Mining the mouse transcriptome of receptive endometrium reveals distinct molecular signatures for the luminal and glandular epithelium

A refined method for high-purity isolation of uterine glandular epithelial cells in mouse

The uterine endometrium consists of luminal epithelium, glandular epithelium and stromal cells, with uterine glands playing a pivotal role in pregnancy success among mammals. Uterine glands secrete essential factors that regulate embryo development and implantation; however, their cellular biology remains poorly understood. This study presents a refined method for isolating three distinct endometrial cell types with high purity, with a specific emphasis on glandular epithelial (GE) cells. The method combines mechanical dissociation, enzymatic digestion and immunomagnetic separation. The isolated GE cells were maintained in culture and exhibited proliferation in response to steroid hormones. Furthermore, oestrogen responsiveness was abrogated by Estrogen Receptor 1 (Esr1) knockdown mediated by siRNA. Here, we present an efficient and reproducible method for isolating uterine GE cells with high purity, enabling their in vitro maintenance, hormone responsiveness assessment and functional gene knockdown. These findings establish a robust platform for advancing our understanding of uterine gland biology, facilitating detailed investigations into molecular mechanisms underlying glandular function and their critical roles in establishing pregnancy success. Future research could explore the contribution of these isolated cells to endometrial receptivity and embryo implantation.

Single-cell insights into epithelial morphogenesis in the neonatal mouse uterus

The uterus is vital for successful reproduction in mammals, and two different types of epithelia (luminal and glandular) are essential for embryo implantation and pregnancy establishment. However, the essential cellular and molecular factors and pathways governing postnatal epithelium maturation, determination, and differentiation in developing uterus are yet to be elucidated. Here, the epithelium of the neonatal mouse uterus was isolated and subjected to single-cell transcriptome (scRNA-seq) analysis. Both the undifferentiated epithelium and determined luminal epithelium were heterogeneous and contained several different cell clusters based on single-cell transcription profiles. Substantial gene expression differences were evident as the epithelium matured and differentiated between postnatal days 1 to 15. Two new glandular epithelium-expressed genes (Gas6 and Cited4) were identified and validated by in situ hybridization. Trajectory analyses provided a framework for understanding epithelium maturation, lineage bifurcation, and differentiation. A candidate set of transcription factors and gene regulatory networks were identified that potentially direct epithelium lineage specification and morphogenesis. This atlas provides a foundation important to discover intrinsic cellular and molecular mechanisms directing uterine epithelium morphogenesis during a critical window of postnatal development.

The endometrial transcriptome transition preceding receptivity to embryo implantation in mice

BACKGROUND

Receptivity of the uterus is essential for embryo implantation and progression of mammalian pregnancy. Acquisition of receptivity involves major molecular and cellular changes in the endometrial lining of the uterus from a non-receptive state at ovulation, to a receptive state several days later. The precise molecular mechanisms underlying this transition and their upstream regulators remain to be fully characterized. Here, we aimed to generate a comprehensive profile of the endometrial transcriptome in the peri-ovulatory and peri-implantation states, to define the genes and gene pathways that are different between these states, and to identify new candidate upstream regulators of this transition, in the mouse.

RESULTS

High throughput RNA-sequencing was utilized to identify genes and pathways expressed in the endometrium of female C57Bl/6 mice at estrus and on day 3.5 post-coitum (pc) after mating with BALB/c males (n = 3-4 biological replicates). Compared to the endometrium at estrus, 388 genes were considered differentially expressed in the endometrium on day 3.5 post-coitum. The transcriptional changes indicated substantial modulation of uterine immune and vascular systems during the pre-implantation phase, with the functional terms Angiogenesis, Chemotaxis, and Lymphangiogenesis predominating. Ingenuity Pathway Analysis software predicted the activation of several upstream regulators previously shown to be involved in the transition to receptivity including various cytokines, ovarian steroid hormones, prostaglandin E2, and vascular endothelial growth factor A. Our analysis also revealed four candidate upstream regulators that have not previously been implicated in the acquisition of uterine receptivity, with growth differentiation factor 2, lysine acetyltransferase 6 A, and N-6 adenine-specific DNA methyltransferase 1 predicted to be activated, and peptidylprolyl isomerase F predicted to be inhibited.

CONCLUSIONS

This study confirms that the transcriptome of a receptive uterus is vastly different to the non-receptive uterus and identifies several genes, regulatory pathways, and upstream drivers not previously associated with implantation. The findings will inform further research to investigate the molecular mechanisms of uterine receptivity.

Prss29 Cre recombinase mice are useful to study adult uterine gland function

All mammalian uteri contain glands in their endometrium that develop only or primarily after birth. In mice, those endometrial glands govern post implantation pregnancy establishment via regulation of blastocyst implantation, stromal cell decidualization, and placental development. Here, we describe a new uterine glandular epithelium (GE) specific Cre recombinase mouse line that is useful for the study of uterine gland function during pregnancy. Utilizing CRISPR-Cas9 genome editing, Cre recombinase was inserted into the endogenous serine protease 29 precursor (Prss29) gene. Both Prss29 mRNA and Cre recombinase activity was specific to the GE of the mouse uterus following implantation, but was absent from other areas of the female reproductive tract. Next, Prss29-Cre mice were crossed with floxed forkhead box A2 (Foxa2) mice to conditionally delete Foxa2 specifically in the endometrial glands. Foxa2 was absent in the glands of the post-implantation uterus, and Foxa2 deleted mice exhibited complete infertility after their first pregnancy. These results establish that Prss29-Cre mice are a valuable resource to elucidate and explore the functions of glands in the adult uterus.

Amino acids activate mTORC1 to release roe deer embryos from decelerated proliferation during diapause

In mammals, embryo development can halt at the hatched blastocyst stage. Uniquely, proliferation of diapausing embryonic roe deer cells decelerates to a doubling time of 2 to 3 wk over a period of 4 mo. We highlight nutrient sensing as an important factor regulating embryonic developmental pace. The resumption of embryo development is characterized by an increase in uterine fluid mTORC1-activating amino acids, embryonic mTORC1 activity, and expression of metabolism and cell cycle genes. We propose selective mTORC1 inhibition via reduced estrogen signaling and high let-7 levels as mechanisms for slow cell cycle progression. We hypothesize that it is the lack of embryonic mTORC2 inhibition during embryonic diapause in the roe deer that enables the continuous decelerated rate of proliferation.

Embryonic diapause in mammals leads to a reversible developmental arrest. While completely halted in many species, European roe deer (Capreolus capreolus) embryos display a continuous deceleration of proliferation. During a 4-mo period, the cell doubling time is 2 to 3 wk. During this period, the preimplantation blastocyst reaches a diameter of 4 mm, after which it resumes a fast developmental pace to subsequently implant. The mechanisms regulating this notable deceleration and reacceleration upon developmental resumption are unclear. We propose that amino acids of maternal origin drive the embryonic developmental pace. A pronounced change in the abundance of uterine fluid mTORC1-activating amino acids coincided with an increase in embryonic mTORC1 activity prior to the resumption of development. Concurrently, genes related to the glycolytic and phosphate pentose pathway, the TCA cycle, and one carbon metabolism were up-regulated. Furthermore, the uterine luminal epithelial transcriptome indicated increased estradiol-17β signaling, which likely regulates the endometrial secretions adapting to the embryonic needs. While mTORC1 was predicted to be inactive during diapause, the residual embryonic mTORC2 activity may indicate its involvement in maintaining the low yet continuous proliferation rate during diapause. Collectively, we emphasize the role of nutrient signaling in preimplantation embryo development. We propose selective mTORC1 inhibition via uterine catecholestrogens and let-7 as a mechanism regulating slow stem cell cycle progression.

