Cultured Mouse Blastocysts Research Articles

Production and metabolism of progesterone and androstenedione by cultured mouse blastocysts.

A study designed to determine the point at which mouse embryo is 1st capable of producing progesterone and androstenedione is presented. Mouse preimplantation embryo and postblastocyst cultures were assayed by radioimmunoassay and thin-layer chromatography. Evidence of progesterone formation in the first 48 hours of culture was absent. A small amount of progesterone production was detected between the 6th-7th equivalent gestation days (EGD). By the 8th-9th EGD a peak production of .53 p mole/blastocyst/day was reached. After the blastocyst has attached to the surface of the dish and trophoblastic outgrowth has taken place progesterone is produced. These results were confirmed by chromatographic analysis and permeability studies. The ability of blastocyst and postblastocyst cultures to produce and metabolize androstenedione was also studied. Postblastocyst cultures were found to convert dehydroepiandrosterone (DHEA) to androstenedione. These results suggest that delta (5) 3beta hydroxysteroid dehydrogenase activity (3beta-HSD) needed to convert DHEA to androstenedione and other enzyme activities involved in the metabolism of progestin and androgen are only acquired by postimplantation conceptuses. This would negate the possibility that steroid biosynthesis by the mouse blastocyst is involved in its implantation.

Control of inner cell mass development in cultured mouse blastocysts.

THE mouse blastocyst consists of a group of cells, the inner cell mass (ICM), attached to a small area of the inside surface of a sphere of trophectoderm cells. The trophecto-derm gives rise to the extraembryonic regions of the conceptus while the ICM forms the embryo proper1. At implantation trophoblast cells invade the uterine epithelium. Those overlying the ICM proliferate to form the ectoplacental cone and the extraembryonic ectoderm and the remainder undergo transformation into giant cells2. The cells of the inner cell mass divide further, and, together with the extraembryonic ectoderm, give rise to a column of cells, the egg cylinder, that extends into the blastocyst cavity (blastocoele). Lactic dehydrogenase A subunits (4A, LDH-5) appear at this time3, and may be synthesised first in tissue deriving from the ICM4. Subsequently LDH-4 (3A1B) and LDH-3 (2A2B) appear as the contribution of B subunits to the pattern increases. If implantation is prevented, further development of the blastocyst is arrested5 and LDH-5 fails to appear3. Implantation therefore seems to act as a trigger, not only for trophoblast proliferation, but also, directly or indirectly, for further development of ICM. In the work reported here we have varied the conditions of culture of isolated blastocysts and have elicited alternative forms of development that mimic those observed in vivo when implantation occurs or is prevented. We have shown further that the triggering of ICM development in vitro may represent the release from an inhibitory effect of trophectoderm.