Animal models of implantation

WNT4 is a key regulator of normal postnatal uterine development and progesterone signaling during embryo implantation and decidualization in the mouse

WNT4, a member of the Wnt family of ligands, is critical for the development of the female reproductive tract. Analysis of Wnt4 expression in the adult uterus during pregnancy indicates that it may play a role in the regulation of endometrial stromal cell proliferation, survival, and differentiation, which is required to support the developing embryo. To investigate the role of Wnt4 in adult uterine physiology, conditional ablation of Wnt4 using the PR(cre) mouse model was accomplished. Ablation of Wnt4 rendered female mice subfertile due to a defect in embryo implantation and subsequent defects in endometrial stromal cell survival, differentiation, and responsiveness to progesterone signaling. In addition to altered stromal cell function, the uteri of PR(cre/+)Wnt4(f/f) (Wnt4(d/d)) mice displayed altered epithelial differentiation characterized by a reduction in the number of uterine glands and the emergence of a p63-positive basal cell layer beneath the columnar luminal epithelial cells. The altered epithelial cell phenotype was further escalated by chronic estrogen treatment, which caused squamous cell metaplasia of the uterine epithelium in the Wnt4(d/d) mice. Thus, WNT4 is a critical regulator not only of proper postnatal uterine development, but also embryo implantation and decidualization.

Transforming growth factor Beta regulates proliferation and invasion of rat placental cell lines

Implantation of an embryo in the endometrium is a critical step for continuation of pregnancy, and implantation failure is a major cause of infertility. In rats, the implantation process involves invasion of the endometrial epithelial lining by the trophoblastic cells in order to reach the underlying stromal cells. Transforming growth factor beta (TGFB) is a multifunctional cytokine that regulates proliferation, differentiation, and invasiveness of multiple cell lineages. We used rat HRP-1 and RCHO-1 placental cell lines to perform this study. HRP-1 cells were derived from midgestation chorioallantoic placental explants of the outbred Holtzman rat, whereas RCHO-1 cells were established from a rat choriocarcinoma. MTT proliferation assays revealed that each TGFB isoform decreased HRP-1 cell growth in a dose-dependent manner, whereas RCHO-1 cells were resistant to the growth-suppressive effect of TGFB1 and TGFB3. Only TGFB2 reduced RCHO-1 cell proliferation. Activation of ERK, MAPK14 (p38 MAPK), or SMAD pathways is known to play a role in cell proliferation, and we found that TGFB activates these pathways in both HRP-1 and RCHO-1 cells in an isoform-specific manner. MTT proliferation assays revealed that ERK pathway is partially implicated in TGFB3-reduced HRP-1 cell proliferation. Hoechst nuclear staining and caspase-3 cleavage demonstrated that TGFB isoforms failed to induce apoptosis in both cell lines. Matrigel invasion assays showed that both HRP-1 and RCHO-1 cells exhibit intrinsic invasive ability under untreated conditions. The capacity of HRP-1 cells to invade the Matrigel was selectively increased by TGFB2 and TGFB3, whereas all TGFB isoforms could increase the invasiveness of RCHO-1 cells. These important functional studies progressively reveal a key role for TGFB in regulating proliferation and invasiveness of placental cells.

Subfertility linked to combined luteal insufficiency and uterine progesterone resistance

Early pregnancy loss is common and can be caused by a range of factors. The Brown Norway (BN) rat exhibits reproductive dysfunction characterized by small litter size and pregnancy failure and represents a model for investigating early pregnancy loss. In this study, we investigated the establishment of pregnancy in the BN rat and gained insight into mechanisms causing its subfertility. Early stages of BN uteroplacental organization are unique. The BN primordial placenta is restricted in its development and correlates with limited BN uterine decidual development. BN uterine decidua was shown to be both structurally and functionally distinct and correlated with decreased circulating progesterone (P4) levels. Ovarian anomalies were also apparent in BN rats and included decreased ovulation rates and decreased transcript levels for some steroidogenic enzymes. Attempts to rescue the BN uterine decidual phenotype with steroid hormone therapy were ineffective. BN uteri were shown to exhibit reduced responsiveness to P4 but not to 17beta-estradiol. P4 resistance was associated with decreased transcript levels for the P4 receptor (Pgr), a P4 receptor chaperone (Fkbp4), and P4 receptor coactivators (Ncoa1 and Ncoa2). In summary, the BN rat exhibits luteal insufficiency and uterine P4 resistance, which profoundly affects its ability to reproduce.