Spatial Transcriptomics analysis of uterine gene expression in enhancer of Zeste homolog 2 (Ezh2) conditional knockout mice

Histone proteins undergo various modifications that alter chromatin structure, including addition of methyl groups. Enhancer of homolog 2 (EZH2), is a histone methyltransferase that methylates lysine residue 27, and thereby, suppresses gene expression. EZH2 plays integral role in the uterus and other reproductive organs. We have previously shown that conditional deletion of uterine EZH2 results in increased proliferation of luminal and glandular epithelial cells, and RNAseq analyses reveal several uterine transcriptomic changes in Ezh2 conditional (c) knockout (KO) mice that can affect estrogen signaling pathways. To pinpoint the origin of such gene expression changes, we used the recently developed spatial transcriptomics (ST) method with the hypotheses that Ezh2cKO mice would predominantly demonstrate changes in epithelial cells and/or ablation of this gene would disrupt normal epithelial/stromal gene expression patterns. Uteri were collected from ovariectomized adult WT and Ezh2cKO mice and analyzed by ST. Asb4, Cxcl14, Dio2, and Igfbp5 were increased, Sult1d1, Mt3, and Lcn2 were reduced in Ezh2cKO uterine epithelium vs. WT epithelium. For Ezh2cKO uterine stroma, differentially expressed key hub genes included Cald1, Fbln1, Myh11, Acta2, and Tagln. Conditional loss of uterine Ezh2 also appears to shift the balance of gene expression profiles in epithelial vs. stromal tissue toward uterine epithelial cell and gland development and proliferation, consistent with uterine gland hyperplasia in these mice. Current findings provide further insight into how EZH2 may selectively affect uterine epithelial and stromal compartments. Additionally, these transcriptome data might provide the mechanistic understanding and valuable biomarkers for human endometrial disorders with epigenetic underpinnings.

Analysis of the transcriptome of bovine endometrial cells isolated by laser micro-dissection (2): impacts of post-partum negative energy balance on stromal, glandular and luminal epithelial cells

BACKGROUND

In post-partum dairy cows, the energy needs to satisfy high milk production induces a status of more or less pronounced Negative Energy Balance (NEB). NEB associated with fat mobilization impairs reproductive function. In a companion paper, we described constitutive gene expression in the three main endometrial cell types (stromal, glandular and luminal epithelial cells) isolated by laser capture micro-dissection (LCM) showing the specificities of their transcriptomic profiles. This study investigates the specific impact of NEB on gene expression in these cells around 80 days after parturition at day 15 of the oestrus cycle and describes their specific response to NEB.

RESULTS

Following the description of their constitutive expression, the transcriptome profiles obtained by RNA sequencing of the three cells types revealed that differences related to the severity of NEB altered mainly specific patterns of expression related to individual cell types. Number of differentially expressed genes between severe NEB (SNEB) and mild NEB (MNEB) cows was higher in ST than in LE and GE, respectively. SNEB was associated with differential expression of genes coding for proteins involved in metabolic processes and embryo-maternal interactions in ST. Under-expression of genes encoding proteins with functions related to cell structure was found in GE whereas genes encoding proteins participating in pro-inflammatory pathways were over-expressed. Genes associated to adaptive immunity were under-expressed in LE.

CONCLUSION

The severity of NEB after calving is associated with changes in gene expression around 80 days after parturition corresponding to the time of breeding. Specific alterations in GEs are associated with activation of pro-inflammatory mechanisms. Concomitantly, changes in the expression of genes encoding proteins involved in cell interactions and maternal recognition of pregnancy takes place in ST. The combination of these effects possibly altering the uterine environment and embryo maternal interactions may negatively influence the establishment of pregnancy.

Analysis of the transcriptome of bovine endometrial cells isolated by laser micro-dissection (1): specific signatures of stromal, glandular and luminal epithelial cells

BACKGROUND

A number of studies have examined mRNA expression profiles of bovine endometrium at estrus and around the peri-implantation period of pregnancy. However, to date, these studies have been performed on the whole endometrium which is a complex tissue. Consequently, the knowledge of cell-specific gene expression, when analysis performed with whole endometrium, is still weak and obviously limits the relevance of the results of gene expression studies. Thus, the aim of this study was to characterize specific transcriptome of the three main cell-types of the bovine endometrium at day-15 of the estrus cycle.

RESULTS

In the RNA-Seq analysis, the number of expressed genes detected over 10 transcripts per million was 6622, 7814 and 8242 for LE, GE and ST respectively. ST expressed exclusively 1236 genes while only 551 transcripts were specific to the GE and 330 specific to LE. For ST, over-represented biological processes included many regulation processes and response to stimulus, cell communication and cell adhesion, extracellular matrix organization as well as developmental process. For GE, cilium organization, cilium movement, protein localization to cilium and microtubule-based process were the only four main biological processes enriched. For LE, over-represented biological processes were enzyme linked receptor protein signaling pathway, cell-substrate adhesion and circulatory system process.

CONCLUSION

The data show that each endometrial cell-type has a distinct molecular signature and provide a significantly improved overview on the biological process supported by specific cell-types. The most interesting result is that stromal cells express more genes than the two epithelial types and are associated with a greater number of pathways and ontology terms.

Uterine infection alters the transcriptome of the bovine reproductive tract three months later

Infection of the postpartum uterus with pathogenic bacteria is associated with infertility months later in dairy cattle. However, it is unclear whether these bacterial infections lead to long-term changes in the reproductive tract that might help explain this infertility. Here we tested the hypothesis that infusion of pathogenic bacteria into the uterus leads to changes in the transcriptome of the reproductive tract 3 months later. We used virgin Holstein heifers to avoid potential confounding effects of periparturient problems, lactation, and negative energy balance. Animals were infused intrauterine with endometrial pathogenic bacteria Escherichia coli and Trueperella pyogenes (n = 4) and compared with control animals (n = 6). Three months after infusion, caruncular and intercaruncular endometrium, isthmus and ampulla of the oviduct, and granulosa cells from ovarian follicles >8 mm diameter were profiled by RNA sequencing. Bacterial infusion altered the transcriptome of all the tissues when compared with control. Most differentially expressed genes were tissue specific, with 109 differentially expressed genes unique to caruncular endometrium, 57 in intercaruncular endometrium, 65 in isthmus, 298 in ampulla, and 83 in granulosa cells. Surprisingly, despite infusing bacteria into the uterus, granulosa cells had more predicted upstream regulators of differentially expressed genes than all the other tissues combined. In conclusion, there were changes in the transcriptome of the endometrium, oviduct and even granulosa cells, 3 months after intrauterine infusion of pathogenic bacteria. These findings imply that long-term changes throughout the reproductive tract could contribute to infertility after bacterial infections of the uterus.

