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ANNE McLAREN

Summary.

When blastocysts from pregnant mice 3½ days p.c. were transferred to the uteri of synchronous pseudopregnant recipients, the time of onset of implantation (judged by the appearance of pontamine blue reactivity in the uterus) was not altered by removal of the zona pellucida. The competence of zona-free blastocysts to elicit the pontamine blue reaction was similar to that of control blastocysts. The low implantation rate of eight-cell embryos from donors 2½ days p.c., transferred to recipients 3½ days p.c., was not increased by previous removal of the zona. It was concluded that, in mice, the decidualizing stimulus from the blastocyst to the uterus stems neither from the zona itself, nor from cellular contact between the vitelline surface and the uterine epithelium.

Removal of the zona by treatment with pronase reduced the viability of transferred blastocysts, so that by mid-gestation the proportion of zona-free blastocysts represented by live embryos was significantly below the control level.

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LA Salamonsen

Implantation of the embryo into the endometrium is a critical step in the establishment of pregnancy and the failure of embryos to implant is a major limiting factor in the success of reproductive technologies. Furthermore, one or more of the molecules of importance at implantation could provide a suitable target for post-coital contraception. While there is considerable species variation in the extent to which the trophoblast invades the maternal endometrium and makes contact with the maternal blood supply, many of the molecular mechanisms are conserved among species. Three families of protease are involved in the matrix degradation required for implantation: the cysteine, serine and matrix metalloproteinases. Other proteases are required for the activation of regulatory molecules. Although trophoblast from all species appears to have a high invasive potential, this is limited by the presence of partner protease inhibitors, the presence of which provides restraint to this invasion. It is the balance between the proteases and their inhibitors at any focal point that determines the site and extent of trophoblast invasion. This review examines the literature regarding proteases and their inhibitors at early implantation sites across a range of species with very different forms of placentation and evaluates their common features and their dissimilarities.

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Haengseok Song, Kyuyong Han and Hyunjung Lim

We previously showed that blastocyst can initiate implantation beyond the normal ‘window’ of uterine receptivity on day 5 of pregnancy and pseudopregnancy (PSP) in mice. In this study, we investigated whether uterine receptivity for blastocyst implantation can be further extended on day 6 of PSP and the role of progesterone (P4) on this event. Embryo transfers, experimentally induced decidualization, in situ hybridization and [3H]thymidine incorporation were performed. Blastocysts initiate attachment reaction within 48 h when transferred on day 5, but not on day 6 of PSP. Likewise, decidualization reaction occurred on days 4 and 5 of PSP, but completely failed on day 6. However, P4 supplementation partially retains uterine receptivity for blastocyst implantation and decidualization on day 6 of PSP. In addition, certain indicators of uterine receptivity, such as cell proliferation profile and expression patterns of implantation-related genes were similarly observed on days 4 and 5 of PSP, but not on day 6. Consistent with embryo transfer and decidualization, exogenous administration of P4 partially restores these indicators on day 6 of PSP. We concluded that critical physiological changes occur between days 4 and 5 of PSP, leading to uterine non-receptivity on day 6, but P4 is able to extend the uterine receptivity through day 6.

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Thaddeus G Golos, M Giakoumopoulos and M A Garthwaite

While the determination of the trophoblast lineage and the facilitation of placental morphogenesis by trophoblast interactions with other cells of the placenta are crucial components for the establishment of pregnancy, these processes are not tractable at the time of human implantation. Embryonic stem cells (ESCs) provide an embryonic surrogate to derive insights into these processes. In this review, we will summarize current paradigms which promote trophoblast differentiation from ESCs, and potential opportunities for their use to further define signals directing morphogenesis of the placenta following implantation of the embryo into the endometrium.

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Michel Guillomot, Annick Turbe, Isabelle Hue and Jean-Paul Renard

The high rates of embryonic mortalities which follow in vitro production of ruminant embryos have emphasized the need for increased knowledge of early development. It is likely that early failures in embryonic development and placenta formation involve abnormal differentiation of mesoderm. The aim of this study was to investigate the pattern of expression of two T-box genes known to control the gastrulation process, Brachyury and Eomesodermin, by whole-mount in situ hybridization. To allow a more precise comparison of both expression patterns between embryos, we describe a new staging of pre-implanted ovine embryos by gross morphology and histology from pre-gastrulation stages to the beginning of neurulation. In pre-streak embryos primitive mesoderm cells delaminated in between the primitive endoderm and the epiblast. At that stage, no expression of Brachyury or Eomesodermin could be detected in the embryos. Early expression of both T-genes was observed by the early-streak stages in epiblast cells located close to the presumptive posterior pole of the embryos. Later on, during gastrulation both genes followed a pattern of expression similar to the ones described in other mammals. These observations suggest that other genes, which remain to be identified, are responsible for extra-embryonic mesoderm differentiation in ruminant embryos.

