The cytoplasmic expression of E-cadherin and beta-catenin in bovine trophoblasts during binucleate cell differentiation

Expression of cadherins and some connective tissue components in cow uterus and placenta during pregnancy

The implantation and placental development processes are regulated with cell adhesion molecules and remodeling of the maternal endometrium's extracellular matrices (ECM) and fetal chorion. This study aimed to investigate the distribution and localization of some classical cadherins (E-, N-, and P-cadherins) and extracellular matrix components collagen type 5α1, fibronectin, and laminin in the cow placentomes during pregnancy using immunohistochemical and Western blotting analyses. The study results confirmed the expression of E- and P-cadherins, collagen type Vα1 (COLVα1), fibronectin, and laminin in the cow placentomes, but not N-cadherin. Throughout the pregnancy, E- and P- cadherins, COLVα1, and laminin were localized in the luminal and glandular epithelium of the inter-caruncular endometrium, caruncular epithelium, and the uninucleate (UNCs) and binucleate trophoblast giant cells (BNCs/TGCs). E- cadherin immunoreactivity in the first pregnancy period was strong in the UNCs while moderate in the BNCs/TGCs. However, it was weak in both trophoblast in the second and third pregnancy periods. In the fetal trophoblasts, P- cadherin and laminin immunostainings were more intense in the BNCs/TGCs than UNCs. The fetal and maternal stromal cells were also positive for P- cadherin, COLVα1, fibronectin, and laminin. The immunostaining intensity of COLVα1 and fibronectin in the stromal extracellular matrix of the placentomes decreased as the pregnancy progressed. The endothelia of fetal and maternal vessels were positive for all proteins. The presence and distinct localization of cadherins and ECM proteins in the cow placentome components support the role of these molecules in regulating placental cell growth, migration, and matrix production during pregnancy.

Mesenchymal Stem Cells in Embryo-Maternal Communication under Healthy Conditions or Viral Infections: Lessons from a Bovine Model

Bovine mesenchymal stem cells are a relevant cell population found in the maternal reproductive tract that exhibits the immunomodulation capacity required to prevent embryo rejection. The phenotypic plasticity showed by both endometrial mesenchymal stem cells (eMSC) and embryonic trophoblast through mesenchymal to epithelial transition and epithelial to mesenchymal transition, respectively, is essential for embryo implantation. Embryonic trophoblast maintains active crosstalk via EVs and soluble proteins with eMSC and peripheral blood MSC (pbMSC) to ensure the retention of eMSC in case of pregnancy and induce the chemotaxis of pbMSC, critical for successful implantation. Early pregnancy-related proteins and angiogenic markers are detected as cargo in EVs and the soluble fraction of the embryonic trophectoderm secretome. The pattern of protein secretion in trophectoderm-EVs changes depending on their epithelial or mesenchymal phenotype and due to the uptake of MSC EVs. However, the changes in this EV-mediated communication between maternal and embryonic MSC populations infected by viruses that cause abortions in cattle are poorly understood. They are critical in the investigation of reproductive viral pathologies.

Parallels between the extracellular matrix roles in developmental biology and cancer biology

Interaction of a tumor with its microenvironment is an emerging field of investigation, and the crosstalk between cancer cells and the extracellular matrix is of particular interest, since cancer patients with abundant and stiff extracellular matrices display a poorer prognosis. At the post-juvenile stage, the extracellular matrix plays predominantly a structural role by providing support to cells and tissues; however, during development, matrix proteins exert a plethora of diverse signals to guide the movement and determine the fate of pluripotent cells. Taking a closer look at the communication between the extracellular matrix and cells of a developing body may bring new insights into cancer biology and identify cancer weaknesses. This review discusses parallels between the extracellular matrix roles during development and tumor growth.

