Light and electron microscopic examination of the mature decidual cells of the rat with emphasis on the antimesometrial decidua and its degeneration

Uterine Gpr83 mRNA is highly expressed during early pregnancy and GPR83 mediates the actions of PEN in endometrial and non-endometrial cells

OBJECTIVE

To characterize the expression and signaling of uterine GPR83 in vivo in the nonpregnant and pregnant mouse and in vitro in human endometrial and nonendometrial cells.

DESIGN

Controlled laboratory study.

SETTING

Not applicable.

PATIENTS

Not applicable.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Expression of uterine Gpr83 was determined by quantitative polymerase chain reaction throughout the estrous cycle and during early pregnancy in ovarian-stimulated and non-ovarian-stimulated mice and pregnant and pseudopregnant mice. Expression was also determined in ovariectomized mice after the administration of oil, E2, P4, or E2 + P4 and in stromal cells following 6 days of in vitro decidualization. GPR83 signaling was studied in human endometrial and embryonic kidney cell lines. Cells were treated by PEN, a GPR83 ligand, and PEN-induced extracellular signal-regulated kinase (ERK) phosphorylation was assayed under conditions that blocked Gα_q/11 and/or β-arrestin signaling.

RESULTS

Uterine Gpr83 is expressed throughout the estrous cycle and during early pregnancy; expression increases dramatically at the time of uterine receptivity, embryo implantation, and stromal cell decidualization. In the ovariectomized mouse, hormone add-back reveals that Gpr83 expression is highly responsive to the combined treatment of E2 and P4, and studies in the ovarian-stimulated mouse show that expression is also very sensitive to changes in E2 and P4 and is therefore tightly regulated by E2 and P4. At the implantation site, expression is elevated up to D6 of pregnancy and then declines rapidly on D7 and D8, suggesting that if there is any involvement in decidualization, it is likely associated with primary but not secondary stromal cell decidualization. This premise was supported by the observation that stromal cell decidualization in vitro progresses with a decline in Gpr83 expression. In ERα/PR-expressing endometrial Ishikawa cells, GPR83 mediates PEN signals in a Gα_q/11-dependent manner, and studies conducted in HEK 293 cells lacking β-arrestin revealed that GPR83 also signals via a β-arrestin-dependent manner. When signaling by either one or both pathways is downregulated, cells exhibit a major reduction in responsiveness to PEN treatment, demonstrating that signaling by both pathways is significant.

CONCLUSION

We hypothesize that PEN/GPR83 signaling regulates uterine receptivity, embryo implantation, and primary stromal cell decidualization by coupling to Gα_q/11- and β-arrestin-dependent pathways.

Spontaneous embryo resorption in the mouse is triggered by embryonic apoptosis followed by rapid removal via maternal sterile purulent inflammation

Background

In normal mammalian development a high percentage of implantations is lost by spontaneous resorption. This is a major problem in assisted reproduction and blastocyst transfer. Which embryo will be resorbed is unpredictable. Resorption is very fast, so that with conventional methods only final haemorrhagic stages are encountered.

Here we describe the histology and immunohistochemistry of 23 spontaneous embryo resorptions between days 7 and 13 of murine development, which were identified by high-resolution ultrasound (US) in a previous study.

Results

In the early resorptions detected at day 7, the embryo proper was replaced by maternal haemorrhage and a suppurate focus of maternal neutrophils. In the decidua maternal macrophages transformed to foam cells and formed a second focus of tissue dissolution.

In the late resorptions detected at day 9, the embryo underwent apoptosis without involvement of maternal cells. The apoptotic embryonic cells expressed caspase 3 and embryonic blood cells developed a macrophage like phenotype. Subsequently, the wall of the embryonic vesicle ruptured and the apoptotic embryo was aborted into the uterine lumen. Abortion was initiated by degeneration of the embryonic lacunar trophoblast and dissolution of the maternal decidua capsularis via sterile inflammation and accompanied by maternal haemorrhage, invasion of the apoptotic embryo by maternal neutrophils, and contraction rings of the uterine muscle layers.

Conclusions

We conclude that spontaneous resorption starts with endogenous apoptosis of the embryo without maternal contribution. After break down of the foetal-maternal border, the apoptotic embryo is invaded by maternal neutrophils, aborted into the uterine lumen, and rapidly resorbed. We assume that the innate maternal unspecific inflammation is elicited by disintegrating apoptotic embryonic cells.

Graphical abstract

T cell behavior at the maternal-fetal interface

Understanding the function of T cells at the maternal-fetal interface remains one of the most difficult problems in reproductive immunology. A great deal of work over the last two decades has led to the view that the T cells that populate the decidua have important roles in both normal and pathological pregnancies, but the exact nature of these roles has remained unclear. Indeed, the old assumption that decidual T cells are uniformly threatening to fetal survival because the placenta is fundamentally an 'allograft' has given way to the idea that different T cell subsets contribute in different ways to pregnancy success or failure. Accordingly, some T cells are thought to protect the placenta from immune rejection and facilitate embryo implantation, while others are thought to contribute to pregnancy pathologies such as preeclampsia and spontaneous abortion. Here, we review the current state of information on the behavior of decidual T cells with a focus on both mouse and human studies, and with an emphasis on the many unresolved areas within this overall emerging framework.

Differences in collagen ultrastructure of human first trimester decidua basalis and parietalis: implications for trophoblastic invasion of the placental bed

AIM

The human embryo-maternal interface in the first trimester of pregnancy is an area of extensive tissue remodeling. Because collagen is the most abundant constituent of the extracellular matrix of the placental bed, successful invasion must involve its rapid turnover. We compared the nature and distribution of collagen fibrils in decidua basalis and parietalis.

METHODS

We used a direct-vision hysteroscopic technique to obtain biopsies of the decidua basalis and parietalis from 11 women undergoing pregnancy termination in the first trimester. The biopsies were subjected to light, transmission and scanning electron microscopy, and immunohistochemical studies using mouse monoclonal antibodies against cytokeratin 7 and collagen types I, III and V.

RESULTS

Collagen fibrils in the stroma of decidua basalis were significantly thicker when compared to those in decidua parietalis (56.48 ± 1.37 nm vs 45.64 ± 0.85 nm; P < 0.0001 [mean ± standard error]) between 9 and 12 weeks gestation, but this difference in thickness was not observed at gestations below 9 weeks. In basalis, the fibrils appeared disrupted at most places surrounding the decidual/trophoblast cells while a uniform regular arrangement was preserved throughout most of parietalis.

CONCLUSION

There are differences in the ultrastructure of collagen fibrils between basalis and parietalis, with thicker and disrupted fibrils within abundant amorphous tissue in basalis, and thinner uniform fibrils in parietalis. These differences may reflect an adaptive response by decidua or a direct consequence of the invading trophoblast cells.

Invasion and genome reproduction of the trophoblast cells of placenta junctional zone in the field vole, Microtus rossiaemeridionalis

In the field vole Microtus rossiaemeridionalis, like in other rodents, invasive secondary giant trophoblast cells (SGTC) form a continuous layer at the foeto-maternal interface in the beginning of placentation. However, in the field vole, at midgestation, clusters of junctional zone (JZ) trophoblast non-giant cells interrupt SGTC layer and progressively replace SGTC at the border of decidua basalis. As a result, 'border' cells form a continuous stratum of cytokeratin-positive glycogen-rich cells at the foeto-maternal interface. SGTC plunge into JZ and line the lacunae with maternal blood. SGTC are bound by their highly cytokeratin-positive sprouts forming a framework that holds other trophoblast cell populations. According to DNA cytophotometry, the 'border' cells show the highest ploidy among the JZ cells (up to 46% of 8c cells). Thus, in M. rossiaemeridionalis the role of barrier between semiallogenic foetal and maternal tissues is shifted from the highly endopolyploid (32c-1024c) SGTC to the specific subpopulation of glycogen-rich non-giant (2c-16c) 'border' trophoblast cells that, however, exceed the ploidy of the deeply located and/or proliferative JZ trophoblast cells.

