EXPRESSION PATTERN OF DIFFERENT GAP JUNCTION CONNEXINS IS RELATED TO EMBRYO IMPLANTATION

Successful implantation in mammals requires a close interaction betwee n the embryo and the uterus. Direct cell-cell communication via gap ju nctions seems to play an important role in the preparation of the uter us for embryo implantation and in the regulation of trophoblast invasi on. During preimplantation in the rat the gap junctional proteins conn exin (cx) 26 and cx43 are suppressed. This loss of cell-cell communica tion seems to be important for transformation of the endometrium into the receptive phase. The suppressive effect is mediated by progesteron e as demonstrated by the application of antigestagens. At implantation , however, a spatial and temporal pattern of connexin expression is in duced in response to embryo recognition. cx26 is locally expressed in the uterine epithelium of the implantation chamber, cx43 in the surrou nding decidua prior to invasion. With progressing invasion, the decidu al cells surrounding the invading trophoblast in addition to cx43 reve al cx26. In this phase, the invasive partner, the blastocyst, is chara cterized by coexpression of cx43 and cx31. During trophoblast invasion however, cx31 becomes restricted to the cells of the invasive ectopla cental cone, cx43 to the embryo proper. It seems that compartmentaliza tion of the trophoblast and the inner cell mass is established by two different connexins. During placental differentiation connexin express ion switches from cx31 to cx26 and cx43, indicating the end of the inv asive phase. The highly regulated pattern of connexin expression in th e endometrium as well as in the trophoblast suggests a key role of thi s different intercellular pathways in regulating the invasion process of the trophoblast into its host tissue, the endometrium.