Embryonic regulation of endometrial epithelial apoptosis during human implantation.

Apoptosis is a mechanism of cell death in which cells undergo a genetically determined programme. The implanting blastocyst has to appose and adhere to the endometrial epithelium and subsequently invade it. Locally regulated uterine epithelial apoptosis induced by the embryo is a crucial step in epithelial invasion in rodents. To address the physiological relevance of this process in humans, we have investigated the effect of single human blastocysts on the regulation of apoptosis in cultured human endometrial epithelial cells (EEC) in the apposition and adhesion phases of implantation. We report a co-ordinated embryonic regulation of EEC apoptosis. In the apposition phase, the presence of a blastocyst rescues EEC from the apoptotic pathway. However, when the blastocyst adheres to the EEC monolayer it induces a paracrine apoptotic reaction.