研究揭示受精卵DNA去甲基化重要机制

正近日,由中科院上海生科院生化与细胞所徐国良研究组、李劲松研究组和北京大学生命科学学院生物动态光学成像中心汤富酬研究组共同完成的一项研究发现,小鼠早期胚胎中母源和父源基因组在单细胞的受精卵阶段,均会发生大规模的DNA主动和被动去甲基化,DNA双加氧酶Tet3介导了主动去甲基化的发生,而糖苷酶TDG并不参与该过程。研究中,科学家利用最近发展的单细胞简并代表性甲基化测序、发夹DNA甲基化测序以     

淀粉质体DNA的研究现状

淀粉质体含有丰富的DNA,平均每个淀粉质体含有数百个基因组拷贝。其分布特点因物种而异,大都集中于拟核区,有的分散于质体内。在淀粉质体发育过程中,DNA含量不断增加,成熟期达到顶峰,以贮藏形态存在,为种子的萌发和幼苗的形态建成提供核苷酸等原料。淀粉质体DNA具有与叶绿体DNA同源的序列,存在一些表达基因,如：16SrRNA、psbA。但在抑制区域富甲基化,尤其是5-甲基胞嘧啶,碱基的甲基化在aDNA基因的表达调控中起重要作用。     

癌症与DNA甲基化异常

DNA甲基化是哺乳动物基因组最常见的修饰方式,它存在于生物体正常的生理过程,DNA异常甲基化和疾病的发生发展有关.该文综述了癌症中存在着的DNA的异常甲基化现象,即抑癌基因的高度甲基化,低表达,及癌基因的低甲基化,高表达,检测这些基因的甲基化状态可以为癌症的早期诊断及治疗提供参考依据.     

亚硝胺类化合物诱导小鼠食管病变与基因组甲基化的关系研究

研究亚硝胺类化合物诱导小鼠食管发生病变与基因甲基化的关系,在亚硝酸钠（NaNO2）和N,N-二甲基苄胺（N,N-Dimethylbenzylamine）混合物诱导小鼠食管病变过程中,定期取小鼠食管,一部分做病理切片观察组织学变化;另一部分提取组织DNA做变性高效液相色谱（Denaturing High Performance Liquid Chromatography,DHPLC）,检测基因组甲基化修饰的改变。结果在亚苄混合物诱导的小鼠食管癌变过程中,全基因组甲基化修饰是逐渐降低的,在达到一定程度后即保持一种稳态。此时组织病理学才发生光镜下可见的改变。说明全基因组甲基化修饰的逐渐降低可能是亚硝胺类化合物诱导食管发生病变的途径之一．这种基因修饰的变化有助于进一步研究食管鳞癌发生的分子机制。     

DNA甲基化异常与人类肿瘤

DNA甲基化是表遗传学上研究最深入的一种机制,是一种酶介导的化学修饰过程,在DNA的某些碱基上增加一个甲基.在人类的肿瘤中都可以发现不同程度的DNA异常甲基化现象.介绍DNA甲基化在基因表达中的作用及其抑制基因转录、表达的机理,尤其发生在抑癌基因CpG岛和其他相关基因的甲基化异常与肿瘤发生、演进的关系,甲基化的检测方法以及去甲基化在肿瘤治疗方面的应用前景.     

DNA甲基化在精神分裂症中的作用:研究进展及挑战（英文）

精神分裂症是一种异质性精神障碍,目前多数学者认为该病由遗传及环境风险因子共同致病.传统的遗传学研究识别了一些精神分裂症的候选基因,然而,外显率及比值比较低,以及可重复性较差,使得这些候选基因在精神分裂症发病机制中的角色受到限制.精神分裂症的流行病学研究发现了一些可能与该病相关的环境风险因子,但仍受到方法学的限制以及互相矛盾的流行病学调查结果的困扰.目前,在环境与基因中间起调解作用的表观遗传学,可能在精神分裂症的发病机制中起重要作用.DNA甲基化是最稳定且研究最深入的一种表观遗传学修饰.本文简要介绍DNA甲基化机制,主要评述精神分裂症中基因组及特异位点如候选基因Reelin与COMT甲基化研究现状,以及DNA甲基化在精神分裂症中的研究困境.     

