Early developing embryos affect the gene expression patterns in the mouse oviduct

Multi-omics analyses and machine learning prediction of oviductal responses in the presence of gametes and embryos

The oviduct is the site of fertilization and preimplantation embryo development in mammals. Evidence suggests that gametes alter oviductal gene expression. To delineate the adaptive interactions between the oviduct and gamete/embryo, we performed a multi-omics characterization of oviductal tissues utilizing bulk RNA-sequencing (RNA-seq), single-cell RNA-sequencing (scRNA-seq), and proteomics collected from distal and proximal at various stages after mating in mice. We observed robust region-specific transcriptional signatures. Specifically, the presence of sperm induces genes involved in pro-inflammatory responses in the proximal region at 0.5 days post-coitus (dpc). Genes involved in inflammatory responses were produced specifically by secretory epithelial cells in the oviduct. At 1.5 and 2.5 dpc, genes involved in pyruvate and glycolysis were enriched in the proximal region, potentially providing metabolic support for developing embryos. Abundant proteins in the oviductal fluid were differentially observed between naturally fertilized and superovulated samples. RNA-seq data were used to identify transcription factors predicted to influence protein abundance in the proteomic data via a novel machine learning model based on transformers of integrating transcriptomics and proteomics data. The transformers identified influential transcription factors and correlated predictive protein expressions in alignment with the in vivo -derived data. In conclusion, our multi-omics characterization and subsequent in vivo confirmation of proteins/RNAs indicate that the oviduct is adaptive and responsive to the presence of sperm and embryos in a spatiotemporal manner.

Significance Statement

We conducted a detailed molecular study of how the oviduct changes its gene expression and protein production in response to sperm and embryos after mating in mice. We found that the oviduct has distinct molecular signatures in different regions - upper versus lower regions. Shortly after mating, inflammatory responses are turned on in the lower regions due to the presence of sperm. A bit later, metabolic genes ramp up in the lower regions, likely to provide nutrients for the developing embryos. Overall, this multi-omics study revealed the oviduct dynamically adapts its molecular makeup over time and space to accommodate and support sperm, eggs and embryos.

Role of reproductive fluids and extracellular vesicles in embryo–maternal interaction during early pregnancy in cattle

The coordinated interaction between the developing embryo and the maternal reproductive tract is essential for the establishment and maintenance of pregnancy in mammals. An early cross-talk is established between the oviduct/uterus and the gametes and embryo. This dialogue will shape the microenvironment in which gamete transport, fertilisation, and early embryonic development occur. Due to the small size of the gametes and the early embryo relative to the volume of the oviductal and uterine lumina, collection of tissue and fluid adjacent to these cells is challenging in cattle. Thus, the combination of in vivo and in vitro models seems to be the most appropriate approach to better understand this fine dialogue. In this respect, the aim of this review is to summarise the recent findings in relation to gamete/embryo-maternal interaction during the pre-elongation period.

Peroxiredoxin 6 Plays Essential Role in Mediating Fertilization and Early Embryonic Development in Rabbit Oviduct

The oviduct is a site for early reproductive events including gamete maturation, fertilization, and early embryo development. Secretory cells lining the oviduct lumen synthesize and secrete proteins that interact with gametes and developing embryos. Although previous studies have identified some of the secretory proteins in the oviduct, however, knowledge and their precise specific functions in the oviduct are poorly understood. In this study, by using proteomic approach, we identified a secretory protein, Peroxiredoxin 6 (PRDX6), and evaluated its role in mediating early pregnancy events, fertilization, and embryo development in rabbit oviduct. The expression of PRDX6 was significantly higher in ampulla and isthmus sections of the oviduct in mated animal groups compared to non-mated controls. Furthermore, significant reduction in number of embryos recovered from PRDX6 siRNA-transfected oviductal horn was observed compared to the control contralateral horn. Moreover, in animals receiving PRDX6 siRNA in their oviductal horn, the number of implanted blastocysts was significantly less in the uterus as observed on day 9 post-coital (p.c.). Further, during embryo-rabbit oviduct epithelial cell (ROEC) co-culture, siRNA-mediated PRDX6 silencing attenuated the early embryonic development. Mechanistically, increased levels of ROS and expression of oxidative stress- and inflammation-related proteins were found in PRDX6 siRNA-treated ROEC cells as compared to control cells, implicating that ablation of PRDX6 in the oviduct creates a stress-induced micro-environment detrimental to early embryonic development in oviduct. Taken together, our data suggest that PRDX6 maintains an optimal micro-environment conducive to successful embryo development and can be considered as a candidate to evaluate its therapeutic potential in IVF strategies.

Nanoparticles from culture media are internalized by in vitro-produced bovine embryos and its depletion affect expression of pluripotency genes

Extracellular vesicles are nanoparticles secreted by cell and have been proposed as suitable markers to identify competent embryos produced in vitro. Characterizing EVs secreted by individual embryos is challenging because culture medium itself contributes to the pool of nanoparticles that are co-isolated. To avoid this, culture medium must be depleted of nanoparticles that are present in natural protein source. The aim of this study was to evaluate if the culture medium subjected to nanoparticle depletion can support the proper in vitro development of bovine embryos. Zygotes were cultured in groups on depleted or control medium for 8 days. Nanoparticles from the medium were characterized by their morphology, size and expression of EVs surface markers. Isolated nanoparticles were labelled and added to depleted medium containing embryos at different developmental stages and evaluated after 24 hours at 2, 8-16 cells, morula and blastocyst stages. There were no statistical differences on blastocyst rate at day 7 and 8, total cell count neither blastocyst diameter between groups. However, morphological quality was better in blastocysts cultured in non-depleted medium and the expression of SOX2 was significantly lower whereas NANOG expression was significantly higher. Few nanoparticles from medium had a typical morphology of EVs but were positive to specific surface markers. Punctuated green fluorescence near the nuclei of embryonic cells was observed in embryos from all developmental stages. In summary, nanoparticles from culture medium are internalized by in vitro cultured bovine embryos and their depletion affects the capacity of medium to support the proper embryo development.

