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

Insights into the single-cell transcriptome characteristics of porcine endometrium with embryo loss

Reproductive disorders are a concern in the pig industry. Successful gestation processes are closely related to a suitable endometrial microenvironment, and the physiological mechanisms leading to failed pregnancy during the peri-implantation period remain unclear. We constructed single-cell transcriptome profiles of peri-implantation embryo loss and successful gestation endometrial tissues and identified 22 cell subpopulations, with epithelial and stromal cells being the predominant endometrial cell types. The two tissues showed marked differences in cell type composition, especially among epithelial cell subpopulations. We also observed functional differences between epithelial and stromal cells in tissues from embryonic loss and successful gestation, as well as the expression levels and differentiation trajectories of genes associated with embryo attachment and endometrial receptivity in epithelial and stromal cells. The results of cell communication interactions analysis showed that ciliated cells were more active in endometrial tissue with embryo loss, and there were differences in the types of endometrial cells with major roles in embryo loss and embryo implantation successful tissues for bone morphogenic protein, insulin-like growth factor, and transforming growth factor-β signaling networks associated with embryo implantation. In addition, we compared the functional differences in immune cells between the two tissue types and the expression levels of genes related to the inflammatory microenvironment. Overall, the present study revealed the molecular features of endometrial cell transcription in embryo-lost endometrial tissues, providing deeper insights into the endometrial microenvironment of reproductive disorders, which may inform the etiological, diagnostic, and therapeutic studies of reproductive disorders.

Genome-wide analysis reveals porcine LIFR regulated by DNA methylation promotes the implantation process via the STAT3 signaling

Embryo-uterine interaction during embryo implantation depends on the coordinated expression of numerous genes in the receptive endometrium. While DNA methylation is known to play a significant role in controlling gene expression, specific molecular mechanisms underlying this regulatory event remain elusive in early porcine pregnancy. Here, we investigated the genome-wide DNA methylation landscape in the Yorkshire and Meishan pig's endometrium. The results revealed a higher degree of DNA methylation modifications on gene promoter regions on day 32 of pregnancy compared to that on day 18 of pregnancy. By integrating the mRNA and methylation profiles, leukemia inhibitory factor receptor (LIFR) was identified as a differentially methylated and expressed gene, crucial in early pregnancy. LIFR expression is epigenetically silenced via promoter hypermethylation from days 18 to 32 of pregnancy. Moreover, functional assays demonstrated that LIFR knockdown inhibited the proliferation, adhesion, and migration of endometrial epithelial cells (EECs) and downregulated the expression of STAT3 signaling and pregnancy-related genes. In vivo studies further revealed a reduction of implanted mouse embryos upon loss of function of LIFR. Furthermore, RUNX1 up-regulates LIFR expression by binding to the differentially methylated region (DMR) of the LIFR promoter. High levels of RUNX1T1, in turn, recruit RUNX1/HDAC1/DNMTs to assemble a regulatory complex that silences LIFR expression through the same locus. Collectively, our findings shed light on the role of dynamic DNA methylation and the epigenetic regulation of LIFR on embryo implantation in early swine pregnancy.

Analysis of differential transcriptome expression reveals that ISG15 provides support for embryo development by promoting angiogenesis in porcine mesometrium

Mesometrium is the "gateway" through which the endometrium exchanges nutrients and substances with the outside world due to blood vessels entering endometrium across mesometrium. Therefore, dissecting the transcription atlas of the mesometrium will be a great help in understanding the role of mesometrium during implantation. In this study, we collected samples from the mesometrium and adjacent endometrium on the 12th day of estrous cycle and pregnancy. Transcription atlas of mesometrium and adjacent endometrium revealed that genes such as ISG15, which are related to the pathway of response to Interferon α and γ, were significantly enriched. The result of immunohistochemistry demonstrated that the core genes within these pathways were mainly located in the vascular endothelial cells both the endometrium and mesometrium. ISG15 interferon assay revealed the down-regulation of ISG15 induced proliferation, migration and tube formation. Taken together, we concluded that down-regulation of genes related to response of interferons promoted angiogenesis in the mesometrium and adjacent endometrium, allowing mesometrium to play an essential supportive role in pregnancy.

In-Depth Analysis of miRNA Binding Sites Reveals the Complex Response of Uterine Epithelium to miR-26a-5p and miR-125b-5p During Early Pregnancy

Posttranscriptional regulation of gene expression by miRNAs likely makes significant contributions to mRNA abundance at the embryo-maternal interface. In this study, we investigated how miR-26a-5p and miR-125b-5p contribute to molecular changes occurring in the uterine luminal epithelium, which serves as the first site of signal exchange between the mother and the developing embryo. To measure de novo protein synthesis after miRNA delivery to primary uterine luminal epithelial cells, we used pulsed stable isotope labeling by amino acids (pSILACs). We found that both miRNAs alter the proteome of luminal epithelial cells, impacting numerous cellular functions, immune responses, as well as intracellular and second messenger signaling pathways. Additionally, we identified several features of miRNA-mRNA interactions that may influence the targeting efficiency of miR-26a-5p and miR-125b-5p. Overall, our study suggests a complex interaction of miR-26a-5p and miR-125b-5p with their respective targets. However, both appear to cooperatively function in modulating the cellular environment of the luminal epithelium, facilitating the morphological and molecular changes that occur during the intensive communication between the embryo and uterus at pregnancy.

Metabolic reprogramming and heterogeneity during the decidualization process of endometrial stromal cells

The human endometrial decidualization is a transformative event in the pregnant uterus that involves the differentiation of stromal cells into decidual cells. While crucial to the establishment of a successful pregnancy, the metabolic characteristics of decidual cells in vivo remain largely unexplored. Here, we integrated the single-cell RNA sequencing (scRNA-seq) datasets on the endometrium of the menstrual cycle and the maternal-fetal interface in the first trimester to comprehensively decrypt the metabolic characteristics of stromal fibroblast cells. Our results revealed that the differentiation of stromal cells into decidual cells is accompanied by increased amino acid and sphingolipid metabolism. Furthermore, metabolic heterogeneity exists in decidual cells with differentiation maturity disparities. Decidual cells with high metabolism exhibit higher cellular activity and show a strong propensity for signaling. In addition, significant metabolic reprogramming in amino acids and lipids also occurs during the transition from non-pregnancy to pregnancy in the uteri of pigs, cattle, and mice. Our analysis provides comprehensive insights into the dynamic landscape of stromal fibroblast cell metabolism, contributing to our understanding of the metabolism at the molecular dynamics underlying the decidualization process in the human endometrium.

