Cytodifferentiation of trophoblast in the anchoring villi and trophoblastic shell in the first half of gestation in the macaque.

The structure of cytotrophoblast cells in cell columns of the anchoring villi and trophoblastic shell were studied by light and transmission electron microscopy during days 19-70 of pregnancy in the macaque. Additional placentas were prepared for 3H-thymidine autoradiography to demonstrate DNA synthesis. The cell columns of the anchoring villi consist of proximal, mid, and distal regions, and similarly the trophoblastic shell has a region forming the base of the intervillous space, a central zone, and a junctional zone. The proximal region of the cell column is composed of closely apposed, largely undifferentiated cytotrophoblast cells lacking intercellular space. In the mid region, the cells, which contain segregated glycogen areas, are separated into branching strands by extensive extracellular matrix. The distal zone abuts the trophoblastic shell and has fewer mostly peripheral cytotrophoblast cells and abundant matrix. Where cytotrophoblast of the shell is exposed to intervillous space or underlies syncytial trophoblast bordering the intervillous space, pads of cuboidal cells are seen. The central zone of the shell is arranged in strands of contiguous cells. Near the maternal junctional zone, the cells have fewer junctional regions and contain lipid rather than glycogen. Results of thymidine incorporation studies are consistent with observations of others using Ki67 distribution, indicating that cell replication occurs in the proximal region of the cell column, with subsequent migration of cells into the trophoblastic shell. Changes with age include an increase in extracellular matrix in the proximal region, a more linear organization in the expanded central zone of the shell, and a decrease in necrosis at the junction of the shell with endometrium, resulting in close association of shell cytotrophoblast cells, maternal decidual cells, large granular lymphocytes, and macrophages. It is concluded that the cytotrophoblast of the cell columns and trophoblastic shell is a pleomorphic cell type responding to adjacent constituents including the matrix it forms.