New Technology Overcomes Epigenetic Barriers to Achieve Efficient Somatic Cell Cloning

In nature, mammals reproduce through strict sexual reproduction, effectively ensuring genetic diversity within populations. However, in various fields such as agriculture and animal husbandry, endangered species conservation, pet cloning, disease model creation, and regenerative medicine research, there is often a need to obtain individuals with identical genomic genetic material. Somatic cell cloning is a technique that involves transferring a somatic cell nucleus into an enucleated oocyte, which, through reprogramming, forms a totipotent embryo that can develop into a cloned animal genetically identical to the donor nucleus. However, for a long time, the low efficiency of somatic cell cloning has severely limited its application in practical production and research. Improving somatic cell cloning efficiency remains a central challenge in this field.

Recently, a research team led by Lu Falong at the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, in collaboration with the teams of Sun Qiang and Liu Zhen at the Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, published a paper titled Efficient somatic cell nuclear transfer by overcoming both pre- and post-implantation epigenetic barriers in Advanced Science. By combining multiple technical strategies, the study simultaneously overcame both pre- and post-implantation epigenetic barriers during somatic cell cloned embryo development, achieving the highest birth rate of cloned mouse embryos to date. This provides a feasible technical strategy for efficient somatic cell cloning in mammals.

Somatic cell cloned embryos contain the complete cytoplasm of the oocyte and a genomic DNA sequence identical to that of the donor cell. Their low developmental efficiency is mainly due to gene expression disorders caused by epigenetic abnormalities. Previous studies have identified multiple abnormal histone modifications, such as H3K9me3, H3K4me3, and histone acetylation, in pre-implantation somatic cell cloned embryos. Intervening in these abnormal modifications can effectively improve pre-implantation embryo development. Furthermore, studies have shown the loss of atypical genomic imprinting in mouse somatic cell cloned embryos. By heterozygously knocking out multiple genes in donor cells to mimic the imprinting expression state of key atypical imprinted genes, researchers confirmed that restoring atypical genomic imprinting could improve post-implantation development. However, no previous studies have successfully addressed both pre- and post-implantation epigenetic barriers simultaneously, and existing methods for repairing post-implantation imprinting defects are technically challenging.

In this study, the research team treated somatic cell cloned embryos with the histone deacetylase inhibitor Trichostatin A (TSA) and injected mRNAs encoding the H3K9me3 demethylase Kdm4d and the H3K4me3 demethylase Kdm5b to correct abnormal histone modifications, effectively resolving pre-implantation epigenetic barriers. Simultaneously, they employed tetraploid complementation to replace the trophectoderm cells of cloned embryos, effectively addressing the loss of atypical genomic imprinting in the placental tissue of cloned embryos, thereby overcoming post-implantation epigenetic barriers. Using this combined strategy to intervene in epigenetic barriers in somatic cell cloned embryos, the team achieved a birth rate of approximately 30% from transferred cloned mouse embryos.

This study is the first to overcome both major pre- and post-implantation epigenetic barriers within a single somatic cell cloned embryo without requiring additional genetic modifications to donor cells, significantly enhancing the overall efficiency of mammalian somatic cell cloning. It offers a promising new technical strategy for cost-effective and efficient reproduction of large mammals through somatic cell cloning in the future.