Reprogramming of the paternal genome upon fertilization involves genome-wide oxidation of 5-methylcytosine
Reprogramming of the paternal genome upon fertilization involves genome-wide oxidation of 5-methylcytosine
复制标题
DOI：
10.1073/pnas.1014033108
复制
发表时间：
2011-03-01
影响因子：
11.1
通讯作者：
Szabo, Piroska E.
中科院分区：
文献类型：
--
作者：
Iqbal, Khursheed;Jin, Seung-Gi;Szabo, Piroska E.
DNA胞嘧啶-5甲基化的全基因组擦除已被报道发生沿着父原核在受精卵母细胞中以明显的复制独立的方式，但这种重编程过程的机制仍然是谜。最近，在某些哺乳动物组织中检测到大量的5-羟甲基胞嘧啶（5 hmC），最可能来源于泰特蛋白对5-甲基胞嘧啶（5 mC）的酶促氧化。5 hmC被认为是一种潜在的活性DNA去甲基化中间体。在这里，我们表明，在先进的原核阶段受精卵的父原核含有大量的5 hmC，但缺乏5 mC。匡威的是，母原核，保留5 mC，但显示很少或没有5 hmC信号。重要的是，5 hmC持续到有丝分裂的单细胞，双细胞，和后来的卵裂阶段的胚胎，这表明5 mC氧化后，并没有立即通过切除修复途径或其他机制的全基因组的5 hmC删除。这一结论得到亚硫酸氢盐测序数据的支持，该数据显示在几个基因位点处修饰的胞嘧啶仅有限地转化为胞嘧啶。5 mC氧化可能是由Tet 3氧化酶进行的。Tet 3，而不是Tet 1或Tet 2，在卵母细胞和受精卵中以高水平表达，在两细胞阶段水平迅速下降。我们的研究结果表明，5 mC氧化是哺乳动物早期生命周期的一部分。
Genome-wide erasure of DNA cytosine-5 methylation has been reported to occur along the paternal pronucleus in fertilized oocytes in an apparently replication-independent manner, but the mechanism of this reprogramming process has remained enigmatic. Recently, considerable amounts of 5-hydroxymethylcytosine (5hmC), most likely derived from enzymatic oxidation of 5-methylcytosine (5mC) by TET proteins, have been detected in certain mammalian tissues. 5hmC has been proposed as a potential intermediate in active DNA demethylation. Here, we show that in advanced pronuclear-stage zygotes the paternal pronucleus contains substantial amounts of 5hmC but lacks 5mC. The converse is true for the maternal pronucleus, which retains 5mC but shows little or no 5hmC signal. Importantly, 5hmC persists into mitotic one-cell, two-cell, and later cleavage-stage embryos, suggesting that 5mC oxidation is not followed immediately by genome-wide removal of 5hmC through excision repair pathways or other mechanisms. This conclusion is supported by bisulfite sequencing data, which shows only limited conversion of modified cytosines to cytosines at several gene loci. It is likely that 5mC oxidation is carried out by the Tet3 oxidase. Tet3, but not Tet1 or Tet2, was expressed at high levels in oocytes and zygotes, with rapidly declining levels at the two-cell stage. Our results show that 5mC oxidation is part of the early life cycle of mammals.