Copy Number Variation Regions Differing in Segregation Patterns Span Different Sets of Genes

Copy number variations regions (CNVRs) can be classified either as segregating, when found in both parents, and offspring, or non-segregating. A total of 65 segregating and 31 non-segregating CNVRs identified in at least 10 individuals within a dense pedigree of the Gochu Asturcelta pig breed was subjected to enrichment and functional annotation analyses to ascertain their functional independence and importance. Enrichment analyses allowed us to annotate 1018 and 351 candidate genes within the bounds of the segregating and non-segregating CNVRs, respectively. The information retrieved suggested that the candidate genes spanned by segregating and non-segregating CNVRs were functionally independent. Functional annotation analyses allowed us to identify nine different significantly enriched functional annotation clusters (ACs) in segregating CNVR candidate genes mainly involved in immunity and regulation of the cell cycle. Up to five significantly enriched ACs, mainly involved in reproduction and meat quality, were identified in non-segregating CNVRs. The current analysis fits with previous reports suggesting that segregating CNVRs would explain performance at the population level, whereas non-segregating CNVRs could explain between-individuals differences in performance.

Novel insights into conceptus-maternal signaling during pregnancy establishment in pigs

Pregnancy establishment in mammals, including pigs, requires coordinated communication between developing conceptuses (embryos with associated membranes) and the maternal organism. Porcine conceptuses signalize their presence by secreting multiple factors, of which estradiol-17β (E2) is considered the major embryonic signal initiating the maternal recognition of pregnancy. During this time, a limited supply of prostaglandin (PGF2α) to the corpora lutea and an increased secretion of luteoprotective factors (e.g., E2 and prostaglandin E2 [PGE2]) lead to the corpus luteum's maintained function of secreting progesterone, which in turn primes the uterus for implantation. Further, embryo implantation is related to establishing an appropriate proinflammatory environment coordinated by the secretion of proinflammatory mediators including cytokines, growth factors, and lipid mediators of both endometrial and conceptus origin. The novel, dual role of PGF2α has been underlined. Recent studies involving high-throughput technologies and sophisticated experimental models identified a number of novel factors and revealed complex relationships between these factors and those already established. Hence, it seems that early pregnancy should be regarded as a sequence of processes orchestrated by pleiotropic factors that are involved in redundancy and compensatory mechanisms that preserve the essential functions critical for implantation and placenta formation. Therefore, establishing the hierarchy between all molecules present at the embryo-maternal interface is now even more challenging.

Reconsidering "low-dose"-Impacts of oral estrogen exposure during preimplantation embryo development

Perturbations of estrogen signaling during developmental stages of high plasticity may lead to adverse effects later in life. Endocrine-disrupting chemicals (EDC) are compounds that interfere with the endocrine system by particularly mimicking the action of endogenous estrogens as functional agonists or antagonists. EDCs compose synthetic and naturally occurring compounds discharged into the environment, which may be taken up via skin contact, inhalation, orally due to contaminated food or water, or via the placenta during in utero development. Although estrogens are efficiently metabolized by the liver, the role of circulating glucuro- and/or sulpho-conjugated estrogen metabolites in the body has not been fully addressed to date. Particularly, the role of intracellular cleavage to free functional estrogens could explain the hitherto unknown mode of action of adverse effects of EDC at very low concentrations currently considered safe. We summarize and discuss findings on estrogenic EDC with a focus on early embryonic development to highlight the need for reconsidering low dose effects of EDC.

Extracellular vesicles: Focus on peri-implantation period of pregnancy in pigs

The establishment of cell-to-cell communication between the endometrium and the developing embryo is the most important step in successful mammalian pregnancy. Close interaction between the uterine luminal epithelium and trophoblast cells requires triggering timely molecular dialog for successful maternal recognition of pregnancy, embryo implantation, and placenta development. Quite recently, extracellular vesicles (EVs) carrying unique molecular cargo emerged as evolutionarily conserved mediators of cell-to-cell communication during early pregnancy. To date, the presence of EVs at the embryo-maternal interface has been demonstrated in numerous mammals, including domestic livestock, such as pigs. However, few studies have focused on revealing the mechanism of EV-mediated crosstalk between developing early embryos and receptive endometrium. Over the past years, it has appeared that understanding the role of EVs in mammalian reproduction can substantially improve our understanding of the biological challenges of successful reproductive performance. This review describes current knowledge of EVs, specifically in relation to the peri-implantation period in pigs, characterized by common features of embryo implantation and high embryonic mortality in mammals.

Proteomic profiles and the function of RBP4 in endometrium during embryo implantation phases in pigs

BACKGROUND

Endometrial receptivity plays a vital role in the success of embryo implantation. However, the temporal proteomic profile of porcine endometrium during embryo implantation is still unclear.

RESULTS

In this study, the abundance of proteins in endometrium on days 9, 10, 11, 12, 13, 14, 15 and 18 of pregnancy (D9, 10, 11, 12, 13, 14, 15 and 18) was profiled via iTRAQ technology. The results showed that 25, 55, 103, 91, 100, 120, 149 proteins were up-regulated, and 24, 70, 169, 159, 164, 161, 198 proteins were down-regulated in porcine endometrium on D10, 11, 12, 13, 14, 15 and 18 compared with that on D9, respectively. Among these differentially abundance proteins (DAPs), Multiple Reaction Monitoring (MRM) results indicated that S100A9, S100A12, HRG and IFI6 were differentially abundance in endometrial during embryo implantation period. Bioinformatics analysis showed that the proteins differentially expressed in the 7 comparisons were involved in important processes and pathways related to immunization, endometrial remodeling, which have a vital effect on embryonic implantation.

CONCLUSION

Our results reveal that retinol binding protein 4 (RBP4) could regulate the cell proliferation, migration and apoptosis of endometrial epithelial cells and endometrial stromal cells to affect embryo implantation. This research also provides resources for studies of proteins in endometrium during early pregnancy.

