Monitoring gene expression changes in bovine oviduct epithelial cells during the oestrous cycle

Role of steroid hormones in the maintenance of focal adhesions in bovine oviductal epithelial cells

The oviduct, the organ of the female reproductive system where fertilization and early embryonic development occur, provides an optimal environment for the final maturation of oocytes, storage, and sperm capacitation and transport of gametes and embryos. During the estrous cycle, the oviduct is affected by ovarian sex hormones, resulting in changes aimed at maintaining an appropriate microenvironment. Normal cell migration is tightly regulated, its role being essential for the development and maintenance of organ and tissue functions as well as for regeneration following injury. Due to their involvement in focal contact formations, focal adhesion kinase (PTK2) and paxillin (PXN) are key proteins in the study of cell migration and adhesion. The objective of this work was to compare the expression of PTK2 and PXN in oviductal cells along the estrous cycle and to determine if their expression is regulated by the presence of 17-β estradiol (E2) and/or progesterone (P4). No transcripts of PTK2 or of PXN were detected in cells corresponding to the luteal phase. Additionally, hormonal stimulation experiments on bovine oviductal cell cultures (BOECs) were carried out, where P4 inhibited the expression of both genes. Migration assays demonstrated that P4 reduced BOECs migration capacity. P4 treatment also reduced cell adhesion, while E2 increased the number of adhered cells. In conclusion, the presence of E2 and P4 regulates the expression of genes involved in the formation of focal contacts and modifies the migration and adhesion of BOECs. Understanding the effect of steroid hormones on BOECs is critical to grasp the impact of steroid control on oviductal function and its contribution to establishing successful pregnancies.

Effect of estrogen and progesterone on intracellular free zinc and zinc transporter expression in bovine oviduct epithelial cells

Zinc (Zn) plays essential roles in numerous cellular processes. However, there is limited understanding of Zn homeostasis within the bovine reproductive system. This study investigated the influence of estradiol (E2) and progesterone (P4) on Zn transporter expression and intracellular free Zn levels in bovine oviduct epithelial cells (BOEC). For this purpose, cells were harvested from slaughtered cows and cultured in vitro. Intracellular Zn concentrations were measured using FluoZin-3AM staining, while real-time polymerase chain reaction assessed Zn transporter gene expression and quantification. Overall, our results confirmed the gene expression of all the evaluated Zn transporters (ZIP6, ZIP8, ZIP14, ZnT3, ZnT7 and ZnT9), denoted and the active role of E2 and P4 in intracellular Zn regulation. Our findings suggest an interaction between Zn, E2 and P4.

The abundance and localization of heat shock proteins (HSP)-60, -70, and -90 in the oviductal ampulla of hamadryas baboon (Papio hamadryas) during the menstrual cycle

The presence of HSPs in female reproductive and their relationship with the steroid hormone fluctuation have been reported in several mammals but not in non-human primates. The present research dealt with the oviductal expression and localization of the more studied HSPs (60, 70, and 90) as well as the morphological changes in the Hamadryas baboon (Papio hamadryas) during the follicular, preovulatory, and luteal phases of the menstrual cycle. Therefore, western blots, histomorphological, and immunohistochemical analyses were carried out. The results of western blot analysis displayed the lowest HSP expression in the luteal phase. The histomorphology showed that the mucosal epithelium consisted of undifferentiated cuboidal cells in follicular and luteal phases and well-distinguishable columnar ciliated and non-ciliated cells during the preovulatory phase. Immunohistochemistry evidenced that the mucosal epithelium contained cytoplasmic and nuclear HSP60, 70, and 90 immunostaining in the follicular and luteal phases. During the preovulatory phase, the non-ciliated cells showed: (i) cytoplasmic HSP60; (ii) nuclear and cytoplasmic HSP90. Ciliated cells showed cytoplasmic and ciliary HSP70 and ciliary HSP90. The stromal cells and myocytes of muscular layer displayed a decreased cytoplasmic HSP60 in the preovulatory phase and nuclear and low cytoplasmic HSP70 throughout the menstrual cycle. Nuclear HSP90 decreased in ampulla stromal cells and the follicular phase myocytes. These findings indicate that the expression pattern of HSP60,70, and 90 is related to the morphofunctional features of the baboon oviductal ampulla during the menstrual cycle and could represent a referent point for further studies in the oviduct of Primates.

In vivo dynamics of pro-inflammatory factors, mucins, and polymorph nuclear neutrophils in the bovine oviduct during the follicular and luteal phase

Dynamic functional changes in the oviductal microenvironment are the prerequisite for the establishment of pregnancy. The objective of this study was to gain the first insights into oestrous cycle-dependent dynamics of polymorph nuclear neutrophils (PMN) and the mRNA abundance of selected genes and their correlations in the oviduct of living cows. Mini-cytobrush samples were taken from the oviducts of healthy heifers (n = 6) and cows (n = 7) during the follicular (FOL) and luteal phase (LUT) by transvaginal endoscopy. Total RNA was isolated from the samples and subjected to reverse transcription-quantitative PCR for selected pro-inflammatory factors, glycoproteins, and a metabolic marker. The percentage of PMN was determined by cytological examination. The mean PMN percentage was 2.8-fold greater during LUT than FOL. During LUT, significantly greater mRNA abundance of the pro-inflammatory factors IL1B, CXCL1, CXCL3, and CXCL8 was observed. The OVGP1 mRNA abundance was twice as high during FOL than in LUT. Pearson correlation, principal component analysis and heatmap analyses indicated characteristic functional patterns with strong correlations among investigated factors. Using this novel approach, we illustrate complex physiological dynamics and interactions of the mRNA expression of pro-inflammatory factors, mucins, OVGP1, and PMN in the oviduct during the oestrous cycle.

Bovine oviductal organoids: a multi-omics approach to capture the cellular and extracellular molecular response of the oviduct to heat stress

BACKGROUND

The mammalian oviduct is a complex, fibromuscular organ known for its role in orchestrating a series of timely and dynamic changes to suitably support early embryogenesis. Climate change-induced heat stress (HS) is one of the largest single stressors compromising reproductive function in humans and farm animals via systemic changes in the redox status of the maternal environment, adversely affecting fertilization and early embryonic development. Oviductal organoids represent a unique 3-dimensional, biomimetic model to study the physiology of the oviduct and its subsequent impact on embryo development under various environmental conditions.