Embryonic Trophectoderm Secretomics Reveals Chemotactic Migration and Intercellular Communication of Endometrial and Circulating MSCs in Embryonic Implantation

Embryonic implantation is a key step in the establishment of pregnancy. In the present work, we have carried out an in-depth proteomic analysis of the secretome (extracellular vesicles and soluble proteins) of two bovine blastocysts embryonic trophectoderm primary cultures (BBT), confirming different epithelial–mesenchymal transition stages in these cells. BBT-secretomes contain early pregnancy-related proteins and angiogenic proteins both as cargo in EVs and the soluble fraction. We have demonstrated the functional transfer of protein-containing secretome between embryonic trophectoderm and maternal MSC in vitro using two BBT primary cultures eight endometrial MSC (eMSC) and five peripheral blood MSC (pbMSC) lines. We observed that eMSC and pbMSC chemotax to both the soluble fraction and EVs of the BBT secretome. In addition, in a complementary direction, we found that the pattern of expression of implantation proteins in BBT-EVs changes depending on: (i) their epithelial–mesenchymal phenotype; (ii) as a result of the uptake of eMSC- or pbMSC-EV previously stimulated or not with embryonic signals (IFN-τ); (iii) because of the stimulation with the endometrial cytokines present in the uterine fluid in the peri-implantation period.

Intermembrane distances at the feto-maternal interface in epitheliochorial placentation

INTRODUCTION

In an epitheliochorial placenta, the apical membranes of trophoblast cells and of uterine epithelial cells are in contact to each other (feto-maternal contact). In addition, there are also folds in which the trophoblast membrane is in contact with itself (feto-fetal contact) and areas where apical uterine epithelial membrane is in contact with itself (materno-maternal contact).

METHODS

We use transmission electron microscopy of placental samples from pigs. (n = 3), cows (n = 2), sheep (n = 2), goat (n = 2) and roe deer (n = 1) to study the intermembrane distance in these three contact types.

RESULTS

The measured intermembrane distances vary between 8 and 25 nm. One common feature is that the distance at feto-fetal contact sites is about 6-10 nm wider than at materno-maternal sites and feto-maternal sites show intermediate values.

DISCUSSION

This finding suggests that the membrane distance at feto-maternal contact sites is determined by heterophilic binding of larger fetal to smaller maternal binding molecules. Homophilic binding of smaller maternal or larger fetal molecules lead to the smaller or wider intermembrane distances at materno-maternal or feto-fetal contact sites respectively. The observation that this similar pattern of membrane distances is present in pigs and in ruminants suggest that an evolutionary mechanism is involved in determining the intermembrane distance in epitheliochorial placentas.

Adhesion molecules in gamete transport, fertilization, early embryonic development, and implantation-role in establishing a pregnancy in cattle: A review

Cell-cell adhesion molecules have critically important roles in the early events of reproduction including gamete transport, sperm-oocyte interaction, embryonic development, and implantation. Major adhesion molecules involved in reproduction include cadherins, integrins, and disintegrin and metalloprotease domain-containing (ADAM) proteins. ADAMs on the surface of sperm adhere to integrins on the oocyte in the initial stages of sperm-oocyte interaction and fusion. Cadherins act in early embryos to organize the inner cell mass and trophectoderm. The trophoblast and uterine endometrial epithelium variously express cadherins, integrins, trophinin, and selectin, which achieve apposition and attachment between the elongating conceptus and uterine epithelium before implantation. An overview of the major cell-cell adhesion molecules is presented and this is followed by examples of how adhesion molecules help shape early reproductive events. The argument is made that a deeper understanding of adhesion molecules and reproduction will inform new strategies that improve embryo survival and increase the efficiency of natural mating and assisted breeding in cattle.

