MUC-1 glycosylation in endometrium: possible roles of the apical glycocalyx at implantation

MUC-1 is a major epithelial apical surface glycoprotein in human endometriu m. It has a large, extended and highly glycosylated ectodomain that contain s keratan sulphate chains. MUG-1 is abundant at the luminal epithelial surf ace in the receptive phase, but keratan sulphate disappears at this time. M UG-1 has been shown experimentally to inhibit cell-cell interactions by ste ric hindrance of binding interactions mediated by receptors, including inte grins and cadherins, so its high abundance at the time of implantation is u nexpected. Here, various models for MUG-I function in implantation are cons idered and its expression in different species compared. The possible evolu tionary advantages of a maternal 'barrier' to implantation are discussed.