长筒石蒜组织培养中器官发生的MSAP分析

采用甲基化敏感扩增多态性技术,从64对MSAP选扩引物中,选出扩增清晰、可辨且可重复的51对MSAP引物组合,扩增获得长筒石蒜种子胚、愈伤组织、苗等3个不同发育时期的DNA胞嘧啶甲基化修饰水平及MSAP扩增图谱。结果表明,种子胚基因组中有68.0%(全甲基化50.2%、半甲基化49.8%)、愈伤组织60.0%(全甲基化52.2%、半甲基化47.8%)、苗64.3%(全甲基化40.8%、半甲基化59.2%)的CCGG/GGCC位点发生胞嘧啶甲基化。3个不同时期甲基化的水平互有差异,依据超甲基化/去甲基化的修饰机理分析,甲基化水平的变化或许导致了长筒石蒜不同的器官发生。     

MSAP在水稻害虫白背飞虱中的应用研究

甲基化敏感的扩增多态性分析方法 (MSAP)是在扩增片段长度多态性技术基础上建立起来的主要用来检测样品基因组DNA甲基化情况的一种方法,特别适用于全基因组范围内检测CCGG位点的胞嘧啶甲基化情况,在高等动物和许多植物上已广泛应用,但尚未有在昆虫中应用该方法的报道。从DNA提取、酶切基因组DNA用量、酶切和接头连接时间、电泳图谱显影方法等方面对MSAP方法进行了改进,并在水稻重要害虫白背飞虱上得到成功应用。这为将来在其它昆虫中使用该方法研究基因组DNA甲基化情况提供了一定借鉴和指导价值。且通过比较白背飞虱雌雄性别间和长短翅型间的MSAP图谱,发现雌雄性别间和长短翅型间的基因组DNA甲基化式样都存在明显的差异,说明DNA甲基化可能参与了性别和翅型分化的调节。     

鞍带石斑鱼、棕点石斑鱼及其杂交子代DNA甲基化的MSAP分析

为了探究海洋鱼类杂交优势的产生机制,以鞍带石斑鱼、棕点石斑鱼及其杂交子一代石斑鱼为研究对象,采用甲基化敏感扩增多态性(MSAP)技术对三个群体的基因组DNA的胞嘧啶甲基化修饰水平进行了研究.实验结果显示,棕点石斑鱼、鞍带石斑鱼、杂交子一代石斑鱼的基因组DNA的总甲基化率分别为57.18%,63.16%,54.76%,在石斑鱼亲本的基因组中,其DNA的甲基化程度较高,而在杂交子代中,其DNA的甲基化程度较低.三个群体的DNA全甲基化率分别为31.66%,39.71%,40.00%,半甲基化率分别为25.52%,23.44%,14.76%,杂交子代的半甲基化率显著低于亲本的半甲基化率.研究表明,鞍带石斑鱼与棕点石斑鱼的杂交子代在基因组层面上和双亲相比发生了较大的甲基化水平的调整,于不同位点,DNA甲基化的增强或减弱对石斑鱼杂种优势可能会产生影响.     

多倍体小麦物种形成可诱发稳定遗传的胞嘧啶甲基化变异

多倍体小麦及其二倍体祖先物种的基因组DNA经一对同位酶(HpaⅡ/Msp工)消化后,与21个不同类型的低拷贝DNA序列进行Southern杂交.结果发现,多倍体小麦实现物种形成后产生了广泛的胞嘧啶甲基化变异.用同样的21种DNA序列为探针与1个人工合成的六倍体小麦及其亲本的Southern杂交结果表明,甲基化变异已存在于该人工小麦的较早期自交世代(S5,S6和S7).而且,在3个自交世代每代随机选取的3个单株之间的限制性酶切片段长度多态(RFLP)谱带均表现为高度一致;这暗示甲基化变异可能发生得更早,或者,甲基化变异具有非随机性.变化后的RFLP谱带在3个自交世代间表现为稳定遗传.甲基化变异虽在整个基因组范围内发生,但可能具有序列特异性.对这种迅速发生的甲基化变异与异源多倍体基因组进化的两个重要属性即遗传二倍化和基因分化之间的可能关系进行了讨论.     

Detection of DNA methylation changes during seed germination in rapeseed （Brassica napus）

DNA methylation is a common yet important modi- fication of DNA in eukaryotic organisms. DNA methy- lation, especially methylation of cytosine (m5C), have both epigenetic and mutagenic effects on various cellu- lar activities such as differential gene exp…     

Gadd45a promotes epigenetic gene activation by repair-mediated DNA demethylation

DNA methylation is an epigenetic modification that is essential for gene silencing and genome stability in many organisms. Although methyltransferases that promote DNA methylation are well characterized, the molecular mechanism underlying active DNA demethylation is poorly understood and controversial. Here we show that Gadd45a (growth arrest and DNA-damage-inducible protein 45 alpha), a nuclear protein involved in maintenance of genomic stability, DNA repair and suppression of cell growth, has a key role in active DNA demethylation. Gadd45a overexpression activates methylation-silenced reporter plasmids and promotes global DNA demethylation. Gadd45a knockdown silences gene expression and leads to DNA hypermethylation. During active demethylation of oct4 in Xenopus laevis oocytes, Gadd45a is specifically recruited to the site of demethylation. Active demethylation occurs by DNA repair and Gadd45a interacts with and requires the DNA repair endonuclease XPG. We conclude that Gadd45a relieves epigenetic gene silencing by promoting DNA repair, which erases methylation marks.     

