Decidualizing HESCs transiently produce factors permissive of embryo implantation in the mouse uterus.

<p>(<i>A</i>) Sterile mated C57BL/6 female mice were subjected to laparotomy and both uterine horns gently flushed with culture supernatant from undifferentiated HESCs (D0) or from cultures decidualized for 4 or 10 days (D4 and D10, respectively). Ten embryos (equivalent to stage 3.5 d.p.c.) were then transferred to the right horn. Each treatment group consisted of 6 animals. The number of implantation sites in the right horn was determined 6.5 d.p.c. Implantation rate was significantly higher after exposure to signals from D4 compared to D10 or D0 HESCs cells (<i>P</i><0.001). (<i>B</i>) Macroscopic appearance of uteri at 6.5 d.p.c. (Scale bar; 1 cm). (<i>C</i>) H&E staining of representative implantation sites. Pathological features such as a poor decidual response with pyknotic and karyorrhectic stromal cell nuclei (arrow heads) were often seen at implantation sites following exposure to soluble factors secreted by D0 HESCs cells. Implantation sites in uteri pretreated with conditioned medium of D4 HESCs appeared normal, showing trophoblast (T) invasion and development of large decidual (D) cells. Epithelial cells were also absent from these implantation sites. Petecchia and focal bleeding (arrows heads) and leukocyte infiltrations (*) were seen at suspect implant sites in uteri pretreated with D10 HESC supernatants. These sites often showed a luminal epithelium and small, non-decidualized stromal cells, suggestive of failed implantation. (Scale bar: 100 µm).