A Comparative View on the Oviductal Environment during the Periconception Period

The oviduct plays important roles in reproductive events: sperm reservoir formation, final gamete maturation, fertilization and early embryo development. It is well known that the oviductal environment affects gametes and embryos and, ultimately, the health of offspring, so that in vivo embryos are better in terms of morphology, cryotolerance, pregnancy rates or epigenetic profile than those obtained in vitro. The deciphering of embryo-maternal interaction in the oviduct may provide a better understanding of the embryo needs during the periconception period to improve reproductive efficiency. Here, we perform a comparative analysis among species of oviductal gene expression related to embryonic development during its journey through the oviduct, as described to date. Cross-talk communication between the oviduct environment and embryo will be studied by analyses of the secreted or exosomal proteins of the oviduct and the presence of receptors in the membrane of the embryo blastomeres. Finally, we review the data that are available to date on the expression and characterization of the most abundant protein in the oviduct, oviductin (OVGP1), highlighting its fundamental role in fertilization and embryonic development.

Effect of mating on mRNA and protein expression of beta nerve growth factor and its receptor, TrKA, in the oviduct of llama (Lama glama)

Copulation produces different stimuli in the female reproductive tract in camelids, which lead to ovulation. Expression of β-nerve growth factor (β-NGF) and its specific receptor, tropomyosin receptor kinase A (TrKA), was studied comparing the oviductal microenvironment of mated and nonmated llamas. β-NGF and TrKA were expressed in the llama ampulla, isthmus, and utero-tubal-junction (UTJ), and they were mainly colocalized in the apical region of the oviductal mucosa. A TrKA immunosignal was also found in muscle cells and blood vessels, with the highest mark in UTJ muscle cells of copulated females. Both β-NGF and TrKA transcripts were expressed in the three oviductal segments. Relative TrKA abundance did not differ between mated and nonmated females, but relative β-NGF abundance was higher in the UTJ of copulated females (p < .05). β-NGF might not be secreted into the oviductal fluid (OF) since the protein was not found in the OF of mated or nonmated females. Therefore, it can be concluded that the llama oviduct expresses the β-NGF/TrKA system and that an increase in β-NGF gene expression in the UTJ 24 h after copulation along with an increase in TrKA protein expression may indicate an important role in the gamete transport and fertilization process in llamas.

Gene expression and metabolic response of bovine oviduct epithelial cells to the early embryo

During its journey through the oviduct, the bovine embryo may induce transcriptomic and metabolic responses, via direct or indirect contact, from bovine oviduct epithelial cells (BOECs). An in vitro model using polyester mesh was established, allowing the study of the local contact during 48 h between a BOEC monolayer and early embryos (2- or 8-cell stage) or their respective conditioned media (CM). The transcriptomic response of BOEC to early embryos was assessed by analyzing the transcript abundance of SMAD6, TDGF1, ROCK1, ROCK2, SOCS3, PRELP and AGR3 selected from previous in vivo studies and GPX4, NFE2L2, SCN9A, EPSTI1 and IGFBP3 selected from in vitro studies. Moreover, metabolic analyses were performed on the media obtained from the co-culture. Results revealed that presence of early embryos or their CM altered the BOEC expression of NFE2L2, GPX4, SMAD6, IGFBP3, ROCK2 and SCN9A. However, the response of BOEC to two-cell embryos or their CM was different from that observed to eight-cell embryos or their CM. Analysis of energy substrates and amino acids revealed that BOEC metabolism was not affected by the presence of early embryos or by their CM. Interestingly, embryo metabolism before embryo genome activation (EGA) seems to be independent of exogenous sources of energy. In conclusion, this study confirms that early embryos affect BOEC transcriptome and BOEC response was embryo stage specific. Moreover, embryo affects BOEC via a direct contact or via its secretions. However transcriptomic response of BOEC to the embryo did not manifest as an observable metabolic response.

Early embryo-maternal communication in the oviduct: A review

An intact embryo-maternal communication is critical for the establishment of a successful pregnancy. To date, a huge number of studies have been performed describing the complex process of embryo-maternal signaling within the uterus. However, recent studies indicate that the early embryo communicates with the oviductal cells shortly after fertilizationand that this is important for the successful establishment of pregnancy. Only if the early embryo is capable to signal the mother within a precise timeframe and to garner a response, will the embryo be able to survive and reach the uterus. This review will give an overview of all the experimental designs which have investigated embryo-maternal interaction in the oviduct. In addition to that, it will provide a comprehensive analysis of the findings to date elucidating the morphological and molecular changes in the oviduct which are induced by the presence of the early embryo highlighting how the tubal responses affect embryo development and survival.

Review: Environmental impact on early embryonic development in the bovine species

Assisted reproduction techniques (ARTs) provide access to early stage embryos whose analysis and assessment deliver valuable information. The handling of embryos, including the in vitro production of bovine embryos, is a rapidly evolving area which nonetheless exposes the embryos to unnatural conditions for a period of time. The Fallopian tube provides innumerable quantitative and qualitative factors, all of which guarantee the successful development of the embryo. It is well known that the Fallopian tube can be bypassed, using embryo transfer, resulting in successful implantation in the target recipient animal and the birth of calves. However, the question arises as to whether such circumvention has a negative impact on the embryo during this sensitive development period. First crosstalk between the embryo and its environment confirms mutual recognition activities and indicate bilateral effects. Nowadays, in vitro production of bovine embryos is a well-established technology. However, it is still evident that in vitro generated embryos are not qualitatively comparable to embryos obtained ex vivo. To counteract these differences, comparative studies between in vitro and ex vivo embryos are advantageous, as embryos grown in their physiological environment can provide a blueprint or gold standard against which to compare embryos produced in vitro. Attempts to harness the bovine oviduct were sometimes very invasive and did not result in wide acceptance and routine use. Long-term development and refinement of transvaginal endoscopy for accessing the bovine oviduct has meanwhile been routinely applied for research as well as in practice. Comparative studies combining in vitro development with development in the cattle oviduct revealed that the environmental conditions to which the embryo is exposed before activation of the embryonic genome can have detrimental and lasting effects on its further development. These effects are manifested as deviations in gene expression profiles and methylation signatures as well as frequency of whole chromosomal or segmental aberrations. Furthermore, it was shown that hormonal superstimulation (multiple ovulation and embryo transfer), varying progesterone concentrations as well as metabolic disorders caused by high milk production, markedly affected embryo development in the postpartum period. Assisted reproductive techniques that allow the production and handling of extra numbers of generated embryos promise to have a very high impact on scientific and practical application. Any influence on the early embryonic life, both in animals and in vitro, is accompanied by a sensitive change in embryonic activity and should be assessed in vivo on the basis of physiological conditions before being used for ART.

