Reproduction Abstracts

Introduction: During implantation, uterine luminal epithelial cells (UECs) disassemble cell–cell and cell–matrix adhesions that contribute to the formation of an epithelial barrier, which is refractory to blastocyst implantation. These changes are critical for successful implantation. We have shown previously that claudin 7 is present in UECs and is lost prior to implantation in the rat. Epithelial cell adhesion molecule (EpCAM) is another protein frequently associated with claudin 7. This study investigated whether EpCAM is present and whether EpCAM is associated with claudin 7 in UECs during early pregnancy. This study also investigated factors that regulate the expression of EpCAM to elucidate its role in UECs during early pregnancy.

Methods: Immunofluorescence and western blotting was performed on uterine tissue from pregnant (day 1 and 6), pseudopregnant (day 6), and cytochalasin D-treated (day 1) rats and ovariectomised rats subjected to ovarian hormone regimes. Co-immunoprecipitation was performed on isolated UECs from day 1 pregnant rats.

Results and discussion: EpCAM localized to the basolateral surfaces of UECs during normal pregnancy and decreased at the time of implantation (day 6) (P<0.05, n=5). At the time of fertilisation (day 1), EpCAM co-localised and co-immunoprecipitated with claudin 7, CD9 and α-actinin. EpCAM was not decreased with ovarian hormone replacement (P>0.05, n=5) or in pseudopregnancy (P>0.05, n=5) but decreased with cytochalasin D treatment (P<0.05, n=5). These results suggest that prior to implantation, EpCAM exists in a protein complex with claudin 7 to mediate intercellular adhesion but during implantation, decreases in response to factors other than ovarian hormones and the blastocyst.