Endometrial biology during trophoblast invasion.

Attainment of successful implantation depends upon the synchronized changes in the endometrium before and after the arrival of blastocyst into the uterine cavity. The cues obtained from the receptive endometrium helps in proliferation and differentiation of the trophoblast cells. During the course of invasive differentiation, the trophoblast cells undergo several morphological, biochemical and molecular changes to gain the invasive capabilities. In turn, close apposition of the developing embryo brings out functional and morphological changes into the hormone primed receptive endometrium. Global gene expression profiling of the endometrium in response to the developing embryo or in response to the pregnancy hormone, human chorionic gonadotropin, in primate and human models, suggest that the endometrial-embryo cross-talk mainly influences three biological processes. Biological processes getting influenced by the blastocyst "signals" are associated with immunomodulation, biosensing and invasion. Pro- and anti-invasive paracrine factors expressed by different endometrial cell populations regulate the trophoblast invasion through activation of diverse signaling pathways. Identification of the gene signatures involved in embryo-endometrial dialogue would enhance our understanding about the pathologies like miscarriages and endometriosis.