Extracellular Vesicles Function as Bioactive Molecular Transmitters in the Mammalian Oviduct: An Inspiration for Optimizing in Vitro Culture Systems and Improving Delivery of Exogenous Nucleic Acids during Preimplantation Embryonic Development

Two technologies, in vitro culture and exogenous gene introduction, constitute cornerstones of producing transgenic animals. Although in vitro embryo production techniques can bypass the oviduct during early development, such embryos are inferior to their naturally produced counterparts. In addition, preimplantation embryos are resistant to the uptake of exogenous genetic material. These factors restrict the production of transgenic animals. The discovery of extracellular vesicles (EVs) was a milestone in the study of intercellular signal communication. EVs in the oviduct, known as oviductosomes (OVS), are versatile delivery tools during maternal–embryo communication. In this review, we discuss the important roles of OVS in these interactions and the feasibility of using them as tools for transferring exogenous nucleic acids during early development. We hypothesize that further accurate characterization of OVS cargoes and functions will open new horizons for research on maternal–embryo interactions and enhance the production of transgenic animals.

Challenges in studying preimplantation embryo-maternal interaction in cattle

A comprehensive understanding of the complex embryo-maternal interactions during the preimplantation period requires the analysis of the very early stages of pregnancy encompassing early embryonic development, maternal recognition and the events leading to implantation. Despite the fact that embryo development until blastocyst stage is somewhat autonomous (i.e., does not require contact with the maternal reproductive tract and can be successfully recapitulated in vitro), many studies on ruminant embryo production have focused on the fundamental question of why: (i) only 30%-40% of immature oocytes develop to the blastocyst stage and (ii) the quality of such blastocysts continually lags behind that of blastocysts produced in vivo. Clear evidence indicates that in vitro culture conditions are far from optimal with deficiencies being manifested in short- and long-term effects on the embryo. Thus, enhanced knowledge of mechanisms controlling embryo-maternal interactions would allow the design of novel strategies to improve in vitro embryo conditions and reproductive outcomes in cattle.

Composing the Early Embryonic Microenvironment: Physiology and Regulation of Oviductal Secretions

The oviductal fluid is the first environment experienced by mammalian embryos at the very beginning of life. However, it has long been believed that the oviductal environment was not essential for proper embryonic development. Successful establishment of in vitro embryo production techniques (which completely bypass the oviduct) have reinforced this idea. Yet, it became evident that in vitro produced embryos differ markedly from their in vivo counterparts, and these differences are associated with lower pregnancy outcomes and more health issues after birth. Nowadays, researchers consider the oviduct as the most suitable microenvironment for early embryonic development and a substantial effort is made to understand its dynamic, species-specific functions. In this review, we touch on the origin and molecular components of the oviductal fluid in mammals, where recent progress has been made thanks to the wider use of mass spectrometry techniques. Some of the factors and processes known to regulate oviductal secretions, including the embryo itself, as well as ovulation, insemination, endogenous and exogenous hormones, and metabolic and heat stress, are summarized. Special emphasis is laid on farm animals because, owing to the availability of sample material and the economic importance of fertility in livestock husbandry, a large part of the work on this topic has been carried out in domestic animals used for dairy and/or meat production.

Extracellular vesicles derived from donor oviduct fluid improved birth rates after embryo transfer in mice

Embryo transfer (ET) is an important procedure for assisted reproduction. However, the relatively lower success rate of ET hampers its application potential. In this study we aimed to elucidate the effects of extracellular vesicles derived from donor oviduct fluid (EDOF) on embryo development after ET. Extracellular vesicles from the oviduct were isolated and purified using ultracentrifugation and identified using transmission electron microscopy, NanoSight, bicinchoninic acid (BCA) protein assay and western blotting. The results revealed that extracellular vesicles were present in donor oviduct fluid in higher concentrations (P<0.05) and contained more proteins (P<0.05) than extracellular vesicles derived from recipient oviduct fluid (EROF). EDOF or EROF were supplemented in an ET medium (ETM) and the results showed that EDOF significantly improved birth rate via resisting apoptosis and promoting differentiation. In conclusion, our study indicated that there are differences in EDOF and EROF and that supplementing EDOF to ETM can improve the efficiency of ET; improved ET efficiency promotes the use of gene editing and benefits assisted reproductive technology and animal welfare.

An approach to study the local embryo effect on gene expression in the bovine oviduct epithelium in vivo

This study aimed to examine the local embryo effect on the transcriptomic response of the epithelial cells of the oviduct in vivo. Fifteen heifers were synchronized and artificially inseminated to a standing heat. All heifers were slaughtered on Day 2.5 after oestrus. The oviducts from 13 animals were isolated, trimmed free of tissue and divided between ampulla/isthmus. The ipsilateral isthmus was divided into smaller sections (2 cm). Each section was sequentially flushed until the embryo was located (4/13) and then opened and scraped longitudinally to obtain the epithelial cells. Cells were snap-frozen in LN₂ for gene expression analysis. All recovered embryos were found at the beginning of the isthmus. The 2 cm sections selected for the transcriptomic analysis were as follows: embryo section (in which the embryo was found); proximal section (through which the embryo had passed); distal section (on the uterine side of the embryo); and contralateral section (section from the contralateral isthmus). The expression pattern of eight genes (STK32A, KERA, QRFPR, MCTP1, PRELP, VAT1L, SOCS3 and CCL20) differentially expressed between the isthmus of pregnant (multiple embryo model) and cyclic heifers were assessed by RT-qPCR. One-way ANOVA and t test was used for statistical analysis. Comparisons between ipsilateral and contralateral oviduct or along the ipsilateral oviduct resulted in no differences for all genes. Despite the failure to detect a site-specific response of a single embryo on the abundance of distinct transcripts in the bovine oviduct in vivo on Day 2.5, the current methodology with proposed modifications would be useful for future studies to examine the local embryo effect.

"Biological Adhesion" is a Significantly Regulated Molecular Process during Long-Term Primary In Vitro Culture of Oviductal Epithelial Cells (Oecs): A Transcriptomic and Proteomic Study

Oviductal epithelial cells (OECs) actively produce stimulating and protecting factors, favoring survival and viability of gametes and early embryos. The oviduct participates in the initial reproductive events, which strongly depends on adhesion. The analysis of differential gene expression in OECs, during long-term in vitro culture, enables recognition of new molecular markers regulating several processes, including "biological adhesion". Porcine oviducts were stained with hematoxylin and eosin, as well as with antibodies against epithelial markers. Then, OECs were long-term in vitro cultured and after 24 h, 7, 15, and 30 days of culture were subjected to transcriptomic and proteomic assays. Microarrays were employed to evaluate gene expression, with Matrix-assisted laser desorption/ionization-time of light (MALDI-TOF) mass spectrometry applied to determine the proteome. The results revealed proper morphology of the oviducts and typical epithelial structure of OECs during the culture. From the set of differentially expressed genes (DEGs), we have selected the 130 that encoded proteins detected by MALDI-TOF MS analysis. From this gene pool, 18 significantly enriched gene ontology biological processes (GO BP) terms were extracted. Among them we focused on genes belonging to "biological adhesion" GO BP. It is suggested that increased expression of studied genes can be attributed to the process of intensive secretion of substances that exhibit favorable influence on oviductal environment, which prime gametes adhesion and viability, fertilization, and early embryo journey.

