Evidence that "embryonic estrogen" is a factor which controls the development of the mouse preimplantation embryo

The spatiotemporal hormonal orchestration of human folliculogenesis, early embryogenesis and blastocyst implantation

The early reproductive events starting with folliculogenesis and ending with blastocyst implantation into the uterine endometrium are regulated by a complex interplay among endocrine, paracrine and autocrine factors. This review examines the spatiotemporal integration of these maternal and embryonic signals that are required for successful reproduction. In coordination with hypothalamic-pituitary-gonadal (HPG) hormones, an intraovarian HPG-like axis regulates folliculogenesis, follicular quiescence, ovulation, follicular atresia, and corpus luteal functions. Upon conception and passage of the zygote through the fallopian tube, the contribution of maternal hormones in the form of paracrine secretions from the endosalpinx to embryonic development declines, with autocrine and paracrine signaling becoming increasingly important as instructional signals for the differentiation of the early zygote/morula into a blastocyst. These maternal and embryonic signals include activin and gonadotropin-releasing hormone 1 (GnRH1) that are crucial for the synthesis and secretion of the 'pregnancy' hormone human chorionic gonadotropin (hCG). hCG in turn signals pre-implantation embryonic cell division and sex steroid production required for stem cell differentiation, and subsequent blastulation, gastrulation, cavitation and blastocyst formation. Upon reaching the uterus, blastocyst hatching occurs under the influence of decreased activin signaling, while the attachment and invasion of the trophoblast into the endometrium appears to be driven by a decrease in activin signaling, and by increased GnRH1 and hCG signaling that allows for tissue remodeling and the controlled invasion of the blastocyst into the uterine endometrium. This review demonstrates the importance of integrative endocrine, paracrine, and autocrine signaling for successful human reproduction.

Expression of 3 beta-hydroxysteroid dehydrogenase in early bovine embryo development

We analyzed the presence of 3 beta-Hydroxysteroid Dehydrogenase/Delta(5-->4)-isomerase enzyme (3 beta-HSD) activity, a key enzyme of the steroid metabolic pathway, the mRNA of this enzyme, and the steroid metabolism in in vitro produced bovine embryos. 3 beta-HSD activity was detected in in vitro matured oocytes (74.4 +/- 1.4%), 1-cell (72.9 +/- 6.1%), 2-cell (61.8 +/- 7.4%), 8-cell (50 +/- 5%), morulae (50.8 +/- 2.6%), blastocysts (94.4 +/- 3%), and hatched blastocysts (100 +/- 0%) meanwhile the 4-cell stage showed a significant reduction (16.7 +/- 4.7%). When total embryonic RNA of different stages was subjected to RT-PCR assays, the mRNA of 3 beta-HSD was found to be present in all developmental stages of in vitro produced bovine embryos, from the oocyte to the blastocyst, with a marked decrease at the 4-cell stage. To determine whether the temporal pattern of enzyme activity was dependent on the maternal to zygotic transition, embryos were incubated in the presence of a transcription inhibitor, alpha-amanitin. The reappearance of the enzyme activity after the 4-cell stage was blocked in alpha-amanitin treated embryos, indicating the requirement of embryonic transcription. On the other hand, the embryonic steroid metabolism was tested by incubating blastocyst with tritiated pregnenolone. Analysis of the metabolites by TLC indicated the production of a compound with a mobility identical to progesterone. These results described the expression of the 3 beta-HSD and the activity of this metabolic enzyme in bovine oocytes and preimplantation embryos, suggesting that steroids may act as autocrine effectors on preimplantation embryo development.

