Separation of a 170-K delayed-implantation-associated protein with inhibitory activity on trophoblast outgrowth and RNA synthesis by mouse embryo

Embryonic dormancy phenomenon in obstructed healthy mouse fallopian tubes

PURPOSE

A mouse model of unilateral oviductal obstruction was designed to study whether healthy oviducts can support embryo development in an advanced stage toward blastocyst hatching and implantation when the embryos in the contralateral side normally move into the uterine cavity.

METHODS

The oviducts of 80 female ICR mice (aged 5-8 weeks) were ligated unilaterally 12-40 hr postcoitus. The ligated oviducts were isolated from day 4 to 19.5 postcoitus. Embryos within the ligated oviducts were then flushed out to record the developmental stage and compared with the conceptuses in the contralateral uterine horns with unligated oviducts. Embryos recovered from ligated oviducts were then cultured in vitro to observe their potential for further development.

RESULTS

In 33 mice, 53.4% (163/305) and 86.1% (241/280) of the morphologically normal blastocysts had hatched from the zona pellucida within the obstructed tube and contralateral uterine horns, respectively, on the 5th day postcoitus. The data demonstrated that the hatching process could take place within the obstructed fallopian tube, but the timing was delayed. From 5.5 to 19.5 days postcoitus, a total of 362 implanted embryos were obtained in unligated control uterine horns, but none of the 404 embryos in the artificially obstructed oviducts were implanted. The embryos within the ligated tubes were dormant in the hatched blastocyst stage as demonstrated by their ability to continue growing (98.2%) when removed from the oviduct to an in vitro environment.

CONCLUSIONS

In this study, we demonstrate that mouse embryos can hatch, although delayed, in obstructed healthy oviducts. Tubal pregnancy is not likely to happen in artificially obstructed healthy mouse fallopian tubes, since all the viable embryos were dormant at the hatched blastocyst stage.

A delayed-implantation-associated protein prevents resumption of DNA synthesis by the trophectoderm of delayed-implanting mouse blastocysts in vitro

Objective of this study was to determine the ability of a delayed-implantation-associated protein (MW 170,000, DIAP170K) to inhibit DNA synthesis by mouse blastocysts. Mice were ovariectomized on day 3 of pregnancy and treated with daily injections with 1 mg progesterone till day 7 to induce delayed implantation. Blastocysts were collected on day 8 with or without a single injection of 25 ng estradiol-17 beta on day 7 that activates blastocyst metabolisms (activated blastocysts and delayed-implanting blastocysts respectively). DNA synthesis was determined by measuring [3H]thymidine incorporation by blastocysts. DIAP170K at 10 micrograms/m/ suppressed resumption of DNA synthesis by delayed-implanting blastocysts and suppression was maximal at 50 micrograms/m/. However, DIAP170K did not affect DNA synthesis by blastocysts obtained on day 5 of pregnancy (normal blastocysts) and activated blastocysts. Resumption of DNA synthesis in the inner cell mass (ICM) and trophectoderm from delayed-implanting blastocysts was then separately assessed. DNA synthesis resumed in the trophectoderm of intact blastocysts during 24-hr culture but not in the trophectoderm cultured apart from the ICM. DIAP170K inhibited the resumption of DNA synthesis by the trophectoderm of intact delayed-implanting blastocysts but did not affect DNA synthesis by the ICM. In conclusion, DIAP170K inhibits resumption of DNA synthesis by trophectoderm of delayed-implanting blastocysts. This action of DIAP170K may play a central role in maintaining, but not achieving, dormancy of DNA synthesis by delayed-implanting blastocysts in mice.