Extracellular Vesicles in the Oviduct: Progress, Challenges and Implications for the Reproductive Success

The oviduct is the anatomical part of the female reproductive tract where the early reproductive events take place, from gamete transport, fertilization and early embryo development to the delivery of a competent embryo to the uterus, which can implant and develop to term. The success of all these events rely upon a two-way dialogue between the oviduct (lining epithelium and secretions) and the gametes/embryo(s). Recently, extracellular vesicles (EVs) have been identified as major components of oviductal secretions and pointed to as mediators of the gamete/embryo-maternal interactions. EVs, comprising exosomes and microvesicles, have emerged as important agents of cell-to-cell communication by the transfer of biomolecules (i.e., mRNAs, miRNAs, proteins) that can modulate the activities of recipient cells. Here, we provide the current knowledge of EVs in the oviductal environment, from isolation to characterization, and a description of the EVs molecular content and associated functional aspects in different species. The potential role of oviductal EVs (oEVs) as modulators of gamete/embryo-oviduct interactions and their implications in the success of early reproductive events is addressed. Lastly, we discuss current challenges and future directions towards the potential application of oEVs as therapeutic vectors to improve pregnancy disorders, infertility problems and increase the success of assisted reproductive technologies.

Transcriptomic analysis of the oviduct of pigs during the peri-conceptional period

The optimal environment in the oviduct is created by adjusting its ultrastructure and secretory capacity to protect gametes and embryos. It was hypothesized that direct contact between the isthmic epithelium and 2- and 4-cell-stage embryos would alter the transcriptomic profile of the isthmus in pigs. Microarray analysis was performed to determine the alterations in gene expression of the isthmus on Days 2-3 of pregnancy in pigs (after natural mating) during embryo presence in the oviduct. Of 43,803 microarray probes, 354 (0.81%) transcripts were altered (P-value ≤ 0.05 and fold-change ≥ 1.2) on the days of pregnancy when assessments were made. Of these 354 transcripts, 118 (33.3%) were up-regulated, and 236 (66.7%) were down-regulated. A total of 57 (48.3%) up-regulated and 73 down-regulated (30.9%) transcripts were classified into gene ontology categories. Of the 354 altered genes, 36 (10.2%) were categorized into the Toll-like or NOD-like receptor signaling pathway, in the immune system subcategory. Selected genes engaged in maternal immune function were down-regulated. The up-regulated genes were involved in epigenetic regulation, the protection of embryos against oxidative stress and xenobiotics and the control of estrogen metabolism. The 2- and 4-cell-stage embryos might, therefore, affect the oviductal transcriptome to optimize the intra-oviductal milieu, which is necessary to support proper development of embryos. The results of this study indicates the pig oviduct has the capacity to alter its transcriptomic profile as a result of early embryo development after natural mating.

Oviduct extracellular vesicles protein content and their role during oviduct-embryo cross-talk

Successful pregnancy requires an appropriate communication between the mother and the embryo. Recently, exosomes and microvesicles, both membrane-bound extracellular vesicles (EVs) present in the oviduct fluid have been proposed as key modulators of this unique cross-talk. However, little is known about their content and their role during oviduct-embryo dialog. Given the known differences in secretions by in vivo and in vitro oviduct epithelial cells (OEC), we aimed at deciphering the oviduct EVs protein content from both sources. Moreover, we analyzed their functional effect on embryo development. Our study demonstrated for the first time the substantial differences between in vivo and in vitro oviduct EVs secretion/content. Mass spectrometry analysis identified 319 proteins in EVs, from which 186 were differentially expressed when in vivo and in vitro EVs were compared (P < 0.01). Interestingly, 97 were exclusively expressed in in vivo EVs, 47 were present only in in vitro and 175 were common. Functional analysis revealed key proteins involved in sperm-oocyte binding, fertilization and embryo development, some of them lacking in in vitro EVs. Moreover, we showed that in vitro-produced embryos were able to internalize in vivo EVs during culture with a functional effect in the embryo development. In vivo EVs increased blastocyst rate, extended embryo survival over time and improved embryo quality. Our study provides the first characterization of oviduct EVs, increasing our understanding of the role of oviduct EVs as modulators of gamete/embryo-oviduct interactions. Moreover, our results point them as promising tools to improve embryo development and survival under in vitro conditions.

Bovine embryo-oviduct interaction in vitro reveals an early cross talk mediated by BMP signaling

Signaling components of bone morphogenetic proteins (BMPs) are expressed in an anatomically and temporally regulated fashion in bovine oviduct. However, a local response of this signaling to the presence of the embryo has yet to be elucidated. The aim of the present study was to evaluate if early embryo-oviduct interaction induces changes in the gene expression of BMP signaling components. For this purpose, we used an in vitro co-culture system to investigate the local interaction between bovine oviductal epithelial cells (BOEC) from the isthmus region with early embryos during two developmental periods: before (from the 2-cell to 8-cell stage) or during (from the 8-cell to 16-cell stage) the main phase of embryonic genome activation (EGA). Exposure to embryos, irrespective of the period, significantly reduced the relative abundance of BMPR1B, BMPR2, SMAD1, SMAD6 and ID2 mRNAs in BOEC. In contrast, embryos that interacted with BOEC before EGA showed a significant increase in the relative abundance of SMAD1 mRNA at the 8-cell stage compared to embryos cultured without BOEC. Moreover, embryos at the 16-cell stage that interacted with BOEC during EGA showed a significant increase in BMPR1B, BMPR2 and ID2 mRNA. These results demonstrate that embryo-oviduct interaction in vitro induces specific changes in the transcriptional levels of BMP signaling, causing a bidirectional response that reduces the expression levels of this signaling in the oviductal cells while increases them in the early embryo. This suggests that BMP signaling pathway could be involved in an early cross talk between the bovine embryo and the oviduct during the first stages of development.