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Anna Piliszek, Jacek A Modliński, Kazimiera Pyśniak and Jolanta Karasiewicz

Foetal fibroblasts (FFs) labelled with vital fluorescent dye were microsurgically introduced into eight-cell mouse embryos, three cells to each embryo. FFs were first identified in the inner cell mass (ICM) in about one-third of embryos, whereas in three quarters of embryos FFs were located among trophoblast cells. Some elimination of FFs from trophoblast occurred later on. Eventually, in blastocysts’ outgrowths, an equally high contribution from FFs progeny (60%) was found in both ICM and trophoblast. Three days after manipulation, FFs resumed proliferation in vitro. More than three FFs were found in 46.2% of embryos on day 4. On the 7th day in vitro in 70% of embryos more than 12 FFs were found, proving at least three cell divisions.

To study postimplantation development, the embryos with FFs were transferred to pseudopregnant recipients a day after manipulation. After implantation, FFs were identified by electrophoresis for isozymes of glucose phosphate isomerase (GPI). A single 11-day embryo delayed to day 8 proved chimeric by expressing both donor isozyme GPI-1B and recipient GPI-1A. Similar chimerism was found in the extraembryonic lineage of 11% of embryos by day 12. Starting from day 11 onwards, in 32% of normal embryos and in 57% of foetal membranes, hybrid GPI-1AB isozyme, as well as recipient isozyme, was present. Hybrid GPI-1AB can only be produced in hybrid cells derived by cell fusion, therefore, we suggest that during postimplantation development, FFs are rescued by fusion with recipient cells. In the mice born, hybrid isozyme was found in several tissues, including brain, lung, gut and kidney.

We conclude that somatic cells (FFs) can proliferate in earlyembryonic environment until early postimplantation stages. Foetuses and the mice born are chimeras between recipient cells and hybrid cells with contributions from the donor FFs. Transdifferentiation as opposed to reprogramming by cell fusion can be considered as underlying cellular processes in these chimeras.

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I. Kola and P. I. Folb

Summary. Chlorpromazine, administered to pregnant CBA mice 56 h after copulation in single doses of 10 or 15 mg/kg bodyweight, inhibited the compaction of embryos, formation of blastocysts, and reduced the mitotic index and cell number of embryos 86 h after copulation but did not adversely influence their viability or induce structural chromosomal aberrations. Blastocyst formation was more severely affected than embryo compaction. When 86-h embryos were treated with chlorpromazine (10 or 15 mg/kg) and subsequently cultured for 120 h, there was delayed hatching from the zona pellucida, delayed attachment to the culture dish, outgrowth of the trophoblast and expansion of the inner cell mass. Mice treated identically and evaluated on the 18th day of gestation had fewer implanted embryos than did controls, and the fetuses weighed less. No resorptions, malformations or significant differences in intrauterine deaths were found. Chlorpromazine given in the same manner but at 0·5 mg/kg did not affect any of the aforementioned criteria. When 56 h embryos were cultured in vitro in the presence of 50 μm-chlorpromazine for a further 40 h, embryo compaction, blastocyst formation, the mitotic index and the total cell number were significantly reduced compared with controls. Blastocyst formation was again more severely affected than embryo compaction. The inhibition of embryo compaction, blastocyst formation, and reduction in mitotic index and cell number associated in this study with chlorpromazine in vivo and in vitro indicate that the drug inhibits the development of cleavage-stage embryos in the mouse. These effects might be mediated by antagonistic effects of calmodulin.