Foxa2 is essential for mouse endometrial gland development and fertility

During embryonic development, Foxa2 is required for the formation of the node and notochord, and ablation of this gene results in defects in gastrulation, neural tube patterning, and gut morphogenesis. Foxa2 has been shown to be expressed specifically in the glandular epithelium of the murine uterus. To study the uterine function of Foxa2, this gene was conditionally ablated in the mouse uterus by crossing mice with floxed Foxa2 alleles, Foxa2(loxP/loxP), with the Pgr(cre) mouse model. Pgr(cre/+) Foxa2(loxP/loxP) mice showed significantly reduced fertility. Analysis of the uterus on Day 5.5 of pregnancy showed disrupted blastocyst implantation. Pgr(cre/+) Foxa2(loxP/loxP) mice also showed a severe impairment of the uterus to respond to the artificial induction of the decidual response. Morphological examination of the uteri of these mice showed a severe reduction in the number of endometrial glands. The loss of endometrial glands resulted in the reduction of leukemia inhibitory factor (Lif) expression. The lack of a decidual response could be partially rescued by an intrauterine injection of LIF before the initiation of the decidual response. This analysis demonstrates that Foxa2 regulates endometrial gland development and that mice with a loss of endometrial glands cannot support implantation in part due to the loss of LIF, which is a requisite for fertility in the mouse.

Long-term progestin contraceptives (LTPOC) induce aberrant angiogenesis, oxidative stress and apoptosis in the guinea pig uterus: A model for abnormal uterine bleeding in humans

Background

Irregular uterine bleeding is the major side effect of, and cause for, discontinuation of long-term progestin-only contraceptives (LTPOCs). The endometria of LTPOC-treated women display abnormally enlarged, fragile blood vessels (BV), decreased endometrial blood flow and oxidative stress. However, obtaining sufficient, good quality tissues have precluded elucidation of the mechanisms underlying these morphological and functional vascular changes.

Methods

The current study assessed the suitability of the guinea pig (GP) as a model for evaluating the uterine effects of LTPOC administration. Thus GPs were treated with a transdermal pellet for 21 days and examined for endometrial histology, angiogenic markers as well as markers of oxidative stress and apoptosis.

Results and Discussion

We now demonstrate that GP uteri were enlarged by both estradiol (E2) and medroxyprogesterone acetate (MPA) (p < 0.001). Effects of MPA on uterine weight differed significantly depending on E2 levels (p < 0.001), where MPA opposed the E2 effect in combined treatments. Angiogenesis parameters were similarly impacted upon: MPA alone increased BV density (p = 0.036) and BV average area (p = 0.002). The presence of E2 significantly decreased these parameters. These changes were associated with highly elevated of the lipid peroxidation product, 8-isoprostane (8-isoP) content in E2+MPA-treated and by nuclear 8-OH-deoxyguanosine (8oxoG) staining compared to all other groups (p < 0.001). Abnormalities in the E2+MPA group were consistent with chromatin redistribution, nuclear pyknosis, karyolysis and increased apoptosis as observed by a marked increase in TUNEL labeling.

Conclusions

LTPOC exposure alters endometrial vascular and tissue morphology consistent with oxidative stress and apoptosis in a complex interplay with endogenous estrogens. These findings are remarkably similar to in vivo change observed in the human uterus following LTPOC administration. Hence, the GP is an excellent model for the study of LTPOC effects on the uterus and will be extremely useful in determining the mechanistic pathways involved in this process which cannot be conducted on humans.

Spacing of the embryo in the uterus is disrupted by the supine position of the body during the peri-implantation period in mice

This study aimed to clarify the mechanism of the spacing of murine embryos along the metrial and anti-metrial (MA) axis of the uterus using our newly developed experimental model. The model mice were produced by keeping mice in the supine position from the pre-implantation to implantation period. The starting points and periods of restraint of the mice in the supine position were set variously during the peri-implantation. Then, the position of the embryo was evaluated morphologically. In only one group (set in the instrument from the second day of pregnancy, Day 2, to Day 5), strong disruption of embryo spacing along the MA axis was observed. On the other hand, there was little abnormality in embryo positioning in the groups that were treated from Day 3 to Day 5 or from Day 3 to Day 6. These results suggested that determination of the position of the embryo in the MA axis is not related to duration of the experiment (2 days or 3 days), but is related to the starting time-point of the experiment, at Day 2 or Day 3. In conclusion, the period between Days 2 and 3 is critical for determination of the position of the embryo along the MA axis.

Gene expression profiles of bovine caruncular and intercaruncular endometrium at implantation

