R. Grummer et al., EXPRESSION PATTERN OF DIFFERENT GAP JUNCTION CONNEXINS IS RELATED TO EMBRYO IMPLANTATION, The International journal of developmental biology, 40(1), 1996, pp. 361-367
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.