Embryo-endometrial interaction.

Embryonic implantation, the process by which the human embryo orientates towards, attaches to and finally invades the underlying maternal endometrial tissue, requires a receptive endometrium, a functionally normal blastocyst and an adequate cross-communication between them. During apposition, human blastocysts find a location in which to implant, while they are guided to a specific area in the maternal endometrium. In the adhesion phase, which occurs 6 to 7 days after ovulation, within the so-called "implantation window", direct contact occurs between the endometrial epithelium (EE) and the trophectoderm (TE). Finally, in the invasion phase, the embryonic trophoblast traverses the basement membrane and passes the endometrial stroma and reaches the uterine vessels. Many molecules (hormones, cytokines, integrins, enzymes, etc.) take part in the dialogue between the human blastocyst and the maternal endometrium to achieve implantation. Here, we present our published data on the embryonic regulation of endometrial epithelial molecules such as chemokine receptors and the leptin system.