Early Placental Vascular Morphogenesis

Abstract

Survival of the eutherian embryo/fetus depends on formation of a transient but vital organ, the placenta. This process, termed placentation, is the first test of the embryo’s differentiative and organogenesis capacity. It has two goals: attaching the conceptus to the uterus, and bringing the fetal and maternal circulations into close proximity to facilitate effective gas and nutrient/waste exchange. These functions require that fetal placental cells (trophoblasts) acquire an invasive phenotype. In mammals that form a hemochorial placenta (e.g., humans and mice), fetal trophoblasts come in direct contact with maternal blood. Thus, placentation also entails the unique requirement for close cooperation and direct cellular contact between two immunologically distinct organisms.