Heparin/heparan sulfate is involved in attachment and spreading of mouse embryos in vitro

The involvement of embryonic cell surface proteoglycans in the attachment and outgrowth of cultured mouse embryos has been investigated. Several lines of evidence indicate that periimplantation stage blastocysts express heparin/heparan sulfate proteoglycans on their cell surfaces that can mediate embryo attachment and trophoblast outgrowth on a variety of matrices. First, in the presence of soluble heparin, the rate at which embryos attach and outgrow on laminin, fibronectin, or monolayers of uterine epithelial cells is reduced considerably. In the case of fibronectin, the rate of outgrowth in the presence of the heparin is slower than in the presence of the Arg-Gly-Asp-Ser-containing peptide that is recognized by a fibronectin receptor. Embryos also attach and exhibit a limited ability to outgrow on platelet factor IV, a heparin binding protein that does not possess the additional binding domains of laminin or fibronectin. Attachment on platelet factor IV is inhibited by heparin. Second, cell surface digestion of attachment-component embryos with heparinase, but not chondroitinase ABC, slows the rate of outgrowth on tissue culture plates in the presence of serum. Third, selective staining for sulfated molecules on the trophectoderm surface of periimplantation stage embryos indicates that such molecules are abundant and uniformly distributed on these cell surfaces. Last, heparin/heparan sulfate proteoglycans are detected as major cell surface components of embryos using vectorial labeling with lactoperoxidase and Na125I. Collectively, these data indicate that heparin/heparan sulfate-bearing molecules have a direct role in attachment and outgrowth of implantation stage blastocysts.