Proteome of equine oviducal fluid: effects of ovulation and pregnancy

The equine oviduct plays a pivotal role in providing the optimal microenvironment for early embryonic development, but little is known about the protein composition of the oviducal fluid in the horse. The aim of the present study was to provide a large-scale identification of proteins in equine oviducal fluid and to determine the effects of ovulation and pregnancy. Four days after ovulation, the oviducts ipsilateral and contralateral to the ovulation side were collected from five pregnant and five non-pregnant mares. Identification and relative quantification of proteins in the oviducal fluid of the four groups was achieved by isobaric tags for relative and absolute quantification (iTRAQ) labelling and HPLC–tandem mass spectrometry. The presence of an embryo in the ipsilateral oviducal fluid of pregnant mares induced upregulation of 11 and downregulation of two proteins compared with the contralateral side, and upregulation of 19 proteins compared with the ipsilateral side of non-pregnant mares. Several of these upregulated proteins are related to early pregnancy in other species. The present study represents the first high-throughput identification of proteins in the oviducal fluid of the mare. The results support the hypothesis that the equine embryo interacts with the oviduct, affecting the maternal secretion pattern of proteins involved in pregnancy-related pathways.

Oviductal response to gametes and early embryos in mammals

The oviduct is a complex and organized thin tubular structure connecting the ovary with the uterus. It is the site of final sperm capacitation, oocyte fertilization and, in most species, the first 3–4days of early embryo development. The oviductal epithelium is made up of ciliary and secretory cells responsible for the secretion of proteins and other factors which contribute to the formation of the oviductal fluid. Despite significant research, most of the pathways and oviductal factors implicated in the crosstalk between gametes/early embryo and the oviduct remain unknown. Therefore, studying the oviductal environment is crucial to improve our understanding of the regulatory mechanisms controlling fertilization and embryo development. In vitro systems are a valuable tool to study in vivo pathways and mechanisms, particularly those in the oviducts which in livestock species are challenging to access. In studies of gamete and embryo interaction with the reproductive tract, oviductal epithelial cells, oviductal fluid and microvesicles co-cultured with gametes/embryos represent the most appropriate in vitro models to mimic the physiological conditions in vivo.

Cross talk during the periconception period

The cross talk between gametes, embryos, and female reproductive tract plays a crucial role in fine tuning of different reproductive events as well as influencing the epigenetic profile of offspring and their health in adulthood. Here, we describe some background to the recent investigations leading to the discovery of this cross talk. We will also point to important requirements for understanding the maternal communication with gametes and embryos. Finally, we mention two probable hypotheses regarding how gametes and embryos are recognized by the female reproductive tract. It is clear that understanding this cross talk is leading to the production of new means for increasing fertility and potentials for affecting the epigenomic profile of an individual.

The Equine Embryo Influences Immune-Related Gene Expression in the Oviduct

Although the equine oviduct clearly affects early embryo development and the selective transport of equine embryos through the oviduct indicates a reciprocal interaction, the influence of the embryo on gene expression in the oviduct remains to be determined in the horse. The aim of this study was to examine this by means of RNA sequencing. Four days after ovulation, epithelial cells ipsilateral and contralateral to the ovulation side from five cyclic and five pregnant mares were collected from the oviduct. RNA was extracted, samples were sequenced, and data analysis was performed to determine differentially expressed genes (DEGs) (P value ≤0.05 and absolute fold change ≥2) and to provide functional interpretation. A total of 10 743 transcripts were identified and 253 genes were found to be upregulated and 108 to be downregulated in the pregnant ipsilateral oviduct when compared to the cyclic ipsilateral oviduct. Comparison of the ipsilateral and the contralateral oviduct indicated 164 DEGs in pregnant mares and 77 DEGs in cyclic mares. Enriched functional categories were detected only in the comparison of pregnant and cyclic ipsilateral oviducts and showed that the equine embryo affects the expression of immune response-related genes in the oviduct, with marked upregulation of interferon-associated genes. This research represents the foundation for further assessment of the role of specific genes in the early embryo-maternal dialogue of the horse.

Differential influence of ampullary and isthmic derived epithelial cells on zona pellucida hardening and in vitro fertilization in ovine

The central role of the oviduct, as the site of zona pellucida (ZP) maturation, fertilization and early embryogenesis, has been recognized. The objective of this study was to investigate whether ampullary and isthmic derived epithelial cells have different effects on in vitro ZP hardening, in vitro fertilization (IVF) and in vitro culture (IVC) of the resulting embryos. Cumulus oocyte complexes (COCs) were matured in a coculture system with ampullary/isthmic epithelial cells, TCM199 supplemented with insulin-like growth factor I (IGF-I) and epithelial derived growth factor (EGF) (GF treated group), conditioned media produced using ampullary (ACM), isthmic (ICM), COCs+ampullary, and COCs+isthmic epithelial cells, contactless culture system, oviductal fluid, GF+ACM/ICM, and drops of TCM199 (control), for 24h. The matured oocytes were randomly divided into two groups: Group I was subjected to ZP digestion; Group II underwent IVF. The duration of the ZP digestion, in a coculture system with ampullary epithelial cells (AE) was significantly increased (p<0.05), compared with other groups. Penetrated oocytes and monospermic fertilization were significantly increased (p<0.05) in the AE group. The mean number of spermatozoa per penetrated oocyte was reduced dramatically for the AE group (p<0.05). A significant increase (p<0.05) in the embryo development was observed in all treated groups, compared to the control. Results revealed that epithelial cells harvested from the ampullary segment of the oviduct had in vitro specialized role in ZP hardening and have subsequent IVF and IVC outcomes.

Transgenerational Developmental Programming of Ovarian Reserve

Exposure to an adverse early-life environment leads to long-term health problems, many of which are recapitulated in subsequent generations. The female reproductive tract is particularly sensitive to early-life influences, and plays a pivotal role in programming the conceptus. We examine the influence of suboptimal grandmaternal diet on reproductive potential of granddaughters in the absence of any further dietary manipulations in the daughters in a rat low-protein diet model. Exposure to low-protein grand-maternal diet leads to decreased ovarian reserve and increased intra-abdominal fat mass in granddaughters, accompanied by accelerated accumulation of oxidative stress and mtDNA copy number instability in the ovaries. Ovarian telomere length declines more rapidly in the exposed granddaughters, indicating accelerated ageing in the reproductive tract. Thus, we demonstrate that suboptimal grandmaternal diet during pregnancy accelerates reproductive ageing across subsequent generations. These findings have important implications for understanding both individual rates of decline in fertility with age, and the clinical impact of current global trends towards delayed childbearing.