Physiological and molecular determinants of embryo implantation

Embryo implantation involves the intimate interaction between an implantation-competent blastocyst and a receptive uterus, which occurs in a limited time period known as the window of implantation. Emerging evidence shows that defects originating during embryo implantation induce ripple effects with adverse consequences on later gestation events, highlighting the significance of this event for pregnancy success. Although a multitude of cellular events and molecular pathways involved in embryo-uterine crosstalk during implantation have been identified through gene expression studies and genetically engineered mouse models, a comprehensive understanding of the nature of embryo implantation is still missing. This review focuses on recent progress with particular attention to physiological and molecular determinants of blastocyst activation, uterine receptivity, blastocyst attachment and uterine decidualization. A better understanding of underlying mechanisms governing embryo implantation should generate new strategies to rectify implantation failure and improve pregnancy rates in women.

Decidualized pseudopregnant rat uterus shows marked reduction in Ang II and Ang-(1-7) levels

Previous studies showed that angiotensin (Ang) II and Ang-(1-7) concentrations were reduced in the implantation site at day 7 of pregnancy in Sprague-Dawley rats as compared to the site immediately adjacent to it, which does not have the embryo attached, clearly showing the importance of the blastocyst in the regulation of renin-angiotensin system (RAS).

OBJECTIVE

The objective of this study was to evaluate the regulation of the RAS in the decidualized uterus in the pseudopregnant rat, a model without the presence of a conceptus.

METHODS

Ovariectomized, adult female rats were sensitized for the decidual cell reaction with steroid treatments; decidualization was induced by oil-injection of the right horn; the left horn served as a control. The uterine content of Ang I, Ang II, and Ang-(1-7) was examined in the decidualized and non-decidualized uteri.

RESULTS

Both Ang-(1-7) and Ang II and ACE and ACE2 mRNA were significantly reduced in the decidualized horn as compared to the non-decidualized horn. Immunocytochemical characterization of Ang II, Ang-(1-7), ACE and ACE2 demonstrated that Ang-(1-7), Ang II, and ACE2 polarize to the anti-mesometrial pole with decidualization.

CONCLUSION

The decidualization process elicits marked reduction in uterine Ang II and Ang-(1-7) content as compared to the non-decidualized horn. The differential immunocytochemical expression of Ang II and Ang-(1-7) with ACE2, but not ACE in the anti-mesometrial pole of the decidualized horn may favor the formation and action of Ang-(1-7) in the anti-mesometrial pole, an area which plays a role in triggering the decidualization process.

Endopolyploid and proliferating trophoblast cells express different patterns of intracellular cytokeratin and glycogen localization in the rat placenta

The presence of keratin intermediate filaments is a characteristic of trophoblast differentiation. Meantime, their intracellular localization in the functionally different subtypes of placental trophoblast is poorly investigated in rodent, whereas their placentae are being broadly investigated in recent years as a model of the feto-maternal interaction. The purpose was to study the intracellular distribution of cytokeratin filaments in correlation with glycogen deposits, both being important constituents of the trophoblast cells in rat placenta. Different rat trophoblast cell populations exhibited different patterns of cytokeratin immunolocalization. The most intensive immunostaining was observed in the highly endopolyploid SGTCs (secondary giant trophoblast cells) at the border with decidua basalis. The most prominent cytokeratin-positive threads were found at the periphery of cytoplasm and in the extensive system of cytoplasmic sprouts by which the SGTC connect each other. Similar cytokeratin intensity and distribution was detected in the TSC (trabecular spongiotrophoblast cells) of the junctional zone of placenta that line the lacunae with the maternal blood. Clusters of highly proliferative pre-glycogen as well as glycogen cells showed some weaker cytokeratin signals mostly in the perinuclear and peripheral zones of cytoplasm. At the 11.5th to the 13.5th day of gestation, the interstitial and endovascular invasive endopolyploid TGTCs (tertiary giant trophoblast cells) prove the intensive cytokeratin staining throughout the cytoplasm and its sprouts. Meantime, the TGTCs were glycogen negative. By contrast, glycogen was heavily accumulated in the glycogen cells that belong both to the junctional zone of placenta and the cuff of the central arterial channel underlying the monolayer of endovascularly invading TGTCs. Thus, the TGTCs that are first to penetrate into the depth of the uterine wall do not contain glycogen but are accompanied by the glycogen-rich cells. The SGTC also contained the prominent deposits of glycogen at the periphery of cytoplasm and in the cytoplasmic sprouts. At the 16th day of gestation, an extensive interstitial invasion of the cytokeratin-positive glycogen trophoblast cells from the junctional zone was observed. The patterns of cytokeratin and glycogen intracellular localization are specific for each subtype of the rat trophoblast; that is, most probably, accounted for by the functional diversity of different trophoblast populations, i.e. patterns of invasion/phagocytosis and their involvement in a barrier at the feto-maternal interface.

Coordinate regulation of tissue macrophage and dendritic cell population dynamics by CSF-1

CSF-1 drives the homeostatic expansion of macrophages within the growing myometrium of pregnant mice by stimulating in situ proliferation and inducing monocyte precursor recruitment from the blood.

Tissue macrophages (Mϕs) and dendritic cells (DCs) play essential roles in tissue homeostasis and immunity. How these cells are maintained at their characteristic densities in different tissues has remained unclear. Aided by a novel flow cytometric technique for assessing relative rates of blood-borne precursor recruitment, we examined Mϕ and DC population dynamics in the pregnant mouse uterus, where rapid tissue growth facilitated a dissection of underlying regulatory mechanisms. We demonstrate how Mϕ dynamics, and thus Mϕ tissue densities, are locally controlled by CSF-1, a pleiotropic growth factor whose in situ level of activity varied widely between uterine tissue layers. CSF-1 acted in part by inducing Mϕ proliferation and in part by stimulating the extravasation of Ly6C^hi monocytes (Mos) that served as Mϕ precursors. Mo recruitment was dependent on the production of CCR2 chemokine receptor ligands by uterine Mϕs in response to CSF-1. Unexpectedly, a parallel CSF-1–regulated, but CCR2-independent pathway influenced uterine DC tissue densities by controlling local pre-DC extravasation rates. Together, these data provide cellular and molecular insight into the regulation of Mϕ tissue densities under noninflammatory conditions and reveal a central role for CSF-1 in the coordination of Mϕ and DC homeostasis.

Extracellular matrix remodelling in rat endometrium during early pregnancy: the role of fibronectin and laminin

The endometrial extracellular matrix (ECM) remodelling has a crucial role in the establishment of a successful pregnancy. In addition to its basic function such as regulation of cell function, differentiation, migration, proliferation, the substantial alterations in the endometrial ECM may play a specific role in the trophoblast invasion, placentation, cell death and formation of the proper and functional implantation chamber around the embryo. In the present study, immunolocalizations of fibronectin and laminin were determined using avidin-biotin complex-peroxidase in rat implantation sites during 7-10 days of pregnancy. Both proteins were present in the basal membrane of blood vessels and in decidual matrix whereas they were absent or had very weak reactivity in the primary decidual zone on day 7. When placentation has begun, the immunoreactivity of both proteins was increased in the placental bed and in the basal membrane of blood vessels of the mesometrial region. The immunolocalization of both proteins seemed to be decreased in the antimesometrial decidua, however, it was increased in the mesometrial decidual matrix on days 9 and 10. Therefore, it could be suggested laminin and fibronectin demonstrating dynamic expressions in relation with the morphological differentiation of endometrial stroma may play crucial roles in the control of trophoblast adhesion and invasion, in placentation and angiogenesis, in the determination of cell shape and fate thus contributing the endometrial receptivity and a successful pregnancy.