Differential Signals From TNFα-Treated and Untreated Embryos in Uterine Tissues and Splenic CD4+ T Lymphocytes During Preimplantation Pregnancy in Mice

The main aim of this study was to examine if a female mouse body in preimplantation pregnancy can distinguish between embryos of normal and impaired biological quality in the local and peripheral compartments. Normal (control group) and TNFα (tumor necrosis factor-α)-treated embryos (experimental group) at the morula stage were non-surgically transferred into the uteri of CD-1 strain [Crl:CD1(Icr)] female murine recipients. Twenty-four hours after the embryo transfer, females were euthanised, and uteri and spleens were dissected. In uterine tissues (local compartment), we assessed the expression of 84 genes comprising nine signal transduction pathways, using a modified RT² Profiler PCR Array. In the spleen (peripheral compartment), we determined the proteome of splenic CD4⁺ lymphocytes using 2D protein electrophoresis with subsequent protein identification by mass spectrometry. Sample clustering and differential gene expression analyses within individual signal transduction pathways revealed differential expression of genes in the uteri of females after transplantation of normal vs. TNFα-treated embryos. The most affected signal transduction cascade was the NFKB (Nuclear factor NF-kappa-B) pathway, where 87.5% of the examined genes were significantly differentially expressed. Proteomic analysis of splenic CD4⁺ T lymphocytes revealed significant differential expression of 8 out of 132 protein spots. Identified proteins were classified as proteins influenced by cell stress, proteins engaged in the regulation of cytoskeleton stabilization and cell motility, and proteins having immunomodulatory function. These results support the hypothesis that even before embryo implantation, the body of pregnant female mice can sense the biological quality of an embryo both at the local and peripheral level.

Endometrial luminal epithelial cells sense embryo elongation in the roe deer independent of interferon-tau†

Numerous intrauterine changes take place across species during embryo development. Following fertilization in July/August, the European roe deer (Capreolus capreolus) embryo undergoes diapause until embryonic elongation in December/January. Embryonic elongation prior to implantation is a common feature among ungulates. Unlike many other ruminants, the roe deer embryo does not secrete interferon-tau (IFNτ). This provides the unique opportunity to unravel IFNτ-independent signaling pathways associated with maternal recognition of pregnancy (MRP). This study aimed at identifying the cell-type-specific endometrial gene expression changes associated with the MRP at the time of embryo elongation that are independent of IFNτ in roe deer. The messenger RNA (mRNA) expression of genes known to be involved in embryo-maternal communication in cattle, pig, sheep, and mice was analyzed in laser capture microdissected (LMD) endometrial luminal, glandular epithelial, as well as stromal cells. The mRNA transcript abundances of the estrogen (ESR1), progesterone receptor (PGR), and IFNτ-stimulated genes were lower in the luminal epithelium in the presence of an elongated embryo compared to diapause. Retinol Binding Protein-4 (RBP4), a key factor involved in placentation, was more abundant in the luminal epithelium in the presence of an elongated embryo. The progesterone receptor localization was visualized by immunohistochemistry, showing an absence in the luminal epithelium and an overall lower abundance with time and thus prolonged progesterone exposure. Our data show a developmental stage-specific mRNA expression pattern in the luminal epithelium, indicating that these cells sense the presence of an elongated embryo in an IFNτ-independent manner.

Embryonic diapause in roe deer: A model to unravel embryo-maternal communication during pre-implantation development in wildlife and livestock species

An alarming number of large mammalian species with low reproduction rates is threatened with extinction. As basic knowledge of reproductive physiology is currently lacking in many species, increasing the understanding of reproductive physiology is imperative and includes the development of novel artificial reproduction technologies. Despite the relatively comprehensive knowledge on molecular mechanisms underlying reproduction in livestock species such as cattle, pregnancy failures are likewise far from understood. Contrary to other wildlife species, the European roe deer (Capreolus capreolus) displays a remarkably high pregnancy rate. In parts, cattle and roe deer exhibit comparable features of preimplantation embryo development. Therefore, understanding the high fertility rate in the roe deer holds a great potential for cross-species knowledge gain. As the only known species among the artiodactylae, the roe deer displays a long period of embryonic diapause. The preimplantation blastocyst reaches a diameter of 1 mm only at around 4 months compared to around 13 days post estrus in cattle. The expanded blastocyst survives in a uterine microenvironment that contains a unique set of yet unidentified factors that allow embryonic stem cells to proliferate at low pace without impairing their developmental potential. Upon reactivation, intimate embryo-maternal communication comparable to those reported in cattle is thought to occur. In this review, current knowledge, parallels and differences of reproductive physiology in cattle and roe deer are reviewed. The roe deer is proposed as a unique model species to (1) enhance our knowledge of fertility processes, (2) define factors that support embryo survival for an extended period, (3) advance knowledge on embryonic stem cells, and (4) unravel potential implications for the development of novel strategies for artificial reproductive technologies.

Cell type-specific endometrial transcriptome changes during initial recognition of pregnancy in the mare

Previous endometrial gene expression studies during the time of conceptus migration did not provide final conclusions on the mechanisms of maternal recognition of pregnancy (MRP) in the mare. This called for a cell type-specific endometrial gene expression analysis in response to embryo signals to improve the understanding of gene expression regulation in the context of MRP. Laser capture microdissection was used to collect luminal epithelium (LE), glandular epithelium and stroma from endometrial biopsies from Day 12 of pregnancy and Day 12 of the oestrous cycle. RNA sequencing (RNA-Seq) showed greater expression differences between cell types than between pregnant and cyclic states; differences between the pregnant and cyclic states were mainly found in LE. Comparison with a previous RNA-Seq dataset for whole biopsy samples revealed the specific origin of gene expression differences. Furthermore, genes specifically differentially expressed (DE) in one cell type were found that were not detectable as DE in biopsies. Overall, this study revealed spatial information about endometrial gene expression during the phase of initial MRP. The conceptus induced changes in the expression of genes involved in blood vessel development, specific spatial regulation of the immune system, growth factors, regulation of prostaglandin synthesis, transport prostaglandin receptors, specifically prostaglandin F receptor (PTGFR) in the context of prevention of luteolysis.

Spatial organization of endometrial gene expression at the onset of embryo attachment in pigs

BACKGROUND

During the preimplantation phase in the pig, the conceptus trophoblast elongates into a filamentous form and secretes estrogens, interleukin 1 beta 2, interferons, and other signaling molecules before attaching to the uterine epithelium. The processes in the uterine endometrium in response to conceptus signaling are complex. Thus, the objective of this study was to characterize transcriptome changes in porcine endometrium during the time of conceptus attachment considering the specific localization in different endometrial cell types.

RESULTS

Low-input RNA-sequencing was conducted for the main endometrial compartments, luminal epithelium (LE), glandular epithelium (GE), blood vessels (BV), and stroma. Samples were isolated from endometria collected on Day 14 of pregnancy and the estrous cycle (each group n = 4) by laser capture microdissection. The expression of 12,000, 11,903, 11,094, and 11,933 genes was detectable in LE, GE, BV, and stroma, respectively. Differential expression analysis was performed between the pregnant and cyclic group for each cell type as well as for a corresponding dataset for complete endometrium tissue samples. The highest number of differentially expressed genes (DEGs) was found for LE (1410) compared to GE, BV, and stroma (800, 1216, and 384). For the complete tissue, 3262 DEGs were obtained. The DEGs were assigned to Gene Ontology (GO) terms to find overrepresented functional categories and pathways specific for the individual endometrial compartments. GO classification revealed that DEGs in LE were involved in 'biosynthetic processes', 'related to ion transport', and 'apoptotic processes', whereas 'cell migration', 'cell growth', 'signaling', and 'metabolic/biosynthetic processes' categories were enriched for GE. For blood vessels, categories such as 'focal adhesion', 'actin cytoskeleton', 'cell junction', 'cell differentiation and development' were found as overrepresented, while for stromal samples, most DEGs were assigned to 'extracellular matrix', 'gap junction', and 'ER to Golgi vesicles'.