RESULTS

Our study is the first to demonstrate an innovative approach to understanding the cascade of molecular changes sustained by bovine oviductal organoids under HS and the subsequent maternal signals harnessed within their secreted extracellular vesicles (EVs). Transcriptomic analysis of oviductal organoids exposed to HS revealed 2,570 differentially expressed genes (1,222 up- and 1,348 downregulated), while EV-coupled miRNome analysis disclosed 18 miRNAs with significant differential expression (12 up- and 6 downregulated) in EVs from thermally stressed organoids compared to EVs released from organoids cultured under thermoneutral conditions. Genes activated in oviductal organoids in response to thermal stress, include: COX1, ACTB, CST6, TPT1, and HSPB1, while miR-1246, miR-148a, miR21-5p, miR-451, and miR-92a represent the top highly abundant EV-coupled miRNAs released in response to HS. Pathway analysis of genes enriched in organoids exposed to thermal stress showed the enrichment of endocrine resistance, cellular senescence, and notch signaling pathways. Similarly, EV-coupled miRNAs released from thermally stressed organoids showed their potential regulation of genes involved in cellular senescence, p53 signaling, and TGF-beta signaling pathways.

CONCLUSIONS

In conclusion, the cellular and extracellular response of bovine oviductal organoids to in vitro HS conditions reveal the prospective impact of environmental HS on the physiology of the oviduct and the probable subsequent impacts on oocyte fertilization and early embryo development. Future studies elucidating the potential impact of HS-associated EVs from oviductal organoids on oocyte fertilization and preimplantation embryo development, would justify the use of an organoid model to optimally understand the oviduct-embryo communication under suboptimal environments.

Heat Stress: A Serious Disruptor of the Reproductive Physiology of Dairy Cows

Global warming is a significant threat to the sustainability and profitability of the dairy sector, not only in tropical or subtropical regions but also in temperate zones where extreme summer temperatures have become a new and challenging reality. Prolonged exposure of dairy cows to high temperatures compromises animal welfare, increases morbidity, and suppresses fertility, resulting in devastating economic losses for farmers. To counteract the deleterious effects of heat stress, cattl e employ various adaptive thermoregulatory mechanisms including molecular, endocrine, physiological, and behavioral responses. These adaptations involve the immediate secretion of heat shock proteins and cortisol, followed by a complex network of disrupted secretion of metabolic and reproductive hormones such as prolactin, ghrelin, ovarian steroid, and pituitary gonadotrophins. While the strategic heat stress mitigation measures can restore milk production through modifications of the microclimate and nutritional interventions, the summer fertility records remain at low levels compared to those of the thermoneutral periods of the year. This is because sustainment of high fertility is a multifaceted process that requires appropriate energy balance, undisrupted mode of various hormones secretion to sustain the maturation and fertilizing competence of the oocyte, the normal development of the early embryo and unhampered maternal-embryo crosstalk. In this review, we summarize the major molecular and endocrine responses to elevated temperatures in dairy cows, as well as the impacts on maturing oocytes and early embryos, and discuss the consequences that heat stress brings about in dairy cattle fertility.

Effect of estrous cycle phases on gene expression in bovine oviduct epithelial cells

Background and Aim: The oviduct environment is of particular importance because it is the site of fertilization and early embryo development. The oviduct, as a component of the reproductive system, responds to ovarian hormone (estradiol [E2] and progesterone [P4]) stimuli depending on the estrous cycle phase. This study aimed to elucidate the effect of estrous cycle phases (follicular and early and late luteal phases) on gene expression patterns in bovine oviduct epithelial cells (BOECs). Materials and Methods: Oviducts were obtained from healthy slaughterhouse animals, corresponding to ipsilateral ovaries with dominant follicles or corpus luteum during early and late luteal phases. BOECs were recovered from the isthmus (IST) and ampulla (AMP), and the expression patterns of genes related to cytokinesis and mitosis mechanisms (rho-associated coiled-coil containing protein kinase and cellular communication network factor 2 [CCN2]), growth factors (insulin-like growth factor-binding protein 3, epidermal growth factor receptor [EGFR], vascular endothelial growth factor A, and EGFR), antioxidant mechanisms (glutathione peroxidase 4 [GPX4]), apoptosis (B-cell lymphoma 2), complement component (C3), energy metabolism (aldose reductase gene family 1-member b1 [AKRIB1] and solute carrier family 2), hormone receptors (estrogen receptor 1 and luteinizing hormone/choriogonadotropin receptor), and specific glycoproteins (oviductal glycoprotein 1) were analyzed. Results: High P4 levels (late luteal phase) affected the expression of important genes related to antioxidant mechanisms (GPX4), energy metabolism (AKRIB1), growth factors (IGBP3 and EGFR), and cell growth regulation (CCN2) in the AMP. Low P4 levels (early luteal phase) affected the expression of AKR1B1, IGBP3, and CCN2. In addition, estrogen likely had an effect on OVPGP expression in the cattle oviduct. Conclusion: Differential gene expression patterns of BOECs in the AMP during the luteal phase (antioxidant mechanisms, energy metabolism, growth factors, and immunological regulators) and in the IST during the follicular phase (glycoproteins) may influence their renewal and population proportions, modulating the oviduct environment as well as gamete and embryo physiology.

miR-17-5p in bovine oviductal fluid affects embryo development

This study identified microRNAs (miRNAs) in bovine oviductal fluids (OFs) and examined the effect of miR-17-5p in OFs on embryonic development to the blastocyst stage. Small RNA-seq of extracellular vesicles of OFs revealed 242 miRNAs. Additionally, analyzing expressions of randomly selected OF-miRNAs with RT-qPCR in the culture medium of oviductal epithelial cells indicated that the abundance of miRNAs in OFs increased during the luteal phase. miR-17-5p mimic-treated eight-cell-stage zona pellucida-free embryos showed improved embryonic development to the blastocyst stage. The effect of the miR-17-5p mimic was confirmed using a dual-luciferase assay and immunostaining. In addition, RNA-seq of the miR-17-5p mimic- or control-treated embryos revealed differentially expressed genes (DEGs), suggesting possible pathways that overlapped with the in silico-predicted pathways for miR-17-5p targeting genes. Furthermore, ingenuity pathway analysis of DEG predicted miR-17 to be a significant upstream regulator. Our results suggest that miR-17-5p in OFs regulates embryonic development in bovines.

