Comparative developmental anatomy of the murine and human definitive placentae

The placenta of eutherian mammals is a remarkable biological structure. It is composed of both zygote-derived and maternal cells, and mediates the complex interactions between the mother and the fetus that are necessary for fetal growth and survival. While the genetic basis of human placental development and function is largely unknown, its understanding is of immense clinical importance because placentopathies of unknown genetic aetiology are thought to be the cause of many types of pregnancy complications including unexplained miscarriage and intrauterine growth retardation. The mouse is the best-studied mammalian experimental genetic model system and research is not restricted by the inherent ethical and practical limitations associated with the human. As a result, knowledge about the genetic control of mouse placental development has expanded greatly in recent years. In order for this to be of benefit to medical practice, extrapolations from murine to human placentation have to be made. However, comprehensive comparisons of the placentae of these two species are rare. This review therefore compares the developmental anatomy of the placenta between humans and mice with emphasis on structures and cell types that might be analogous between the two species. This could be of particular benefit to mouse developmental geneticists who study placental development and have an interest in the possible clinical implications of their work.