CONCLUSIONS

The localization of differential gene expression to different endometrial cell types provided a significantly improved view on the regulation of biological processes involved in conceptus implantation, such as the control of uterine fluid secretion, trophoblast attachment, growth regulation by Wnt signaling and other signaling pathways, as well as the modulation of the maternal immune system.

Uterine Glands: Developmental Biology and Functional Roles in Pregnancy

All mammalian uteri contain glands in the endometrium that develop only or primarily after birth. Gland development or adenogenesis in the postnatal uterus is intrinsically regulated by proliferation, cell-cell interactions, growth factors and their inhibitors, as well as transcription factors, including forkhead box A2 (FOXA2) and estrogen receptor α (ESR1). Extrinsic factors regulating adenogenesis originate from other organs, including the ovary, pituitary, and mammary gland. The infertility and recurrent pregnancy loss observed in uterine gland knockout sheep and mouse models support a primary role for secretions and products of the glands in pregnancy success. Recent studies in mice revealed that uterine glandular epithelia govern postimplantation pregnancy establishment through effects on stromal cell decidualization and placental development. In humans, uterine glands and, by inference, their secretions and products are hypothesized to be critical for blastocyst survival and implantation as well as embryo and placental development during the first trimester before the onset of fetal-maternal circulation. A variety of hormones and other factors from the ovary, placenta, and stromal cells impact secretory function of the uterine glands during pregnancy. This review summarizes new information related to the developmental biology of uterine glands and discusses novel perspectives on their functional roles in pregnancy establishment and success.

Cell type-specific analysis of transcriptome changes in the porcine endometrium on Day 12 of pregnancy

BACKGROUND

Along with trophoblast elongation (Days 10 to 12), estradiol is secreted in increasing amounts for recognition of pregnancy. Endometrial secretions driven by ovarian progesterone and conceptus signals are essential for conceptus growth and development. Results of transcriptome analyses of whole endometrial tissue samples in the pig indicated the need for cell type-specific endometrial gene expression analysis for a better understanding of transcriptome changes associated with establishment of pregnancy.

RESULTS

The most distinct transcriptome profile and the majority of differentially expressed genes (DEGs) were identified in luminal epithelium (LE). Many DEGs were found only in the cell type-specific analysis. The functional classification of DEGs identified in specific endometrial cell types revealed various distinct functions and pathways. Genes related to immune activation, estrogen signaling pathway, embryo development, and cell proliferation were upregulated in LE of pregnant gilts. Genes involved in sterol biosynthetic and metabolic processes and extracellular matrix were upregulated in stroma. Genes associated with cell communication such as via exosomes and vesicles were found as differential in LE, glandular epithelium (GE), and stroma (S).

CONCLUSIONS

This study revealed that conceptus signals induce different transcriptomic regulations in the endometrial compartments/cell types related to their specific function during recognition and establishment of pregnancy.

Identifying stably expressed housekeeping genes in the endometrium of fertile women, women with recurrent implantation failure and recurrent miscarriages

Housekeeping genes (HKG) are presumed to be constitutively expressed throughout tissue types but recent studies have shown they vary with pathophysiology. Often, validation of appropriate HKG is not made. There is no consensus on which HKGs are most stably expressed in endometrial tissue so this study aimed to identify the most stable HKG in the endometrium of women with recurrent implantation failure (RIF) and recurrent miscarriages (RM). Inclusion criteria were women between 25-45 years (n = 45) suffering recurrent miscarriage (RM), recurrent implantation failure (RIF) or fertile controls. Endometrial biopsies were taken and total RNA extraction, cDNA synthesis and PCR was performed using 10 candidate HKG. The genes were arranged in terms of stability and normalisation was determined. Several HKGs not previously tested in endometrial samples were found to be more stable than those previously identified as the most stable. Of these, the 5 most stable HKG (in order of stability) were Prdm4 (PR domain 4) > Ube4a (Ubiquitin-Conjugating Enzyme 4a) > Enox2 (Ecto-NOX Disulfide-Thiol Exchanger 2) > Ube2d2 (Ubiquitin-conjugating enzyme E2D 2) > Actb (Actin beta). We therefore recommend using at least four of the aforementioned HKG for normalisation of endometrial tissues taken from patients with RM and RIF.

Age and Nursing Affect the Neonatal Porcine Uterine Transcriptome

The lactocrine hypothesis for maternal programming of neonatal development was proposed to describe a mechanism through which milk-borne bioactive factors, delivered from mother to nursing offspring, could affect development of tissues, including the uterus. Porcine uterine development, initiated before birth, is completed postnatally. However, age- and lactocrine-sensitive elements of the neonatal porcine uterine developmental program are undefined. Here, effects of age and nursing on the uterine transcriptome for 48 h from birth (Postnatal Day [PND] = 0) were identified using RNA sequencing (RNAseq). Uterine tissues were obtained from neonatal gilts (n = 4 per group) within 1 h of birth and before feeding (PND 0), or 48 h after nursing ad libitum (PND 2N) or feeding a commercial milk replacer (PND 2R). RNAseq analysis revealed differentially expressed genes (DEGs) associated with both age (PND 2N vs. PND 0; 3283 DEGs) and nursing on PND 2 (PND 2N vs PND 2R; 896 DEGs). Expression of selected uterine genes was validated using quantitative real-time PCR. Bioinformatic analyses revealed multiple biological processes enriched in response to both age and nursing, including cell adhesion, morphogenesis, and cell-cell signaling. Age-sensitive pathways also included estrogen receptor-alpha and hedgehog signaling cascades. Lactocrine-sensitive processes in nursed gilts included those involved in response to wounding, the plasminogen activator network and coagulation. Overall, RNAseq analysis revealed comprehensive age- and nursing-related transcriptomic differences in the neonatal porcine uterus and identified novel pathways and biological processes regulating uterine development.

Comparative analysis between endometrial proteomes of pregnant and non-pregnant ewes during the peri-implantation period

BACKGROUND

Early pregnancy failure has a profound impact on both human reproductive health and animal production. 2/3 pregnancy failures occur during the peri-implantation period; however, the underlying mechanism(s) remains unclear. Well-organized modification of the endometrium to a receptive state is critical to establish pregnancy. Aberrant endometrial modification during implantation is thought to be largely responsible for early pregnancy loss.

RESULT

In this study, using well-managed recipient ewes that received embryo transfer as model, we compared the endometrial proteome between pregnant and non-pregnant ewes during implantation period. After embryo transfer, recipients were assigned as pregnant or non-pregnant ewes according to the presence or absence of an elongated conceptus at Day 17 of pregnancy. By comparing the endometrial proteomic profiles between pregnant and non-pregnant ewes, we identified 94 and 257 differentially expressed proteins (DEPs) in the endometrial caruncular and intercaruncular areas, respectively. Functional analysis showed that the DEPs were mainly associated with immune response, nutrient transport and utilization, as well as proteasome-mediated proteolysis.