Free access

E Kautz, A Gram, S Aslan, S S Ay, M Selçuk, H Kanca, E Koldaş, E Akal, K Karakaş, M Findik, A Boos and M P Kowalewski

Although there is no acute luteolytic mechanism in the absence of pregnancy in the bitch, a precise and well-timed embryo–maternal interaction seems to be required for the initiation and maintenance of gestation. As only limited information is available about these processes in dogs, in this study, the uterine expression of possible decidualization markers was investigated during the pre-implantation stage (days 10–12) of pregnancy and in the corresponding nonpregnant controls. In addition, the expression of selected genes associated with blastocyst development and/or implantation was investigated in embryos flushed from the uteri of bitches used for this study (unhatched and hatched blastocysts). There was an upregulated expression of prolactin receptor (PRLR) and IGF2 observed pre-implantation. The expression of PRL and of IGF1 was unaffected, and neither was the expression of progesterone- or estrogen receptor β (ESR2). In contrast, (ESR1) levels were elevated during early pregnancy. Prostaglandin (PG)-system revealed upregulated expression of PGE2-synthase and its receptors, PTGER2 and PTGER4, and of the PG-transporter. Elevated levels of AKR1C3 mRNA, but not the protein itself, were noted. Expression of prostaglandin-endoperoxide synthase 2 (PTGS2) remained unaffected. Most of the transcripts were predominantly localized to the uterine epithelial cells, myometrium and, to a lesser extent, to the uterine stroma. PGES (PTGES) mRNA was abundantly expressed in both groups of embryos and appeared higher in the hatched ones. The expression level of IGF2 mRNA appeared higher than that of IGF1 mRNA in hatched embryos. In unhatched embryos IGF1, IGF2, and PTGS2 mRNA levels were below the detection limit.

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BM Bany, MB Harvey and GA Schultz

During implantation, matrix metalloproteinases are believed to play roles in the tissue remodelling that accompanies decidualization in the endometrium and in embryo invasion. The objective of this study was to characterize further the expression of matrix metalloproteinases 2 and 9 in the mouse uterus during early pregnancy and oil-induced decidualization. mRNA encoding matrix metalloproteinase 2 was detected in pregnant uteri and uteri undergoing oil-induced decidualization by northern blot analyses. The steady-state concentrations of mRNA encoding matrix metalloproteinase 2 did not change significantly in implantation compared with inter-implantation areas on days 5-8 of pregnancy but were significantly lower in stimulated compared with non-stimulated uterine horns during artificially induced decidualization. mRNA encoding matrix metalloproteinase 9 was also detected in uteri undergoing oil-induced decidualization but not in pregnant uteri. Its concentration was significantly greater in uterine horns undergoing oil-induced decidualization compared with control horns. Immunoreactive matrix metalloproteinases 2 and 9 were detected in the uterus during early pregnancy and oil-induced decidualization by immunohistochemistry, localized to the endometrial stroma, but the staining progressively became weaker and was absent in areas that had undergone decidualization. By day 8 of pregnancy and 72 h after the induction of decidualization, matrix metalloproteinase 2 and 9 proteins remained mainly in the region of non-decidualized stromal cells adjacent to the myometrium. In implantation segments, they were also localized to the region of the trophoblast giant cells. The second objective of the present study was to determine whether endometrial stromal cells isolated from uteri sensitized for decidualization express matrix metalloproteinases 2 and 9. Northern blot analyses and gelatin zymography showed that these cultured cells expressed matrix metalloproteinase 2 and 9, and that transforming growth factor beta1 significantly increased matrix metalloproteinase 9 expression. The results of the present study further characterize matrix metalloproteinases 2 and 9 expression in the uterus during implantation and artificially induced decidualization.

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G. Acker, P. Braquet and J. M. Mencia-Huerta

Summary. Injection of PAF into the left uterine horn induced a dose-dependent decidua-like reaction in the pseudopregnant rat. This reaction was maximal when PAF was injected at Day 5 of pseudopregnancy and was blocked by the specific PAF antagonist, BN 52021. BN 52021 did not interfere with the decidual reaction induced by prostaglandin E-2 or insertion of a cotton thread in the uterine horn. In contrast, a decidua-like reaction was not evoked by the inactive lyso-PAF, demonstrating the specificity of the action of PAF. The decidua-like reaction induced by PAF involves the generation of cyclooxygenase metabolites of arachidonic acid since it was inhibited by indomethacin. The histological alterations induced by PAF were similar to those observed after embryo implantation, strengthening the postulate for a role of the autacoid in the early stages of pregnancy.

Keywords: decidual reaction; platelet-activating factor; prostaglandin; implantation; rat