The fertilized egg undergoes several cleavage divisions to form the blastocyst in the oviduct. The blastocyst then is transferred to the uterus to initiate implantation, and trophectoderm-derived cells interact with the maternal uterus. The dialogue between mother and embryo is prerequisite for the following embryonic development because a disturbance of this process mainly account for 60% pregnancy loss in human early post-implantation (Emiliani et al., 2005). After implantation, the embryo initiates the milestone event—gastrulation—during which multipotent epiblast cells (EPI) undergo an orchestrated process of morphogenetic cellular movement and differentiation. Through gastrulation, three germ layers (ectoderm, mesoderm, and endoderm) are specified to establish the body plan. Because the embryo is engulfed by maternal tissues and inaccessible, the direct observations and manipulations are obstructed. Currently, the knowledge on human early post-implantation development remains largely unknown.
