Sandra Schlafke

Preference of Invasive Cytotrophoblast for Maternal Vessels in Early Implantation in the Macaque

The interaction of cytotrophoblast with maternal endometrium, especially endometrial blood vessels, was examined in macaque gestational stages between 2 and 8 days after the onset of implantation. Serial sectioning of these early implantation sites allowed immunostaining of consecutive sections with a number of different antibodies, facilitating cell identification. In the earliest implantation site, immunostaining showed that antibody to cytokeratin stained cytotrophoblast, syncytial trophoblast, epithelial plaque and endometrial gland cells. However, only those cytotrophoblast cells near the maternal-fetal border and within vessels showed surface staining for neural cell adhesion molecules and only syncytial trophoblast showed SP1 reactivity. Even at this early stage cytotrophoblast filled the lumen of superficial arterioles, whereas dilated venules contained only a few cytotrophoblast cells. In later stages endovascular cytotrophoblast not only plugged many spiral arterioles but also migrated into the walls of these arterioles, and progressed into deeper coils. Displacement of endothelial cells and disruption of vessel walls were illustrated with antibody to factor VIII, TGF alpha, and desmin. Clusters of cytotrophoblast cells at the fetal-maternal interface tended to bypass clusters of epithelial plaque cells and larger clusters of maternal fibroblasts, but readily entered all vascular spaces. Consequently the vascular system constituted a major pathway of invasion, although the arterioles were the only component substantially invaded beyond the trophoblastic-shell/endometrial border.

Ultrastructural localization of pregnancy-specific β1-glycoprotein (SP1) and cathepsin B in villi of early placenta of the macaque

Pregnancy-specific beta 1-glycoprotein (SP1) is found in maternal serum very early in gestation in both human and non-human primates. As judged by light microscopic immunocytochemistry, the major source of SP1 is the syncytial trophoblast, but little is known of the subcellular localization of SP1 indicative of the cellular pathway involved in secretion of the hormone. To study subcellular distribution of SP1, we used electron microscopic immunocytochemistry carried out on macaque placental villi from early (3-4 weeks) gestation. Both light and electron microscopic results confirmed localization confined to syncytial trophoblast in the villi. Within syncytial trophoblast labeling was predominantly over small granules in the apical cytoplasm. The Golgi complex also showed labeling, and light labeling was associated with the endoplasmic reticulum. For comparison, we also localized cathepsin B, a lysosomal protease. By way of contrast this enzyme was localized primarily in large cytoplasmic granules. The results are consistent with a secretory pathway including synthesis in the ER, processing by the Golgi complex, and exocytotic release into maternal blood in the intervillous space.

Morphology of development in the primate: Blastocyst to villous placental stage

Examination of plastic-embedded rhesus monkey and baboon blastocysts through the implantation period has provided information on normal differentiation and development. The blastocysts show many features in common with non-primate laboratory animals, including differentiation of endoderm and its extension beyond the inner cell mass prior to implantation. However, there appears to be more cell death, and more aberrations in development. Implantation involves the adherence of trophoblast to healthy uterine luminal epithelial cells, and intrusion of syncytial trophoblast between these cells, followed by lateral expansion of the site of invasion prior to penetration of the uterine epithelial basal lamina. An amnionic cavity is formed within the inner cell mass, and is preceded by establishment of cell polarity. The definitive yolk sac is formed by an aggregation of endodermal cells adjacent to the inner cell mass. The trophoblast does not give rise to mesodermal cells, but some of these cells may be formed from endoderm prior to primitive streak formation. In both rhesus monkey and baboon, syncytial trophoblast taps the maternal vascular system relatively rapidly. In the baboon in particular large blood-filled spaces elevate the implantation site from the level of the endometrium at the stage of primary and secondary villus formation.