Ectoplacental Cone Isolation, Culture and Assessment

Chapter Summary During rodent development, a transient stage that is rapidly assembled in the extraembryonic placental compartment is the ectoplacental cone, which supports the first functional maternal–fetal interactions before completion of the placenta. During this period (gd 6–8.5), the ectoplacental cone plays a remarkable set of vital functions, finally contributing to cellular subtypes of placental development (to form the junctional zone: the secondary giant and spongiotrophoblast cells, in close association with the chorion involved in placental labyrinth differentiation). Specialized cells that arise from the ectoplacental cone, called secondary trophoblast giant cells (TGCs), are responsible for specific interactions with maternal tissues, which include displacement of uterine epithelium, invasion of the basement membrane and endometrial stroma, phagocytosis of maternal cells, opening of endometrial vessels, and replacement of endothelial cells. Association of TGCs with the maternal vessels guarantees a blood source that, having embedded the embryo, allows molecular exchange and embryonic development. In some rodent species, further invasion also occurs through the maternal vascular lumen. Along with a mechanical tissue involved with the lodging of the embryo into the uterine stroma, TGCs are actively synthetic cells that produce a large variety of regulatory molecules that act as endocrine, paracrine, and autocrine signals. TGCs are polyploidy, which is thought to accelerate differentiation and therefore increases the intensity and complexity of their roles. In this chapter, we describe and discuss the use of in vitro techniques that have been adapted for the study of the maternal–fetal interaction before placenta completion. Since the cells and the structure belonging to the ectoplacental cone are described in Chapter 10 , we will focus here on the techniques used to establish TGCs in vitro by culturing blastocysts or taking ectoplacental explants. Identification of the cells and cocultures mimicking heterotypic cell–cell interactions in vivo are also described.