Luminal uterine epithelial cells (UEC) are a polarised cell type. They are characterised by distinct domains that are both structural and functional, including an apical domain that faces the lumen, a lateral domain where junctional complexes are found and the basal domain. During early pregnancy these domains of UECs undergo many changes to become receptive to blastocyst implantation. One of the changes recently published by our lab is the loss of a morphological adherens junction (AJ) at the time of implantation (TOI). Despite the loss of this morphological structure UECs retain their cell polarity. Afadin and PLEKHA7 are proteins found at cell-cell AJs. Afadin has been reported to be associated with both the AJ and the tight junction (TJ) in other epithelial cells. This study investigated proteins known to be associated with the AJ to explore their roles in the maintenance of UEC polarity during early pregnancy.
Afadin was found to localise to apical junctions between UECs at both the time of fertilisation (TOF) and TOI, and co-localise with ZO-1 at the TOI but not completely at the TOF. Afadin protein abundance was reduced at the TOI in isolated UECs. PLEKHA7 was also localised to apical junctions between UECs at both the TOI and TOF, and also co-localise with afadin at the TOF and less so at the TOI.
The localisation of both AJ proteins at the TOF is consistent with the presence of an intact AJ at this time. However, their localisation at the AJ region at the TOI when the morphological structure is absent is an interesting observation. We suggest that afadin and PLEKHA7 not only facilitates the formation of a morphological AJ at the TOF, but are also associated with the TJ at both the TOF and TOI; thereby contributing to the maintenance of a polarised epithelium.