Adaptation of the Porcine Pituitary Transcriptome, Spliceosome and Editome during Early Pregnancy

The physiological mechanisms of the porcine reproduction are relatively well-known. However, transcriptomic changes and the mechanisms accompanying transcription and translation processes in various reproductive organs, as well as their dependence on hormonal status, are still poorly understood. The aim of this study was to gain a principal understanding of alterations within the transcriptome, spliceosome and editome occurring in the pituitary of the domestic pig (Sus scrofa domestica L.), which controls basic physiological processes in the reproductive system. In this investigation, we performed extensive analyses of data obtained by high-throughput sequencing of RNA from the gilts' pituitary anterior lobes during embryo implantation and the mid-luteal phase of the estrous cycle. During analyses, we obtained detailed information on expression changes of 147 genes and 43 long noncoding RNAs, observed 784 alternative splicing events and also found the occurrence of 8729 allele-specific expression sites and 122 RNA editing events. The expression profiles of the selected 16 phenomena were confirmed by PCR or qPCR techniques. As a final result of functional meta-analysis, we acquired knowledge regarding intracellular pathways that induce changes in the processes accompanying transcription and translation regulation, which may induce modifications in the secretory activity of the porcine adenohypophyseal cells.

Integrating Transcriptomic and ChIP-Seq Reveals Important Regulatory Regions Modulating Gene Expression in Myometrium during Implantation in Pigs

The myometrium is the outer layer of the uterus. Its contraction and steroidogenic activities are required for embryo implantation. However, the molecular mechanisms underlying its functions remain unknown in pigs. The myometrium includes the inner circular muscle (CM) and the outer longitudinal muscle (LM) layers. In this study, we collected the CM and LM samples from the mesometrial side (named M) of the uterus on days 12 (pre-implantation stage) and 15 (implantation stage) of pregnancy and day 15 of the estrous cycle. The transcriptomic results revealed distinct differences between the uterine CM and LM layers in early pregnancy: the genes expressed in the LM layer were mainly related to contraction pathways, whereas the transcriptional signatures in the CM layer on day 15 of pregnancy were primarily involved in the immune response processes. Subsequent comparisons in the CM layer between pregnant and cyclic gilts show that the transcriptional signatures of the CM layer are implantation-dependent. Next, we investigated the genome-wide profiling of histone H3 lysine 27 acetylation (H3K27ac) and histone H3 lysine 4 trimethylation (H3K4me3) in pig uterine CM and LM layers. The genomic regions that had transcriptional activity and were associated with the expression of genes in the two layers were characterized. Taken together, the regulatory regions identified in the study may contribute to modulating the gene expression in pig uterine CM and LM layers during implantation.

Effect of miR-143-3p from Extracellular Vesicles of Porcine Uterine Luminal Fluid on Porcine Trophoblast Cells

Extracellular vesicles (EVs) in uterine luminal fluid (ULF) can reportedly affect the proliferation and migration function of porcine trophoblast cells (PTr2 cells) by mediating the maternal-fetal exchange of information. miR-143-3p is considered a crucial miRNA in early pregnancy in mammals; however, little is currently known about how it regulates the function of PTr2 cells. This study aimed to investigate the effects of ssc-miR-143-3p in ULF-EVs on the function of PTr2 cells during porcine embryo implantation. The uptake of ULF-EVs by PTr2 cells was confirmed, which significantly increased the expression of ssc-miR-143-3p. Ssc-miR-143-3p was found to facilitate the proliferation and migration of PTr2 cells in the CCK-8, EdU and wound-closure assays, while the opposite findings were observed after the knockdown of ssc-miR-143-3p. Bioinformatics analysis and the luciferase reporter assay showed that glycerol-3 phosphate dehydrogenase 2 (GDP2) was directly targeted by miR-143-3p. Inhibition of miR-143-3p was validated in mice to inhibit embryo implantation. In summary, ssc-miR-143-3p in ULF-EVs affects the proliferation and migration of PTr2 cells by mediating GPD2, thereby affecting embryo implantation.

Luminal and Glandular Epithelial Cells from the Porcine Endometrium maintain Cell Type-Specific Marker Gene Expression in Air-Liquid Interface Culture

Two different types of epithelial cells constitute the inner surface of the endometrium. While luminal epithelial cells line the uterine cavity and build the embryo-maternal contact zone, glandular epithelial cells form tubular glands reaching deeply into the endometrial stroma. To facilitate investigations considering the functional and molecular differences between the two populations of epithelial cells and their contribution to reproductive processes, we aimed at establishing differentiated in vitro models of both the luminal and the glandular epithelium of the porcine endometrium using an air–liquid interface (ALI) approach. We first tested if porcine luminal endometrium epithelial cells (PEEC-L) reproducibly form differentiated epithelial monolayers under ALI conditions by monitoring the morphology and the trans-epithelial electrical resistance (TEER). Subsequently, luminal (PEEC-L) and glandular epithelial cells (PEEC-G) were consecutively isolated from the endometrium of the uterine horn. Both cell types were characterized by marker gene expression analysis immediately after isolation. Cells were separately grown at the ALI and assessed by means of histomorphometry, TEER, and marker gene expression after 3 weeks of culture. PEEC-L and PEEC-G formed polarized monolayers of differentiated epithelial cells with a moderate TEER and in vivo-like morphology at the ALI. They exhibited distinct patterns of functional and cell type-specific marker gene expression after isolation and largely maintained these patterns during the culture period. The here presented cell culture procedure for PEEC-L and -G offers new opportunities to study the impact of embryonic signals, endocrine effectors, and reproductive toxins on both porcine endometrial epithelial cell types under standardized in vitro conditions.

