Consequences of assisted reproductive techniques on the embryonic epigenome in cattle

Procedures used in assisted reproduction have been under constant scrutiny since their inception with the goal of improving the number and quality of embryos produced. However, in vitro production of embryos is not without complications because many fertilised oocytes fail to become blastocysts, and even those that do often differ in the genetic output compared with their in vivo counterparts. Thus only a portion of those transferred complete normal fetal development. An unwanted consequence of bovine assisted reproductive technology (ART) is the induction of a syndrome characterised by fetal overgrowth and placental abnormalities, namely large offspring syndrome; a condition associated with inappropriate control of the epigenome. Epigenetics is the study of chromatin and its effects on genetic output. Establishment and maintenance of epigenetic marks during gametogenesis and embryogenesis is imperative for the maintenance of cell identity and function. ARTs are implemented during times of vast epigenetic reprogramming; as a result, many studies have identified ART-induced deviations in epigenetic regulation in mammalian gametes and embryos. This review describes the various layers of epigenetic regulation and discusses findings pertaining to the effects of ART on the epigenome of bovine gametes and the preimplantation embryo.