Spatiotemporal profiling of the bovine oviduct fluid proteome around the time of ovulation

Understanding the composition of the oviduct fluid (OF) is crucial to better comprehend the microenvironment in which sperm capacitation, fertilization and early embryo development take place. Therefore, our aim was to determine the spatiotemporal changes in the OF proteome according to the anatomical region of the oviduct (ampulla vs. isthmus), the proximity of the ovulating ovary (ipsilateral vs. contralateral side) and the peri-ovulatory stage (pre-ovulatory or Pre-ov vs. post-ovulatory or Post-ov). Oviducts from adult cyclic cows were collected at a local slaughterhouse and pools of OF were analyzed by nanoLC-MS/MS and label-free protein quantification (n = 32 OF pools for all region × stage × side conditions). A total of 3760 proteins were identified in the OF, of which 65% were predicted to be potentially secreted. The oviduct region was the major source of variation in protein abundance, followed by the proximity of the ovulating ovary and finally the peri-ovulatory stage. Differentially abundant proteins between regions, stages and sides were involved in a broad variety of biological functions, including protein binding, response to stress, cell-to-cell adhesion, calcium homeostasis and the immune system. This work highlights the dynamic regulation of oviduct secretions and provides new protein candidates for interactions between the maternal environment, the gametes and the early embryo.

Integrated multiple transcriptomes in oviductal tissue across the porcine oestrous cycle reveal functional roles in oocyte maturation and transport

Understanding the changes in the swine female reproductive system is important for solving issues related to reproductive failure and litter size. Elucidating the regulatory mechanisms of the natural oestrous cycle in the oviduct under non-fertilisation conditions can improve our understanding of its role in the reproductive system. Herein, whole transcriptome RNA sequencing of oviduct tissue samples was performed. The differentially expressed genes (DEGs) were identified for each time point relative to Day 0 and classified into three clusters based on their expression patterns. Clusters 1 and 2 included genes involved in the physiological changes through the oestrous cycle. Cluster 1 genes were mainly involved in PI3K-Akt signalling and steroid hormone biosynthesis pathways. Cluster 2 genes were involved in extracellular matrix-receptor interactions and protein digestion pathways. In Cluster 3, the DEGs were downregulated in the luteal phase; they were strongly associated with cell cycle, calcium signalling, and oocyte meiosis. The gene expression in the oviduct during the oestrous cycle influenced oocyte transport and fertilisation. Our findings provide a basis for successfully breeding pigs and elucidating the mechanisms underlying the changes in the pig oviduct during the oestrous cycle.

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.

Spatiotemporal transcriptional dynamics of the cycling mouse oviduct

Female fertility in mammals requires iterative remodeling of the entire adult female reproductive tract across the menstrual/estrous cycle. However, while transcriptome dynamics across the estrous cycle have been reported in human and bovine models, no global analysis of gene expression across the estrous cycle has yet been reported for the mouse. Here, we examined the cellular composition and global transcriptional dynamics of the mouse oviduct along the anteroposterior axis and across the estrous cycle. We observed robust patterns of differential gene expression along the anteroposterior axis, but we found surprisingly few changes in gene expression across the estrous cycle. Notable gene expression differences along the anteroposterior axis included a surprising enrichment for genes related to embryonic development, such as Hox and Wnt genes. The relatively stable transcriptional dynamics across the estrous cycle differ markedly from other mammals, leading us to speculate that this is an evolutionarily derived state that may reflect the extremely rapid five-day mouse estrous cycle. This dataset fills a critical gap by providing an important genomic resource for a highly tractable genetic model of mammalian female reproduction.

Changes in Oviductal Cells and Small Extracellular Vesicles miRNAs in Pregnant Cows

Early embryonic development occurs in the oviduct, where an ideal microenvironment is provided by the epithelial cells and by the oviductal fluid produced by these cells. The oviductal fluid contains small extracellular vesicles (sEVs), which through their contents, including microRNAs (miRNAs), can ensure proper cell communication between the mother and the embryo. However, little is known about the modulation of miRNAs within oviductal epithelial cells (OECs) and sEVs from the oviductal fluid in pregnant cows. In this study, we evaluate the miRNAs profile in sEVs from the oviductal flushing (OF-sEVs) and OECs from pregnant cows compared to non-pregnant, at 120 h after ovulation induction. In OF-sEVs, eight miRNAs (bta-miR-126-5p, bta-miR-129, bta-miR-140, bta-miR-188, bta-miR-219, bta-miR-345-3p, bta-miR-4523, and bta-miR-760-3p) were up-regulated in pregnant and one miRNA (bta-miR-331-5p) was up-regulated in non-pregnant cows. In OECs, six miRNAs (bta-miR-133b, bta-miR-205, bta-miR-584, bta-miR-551a, bta-miR-1193, and bta-miR-1225-3p) were up-regulated in non-pregnant and none was up-regulated in pregnant cows. Our results suggest that embryonic maternal communication mediated by sEVs initiates in the oviduct, and the passage of gametes and the embryo presence modulate miRNAs contents of sEVs and OECs. Furthermore, we demonstrated the transcriptional levels modulation of selected genes in OECs in pregnant cows. Therefore, the embryonic-maternal crosstalk potentially begins during early embryonic development in the oviduct through the modulation of miRNAs in OECs and sEVs in pregnant cows.

New insights into molecular aspects of sperm-oviductal binding in Egyptian buffaloes using an in vitro model: Effects of oviductal segments and media

We aimed (I) to simulate an in vivo milieu, through establishing an in vitro paradigm to study sperm-oviductal interactions using different segments of oviduct, as well as different incubation media, and (II) to investigate spatial changes of oviductal gene expression. Two experiments were designed; one was to investigate the yield of oviduct aggregates from different oviduct segments; in the second experiment, we observed effects of different incubation media on sperm-oviductal binding. Oviduct cell pellets before (control) and after sperm binding were collected for RNA isolation and gene expression. Isthmus resulted in a higher aggregate yield and possessed the highest affinity towards spermatozoa. The different segments of oviduct showed clear changes in gene expression after sperm binding. TALP medium promoted formation of a higher number of oviduct aggregates towards spermatozoa. Different media resulted in profound alterations in isthmus gene expression. Collectively, isthmus segment in TALP media showed the highest binding affinity to spermatozoa. At the molecular level, our in vitro model was successful for simulation in vivo milieu. Thus, our findings could be used as a simple tool to gain more insights into the molecular regulation of sperm movement, selection and affinity for oviductal binding in buffaloes.