Effects of exogenous progesterone on the expression of mineral regulatory molecules by ovine endometrium and placentomes†

This study aimed to determine whether the acceleration of conceptus development induced by the administration of exogenous progesterone (P4) during the preimplantation period of pregnancy alters calcium, phosphate, and vitamin D signaling at the maternal-conceptus interface. Suffolk ewes (n = 48) were mated to fertile rams and received daily intramuscular injections of either corn oil (CO) vehicle or 25 mg of progesterone in CO (P4) for the first 8 days of pregnancy and hysterectomized on either Day 9 (CO, n = 5; P4, n = 6), 12 (CO, n = 9; P4, n = 4) or 125 (CO, n = 14; P4, n = 10) of gestation. The expression of S100A12 (P < 0.05) and fibroblast growth factor receptor (FGFR2) (P < 0.01) messenger RNAs (mRNAs) was lower in endometria from P4-treated ewes on Day 12. The expression of ADAM10 (P < 0.05) mRNA was greater in endometria from P4-treated ewes on Day 125. The expression of ADAM10 (P < 0.01), FGFR2 (P < 0.05), solute carrier (SLC)20A1 (P < 0.05), TRPV5 (P < 0.05), and TRPV6 (P < 0.01) mRNAs was greater, but KL mRNA expression was lower (P < 0.05) in placentomes from P4-treated ewes at Day 125. There was lower endometrial and greater placentomal expression of mRNAs involved in mineral metabolism and transport in twin compared to singleton pregnancies. Further, the expression of mRNAs involved in mineral metabolism and transport was greater in P4-treated twin placentomes. KL, FGF23, vitamin D receptor (VDR), S100A9, S100A12, S100G, and CYP27B1 proteins were immunolocalized in endometria and placentomes. Exogenous P4 in early pregnancy altered the expression of regulators of calcium, phosphate, and vitamin D on Day 125 of pregnancy indicating a novel effect of P4 on mineral transport at the maternal-conceptus interface.

Effects of progesterone and interferon tau on ovine endometrial phosphate, calcium, and vitamin D signaling†

Given recent reports of expression of postnatal mineral transport regulators at the maternal-conceptus interface during the peri-implantation period, this study tested the hypothesis that progesterone (P4) and interferon tau (IFNT) regulate phosphate, calcium, and vitamin D signaling in the ovine endometrium. Mature Rambouillet ewes (n = 24) were surgically fitted with intrauterine catheters on day 7 of the estrous cycle. Ewes received daily intramuscular injections of 50 mg of P4 in corn oil vehicle and 75 mg of progesterone receptor antagonist (RU486) in corn oil from days 8 to 15, and twice-daily intrauterine injections of either control proteins (CX) or IFNT (25 μg/uterine horn/day) from days 11 to 15 resulting in four treatment groups: P4 + CX; P4 + IFNT; RU486 + P4 + CX; and RU486 + P4 + IFNT. On day 16, ewes were hysterectomized. RU486 + P4 + CX treated ewes had lower concentrations of 25 (OH) D in plasma than P4 + CX treated ewes (P < 0.05). Endometria from ewes treated with IFNT had greater expression of FGF23 (P < 0.01), S100A9 (P < 0.05), and S100A12 (P = 0.05) mRNAs and lower expression of ADAM10 mRNA (P < 0.01) than of ewes treated with CX proteins. Expression of FGF23 mRNA was greater in endometria of ewes that received RU486 + P4 + IFNT than in ewes that received RU486 + P4 + CX (hormone × protein interaction, P < 0.05). The expression of S100G mRNA was greater in endometria of ewes that received P4 + IFNT compared to ewes that received RU486 + P4 + IFNT (P < 0.05; hormone × protein interaction, P < 0.01). These data implicate P4 and IFNT in the regulation of phosphate, calcium, and vitamin D signaling during the peri-implantation period of pregnancy and provide a platform for continued mechanistic investigations.

Transcriptome regulation of extracellular vesicles derived from porcine uterine flushing fluids during peri-implantation on endometrial epithelial cells and embryonic trophoblast cells

The extracellular vesicles (EVs) in uterine fluids play a vital role in embryo implantation by mediating intrauterine communication between conceptus and maternal endometrium in pigs. However, the regulatory mechanism of EVs in uterine fluids is largely unclear. In order to understand the effect of EVs in uterine flushing fluids (UFs) during embryo implantation on endometrial epithelial cells (EECs) and embryonic trophoblast cells (PTr2 cells). The UFs-EVs on day 13 of pregnancy (D13) were added to the culture medium of EECs and PTr2 cells. It was found that PKH-67 labeled UFs-EVs could be taken up in EECs and PTr2 cells. Transcriptome sequencing analysis showed that a total of 1793 and 6279 genes were differentially expressed in the EECs and PTr2 cells after the treatment of UFs-EVs on D13, respectively. Among these genes, real-time quantitative PCR (RT-qPCR) results indicated that ID2, ITGA5, CXCL10 and CXCL11 genes were differentially expressed in both EECs and PTr2 cells after treatment. Bioinformatics analysis showed that the differentially expressed (DE) genes in EECs and PTr2 cells after treatment are involved in immune regulation, cell migration, cell adhesion and the secretion and uptake of EVs. Our research offers novel insight into the regulation mechanism of UFs-EVs on D13 in EECs and PTr2 cells.

Revisiting the Transcriptome Landscape of Pig Embryo Implantation Site at Single-Cell Resolution

Litter size is one of the most economically important traits in commercial pig farming. It has been estimated that approximately 30% of porcine embryos are lost during the peri-implantation period. Despite rapid advances over recent years, the molecular mechanism underlying embryo implantation in pigs remains poorly understood. In this study, the conceptus together with a small amount of its surrounding endometrial tissues at the implantation site was collected and subjected to single-cell RNA-seq using the 10x platform. Because embryo and maternal endometrium were genetically different, we successfully dissected embryonic cells from maternal endometrial cells in the data according to single nucleotide polymorphism information captured by single-cell RNA-seq. Undoubtedly, the interaction between trophoblast cells and uterine epithelial cells represents the key mechanism of embryo implantation. Using the CellChat tool, we revealed cell-cell communications between these 2 cell types in terms of secreted signaling, ECM-receptor interaction and cell-cell contact. Additionally, by analyzing the non-pregnant endometrium as control, we were able to identify global gene expression changes associated with embryo implantation in each cell type. Our data provide a valuable resource for deciphering the molecular mechanism of embryo implantation in pigs.