Trophoblast glycogen cells differentiate early in the mouse ectoplacental cone: putative role during placentation

The role of differentiated trophoblast glycogen cells (GCs) in the ectoplacental cone (EPC) has not been elucidated yet. Recently, GC progenitors have been shown to be present from embryonic day 7.5 (E7.5), but glycogen is found in GC only from E10.5. Herein, we investigated the origin, localization and characterization of mouse GCs in EPC and their relationship with blood cells and trophoblast giant cells (TGCs) during placentation. Implantation sites (E5.5-E12.5) were processed for histological studies, histochemical detection (glycogen) and immunohistochemical staining (Ki67). Three-dimensional reconstruction of the EPC was obtained from suitably oriented embryos at E7.5. Our findings evidence that GCs are present and assembled in clusters from E6.5 to E12.5, and that they exhibit the classic vacuolated appearance and contain PAS-positive glycogen, which is amylase-sensitive and acetylation-resistant. In fact, only GCs were stained after acetylation, confirming unequivocally their presence in tissues. At E6.5, GCs showed numerous mitoses and vacuoles with scattered glycogen particles. At E7.5, GCs showed low numbers of mitoses and abundant vacuoles full of glycogen. During E7.5-E8.5, GCs were in close proximity to TGCs, and cells were intercalated by thin maternal blood spaces; placental GCs lost maternal blood contact during E9.5-E12.5. Our results indicate that GCs are originated and proliferate in the upper portion in the midregion of EPC at E6.5, and that at E7.5-E8.5 they show consistent glycogen deposits, which are likely metabolized to glucose. This compound may be directly transferred to circulating maternal blood, and used as a source of energy by GCs and TGCs during placentation.

Trypsin digest coupled with two-dimensional shotgun proteomics reveals the involvement of multiple signaling pathways in functional remodeling of late-gestation uteri in rats

Pregnant uteri become quiescent after functional remodeling but details are not fully known. Here we revealed uterine proteins of late-gestation rats by 2-D shotgun proteomic analysis and correlated protein expression with uterine functions. After duplication, 239 proteins were identified. About 190 proteins commonly found in duplicate analyses were subjected to functional annotation. The proteins associated with signal transduction fell into three known pathways. Western blotting and functional data indicated that: (i) a reduction of Na(+)/K(+)-ATPase-related proteins was associated with the decrease of contraction rate, (ii) a reduction of tyrosine hydroxylase and cyclic AMP-dependent protein kinase type II-alpha regulatory chain (PKARII alpha) was associated with an increase in the relaxation response to 8-bromo-cAMP, and (iii) in the presence of Ras, an increased expression of nucleolin was associated with the elevation of Bcl-xL, an antiapoptotic protein. In conclusion, 2-D shotgun proteomic analysis provides a global database of uterine proteins for hypothesis-driven studies. Our data suggest that in late-gestation uteri down-regulation of PKARII alpha and Na(+)/K(+)-ATPase may cause functional remodeling and lead to uterine quiescent. Up-regulation of antiapoptotic proteins (nucleolin and Bcl-xL) in the Ras-mediated pathway may maintain cell survival and counteract cell loss during remodeling.

Distribution of laminin, vimentin and desmin in the rat uterus during initial stages of implantation

The aim of this study was to investigate the immunohistochemical distribution of laminin, vimentin and desmin during the implantation period in the rat since ECM remodelling and the expression of intermediate filaments (Ifs) is essential for successful decidualization and implantation. On day 4 of pregnancy, laminin was found in a few endometrial stromal cells (ESC), the basement membrane of the numerous endometrial blood vessels, in endometrial glands and as well as in the uterine epithelium. The localization of vimentin on day 4 of pregnancy was widespread in the ESC. However, desmin immunoreactivity was low in ESC on this day of pregnancy. On day 6 of pregnancy, laminin and vimentin were localized in the decidual area underlying luminal epithelium and around the implanting embryo. Additionally, desmin was found to be present densely in decidual cells of the anti-mesometrial region where implantation takes place. Finally, on day 8 of pregnancy, laminin was present in decidual and parietal endodermal cells, whereas vimentin was immunolocalized in primary and secondary decidual regions in the endometrium. In contrast, desmin was detected in some parts of the secondary decidual zone. In conclusion, these proteins could have crucial roles in decidualization and implantation.

Post-implantation mouse conceptuses produce paracrine signals that regulate the uterine endometrium undergoing decidualization

The uterus undergoes a series of dramatic changes in response to an implanting conceptus that, in some mammalian species, includes differentiation of the endometrial stroma into decidual tissue. This process, called decidualization, can be induced artificially in rodents indicating that the conceptus may not be essential for a proper maternal response in early pregnancy. In order to test this hypothesis, we determined if and how the conceptus affects uterine gene expression. We identified 5 genes (Angpt1, Angpt2, Dtprp, G1p2 and Prlpa) whose steady-state levels in the uterus undergoing decidualization depends on the presence of a conceptus. In situ hybridization revealed region-specific effects which suggested that various components of the conceptus and more than one signal from the conceptus are likely responsible for altering decidual cell function. Using cell culture models we found that trophoblast giant cells secrete a type I interferon-like molecule which can induce G1p2 expression in endometrial stromal cells. Finally, decidual Prlpa expression was reduced in the uterus adjacent to Hand1- and Ets2-deficient embryos, suggesting that normal trophoblast giant cells in the placenta are required for the conceptus-dependent effects on Prlpa expression in the mesometrial decidua. Overall, these results provide support for the hypothesis that molecular signals from the mouse conceptus have local effects on uterine gene expression during decidualization.

Trophoblast cells exhibit differential responses to laminin isoforms

Extracellular matrix (ECM) has specific effects on cell behavior that influence many aspects of early development. In the early postimplantation mouse embryo the ECM component laminin promotes polarization and survival of the embryonic ectoderm and formation of Reichert's membrane. In addition, dynamic patterns of laminins 1 and 10/11 expression in the embryo and the uterus correlate with the progression of implantation. In the implanting blastocyst, laminin 1 is strongly expressed in the trophectoderm basement membrane, whereas laminin 10/11 is expressed only in the inner cell mass and polar trophectoderm. In the uterus, laminin 10/11 is strongly expressed in the decidualizing matrix of the stroma. We show here that laminins 1 and 10/11 have distinct effects on trophoblast cell behavior that influence the process of implantation. Laminin 1 promotes random migration and decreases spreading, whereas laminin 10/11 promotes both spreading and persistent migration. When presented as adjacent substrates, cells stop at the boundary and do not enter the region containing laminin 1. Laminin 1 also affects cell-cell adhesion through changes in the localization of vascular endothelial (VE) cadherin. Cultured cells and primary trophoblast explants become single cells or very small groups on laminin 1 and VE-cadherin localization at regions of cell-cell contact decreases dramatically. In contrast, trophoblast cells maintain strong cell-cell contacts on substrates of laminins 10/11, and exhibit strong staining of VE-cadherin in all regions of cell-cell contact. These effects, and the localization of laminin 1 in Reichert's membrane and laminin 10/11 in the surrounding decidual matrix, suggest that these laminin isoforms influence the direction and quality of invasion of trophoblast cells during implantation, and provide epigenetic cues that drive the morphogenesis of the yolk sac placenta.

Synergistic induction of apoptosis in primary rat decidual cells by INF-γ and TNF

In the rat, in response to blastocyst implantation, stromal cells of the endometrium proliferate and differentiate into decidual cells, forming the decidua. After reaching its maximum development, the decidua undergoes regression. This phenomenon appears to be due to an active process involving apoptosis. As there is sparse knowledge concerning the mechanisms of induction of decidual cell death, the potential role of cytokines present in the uterine environment during pregnancy, such as tumor necrosis factor (TNF) and interferon-gamma (INF-gamma) was explored in primary cultures of rat decidual cells. The effects of these factors upon cellular viability, nuclear morphologic alterations, expression, and enzymatic activities of the effector caspases-3/7 were evaluated. The results obtained demonstrated that in contrast to TNF, which did not induce any alteration, INF-gamma and in association with TNF caused a decrease in cell viability and an increase in the appearance of apoptotic bodies in a time-dependent manner that was augmented in the co-presence of TNF. An increase in caspase-3/7 activities after 12 hr of TNF/INF-gamma treatment was also observed. These findings suggest that INF-gamma expressed in the uterine environment may play an important role in regulating apoptosis through potential synergistic mechanisms with TNF and thereby modulate decidual stability and regression during pregnancy.

