Maternal-embryonic cross-talk.

The human menstrual cycle evolved to prepare the uterus for blastocyst implantation, which is fundamentally under the control of gonadal steroids. Ovarian hormones induce marked morphological, physiological, and biochemical changes within reproductive tissues. These changes in turn induce alterations in the biosynthetic activity and release of a myriad of locally produced proteins into the microenvironment of the reproductive tract. These same factors may be further modified by proteins secreted by the developing embryo and accompanying cumulus cells in intimate contact with reproductive epithelium in a network signaling process. Communication is not one-way, but rather maternal-embryonic cross-talk may occur as maternal proteins are secreted into the microenvironment of the oviduct and uterus, facilitating fertilization and early embryo development and serving as homing beacons for blastocyst nidation. The communicating language facilitating this dialogue includes cytokines, growth factors, angiogenic factors, apoptotic factors, adhesion molecules, and, potentially, homeotic genes.