Figure 1: Mouse model of implantation and delayed implantation.

(a) Mouse embryos escape the zona pellucida on day 4.5 of pregnancy and implant. In mice, implantation requires ovarian estrogen secreted on the morning of day 4. Ovariectomy (OVX) on the morning of day 4 of pregnancy removes the source of estrogen and thus delays implantation. Pregnancy was maintained by daily injections of progesterone (P4) but blastocysts enter a dormant state (“dormant blastocyst”). These embryos live longer than normal blastocysts and exhibit heightened autophagic activation5. When an injection of 17β-estradiol (E2) is given, dormant blastocysts are activated and implantation is initiated (“activated blastocyst”). We previously showed that dormant blastocysts exhibit heightened autophagy, and activated blastocysts accumulate MVB in the trophectoderm. (b) Transmission electron microscopy analysis of a day 8 activated blastocyst. A trophectoderm cell is shown at 3000X. Arrows, multivesicular bodies (MVB); asterisks, late endosomes.