Epigenetic Reprogramming and Somatic Cell Nuclear Transfer.

Epigenetics is an area of genetics that studies the heritable modifications in gene expression and phenotype that are not controlled by the primary sequence of DNA. The main epigenetic mechanisms are DNA methylation, post-translational covalent modifications in histone tails, and non-coding RNAs. During mammalian development, there are two global waves of epigenetic reprogramming. The first one occurs during gametogenesis and the second one begins immediately after fertilization. Environmental factors such as exposure to pollutants, unbalanced nutrition, behavioral factors, stress, in vitro culture conditions can negatively affect epigenetic reprogramming events. In this review, we describe the main epigenetic mechanisms found during mammalian preimplantation development (e.g., genomic imprinting, X chromosome inactivation). Moreover, we discuss the detrimental effects of cloning by somatic cell nuclear transfer on the reprogramming of epigenetic patterns and some molecular alternatives to minimize these negative impacts.