Oviductal Transcriptome Is Modified after Insemination during Spontaneous Ovulation in the Sow

Gene Expression Microarray technology was used to compare oviduct transcriptome between inseminated and non-inseminated pigs during spontaneous oestrus. We used an in vivo model approaching the study from a physiological point of view in which no hormonal treatment (animals were in natural oestrus) and no artificial sperm selection (selection was performed within the female genital) were imposed. It is therefore emphasised that no surgical introduction of spermatozoa and no insemination at a site other than the physiological one were used. This approach revealed 17 genes that were two-fold or more up-regulated in oviducts exposed to spermatozoa and/or developing embryos and 9 genes that were two-fold or more down-regulated. Functional analysis of the genes revealed that the top canonical pathways affected by insemination were related to the inflammatory response and immune system (Network 1) to molecular transport, protein trafficking and developmental disorder (Network 2) and to cell-to-cell signalling and interaction (Network 3). Some of the genes in network 1 had been previously detected in the oviduct of human and animals, where they were over-expressed in the presence of spermatozoa or pre-implantation embryos (C3, IGHG1, ITIH4, TNF and SERPINE1) whereas others were not previously reported (SAA2, ALOX12, CD1D and SPP1). Genes in Network 2 included RAB1B and TOR3A, the latter being described for the first time in the oviduct and clearly expressed in the epithelial cells of the mucosa layer. Network 3 integrated the genes with the highest down-regulation level (CYP51, PTH1R and TMOD3). Data in the present study indicate a change in gene expression during gamete encounter at the site of fertilization after a natural sperm selection within the female genital tract. These changes would indicate a modification of the environment preparing the oviduct for a successful fertilization and for an adequate embryo early development.

Oviduct-Embryo Interactions in Cattle: Two-Way Traffic or a One-Way Street?

This study examined the effect of the presence of single or multiple embryos on the transcriptome of the bovine oviduct. In experiment 1, cyclic (nonbred, n = 6) and pregnant (artificially inseminated, n = 11) heifers were slaughtered on Day 3 after estrus, and the ampulla and isthmic regions of the oviduct ipsilateral to the corpus luteum were separately flushed. Oviductal epithelial cells from the isthmus region, in which all oocytes/embryos were located, were snap-frozen for microarray analysis. In experiment 2, heifers were divided into cyclic (nonbred, n = 6) or pregnant (multiple embryo transfer, n = 10) groups. In vitro-produced presumptive zygotes were transferred endoscopically to the ipsilateral oviduct on Day 1.5 postestrus (n = 50 zygotes/heifer). Heifers were slaughtered on Day 3, and oviductal isthmus epithelial cells were recovered for RNA sequencing. Microarray analysis in experiment 1 failed to detect any difference in the transcriptome of the oviductal isthmus induced by the presence of a single embryo. In experiment 2, following multiple embryo transfer, RNA sequencing revealed 278 differentially expressed genes, of which 123 were up-regulated and 155 were down-regulated in pregnant heifers. Most of the down-regulated genes were related to immune function. In conclusion, the presence of multiple embryos in the oviduct resulted in the detection of differentially expressed genes in the oviductal isthmus; failure to detect changes in the oviduct transcriptome in the presence of a single embryo may be due to the effect being local and undetectable under the conditions of this study.

Osteopontin is expressed in the oviduct and promotes fertilization and preimplantation embryo development of mouse

Osteopontin (OPN) is a multifunctional phosphoprotein that is detected in various tissues, including male and female reproductive tracts. In this study, we evaluated OPN expression in mouse oviducts during the estrus cycle, and at days 1–5 of pregnancy and pseudopregnancy by reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry. The mice oocytes, sperm and embryos were treated with different concentrations of anti-OPN antibody in vitro to detect the function of OPN in fertilization and preimplantation embryo development. OPN mRNA and protein expression in mouse oviducts were cyclic dependent throughout the estrous cycle, which was highest at estrous and lowest at diestrous. Such a phenomenon was consistent with the change in estrogen level in mice. The expression levels of OPN in mice oviduct of normal pregnancy and pseudopregnancy were significantly different, which indicated that OPN expression in mouse oviducts was depend on estrogen and preimplantation embryo. Furthermore, anti-OPN antibody treatment could reduce the rates of fertilization, cleavage and blastocyst formation in vitro in a dose-dependent way. Overall, our results indicated that the expression of OPN in mouse oviducts during the estrous cycle and early pregnancy is likely regulated by estrogen and the embryo, and OPN may play a vital role in oocyte fertilization and preimplantation embryo development.

Effects of spermatozoa-oviductal cell coincubation time and oviductal cell age on spermatozoa-oviduct interactions

The oviduct plays a crucial role in sperm storage, maintenance of sperm viability and sperm transport to the site of fertilisation. The aim of the present study was to investigate the effects of oviductal cell culture passage number, oviductal cell age and spermatozoa-oviduct coincubation times on gene expression in oviductal cells. Immortalised oviductal epithelial cells (OPEC) obtained from two different cell passages (36 and 57) were subcultured three times with and without spermatozoa for 24 h (control group). In a second study, OPEC were cocultured with spermatozoa for different time intervals (0, 4, 12 and 24 h). Expression of adrenomedullin (ADM), heat shock 70 kDa protein 8 (HSPA8) and prostaglandin E synthase (PGES) in OPEC was measured by quantitative polymerase chain reaction. The expression of ADM and HSPA8 was decreased significantly in OPEC cells from Passage 57, particularly in the later subculture group. These effects on HSPA8, but not ADM, expression in OPEC were further altered after coculture with spermatozoa for 24 h. We also demonstrated that spermatozoa-oviduct coculture for 12 and 24 h resulted in significantly higher expression of ADM, HSPA8 and PGES in OPEC. Overall, the data suggest that the OPEC lose some of their properties as a result of oviductal cell aging and that there are spermatozoa-oviduct interactions leading to increased oviductal cell gene expression.

The ART of studying early embryo development: progress and challenges in ruminant embryo culture

The study of preimplantation mammalian embryo development is challenging due to difficulties in accessing in vivo-derived embryos in large numbers at the early stages and the inability to culture embryos in vitro much beyond the blastocyst stage. Nonetheless, embryos exhibit an amazing plasticity and tolerance when it comes to adapting to the environment in which they are cultured. They are capable of developing in media ranging in composition from simple balanced salt solutions to complex systems involving serum and somatic cells. At least a proportion of the blastocysts that develop in culture are developmentally competent as evidenced by the fact that live offspring have resulted following transfer. However, several studies using animal models have shown that such embryos are sensitive to environmental conditions that can affect future pre- and post-natal growth and developmental potential. This review summarises some key aspects of early embryo development and the approaches taken to study this important window in early life.