CONCLUSION

These analysis imply that dysfunction of these biological processes or pathways of DEP in the endometrium is highly associated with early pregnancy loss. In addition, many proteins that are essential for the establishment of pregnancy showed dysregulation in the endometrium of non-pregnant ewes. These proteins, as potential candidates, may contribute to early pregnancy loss.

Uterine glands: biological roles in conceptus implantation, uterine receptivity and decidualization

All mammalian uteri contain glands in the endometrium that synthesize or transport and secrete substances essential for survival and development of the conceptus (embryo/fetus and associated extraembryonic membranes). This review summarizes information related to the biological roles of uterine glands and their secretions in uterine receptivity, blastocyst/conceptus survival and implantation, and stromal cell decidualization. Studies with the ovine uterine gland knockout (UGKO) model support a primary role for uterine glands and, by inference, their secretions present in uterine luminal fluid histrotroph for conceptus survival and development. In rodents, studies with mutant and progesterone-induced UGKO mice found that uterine glands and their secretions are unequivocally required for establishment of uterine receptivity and blastocyst implantation and also may influence blastocyst trophectoderm activation and stromal cell decidualization in the uterus. Similarly in humans, histotroph from uterine glands appears critical for blastocyst implantation, uterine receptivity, and conceptus nutrition during the first trimester and uterine glands likely have a role in stromal cell decidualization. An increased understanding of uterine gland biology is important for diagnosis, prevention and treatment of fertility problems, particularly infertility and recurrent pregnancy loss, in domestic animals and humans.

Biological roles of uterine glands in pregnancy

All mammalian uteri contain glands in the endometrium that synthesize or transport and secrete substances essential for survival and development of the conceptus (embryo/fetus and associated extraembryonic membranes). This review summarizes information related to the biological roles of uterine glands and their secretions in blastocyst/conceptus survival and implantation, uterine receptivity, and stromal cell decidualization in humans and animal models. The infertility and recurrent pregnancy loss observed in the ovine uterine gland knockout (UGKO) model unequivocally supports a primary role for uterine glands and, by inference, their secretions present in uterine luminal fluid in survival and development of the conceptus. Further, studies with mutant and progesterone-induced UGKO mice found that uterine glands and their secretions are required for establishment of uterine receptivity and blastocyst implantation as well as stromal cell decidualization. Similarly in humans, uterine glands and their secretory products are likely critical regulators of blastocyst implantation, uterine receptivity, and conceptus growth and development during the first trimester. Circumstantial evidence suggests that deficient glandular activity may be a causative factor in pregnancy failure and complications in humans. Thus, an increased understanding of uterine gland biology is important for diagnosis, prevention, and treatment of fertility and pregnancy problems in mammals.

In the secretory endometria of women, luminal epithelia exhibit gene and protein expressions that differ from those of glandular epithelia

OBJECTIVE

To characterize the transcriptome of luminal epithelia (LE) of fertile secretory endometria and compare the results with those from glandular epithelia (GE).

DESIGN

Endometrial samples were collected at 2 and 7 days after initial blood LH surge in separate menstrual cycles. LE were obtained with the use of laser microdissection. mRNA was amplified with the use of linear polymerase chain reaction and hybridized to Agilent 4×44 microarrays. Gene analysis was used to identify differentially expressed mRNAs. Immunohistochemistry was used to assess nine proteins.

SETTING

One IVF clinic.

PATIENT(S)

Seven Caucasian fertile cycling women.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Cycle dating with the use of blood endocrinologic markers, microarrays of laser-microdissected LE, immunohistochemical analysis.

RESULT(S)

One hundred sixty-one (of 401) differentially expressed mRNAs in LE were identified from the metabolism pathway. Increased selective protein expression in LE at 7 days after initial LH surge was observed. LE mRNA expression was the converse of that in GE. The two cell types each had a different significant biologic pathway identified.

CONCLUSION(S)

Our results introduce a new concept that LE differentially expressed mRNAs are in the converse direction to that of GE, indicating different biologic processes despite the GE being continuous with the luminal monolayer. This probable distinction of biologic roles has not been noted previously. Further investigations must take cognizance of this observation.

Cell-specific transcriptional profiling reveals candidate mechanisms regulating development and function of uterine epithelia in mice

All mammalian uteri have luminal (LE) and glandular epithelia (GE) in their endometrium. The LE mediates uterine receptivity and blastocyst attachment for implantation, and the GE synthesize and secrete or transport bioactive substances involved in blastocyst implantation, uterine receptivity, and stromal cell decidualization. However, the mechanisms governing uterine epithelial development after birth and their function in the adult are not fully understood. Here, comprehensive microarray analysis was conducted on LE and GE isolated by laser capture microdissection from uteri on Postnatal Day 10 (PD 10) and day of pseudopregnancy (DOPP) 2.5 and 3.5. This data was integrated with analysis of uteri from gland-containing control and aglandular progesterone-induced uterine gland knockout mice from PD 10 and DOPP 3.5. Many genes were expressed in both epithelia, but there was greater expression of genes in the LE than in the GE. In the neonate, GE-expressed genes were enriched for morphogenesis, development, migration, and retinoic acid signaling. In the adult, LE-expressed genes were enriched for metabolic processes and steroid biosynthesis, whereas retinoid signaling, tight junction, extracellular matrix, and regulation of kinase activity were enriched in the GE. The transcriptome differences in the epithelia support the idea that each cell type has a distinct and complementary function in the uterus. The candidate genes and regulatory networks identified here provide a framework to discover new mechanisms regulating development of epithelia in the postnatal uterus and their functions in early pregnancy.

Comparative analysis of proteomic profiles between endometrial caruncular and intercaruncular areas in ewes during the peri-implantation period

The endometrium of sheep consists of plenty of raised aglandular areas called caruncular (C), and intensely glandular intercaruncular areas (IC). In order to better understand the endometrium involved mechanisms of implantation, we used LC-MS/MS technique to profile the proteome of ovine endometrial C areas and IC areas separately during the peri-implantation period, and then compared the proteomic profiles between these two areas. We successfully detected 1740 and 1813 proteins in C areas and IC areas respectively. By comparing the proteome of these two areas, we found 170 differentially expressed proteins (DEPs) (P < 0.05), functional bioinformatics analysis showed these DEPs were mainly involved in growth and remodeling of endometrial tissue, cell adhesion and protein transport, and so on. Our study, for the first time, provided a proteomic reference for elucidating the differences between C and IC areas, as an integrated function unit respectively, during the peri-implantation period. The results could help us to better understand the implantation in the ewes. In addition, we established a relatively detailed protein database of ovine endometrium, which provide a unique reference for further studies.