Expression of nidogens in rat uterus and embryo during decidualization and implantation

The purpose of this study was to demonstrate the expression of nidogen-1 and nidogen-2 and their possible role in decidualization and implantation events during early pregnancy in rats. The tissue samples were examined from pregnant animals between gestational days 1-8 using immunocytochemistry. The uterine luminal epithelium, the glandular epithelium, and the myometrial smooth muscle cells stained strongly from gestational days 1-8 with both nidogen antibodies. At day 4 the decidual reaction areas began to appear in the stromal matrix and immunostaining of both nidogens revealed that the basement membrane of the surface epithelium was discontinuous. The differentiation of stromal cells into decidual cells was seen at gestational day 5 and both nidogens were weakly expressed in the decidualizing cells. At day 6, nidogen-2 immunoreactivity was higher in the primary decidual cells close to the embryo than nidogen-1, and during development of the decidual tissue both nidogens appeared in the endometrial stromal cells. At day 7, while expression of both nidogens declined in the primary decidual cells, their expression was markedly observed in the secondary decidual cells close to the myometrium. At day 8, expression of both nidogens was also observed to increase in the primary decidual cells. While nidogen-2 expression was seen in the parietal endoderm and primary ectoderm of the rat embryos at this developmental stage, nidogen-1 expression was only detected in the parietal endoderm. These results indicate that nidogen-1 and nidogen-2 could play important roles during embryogenesis, decidualization, and implantation in the endometrium of rat uterus.

The effect of experimental Bothrops jararaca envenomation on pregnant mice

The injury caused by the intramuscular injection of a single dose of Bothrops jararaca venom (0.24 mg/kg body weight) to mice on day 8 of pregnancy and examined on day 9 was investigated. Macroscopic and histological examination showed that the bothropic venom caused an increase in the incidence of fetal resorptions. Histologically, a characteristic involution of mature decidua was noticed in saline-treated mice; however, necrotic trophoblast giant cells and decidual cells were also present in this region of mice treated with B. jararaca venom, mainly close to the embryo. Hemorrhagic areas were also observed at maternal-fetal interface, which contained maternal erythrocytes and polymorphonuclears. Plasma fibrinogen levels were lower in envenomed group (p < or = 0.0001), but prothrombin time and activated partial thromboplastin time remained unaltered. Total and differential white blood cell counts were not statistically different between groups. Thus, B. jararaca venom causes injuries not only to the fetus, but also to decidual tissue and blood coagulation of pregnant mice. It is not clear, nonetheless, whether disturbances during the development of pregnancy are due to a direct effect of venom on uterus/fetus or to homeostatic changes in dams, such as clotting disturbances, or to both of them.

Hoxa-10 deficiency alters region-specific gene expression and perturbs differentiation of natural killer cells during decidualization

Uterine decidualization, a key event for successful implantation, is critically controlled by stromal cell proliferation and differentiation. One hallmark event of decidualization is the acquisition of stromal cell polyploidy through terminal differentiation at the anti-mesometrial pole of the implantation site. Hoxa-10, a developmentally regulated homeobox transcription factor, is highly expressed in decidualizing stromal cells, and targeted deletion of Hoxa-10 in mice shows severe decidualization defects, primarily due to reduced stromal cell responsiveness to progesterone. However, the underlying molecular mechanism by which Hoxa-10 regulates this process remains largely unknown. Here, we show that Hoxa-10 deficiency confers diminished core cell cycle activity during stromal cell proliferation without disturbing polyploidy, suggesting that these events depend on local regulators that impact cell cycle machinery. To further address this question, we compared global gene expression profiles in uteri of wild-type and Hoxa-10(-/-) mice after inducing decidualization. Our studies show two major aspects of decidualization downstream of Hoxa-10. First, Hoxa-10 deficiency results in the aberrant region-specific expression of cyclin-dependent kinase-4 (cdk4) and -6 (cdk6), growth differentiation factor 10 (Gdf10), hepatocyte growth factor (Hgf) and Snail2. Second, Hoxa-10 deficiency compromises natural killer (NK) cell differentiation without altering trafficking of NK precursor cells during decidualization. Collectively, the results provide evidence that Hoxa-10 influences a host of genes and cell functions necessary for propagating normal decidual development during the post-implantation period.

Interferon-gamma alters the phagocytic activity of the mouse trophoblast

Interferon-gamma (IFN-gamma) mediates diverse functions in bone marrow-derived phagocytes, including phagocytosis and microbe destruction. This cytokine has also been detected at implantation sites under both physiological and pathological conditions in many different species. At these particular sites, the outermost embryonic cell layer in close contact with the maternal tissues, the trophoblast exhibits intense phagocytic activity. To determine whether IFN-gamma affects phagocytosis of mouse-trophoblast cells, ectoplacental cone-derived trophoblast was cultured and evaluated for erythrophagocytosis. Phagocytic activity was monitored ultrastructurally and expressed as percentage of phagocytic trophoblast in total trophoblast cells. Conditioned medium from concanavalin-A-stimulated spleen cells significantly enhanced trophoblast phagocytosis. This effect was blocked by pre-incubation with an anti-IFN-gamma neutralizing antibody. Introduction of mouse recombinant IFN-gamma (mrIFN-gamma) to cultures did not increase cell death, but augmented the percentage of phagocytic cells in a dose-dependent manner. Ectoplacental cones from mice deficient for IFN-gamma receptor alpha-chain showed a significant decrease of the phagocytosis, even under mrIFN-gamma stimulation, suggesting that IFN-gamma-induced phagocytosis are receptor-mediated. Reverse transcriptase-PCR analyses confirmed the presence of mRNA for IFN-gamma receptor alpha and beta-chains in trophoblast cells and detected a significant increase in the mRNA levels of IFN-gamma receptor beta-chain, mainly, when cultured cells were exposed to IFN-gamma. Immunohistochemistry and Western blot analyses also revealed protein expression of the IFN-gamma receptor alpha-chain. These results suggest that IFN-gamma may participate in the phagocytic activation of the mouse trophoblast, albeit the exact mechanism was not hereby elucidated. Protective and/or nutritional fetal benefit may result from this physiological response. In addition, our data also shed some light on the understanding of trophoblast tolerance to inflammatory/immune cytokines during normal gestation.

TGF-beta expression during rat pregnancy and activity on decidual cell survival

BACKGROUND

During early rat pregnancy, trophoblast of the tiny embryo joins with the endometrium and epithelial cells undergo apoptosis. Near the end of pregnancy, regression of the decidua basalis (DB) is also observed (from day 14 to 20). However, little is known about the intra-cellular and molecular mechanisms involved in apoptosis regulation in the uterus during pregnancy. The objective of the present study was to investigate the presence and the developmental expression of transforming growth factor-beta isoforms (TGF-beta well known differentiation factor) in the rat endometrium throughout pregnancy and its action in vitro using cultured endometrial stromal cells.

METHODS

In vivo: Rats were killed at different days of pregnancy (days 2-20) and uteri removed to collect endometrial protein extracts or the uteri were fixed, embedded and sectioned for immunohistochemistry (IHC) and in situ cell death analyses using TdT-mediated dUTP nick end labeling (TUNEL). In vitro: Rats were ovariectomized and decidualization was induced using sex steroids. Endometrial stromal decidual cells were then collected and cultured.