Progesterone differentially affects the transcriptomic profiles of cow endometrial cell types

Background

The endometrium is a heterogeneous tissue composed of luminal epithelial (LE), glandular epithelial (GE), and stromal cells (ST), experiencing progesterone regulated dynamic changes during the estrous cycle. In the cow, this regulation at the transcriptomic level was only evaluated in the whole tissue. This study describes specific gene expression in the three types of cells isolated from endometrial biopsies following laser capture microdissection and the transcriptome changes induced by progesterone in GE and ST cells.

Results

Endometrial LE, GE, and ST cells show specific transcriptomic profiles. Most of the differentially expressed genes (DEGs) in response to progesterone are cell type-specific (96%). Genes involved in cell cycle and nuclear division are under-expressed in the presence of progesterone in GE, highlighting the anti-proliferative action of progesterone in epithelial cells. Elevated progesterone concentrations are also associated with the under-expression of estrogen receptor 1 (ESR1) in GE and oxytocin receptor (OXTR) in GE and ST cells. In ST cells, transcription factors such as SOX17 and FOXA2, known to regulate uterine epithelial-stromal cross-talk conveying to endometrial receptivity, are over-expressed under progesterone influence.

Conclusions

The results from this study show that progesterone regulates endometrial function in a cell type-specific way, which is independent of the expression of its main receptor PGR. These novel insights into uterine physiology present the cell compartment as the physiological unit rather than the whole tissue.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08323-z.

Spatiotemporal endometrial transcriptome analysis revealed the luminal epithelium as key player during initial maternal recognition of pregnancy in the mare

During the period of maternal recognition of pregnancy (MRP) in the mare, the embryo needs to signal its presence to the endometrium to prevent regression of the corpus luteum and prepare for establishment of pregnancy. This is achieved by mechanical stimuli and release of various signaling molecules by the equine embryo while migrating through the uterus. We hypothesized that embryo's signals induce changes in the endometrial gene expression in a highly cell type-specific manner. A spatiotemporal transcriptomics approach was applied combining laser capture microdissection and low-input-RNA sequencing of luminal and glandular epithelium (LE, GE), and stroma of biopsy samples collected from days 10-13 of pregnancy and the estrous cycle. Two comparisons were performed, samples derived from pregnancies with conceptuses ≥ 8 mm in diameter (comparison 1) and conceptuses ≤ 8 mm (comparison 2) versus samples from cyclic controls. The majority of gene expression changes was identified in LE and much lower numbers of differentially expressed genes (DEGs) in GE and stroma. While 1253 DEGs were found for LE in comparison 1, only 248 were found in comparison 2. Data mining mainly focused on DEGs in LE and revealed regulation of genes related to prostaglandin transport, metabolism, and signaling, as well as transcription factor families that could be involved in MRP. In comparison to other mammalian species, differences in regulation of genes involved in epithelial barrier formation and conceptus attachment and implantation reflected the unique features of equine reproduction at the time of MRP at the molecular level.

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.

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.

Novel mineral regulatory pathways in ovine pregnancy: II. Calcium-binding proteins, calcium transporters, and vitamin D signaling

Mineralization of the fetal mammalian skeleton requires a hypercalcemic gradient across the placenta from mother to fetus. However, the mechanisms responsible for maintaining the placental transport of calcium remain poorly understood. This study aimed to identify calcium and vitamin D regulatory pathway components in ovine endometria and placentae across gestation. Suffolk ewes were bred with fertile rams upon detection of estrus (Day 0). On Days 9, 12, 17, 30, 70, 90, 110, and 125 of pregnancy (n=3-14/Day), ewes were euthanized and hysterectomized. Calcium abundance was influenced by gestational day in uterine flushings and allantoic fluid (P<0.05). The expression of S100G, S100A9, S100A12, ATP2B3, ATP2B4, TRPV5, TRPV6, CYP11A1, CYP2R1, CYP24, and VDR mRNAs known to be involved in calcium binding, calcium transport, and vitamin D metabolism were quantified by qPCR. Mediators of calcium and vitamin D signaling were expressed by Day 17 conceptus tissue, and endometria and placentae across gestation. Gestational day influenced the expression of S100G, S100A9, S100A12, TRPV6, VDR, and CYP24 mRNAs in endometria and placentae (P<0.05). Gestational day influenced endometrial expression of ATP2B3, and placental expression of TRPV5, ATP2B4, and CYP11A1 (P<0.05). VDR protein localized to the endoderm and trophectoderm (Day 17 conceptus) and was expressed in endometria and placentae throughout gestation. The observed spatiotemporal profile suggests a potential role of calcium and vitamin D in the establishment of pregnancy and regulation of fetal and placental growth, providing a platform for further mechanistic investigation.

Creatine Metabolism in Female Reproduction, Pregnancy and Newborn Health

Creatine metabolism is an important component of cellular energy homeostasis. Via the creatine kinase circuit, creatine derived from our diet or synthesized endogenously provides spatial and temporal maintenance of intracellular adenosine triphosphate (ATP) production; this is particularly important for cells with high or fluctuating energy demands. The use of this circuit by tissues within the female reproductive system, as well as the placenta and the developing fetus during pregnancy is apparent throughout the literature, with some studies linking perturbations in creatine metabolism to reduced fertility and poor pregnancy outcomes. Maternal dietary creatine supplementation during pregnancy as a safeguard against hypoxia-induced perinatal injury, particularly that of the brain, has also been widely studied in pre-clinical in vitro and small animal models. However, there is still no consensus on whether creatine is essential for successful reproduction. This review consolidates the available literature on creatine metabolism in female reproduction, pregnancy and the early neonatal period. Creatine metabolism is discussed in relation to cellular bioenergetics and de novo synthesis, as well as the potential to use dietary creatine in a reproductive setting. We highlight the apparent knowledge gaps and the research “road forward” to understand, and then utilize, creatine to improve reproductive health and perinatal outcomes.