[Use of an in vitro model in bovine to evidence a functional and molecular dialogue between preimplantation embryo and oviduct epithelial cells]

Beyond being a pipe between ovary and uterus, the oviduct is an active player in different aspects of early reproductive processes, in particular in the transport of embryos to the site of implantation and the regulation of its early development. Different studies evidenced a communication between oviduct and early embryo at the molecular and functional levels. Since the study of these interactions is difficult in vivo, different in vitro systems have been developed to mimic the maternal milieu during early development. These systems allowed to confirm the action of the cells on the quality of early development (blastocyst rate and viability). In turn, the embryos are producing signals that are able to modify and adapt the activity of maternal cells.

Suboptimal nutrition in utero causes DNA damage and accelerated aging of the female reproductive tract

Early life exposure to adverse environments can lead to a variety of metabolic and cardiovascular diseases in offspring. We hypothesize that female reproductive function may also be affected, with subsequent implications for fertility. We used an established maternal low-protein model where animals are born small but undergo rapid postnatal catch-up growth by suckling a control-fed dam (recuperated offspring). Markers of oxidative stress and cellular aging in reproductive tract tissues were assessed at 3 and 6 mo of age. Recuperated offspring had lower birth weight than controls (P<0.01) but caught up during lactation. 4-Hydroxynonenal (4HNE; an indicator of oxidative stress) was increased in recuperated animals compared with controls in both ovaries and oviducts at 6 mo. At 3 and 6 mo, ovaries and oviducts of recuperated offspring had increased mitochondrial (mt)DNA copy number (P<0.01). By contrast, germ-line cells showed no difference in mtDNA copy number, suggesting they were protected from suboptimal maternal nutrition. Oviduct and somatic ovarian telomere length declined more rapidly with age in recuperated animals. This accelerated cellular aging was associated with a declined ovarian reserve in developmentally programmed animals. These findings have significant clinical implications in light of worldwide trends to delayed childbearing.

Oviductal, endometrial and embryonic gene expression patterns as molecular clues for pregnancy establishment

In higher animals, the beginning of new life and transfer of genetic material to the next generation occurs in the oviduct when two distinct gametes cells unite resulting in the formation of a zygote. The zygote then undergoes serial developmental processes in the oviduct and enters into the uterus where it faces challenges and scrutiny from the endometrial ecosystem. Thus, embryos that are able to establish an appropriate embryo-maternal dialogue are capable of developing to term whereas the incompetent ones can perish any time during the gestation period. Although several lines of evidences indicated that pregnancy loss is a multi-factorial phenomenon, the biochemical composition of the embryo and maternal environment are the main players to determine pregnancy outcome. Indeed, expression patterns of the genes are the driving forces that induce biochemical composition changes in embryo, oviduct and uterine environment. Thus, examining the molecular signals that are associated with oviductal or endometrial receptivity and embryo implantation is essential for establishing strategies to improve pregnancy success. Therefore, this review focuses on the contribution of oviduct and its transcriptome profile on early stage embryo development and the impact of endometrium and its transcriptome changes on peri and post embryo implantation. In addition, this paper integrates established facts about hormonal and molecular signatures associated with endometrial receptivity. Finally, the blastocyst and pre-conception endometrial gene expression profiles have been discussed in relation to the pregnancy outcome to highlight the potentials of blastocyst and pre-transfer endometrial transcriptome profile approach for selecting appropriate recipient and developmentally competent embryo.

Early developing pig embryos mediate their own environment in the maternal tract

The maternal tract plays a critical role in the success of early embryonic development providing an optimal environment for establishment and maintenance of pregnancy. Preparation of this environment requires an intimate dialogue between the embryo and her mother. However, many intriguing aspects remain unknown in this unique communication system. To advance our understanding of the process by which a blastocyst is accepted by the endometrium and better address the clinical challenges of infertility and pregnancy failure, it is imperative to decipher this complex molecular dialogue. The objective of the present work is to define the local response of the maternal tract towards the embryo during the earliest stages of pregnancy. We used a novel in vivo experimental model that eliminated genetic variability and individual differences, followed by Affymetrix microarray to identify the signals involved in this embryo-maternal dialogue. Using laparoscopic insemination one oviduct of a sow was inseminated with spermatozoa and the contralateral oviduct was injected with diluent. This model allowed us to obtain samples from the oviduct and the tip of the uterine horn containing either embryos or oocytes from the same sow. Microarray analysis showed that most of the transcripts differentially expressed were down-regulated in the uterine horn in response to blastocysts when compared to oocytes. Many of the transcripts altered in response to the embryo in the uterine horn were related to the immune system. We used an in silico mathematical model to demonstrate the role of the embryo as a modulator of the immune system. This model revealed that relatively modest changes induced by the presence of the embryo could modulate the maternal immune response. These findings suggested that the presence of the embryo might regulate the immune system in the maternal tract to allow the refractory uterus to tolerate the embryo and support its development.

Exploring the application of high-throughput genomics technologies in the field of maternal-embryo communication

Deciphering the complex molecular dialogue between the maternal tract and embryo is crucial to increasing our understanding of pregnancy failure, infertility problems and in the modulation of embryo development, which has consequences through adulthood. High-throughput genomic technologies have been applied to look for a holistic view of the molecular interactions occurring during this dialogue. Among these technologies, microarrays have been widely used, being one of the most popular tools in maternal-embryo communication. Today, next generation sequencing technologies are dwarfing the capabilities of microarrays. The application of these new technologies has broadened to almost all areas of genomics research, because of their massive sequencing capacity. We review the current status of high-throughput genomic technologies and their application to maternal-embryo communication research. We also survey next generation technologies and their huge potential in many research areas. Given the diversity of unanswered questions in the field of maternal-embryo communication and the wide range of possibilities that these technologies offer, here we discuss future perspectives on the use of these technologies to enhance maternal-embryo research.