At implantation the endometrium undergoes modifications necessary for its physical interactions with the trophoblast as well as the development of the conceptus. We aim to identify endometrial factors and pathways essential for a successful implantation in the caruncular (C) and the intercaruncular (IC) areas in cattle. Using a 13,257-element bovine oligonucleotide array, we established expression profiles at day 20 of the estrous cycle or pregnancy (implantation), revealing 446 and 1,295 differentially expressed genes (DEG) in C and IC areas, respectively (false discovery rate = 0.08). The impact of the conceptus was higher on the immune response function in C but more prominent on the regulation of metabolism function in IC. The C vs. IC direct comparison revealed 1,177 and 453 DEG in cyclic and pregnant animals respectively (false discovery rate = 0.05), with a major impact of the conceptus on metabolism and cell adhesion. We selected 15 genes including C11ORF34, CXCL12, CXCR4, PLAC8, SCARA5, and NPY and confirmed their differential expression by quantitative RT-PCR. The cellular localization was analyzed by in situ hybridization and, upon pregnancy, showed gene-specific patterns of cell distribution, including a high level of expression in the luminal epithelium for C11ORF34 and MX1. Using primary cultures of bovine endometrial cells, we identified PTN, PLAC8, and CXCL12 as interferon-tau (IFNT) target genes and MSX1 and CXCR7 as IFNT-regulated genes, whereas C11ORF34 was not an IFNT-regulated gene. Our transcriptomic data provide novel molecular insights accounting for the biological functions related to the C or IC endometrial areas and may contribute to the identification of potential biomarkers for normal and perturbed early pregnancy.

The role of MTOR in mouse uterus during embryo implantation

Mammalian target of rapamycin (MTOR) is a protein kinase that plays a central role in cell growth and proliferation. It is a part of the signaling network transmitting growth factor signaling to translational control. Previous studies have shown that MTOR is involved in embryo implantation, but its expression in the uterus and its role in implantation are unclear. Here, we have investigated the expression and role of MTOR in mouse uterus during early pregnancy. RT-FQ PCR showed that the mRNA levels of Mtor in endometria of pregnant mice were higher than those of nonpregnant mice. The mRNA levels in the pregnant mice gradually increased from D3 of pregnancy, reached maximum on D5, and then declined afterward. In situ hybridization and immunohistochemical analysis showed that the mRNA and protein of MTOR were mainly located in stromal cells. The levels of the expressed MTOR protein correlate with those of mRNA. The number of implantation sites was greatly decreased by the intrauterine injection with rapamycin in the early morning of D4 of the pregnancy. These findings suggest that MTOR may play an important role in embryo implantation in mice.

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.

Differential gene expression in the uterus and blastocyst during the reactivation of embryo development in a model of delayed implantation

Delayed implantation, a reversible arrest in embryo development while the embryo is at the blastocyst stage, provides an interesting window for observation of the preparation for implantation on both the embryonic and maternal sides. The American mink (Mustela vison) is a species in which delayed implantation is a normal aspect of embryo development as it consistently occurs at each breeding season. We used a transcriptome-wide approach to screen global gene expression and to identify new key genes expressed in the uterus and in the endometrium at the resumption of the embryo development, after delayed implantation. By using the suppressive subtractive hybridization (SSH) technique, two libraries of differentially expressed cDNAs, one at the uterine level and a second one at the blastocyst level, were successfully generated. Candidate genes from those two libraries were selected and their differentially expressed pattern of expression between reactivation and delayed implantation was investigated by real-time PCR and immunolocalization.

Effect of polymorphisms in four candidate genes for fertility on litter size in a German pig line

We carried out an SNP discovery project in pigs for candidate genes playing potentially important roles in embryonic development. Using eight pigs one each from eight breeds (Meishan, Mangalitza, Duroc, Pietrain, German Landrace, Hampshire, Husum Red Pied, German Large White), 36 SNPs were identified in intronic sequences of 21 porcine candidate genes based on sequencing of PCR products. The primer pairs were designed using porcine EST sequences allowing amplification of introns. These SNPs were tested for their association with the number of piglets born alive in German Large White sows using a discordant approach. Significant effects (p < 0.001 and p < 0.05, respectively) of intronic SNPs on litter size were found for four genes: mitogen-activated protein kinase kinase kinase 3 (MAP3K3), vascular endothelial growth factor receptor (KDR), erbb2 interacting protein (ERBB2IP) and peroxisome proliferator-activated receptor delta (PPARD). These SNPs can be further tested in upcoming association studies for their influence on litter size in different breeds using larger sample sizes.

Implantation of the human embryo requires Rac1-dependent endometrial stromal cell migration

Failure of the human embryo to implant into the uterine wall during the early stages of pregnancy is a major cause of infertility. Implantation involves embryo apposition and adhesion to the endometrial epithelium followed by penetration through the epithelium and invasion of the embryonic trophoblast through the endometrial stroma. Although gene-knockdown studies have highlighted several molecules that are important for implantation in the mouse, the molecular mechanisms controlling implantation in the human are unknown. Here, we demonstrate in an in vitro model for human implantation that the Rho GTPases Rac1 and RhoA in human endometrial stromal cells modulate invasion of the human embryo through the endometrial stroma. We show that knockdown of Rac1 expression in human endometrial stromal cells inhibits human embryonic trophoblast invasion into stromal cell monolayers, whereas inhibition of RhoA activity promotes embryo invasion. Furthermore, we demonstrate that Rac1 is required for human endometrial stromal cell migration and that the motility of the stromal cells increases at implantation sites. This increased motility correlates with a localized increase in Rac1 activation and a reciprocal decrease in RacGAP1 levels. These results reveal embryo-induced and localized endometrial responses that may govern implantation of the human embryo.