RESULTS

An increase of apoptosis in the DB on days 14, 16 and 18 was observed. Cleaved caspase-3 was clearly detected during regression of the DB by Western analysis and immunofluorescence. Western analyses using endometrial protein extracts demonstrated that TGF-beta1, TGF-beta2 and TGF-beta3 were highly expressed at the time of DB regression (day 14). During early pregnancy, TGF-beta1 and -beta2 expressions raised at days 5.5 to 6.5. TGF-beta3 protein was not detected during early pregnancy. IHC analyses revealed that TGF-beta1 and -2 were found surrounding both epithelium (luminal and glandular) in the stroma compartment at the implantation site, and TGF-beta3 was mainly located surrounding endometrial epithelium in the stroma compartment. Smad2 phosphorylation was increased at the time of DB regression. In vitro studies using decidual endometrial stromal cells revealed that TGF-beta1 induced apoptosis and Smad2 phosphorylation. Moreover, TGF-beta1 reduced both Akt (a well known survival factor) phosphorylation and XIAP (X-linked inhibitor of apoptosis protein) expression in decidual endometrial stromal cells in vitro.

CONCLUSION

Taken together, these results suggest that TGF-beta isoforms are regulated differently during pregnancy and may have an important role in the control of apoptosis and cell survival at specific stages during pregnancy.

Patterns of Uterine Cellular Proliferation and Apoptosis in the Implantation Site of the Rat During Pregnancy

During gestation, the balance between cell proliferation and death is crucial for successful embryo implantation and maintenance of pregnancy. The uterine endometrium responds to blastocyst implantation with extensive proliferation and differentiation of stromal cells into decidual cells, forming the antimesometrial and mesometrial decidua, which regress by apoptosis. In the latter region it is also observed the growth of metrial gland. To elucidate the events underlying this tissue remodelling we investigated the spatial and temporal pattern of expression of the proliferating cell nuclear antigen (PCNA) and localized the apoptotic cells, by the TUNEL assay and by the expression of active caspase-3. We found that PCNA is expressed at high levels during decidualization until day 12 of gestation declining thereafter abruptly. On the contrary, the appearance of apoptotic cells was detected, by the TUNEL and active caspase-3 expression, in the mesometrial decidua on day 12, increasing from days 14 to 16 in the decidua and metrial gland. In the antimesometrial decidua apoptosis was observed from early to day 12 of pregnancy. However, on day 13 only cell debris and neutrophils were observed, indicating also the presence of necrosis. These results suggest that decidual cells undergo, in distinct regions and at different stages of pregnancy, cell death by apoptosis and secondary necrosis.

Modulation of Connexin Expression in Sheep Endometrium in Response to Pregnancy

The expression pattern of two typical gap junction channel proteins, connexin 43 and connexin 26 (Cx43 and Cx26), was identified in the endometrium of sheep, a species with epitheliochorial type of implantation, by indirect immunohistochemistry during the cyclic phases, early and late pregnancy, and immediately after birth. The extent of Cx43 immunoreaction bound to endometrial stromal cells of the early implantation stage (day 15 p.c.) was comparable to the situation observed in oestrus. The subsequent intensification of feto-maternal contact correlated with a striking increase of stromal Cx43 in the intercaruncular and caruncular regions of the uterus (days 18 and 21 p.c.) and the induction of Cx26 in the glandular epithelium of late implantation (day 21 p.c.). In contrast, both gap junction proteins, coexpressed in the stroma of placentomes and interplacentomal sections on days 131 and 145 p.c., decreased during late pregnancy, while an intense and augmenting staining for Cx26 was detected at the cell borders of the glandular and luminal epithelium. The spatial and temporal distribution of both connexins suggests that, under embryonal and hormonal influences, gap junctional communication is involved in the implantation process and the regulation of endometrial tissue functions during sheep pregnancy and indicates further, that this connexin expression path resembles more the invasive type of implantation.

Specific and transient up-regulation of proprotein convertase 6 at the site of embryo implantation and identification of a unique transcript in mouse uterus during early pregnancy

The present investigation was conducted to identify and characterize an mRNA that was found by RNA differential display to be uniquely regulated at the sites of embryo implantation in mouse uterus. This mRNA was upregulated at the sites of blastocyst attachment at implantation and was identified as proprotein convertase 6 (PC6). PC6 mRNA level was low in the nonpregnant and early pregnant uterus before embryo implantation commenced (before Day 4.5, vaginal plug = Day 0). During the initiation and progression of blastocyst attachment (around Day 4.5), the mRNA was dramatically upregulated only at the implantation sites. The increased transcription was maintained on Day 5.5; the mRNA level declined slightly on Day 6.5 and then fell sharply to reach the nonpregnant level around Days 8.5-10.5. Thus, the upregulation is transient and coincides with the period of embryo attachment and implantation; it is also very specific to implantation sites. In situ hybridization analysis localized the mRNA expression predominantly in the decidual cells immediately surrounding the implanting embryo at the antimesometrial pole. Additionally, multiple mRNA species resulting from alternative splicing were observed in the uterus, as previously reported in the intestine and brain, and further analysis of these transcripts identified a uterine-specific PC6 mRNA. These data lead us to suggest that PC6 plays an important role in the processes of stromal cell decidualization and embryo implantation.

Life Cycle of Decidual Cells

The decisive events in the development of decidual cells (DC) are presented through examples of human and rodent decidua. Human decidua is formed by large decidual cells (LDC), endometrial granulated cells (eGC), and small decidual cells. The LDC form the main type of decidual membranes, which determine the morphological characteristics of the decidua as a tissue. Immediate precursor cells of LDC are located below the basement membrane of the uterine epithelium before and during implantation. At the next stage of differentiation, LDC acquire a spindle-like shape. Rodent LDC form an epithelium-like structure with gland properties at the terminal stage of differentiation. The single-cell structure of human decidua is a derivative of the epithelial organization of rodent decidua. Spindle-like rat LDC are characterized by a high level of protein, RNA, and DNA synthesis and by intensive proliferation. At the beginning of pregnancy, a cell proliferation predominates over cell loss. By Days 12-13 of rat pregnancy LDC loss reaches 80% per day. Terminally differentiated LDC (tLDC) disappear from decidua due to apoptosis. Apoptosis of tLDC and the exhaustion of their precursors account for the disappearance of LDC in the middle of rat pregnancy. Human term decidua is composed of living cells. Human LDC (hLDC) comprise the largest part of human decidual cells (hLDC). hLDC account for 60-90% of hDC but their relative amount can decrease to 35% in the case of significant cell loss under unfavorable conditions. A decrease of LDC is not accompanied by DC proliferation. The lack of ability of decidua to compensate for DC loss suggests DC is a growing type of cell population without cambial cells. LDC function largely by blebbing and budding. Human and rat endometrial granulated cells (eGC) are characterized by a low level of natural killer (NK) activity and a high level of natural suppressor (NS) activity. The combination of NK and NS properties is characteristic of the eGC immunoregulatory function. Other functions of decidua include control of inflammation and trophoblast growth and expansion in the uterus. The life span of decidual cells is limited by pregnancy.

Variations of mt1 melatonin receptor density in the rat uterus during decidualization, the estrous cycle and in response to exogenous steroid treatment

The expression of mt1 receptor protein in the rat uterus was investigated using an anti-mt1 polyclonal antibody against the rat mt1 receptor. A melatonin receptor protein of 37 kDa was detectable by Western blotting in the rat uterine membrane preparations. Autoradiography with the melatonin ligand, 2-[125I]iodomelatonin, was used to localize melatonin receptors in the uterus of the estrous rats and to study the changes of melatonin receptors in pregnancy. Melatonin receptors were found to be localized in the estrous rat uterine antimesometrial stroma. As decidualization of the uterine stroma progressed during pregnancy, the melatonin binding sites were progressively reduced and became confined to the antimesometrial non-decidualized outer stroma. 2-[125I]Iodomelatonin binding sites were not seen in the mesometrial stromal cells during pregnancy. The role of ovarian hormones in the regulation of uterine melatonin receptors was examined by studying the binding at various phases of the estrous cycle, after ovariectomy with and without follow-on treatment of estradiol (E2), progesterone (P4) or both. 2-[125I]Iodomelatonin binding in the rat uterus fluctuated during the estrous cycle, being lowest during metestrus. Ovariectomy caused an almost 70% reduction of 2-[125I]iodomelatonin binding compared with the control. Injections of ovariectomized (OVX) rats with E2 or P4 alone or in combination for 11 days induced a partial restoration of 2-[125I]iodomelatonin binding in the OVX rats. The results show that mt1 melatonin receptors in the rat antimesometrial stroma are regulated by ovarian hormones.