Characterisation of an in vitro system to study maternal communication with spermatozoa

In vivo, gamete maturation, fertilisation and early embryonic development take place inside the oviduct. Several studies have indicated that local responses towards gametes and embryos are generated by the maternal reproductive tract. However, no defined in vitro model currently exists to allow detailed and systematic investigation of maternal communications with gametes and embryos. Therefore, we characterised an in vitro model based on the interaction of boar spermatozoa with an immortalised porcine oviduct epithelial cell line to evaluate different factors that may affect this model. The factors tested were sperm viability, source of spermatozoa, cell passage effect and the effect of reproductive and non-reproductive epithelial cells in the interaction with spermatozoa. After 24 h of co-incubation, RNA was extracted and used to synthesise cDNA for quantitative real-time PCR. Alteration in the expression of genes such as adrenomedullin, heat-shock 70-kDa protein 8 and prostaglandin E synthase was considered as the end point of this assay. The results showed that sperm viability and cell passage number had an effect on oviductal gene expression in response to spermatozoa. Oviductal cells showed significant alterations in gene expression when compared with non-reproductive epithelial cells. The simple in vitro system described here has potential application for further studies in our understanding of mechanisms involved in maternal interactions with spermatozoa.

Adrenomedullin increases ciliary beat frequency and decreases muscular contraction in the rat oviduct

Our laboratory previously showed that oviduct produced the greatest amount of adrenomedullin (ADM) in the rat female reproductive tract. The aim of this study is to investigate the changes in ADM levels resulting from the contact between the sperm and the oviduct and the possible roles of ADM in ciliary beating and oviductal contractility. Oviducts from Sprague–Dawley rats removed at pre- and post-ovulatory stages were cut open longitudinally and treated with ADM and/or receptor blockers before ciliary beat frequency (CBF) was measured. The effects of sperm on ADM production and CBF in the oviduct were also determined. The contraction of the oviduct after treatment with ADM and receptor antagonists was measured using the organ-bath technique. The results showed that ADM increased the CBF in rat oviduct and this stimulating effect was blocked by the calcitonin-gene-related peptide (CGRP) receptor antagonist, hCGRP8–37. CBF was lower in post-ovulatory than pre-ovulatory oviducts. The presence of sperm in the oviduct increased both the ADM level and CBF. ADM treatment was shown to inhibit the contractility of the oviduct by lowering the basal tone and decreasing the contraction amplitude. The ADM receptor antagonist, hADM22–52, was effective in counteracting the relaxation effect of ADM in the oviduct. All in all, these results indicate that ADM may play a crucial role in transporting the gametes/embryos by regulating ciliary beating and muscular contraction.

In vitro systems for intercepting early embryo-maternal cross-talk in the bovine oviduct

A comprehensive understanding of the complex embryo-maternal interactions during the preimplantation period requires the analysis of very early stages of pregnancy. These are difficult to assess in vivo due to the small size of the embryo exerting local paracrine effects. Specifically designed experiments and holistic transcriptome and proteome analyses to address the early embryo-maternal cross-talk in the oviduct require sufficient numbers of well-defined cells in a standardized experimental environment. The pronounced estrous cycle-dependent changes in gene expression and morphology of bovine oviduct epithelial cells (BOECs) clearly show that a precise definition of the stage of estrous cycle is essential for obtaining a well-defined homogenous population of functional cells. The number of intact cells isolated from individual ampullae by solely mechanical means was 10-fold higher than previously reported cell yields after enzymatic treatment, and the purity was comparable. Bovine oviduct epithelial cells have been cultured as monolayers or in suspension. Proliferating cells grown in monolayers dedifferentiated, with a concomitant loss of important morphologic characteristics. After several days in culture, BOECs in monolayers are less likely to mimic the oviduct environment in vivo than BOEC vesicles formed of epithelial sheets in short-term suspension culture. A 24-h culture system for BOECs isolated on Day 3.5 of the estrous cycle showed excellent preservation of morphologic criteria, marker gene expression, and hormone responsiveness. The short-term BOEC culture system provides well-defined and functional BOECs in sufficient quantities for studies of early embryo-maternal interactions in experiments that mimic the environment in the oviduct in vivo.

Gamete/embryo – oviduct interactions: implications onin vitroculture

Fertilization and development of mouse embryos occur in the oviduct. Accumulating data suggested that embryo-maternal communication exists in the preimplantation period, with the female reproductive tract providing the optimal microenvironment conducive to the development of embryos. Signals produced from the developing embryos not only affect their own transport in the oviduct, but the physiology and gene expression patterns of the oviduct. As a step towards understanding the action of embryos on oviductal physiology, both genomics and proteomics approaches are being used to unveil the underlying mechanism of embryo-maternal interaction at the preimplantation stage. Results from recent studies allow us to better understand the roles and the use of oviductal secretory proteins or factors that affect embryo development in vivo and in vitro. It has been shown that in vitro culture alters gene expression of the cultured embryos and may predispose the embryo to certain disease. Therefore, the interaction between gamete/embryo and oviduct in vitro and in vivo, and the long-term effects of embryo culture on foetal development warrant further investigation.

Oviductal microsomal epoxide hydrolase (EPHX1) reduces reactive oxygen species (ROS) level and enhances preimplantation mouse embryo development

Somatic cell-embryo coculture enhances embryo development in vitro by producing embryotrophic factor(s) and/or removing harmful substances from the culture environment. Yet, the underlying molecular mechanisms on how somatic cells remove the toxicants from the culture medium remain largely unknown. By using suppression subtractive hybridization, we identified a number of mouse oviductal genes that were up-regulated when developing preimplantation embryos were present in the oviduct. Epoxide hydrolase 1, microsomal (Ephx1 previously known as mEH) was one of these genes. EPHX1 detoxifies genotoxic compounds and participates in the removal of reactive oxygen species (ROS). The transcript of Ephx1 increases in the oviductal epithelium at the estrus stage and in Day 3 of pregnancy as well as in the uterus of ovariectomized mice injected with estrogen or progesterone. Human oviductal epithelial cells OE-E6/E7 express EPHX1 and improve mouse embryo development in vitro. Addition of an EPHX1 inhibitor, cyclohexene oxide (CHO) or 1,1,1-trichloropropene 2,3-oxide (TCPO), to the culture medium increased intracellular and extracellular ROS levels of OE-E6/E7 cells and suppressed the beneficial effect of the cells on embryo development; CHO and TCPO at these concentrations had no adverse effect on OE-E6/E7 growth and embryo development in vitro. Taken together, EPHX1 in oviductal cells may enhance the development of cocultured embryos by protecting them from oxidative stress. Our result supports the notion that somatic cell coculture may enhance embryo development via removal of deleterious substances in the culture medium.