Integrating LCM-Based Spatio-Temporal Transcriptomics Uncovers Conceptus and Endometrial Luminal Epithelium Communication that Coordinates the Conceptus Attachment in Pigs

Attachment of conceptus to the endometrial luminal epithelium (LE) is a critical event for early placentation in Eutheria. Since the attachment occurs at a particular site within the uterus, a coordinated communication between three spatially distinct compartments (conceptus and endometrial LE from two anatomical regions of the uterus to which conceptus attaches and does not attach) is essential but remains to be fully characterized. Using the laser capture microdissection (LCM) technique, we firstly developed an approach that can allow us to pair the pig conceptus sample with its nearby endometrial epithelium sample without losing the native spatial information. Then, a comprehensive spatio-temporal transcriptomic profile without losing the original conceptus-endometrium coordinates was constructed. The analysis shows that an apparent difference in transcriptional responses to the conceptus exists between the endometrial LE from the two anatomically distinct regions in the uterus. In addition, we identified the communication pathways that link the conceptus and endometrial LE and found that these pathways have important roles in conceptus attachment. Furthermore, a number of genes whose expression is spatially restricted in the two different anatomical regions within the uterus were characterized for the first time and two of them (SULT2A1 and MEP1B) may cooperatively contribute to establish conceptus attachment in pigs. The results from our study have implications in understanding of conceptus/embryo attachment in pigs and other large polytocous species.

Ssc-miR-21-5p regulates endometrial epithelial cell proliferation, apoptosis and migration via the PDCD4/AKT pathway

Endometrial receptivity plays a vital role in successful embryo implantation in pigs. MicroRNAs (miRNAs), known as regulators of gene expression, have been implicated in the regulation of embryo implantation. However, the role of miRNAs in endometrial receptivity during the pre-implantation period remains elusive. In this study, we report that the expression level of Sus scrofa (ssc)-miR-21-5p in porcine endometrium tissues was significantly increased from day 9 to day 12 of pregnancy. Knockdown of ssc-miR-21-5p inhibited proliferation and migration of endometrial epithelial cells (EECs), and induced their apoptosis. We verified that programmed cell death 4 (PDCD4) was a target gene of ssc-miR-21-5p. Inhibition of PDCD4 rescued the effect of ssc-miR-21-5p repression on EECs. Our results also revealed that knockdown of ssc-miR-21-5p impeded the phosphorylation of AKT (herein referring to AKT1) by targeting PDCD4, which further upregulated the expression of Bax, and downregulated the levels of Bcl2 and Mmp9. Furthermore, loss of function of Mus musculus (mmu)-miR-21-5p in vivo resulted in a decreased number of implanted mouse embryos. Taken together, knockdown of ssc-miR-21-5p hampers endometrial receptivity by modulating the PDCD4/AKT pathway.

Creatine metabolism in the uterus: potential implications for reproductive biology

Creatine is an amino acid derivative synthesized from arginine, glycine and methionine. It serves as the substrate for the creatine kinase system, which is vital for maintaining ATP levels in tissues with high and fluctuating energy demand. There exists evidence that the creatine kinase system operates in both the endometrial and myometrial layers of the uterus. While use and regulation of this system in the uterus are not well understood, it is likely to be important given uterine tissues undergo phases of increased energy demand during certain stages of the female reproductive cycle, pregnancy, and parturition. This review discusses known adaptations of creatine metabolism in the uterus during the reproductive cycle (both estrous and menstrual), pregnancy and parturition, highlighting possible links to fertility and the existing knowledge gaps. Specifically, we discuss the adaptations and regulation of uterine creatine metabolite levels, cell creatine transport, de novo creatine synthesis, and creatine kinase expression in the various layers and cell types of the uterus. Finally, we discuss the effects of dietary creatine on uterine metabolism. In summary, there is growing evidence that creatine metabolism is up-regulated in uterine tissues during phases where energy demand is increased. While it remains unclear how important these adaptations are in the maintenance of healthy uterine function, furthering our understanding of uterine creatine metabolism may uncover strategies to combat poor embryo implantation and failure to conceive, as well as enhancing uterine contractile performance during labor.

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.

Identification of Differentially Expressed Gene Transcripts in Porcine Endometrium during Early Stages of Pregnancy

During the early stages of pregnancy, the uterine endometrium undergoes dramatic morphologic and functional changes accompanied with dynamic variation in gene expression. Pregnancy-stage specific differentially expressed gene (DEG)-transcript-probes were investigated and identified by comparing endometrium transcriptome at 9th day (9D), 12th day (12D) and 16th day (16D) of early pregnancy in Polish large-white (PLW) gilts. Endometrium comparisons between 9D-vs-12D, 9D-vs-16D and 12D-vs-16D of early pregnancy identified 6049, 374 and 6034 highly significant DEG-transcript-probes (p < 0.001; >2 FC). GO term enrichment analysis identified commonly shared upregulated endometrial DEG-transcript-probes (p < 0.001; >2 FC), that were regulating the gene functions of anatomic structure development and transport (TG), DNA-binding and methyltransferase activity (ZBTB2), ion-binding and kinase activity (CKM), cell proliferation and apoptosis activity (IL1B). Downregulated DEG-transcript-probes (p < 0.001; >2 FC) were involved in regulating the gene functions of phosphatase activity (PTPN11), TC616413 gene-transcript and Sus-scrofa LOC100525539. Moreover, blastn comparison of microarray-probes sequences against sus-scrofa11 assembly identified commonly shared upregulated endometrial DEG-transcript-probes (E < 0.06; >2 FC), that were regulating the gene functions of reproduction and growth (SELENOP), cytoskeleton organization and kinase activity (CDC42BPA), phosphatase activity (MINPP1), enzyme-binding and cell-population proliferation (VAV3), cancer-susceptibility candidate gene (CASC4), cytoskeletal protein-binding (COBLL1), ion-binding, enzyme regulator activity (ACAP2) Downregulated endometrial DEG-transcript-probes (E < 0.06; >2FC) were involved in regulating the gene functions of signal-transduction (TMEM33), catabolic and metabolic processes (KLHL15). Microarray validation experiment on selected candidate genes showed complementarity to significant endometrial DEG-transcript-probes responsible for the regulation of immune response (IL1B, S100A11), lipid metabolism (FABP3, PPARG), cell-adhesion (ITGAV), angiogenesis (IL1B), intercellular transmission (NMB), cell-adhesion (OPN) and response to stimuli (RBP4) was confirmed by RT-PCR. This study provides a clue that identified pregnancy-stage specific microarray transcript probes could be considered as candidate genes for recognition and establishment of early pregnancy in the pig.

