Cell signaling in trophoblast-uterine communication.

Intricate and precise communication between the blastocyst and the uterus orchestrates embryo implantation. However, many questions remain unanswered regarding the molecular complexities of implantation. On-time implantation requires a receptive uterus and a mature blastocyst with trophoblast cells capable of adhering to and invading the endometrium. Defects in uterine receptivity or embryo/uterine signaling can cause implantation failure or early pregnancy loss, whereas deficient trophoblast differentiation can generate placental abnormalities that produce adverse pregnancy outcomes. This review will discuss several examples of signaling pathways that regulate trophoblast and uterine development during this period. Leukemia inhibitory factor is involved in uterine priming for implantation. The epidermal growth factor signaling system contributes to trophoblast-uterine communication, as well as trophoblast adhesion and invasion. Indian hedgehog signaling synchronizes tissue compartments within the uterus, and WNT signaling mediates numerous interactions within the implantation site and developing placenta. The autocrine, paracrine and juxtacrine interactions mediated by these signaling pathways contribute significantly to the establishment of pregnancy, although there are many other known and yet to be discovered factors that synchronize the maternal and embryonic developmental programs.