Epigenetics of Cloned Livestock Embryos and Offspring

Epigenetic reprogramming of the transferred somatic cell nucleus from its differentiated status into the totipotent state of the early embryo is the most critical factor for the success of somatic cell nuclear transfer (SCNT)-based cloning. This involves erasure of the gene expression profile of the donor cell and the establishment of the well-orchestrated sequence of expression of an estimated number of 10,000–12,000 genes regulating embryonic and fetal development. SCNT may be associated with pathological changes in the fetal and placental phenotype in a certain proportion of cloned offspring, specifically in ruminants, that are probably caused by aberrant epigenetic reprogramming. Improvements in our understanding of this dramatic epigenetic reprogramming event will be instrumental in realizing the great potential of SCNT for basic biological research and for various agricultural and biomedical applications. This chapter reviews the current knowledge of the epigenetic reprogramming after the use of SCNT in livestock, with emphasis on gene-specific and global DNA methylation, imprinting, X-chromosome inactivation, and telomere length restoration in early development.