Leukemia inhibitory factor and interleukin-11: cytokines with key roles in implantation

Members of the interleukin-6 family of cytokines include leukaemia inhibitory factor (LIF), interleukin-6, interleukin-11, cardiotrophin, ciliary neurotropic growth factor, oncostatin M and the recently discovered cardiotropin-like cytokine (NNT-1). These ligands signal via heterodimeric receptors composed of ligand-specific alpha chains and the common signal-transducing subunit gp130. Gene targeting in mice provided the first indication of a role for interleukin 6 family cytokines in implantation with the generation of mice with a null mutation of the gene encoding LIF. LIF null female mice were infertile because of failure of blastocyst implantation. More recently, interleukin-11 signalling has been shown to be required for the uterine decidualization response. This review describes the insights into the role of interleukin-6 family cytokines in female fertility that have come from gene targeting experiments in mice.

Progesterone-action in the decidual mesometrium of pregnancy

The mesometrial decidua is absolutely dependent on progesterone action for its maintenance and growth. Hormone action is mediated by intranuclear progesterone receptors (PR) that regulate target cell gene transcription. In early pregnancy of the rat gene expression is particularly enhanced for regulators of cell cycle progression, growth factors and their cognate receptors; cell cycle arrest proteins are suppressed. Cell survival proteins such as Bcl2 are also up-regulated. These events are associated with abundant expression of PR-A and PR-B isoforms and STAT (signal transducers and activators of transcription) family members. Proliferation of decidual cells no longer occurs after mid-pregnancy despite high levels of circulating progesterone and the decidua begins a slow process of regression, which continues to term. Regression is characterized by an increase in abundance of proteins that promote apoptosis such as p27, Bax and Caspase-3. These late pregnancy changes are associated with a relative increase in PR-C, a third form of the PR molecule, that binds progesterone but probably has limited transcriptional activity. Protein kinase C, which is suppressed by progesterone in early pregnancy, may be a key mediator of these processes.

Polyploidization in the trophoblast and uterine glandular epithelium of the endotheliochorial placenta of silver fox (Vulpes fulvus Desm.), as revealed by the DNA content

Dynamics of genome multiplication during establishment of interrelations between trophoblast and glandular epithelium of the endometrium has been studied in the course of formation of placenta in the silver fox. During formation of the placenta, penetration of the trophoblast into the zone of the endometrial glandular epithelium and of endometrial blood vessels into the zone of expanding trophoblast occurs. The trophoblast, which gradually replaces epithelium and a part of the stroma of the endometrium, closely adjoins endometrial vessels but does not disrupt them, thereby the endotheliochorial placenta is formed. Cytophotometric measurements of the DNA content in trophoblast nuclei have shown that most of them are polyploid: predominantly 4-64c, occasionally 128c and 256c. Polyploidy of the trophoblast may be a consequence of various types of polyploidizing mitoses. Cytophotometric measurements of the DNA content in mitotic figures have revealed the presence of mitoses of diploid cells, i.e. with the DNA amount of 4c (2n), and polyploid cells, i.e. 8c (4n), and 16c (8n), therefore trophoblast cells in the silver fox placenta are able to enter mitosis up to the octaploid level. Higher degrees of polyploidy in the trophoblast cells seem to be achieved by endoreduplication. Polyploidization of the uterine glandular epithelial cells during placentation in the silver fox occurs until the level of 8c. Thus, the tissue-specific response of the uterus to the implanting embryo consists of active proliferation and polyploidization of the glandular epithelium, which may compensate formation of prominent population of decidual cells (i.e., connective tissue cells). In the endotheliochorial placenta of the silver fox the regularity is confirmed that cells of both maternal and fetal origin are, as a rule, polyploid in sites of their contact in placenta, which may be of protective significance in the contact of allogenic organisms.

Acute food restriction increases collagen breakdown and phagocytosis by mature decidual cells of mice

An ultrastructural study was undertaken on antimesometrial mature decidual tissue of fed and food-restricted mice, on day 9 of pregnancy. The mean ad libitum food intake was established on mice from the 8th till the 9th day of pregnancy. Fed mice were used as controls. Experimental animals were divided into two groups: one was allowed to feed 25% of normal diet and the other 50%. Extracellular collagen fibrils were scarce in fed animals and conspicuous in food restriction. Granular electron-dense deposits and filamentous aggregates of disintegrating collagen fibrils were observed in all food-deprived mice but were rarely noted in fed animals. Intracellular vacuolar structures exhibited other typical cross-banded collagen immersed in finely granular electron-translucent material (clear vacuole) or electron-dense material containing collagen fibrils with a faint periodicity (dark vacuole). The clear and dark vacuoles were scarce in fed animals and evident in food-restricted mice, mainly in those 25% food restricted. Although collagen breakdown may be part of the normal process of decidual tissue remodelling our results suggest that it is enhanced in food-restricted animals. Thus it seems that collagen breakdown is a normal mechanism that may be regulated by the food intake of the pregnant animal.

Coexpression of cytokeratin and vimentin in mice trophoblastic giant cells

Trophoblastic giant cells reach their maximum size and exhibit a conspicuous synthetic and invasive activity during mouse placentation. The cytoskeleton, given the complex functions of the cells, shows a well-developed network of intermediate filament proteins. Immunohistochemistry combined with confocal and conventional immunofluorescence studies of intermediate filaments proteins cytokeratin and vimentin were performed in mice trophoblastic giant cells on days 9-11 of pregnancy. Specimens were fixed in phosphate-buffered formaldehyde and tissues were processed for routine paraffin embedding. Trophoblastic giant cells from antimesometrial, lateral or mesometrial uterine regions, through days 9-11 of pregnancy, expressed the same staining with both immunoperoxidase and immunofluorescent techniques. Cytokeratin filamentous structures were intensely immunoreactive and were detected throughout the cells cytoplasm; a few cells exhibited strongest fluorescence in the peripheral cytoplasm. Vimentin-positive staining was often distributed throughout the cells cytoplasm, most frequently and more intensely in the peripheral region; in some cells, it was present only in the peripheral regions. It is probable that expression of vimentin in midpregnancy trophoblastic giant cells may be associated with the rapid and conspicuous increase in size and synthetic activity of the cells and also with phagocytosis of degraded materials and invasion of decidual tissue.

Molecular genetics of implantation in the mouse

Embryo implantation is a complex developmental process requiring precise coordination between mother and offspring to ensure success. Implantation failure is clinically relevant to in vitro fertilization programs and to an understanding of diseases of pregnancy like preeclampsia. Basic and clinical research have identified a number of proteins involved in peri-implantation development, but an understanding of the implantation process and its cellular and molecular components is just beginning. This review will focus on the implantation and development of the murine embryo and placenta. The significance of ectopic expression and targeted mutagenesis models to these processes will be discussed.

Ontogeny of adenosine deaminase in developing trophoblast and decidual cells of rat and hamster

The enzyme adenosine deaminase (ADA) is expressed at high level in the tissue of foeto-maternal interface during early pregnancy. As the main constituents of this interface are trophoblast (TR) and decidual cells (DC), the enzyme was estimated in isolated TR and DC to determine the extent of contribution by the respective cells. The enzyme level was estimated in cytosolic fraction, cell lysate and in conditioned media of these cells in rat and hamster. In both species the concentration of ADA was found to be markedly high in cytosolic fraction over to the cell lysate and the conditioned media in both TR and DC. Species-wise, it was higher in hamster. Cell-wise, the enzyme activity was significantly higher in TR than DC in rat but equal in hamster. In the conditioned medium, also, the enzyme activity was higher in TR in both species. The inference drawn from the results are: 1) the maximum enzyme activity in cytosolic fraction of TR and DC of both species clearly indicates equal involvement of the cells that constitute foeto-maternal unit, 2) the enhanced level of enzyme in TR and DC of hamster over to those of rat is possibly due to the higher proliferative activity in the cells of this species because of shorter gestation (16-17 days in hamster and 22-23 days in rats).

