Genetic-epigenetic intersection in trophoblast differentiation: Implications for extraembryonic tissue function

Recent years have seen considerable advances in our understanding of early mammalian development leading up to the establishment of the first cell lineages, with important implications for the behaviour of stem cells derived from the early embryo. Dramatic new insights have also propelled the field of epigenetics with the identification of 5-hydroxymethylcytosine as an additional base modification and the pervasiveness of asymmetrical non-CG DNA methylation specifically in ES cells. Prompted by our findings on the role of DNA methylation in cell lineage commitment, this review highlights recent insights into the genetic-epigenetic intersection in the establishment of the placental trophoblast lineage that is essential for embryo implantation, nutrition and survival. The unique trophoblast epigenotype is instrumental for normal trophoblast differentiation and placental function, and consequently trophoblast is particularly susceptible to regrogramming failures.