Induction of ovine trophoblast cell fusion by fematrin-1 in vitro

Endogenous retroviruses present in the genomes take a specific role in placental formation in various vertebrates, including bovine and sheep. Fematrin-1, which is the envelope (Env) protein of bovine endogenous retrovirus found in bovine placenta, is involved in the formation of fetomaternal hybrid cells in cattle placenta. This study was conducted to clarify whether fematrin-1 possesses fusogenic activity in trophoblast cells. Another question is whether Env proteins only have species-specific activity or not. For this, fematrin-1 gene was transfected in ovine trophoblast cells, and we examined fusogenic activity with Cos-7 cells. Although fematrin-1 fusogenic activity was detected in both neutral and acidic pH conditions, acidic condition significantly enhanced it. These activities were rather weaker than those of vesicular stomatitis virus G protein as a positive control. However, the ratio of fematrin-1 and vesicular stomatitis virus G protein fusion index was confirmed similar to those in the previous reports. Some fusion cells showed multinucleate cells. These results imply that fematrin-1 is involved in the formation of trophoblast hybrid cells even in different species trophoblastic cells.

Comparison of the global gene expression profiles in the bovine endometrium between summer and autumn

Heat stress compromises fertility during summer in dairy and beef cows by causing nutritional, physiological and reproductive damages. To examine the difference in endometrial conditions in cows between summer and autumn, gene expression profiles were compared using a 15 K bovine oligo DNA microarray. The trial was conducted in the summer (early in September) and autumn (mid-November) seasons of two consecutive years (2013–2014) in Morioka, Japan. Endometrial samples were collected from the cows using a biopsy technique. The expressions of 268 genes were significantly higher in the endometrium collected in summer than those collected in autumn, whereas the expressions of 369 genes were lower (P<0.05 or lower). Messenger RNA expressions of glycoprotein 2 (GP2), neurotensin (NTS),E-cadherin (CDH1) and heat shock 105kDa/110kDa protein 1 (HSPH1) were validated by quantitative real-time PCR. Transcripts of GP2 and NTS were more abundant in the endometrium from summer than in the endometrium from autumn (P < 0.05). In contrast, the mRNA expressions of CDH1 were lower (P < 0.05) and those of HSPH1 tended to be low (P = 0.09) in the endometrium from summer. Immunohistochemical staining showed that GP2, NTS and HSPH1 were expressed in the endometrial epithelial or glandular epithelial cells. The serum concentrations of NTS collected from the cows in summer were higher than those collected from cows in autumn (P < 0.05). Collectively, the different gene expression profiles may contribute to functional differences in the endometrium between summer and autumn, and the increases in GP2 and NTS may have a relationship with the endometrial deficiency that causes infertility of cows in summer.

CDX2 regulates multiple trophoblast genes in bovine trophectoderm CT-1 cells

The bovine trophectoderm (TE) undergoes a dramatic morphogenetic transition prior to uterine endometrial attachment. Many studies have documented trophoblast-specific gene expression profiles at various pre-attachment stages, yet genetic interactions within the transitioning TE gene regulatory network are not well characterized. During bovine embryogenesis, transcription factors OCT4 and CDX2 are co-expressed during early trophoblast elongation. In this study, the bovine trophectoderm-derived CT-1 cell line was utilized as a genetic model to examine the roles of CDX2 and OCT4 within the bovine trophoblast gene regulatory network. An RT-PCR screen for TE-lineage transcription factors identified expression of CDX2, ERRB, ID2, SOX15, ELF5, HAND1, and ASCL2. CT-1 cells also express a nuclear-localized, 360 amino acid OCT4 ortholog of the pluripotency-specific human OCT4A. To delineate the roles of CDX2 and OCT4 within the CT-1 gene network, CDX2 and OCT4 levels were manipulated via overexpression and siRNA-mediated knockdown. An increase in CDX2 negatively regulated OCT4 expression, but increased expression of IFNT, HAND1, ASCL2, SOX15, and ELF5. A reduction of CDX2 levels exhibited a reciprocal effect, resulting in decreased expression of IFNT, HAND1, ASCL2, and SOX15. Both overexpression and knockdown of CDX2 increased ETS2 transcription. In contrast to CDX2, manipulation of OCT4 levels only revealed a positive autoregulatory mechanism and upregulation of ASCL2. Together, these results suggest that CDX2 is a core regulator of multiple trophoblast genes within CT-1 cells.

