[The effects of genomic imprinting on animal development and cloning].

In placental mammals, there is a small group of special genes, which are imprinted so that only one of the parental alleles is actually expressed in target cells. This epigenetic process is named genomic imprinting. Till now, about eighty genes are found to be imprinted in mice and human, and imprinting is conserved in ruminant species as well. This paper emphasized the effects of genomic imprinting on development and animal cloning, exhibited the function of imprint genes by analyzing their origin, and discussed their formation mechanism for understanding the profound effects of this epigenetic modification on development. Many imprinted genes are involved in fetal development, and may influence fetal growth and behavior. Imprinting appears to be particularly important for placental development. Epigenetic deregulation of imprinting may lead to complex diseases in human. And there is now a large body of evidence for loss of appropriate imprinting in numerous tumors. So far, nuclear transfer is a very inefficient process. The rate of cloned animals' surviving was very poor, and there were also frequent inherent anomalies. The most common abnormal phenotypes had the similar characteristics of the consequence due to deregulated expression of imprinted genes,indicating that the key factor to limite cloning efficiency might be the aberrant expression of imprinted genes.