Progesterone regulation of glutathione S-transferase Mu2 expression in mouse uterine luminal epithelium during preimplantation period

OBJECTIVE

To investigate the differential expression and regulation of Gstm2 in mouse uterus during early pregnancy.

DESIGN

Experimental animal study.

SETTING

University research laboratory.

ANIMAL(S)

Sexually mature female Kunming white strain mice.

INTERVENTION(S)

Delayed and activated implantation, pseudopregnancy, hormonal treatment.

MAIN OUTCOME MEASURE(S)

The expression of Gstm2 mRNA was detected by in situ hybridization and reverse-transcription polymerase chain reaction (RT-PCR).

RESULT(S)

By in situ hybridization, there were a low level of Gstm2 expression in luminal epithelium on day 3 and a strong level in the luminal epithelium on day 4 during early pregnancy. The expression pattern of Gstm2 in the pseudopregnant uterus was similar to that during early pregnancy. By RT-PCR, Gstm2 was strongly detected in the uteri on days 3 and 4 of pregnancy and pseudopregnancy. Gstm2 expression was strongly detected in the luminal epithelium under delayed implantation, but not seen after delayed implantation was activated by estrogen. In the ovariectomized mouse uterus, Gstm2 expression was strongly up-regulated by progesterone via progesterone receptor.

CONCLUSION(S)

The results showed that Gstm2 was highly expressed in the uterine luminal epithelium during preimplantation period and up-regulated by progesterone.

Implantation-related expression of epidermal growth factor family molecules and their regulation by progesterone in the pregnant rat

The uterine expressions of epidermal growth factor(EGF) family are examined to elucidate their exact role(s) in rat pregnancy. EGF and its receptors' (EGF-R) mRNA levels increased significantly at implantation after which their expression gradually decreased. Heparin-binding EGF (HB-EGF) and transforming growth factor-alpha (TGF-alpha) showed a modest expression at gestation day (GD), GD4 and GD3, respectively, but were much strongly expressed at mid-pregnancy.Amphiregulin (Areg) was strongly expressed around implantation (GD4) and at mid-pregnancy (GD12).Treatment of pregnant rats with RU486 at GD5 or GD8 blocked the expression of all the genes, and administration of immature rats with progesterone (P4) induced the uterine expression of all the genes except HB-EGF. In addition, HB-EGF,TGF-alpha, and Areg proteins in the uterine and glandular epitheliums may participate in mid-pregnancy. Taken together, all of these activities are likely to be controlled by P4 in the uterus of pregnant rats.

Uterine NK cells in murine pregnancy

Murine uterine natural killer (uNK) cells are transient, short-lived, terminally differentiated lymphocytes found in decidualized endometrium. Cells expressing natural killer cell surface markers are present in uteri of infant mice. Terminal uNK cell differentiation coincides with mesometrial decidual development subsequent to blastocyst implantation and begins about gestation day 5. uNK cells proliferate rapidly and, within 3 days, senescent uNK cells appear in normal implantation sites. Mid-gestation, senescent cells become dominant and uNK cell numbers decline until term when remaining cells are shed with the placenta. Transplantable uNK cell progenitors occur outside the uterus, suggesting that blood cell homing augments any in-utero progenitors. Early in healthy pregnancies, uNK cells produce cytokines and angiogenic molecules. Their lytic capacity in normal gestation and in pregnancy failure is incompletely defined. A significant shift recently occurred in thinking about major uNK cell functions. Activated uNK cells are now considered critical for appropriate endometrial angiogenesis in early implantation site development and in non-gestational endometrium. Because analogous cells appear in the endometria of women during each menstrual cycle and become abundant in early pregnancy, studies involving experimental pregnancy termination in genetically manipulated mice continue to have great importance for understanding regulation at the human maternal-fetal interface.

Virtues and limitations of the preimplantation mouse embryo as a model system

The mouse is the most widely used model of preimplantation embryo development, but is it a good model? Its small size, prolificacy and ease of handling make the mouse a relatively low cost, readily available and attractive alternative when embryos from other species are difficult or expensive to obtain. However, the real power of the mouse as a model lies in mouse genetics. The development of inbred mouse strains facilitated gene discovery as well as our understanding of gene function and regulation while the development of tools to introduce precise genetic modifications uniquely positioned the mouse as a powerful model system for uncovering gene function. However, all models have limitations; the small size of the mouse limits tissue availability and manipulations that can be performed and differences in physiology among species may make it inappropriate to extrapolate from the mouse to other species. Thus, rather than extrapolating directly from the mouse to other species, it may be more useful to use the mouse as a model system for developing and refining hypotheses to be tested directly in species of interest. In this brief review, the value of the preimplantation mouse embryo as a model is considered, both as a model for other species and as a model for the mouse, as understanding the virtues and limitations of the mouse as a model system is essential to its appropriate use.