Aberrant expression of E-cadherin and β-catenin proteins in placenta of bovine embryos derived from somatic cell nuclear transfer

Abnormal placental development is common in the bovine somatic cell nuclear transfer (SCNT)-derived fetus. In the present study, we characterised the expression of E-cadherin and β-catenin, structural proteins of adherens junctions, in SCNT gestations as a model for impaired placentation. Cotyledonary tissues were separated from pregnant uteri of SCNT (n = 6) and control pregnancies (n = 8) obtained by artificial insemination. Samples were analysed by western blot, quantitative RT-PCR (qRT-PCR) and immunohistochemistry. Bovine trophectoderm cell lines derived from SCNT and control embryos were analysed to compare with the in utero condition. Although no differences in E-cadherin or β-catenin mRNA abundance were observed in fetal tissues between the two groups, proteins encoded by these genes were markedly under-expressed in SCNT trophoblast cells. Immunohistochemistry revealed a different pattern of E-cadherin and total β-catenin localisation in SCNT placentas compared with controls. No difference was observed in subcellular localisation of dephosphorylated active-β-catenin protein in SCNT tissues compared with controls. However, qRT-PCR confirmed that the wingless (WNT)/β-catenin signalling pathway target genes CCND1, CLDN1 and MSX1 were downregulated in SCNT placentas. No differences were detected between two groups of bovine trophectoderm cell lines. Our results suggest that impaired expression of E-cadherin and β-catenin proteins, along with defective β-catenin signalling during embryo attachment, specifically during placentation, is a molecular mechanism explaining insufficient placentation in the bovine SCNT-derived fetus.

Bovine trophoblastic cell differentiation and binucleation involves enhanced endogenous retrovirus element expression

BACKGROUND

Endogenous retrovirus (ERV) envelope (env) genes are involved in the differentiation of trophoblastic cells in humans and mice. However, there is limited information about their roles in ruminant trophoblastic cells. Thus, we attempted to explore the possible roles of ERV elements in the binucleation of bovine trophoblastic cells using in vitro bovine trophoblastic (BT) cell lines.

METHODS

In this study, blastocysts and elongated embryos were obtained from Japanese Black cows, and endometrial and fetal membrane tissues were collected from day 17 to 37 of gestation. The gene expression levels of four ERV elements, bERVE (bovine endogenous retrovirus envelope element-like transcript) -A, bERVE-B, BERV (bovine endogenous retrovirus) -K1 env, and BERV-K2 env, were analyzed in the fetal and endometrial tissue and cultured BT cell lines using quantitative RT-PCR. On-Matrigel gel and on-collagen gel culturing were used to induce binucleate cell (BNC) formation in the BT cell lines. How the culture conditions affected the expression of BNC-specific genes and ERV elements was examined by quantitative RT-PCR and immunocytochemistry.

RESULTS

bERVE-A, bERVE-B, BERV-K1 env, and BERV-K2 env were expressed in almost all BT cell lines; however, only bERVE-A and BERV-K1 env were detected in trophoblastic tissues during the peri-implantation period. In the on-Matrigel cultures, the expression levels of BNC-specific genes and molecules were enhanced in the BT cells. The expression levels of bERVE-A and BERV-K1 env were also increased in the BT cells during on-Matrigel culturing. The BT cell expression levels of these ERV elements were consistent with those of BNC-specific genes during on-Matrigel culturing (P < 0.01).

CONCLUSIONS

These results suggest that bERVE-A and BERV-K1 env are involved in the expression of BNC-specific genes and the progression of bovine trophoblastic cell binucleation, as their expression levels increased during periods of increased BNC-specific molecule expression, which is strongly suggestive of the development of BNC from mononucleate trophoblastic cells. The on-Matrigel culture system is a convenient in vitro tool for studying bovine trophoblastic cell lineages.