Demethylation of CpG islands in embryonic cells

DNA in differentiated somatic cells has a fixed pattern of methylation, which is faithfully copied after replication. By contrast, the methylation patterns of many tissue-specific and some housekeeping genes are altered during normal development. This modification of DNA methylation in the embryo has also been observed in transgenic mice and in transfection experiments. Here we report the fate in mice of an in vitro-methylated adenine phosphoribosyltransferase transgene. The entire 5' CpG island region became demethylated, whereas the 3' end of the gene remained modified and was even methylated de novo at additional sites. Transfection experiments in vitro show that the demethylation is rapid, is specific for embryonic cell-types and affects a variety of different CpG island sequences. This suggests that gene sequences can be recognized in the early embryo and imprinted with the correct methylation pattern through a combination of demethylation and de novo methylation.     

DNA甲基化与基因调控

ＤＮＡ甲基化或去甲基化,改变了ＤＮＡ分子构象,导致某些重要基团的隐蔽或暴露,削弱或增强了ＤＮＡ与蛋白质因子的结合能力,从而改变了基因表达．     

DNMT1 and DNMT3b cooperate to silence genes in human cancer cells

Inactivation of tumour suppressor genes is central to the development of all common forms of human cancer. This inactivation often results from epigenetic silencing associated with hypermethylation rather than intragenic mutations. In human cells, the mechanisms underlying locus-specific or global methylation patterns remain unclear. The prototypic DNA methyltransferase, Dnmt1, accounts for most methylation in mouse cells, but human cancer cells lacking DNMT1 retain significant genomic methylation and associated gene silencing. We disrupted the human DNMT3b gene in a colorectal cancer cell line. This deletion reduced global DNA methylation by less than 3%. Surprisingly, however, genetic disruption of both DNMT1 and DNMT3b nearly eliminated methyltransferase activity, and reduced genomic DNA methylation by greater than 95%. These marked changes resulted in demethylation of repeated sequences, loss of insulin-like growth factor II (IGF2) imprinting, abrogation of silencing of the tumour suppressor gene p16INK4a, and growth suppression. Here we demonstrate that two enzymes cooperatively maintain DNA methylation and gene silencing in human cancer cells, and provide compelling evidence that such methylation is essential for optimal neoplastic proliferation.     

抗白粉病小麦近等基因系DNA甲基化的MSAP分析

应用甲基化敏感扩增多态性（MSAP）技术检测小麦抗白粉病代换系6A／6V与感病品系京411的近等基因系NILs,及其亲本6A／6V和京411的基因组DNA甲基化变化．结果表明,NILs的整体甲基化水平（22．9％）略高于6A／6V（21．2％）,低于京411（23．4％）．分析其甲基化模式发现,NILs相对京411甲基化水平降低条带比例（2．89％）明显高于甲基化提高条带（0．55％）,而相对抗病亲本6A／6V,NILs甲基化水平降低条带比例（2．96％）明显低于甲基化提高条带（4．20％）,说明NILs的整体基因表达水平低于6A／6V,高于京411．     

IDH mutation impairs histone demethylation and results in a block to cell differentiation

Recurrent mutations in isocitrate dehydrogenase 1 (IDH1) and IDH2 have been identified in gliomas, acute myeloid leukaemias (AML) and chondrosarcomas, and share a novel enzymatic property of producing 2-hydroxyglutarate (2HG) from α-ketoglutarate. Here we report that 2HG-producing IDH mutants can prevent the histone demethylation that is required for lineage-specific progenitor cells to differentiate into terminally differentiated cells. In tumour samples from glioma patients, IDH mutations were associated with a distinct gene expression profile enriched for genes expressed in neural progenitor cells, and this was associated with increased histone methylation. To test whether the ability of IDH mutants to promote histone methylation contributes to a block in cell differentiation in non-transformed cells, we tested the effect of neomorphic IDH mutants on adipocyte differentiation in vitro. Introduction of either mutant IDH or cell-permeable 2HG was associated with repression of the inducible expression of lineage-specific differentiation genes and a block to differentiation. This correlated with a significant increase in repressive histone methylation marks without observable changes in promoter DNA methylation. Gliomas were found to have elevated levels of similar histone repressive marks. Stable transfection of a 2HG-producing mutant IDH into immortalized astrocytes resulted in progressive accumulation of histone methylation. Of the marks examined, increased H3K9 methylation reproducibly preceded a rise in DNA methylation as cells were passaged in culture. Furthermore, we found that the 2HG-inhibitable H3K9 demethylase KDM4C was induced during adipocyte differentiation, and that RNA-interference suppression of KDM4C was sufficient to block differentiation. Together these data demonstrate that 2HG can inhibit histone demethylation and that inhibition of histone demethylation can be sufficient to block the differentiation of non-transformed cells.