Morphological evidence for the 'implantation window' in human luminal endometrium

Endometrial tissue was taken from 21 normal fertile women (aged 18-40 years) between 4 and 13 days after the luteinizing hormone (LH) surge. Systematic random samples of luminal epithelium were taken for both light and electron microscopy and examined morphometrically. Throughout the luteal phase there were remarkably few changes in the volume fraction of nucleus, mitochondria, rough endoplasmic reticulum and 'vesicular system' to cell. Nuclear profile dimensions and cell height also did not change over time. Cell and organelle volume (estimated as volume weighted mean volume) did not change significantly, but showed numerically smallest values on day LH + 13. However the ratio of desmosomes to whole cell and both arithmetic mean thickness and harmonic mean thickness of basement membrane were minimal at the time when implantation would be most likely to occur, i.e. approximately 6 days after the LH peak. Therefore it appears that while some morphometric parameters in human luminal epithelial cells change little during the luteal phase, specific cellular changes occur to the basement membrane and desmosomes which may facilitate embryo implantation. These changes occurred around day LH+ 6 and may be a morphological representation of the 'implantation window'.

Transitory expression of the A2b adenosine receptor during implantation chamber development

Adenosine is a short-range signal molecule that surges in the mouse uterus immediately after blastocyst implantation (Blackburn et al. [1992] Dev. Dyn. 194:155-168). The present study has investigated patterns of uterine adenosine receptor expression during early post-implantation development. Strong expression of the A2b adenosine receptor was observed. Utilizing northern blot analysis, in situ hybridization, and immunostaining, the source of expression was mapped to the primary and secondary decidua of the antimesometrial region, between days 4-8 of gestation. Distribution of the A2b receptor protein followed that of the corresponding transcript by about one gestational day and reflected the dynamics of antimesometrial tissue organization during implantation chamber development. Uterine adenosine surges to levels sufficient for A2b receptor engagement during a defined period (i.e., days 4-6) after blastocyst implantation. Decidual A2b receptor expression thus defines a transitory window of murine gestation that corresponds to a period of human gestation encompassing most spontaneous pregnancy losses. Because adenosine receptors are sensitive to metabolically stable adenosine analogues, their differential expression during implantation chamber development may hold therapeutic potential in the prevention of early pregnancy loss. Dev Dyn 1999;216:127-136.

A possible role for activated complement component 3 in phagocytic activity exhibited by the mouse trophoblast

PROBLEM

To determine whether any blood plasma factor may play a regulatory role in trophoblast phagocytosis in rodent early pregnancy.

METHOD OF STUDY

The effects of alloplasma on the phagocytosis of cultured mouse trophoblast cells (TCs) were evaluated using erythrocytes as target cells, in the presence of 10% fresh, normal plasma; 10% heat-inactivated plasma; 10% component 3 (C3)-depleted plasma; or medium alone. The possible activation of C3 complement, the phagocytosis of zymosan bound or unbound to C3b, and immunoreactivity to C3b receptor were also estimated. Phagocytic activity was expressed as the percentage of phagocytic TCs, and as the number of phagosomes/TCs.

RESULTS

The use of complement sufficient plasma significantly enhanced the phagocytosis of the TCs while the use of heat-inactivated plasma eliminated the erythrophagocytosis. Very low levels of phagocytic activity were seen when the plasma was C3-complement deficient. Phagocytosis of C3b-bound zymosan was remarkable in comparison to zymosan alone, and immunoreactivity to C3b-receptors was seen on the TCs.

CONCLUSION

These results indicate the participation of thermosensitive molecules mediating the phagocytosis of TCs and suggest, as in macrophages, a role for C3-C3b in this process.

Apoptotic cell death in artificially induced deciduoma of pseudopregnant mice

Deciduoma induced by mechanical stimulation in pseudopregnant mice is similar to the decidua in normal pregnancy and it undergoes regression after a certain period. Therefore, we examined cell death in deciduomas which were induced by artificial stimulation. To analyze the regression mechanism of artificially induced deciduoma, DNA fragmentation, in situ 3'-DNA nick end labeling, and RT-PCR were performed on day 6 to 14 of pseudopregnancy. DNA fragmentation appeared on day 8 and it increased to day 10 of pseudopregnancy in the traumatized uterine horn. A large number of apoptotic cells were found on day 10 in the periphery of deciduoma at the antimesometrial side. Deciduoma underwent degeneration on day 11 of pseudopregnancy. Expression of tumor necrosis factor-alpha (TNF-alpha) mRNA was high on days 8 and 10, then decreased, whereas the expression increased again on day 14. TNF-alpha protein was expressed from day 8 to day 12, showing a peak expression on day 10 when deciduoma reached maximum weight. Serum progesterone level was high in the traumatized pseudopregnant mice on day 6, then it gradually decreased. Life span of deciduoma was prolonged 4 days more by daily injection of progesterone. A reduction in serum progesterone coincides with TNF-alpha increase, resulting in an increase of apoptotic deciduomal cells at the regression period, and that the life span of deciduoma is prolonged by additive supply of progesterone.

Demonstration of extracellular acid phosphatase activity in the involuting, antimesometrial decidua in fed and acutely fasted mice by combined cytochemistry and electron microscopy

An ultrastructural cytochemical study of acid phosphatase activity in the antimesometrial decidua on days 9-11 of pregnancy was performed in fed and acutely fasted mice. Specimens were fixed in a buffered mixture of paraformaldehyde and glutaraldehyde and were incubated in a buffered medium containing sodium beta-glycerophosphate and cerium chloride for ultrastructural localization of acid phosphatase activity. Fed and fasted animals showed extracellular acid phosphatase reaction product in the decidual-trophoblast interface, in the region of loosely and tightly packed, mature decidual cells, and in the region of predecidual cells. Reaction product was absent in the region of nondecidualized stromal cells. Extracellular acid phosphatase activity was more conspicuous in the region of mature decidual cells in fasted mice than in fed mice, and it was apparently similar in the region of predecidual cells in both fed and fasted mice. Acid phosphatase reaction product was also observed in lysosomes in all cells studied. Because acid phosphatase activity reflects the presence of lysosomal hydrolases in general, our results suggest that there is matrix degradation by lysosomal enzymes in both fed and fasted mice. These events may be part of the process of tissue remodeling in regions of predecidual cells and mature decidual cells. However, it is also possible that, in the region of mature decidual cells, breakdown of matrix constituents is a mechanism to provide nutrients for the growing fetus. This mechanism is probably enhanced in fasted mice.

Maternal IL-11Ralpha function is required for normal decidua and fetoplacental development in mice

In eutherian mammals, implantation and establishment of the chorioallantoic placenta are essential for embryo development and survival. As a maternal response to implantation, uterine stromal cells proliferate, differentiate, and generate the decidua, which encapsulates the conceptus and forms the maternal part of the placenta. Little is known about decidual functions and the molecular interactions that regulate its development and maintenance. Here we show that the receptor for the cytokine interleukin-11 (IL-11Ralpha) is required specifically for normal establishment of the decidua. Females homozygous for a hypomorphic IL-11Ralpha allele are fertile and their blastocysts implant and elicit the decidual response. Because of reduced cell proliferation, however, only small deciduae form. Mutant deciduae degenerate progressively, and consequently embryo-derived trophoblast cells generate a network of trophoblast giant cells but fail to form a chorioallantoic placenta, indicating that the decidua is essential for normal fetoplacentation. IL-11Ralpha is expressed in the decidua as well as in numerous other tissues and cell types, including the ovary and lymphocytes. The differentiation state and proliferative responses of B and T-lymphocytes in mutant females were normal, and wild-type females carrying IL-11Ralpha mutant ovaries had normal deciduae, suggesting that the decidualization defects do not arise secondarily as a consequence of perturbed IL-11Ralpha signaling defects in lymphoid organs or in the ovary. Therefore, IL-11Ralpha signaling at the implantation site appears to be required for decidua development.