The antiestrogen ICI 182,780 abolishes developmental injury for murine embryos exposed in vitro to o,p'-DDT(1)

Previously, we reported that in vitro exposure of murine embryos to 0.1 microg/ml o,p'-DDT (an estrogenic pesticide) significantly reduced development to blastocyst and mean cell number per embryo, and increased percent cell death by 96 h of culture. The objective of the present study was to determine if developmental injury induced by o,p'-DDT resulted from estrogenic, antiestrogenic, or unrelated adverse biologic mechanisms. Toward this objective, pronuclear embryos from CD-1 mice were cultured 96 h in medium supplemented with 0.1% ethanol (control) or 0.1 microg/ml o,p'-DDT, 17beta-estradiol, or ICI 182,780 dissolved in ethanol as single agents or as paired mixtures. As single agents, development to blastocyst and mean cell numbers were significantly reduced and percent apoptosis was significantly increased for embryos cultured in the presence of o,p'-DDT or ICI 182,780. Development to blastocyst was significantly reduced for embryos cultured in the presence of 17beta-estradiol. Beneficial interaction occurred when the receptor antagonist ICI 182,780 was combined with either receptor agonist (o,p'-DDT or 17beta-estradiol). In contrast, interaction was not significant when the two agonists were combined. The results indicate that developmental injury due to the estrogenic pesticide o,p'-DDT was abolished by the addition of the receptor antagonist ICI 182,780 and not by the receptor agonist 17beta-estradiol. The findings underscore the utility of the model for uncovering mechanisms of developmental injury.

Developmental ability of porcine oocytes matured and fertilized in vitro

The developmental abilities of porcine oocytes matured and fertilized in vitro were examined in vivo and in vitro. Cumulus-oocyte complexes were cultured in mM199 supplemented with 10% porcine follicular fluid (PFF) and hormonal supplements (PMSG, hCG and estradiol-17beta) for 20 h and then without hormonal supplements for an additional 20 h. In Experiment 1, oocytes were then co-cultured for 6 h with spermatozoa which had been preincubated with 1% PFF (PFF-treated) or without (control). Oocytes were transferred to oviducts of gilts or cultured in modified Whitten's medium for 5 d. The percentages of oocytes with monospermic penetration (59%, 42 71 ) and with monospermic penetration and male and female pronuclei (32%, 23 71 ) were higher (P < 0.01) in the PFF-treated group than in controls (25%, 18 71 and 8%, 6 71 , respectively). After 5 d, the percentages of oocytes that developed to the morula or blastocyst stages in vitro and in vivo in the PFF-treated group (10%, 28 288 and 13%, 41 318 , respectively) were also higher (P < 0.05) than in controls (2%, 6 284 and 6%, 16 248 , respectively). Whereas some oocytes that were matured and fertilized in vitro developed to the blastocyst stage after 5 d in vivo culture (3%, 9 288 in PFF-treated group and 2%, 6 284 in control), no blastocysts were observed after 5 d when oocytes were cultured in vitro. When the progression of in vitro development of porcine oocytes that were matured and fertilized in vitro was examined in Experiment 2, morulae appeared after 72 h of culture, and 3% (3 100 ) of the oocytes developed to the blastocyst stage after 144 h (6 d) of culture. These results demonstrate that decreasing polyspermic penetration and increasing monospermic male pronuclear formation, as a result of PFF treatment of maturing spermatozoa, improved the developmental ability of porcine oocytes matured and fertilized in vitro. However, development in vitro was delayed by approximately 24 h compared with in vivo development, most of the embryos were blocked at the morula stage.

Estrogen receptor and progesterone receptor genes are expressed differentially in mouse embryos during preimplantation development

Estrogen and progesterone play an important role in the development and implantation of preimplantation embryos. However, it is controversial whether these hormones act directly on the embryos. The effects of these hormones depend on the existence of their specific receptors. To determine whether estrogen receptor (ER) and progesterone receptor genes are expressed in mouse preimplantation embryos, we examined RNA from embryos at different stages of preimplantation development by reverse transcription-polymerase chain reaction techniques. ER mRNA was found in oocytes and fertilized eggs. The message level began to decline at the two-cell stage and reached its lowest level at the five- to eight-cell stage. ER mRNA was not detectable at the morula stage but reappeared at the blastocyst stage. Progesterone receptor mRNA was not detectable until the blastocyst stage. The embryonic expression of ER and progesterone receptor genes in the blastocyst suggests a possible functional requirement for ER and progesterone receptor at this stage of development. These results provide a basis for determining the direct role of estrogen and progesterone in preimplantation embryos.

