Cell surface glycoconjugates as modulators of embryo attachment to uterine epithelial cells

Attachment of mammalian embryos to the uterine wall involves the coordinated development of both the embryo and the uterine epithelium to an attachment-competent state. This coordination is achieved directly or indirectly through the actions of ovarian steroids. Acquisition of attachment competence is proposed to reflect two processes. The first is the loss of non-adhesive glycoproteins at the cell surface of embryos, e.g. zona pellucida subunits, as well as uterine epithelial cells, e.g. mucin glycoproteins. The second process is the functional expression of complementary adhesion-promoting molecules at these cell surfaces. A series of studies indicates that heparan sulfate proteoglycans and their corresponding binding sites can play an important role in the initial stage of embryo attachment to the uterine surface.