Apoptosis occurs in implantation site of the rhesus monkey during early stage of pregnancy

The exact role of apoptosis that occurs in human placenta during the early stage of pregnancy remains unknown because of the difficulty in obtaining the intact implantation site. In this study, we used rhesus monkey as an animal model to examine apoptosis occurring in the implantation site at various stages of early pregnancy. It was shown that Fas and FasL mRNA and protein were localized in both the chorionic villi and glandular epithelium from day 15 to day 30 of pregnancy. Fas and FasL protein were also expressed in the epithelial plaque on day 15 of pregnancy. In situ 3'-end-labeling results showed that glandular epithelial cells underwent extensive apoptosis with obvious morphological degradation during the early stage of pregnancy. It was found that the cells that were 3'-end-labeled in the chorionic villi and anchoring villi were mainly localized in cytotrophoblast and cytotrophoblast column. It is therefore suggested that in primates apoptosis, which may be involved in the regulation of proliferation of trophoblast villi and degradation of epithelial plaque, as well as remodeling of the glands in the maternal decidua, may play an important role during the early stage of implantation and placentation.