Pregnane derivatives as pregnancy interceptive agents: efficacy determination on growing trophoblasts (in vitro) and in pregnant hamsters (in vivo)

An in vitro test system was standardized to study potentiality of five hormonally inert pregnane derivatives on growing trophoblasts isolated from ectoplacental cone (EPC) of day 8 hamster embryo. Cells were incubated with different concentrations of respective compounds in surface droplets. The response was determined by analyzing the sequence of changes in cell morphology like attachment, growth, proliferation, differentiation and/or degeneration within 24 or 48 h following seeding. The in vivo efficacy of these compounds was determined in hamster during peri- and immediate post-implantation periods (days 3-8 post coitum). Two compounds 88/583 and 88/585 were found to inhibit not only growth and proliferation of the cells but caused total degeneration within 24 h. The same compounds induced partial to complete resorption of the foetuses in treated animals. Whereas, the other three compounds 88/506, 88/594 and 89/43 that showed lack of comparable potentiality in vitro were found to be equally ineffective in vivo. The results indicate a positive correlationship between in vitro and in vivo activity.

Regulation of protein synthesis in the first trimester human placenta by 17 beta-oestradiol and progesterone

Addition of 17 beta-oestradiol or progesterone to first trimester human placental explants in vitro resulted in the stimulation of protein synthesis, as seen by autofluorographic analysis of placental tissue and medium proteins. An increase in the incorporation of [35S]methionine into trichloroacetic acid-precipitable proteins was seen, following the addition of 17 beta-oestradiol. Use of aromatase inhibitor to block the synthesis of 17 beta-oestradiol inhibited the protein synthesis and while addition of cyclohexamide blocked both basal- and 17 beta-oestradiol-induced protein synthesis, actinomycin-D blocked only 17 beta-oestradiol induced protein synthesis. Double labelling of placental proteins in the presence and absence of 17 beta-oestradiol also indicated that there is a significant stimulation of protein synthesis by 17 beta-oestradiol. Based on these results it is suggested that oestradiol has a role in regulation of placental protein synthesis.

Possible function of 17 beta-hydroxysteroid dehydrogenase in preimplantation hamster embryos

17 beta-Hydroxysteroid dehydrogenase (17 beta-HSD) catalyzes the interconversion of estradiol-17 beta (E2) and estrone (E1). The present study is designed to investigate the following: (1) the developmental stage of hamster embryos at which 17 beta-HSD activity first becomes detectable, and (2) the E1----E2 and E2----E1 conversion rate in the preimplantation hamster embryo. Embryos obtained from superovulated hamsters on days 1-4 were cultured in medium containing 107 ng [3H]E1 or -E2/ml and the respective conversion product, [3H]E2 or -E1, was isolated and assayed. The results show that (1) E1----E2 conversion was active in all embryos at the rate of 0.57, 0.66, 0.54 and 0.48 fmol/embryo/hr for day 1 (one-cell), 2 (two-cell), 3 (eight-cell) and 4 (blastocyst), respectively, and (2) E2----E1 conversion was not detectable in hamster embryos. In long-term blastocyst culture, E2----E1 conversion becomes detectable at 25 hours and increases sharply from 25 to 47 hours. These results suggest that (1) 17 beta-HSD may function mainly to convert E1 into E2 in preimplantation hamster embryos and (2) E2----E1 conversion may become active only during and after implantation.

