Introduction

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 adequate cross-communication between endometrium and blastocyst. 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 six to seven days after ovulation, within the ‘implantation window’, direct contact occurs between the endometrial epithelium and the trophectoderm. Finally, in the invasion phase, the embryonic trophoblast traverses the basement membrane and passes the endometrial stroma to reach 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. We present here our published data on the embryonic regulation of endometrial epithelial molecules such as chemokine receptors, the leptin system and the relaxin receptor LGR7. A final section on gene profiling is also included.

Chemokine receptors at the maternal-embryonic interface

Chemokines, a family of small polypeptides with molecular weights in the range 8—12 kDa, attract specific leucocyte subsets by binding to cell-surface receptors. In reproductive biology, these molecules have been implicated in crucial processes such as ovulation, menstruation and parturition, and in pathological processes such as preterm delivery, HIV infection, endometriosis and ovarian hyperstimulation syndrome, as well as in embryo implantation.