A decrease in DKK1, a WNT inhibitor, contributes to placental lipid accumulation in an obesity-prone rat model

Placenta, as the sole transport mechanism between mother and fetus, links the maternal physical state and the immediate as well as lifelong outcomes of the offspring. The present study examined the consequences of maternal obesity on placental lipid accumulation and metabolism. Pregnant obesity-prone (OP) and obesity-resistant (OR) rat strains were fed a control diet throughout gestation. Placentas were collected on Gestational Day 21 for mRNA and oxidative stress analysis, and frozen placental sections were analyzed for fat accumulation as well as beta-catenin and Dickkopf homolog 1 (Xenopus laevis) (DKK1) localization. JEG3 trophoblast cells were cultured in vitro to determine the relationship between DKK1 and lipid accumulation. Maternal plasma and placental nonesterified fatty acids and triglycerides (TG) were elevated in OP dams. Placental Dkk1 mRNA content was 4-fold lower in OP placentas, and a significant increase was noted in beta-catenin accumulation as well as in mRNA content of fat transport and TG synthesis genes, including Ppard (peroxisome proliferator-activated receptor delta), Slc27a1 (fatty acid transport protein 1; also known as Fatp1), Cd36 (cluster of differentiation 36; also known as fatty acid translocation [Fat]), Lipin1, and Lipin3. Significant lipid accumulation was found within the decidual zones in OP, but not OR, placentas, and thickness of the decidual and junctional zones was significantly smaller in OP than in OR placentas. Overexpression of DKK1 in JEG3 cells decreased lipid accumulation and mRNA content of PPARD, SLC27A1, CD36, LIPIN1, and LIPIN3. Our results demonstrate that DKK1 is regulating certain aspects of placental lipid metabolism through the WNT signaling pathway.

Dickkopf-1 expression during early bovine placentation and its down-regulation in somatic cell nuclear transfer (SCNT) pregnancies

The precise role of Dickkopf-1 (Dkk-1) during early bovine trophoblast development and subsequent placentation is not fully understood. Using somatic cell nuclear transfer (SCNT) generated pregnancies as a model of poor placentation we have found that mean levels of Dkk-1 mRNA were 1.5 fold lower in SCNT fetal cotyledon tissue at Day 50 of gestation than those resulting from artificial insemination (AI) and 2 fold lower at Days 100 and 150 (P<0.004). Dkk-1 expression in cotyledon tissue was localized by in situ hybridization to fetal binucleate cells (BNCs). Examining conceptuses from blastocyst stage we show that Dkk-1 mRNA was first evident between Days 15-20 of gestation in trophoblast tissue (when BNCs first appear) prior to the initial expression of the BNC specific bovine placental lactogen (bPL) on Day 20. Dkk-1 mRNA levels were higher than bPL in trophoblast tissue throughout the pre-attachment period (Days 24-31), however, this reversed during cotyledon development with only a subset of the bPL immunoreactive BNCs also containing Dkk-1 protein, suggesting a specific role for Dkk-1 during early placentation. One function of Dkk-1 is as an antagonist of the Wnt signaling pathway and, although Wnt5A and Wnt7A mRNAs were expressed in Day 50 bovine cotyledons, their expression levels were similar between AI and SCNT. In addition, the nuclear localization of beta-catenin, which is an indicator of activation of the Wnt pathway, was also similar between AI and SCNT cotyledon tissue. Transcriptional control of Dkk-1 was not due to changes in DNA methylation levels in the promoter region as methylation levels were no different when comparing AI and SCNT tissues. The decreased expression of Dkk-1 in SCNT cotyledons that are prone to abnormal placentation suggests a role in cotyledon formation but the mechanism and regulatory control is yet to be revealed.

