MUC1 is a scaffold for selectin ligands in the human uterus

MUC1 is a large, transmembrane mucin glycoprotein abundantly expressed at the apical surface of uterine epithelia in all species examined to date. Loss of MUC1 at the time of embryo implantation occurs in many species; however, this does not appear to be the case in humans. Recent studies indicate that human blastocysts express L-selectin at their external surfaces raising the possibility that selectin ligands expressed at the apical surface of the uterine epithelium support early stages of blastocyst attachment. In the current study, we have used a panel of antibodies specific for selectin ligands to determine if MUC1 functions as a scaffold for these carbohydrate motifs in fertile women. The results demonstrate that MUC1 carries selectin ligands throughout the secretory phase of the menstrual cycle, including the mid-secretory (receptive) phase. Consequently, MUC1 represents a potential ligand for selectins expressed by human blastocysts.