Mucin 15 is lost but mucin 13 remains in uterine luminal epithelial cells and the blastocyst at the time of implantation in the rat

The glycocalyx of the uterine luminal epithelium in the rat undergoes considerable reduction before implantation. In particular, the reduction of some mucins is necessary to facilitate blastocyst adhesion and subsequent implantation. The present study investigated the localisation, abundance and hormonal control of two mucin proteins, Muc13 and Muc15, in rat uterine epithelial cells during early pregnancy to determine whether they are likely to play a role in uterine receptivity for implantation. Muc13 and Muc15 are localised to the uterine luminal epithelium but show a presence and an absence, respectively, at the apical cell surface at the time of implantation. This localisation corresponds to changes in the molecular weights of Muc13 and Muc15, as shown with western blotting analysis. Furthermore, the localisation of Muc13 and Muc15 was shown to be controlled by the ovarian hormones, oestrogen and progesterone, and they were also localised in preimplantation rat blastocysts. Our results suggest that Muc15 may operate in an anti-adhesive capacity to prevent implantation while Muc13 potentially functions in either an adhesive or cell-signalling role in the events of implantation.