Comparative implantation and placentation

In all placental mammals, the establishment of an intimate contact between the embryo and the mother follows a succession of common critical steps whose chronology and timing may considerably vary from species to species. These processes present a great diversity based on the anatomy and the histology of the uterus, the developmental stage of the embryo at the time of implantation, and the endocrine and molecular interactions between the uterine and the embryonic tissues. This paper provides an overview of the general mechanical, endocrinological and cellular aspects involved in implantation in mammals with an emphasis on domestic species.

Immunoendocrine aspects of endometrial function and implantation

Effective ovarian and uterine function relies on a complex interplay between the endocrine and immune systems. It is generally accepted that in reproductive tissues, oestradiol and progesterone have pro- and anti-inflammatory activities respectively and, in this regard, the paracrine effects of the sex steroids on the ovary are similar to the endocrine effects on the uterus. Ovarian leukocyte recruitment and cytokine release are central to follicle development, ovulation and corpus luteum function. At the uterine level, the cyclical changes in sex steroids regulate the number and distribution of endometrial and decidual immune cells as well as other immune signalling and surveillance factors. The uterine mucosa is unique, in that it must tolerate sperm and the allogeneic blastocyst in a way that does not compromise uterine immune surveillance against bacteria, yeast and viruses. Crosstalk between the sex steroids and immune mediators (systemic and local) are central to these functions, and this article will review these mechanisms and their importance for successful reproductive function and pregnancy success.

Mouse models of implantation

The process of implantation, necessary for nearly all viviparous birth, consists of tightly regulated reactions including apposition of the blastocyst, attachment to the uterine epithelium and decidualization of the uterine stroma. In order for implantation to be successful, a reciprocal interaction between an implantation competent blastocyst and receptive uterus must be achieved. A more thorough understanding of the molecular mechanisms that regulate uterine receptivity and implantation is of clinical relevance to correct implantation failure and improve pregnancy rates. As molecular methodologies have evolved in recent times, the use of in vivo models to elucidate the molecular mechanisms involved in implantation has increased. The mouse has emerged as a powerful model to investigate implantation owing to the ability to control uterine physiology through exogenous stimuli, and more recently, the ability to manipulate gene expression. This review describes the evolution of the mouse as a model for understanding uterine implantation, including exciting new advances in this field, and describes a novel genetic pathway that can be elucidated from these models.

The role of the endometrium and embryo in human implantation

Despite many advances in assisted reproductive technologies (ART), implantation rates are still low. The process of implantation requires a reciprocal interaction between blastocyst and endometrium, culminating in a small window of opportunity during which implantation can occur. This interaction involves the embryo, with its inherent molecular programme of cell growth and differentiation, and the temporal differentiation of endometrial cells to attain uterine receptivity. Implantation itself is governed by an array of endocrine, paracrine and autocrine modulators, of embryonic and maternal origin. Implantation failure is thought to occur as a consequence of impairment of embryo developmental potential and/or impairment of uterine receptivity and the embryo-uterine dialogue. Therefore a better comprehension of implantation, and the relative importance of the factors involved, is warranted. New techniques for monitoring changes in the endometrium and/or the embryo at the level of gene regulation and protein expression may lead to the identification of better markers for implantation. Moreover, the use of predictive sets of markers may prove to be more reliable than a single marker. Continuing refinements to ART protocols, such as optimizing ovarian stimulation regimens, the timing of human chorionic gonadotrophin injection, or the timing of embryo transfer, should help to increase implantation rates further.

Bmp2 is critical for the murine uterine decidual response

The process of implantation, necessary for all viviparous birth, consists of tightly regulated events, including apposition of the blastocyst, attachment to the uterine lumen, and differentiation of the uterine stroma. In rodents and primates the uterine stroma undergoes a process called decidualization. Decidualization, the process by which the uterine endometrial stroma proliferates and differentiates into large epithelioid decidual cells, is critical to the establishment of fetal-maternal communication and the progression of implantation. The role of bone morphogenetic protein 2 (Bmp2) in regulating the transformation of the uterine stroma during embryo implantation in the mouse was investigated by the conditional ablation of Bmp2 in the uterus using the (PR-cre) mouse. Bmp2 gene ablation was confirmed by real-time PCR analysis in the PR-cre; Bmp2fl/fl (termed Bmp2d/d) uterus. While littermate controls average 0.9 litter of 6.2+/-0.7 pups per month, Bmp2d/d females are completely infertile. Analysis of the infertility indicates that whereas embryo attachment is normal in the Bmp2d/d as in control mice, the uterine stroma is incapable of undergoing the decidual reaction to support further embryonic development. Recombinant human BMP2 can partially rescue the decidual response, suggesting that the observed phenotypes are not due to a developmental consequence of Bmp2 ablation. Microarray analysis demonstrates that ablation of Bmp2 leads to specific gene changes, including disruption of the Wnt signaling pathway, Progesterone receptor (PR) signaling, and the induction of prostaglandin synthase 2 (Ptgs2). Taken together, these data demonstrate that Bmp2 is a critical regulator of gene expression and function in the murine uterus.

