Biology of the Ectoplacental Cone

Histology Atlas of the Developing Mouse Placenta

“…30,40 The parietal giant cells maintain close connections with the decidua and are responsible for much of the uterine remodeling done in preparation for the formation of the junctional zone, which involves reconfiguring the maternal vascularization. 40,42 Around E6.0, some decidual cells on the mesometrial side of the uterus undergo apoptosis to increase the channel volume of the MBS. 27,30 At this time, the MBS in the vicinity of the ectoplacental cone begins to accumulate maternal anucleated red blood cells (aRBCs).…”

“…40 Because these trophoblast giant cells exhibit some phagocytic characteristics, after the proliferation and migration of secondary trophoblast cells, both leukocytes and erythrocytes may be seen among their intracellular spaces. 5,40 Beginning at E5.5, the uterine wall is undergoing the substantial modifications necessary to facilitate initial placenta formation. 22,43 These modifications include the collection of specialized innate immune cells, variously designated uterine natural killer (uNK) cells or granulated metrial gland cells, 43 along the triangular area of ectoplacental cone invasion.…”

“…34,40,42 These characteristics include sizable nuclei as well as the accumulation of free ribosomes on the Golgi apparatus and endoplasmic reticulum. 40 Secondary trophoblast cells that arise from further differentiation of the primary giant cells after implantation has occurred continue to retain these same cell characteristics as well. 34,42 Extending from the outer region of the ectoplacental cone, secondary trophoblast cells termed parietal giant cells come to surround the entire ectoplacental cone and eventually the entire embryo.…”

“…By E5.0, the cells of the mural trophoblast are continuing to divide, resulting in elongation of the blastocyst. 27,40 This unidirectional expansion away from the mesometrial side of the implantation site leads to formation of the elongated egg cylinder (Figure 18). 27 The polar trophoblast cells surrounding the ICM, now positioned near the mesometrial wall of the uterus, have continued to differentiate and form the EE, which impinges on the epiblast and the primitive endoderm of the ICM.…”

“…27 Moving outward, these secondary trophoblast cells become larger and further spaced from one another, with more randomized shapes due to their multiple cytoplasmic connections with neighboring cells. 40 They form the basis of the separating layer that will ultimately become the junctional zone and contribute to the development of the villous blood spaces. 40 Because these trophoblast giant cells exhibit some phagocytic characteristics, after the proliferation and migration of secondary trophoblast cells, both leukocytes and erythrocytes may be seen among their intracellular spaces.…”