Wnt genes in the mouse uterus: potential regulation of implantation

Wnt genes are involved in critical developmental and growth processes. The present study comprehensively analyzed temporal and spatial alterations in Wnt and Fzd gene expression in the mouse uterus during peri-implantation of pregnancy. Expression of Wnt4, Wnt5a, Wnt7a, Wnt7b, Wnt11, Wnt16, Fzd2, Fzd4, and Fzd6 was detected in the uterus during implantation. Wnt4 mRNA was most abundant in the decidua, whereas Wnt5a mRNA was restricted to the mesometrial decidua during decidualization. Wnt7a, Wnt7b, and Wnt11 mRNAs were abundantly detected in the endometrial epithelia. The expression of Wnt7b was robust in the luminal epithelium (LE) at the implantation site on Gestational Day 5, whereas Wnt11 mRNA disappeared in the LE adjacent to the embryo in the antimesometrial implantation chamber but remained abundant in the LE. Wnt16 mRNA was localized to the stroma surrounding the LE on Day 4 and remained in the stroma adjacent to the LE but not in areas undergoing the decidual reaction. Fzd2 mRNA was detected in the decidua, Fzd4 mRNA was in the vessels and stroma surrounding the embryo, and Fzd6 mRNA was observed in the endometrial epithelia, stroma, and some blood vessels during implantation. Ovarian steroid hormone treatment was found to regulate Wnt genes and Fzd receptors in ovariectomized mice. Especially, single injections of progesterone stimulated Wnt11 mRNA, and estrogen stimulated Wnt4 and Wnt7b. The temporal and spatial alterations in Wnt genes likely play a critical role during implantation and decidualization in mice.

WNTs in the ovine uterus: potential regulation of periimplantation ovine conceptus development

WNTs (Wingless-type MMTV integration site family member) are involved in critical developmental and growth processes in animals. These studies investigated WNT pathways in the ovine uterus and conceptus during the periimplantation period of pregnancy. WNT2 and WNT2B mRNAs were detected in endometrial stroma. WNT5A and WNT5B mRNAs were most abundant in the stroma and less so in the luminal epithelium, whereas WNT11 mRNA was detected primarily in the glands. WNT7A mRNA was present in the luminal epithelium on d 10, absent on d 12 and 14, and increased between d 16 and 20. Only WNT2, WNT2B, and WNT4 were detected in conceptus trophectoderm. FZD6/8 (frizzled receptor) and GSK3B (glycogen synthase kinase 3beta) mRNAs were detected primarily in endometrial epithelia and conceptus trophectoderm, whereas the LRP5/6 (low-density lipoprotein receptor-related proteins 5 and 6) coreceptor was present in all endometrial cells and the trophectoderm. DKK1 (Dickkopf), a WNT signaling inhibitor, increased in the endometrium from d 16-20. CTNNB1 [catenin (cadherin associated protein) beta1] and CDH1 (E-cadherin) mRNAs were most abundant in the endometrial epithelia and trophectoderm. LEF1 (lymphoid enhancer-binding factor 1) mRNA was expressed primarily in uterine epithelia, whereas TCF7L2 [(transcription factor 7-like 2 (T-cell specific, HMG-box)] was primarily in the conceptus. CTNNB1 and TCF7L2 proteins were both abundant in the nuclei of trophoblast giant binucleate cells. WNT7A stimulated a TCF/LEF-luciferase reporter activity in ovine trophectoderm cells that was inhibited by dominant-negative TCF and Sfrp2 (secreted FZD-related protein 2). WNT7A increased trophectoderm cell proliferation as well as MSX2 (msh homeobox 2) and MYC (myelocytomatosis oncogene) mRNA levels. Wnt5a increased trophectoderm cell migration in a Rho kinase-dependent manner. These results support the hypotheses that canonical and noncanonical WNT signaling pathways are conserved regulators of conceptus-endometrial interactions in mammals and regulate periimplantation ovine conceptus development.

Gene expression and maintenance of pregnancy in bovine: roles of trophoblastic binucleate cell-specific molecules

Cell to cell interaction plays a pivotal role in the regulation of placentogenesis and exchange of stage-specific developmental signals between the fetal and maternal units. Specifically, these interactions are paramount for programmed fetal growth, maternal adaptation to pregnancy and coordination of parturition. However, little is known about the precise regulation of placentation and maintenance of gestation in cattle. Therefore, the aim of the present study was to decipher the complex networks of cell communication to gain an insight into the multifaceted developmental process and understand the profound consequences of flawed communication. In the ruminant, the binucleate cell plays a central role in forming the structures and secretions at the fetomaternal interface that are crucial in establishing and maintaining pregnancy. Herein, we summarise differences in the abundance of specific RNA transcripts in the bovine cotyledon and caruncle using global gene expression profiling and further investigate the relationship of mRNA abundance for selected pregnancy-specific genes of interest (identified from microarray studies) that are localised exclusively to the binucleate cell, such as placental lactogen, prolactin-related proteins and pregnancy-associated glycoproteins. The results suggest that a well-orchestrated transcriptional command from binucleate cells is pivotal to the establishment and progression of pregnancy in cattle.