Distribution Patterns of Uterine Glands and Embryo Spacing in the Mouse

To clarify the mechanism of implantation, relationship between positioning of the mouse embryo in the uterus and distribution of uterine glands along the long axis of the uterine horn was examined by three-dimensional remodelling of the uterine endometrium. There were two unique regions in the endometrium. Uterine glands were distributed widely from mesometrial to anti-mesometrial side in one region. It was localized from lateral to anti-mesometrial side in another. These different regions were alternately aligned throughout the uterine horn. The number and position of embryos was consistent with that of the latter region. This study suggests that the type of distribution of uterine glands is closely related to the positioning of the embryo in mice.

Eph-ephrin A system regulates murine blastocyst attachment and spreading

Although numerous adhesion molecules are expressed on mammalian endometrial epithelial cells, there have not been any studies of a mechanism to prevent premature attachment of the embryo. In this study, we examined the possible involvement of Eph-ephrin interaction, which can induce repulsive forces. In mice, Eph A1, A2, and A4 were expressed on endometrial epithelial cells and ephrin A1-4 on blastocysts. Reverse transcriptase-polymerase chain reaction showed that mRNA expression of ephrin A1-4 on embryos transiently decreased around the implantation period. Immunohistochemistry demonstrated that the expression of Eph A1 on endometrial epithelial cells and ephrin A1 and A3 expression on embryos decreased at implantation sites. Recombinant Eph A1 reacted with cell the surface of ephrin A-bearing trophectoderm cells. Attachment assays using Eph A1-coated dishes showed that blastocyst attachment was reversibly inhibited by Eph A1. These findings suggest an important role of the Eph-ephrin A system in regulating the initial embryo-maternal contact during the cross-talk period that precedes embryo implantation.

Expression of syndecans, cell-cell interaction regulating heparan sulfate proteoglycans, within the human endometrium and their regulation throughout the menstrual cycle

OBJECTIVE

To evaluate the expression of syndecan-1, -2, -3, and -4 in different phases of eutopic endometrium of normal cycling women.

DESIGN

Prospective observational study.

SETTING

University-based research center for reproductive medicine.

PATIENT(S)

Twenty-nine healthy ovulatory volunteers.

INTERVENTION(S)

mRNA and protein expression of syndecan-1 to -4 in human endometrium.

MAIN OUTCOME MEASURE(S)

Real-time polymerase chain reaction of syndecan members and further characterization of mRNA expression of syndecan-1 and -4 with multiprobe RNase protection assays of epithelial and stromal cells after purification with antibody-coated magnetic beads. For confirmation of results, protein expression and localization using immunohistochemistry for syndecan-1 and -4 was performed.

RESULT(S)

All syndecans were expressed within human endometrium. Syndecan-1 and -4 proved to be significantly upregulated in whole endometrium during the secretory phase (2.73-fold and 2.85-fold, respectively). Using multiprobe RNase protection assays, a significant upregulation of mRNA was noted in epithelial cells during the secretory phase for both syndecan-1 and -4 (7.46-fold and 2.52-fold, respectively) and confirmed by immunohistochemistry.

CONCLUSION(S)

Cycle-dependent expression of syndecan-1 and -4 suggests that these adhesion proteins are involved in the regulation of the cycling endometrium.

The role of paternal chromosomes and sperm morphology on the outcome of intracytoplasmic sperm injection

The study investigated the possible relationship between the X/Y chromosomes bearing spermatozoa and the outcome of intracytoplasmic sperm injection (ICSI) therapy and morphological appearance/shape (Tygerberg criteria) of the sperm cell injected into the oocyte during ICSI therapy and fertilisation. Thirty-nine patients were recruited for the study from an assisted reproductive programme. Semen samples were prepared by using gradient centrifugation techniques. Prior to injection sperm images were captured using high-quality video graphic equipment. Sperm selection was based on the concept of 'best-looking' spermatozoa i.e. spermatozoa lacking gross and obvious malformations such as broken necks, cytoplasmic droplets, amorphous or elongated heads. Photomicrographs of each sperm cell were produced from video footage. The photographical material was used to determine the basic shape and the actual length-to-width ratio of the injected sperm heads. Embryo biopsies and fluorescent in situ hybridisation (FISH) was performed on 12 randomly selected couples from a set of 39. Embryos were evaluated on day 3 for development and embryo transfer. Embryo biopsies and FISH analyses were performed on those embryos that showed no developmental potential following injection. It was found that 70% of the embryos that showed no developmental potential were Y chromosome-bearing embryos. The sperm selection process for ICSI based on the approach of choosing the 'best-looking' spermatozoon in the ejaculate seems to provide cells that can be classified as normal based on the length-to-width ratio set by the World Health Organization for normal cells.

