In vitro models of human blastocysts and early embryogenesis

Mammalian embryogenesis begins with the fertilization of the egg, and a totipotent zygote is formed in the process, which is capable of developing into the morula and then the blastocyst. As development progresses, cells of the epiblast (EPI) lineage within the blastocyst will develop into the embryo proper, whereas cells of the trophectoderm (TE) and primitive endoderm (PE), also known as hypoblast, will eventually give rise to the placenta and yolk sac, respectively. Understanding the embryogenesis has been an important task over the past decades, as any desynchronization or inaccuracy occurring during the embryonic development could often lead to defective pregnancy and potentially miscarriage. As such, different in vitro stem cell models have been developed in the scientific community to facilitate the study of human embryogenesis. In this review, we will discuss multiple in vitro models of the human blastocysts and their associated applications and limitations.