Exosomes as a Potential Tool for Supporting Canine Oocyte Development

Simple Summary

To date, extracellular vesicles, including exosomes, have markedly gained attention in scientific research because of their physiological homogeneity as well as stability for transporting regulatory molecules to recipient cells. Recently, it has been shown that exosomes impact gametes and embryo development in several mammalian species; however, there is still scant information on the physiological effects of exosomes on the canine reproduction system. In this regard, we elucidate the possible roles of exosomes involvement in oviduct and cumulus-oocyte complexes mutual communications and how oviduct regulates their development via molecular signaling pathways.

Abstract

The canine oviduct is a unique reproductive organ where the ovulated immature oocytes complete their maturation, while the other mammals ovulate matured gametes. Due to their peculiar reproductive characteristics, the in vitro maturation of dog oocytes is still not wellestablished compared with other mammals. Investigations of the microenvironment conditions in the oviductal canal are required to establish a reliable in vitro maturation system in the dog. Previous studies have suggested that the oviduct and its derivatives play a key role in improving fertilization as well as embryo development. In particular, the biological function of oviduct-derived exosomes on sperm and early embryo development has been investigated in porcine, bovine, and murine species. However, the information about their functions on canine cumulus-oocyte complexes is still elusive. Recent canine reproductive studies demonstrated how oviduct-derived extracellular vesicles such as microvesicles and exosomes interact with oocyte-cumulus complexes and how they can play roles in regulating canine cumulus/oocyte communications. In this review, we summarize the physiological characteristics of canine oviduct-derived exosomes and their potential effects on cumulus cells development as well as oocyte in vitro maturation via molecular signaling pathways.

Effect of oviductal fluid on bull sperm functionality and fertility under non-capacitating and capacitating incubation conditions

This study investigated the effect of bovine oviductal fluid from late follicular (LF) and early luteal (EL) phases on bull sperm functionality under non-capacitating (NCAP) and capacitating (CAP) conditions. Frozen-thawed semen samples from five bulls were thawed and incubated (0, 1 or 2 h) in NCAP and CAP media supplemented with 1% bovine oviductal fluid (LF and EL groups) and in absence of fluid (C group). Motion parameters were assessed by CASA; sperm viability, acrosomal integrity and membrane lipid disorder parameters were evaluated by flow cytometry; and sperm DNA fragmentation was evaluated by the Comet assay. Finally, in vitro fertilization with sperm treated under CAP conditions was performed and further embryo culture results evaluated. In NCAP medium, addition of LF and EL fluid increased the total and progressive motility, and LF fluid improved the stability of sperm DNA. However, under CAP conditions addition of LF and EL fluid decreased some sperm motion parameters and some parameters of sperm DNA stability. Proportion of viable sperm cells with low lipid disorder was higher in NCAP than CAP medium and addition of LF fluid markedly increased the proportion of viable spermatozoa with high lipid disorder and acrosome alteration (spontaneous acrosome reaction). Under current conditions, incubation of bull sperm with oviductal fluid before insemination did not affect detrimentally the IVF results nor embryo development, being blastocyst rate similar between CAP-LF, CAP-EL and control groups. In conclusion, oviductal fluid positively influences sperm functionality and modulate in vitro capacitation.

Impact of extracellular folic acid levels on oviductal gene expression

Folate plays a specific role as methyl donor for nucleotide synthesis and genomic methylation patterns, which in turn are important epigenetic determinants in gene expression. Previous studies have revealed the presence of folate in bovine oviductal fluid as well as the existence of a fine-tuned regulation of the gene expression of folate receptors and transporters in bovine oviduct epithelial cells (BOECs). However, the functional implications of folate in the oviduct remain unknown. The present study aimed to assess the effect of folic acid (FA) on expression levels of selected genes that potentially respond to the folate status in in vitro BOECs. To obtain an insight into the optimization of a culture system for assays, gene expression of folate receptors and transporters was compared between BOECs grown in monolayers and in suspension. The results showed that BOECs from isthmus and ampulla in suspension culture better preserved the region-dependent gene expression profile than in monolayers. Subsequently, BOECs from both anatomical regions were separately cultured in suspension for 24 h assaying different FA concentrations: I) TCM-199 (control); II) TCM-199 + 1 μM FA (similar to the oviduct concentration); III) TCM-199 + 10 μM FA and IV) TCM-199 + 100 μM FA. Expression analysis of genes related to important cellular processes including folate transport, DNA methylation, cell-cell interaction, antioxidant activity and signaling pathways was performed in BOECs using RT-qPCR. Our data demonstrated that addition of 1 μM FA did not affect mRNA levels of most genes analyzed. In contrast, BOECs cultured with 10 μM FA exhibited increased mRNA expression levels of genes involved in folate intake, DNA methylation and antioxidant protection. It is worth noting that at 100 μM FA, transcriptional response in BOECs mainly resulted in decreased mRNA levels of the majority of the genes assayed. Interestingly, cytotoxicity analysis showed a similar LDH activity in the culture media of the experimental groups, indicating that cell integrity was not affected by the FA concentrations assayed. In conclusion, our findings suggest that folate can affect BOECs, promoting changes in gene activity in a framework of functional readjustments in response to environmental conditions.

