Sheep blastocysts (Day 13-21) incubated in a modified Minimum Essential Medium released proteins into the medium at an approximately linear rate over a 24-h period. Single Day-16 blastocysts converted 2-8% of the radioactivity supplied (100 muCi L-[3H]leucine) into non-dialysable macromolecules which were released into the medium. Two-dimensional polyacrylamide gel electrophoresis revealed that at Day 13 there was only one major product (Protein X), consisting of three closely similar isoelectric species of (pI of denatured polypeptides about 5.5), each with molecular weights of 17 000. Between Days 14 and 21 additional proteins were detected. One of these was of high molecular weight (greater than 660 000) and did not appear on the two-dimensional gels, but Protein X continued to predominate until Day 23 when it could not be detected. Explants of chorion from Day 30 of pregnancy failed to secrete Protein X. Protein X was released in significant quantities (50-100 micrograms per 24 h) by the trophoblast but not the yolk sac of Day-14 and Day-16 conceptuses, but was present in very low amounts in the tissues. Protein X from the incubation medium of Day-14 and Day-16 conceptuses was purified by successive DEAE ion exchange and Sephacryl S-200 gel chromatography. Because Protein X and some of the other proteins are produced transiently between Days 13 and 21, it is possible that they may play a role in maternal recognition of pregnancy in sheep.

The likely functions of uterine secretions, often termed histotroph, in the nurture of the early conceptus are reviewed. Particular emphasis has been placed on the pig in which the uterus synthesizes and secretes large amounts of protein in response to progesterone. In this species, which possesses a non-invasive, diffuse type of epitheliochorial placentation, the secretions provide a sustained embryotrophic environment which is distinct from that of serum. A group of basic proteins dominates these uterine secretions after Day 11 of pregnancy and its best characterized member is uteroferrin, an iron-containing acid phosphatase with a deep purple colour. Evidence has accumulated to suggest that uteroferrin, rather than functioning as an acid phosphatase, is involved in transporting iron to the conceptus. Three basic polypeptides which are found noncovalently associated with uteroferrin have been shown to be antigenically closely related to one another and to have arisen by post-translational processing from a common precursor molecule. Their function is unknown. A group of basic protease inhibitors has been identified which bear considerable sequence homology to bovine pancreatic trypsin inhibitor (aprotinin) and may control intrauterine proteolytic events initiated by the conceptuses. The last basic protein so far characterized is lysozyme which is presumed to have an antibacterial role. Finally, two low molecular weight (Mr approximately 18,000) acidic polypeptides have been purified and have sequence homology to a plasma retinol binding protein. Like uteroferrin, these proteins may be responsible for transport of an essential nutrient to the conceptus.

Assisted reproductive technologies in all mammals are critically dependent on the quality of the oocytes used to produce embryos. For reasons not fully clear, oocytes matured in vitro tend to be much less competent to become fertilized, advance to the blastocyst stage, and give rise to live young than their in vivo-produced counterparts, particularly if they are derived from immature females. Here we show that a chemically defined maturation medium supplemented with three cytokines (FGF2, LIF, and IGF1) in combination, so-called "FLI medium," improves nuclear maturation of oocytes in cumulus-oocyte complexes derived from immature pig ovaries and provides a twofold increase in the efficiency of blastocyst production after in vitro fertilization. Transfer of such blastocysts to recipient females doubles mean litter size to about nine piglets per litter. Maturation of oocytes in FLI medium, therefore, effectively provides a fourfold increase in piglets born per oocyte collected. As they progress in culture, the FLI-matured cumulus-oocyte complexes display distinctly different kinetics of MAPK activation in the cumulus cells, much increased cumulus cell expansion, and an accelerated severance of cytoplasmic projections between the cumulus cells outside the zona pellucida and the oocyte within. These events likely underpin the improvement in oocyte quality achieved by using the FLI medium.cumulus cell | embryo development | genetic modification | in vitro fertilization | MAPK signaling

D-glucose at 5.6 mM reduces the progression of in vitro-produced (IVP) bovine embryos from the morula to the blastocyst stage and skews sex ratio towards males. Possibly, the presence of two transcriptionally active X-chromosomes compromises female embryo development through imbalance in glucose metabolism. Here, we have determined the threshold of embryo sensitivity to glucose, whether substitution of D-fructose for glucose reduces the selective loss of female embryos, and whether inhibition of an X-linked gene product, glucose 6-phosphate dehydrogenase (G6PD), normalizes sex ratio among bovine blastocysts. IVP zygotes were cultured in glucose-free medium to 72 hr post-insemination, at which time 8-cell embryos were selected for treatment and cultured until 144 hr post-insemination. Addition of 4 mM glucose at the 8-cell stage reduced (P < 0.05) the number of blastocyst that formed, whereas 2.5 and 1 mM glucose had no effect. Sex ratio in the presence of 4 and 2.5 mM glucose differed significantly from 0.5, while 1 mM glucose had no effect. D-fructose (5.6 mM) did not compromise development to blastocyst and did not alter the sex ratio of blastocysts that formed. When G6PD inhibitors (dehydroepiandrosterone: DHEA and 6-aminonicotinamide: 6-AN), which effectively inhibit the reduction of the NADPH-sensitive dye, brilliant cresyl blue (BCB) in bovine morulae, were added to the culture medium containing 4 mM glucose, embryo development was moderately reduced, but sex ratio skewing was corrected (with 6-AN) or lowered (with DHEA). In conclusion, glucose above 2.5 mM impairs bovine embryo development and increases sex ratio, most likely as a result of increased pentose-phosphate (PP) pathway activity in female embryos.

purified from conceptus incubation medium and injected (0\m=.\2mg protein/day) into the uterine lumen of 3 animals. Plasma progesterone concentrations indicated that oTP-1\\x=req-\ treated animals maintained luteal function 4 days longer than did control animals. We suggest that conceptus proteins and specifically oTP-1 are involved in the maintenance of luteal function during early pregnancy, and that this action is probably mediated through interaction with the uterine endometrium.