Integrated chromatin immunoprecipitation sequencing and microarray analysis identifies FOXA2 target genes in the glands of the mouse uterus

Uterine glands and their secretions are indispensable for endometrial function and fertility; however, the mechanisms regulating their development and function are not well understood. Forkhead transcription factor box A2 (FOXA2) is uniquely expressed in the glandular epithelial (GE) cells of the uterus, and conditional deletion of Foxa2 after birth impedes uterine gland development. An integrative approach was used here to define the FOXA2 cistrome in the murine uterus. Genome-wide mapping of FOXA2 binding sites was combined with transcriptomic analyses of isolated GE and Foxa2-deleted uteri. ChIP-Seq analyses found the number of FOXA2 target genes was substantially greater in the adult (8893) than neonatal uterus (1101). In the neonatal uterus, FOXA2-bound and GE-expressed genes (469) were enriched for developmentally related processes, including cell cycle, cell junction, focal adhesion, and WNT signaling. In the adult uterus, FOXA2-bound and GE-expressed genes (3730) were enriched for functional processes, including metabolic pathways, focal adhesion, bacterial invasion of epithelial cells, and WNT signaling. Analysis of the uterine FOXA2 cistrome provides novel insights into mechanisms governing endometrial gland development and function, which are important to understand fundamental aspects of uterine differentiation, regeneration and disease.

In-vitro model systems for the study of human embryo-endometrium interactions

Implantation requires highly orchestrated interactions between the developing embryo and maternal endometrium. The association between abnormal implantation and reproductive failure is evident, both in normal pregnancy and in assisted reproduction patients. Failure of implantation is the pregnancy rate-limiting step in assisted reproduction, but, as yet, empirical interventions have largely failed to address this problem. Better understanding of the mechanisms underlying human embryo-endometrium signalling is a prerequisite for the further improvement of assisted reproduction outcomes and the development of effective interventions to prevent early pregnancy loss. Studying human embryo implantation is challenging since in-vivo experiments are impractical and unethical, and studies in animal models do not always translate well to humans. However, in recent years in-vitro models have been shown to provide a promising way forward. This review discusses the principal models used to study early human embryo development and initial stages of implantation in vitro. While each model has limitations, exploiting these models will improve understanding of the molecular mechanisms and embryo-endometrium cross-talk at the early implantation site. They provide valuable tools to study early embryo development and pathophysiology of reproductive disorders and have revealed novel disease mechanisms such as the role of epigenetic modifications in recurrent miscarriage.

Differential gene expression profiling of mouse uterine luminal epithelium during periimplantation

Uterine luminal epithelium (LE) is critical for establishing uterine receptivity. Microarray analysis of gestation day 3.5 (D3.5, preimplantation) and D4.5 (postimplantation) LE from natural pregnant mice identified 382 upregulated and 245 downregulated genes in the D4.5 LE. Gene Ontology annotation grouped 186 upregulated and 103 downregulated genes into 22 and 15 enriched subcategories, respectively, in regulating DNA-dependent transcription, metabolism, cell morphology, ion transport, immune response, apoptosis, signal transduction, and so on. Signaling pathway analysis revealed 99 genes in 21 significantly changed signaling pathways, with 14 of these pathways involved in metabolism. In situ hybridization confirmed the temporal expression of 12 previously uncharacterized genes, including Atp6v0a4, Atp6v0d2, F3, Ggh, Tmprss11d, Tmprss13, Anpep, Fxyd4, Naip5, Npl, Nudt19, and Tpm1 in the periimplantation uterus. This study provides a comprehensive picture of the differentially expressed genes in the periimplantation LE to help understand the molecular mechanism of LE transformation upon establishment of uterine receptivity.

Endometrial glands are essential for blastocyst implantation and decidualization in the mouse uterus

Uterine glands and their secretions are hypothesized to be essential for blastocyst implantation and decidualization in the uterus of rodents and humans. One factor solely expressed by uterine glands in mice is leukemia inhibitory factor (LIF), and Lif null mice are infertile because of defective blastocyst attachment to the uterine luminal epithelium (LE). Progesterone treatment of neonatal mice permanently ablates differentiation of uterine glands, resulting in an aglandular uterus in the adult. Progesterone-induced uterine gland knockout (PUGKO) mice were used to investigate the biological role of uterine glands in blastocyst implantation and stromal cell decidualization. As compared to controls, PUGKO mice cycled normally but were infertile. Histological assessment of PUGKO uteri on Days 5.5 and 8.5 postmating found a hatched blastocyst apposed to an intact LE without evidence of implantation or stromal cell decidualization. Expression of several implantation-related factors, including Lif and PTGS2, were altered in the PUGKO uterus, whereas expression of steroid hormone receptors and their regulated genes was not different. Artificial decidualization was observed in the uteri of control but not PUGKO mice. Further, intrauterine administration of LIF failed to promote artificial decidualization in the uterus of PUGKO mice. Thus, uterine glands and their secretions have important biological roles in blastocyst implantation and stromal cell decidualization in the uterus.

Differential expression of Wnt signaling molecules between pre- and postmenopausal endometrial epithelial cells suggests a population of putative epithelial stem/progenitor cells reside in the basalis layer

The human endometrium undergoes extensive monthly regeneration in response to fluctuating levels of circulating estrogen and progesterone in premenopausal (Pre-M) women. In contrast, postmenopausal (Post-M) endometrium is thin and quiescent with low mitotic activity, similar to the Pre-M endometrial basalis layer. Clonogenic epithelial stem/progenitor (ESP) cells, likely responsible for regenerating endometrial epithelium, have been identified in Pre-M and Post-M endometrium, but their location is unknown. We undertook transcriptional profiling of highly purified epithelial cells from full-thickness Pre-M and Post-M endometrium to identify differentially regulated genes that may indicate a putative ESP cell population resides in the basalis of Pre-M and basalis-like Post-M endometrium. Of 1077 differentially expressed genes identified, the Wnt signaling pathway, important in endometrial development and stem cell regulation, was one of the main gene families detected, including 22 Wnt-associated genes. Twelve genes were validated using quantitative RT-PCR, and all were concordant with microarray data. Immunostaining showed glandular epithelial location of Wnt-regulated genes, Axin-related protein 2 and β-catenin. Axin2 localized to the nucleus of basalis Pre-M and Post-M and cytoplasm of functionalis Pre-M endometrium, suggesting that it regulates β-catenin. Comparison of our Post-M gene profile with published gene microarray datasets revealed similarities to Pre-M basalis epithelial profiles. This differential expression of multiple Wnt-associated genes in human Pre-M and Post-M endometrial epithelial cells and the similar gene profile of Post-M and Pre-M basalis epithelium suggests that a population of putative endometrial ESP may reside in the basalis of Pre-M endometrium, which may be responsible for regenerating glandular epithelium each month.

The genomics of the human endometrium

The endometrium is a complex tissue that lines the inside of the endometrial cavity. The gene expression of the different endometrial cell types is regulated by ovarian steroids and paracrine-secreted molecules from neighbouring cells. Due to this regulation, the endometrium goes through cyclic modifications which can be divided simply into the proliferative phase, the secretory phase and the menstrual phase. Successful embryo implantation depends on three factors: embryo quality, the endometrium's state of receptivity, and a synchronised dialogue between the maternal tissue and the blastocyst. There is a need to characterise the endometrium's state of receptivity in order to prevent reproductive failure. No single molecular or histological marker for this status has yet been found. Here, we review the global transcriptomic analyses performed in the last decade on a normal human endometrium. These studies provide us with a clue about what global gene expression can be expected for a non-pathological endometrium. These studies have shown endometrial phase-specific transcriptomic profiles and common temporal gene expression patterns. We summarise the biological processes and genes regulated in the different phases of natural cycles and present other works on different conditions as well as a receptivity diagnostic tool based on a specific gene set profile. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.