Effect of antiestrogen CI-628 on the morphology and 17 beta-hydroxysteroid dehydrogenase activity of mouse blastocysts in culture

The effect of CI-628 on the morphology and 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) activity of mouse blastocysts were compared in culture. When Day 4 mouse blastocysts were cultured in Eagle's medium containing 214 ng 3H-estradiol (E2) and CI-628 at 0, 1.5, 3, 6, 12 and 18 micrograms/ml, shedding of the zona pellucida was prevented by CI-628. The effect of CI-628 on the morphology was dose-dependent: little effects were seen at 1.5 and 3 micrograms/ml during the first 2 days, but the blastocysts became small, dense and eventually collapsed inside the zona. At 6 micrograms/ml and higher, the effect was quite pronounced. The earliest change was seen at 10 hours in 12 and 18 micrograms/ml CI-628 medium when 1/3 of the embryos became dense and smaller. All were collapsed by 22 h. CI-628 reduced the 17 beta-HSD activity slightly during the first 5 h. Nevertheless, the enzyme activity continued to increase, though at a slower rate than the control (0 microgram/ml) group, up to 22 h in the 12 and 18 micrograms/ml group, and up to 46 h in the 1.5, 3 and 6 micrograms/ml group. In the latter 3 groups, the 17 beta-HSD activity remained fairly high throughout the culture. It appears that, in comparison with the morphology, the 17 beta-HSD activity is relatively resistant to CI-628 effects. In the blastocyst homogenate, CI-628 had no effect on E2-greater than E1 conversion. It is concluded that CI-628 causes degeneration of blastocysts through mechanisms other than interfering with 17 beta-HSD activities.

Effect of an estrogen antagonist on development of blastocysts and implantation in the hamster

CI 628 citrate, an estrogen antagonist, was given as a single intraluminal injection (5 micrograms) on day 3 to ovariectomized, progesterone-treated hamsters. This significantly reduced embryo cleavage rate, transformation of morula into blastocyst, and completely inhibited implantation. The effects of the drug could be reversed by estradiol-17B (1 microgram) but not estradiol-17 alpha (1 microgram) injected intraluminally with CI 628 citrate. Our finding suggests a role of estrogen present in hamster preimplantation embryo in the triggering of embryonic differentiation and implantation of the blastocyst.

The presence of 17 beta-hydroxysteroid dehydrogenase activity in preimplantation rat and mouse blastocysts

When Day 5 rat blastocysts and Day 4 and 5 mouse blastocysts were cultured in 53 microliters of medium containing 1340 or 2680 pg [3H]estradiol (E2), large amounts of [3H]estrone (E1) were detected in the medium at daily intervals for up to 5 days. This indicates the presence of 17 beta-hydroxysteroid dehydrogenase in the embryos. The activity was higher at a higher concentration of E2 and was also higher in mouse than in rat blastocysts. In the mouse, the activity was higher in Day 5 than Day 4 blastocysts during the first day in culture; then it decreased in Day 5 but increased in Day 4 blastocysts. The importance of E2 in embryonic development and implantation as suggested by others may be related to the activity of 17 beta-hydroxysteroid dehydrogenase.

A possible role of estrogens in carcinogenesis of non-target tissues

The mitogenic action of the estrogen-receptor complex is supposedly similar in both normal and malignant target tissues. As receptors are present in several types of non-target tissues, in the case of lesions at the nuclear acceptor sites, the complex in those might be able to cause successive mitoses. Estrogen-dependent tumors of non-target tissues have been reported by several investigators. In normal and malignant cells of the breast and some other types of non-endocrine cells, the ability to produce their own estrogens (from circulating precursors) has been shown. The locally formed estrogens might have a role in the initiation of some malignant transformations. Indications of this process are the switching to estrogen production of some neoplastic endocrine or undifferentiated cells, certain ectopic effects displayed by some cancerous tissues, and the possible roles of GH, PRL and cholesterol in the development of some malignancies. The present endocrine system for the synthesis of the sexual hormones might be a specialization of a system at the cellular level. Polypeptide hormones might evolve from regulatory parts of cyclases or phosphodiesterases. Traces of the original biological processes might still be maintained by several cell-types.

Does "blastocyst estrogen" initiate implantation?

Fertilized eggs were incubated for 2 hours in a medium containing estradiol-17beta and then transferred into the uteri of day 5 pseudopregnant rats. These eggs, but not estrogen-free control eggs, induced a local increase in capillary permeability. We suggest that the blastocyst factor which induces the local increase in capillary permeability during early pregnancy is estrogen synthesized by the blastocyst.