Figure 1.

Processes of conceptus implantation to the maternal endometrium; hatching, attachment, invasion, and syncytialization or cell fusion. During the implantation period, molecules related to lymphocyte homing and EMT are used in both human and bovine species. Upper human implantation. Cell structures of cytotrophoblast and syncytiotrophoblast are shown in the black box. Lower Bovine (cattle) implantation. Unique to the ruminant ungulates, the trophoblast after hatching elongates (conceptus) and the elongated conceptus attachment to the maternal luminal epithelium occurs, but the TE cell invasion is kept minimal. During conceptus elongation, binucleate cells form in the TE cell layer, which take on nuclei from the epithelial cells of maternal endometrium, resulting in the formation of trinucleate cells