Gene and protein expression signature of endometrial glandular and stromal compartments during the window of implantation

OBJECTIVE

To map the changes in messenger RNA (mRNA) and protein abundance during the window of implantation in specifically endometrial stromal and glandular epithelial cells obtained using laser microdissection microscopy (LDM).

DESIGN

Endometrial samples were collected from two menstrual cycles at 2 and 7 days after first significant rise in blood LH, and separate cell populations were obtained using LDM. A new generation linear polymerase chain reaction (PCR) amplified the mRNA, which were hybridized to both Affymetrix U133 Plus2 and Agilent 4x44K microarrays followed by gene set analysis. Immunohistochemistry assessed protein expression between the two collection times.

SETTING

In vitro fertilization clinic.

PATIENT(S)

Nine Caucasian, fertile, cycling women.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Cycle dating using blood markers; microarrays on laser microdissected glands and stroma; dual platform microarray confirmation; immunohistochemical analysis of cell cycle proteins.

RESULT(S)

The two microarray platforms showed concordance. During the window of implantation, a statistically significant network of 22 mRNA associated with the cell cycle was down-regulated. Immunohistochemistry identified altered localization in stroma.

CONCLUSION(S)

Microarrays demonstrated glands and stroma have distinct mRNA signatures, each dependent on the day of the cycle. We characterized two compartments of the receptive endometrium with a transcriptomic signature identifying regulation of only the cell cycle. Immunohistochemical analysis of cell cycle proteins identified a signature staining pattern of nuclear relocalization of a group of cyclins of stromal cells, which may be clinically applicable.

Unique uterine localization and regulation may differentiate LPA3 from other lysophospholipid receptors for its role in embryo implantation

OBJECTIVE

To determine factors differentiating LPA3 from other lysophospholipid (LP) receptors for its role in embryo implantation.

DESIGN

Experimental mouse models.

SETTING

Institute/university research laboratories.

ANIMAL(S)

Wild-type, Lpar3(-/-), Lpar1(-/-)Lpar2(-/-), and S1pr2(-/-)S1pr3(-/-) mice.

INTERVENTION(S)

Ovariectomy.

MAIN OUTCOME MEASURE(S)

Blue dye injection for determining implantation sites on gestation day 4.5. Real-time polymerase chain reaction for measuring gene expression in whole uterus and separated uterine layers. In situ hybridization for detecting progesterone (P)-induced Lpar3 expression in the uterine luminal epithelium (LE).

RESULT(S)

Normal implantation was observed in Lpar1(-/-)Lpar2(-/-) and S1pr2(-/-)S1pr3(-/-) females. Temporal expression showed peak expression of Lpar3 in the preimplantation uterus and constitutive expression of the other nine LP receptors in the periimplantation uterus. Spatial localization revealed main expression of Lpar3 in the LE and broad expression of the remaining LP receptors in all three main uterine layers: LE, stromal, and myometrial layers. Hormonal regulation in ovariectomized uterus indicated up-regulation of Lpar3 but down-regulation or no effect of the remaining nine LP receptors by P, and down-regulation of most LP receptors, including Lpar3, by 17β-estradiol.

CONCLUSION(S)

LE localization and up-regulation by P differentiate LPA3 from the other nine LP receptors and may underlie its essential role in embryo implantation.

Progesterone and interferon tau-regulated genes in the ovine uterine endometrium: identification of periostin as a potential mediator of conceptus elongation

During early pregnancy in ruminants, progesterone (P4) and interferon tau (IFNT) act on the endometrium to regulate genes hypothesized to be important for conceptus development and implantation. The present study was conducted to verify several candidate genes (actin α-2, smooth muscle, aorta (ACTA2), collagen, type III, α-1 (COL3A1), periostin (POSTN), secreted protein acidic cysteine-rich (SPARC), S100 calcium-binding protein A2 (S100A2),STAT5Aand transgelin (TAGLN)) regulated by pregnancy, P4, and/or IFNT in the endometrium determined using a custom ovine cDNA array.S100A2mRNA was detected primarily in endometrial epithelia and conceptuses.S100A2mRNA increased in endometrial epithelia from days 10 to 16 in cyclic ewes and from days 10 to 14 in pregnant ewes and declined thereafter. The abundance ofS100A2mRNA was less in endometrial luminal epithelium of IFNT-infused ewes receiving P4. Expression ofCOL3A1, SPARC, ACTA2, andTAGLNwas independent of pregnancy, P4, or IFNT.POSTNmRNA was detected primarily in compact stroma of intercaruncular and caruncular endometria, but not in the conceptus. EndometrialPOSTNmRNA increased between days 12 and 14 in pregnant but not cyclic ewes, andPOSTNmRNA was more abundant in uterine stroma of ewes treated with P4. POSTN protein was detected in uterine flushings of pregnant ewes and found to mediate attachment and stimulate migration of ovine trophectoderm cellsin vitro. These results support the ideas that POSTN and S100A2 are regulated by P4and IFNT respectively, and that POSTN is involved in conceptus elongation during early pregnancy.

Lithium chloride treatment induces epithelial cell proliferation in xenografted human endometrium

BACKGROUND

In mouse endometrium, glycogen synthase kinase-3beta (GSK3beta) is a key enzyme controlling nuclear localization of cyclin D1. We developed a functional model of xenografted human endometrium to test whether similar mechanisms are operative in the human by using Lithium chloride (LiCl), an inhibitor of GSK3beta.

METHODS

Human endometrial samples were obtained from normal volunteers, then implanted under the kidney capsule of nude mice, and treated with estradiol-17beta (E2) or LiCl. Xenografts were assessed for protein expression of MKI-67, mini-chromosome maintenance protein-2, estrogen receptor (ER), progesterone receptor (PR) and cyclin D1.

RESULTS

Both E2 and LiCl induced a robust proliferative response in the epithelium. Only lithium treatment produced clear nuclear localization of cyclin D1 consistent with the proliferative response observed. Regenerated endometrium had detectable ER and PR expression.

CONCLUSION

Xenografted human endometrium provides a dynamic model of uterine biology. Administration of LiCl in the absence of E2 induced epithelial proliferation, supporting the hypothesis that human and murine endometrial proliferation may share key regulatory pathways. These data suggest a possible link between the increased menstrual disturbances in women with affective disorders taking lithium and the consequent potential for the development of endometrial proliferative disorder.

Genes involved in conceptus–endometrial interactions in ruminants: insights from reductionism and thoughts on holistic approaches

This review summarizes new knowledge on expression of genes and provides insights into approaches for study of conceptus–endometrial interactions in ruminants with emphasis on the peri-implantation stage of pregnancy. Conceptus–endometrial interactions in ruminants are complex and involve carefully orchestrated temporal and spatial alterations in gene expression regulated by hormones from the ovary and conceptus. Progesterone is the hormone of pregnancy and acts on the uterus to stimulate blastocyst survival, growth, and development. Inadequate progesterone levels or a delayed rise in progesterone is associated with pregnancy loss. The mononuclear trophectoderm cells of the elongating blastocyst synthesize and secrete interferon-τ (IFNT), the pregnancy recognition signal. Trophoblast giant binucleate cells begin to differentiate and produce hormones including chorionic somatomammotropin 1 (CSH1 or placental lactogen). A number of genes, induced or stimulated by progesterone, IFNT, and/or CSH1 in a cell-specific manner, are implicated in trophectoderm adhesion to the endometrial luminal epithelium and regulation of conceptus growth and differentiation. Transcriptional profiling experiments are beginning to unravel the complex dynamics of conceptus–endometrial interactions in cattle and sheep. Future experiments should incorporate physiological models of pregnancy loss and be complemented by metabolomic studies of uterine lumen contents to more completely define factors required for blastocyst survival, growth, and implantation. Both reduction and holistic approaches will be important to understand the multifactorial phenomenon of recurrent pregnancy loss and provide a basis for new strategies to improve pregnancy outcome and reproductive efficiency in cattle and other domestic animals.

