheless, DMR patterns do not seem to be conserved among mammals. To identify uniform rules underlying mammalian DMRs, we explored DMRs of diverse mammalian zygotes. Of the zygotes studied, of particular interest was the bovine zygote; the paternal DNA methylation first decreased and was then rapidly restored almost to the maternal methylation level even before the two-cell stage. The 5-azadeoxycytidine treatment led to complete demethylation of the male pronucleus. The unusually dramatic changes in DNA methylation levels indicate that the bovine male pronucleus undergoes active demethylation, which is followed by de novo methylation. Our results show that, in bovine, the compound processes of active DNA demethylation and de novo DNA methylation, along with de novo H3-K9 trimethylation also, take place altogether within this very narrow window of pronucleus development.     

Roles of repressive epigenetic machinery in lineage decision of T cells

DNA methylation and histone modifications are central to epigenetic gene regulation, which has been shown to play a crucial role in development. Epigenetics has often been discussed in the context of the maintenance of cell identity because of the heritable nature of gene expression status. Indeed, crucial roles of the epigenetic machinery in establishment and maintenance of particular lineages during early development have been well documented. However, unexpected observation of a developmental plasticity retained in mature T lymphocytes, in particular in CD4⁺ T‐cell subsets, by recent studies is accelerating studies that focus on roles of each epigenetic pathway in cell fate decisions of T lymphocytes. Here, we focus on the repressive epigenetic machinery, i.e. DNA methylation, histone deacetylation, H3K9 methylation and Polycomb repressive complexes, and briefly review the studies examining the role of these mechanisms during T‐lymphocyte differentiation. We also discuss the current challenges faced when analysing the function of the epigenetic machinery and potential directions to overcome the problems.