Eran Gershon1, Michal Elbaz1, Evan Booker2, Moran Mutchnik1, and Peter C. Gray2
1 Department of Ruminant Science, Agricultural Research Organization, Bet Dagan, Israel. 2 Clayton Foundation Laboratories for Peptide Biology, Salk Institute for Biological Studies, La Jolla, CA
Many embryonic and maternal factors regulate embryo-maternal recognition and embryo implantation. One such factor is Cripto (Cripto-1, TDGF1), a small, GPI-anchored/secreted stem cell factor. Cripto stimulates cell proliferation, migration, angiogenesis and endothelial to mesenchymal transition (EMT) in embryogenesis and tumorigenesis. We identified GRP78, an HSP70 family member, as a cell surface Cripto signaling partner. Previous papers show that Cripto and GRP78 are expressed in the endometrium of many species and we are investigating the role of Cripto/GRP78 signaling in embryo implantation. We demonstrate that Cripto is expressed in mouse uterus in a hormone and pregnancy dependent manner and we also find that human endometrial and trophoblast cell lines express Cripto. In mice, Cripto expression is restricted to endometrium at day 3 of pregnancy whereas at day 4.5 of pregnancy, Cripto localizes only to uterine stromal cells in implantation sites and is also expressed by the implant blastocyst. At later days, Cripto localizes on both the maternal and embryonic sides of the placenta. Interestingly, GRP78 is expressed mostly by the stromal cells surrounding the embryo, and not by stromal cells where Cripto is expressed nor by the blastocyst. Using an in vitro implantation model,we find that adding Cripto to the incubation medium improves spheroid attachment to endometrial cells. Conversely, neutralizing GRP78 antibodies that block Cripto signaling reduce the efficiency of spheroid attachment. These studies suggest that Cripto/GRP78 singling may play key roles in embryo implantation and have implications for treating poor fertility.