Figure 2.

Embryo-endometrium crosstalk at implantation. Schematic representation of the crosstalk between endometrial glands, decidualised stromal cells, corpus luteum, and trophoblasts cells of the invading embryo. During pregnancy, the syncytiotrophoblast cells produce hCG to maintain the corpus luteum so progesterone can be continually produced. Progesterone is essential for the maintenance of the decidualised cell and differentiated glands. A key secretion of the decidual cells at implantation is PRL, which acts on the glands through PRLR to maintain the glandular secretory phenotype. Additionally, trophoblast cells act directly on the glands through hCG and hPL secretion, resulting in the production of growth factors, nutrients, and receptivity markers such as LIF and glycodelin. In turn, these factors improve trophoblast invasion, thus forming a positive feedback loop.