Exosomes and Female Infertility

BACKGROUND

Exosomes are small Extracellular Vesicles (EVs) (40-100 nm) secreted by living cells and mediate the transmission of information between cells. The number and contents of exosomes are associated with diseases such as inflammatory diseases, cancer, metabolic diseases and what we are focusing in this passage-female infertility.

OBJECTIVE

This review focused on the role of exosomes in oocyte development, declined ovarian function, PCOS, uterine diseases, endometrial receptivity and fallopian tube dysfunction in the female.

METHODS

We conducted an extensive search for research articles involving relationships between exosomes and female infertility on the bibliographic database.

RESULTS

It has been reported that exosomes can act as a potential therapeutic device to carry cargoes to treat female infertility. However, the pathophysiological mechanisms of exosomes in female infertility have not been entirely elucidated. Further researches are needed to explore the etiology and provide evidence for potential clinical treatment.

CONCLUSIONS

This review systematically summarized the role exosomes play in female infertility and its potential as drug delivery.

Genome-Wide Association Study Reveals Candidate Genes for Litter Size Traits in Pelibuey Sheep

The Pelibuey sheep has adaptability to climatic variations, resistance to parasites, and good maternal ability, whereas some ewes present multiple births, which increases the litter size in farm sheep. The litter size in some wool sheep breeds is associated with the presence of mutations, mainly in the family of the transforming growth factor β (TGF-β) genes. To explore genetic mechanisms underlying the variation in litter size, we conducted a genome-wide association study in two groups of Pelibuey sheep (multiparous sheep with two lambs per birth vs. uniparous sheep with a single lamb at birth) using the OvineSNP50 BeadChip. We identified a total of 57 putative SNPs markers (p < 3.0 × 10^-3, Bonferroni correction). The candidate genes that may be associated with litter size in Pelibuey sheep are CLSTN2, MTMR2, DLG1, CGA, ABCG5, TRPM6, and HTR1E. Genomic regions were also identified that contain three quantitative trait loci (QTLs) for aseasonal reproduction (ASREP), milk yield (MY), and body weight (BW). These results allowed us to identify SNPs associated with genes that could be involved in the reproductive process related to prolificacy.

Estradiol-17β-Induced Changes in the Porcine Endometrial Transcriptome In Vivo

Estradiol-17β (E2) is a key hormone regulating reproductive functions in females. In pigs, E2, as the main conceptus signal, initiates processes resulting in prolonged corpus luteum function, embryo development, and implantation. During early pregnancy the endometrium undergoes morphological and physiological transitions that are tightly related to transcriptome changes. Recently, however, the importance of E2 as a primary conceptus signal in the pig has been questionable. Thus, the aim of the present study was to determine the effects of E2 on the porcine endometrial transcriptome in vivo and to compare these effects with transcriptome profiles on day 12 of pregnancy. Microarray analysis revealed differentially expressed genes (DEGs) in response to E2 with overrepresented functional terms related to secretive functions, extracellular vesicles, cell adhesion, proliferation and differentiation, tissue rearrangements, immune response, lipid metabolism, and many others. Numerous common DEGs and processes for the endometrium on day 12 of pregnancy and E2-treated endometrium were identified. In summary, the present study is the first evidence for the effect of E2 on transcriptome profiles in porcine endometrium in vivo in the period corresponding to the maternal recognition of pregnancy. The presented results provide a valuable resource for further targeted studies considering genes and pathways regulated by conceptus-derived estrogens and their role in pregnancy establishment.

Changes in the expression and distribution of junction and polarity proteins in the porcine endometrium during early pregnancy period

The maternal endometrium undergoes transformations during early pregnancy period to regulate the paracellular permeability across the epithelium and to enable adhesion between the trophoblast and endometrial epithelial cells. These transformations, under the influence of ovarian hormones, are associated with a partial loss in polarity of epithelial cell that is regulated by tight junctions (TJ), adherens junctions (AJ) and associated polarity protein complexes. This study examined the change in expression and distribution of proteins associated with TJs, AJs and apical partition defective (PAR) complex in porcine endometrium on Days 10, 13 and 16 of estrous cycle and pregnancy. Moreover, effect of hormones, progesterone (P4) and 17-β estradiol (E2) on polar phenotype of endometrial epithelial cells was also investigated in vitro. There was pregnancy induced increase in gene and protein expression of TJ associated claudin-1 (CLDN1) on Day 13 of pregnancy as compared to corresponding day of estrous cycle and a decrease in TJ protein, zona occludens-1 (ZO-1) and PAR complex associated PAR6 expression levels on Day 16 of pregnancy (P < 0.05). Immunofluorescence studies revealed that on Days 10 and 13, TJ proteins occludin (OCLN) and ZO-1were primarily present in the apical region of lateral epithelial membrane. On Day 16 of pregnancy, whereas, OCLN redistributed into cytoplasm, ZO-1 decreased apically but was found to localize in the basal epithelium. The AJ proteins cadherin and β-catenin were located at the apical epithelium on Day 10 of estrous cycle and pregnancy and Day 13 of estrous cycle. On Days 13 and 16 of pregnancy both proteins were expressed in the lateral membrane and co-localization between these proteins was observed on Day 16. On Day 10, PAR complex proteins PAR3, cell division control protein 42 (CDC42) and atypical protein kinase C (aPKC) ζ were observed in apical epithelium and in lateral membrane and CDC42 was also present in the cytoplasm of epithelium. Pregnancy induced redistribution of aPKCζ to cytoplasm and CDC42 to apical surface of luminal epithelium was observed on Days 13 and 16. The in vitro P4 and E2 treatment of epithelial cells mimicked in vivo results. These results indicate that P4 and E2 regulate alterations in epithelium that may facilitate embryo implantation and given the role of cadherin, catenin and CDC42 in embryo invasion, change in distribution of these proteins may limit the invasiveness of porcine conceptuses into the stroma.

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.