Reduced maternal expression of adrenomedullin disrupts fertility, placentation, and fetal growth in mice

Adrenomedullin (AM) is a multifunctional peptide vasodilator that is essential for life. Plasma AM expression dramatically increases during pregnancy, and alterations in its levels are associated with complications of pregnancy including fetal growth restriction (FGR) and preeclampsia. Using AM+/- female mice with genetically reduced AM expression, we demonstrate that fetal growth and placental development are seriously compromised by this modest decrease in expression. AM+/- female mice had reduced fertility characterized by FGR. The incidence of FGR was also influenced by the genotype of the embryo, since AM-/- embryos were more often affected than either AM+/- or AM+/+ embryos. We demonstrate that fetal trophoblast cells and the maternal uterine wall have coordinated and localized increases in AM gene expression at the time of implantation. Placentas from growth-restricted embryos showed defects in trophoblast cell invasion, similar to defects that underlie human preeclampsia and placenta accreta. Our data provide a genetic in vivo model to implicate both maternal and, to a lesser extent, embryonic levels of AM in the processes of implantation, placentation, and subsequent fetal growth. This study provides the first genetic evidence to our knowledge to suggest that a modest reduction in human AM expression during pregnancy may have an unfavorable impact on reproduction.

Ovarian stimulation with GnRH agonist, but not GnRH antagonist, partially restores the expression of endometrial integrin 3 and leukaemia-inhibitory factor and improves uterine receptivity in mice

BACKGROUND

The impact of different ovarian stimulation (OS) protocols on endometrial receptivity remains controversial. In this study, the effects of different OS on the expression of endometrial integrin beta3 subunit and leukaemia-inhibitory factor (LIF) during the implantation window and the implantation rate in mice were investigated.

METHODS

Three OS protocols were used, involving either pregnant mare's serum gonadotrophin (PMSG) alone, PMSG plus GnRH agonist or PMSG plus GnRH antagonist. Uterus samples were collected at 48 h after OS or ovulation and were detected with immunohistochemistry, Western blot and RT-PCR analyses. Normal embryos at gestation day 4 were transferred into the uteri of mice in the control and OS groups.

RESULTS

All OS groups showed a significant decrease in the expression of both the endometrial integrin beta3 subunit and LIF during the implantation window and the implantation rate. Among the three OS groups, GnRH agonist-treated mice showed a higher endometrial integrin beta3 subunit and LIF expression and a higher implantation rate. No significant difference was found in the measured indices between the GnRH antagonist and PMSG groups.

CONCLUSIONS

OS may inhibit the expression of endometrial integrin beta3 subunit and LIF and impair endometrial receptivity in mice. OS with GnRH agonist, but not GnRH antagonist, may partially restore the endometrial physiological secretion and improve uterine receptivity.

Endometrial receptivity: Clinical assessment in relation to fertility, infertility, and antifertility

Fertility in humans and other mammalian species depends absolutely on synchronous events that render the developing blastocyst and the receiving uterus competent for implantation. Endometrial receptivity is defined as the period during which the endometrial epithelium acquires functional, but transient, ovarian steroid-dependent status supportive to blastocyst acceptance and implantation. Once inside the uterus, the blastocyst is surrounded by an intact luminal epithelium, which is considered to act as barrier to its attachment, except for this short period of high endometrial receptivity to blastocyst signal(s). Its transport and permeability properties, in conjunction with cellular action of the endometrium and the embryo, have been suggested to influence creation and maintenance of informational and nutritional status of uterine luminal milieu. This period, also termed as the 'window of implantation,' is limited to days 20-24 of menstrual cycle in humans. However, establishment of endometrial receptivity is still a biological mystery that remains unsolved despite marked advances in our understanding of endometrial physiology following extensive research associated with its development and function. This review deals with various structural, biochemical, and molecular events in the endometrium coordinated within the implantation window that constitute essential elements in the repertoire that signifies endometrial receptivity and is aimed to achieve a better understanding of its relationship to fertility, infertility, and for the development of targeted antifertility agents for human use and welfare.

