Nectin-3 Is Increased in the Cell Junctions of the Uterine Epithelium at Implantation

Uterine luminal epithelial cells (UECs) undergo the plasma membrane transformation in the transition to receptivity. This involves transient alterations in the apical junctional complex (AJC) including increases to the depth and complexity of the tight junction, loss of the adherens junction, and a decrease in the number of desmosomes along the lateral cell membranes. Nectin-3 is key protein involved in the structure and function of the AJC. This study, used immunofluorescence, Western blotting, colocalization, and coimmunoprecipitation analyses, to investigate whether nectin-3 was present in the rat uterus and was regulated by hormones and the blastocyst during early pregnancy. The results showed that nectin-3 was present in UECs as 3 molecular weight protein isoforms (80 kDa, 60 kDa, and 32 kDa). At the time of fertilization (day 1 of pregnancy), nectin-3 was localized basally, but at the time of implantation, (day 6 of pregnancy) when UECs were receptive, nectin-3 increased in the cellular junctions. When UECs returned to the nonreceptive state (day 9 of pregnancy), nectin-3 redistributed back to the cell cytoplasm. This study also showed that nectin-3 localization at the cell junctions was likely to be controlled by progesterone; however, neither ovarian hormones nor the blastocyst regulated protein abundance. This study further showed that while nectin-3 localized to the tight junction at the time of implantation, it did not interact with occludin or l-afadin. These results suggest that at the time of implantation, nectin-3 may contribute to the formation of the tight junction in a protein complex independent from occludin and l-afadin.