Limited demethylation leaves mosaic-type methylation states in cloned bovine pre-implantation embryos
Limited demethylation leaves mosaic-type methylation states in cloned bovine pre-implantation embryos
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DOI：
10.1093/emboj/21.5.1092
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发表时间：
2002-03-01
期刊：
影响因子：
11.4
通讯作者：
Han, YM
中科院分区：
文献类型：
--
作者：
Kang, YK;Park, JS;Han, YM
核移植克隆技术困难重重：大多数克隆人在出生前就死亡，存活下来的克隆人经常表现出生长异常。在克隆胎儿/动物中观察到的异常的跨物种相似性使我们怀疑供体基因组的表观遗传重编程的保真度。在这里，我们发现，单拷贝序列，不像卫星序列，在植入前NT胚胎去甲基化。通过分析单个囊胚证实了基因组序列之间的差异去甲基化模式。这表明NT胚胎中其他发育重要基因的选择性去甲基化。我们还观察到甲基化水平和内细胞团与滋养外胚层（ICM/TE）比率之间的反向关系，这被发现是NT囊胚中发生的另一种类型的差异去甲基化的结果;其中ICM和TE区域之间保持不相等的甲基化。TE定位的甲基化异常表明在胚胎外区域存在广泛的基因失调，从而导致克隆胎儿/动物所熟悉的胎盘功能障碍。基因组序列之间和不同分配的细胞之间的这些差异去甲基化产生不同的整体，但指定的甲基化模式，表明表观遗传重编程发生在NT胚胎中以有限的方式。
Cloning by nuclear transfer (NT) has been riddled with difficulties: most clones die before birth and survivors frequently display growth abnormalities. The cross-species similarity in abnormalities observed in cloned fetuses/animals leads us to suspect the fidelity of epigenetic reprogramming of the donor genome. Here, we found that single-copy sequences, unlike satellite sequences, are demethylated in pre-implantation NT embryos. The differential demethylation pattern between genomic sequences was confirmed by analyzing single blastocysts. It suggests selective demethylation of other developmentally important genes in NT embryos. We also observed a reverse relationship between methylation levels and inner cell mass versus trophectoderm (ICM/TE) ratios, which was found to be a result of another type of differential demethylation occurring in NT blastocysts; where unequal methylation was maintained between ICM and TE regions. TE-localized methylation aberrancy suggests a widespread gene dysregulation in an extra-embryonic region, thereby resulting in placental dysfunction familiar to cloned fetuses/animals. These differential demethylations among genomic sequences and between differently allocated cells produce varied overall, but specified, methylation patterns, demonstrating that epigenetic reprogramming occurs in a limited fashion in NT embryos.