Confinement and clearance of OCT4 in the porcine embryo at stereomicroscopically defined stages around gastrulation

In the areas of developmental biology and embryonic stem cell research, reliable molecular markers of pluripotency and early lineage commitment are sparse in large animal species. In this study, we present morphological and immunohistochemical findings on the porcine embryo in the period around gastrulation, days 8-17 postinsemination, introducing a stereomicroscopical staging system in this species. In embryos at the expanding hatched blastocyst stage, OCT4 is confined to the inner cell mass. Following detachment of the hypoblast, and formation of the embryonic disk, this marker of pluripotency was selectively observed in the epiblast. A prominent crescent-shaped thickening at the posterior region of the embryonic disk marked the first polarization within this structure reflecting incipient cell ingression. Following differentiation of the epiblast, clearance of OCT4 from the three germ layers was observed at defined stages, suggesting correlations to lineage specification. In the endoderm, clearance of OCT4 was apparent from early during its formation at the primitive streak stage. The endoderm harbored progenitors of the "fourth germ layer," the primordial germ cells (PGCs), the only cells maintaining expression of OCT4 at the end of gastrulation. In the ectodermal and mesodermal cell lineages, OCT4 became undetectable at the neural groove and somite stage, respectively. As in the mouse, PGCs showed onset of c-kit expression when located in extraembryonal compartments. They appeared to follow the endoderm during extraembryonal allocation and the mesoderm on return to the genital ridge.

Roles of LPA3 and COX-2 in implantation

Lysophosphatidic acid (LPA) is a lipid-derived G-protein-coupled receptor (GPCR) agonist that is involved in a variety of physiological and pathological processes, including cell survival, proliferation and differentiation, cytoskeletal rearrangement, cell-cell interactions, tumorigenesis and cell invasion. LPA also stimulates oocyte maturation, the preimplantation development of two- or four-cell embryos to the blastocyst stage and embryo transport in the oviduct. Recent studies revealed that targeted deletion of the LPA(3) receptor results in delayed implantation and altered embryo spacing, and significantly reduced litter size in mice. This was attributable to selective downregulation of uterine cyclooxygenase-2 (COX-2), which generates prostaglandins (PGs) E(2) and I(2). Exogenous administration of PGE(2) or the PGI(2) analogue, carba-prostacyclin, to LPA(3)-deficient female mice rescued delayed implantation but did not prevent defects in embryo spacing. These findings indicate that LPA-induced COX-2 induction has a crucial role in implantation and mammalian reproduction.

System B0,+ amino acid transport regulates the penetration stage of blastocyst implantation with possible long-term developmental consequences through adulthood

Amino acid transport system B(0,+) was first characterized in detail in mouse blastocysts over two decades ago. Since then, this system has been shown to be involved in a wide array of developmental processes from blastocyst implantation in the uterus to adult obesity. Leucine uptake through system B(0,+) in blastocysts triggers mammalian target of rapamycin (mTOR) signalling. This signalling pathway selectively regulates development of trophoblast motility and the onset of the penetration stage of blastocyst implantation about 20 h later. Meanwhile, system B(0,+) becomes inactive in blastocysts a few hours before implantation in vivo. System B(0,+) can, however, be activated in preimplantation blastocysts by physical stimuli. The onset of trophoblast motility should provide the physiological physical stimulus activating system B(0,+) in blastocysts in vivo. Activation of system B(0,+) when trophoblast cells begin to penetrate the uterine epithelium would cause it to accumulate its preferred substrates, which include tryptophan, from uterine secretions. A low tryptophan concentration in external secretions next to trophoblast cells inhibits T-cell proliferation and rejection of the conceptus. Suboptimal system B(0,+) regulation of these developmental processes likely influences placentation and subsequent embryo nutrition, birth weight and risk of developing metabolic syndrome and obesity.

An emerging role for comprehensive proteome analysis in human pregnancy research

Elucidation of underlying cellular and molecular mechanisms is pivotal to the comprehension of biological systems. The successful progression of processes such as pregnancy and parturition depends on the complex interactions between numerous biological molecules especially within the uterine microenvironment. The tissue- and stage-specific expression of these bio-molecules is intricately linked to and modulated by several endogenous and exogenous factors. Malfunctions may manifest as pregnancy disorders such as preterm labour, pre-eclampsia and fetal growth restriction that are major contributors to maternal and perinatal morbidity and mortality. Despite the immense amount of information available, our understanding of several aspects of these physiological processes remains incomplete. This translates into significant difficulties in the timely diagnosis and effective treatment of pregnancy-related complications. However, the emergence of powerful mass spectrometry-based proteomic techniques capable of identifying and characterizing multiple proteins simultaneously has added a new dimension to the field of biomedical research. Application of these high throughput methodologies with more conventional techniques in pregnancy-related research has begun to provide a novel perspective on the biochemical blueprint of pregnancy and its related disorders. Further, by enabling the identification of proteins specific to a disease process, proteomics is likely to contribute, not only to the comprehension of the underlying pathophysiologies, but also to the clinical diagnosis of multifactorial pregnancy disorders. Although the application of this technology to pregnancy research is in its infancy, characterization of the cellular proteome, unearthing of functional networks and the identification of disease biomarkers can be expected to significantly improve maternal healthcare in the future.