后生遗传修饰及其对动物克隆的影响

近年来，不断有新的哺乳动物和两栖类动物被成功克隆，但这并不能掩盖克隆效率过低和克隆动物异常的现实，为了解决这一问题，人们对克隆机理进行了大量研究。高度分化的体细胞核在去核的卵质中去分化和再程序化不完全是导致动物克隆失败的主要原因，而去分化和再程序化不完全主要是由于基因组去甲基化不充分和过早再甲基化引起克隆胚中甲基化水平比正常胚中偏高所至，这可引起一些重要基因的异常表达，尤其是印记基因。这些机制的研究对提高克隆效率有着重要意义。

Epigenetic Modifications and Its Impact on Animal Cloning

Despite recent successes in cloning various mammals and amphibians, the low efficiency of animals production and abnormal symptoms in many cloned animals are crucial problems in cloning technology. To overcome these problems, scientists focus on mechanisms of cloning. A possible cause of the low success frequency of cloning is the insufficient dedifferentiation and the inadequate reprogramming of the high differentiated adult somatic nucleus in enucleated oocytes, which caused by incomplete methylation and premature de novo remethylation of donor DNA. In cloned embryos the methylation level is higher than normal embryos, and this may cause aberrant expression of several important genes, especially imprinting genes. Study on these mechanisms is very important to improve the rate of successful cloned animals.