Sperm Proteome after Interaction with Reproductive Fluids in Porcine: From the Ejaculation to the Fertilization Site

Ejaculated sperm are exposed to different environments before encountering the oocyte. However, how the sperm proteome changes during this transit remains unsolved. This study aimed to identify proteomic changes in boar sperm after incubation with male (seminal plasma, SP) and/or female (uterine fluid, UF; and oviductal fluid, OF) reproductive fluids. The following experimental groups were analyzed: (1) SP: sperm + 20% SP; (2) UF: sperm + 20% UF; (3) OF: sperm + 20% OF; (4) SP + UF: sperm + 20% SP + 20% UF; and (5) SP+OF: sperm + 20% SP + 20% OF. The proteome analysis, performed by HPLC-MS/MS, allowed the identification of 265 proteins. A total of 69 proteins were detected in the UF, SP, and SP + UF groups, and 102 proteins in the OF, SP, and SP + OF groups. Our results showed a higher number of proteins when sperm were incubated with only one fluid than when they were co-incubated with two fluids. Additionally, the number of sperm-interacting proteins from the UF group was lower than the OF group. In conclusion, the interaction of sperm with reproductive fluids alters its proteome. The description of sperm-interacting proteins in porcine species after co-incubation with male and/or female reproductive fluids may be useful to understand sperm transport, selection, capacitation, or fertilization phenomena.

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.

The Expression of ERK1/2 in Female Yak (Bos grunniens) Reproductive Organs

The main reproductive organs undergo different histological appearances and physiological processes under different reproductive statuses. The variation of these organs depends on a delicate regulation of cell proliferation, differentiation, and apoptosis. Extracellular signal-regulated kinases1/2 (ERK1/2) are members of the mitogen-activated protein kinase (MAPK) super family. They have important roles in regulating various biological processes of different cells, tissues, and organ types. Activated ERK1/2 generally promotes cell survival, but under certain conditions, ERK1/2 also have the function of inducing apoptosis. It is widely believed that ERK1/2 play a significant role in regulating the reproductive processes of mammals. The goal of our research is to investigate the expression and distribution of ERK1/2 in the yak's main reproductive organs during different stages. In the present study, samples of the ovary, oviduct, and uterus of 15 adult female yak were collected and used in the experiment. The ERK1/2 proteins, localization, and quantitative expression of their mRNA were investigated using immunohistochemistry (IHC), western blot (WB) and relative quantitative real-time polymerase chain reaction (RT-PCR). The results indicated that ERK1/2 proteins and their mRNA were highly expressed in the ovary of the luteal phase and gestation period, in the oviduct of the luteal phase, and in the uterus of the luteal phase and gestation period. Immunohistochemical analysis revealed a strong distribution of ERK1/2 proteins in follicular granulosa cells, granular luteal cells, villous epithelial cells of the oviduct, endometrial glandular epithelium, and luminal epithelium. These results demonstrated that the expression of ERK1 and ERK2 proteins and their mRNA in the yak's ovary, oviduct, and uterus varies with the stage of the reproductive cycle. The variation character of ERK1 and ERK 2 expression in the yak's main reproductive organs during different stages implies that they play an important role in regulating the reproductive function under different physiological statuses.

Possible roles of local oviductal estradiol-17β in luteal formation phase on the function of bovine oviductal epithelium

Oviducts play an important role in the reproductive process, such as in gamete transport, fertilization, and early embryonic development. However, the regulation of oviductal function during luteal formation phase (3−5 days post-ovulation), which is a crucial phase for early embryonic development, remains poorly understood. This study investigated the roles of oviductal estradiol-17β (E2) and progesterone (P4) concentrations on bovine oviductal functions in the luteal formation phase using RT-qPCR for some genes of oviductal epithelial cells. Bovine oviducts ipsilateral to the corpus luteum (CL) in the luteal formation phase were collected from a slaughterhouse. The concentration of oviductal E2 was positively correlated with the mRNA expressions of nuclear P4 receptor (PGR) and protein disulfide isomerase family A member 4 (PDIA4), which is related to protein secretion, in the ampulla and with estrogen receptor α (ESR1) mRNA expression in the isthmus. In contrast, the concentration of oviductal P4 was not correlated with oviductal mRNA expressions in either regions. Furthermore, for the candidate factor related to the oviductal E2 concentration, the CL parameters (CL size and tissue P4 concentration), first-wave dominant follicle (W1DF) parameters (follicle size and intrafollicular E2 concentration), and W1DF location (ipsilateral or contralateral to CL) did not influence the oviductal E2 concentration. In conclusion, our results suggest that the local oviductal E2 is a potential oviductal function regulator during the luteal formation phase.

Sex steroids drive the remodeling of oviductal extracellular matrix in cattle

The extracellular matrix (ECM) is a group of molecules that offer structural and biochemical support to cells and interact with them to regulate their function. Also, growth factors (GFs) stored in the ECM can be locally released during ECM remodeling. Here, we hypothesize that the balance between ECM components and remodelers is regulated according to the ovarian steroid milieu to which the oviduct is exposed during the periovulatory period. Follicular growth was manipulated to generate cows that ovulated small follicles (SF-small corpus luteum [SCL]; n = 20) or large follicles (LF-large corpus luteum [LCL]; n = 21) and possess corresponding Estradiol (E2) and Progesterone (P4) plasmatic concentrations. Ampulla and isthmus samples were collected on day 4 (day 0 = ovulation induction) and immediately frozen or fixed. The transcriptional profile (n = 3/group) was evaluated by RNA sequencing. MMP Antibody Array was used to quantify ECM remodelers' protein abundance and immunohistochemistry to quantify type I collagen. Transcriptome analysis revealed the over-representation of ECM organization and remodeling pathways in the LF-LCL group. Transcription of ECM components (collagens), remodelers (ADAMs and MMPs), and related GFs were upregulated in LF-LCL. Protein intensities for MMP3, MMP8, MMP9, MMP13, and TIMP4 were greater for the LF-LCL group. Type I collagen content in the mucosa was greater in SF-SCL group. In conclusion, that the earlier and more intense exposure to E2 and P4 during the periovulatory period in LF-LCL animals stimulates ECM remodeling. We speculate that differential ECM regulation may contribute to oviductal receptivity to the embryo.

