Fig. 1. Expression of MT1-MMP and uPAR during mouse embryo implantation. Implantation sites (7.5 dpc and 8.5 dpc) and 12.5 dpc placentas from wild-type mice were analyzed by in situ hybridization for MT1-MMP mRNA (A,E,I,M) and immunohistochemistry for uPAR (C,G,K,O). As controls, a sense probe for MT1-MMP (B,F,J,N) and preimmune rabbit IgG (D,H,L,P), were included. At 7.5 (A) and 8.5 (E) dpc MT1-MMP signal was seen in cells bordering the remnants of the uterus lumen (white arrows), as well as in the undifferentiated decidua cells and the maternal vessels (thin red arrows). In addition, at 8.5 dpc a few cells present at the mesometrial side close to the embryo contained mRNA for MT1-MMP (curved red arrows). At later stages of placental development (12.5 dpc), MT1-MMP was still expressed by the undifferentiated decidual cells, as well as in the maternal vessels (thin red arrows). In addition, MT1-MMP mRNA was detected in cells lying in close proximity to spongiotrophoblast cells (bold red arrow) (I). At 7.5 dpc (C) and 8.5 dpc (G) uPAR immunoreactivity was detected in the decidual cells, as well as in the maternal vessels. Weak staining could also be seen in the trophoblast cells. At 12.5 dpc, placentas the remaining mesometrial decidua cells, as well as the giant trophoblast cells, were positive for uPAR immunoreactivity. uPAR staining was also seen in the maternal and embryonic vessels as well as in the spongiotrophoblast cells (K). The areas boxed in E-H are shown at higher magnification in MP, respectively. am, antimesometrial; d, decidua; e, embryo; ec, ectoplacental cone; l, labyrinth layer; m, mesometrial; s, spongiotrophoblast layer. Scale bars: 500 µm in A-L; 100 µm in M-P.