Diet-derived polyphenol metabolite enterolactone is a tissue-specific estrogen receptor activator

Numerous dietary compounds can modify gene expression by binding to the members of the nuclear receptor superfamily of transcription factors. For example, dietary polyphenols, such as soy isoflavones genistein and daidzein, modulate the activity of the estrogen receptors (ERs)-alpha and ERbeta. An additional class of dietary polyphenols that modulate cellular signaling pathways are lignans, compounds that are common constituents of Western diets. In this study, we show that a metabolite of dietary lignans, enterolactone, at physiological concentrations, activates ER-mediated transcription in vitro with preference for ERalpha. The effects of enterolactone are mediated by the ER ligand binding domain and are susceptible to antiestrogen treatment. Furthermore, the affinity of enterolactone toward ERalpha, measured by a novel ligand binding assay, is augmented in cell culture conditions. Moreover, our results demonstrate for the first time that enterolactone has estrogenic activity in vivo. In transgenic estrogen-sensitive reporter mice, enterolactone induces tissue-specific estrogen-responsive reporter gene expression as well as promotes uterine stromal edema and expression of estrogen-responsive endogenous genes (CyclinD1 and Ki67). Taken together, our data show that enterolactone is a selective ER agonist inducing ER-mediated transcription both in vitro in different cell lines and in vivo in the mouse uterus.

The postimplantation embryo differentially regulates endometrial gene expression and decidualization

Transcriptomal changes in the uterine endometrium induced in response to the implanting embryo remain largely unknown. In this study, using Affymetrix mRNA expression microarray analysis, we identified genes differentially expressed in the murine endometrium in the presence or absence of the embryo. Compared with the pseudopregnant deciduoma induced by a mechanical stimulus in the absence of an embryo, approximately 1500 genes (753 up-regulated, 686 down-regulated; P < 0.05) were differentially expressed by at least 1.2-fold in the uterine decidua of pregnancy. Most of these genes fall into five major biological categories that include binding (45%), catalysis (24%), signal transduction (10%), transcriptional regulators (5%), and transporters (5%). This strong, embryo-induced transcriptomal impact represented approximately 10% of the total number of genes expressed in the decidualizing endometrium. Validation studies with mRNA and protein confirmed existence of the phylogenetically conserved, embryo-regulated genes involved in the following: 1) hemostasis and inflammation; 2) interferon signaling; 3) tissue growth and remodeling; and 4) natural killer cell function. Interestingly, whereas expression of many growth factors and their cognate receptors were not different between the decidual and deciduomal endometria, a number of proteases that degrade growth factors were selectively up-regulated in the decidual tissue. Increased expression of IGF and activin A neutralizing factors (i.e. HtrA1 and Fstl3) correlated with reduced stromal cell mitosis, tissue growth, and mitogenic signaling in the decidual endometrium. These results support the hypothesis that the implanting murine embryo takes a proactive role in modulating endometrial gene expression and development during early gestation.

Assessment of the proliferative status of epithelial cell types in the endometrium of young and menopausal transition women

BACKGROUND

We determined protein and mRNA expressions of markers of normal human endometrial proliferation and hypothesized that dysregulation of the endometrial response to estradiol (E(2)) and progesterone would be observed in the older menopausal transition (MT) women compared with mid-reproductive age (MRA) controls.

METHODS

Endometrial biopsies were prospectively obtained from MRA and MT non-randomized healthy volunteers during proliferative (+/- exogenous E(2)) and secretory (MRA only) menstrual cycle phases. mRNA and/or nuclear protein expressions of proliferative markers (MKI67, PCNA and MCM2), cell-cycle regulators (cyclins A1, E1 and D1 and cyclin dependent kinase Inhibitor B; CCNA1, CCNE1, CCND1 and CDKN1B) and sex-steroid receptors [estrogen receptor (ER) and progesterone receptor (PR)] were assessed in endometrial lumen, gland and stroma.

RESULTS

MRA women had significantly higher proliferative than secretory expression of MKI67, PCNA, MCM2, CCNA1, CCNE1, ESR1 and PGR in lumen and gland (minimal stromal changes), whereas CDKN1B protein expression was higher during the secretory phase. E(2)-treatment of MT women led to relatively less MKI67 glandular protein expression compared with MRA women; no other age-related differences were observed.

CONCLUSION

Although the MT does not appear to alter the proliferative cell phenotype of endometrial epithelium and stroma, the data suggest that prior to the MT, age is associated with a decrease in some proliferative markers and steroid receptor expression status within different endometrial cell types.

Embryo implantation: the molecular mechanism remains elusive

Low rates of implantation are an impediment to more efficient assisted reproduction techniques. Improved endometrial receptivity and embryo preparation should lead to higher pregnancy rates, lower rates of early pregnancy failure and fewer multiple pregnancies. As the first site of contact between embryo and endometrium, the luminal epithelium (LE) is responsible for the non-receptive status of proliferative and early secretory tissue, and transformation to receptivity in the mid-secretory phase presumably requires alterations in expression, organization or activation of adhesion systems. Luminal cells are less abundant than their glandular counterparts, and are under-represented in global tissue datasets. Furthermore, alterations in cell surface composition can be readily accomplished by mechanisms that do not rely on altered transcription or translation. Current data from in-vitro models are consistent with initial attachment to mucin in the apical glycocalyx, perhaps via a carbohydrate-mediated interaction, after which the epithelial phenotype is modified by a medium- or short-range embryonic signal. A cascade of interactions follows, mediating embryo migration across the epithelium. Strikingly, numerous potential mediators of adhesion at implantation are located in the lateral rather than the apical surface of LE cells. Attached embryos appear to gain rapid access to this highly adhesive lateral membrane domain.

Wide genomic analysis of human endometrial receptivity: new times, new opportunities

Microarray technology has broadened the insight into many research fields allowing scientists to analyse the expression of many genes in quick and efficient experiments aimed at translating these findings into clinical applications. In reproductive medicine, researchers have exploited microarrays to increase understanding of the molecular mechanisms involved in endometrial receptivity and how a possible therapeutic translation can be feasible. In the last 4 years, several studies have focused on the genomics of the human endometrium in different physiological and pathological conditions, and these studies have generated a large amount of information about the regulation and dysregulation of the window of implantation (WOI) genes in fertile, subfertile and refractory conditions. However, the key molecules/mechanisms in endometrial receptivity remain to be elucidated. In this comprehensive review, we have analysed the available results obtained in our own and other laboratories, defining the genomic profile of the receptive endometrium in different situations and its possible clinical application.