Equine chorionic gonadotropin increases estradiol levels in the bovine oviduct and drives the transcription of genes related to fertilization in superstimulated cows

In the bovine oviduct, estradiol (E2) stimulates secretion and cell proliferation, whereas progesterone (P4) suppresses them. In this study, we have evaluated the effect of two superstimulatory protocols (follicle-stimulating hormone [FSH] or FSH combined with equine chorionic gonadotropin [eCG]) on the oviductal levels of E2 and P4 and its outcome on oviductal cells. Compared with the control group (a single pre-ovulatory follicle), we have observed that the cows submitted to FSH/eCG treatment showed a higher concentration of E2 in the oviduct tissue, together with a higher abundance of messenger RNA encoding steroid receptors (ESR1 and progesterone receptor), and genes linked to gamete interactions and regulation of polyspermy (oviduct-specific glycoprotein 1, heat-shock protein family A member 5, α-l-fucosidase 1 [FUCA1], and FUCA2) in the infundibulum and ampulla segments of the oviduct. However, we did not observe any modulation of gene expression in the isthmus segment. Even though the FSH protocol upregulated some of the genes analyzed, we may infer that the steady effect of FSH combined with eCG on oviduct regulation might benefit fertilization and may potentially increase pregnancy rates.

"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.

A novel approach to study the bovine oviductal fluid proteome using transvaginal endoscopy

The oviduct provides the optimal micro milieu for early embryo development. However, accessing the bovine oviductal fluid in vivo for analysis is still challenging and therefore the oviductal fluid is usually collected post mortem. In the study presented here we introduce a novel approach to gain minimal invasive access to the bovine oviductal fluid proteome in vivo by transvaginal endoscopy at different stages of the estrous cycle. The first experiment aimed at transferring C4 derivatised magnetic beads to bind the oviductal fluid proteome in situ. Protein carrying beads were recovered by flushing the oviduct and proteins were eluted. In the second experiment a flushing solution was injected into and aspirated from the oviduct repeatedly. The flushing solution was centrifuged to separate the fluid from the cellular debris. Proteins were identified by nano-LC-MS/MS. Two different stages of the estrous cycle (Day 1 and Day 3) were analyzed in samples from 30 heifers. Both methods were applied successfully and in total, more than 3000 proteins were identified, so far representing the most comprehensive OF proteome published. This new minimal invasive approach to access the bovine oviductal fluid proteome facilitates future innovative experimental designs to study the role of the oviductal micro environment during early embryo development.

Dysregulated erythropoietin-producing hepatocellular receptor A2 (EphA2) is involved in tubal pregnancy via regulating cell adhesion of the Fallopian tube epithelial cells

BACKGROUND

Tyrosine kinase receptor erythropoietin-producing hepatocellular receptor A2 (EphA2) is abundant in the endometrium and plays a role in the establishment of eutopic implantation. A similar molecular mechanism may exist between uterine implantation and tubal implantation, therefore EphA2 involvement in tubal pregnancy is suspected. Due to the limited availability of human Fallopian tube specimens, EphA2 expression in human Fallopian tube epithelium remains largely unknown.

METHODS

A total of 31 women with tubal pregnancy and 41 non-pregnant women with benign uterine diseases were enrolled in this study. Immunohistochemistry was used to investigate the expression pattern of EphA2 in the Fallopian tube epithelium of non-pregnant women (n = 29) and women with tubal pregnancy (n = 17). The changes of EphA2 and its activated form, phosphorylated-EphA2 (Pho-EphA2), in the Fallopian tube epithelium from non-pregnant women (n = 12) and women with tubal pregnancy (n = 14) were compared by quantitative RT-PCR and western blot assay.

RESULTS

EphA2 was expressed throughout the Fallopian tube epithelium, including the isthmus, the ampulla and the infundibulum. EphA2 concentration remained unchanged throughout the whole menstrual cycle, irrespective of menstrual phases and tubal regions. EphA2 mRNA in the Fallopian tube epithelium did not differ between normal women and women with tubal pregnancy (P > 0.05). With respect to the protein level, a significantly higher ratio of EphA2 over Pho-EphA2 was shown in women with tubal pregnancy (P < 0.05).

CONCLUSIONS

EphA2 is widely expressed in human Fallopian tube epithelium in a temporospatial-independent manner. Dysregulated EphA2 and its phosphorylation-dependent regulatory mechanism may unexpectedly enhance the cell adhesion activity of the Fallopian tube epithelial cells, leading to a mis-contact between the Fallopian tube epithelium and the embryo.

Can the antral follicular count modulate the gene expression of bovine oviducts in Aberdeen Angus and Nelore heifers?

The number of visible ovarian antral follicles (antral follicle count—AFC) is repeatable in bovine individuals, but highly variable between animals, and with differences between Bos taurus and Bos indicus breeds. Several studies have tried to determine the correlation between AFC and increased fertility in cattle. While the impacts of AFC on embryo production, hormonal levels, and pregnancy rates have been described, the molecular effects of AFC on bovine oviducts have not yet been investigated. Here, the aim was to investigate the impact of breeds, such as Aberdeen Angus and Nelore heifer with high or low AFC, on abundance of transcripts and protein related to oviductal transport, sperm reservoir formation, monospermy control, and gamete interaction in the oviducts. In summary, the ovulation side was the major factor that affected transcript abundance on bovine oviducts. However, a discreet effect among AFC and cattle breeds was also observed. Based on this, we concluded and reinforced here that differential microenvironments between ipsilateral and contralateral oviducts have a major effect on modulating the transcripts related to oviductal transport, sperm reservoir formation, monospermy control, and gamete interaction. However, we cannot exclude that there is minimal effect of AFC or breed on regulation of some genes (such as AGTR1, ACE1, FUCA1, and VEGFA) in bovine oviducts.

Deciphering the oviductal extracellular vesicles content across the estrous cycle: implications for the gametes-oviduct interactions and the environment of the potential embryo

Background

The success of early reproductive events depends on an appropriate communication between gametes/embryos and the oviduct. Extracellular vesicles (EVs) contained in oviductal secretions have been suggested as new players in mediating this crucial cross-talk by transferring their cargo (proteins, mRNA and small ncRNA) from cell to cell. However, little is known about the oviductal EVs (oEVS) composition and their implications in the reproductive success. The aim of the study was to determine the oEVs content at protein, mRNA and small RNA level and to examine whether the oEVs content is under the hormonal influence of the estrous cycle.

