Cell membrane changes of uterine epithelium and trophoblasts during blastocyst attachment in rat

A historical review of blastocyst implantation research

Research development on blastocyst implantation was reviewed in three sections: primate implantation, ungulate farm animal implantation, and the general process of blastocyst implantation in small rodents. Future research directions of this area are suggested.

Concurrent administration of diethylhexyl phthalate reduces the threshold dose at which bisphenol A disrupts blastocyst implantation and cadherins in mice

Many people are repeatedly exposed to both bisphenol A (BPA) and diethylhexyl phthalate (DEHP), but there has been little research concerning their effects in combination. Both can disrupt blastocyst implantation in inseminated females, albeit at high doses. We exposed mice on gestation days (GD) 1-4 to combinations of BPA and DEHP in doses below the threshold necessary to disrupt implantation on their own. On GD 6, there were fewer normally-developed implantation sites and more underdeveloped implantation sites in females given the combined subthreshold doses. Uterine epithelial cadherin (e-cadherin), a protein that assists in blastocyst adhesion to the uterine epithelium, was significantly reduced by these combined doses, but not by the individual doses. A similar trend was seen in integrin αvβ3, another uterine adhesion molecule. Cadherin-11 was disrupted by BPA but not DEHP. These data are consistent with competition of BPA and DEHP for conjugating enzymes.

Stress lowers the threshold dose at which bisphenol A disrupts blastocyst implantation, in conjunction with decreased uterine closure and e-cadherin

Exposure to stress can disrupt blastocyst implantation in inseminated female mice, and evidence implicates elevation of the female's estrogen:progesterone ratio. Exposure to the xenoestrogen, bisphenol A (BPA) can also disrupt implantation. Undisturbed control female CF-1 mice were compared to other females that were exposed to predators (rats) across a wire-mesh grid during gestation days (GD) 1-4, a procedure that elevates corticosterone but does not on its own disrupt implantation in this genetic strain. They were concurrently exposed to varied doses of BPA that on their own were below the threshold dose sufficient to disrupt implantation. On GD 6, we measured the number of intrauterine implantation sites and extracted their uteri, which subsequently were stained and analyzed for uterine luminal area and epithelial cadherin (e-cadherin), a molecule that causes uterine closure and adhesion of blastocysts to the uterine epithelium. The combination of rat-exposure stress and BPA significantly disrupted implantation and increased uterine luminal area, whereas either manipulation on its own did not. E-cadherin was significantly reduced by exposure to BPA, positively correlated with the number of implantation sites, and inversely correlated with luminal area. BPA exposure was also associated with nonmonotonic perturbation of urinary corticosterone concentrations and increased urinary estradiol concentrations on GD 6. These data are consistent with a potential summation of stress-induced estrogen and xenoestrogen activity.

Novel male exposure reduces uterine e-cadherin, increases uterine luminal area, and diminishes progesterone levels while disrupting blastocyst implantation in inseminated mice

Exposure to novel male mice disrupts blastocyst implantation in inseminated female mice, and evidence increasingly implicates the female's absorption of male urinary estrogens. We observed implantation sites in male-exposed and isolated control female mice during gestation days (GD) 2-8, observing a significant reduction in male-exposed females compared to controls, particularly on GD 6 and 8. We also measured transitions in uterine luminal area and e-cadherin expression, as these processes are modulated by estrogens. Luminal area was greater in male-exposed females than in controls during the post-implantation period (GD 5-7). E-cadherin levels were suppressed by male exposure, particularly during GD 4-6 Serum progesterone levels were also reduced in male-exposed females. The effects of male exposure on uterine closure and e-cadherin levels are consistent with established effects of estrogens, and suggest a possible mechanism that could contribute to implantation failure. This article is part of a Special Issue entitled 'Pregnancy and Steroids'.

Spatiotemporal expression of cyclooxygenase 1 and cyclooxygenase 2 during delayed implantation and the periimplantation period in the Western spotted skunk

Embryonic development in the western spotted skunk is arrested after blastocyst formation for about 200 days. This developmental arrest is believed to be due to insufficiency of uterine conditions to support continuous development. Implantation and decidualization are defective in cyclooxygenase 2 (Cox2)-, but not Cox1-, deficient mice. We therefore used Northern and in situ hybridization to investigate changes in uterine expression of Cox1 and Cox2 genes during various stages of pregnancy in the spotted skunk. Cox1 was constitutively expressed at all stages of pregnancy examined, but it did exhibit localized up-regulation in the trophoblast and necks of uterine glands at early implantation sites. Cox2 expression was highly regulated with little or no expression during delayed implantation. Cox2 expression was first detected in the uterus and trophoblast prior to blastocyst attachment and remained detectable for 5-6 days after blastocyst attachment. Cox2 expression was also localized in the luminal and glandular epithelia of uterine segments located between implantation chambers. Changes in Cox expression were not correlated with the abrupt increase in uterine weight that occurs simultaneously with renewed embryonic development but was correlated with an influx of serum proteins into the uterus observed in a previous study.

Uptake of tritiated uteroglobin by the endometrium of the rabbit during peri-implantation

Uteroglobin, labelled with N-succinimidyl-(2-3-3H)-propionate, was applied in vivo for 3 h to pregnant rabbit uteri 7 and 9 days after mating. Light- and electron-microscopic autoradiographs showed that the endometrial epithelium, both ciliated and non-ciliated cells, is able to take up 3H-uteroglobin, however, with differing intensity. Large areas of labelling were found in the luminal epithelium, whereas the glandular epithelium contained fewer silver grains. Moreover, intensively labelled single cells or symplasms occurred in both luminal and glandular epithelium. They were identified as degenerating or dead cells. After internalization by pinocytosis or phagocytosis, the tritiated uteroglobin was observed in multivesicular bodies or in lysosomes with floccular content. Later, radioactivity was either found within residual bodies or distributed throughout the entire epithelium and the subepithelial stroma, i.e., the silver grains could no longer be assigned to specific cell organelles.

Conceptus attachment in the ewe: an ultrastructural study

Scanning and transmission electron microscopic observations were made on trophoblast, caruncles and intercaruncular areas during the attachment of the conceptus. Three stages were determined: 1. From day 14 on, precontact was established and the conceptus appeared to be immobilized in the uterine lumen. On the centres of the caruncles which were depressed and folded the epithelial cells developed bulbous cytoplasmic protrusions. Throughout the free life of the conceptus, the trophoblast cells showed an abundant covering of microvilli. 2. On day 15, apposition occurred: most microvilli on the surface of the trophoblast disappeared. 3. Between days 16 and 18, adhesion began as a result of the interpenetration of the uterine microvilli and cytoplasmic projections of the trophoblast cells. During that stage trophoblast giant cells appeared and the uterine epithelium was turned into syncytial masses; however, it was apparently not destroyed later on. Between the caruncles, the trophoblast developed finger-like villi which invaded the lumen of the uterine glands from days 15 to 18. During their short life-time (they vanish at day 20), these trophoblastic differentiations may anchor the pre-attachment conceptus and absorb the histotrophic secretions of the glands.