The Wilms' tumor 1 gene: oncogene or tumor suppressor gene?

The Wilms' tumor 1 (wt1) gene is one of at least three genes that are involved in the development of Wilms' tumor, a pediatric kidney cancer. The expression pattern of the gene indicates that wt1 not only plays a role during kidney development but is also involved in the development and homeostasis of several other tissues. The physiological function of the gene, however, remains to be elucidated. The gene products have been implicated in many processes like proliferation, differentiation, and programmed cell death (apoptosis). The WT1 proteins function as transcription factors but may additionally be involved in splicing. Disruption of these activities may lead to aberrant development. In this paper we will discuss the role of the wt1 gene during normal development and homeostasis of several tissues. In addition, we will address the involvement of the gene products in processes like apoptosis and tumorigenesis.

Genetically engineered mice demonstrate that adenosine deaminase is essential for early postimplantation development

Adenosine deaminase (ADA) is an essential enzyme of purine metabolism that is enriched at the maternal-fetal interface of mice throughout postimplantation development. During early postimplantation stages Ada is highly expressed in both maternally derived decidual cells and zygotically derived trophoblast cells. For the current study we utilized genetically modified mice to delineate the relative contribution and importance of decidual and trophoblast ADA at the maternal-fetal interface. In females genetically engineered to lack decidual ADA a striking pattern of expression was revealed in giant trophoblast cells that surround the early postimplantation embryo. Embryos within gestation sites lacking both decidual and trophoblast ADA died during the early postimplantation period, whereas expression in trophoblast cells alone was sufficient for survival through this period. Severe disturbances in purine metabolism were observed in gestation sites lacking decidual ADA, including the accumulation of the potentially toxic ADA substrates adenosine and 2′-deoxyadenosine. These experiments provide genetic evidence that Ada expression at the maternal-fetal interface is essential for early postimplantation development in mice.

Induction of erythrophagocytic activity in cultured mouse trophoblast cells by phorbol myristate acetate and all-trans-retinal

Phorbol myristate acetate (PMA) and all-trans-retinal (retinal) were evaluated as possible phagocytic stimulators of cultured, post implantation, trophoblast cells. Ectoplacental cones dissected from 7.5 day-old mouse embryos provided the source of trophoblastic cells. Co-cultures were performed using stimulated and non-stimulated trophoblast cells and erythrocytes under standard conditions. Phagocytic activity was expressed as the total number of phagocytic cells per ectoplacental cone, and as phagosomic vacuoles per trophoblast giant cell, either in the presence or absence of the stimulators. Both chemical agents had similar effects, less than 12 h after stimulation, statistically significant numbers of erythrophagosomes appear in the trophoblast giant cells (TGC). These findings demonstrate that TGC, like neutrophils and macrophages, can be activated to phagocytosis by exogenous factors. This enhanced activity may result from the generation and release of reactive oxygen species. In conclusion, our data suggest that, because stimulation was provided, the remarkable in vivo phagocytic activity of the trophoblast can be maintained under in vitro conditions, allowing study of the pathways and regulatory steps involved in this process.

Expression and function of matrix metalloproteinases and their inhibitors at the maternal-embryonic boundary during mouse embryo implantation

Gelatinase B, a matrix metalloproteinase (MMP) of high specific activity, is highly expressed and activated by mouse blastocysts in culture, and inhibition of this enzyme activity inhibits lysis of extracellular matrix (Behrendtsen, O., Alexander, C. M. and Werb, Z. (1992) Development 114, 447–456). Because gelatinase B expression is linked to invasive potential, we studied the expression of gelatinase B mRNA and protein in vivo, in implanting trophoblast giant cells, and found that it was expressed and activated during colonization of the maternal decidua. mRNAs for several other MMPs (stromelysin-1, stromelysin-3 and gelatinase A) and MMP inhibitors (TIMP-1 and TIMP-2) were expressed in the undifferentiated stroma toward the outside of the decidua, and TIMP-3 mRNA was expressed in primary and some mature decidual cells during their differentiation. Both mRNA and TIMP-3 protein were present at high concentrations transiently, and declined from 6.5 days post coitum onward, as the cells underwent apoptosis during the main period of gelatinase B expression and ectoplacental growth and expansion. To assess the function of MMPs during implantation and decidual development, we either injected a peptide hydroxamate MMP inhibitor into normal mice or studied transgenic mice overexpressing TIMP-1. In both cases, decidual length and overall size were reduced, and the embryo was displaced mesometrially. Embryo orientation was less strictly regulated in inhibitor-treated deciduae than in control deciduae. Morphogenesis and development of oil-induced deciduomas were also slowed in the presence of the inhibitor. We conclude that administration of MMP inhibitors retards decidual remodeling and growth, and we suggest that the MMPs expressed in precursor stromal cells promote their differentiation and expansion.

Death and replacement of uterine epithelial cells during oil-induced deciduoma development in the mouse

BACKGROUND

A decidual cell reaction can be induced in rodent endometrium by an intrauterine injection of oil. The epithelial lining is thought to be instrumental to transduce intralumenal stimuli for decidualization. One of the consequences of oil injection is the death of uterine epithelial cells. No information is available on the effect that sustained contact with oil has on the epithelium.

METHODS

A decidual cell reaction was induced in 4-day pseudopregnant mice by injection of 30 microliters of arachis oil into the uterine lumen. Samples from the uteri were collected 24, 48, and 72 h after the injection and prepared for transmission electron microscopy.

RESULTS

Twenty-four hours after the oil injection, some of the initial modifications of epithelial cell surfaces were very similar to those induced by the contact with the blastocyst during normal pregnancy. Uterine epithelial cells internalized injected oil and many cells were seen in various stages of degeneration. At 48 h, many epithelial cells were detached from the basal lamina. At 72 h, the uterine lining was re-established by flattened cells.

CONCLUSIONS

The contact of oil with the uterine epithelium of pseudo pregnant mice induces epithelial cell death in the antimesometrial region of the uterine crypt. There is, however, replacement of epithelial lining by epithelial cells, which probably migrate from the mesometrial region of the crypt. The prolonged presence of oil within the uterine lumen seems to induce cycles of epithelial cell death and replacement.

Modelling of purine nucleoside metabolism during mouse embryonic development: relative routes of adenosine, deoxyadenosine, and deoxyguanosine metabolism

The individual activities for adenosine kinase, deoxyadenosine kinase, adenosine deaminase, deoxyguanosine kinase, and purine nucleoside phosphorylase were determined during days 7 to 13 of mouse embryonic development. Adenosine deaminase increased 74-fold between days 7 and 9; deoxyadenosine kinase increased 5.4-fold during the same interval. Adenosine kinase, deoxyguanosine kinase, and purine nucleoside phosphorylase exhibited less than 2-fold changes in activity between days 7 and 13. Using Michaelis constants for each enzyme and the maximal velocities determined from enzyme assay, the relative routes of adenosine and deoxyadenosine metabolism via phosphorylation or deamination were modeled as a function of nucleoside concentration for days 7 through 13. For days 7 and 8, phosphorylation of adenosine is the principle route of metabolism at physiological concentrations. A switch occurred at day 9 and following where deamination is at least 5-fold greater than phosphorylation at all substrate concentrations. Deoxyadenosine phosphorylation was at most 10% of deamination at day 7 and then declined to less than 1% for days 9 to 13. Phosphorolysis was the principle route of deoxyguanosine metabolism through the 7 to 13 day period. Thus catabolism rather than phosphorylation was the principle pathway for purine deoxynucleoside metabolism during this period.