Results

We identified the presence of oEVs, exosomes and microvesicles, in the bovine oviductal fluid at different stages of the estrous cycle (postovulatory-stage, early luteal phase, late luteal phase and pre-ovulatory stage) and demonstrated that their composition is under hormonal regulation. RNA-sequencing identified 903 differentially expressed transcripts (FDR < 0.001) in oEVs across the estrous cycle. Moreover, small RNA-Seq identified the presence of different types of ncRNAs (miRNAs, rRNA fragments, tRNA fragments, snRNA, snoRNA, and other ncRNAs), which were partially also under hormonal influence. Major differences were found between post-ovulatory and the rest of the stages analyzed for mRNAs. Interesting miRNAs identified in oEVs and showing differential abundance among stages, miR-34c and miR-449a, have been associated with defective cilia in the oviduct and infertility. Furthermore, functional annotation of the differentially abundant mRNAs identified functions related to exosome/vesicles, cilia expression, embryo development and many transcripts encoding ribosomal proteins. Moreover, the analysis of oEVs protein content also revealed changes across the estrous cycle. Mass spectrometry identified 336 clusters of proteins in oEVs, of which 170 were differentially abundant across the estrous cycle (p-value< 0.05, ratio < 0.5 or ratio > 2). Our data revealed proteins related to early embryo development and gamete-oviduct interactions as well as numerous ribosomal proteins.

Conclusions

Our study provides with the first molecular signature of oEVs across the bovine estrous cycle, revealing marked differences between post- and pre-ovulatory stages. Our findings contribute to a better understanding of the potential role of oEVs as modulators of gamete/embryo-maternal interactions and their implications for the reproductive success.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4982-5) contains supplementary material, which is available to authorized users.

Effects of recombinant OVGP1 protein on in vitro bovine embryo development

Previously, our group demonstrated that recombinant porcine oviductin (pOVGP1) binds to the zona pellucida (ZP) of in vitro-matured (IVM) porcine oocytes with a positive effect on in vitro fertilization (IVF). The fact that pOVGP1 was detected inside IVM oocytes suggested that this protein had a biological role during embryo development. The aim of this study was to evaluate the effects of pOVGP1 on bovine in vitro embryo development. We applied 10 or 50 µg/ml of pOVGP1 during IVF, embryonic in vitro culture (IVC), or both, to evaluate cleavage and embryo development. Blastocyst quality was assessed by analyzing the expression of important developmental genes and the survival rates after vitrification/warming. pOVGP1 was detected in the ZP, perivitelline space, and plasma membrane of blastocysts. No significant differences (P > 0.05) were found in cleavage or blastocyst yield when 10 or 50 µg/ml of pOVGP1 was used during IVF or IVC. However, when 50 µg/ml pOVGP1 was used during IVF + IVC, the number of blastocysts obtained was half that obtained with the control and 10 µg/ml pOVGP1 groups. The survival rates after vitrification/warming of expanded blastocysts cultured with pOVGP1 showed no significant differences between groups (P > 0.05). The use of pOVGP1 during IVF, IVC, or both, increased the relative abundance of mRNA of DSC2, ATF4, AQP3, and DNMT3A, the marker-genes of embryo quality. In conclusion, the use of pOVGP1 during bovine embryo in vitro culture does not affect embryo developmental rates but produces embryos of better quality in terms of the relative abundance of specific genes.

Epi-nutrients in the oviductal environment: Folate levels and differential gene expression of its receptors and transporters in the bovine oviduct

Recent studies have demonstrated that the oviductal environment plays an active role in modulating the epigenetic marks of the preimplantation embryo genome, but the molecular factors that mediate this epigenetic effect are unknown. Folate is a well-known epi-nutrient that can impact on cell epigenetic machinery during embryonic and fetal development. However, the study of this epi-nutrient in the oviduct is still limited. The present study was conducted to confirm the presence and physiological concentration of folate in bovine oviductal fluid (OF) and to determine if bovine oviduct epithelial cells (BOECs) are able to regulate the uptake of this micronutrient. Samples of OF from ipsi- and contralateral oviducts were collected at different stages of the estrous cycle and folate levels were determined using a competitive receptor binding immunoassay. In addition, gene expression of folate receptors (FOLR1, FOLR2) and transporters (SLC19A1, SLC46A1) were analyzed in BOECs from ampulla and isthmus regions during different stages of the estrous cycle using RT-qPCR. In vitro culture assays were also performed to evaluate whether expression of these genes responds to hormonal stimulation. Our results demonstrated presence of folate in the OF, showing changes of its concentration in the ipsilateral oviduct during the estrous cycle and significantly lower levels at the postovulatory stage. Moreover, gene expression of folate receptors and transporters was detected in BOECs, showing regional and cycle-dependent changes. In particular, differential expression of FOLR1 mRNA was observed in BOECs from the isthmus region, reaching significantly higher levels during the postovulatory stage. Under in vitro culture conditions, gene expression of folate receptors and transporters was maintained in BOEC explants and a particular susceptibility to steroid hormone stimulation was observed. In conclusion, the present study confirms the presence of folate in the bovine oviduct and proves the existence of a fine-tuned regulation of the expression of its receptors and transporters, highlighting the importance to expand the knowledge about this epi-nutrient in the oviductal context.

Influence of elevated temperature on bovine oviduct epithelial cells (BOECs)

The aim of this study was to evaluate the influence of elevated temperature on bovine oviduct epithelial cells (BOECs), based on the expression and localization of both heat shock protein 70 (HSP70), responsible for the cellular defence mechanism, and oviduct specific glycoprotein 1 (OVGP1) which is the most important embryotrophic protein. BOECs were cultured alone and co-cultured with cattle embryos at control (38.5°C) and elevated temperature (41°C) for 168 h. The elevated temperature had no effect on the viability of BOECs but exerted a negative effect on embryo development. The elevated temperature increased the expression of HSP70 and decreased the expression of OVGP1 at both mRNA and protein levels in BOECs cultured alone and those co-cultured with embryos. However, the presence of embryos limited the decrease in OVGP1 expression in BOECs at elevated temperature but did not alter the expression of HSP70. These results demonstrate for the first time the influence of elevated temperature on BOECs, consequently providing insights into the interactions between the embryo and the oviduct at elevated temperature.

