Human embryonic stem cells as a model for trophoblast differentiation.

The earliest stages of human development profoundly influence the success of pregnancy and maternal as well as fetal health. One of the most critical developmental processes is the specification of the trophoblast lineage and the formation of the placenta, yet this is the stage that is most difficult to study because of the general inability to do in vitro studies with human embryos or conduct in vivo clinical research during the initial weeks of pregnancy. Embryonic stem cells potentially provide a novel surrogate for the undifferentiated pluripotent cells of the preimplantation embryo, and current research indicates that human embryonic stem cells are capable of differentiation to the trophoblast lineage under the influence of diverse soluble, transcriptional, and environmental cues. This review summarizes current areas of research in these different approaches to the study of placental cell differentiation and suggests avenues of investigation that are both unique and promising in this area.