Identification of loci associated with conception rate in primiparous Holstein cows

BACKGROUND

Subfertility is a major issue facing the dairy industry as the average US Holstein cow conception rate (CCR) is approximately 35%. The genetics underlying the physiological processes responsible for CCR, the proportion of cows able to conceive and maintain a pregnancy at each breeding, are not well characterized. The objectives of this study were to identify loci, positional candidate genes, and transcription factor binding sites (TFBS) associated with CCR and determine if there was a genetic correlation between CCR and milk production in primiparous Holstein cows. Cows were bred via artificial insemination (AI) at either observed estrus or timed AI and pregnancy status was determined at day 35 post-insemination. Additive, dominant, and recessive efficient mixed model association expedited (EMMAX) models were used in two genome-wide association analyses (GWAA). One GWAA focused on CCR at first service (CCR1) comparing cows that conceived and maintained pregnancy to day 35 after the first AI (n = 494) to those that were open after the first AI (n = 538). The second GWAA investigated loci associated with the number of times bred (TBRD) required for conception in cows that either conceived after the first AI (n = 494) or repeated services (n = 472).

RESULTS

The CCR1 GWAA identified 123, 198, and 76 loci associated (P < 5 × 10- 08) in additive, dominant, and recessive models, respectively. The TBRD GWAA identified 66, 95, and 33 loci associated (P < 5 × 10- 08) in additive, dominant, and recessive models, respectively. Four of the top five loci were shared in CCR1 and TBRD for each GWAA model. Many of the associated loci harbored positional candidate genes and TFBS with putative functional relevance to fertility. Thirty-six of the loci were validated in previous GWAA studies across multiple breeds. None of the CCR1 or TBRD associated loci were associated with milk production, nor was their significance with phenotypic and genetic correlations to 305-day milk production.

CONCLUSIONS

The identification and validation of loci, positional candidate genes, and TFBS associated with CCR1 and TBRD can be utilized to improve, and further characterize the processes involved in cattle fertility.

Spatial Transcriptomic and miRNA Analyses Revealed Genes Involved in the Mesometrial-Biased Implantation in Pigs

Implantation failure is a major cause of early embryonic loss. Normally, the conceptus attachment is initiated at mesometrial side of the uterus and then spread to the anti-mesometrial side in pigs, however, the mechanisms that direct the mesometrial-biased attachment are largely unknown. In this study, the histological features of the entire uterine cross-section from gestational days 12 (pre-attachment stage) and 15 (post-attachment stage) were investigated and the differences in histological features between the mesometrial and anti-mesometrial side of the uterus were observed. Then, transcriptomic and miRNA analyses were performed on mesometrial and anti-mesometrial endometrium obtained from gestational days 12 and 15, respectively. Differentially expressed genes (DEGs) and miRNAs (DE-miRs) that were common to both or unique to either of the two anatomical locations of uterus were identified, respectively, indicating that differences in molecular response to the implanting conceptus exist between the two anatomical locations. In addition, we detected DEGs and DE-miRs between the two anatomical locations on the two gestational days, respectively. Of these DEGs, a number of genes, such as chemokine and T cell surface marker genes, were found to be significantly up-regulated mesometrially. Furthermore, we detected the interaction of CXCR4, CXCL11 and miR-9 using dual luciferase reporter assay. Taken together, this study revealed genes and pathways that might play the role of creating a receptive microenvironment at the mesometrial side, which is required to guide a proper positioning of conceptus in the uterus in pigs.

Differential transcriptome dynamics during the onset of conceptus elongation and between female and male porcine embryos

BACKGROUND

Porcine embryos undergo rapid differentiation and expansion between Days 8 and 12 before attaching to the maternal uterine epithelial surface after Day 13. It is known that maternal recognition of pregnancy and successful implantation are driven by mutual interactions between the elongated conceptus and the maternal endometrium. While most of the genes involved in regulation of embryo development are located on autosomal chromosomes, gene expression on sex chromosomes is modulating development through sex-specific transcription. To gain more insights into the dynamic transcriptome of preimplantation embryos at the onset of elongation and into X-linked gene expression, RNA-seq analyses were performed for single female and male porcine embryos collected on Days 8, 10, and 12 of pregnancy.

RESULTS

A high number of genes were differentially expressed across the developmental stages (2174 and 3275 for Days 8 vs 10, and 10 vs 12, respectively). The majority of differentially expressed genes (DEGs) were involved in embryo elongation, development, and embryo-maternal interaction. Interestingly, a number of DEGs was found with respect to embryo sex (137, 37, and 56 on Days 8, 10 and 12, respectively). At Day 8, most of these DEGs were X-linked (96). Strikingly, the number of DEGs encoded on the X chromosome dramatically decreased from Day 10 to Day 12.

CONCLUSIONS

The obtained results deepen the understanding about temporary transcriptomic changes in porcine embryos during the phase of conceptus elongation, meanwhile reveal dynamic compensation of X chromosome in the female and distinct transcriptional differences between female and male embryos.

Exposure of pregnant sows to low doses of estradiol-17β impacts on the transcriptome of the endometrium and the female preimplantation embryos†

Maternal exposure to estrogens can induce long-term adverse effects in the offspring. The epigenetic programming may start as early as the period of preimplantation development. We analyzed the effects of gestational estradiol-17β (E2) exposure with two distinct low doses, corresponding to the acceptable daily intake "ADI" and close to the no-observed-effect level "NOEL", and a high dose (0.05, 10, and 1000 μg E2/kg body weight daily, respectively). The E2 doses were orally applied to sows from insemination until sampling at day 10 of pregnancy and compared to carrier-treated controls leading to a significant increase in E2 in plasma, bile and selected somatic tissues including the endometrium in the high-dose group. Conjugated and unconjugated E2 metabolites were as well elevated in the NOEL group. Although RNA-sequencing revealed a dose-dependent effect of 14, 17, and 27 differentially expressed genes (DEG) in the endometrium, single embryos were much more affected with 982 DEG in female blastocysts of the high-dose group, while none were present in the corresponding male embryos. Moreover, the NOEL treatment caused 62 and 3 DEG in female and male embryos, respectively. Thus, we detected a perturbed sex-specific gene expression profile leading to a leveling of the transcriptome profiles of female and male embryos. The preimplantation period therefore demonstrates a vulnerable time window for estrogen exposure, potentially constituting the cause for lasting consequences. The molecular fingerprint of low-dose estrogen exposure on developing embryos warrants a careful revisit of effect level thresholds.