Activation of the canonical wingless/T-cell factor signaling pathway promotes invasive differentiation of human trophoblast

The molecular mechanisms governing invasive differentiation of human trophoblasts remain largely elusive. Here, we investigated the role of Wnt-beta-catenin-T-cell factor (TCF) signaling in this process. Reverse transcriptase-polymerase chain reaction and Western blot analyses demonstrated expression of Wnt ligands, frizzled receptors, LRP-6, and TCF-3/4 transcription factors in total placenta and different trophoblast cell models. Immunohistochemistry of placental tissues and differentiating villous explant cultures showed that expression of TCF-3/4 strongly increased in invading trophoblasts. Some of these cells also accumulated dephosphorylated beta-catenin in the nucleus. Wnt3A treatment of primary cytotrophoblasts and SGHPL-5 cells induced activity of TCF-luciferase reporters. Accordingly, the ligand provoked interaction of TCF-3/4 with beta-catenin as assessed in electrophoretic mobility shift assays (EMSAs) and up-regulation of Wnt/TCF target genes as observed by Western blot analyses. Wnt3A stimulated trophoblast migration and invasion through Matrigel, which could be blocked by addition of Dickkopf-1, mediating in-hibition of canonical Wnt signaling. Dickkopf-1 also reduced basal migration, invasion, and proliferation of cytotrophoblasts, suggesting expression of endogenous Wnt ligand(s). Immunohistochemistry revealed that the percentage of extravillous trophoblasts containing nuclear beta-catenin was significantly higher in placentas of complete hydatidiform mole pregnancies as compared to normal placentas. Thus, canonical Wnt signaling may promote invasive trophoblast differentiation, and exaggerated activation of the path-way could contribute to trophoblastic hyperplasia and local invasion.

Placental expression of secreted frizzled related protein-4 in the rat and the impact of glucocorticoid-induced fetal and placental growth restriction

Wnt genes regulate a diverse range of developmental processes, including placental formation. Activation of the WNT pathway results in translocation of beta-catenin (CTNNB1) into the nucleus and the subsequent activation of transcription factors that promote proliferation. The secreted frizzled related proteins (SFRPs) are thought to inhibit WNT signaling by binding to the WNT ligand or its frizzled receptor. In this study, we compared the expression patterns of one of these secreted molecules, SFRP4, in the two morphologically and functionally distinct regions of the rat placenta during the last third of pregnancy. In addition, we assessed whether placental SFRP4 expression is altered in a model of glucocorticoid-induced placental growth restriction. Temporal analyses of the rat placenta by quantitative RT-PCR, in situ hybridization, and immunohistochemistry during the final third of pregnancy demonstrated elevated levels of Sfrp4 mRNA and SFRP4 protein near term, specifically in trophoblast cells of the basal zone. This increase in expression of SFRP4 in basal zone trophoblasts was associated with a reduction in CTNNB1 nuclear translocation, consistent with inhibition of the WNT pathway. Maternal dexamethasone treatment (1 microg/ml of drinking water, Days 13-22), which has previously been shown to reduce placental growth, further increased the expression of Sfrp4 mRNA in both the basal and labyrinth zones of the placenta at Day 22. Collectively, these data demonstrate that increased expression of SFRP4 is associated with reduced growth of placental regions in normal pregnancy and after glucocorticoid-induced growth retardation. These observations, together with associated changes in CTNNB1 localization, support the hypothesis that increased placental expression of SFRP4 inhibits the WNT pathway and thereby influences placental growth via effects on cell fate signaling.