The role of trophoblastic binucleate cells in implantation in the goat: a morphological study.

In the goat conceptus individual intra-epithelial trophectodermal binucleate cells first appear 18 days post coitum and their incidence rapidly increases where the trophectoderm is apposed to the caruncular and intercaruncular sites of initial attachment to the uterine epithelium. Special staining techniques reveal that these cells, when mature, contain prominent Golgi bodies and numerous characteristic granules. Our evidence shows that at 19 days post coitum the binucleate cells migrate to the microvillar junction and fuse with individual uterine epithelial cells to form hybrid feto-maternal trinucleate cells. It is proposed that subsequent continued binucleate cell migration and fusion with trinucleate cells produce the syncytial plaques typical of the remainder of pregnancy. It is further suggested that the fusion is important in facilitating the delivery of the characteristic granules to the base of the uterine epithelial layer with subsequent exocytosis of their contents into maternal tissue.