Sex Steroid-Mediated Control of Oviductal Function in Cattle

In cattle, the oviduct is a tubular organ that connects the ovary and the uterus. The oviduct lumen stages a dynamic set of cellular and molecular interactions to fulfill the noble role of generating a new individual. Specific anatomical niches along the oviduct lumen provide the appropriate microenvironment for final sperm capacitation, oocyte capture and fertilization, and early embryo development and transport. To accomplish such complex tasks, the oviduct undergoes spatially and temporally-regulated morphological, biochemical, and physiological changes that are associated with endocrine events of the estrous cycle. Specifically, elevated periovulatory concentrations of estradiol (E2) and progesterone (P4) influence gene expression and morphological changes that have been associated positively to fertility in beef cattle. In this review, we explore how E2 and P4 influence oviductal function in the beginning of the estrous cycle, and prepare the oviductal lumen for interactions with gametes and embryos.

Non-esterified fatty acids in early luteal bovine oviduct fluid mirror plasma concentrations: An ex vivo approach

We investigated whether and to which extent plasma non-esterified fatty acids (NEFAs) are reflected in oviduct fluid (OF) using an improved ex vivo flushing method. OF and plasma NEFA concentrations were respectively 0.29±0.19 and 0.31±0.14mmol/L, they didn't differ significantly (P=0.13) and tended to be positively correlated (Pearson correlation coefficient=0.56; P=0.07). Results suggest that OF NEFAs mirror the concentrations seen in plasma of healthy cattle.

Differential gene expression in porcine oviduct during the oestrous cycle

The oviduct undergoes changes under the influence of steroid hormones during the oestrous cycle. However, the molecular mechanisms underlying oviductal regulation are not fully understood. The aim of the present study was to identify the gene expression profile of the porcine oviduct in different stages of the cycle using microarray technology. A systematic study was performed on animals at four different stage: prepubertal gilts, and sows in the preovulatory, postovulatory and luteal phase of the oestrous cycle. The porcine oviduct expressed a total of 4929 genes. Moreover, significant differences in the expression of several genes were detected as the oestrous cycle progressed. Analysis of the differentially expressed genes indicated that a total of 86, 89 and 15 genes were upregulated in prepubertal gilts, preovulatory and luteal sows respectively compared with levels observed in postovulatory sows. Moreover, 80, 51 and 64 genes were downregulated in prepubertal, preovulatory and luteal animals respectively compared with the postovulatory sows. The concentrations of 10 selected transcripts were quantified by real-time reverse transcription–polymerase chain reaction to validate the cDNA array hybridisation data. Conversely, for some genes, localisation of corresponding protein expression in the oviduct was analysed by immunohistochemistry (i.e. cholecystokinin, glutathione peroxidase 2, mucin 1, phosphatidylethanolamine binding protein 4 and tachykinin 3) and mass spectrometry analysis of oviductal fluid allowed identification of peptides from all five proteins. The results of the present study demonstrate that gene expression in the porcine oviduct is clearly regulated during the oestrous cycle, with some oviductal proteins that could be related to several reproductive processes described here for the first time.

Regulation of the bovine oviductal fluid proteome

Our objective was to investigate the regulation of the proteome in the bovine oviductal fluid according to the stage of the oestrous cycle, to the side relative to ovulation and to local concentrations of steroid hormones. Luminal fluid samples from both oviducts were collected at four stages of the oestrous cycle: pre-ovulatory (Pre-ov), post-ovulatory (Post-ov), and mid- and late luteal phases from adult cyclic cows (18–25 cows/stage). The proteomes were assessed by nanoLC–MS/MS and quantified by label-free method. Totally, 482 proteins were identified including a limited number of proteins specific to one stage or one side. Proportions of differentially abundant proteins fluctuated from 10 to 24% between sides at one stage and from 4 to 20% among stages in a given side of ovulation. In oviductal fluids ipsilateral to ovulation, Annexin A1 was the most abundant protein at Pre-ov compared with Post-ov while numerous heat shock proteins were more abundant at Post-ov compared with Pre-ov. Among differentially abundant proteins, seven tended to be correlated with intra-oviductal concentrations of progesterone. A wide range of biological processes was evidenced for differentially abundant proteins, of which metabolic and cellular processes were predominant. This work identifies numerous new candidate proteins potentially interacting with the oocyte, spermatozoa and embryo to modulate fertilization and early embryo development.

Modelling oviduct fluid formation in vitro

Oviduct fluid is the microenvironment that supports early reproductive processes including fertilisation, embryo cleavage, and genome activation. However, the composition and regulation of this critical environment remains rather poorly defined. This study uses an in vitro preparation of the bovine oviduct epithelium, to investigate the formation and composition of in vitro derived oviduct fluid (ivDOF) within a controlled environment. We confirm the presence of oviduct specific glycoprotein 1 in ivDOF and show that the amino acid and carbohydrate content resembles that of previously reported in vivo data. In parallel, using a different culture system, a panel of oviduct epithelial solute carrier genes, and the corresponding flux of amino acids within ivDOF in response to steroid hormones were investigated. We next incorporated fibroblasts directly beneath the epithelium. This dual culture arrangement represents more faithfully the in vivo environment and impacts on ivDOF composition. Lastly, physiological and pathophysiological endocrine states were modelled and their impact on the in vitro oviduct preparation evaluated. These experiments help clarify the dynamic function of the oviduct in vitro and suggest a number of future research avenues, such as investigating epithelial-fibroblast interactions, probing the molecular aetiologies of subfertility, and optimising embryo culture media.

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.

Human fallopian tube epithelium co-culture with murine ovarian follicles reveals crosstalk in the reproductive cycle

STUDY QUESTION

Do interactions between human fallopian tube epithelium and murine follicles occur during an artificial reproductive cycle in a co-culture system in vitro?

SUMMARY ANSWER

In a co-culture system, human fallopian tissues responded to the menstrual cycle mimetic by changes in morphology and levels of secreted factors, and increasing murine corpus luteum progesterone secretion.

WHAT IS KNOWN ALREADY

The entire fallopian tube epithelium, including ciliated and secretory cells, can be regulated in the reproductive cycle. Currently, there are no in vitro culture models that can monitor fallopian tissues in real time in response to factors produced by the ovary. In addition, there are no reports on the impact of fallopian tissue on ovarian function during the menstrual cycle.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

Human fallopian tissue (n = 24) was obtained by routine hysterectomies from women (aged 26-50 years, mean age = 43.6) who had not undergone exogenous hormonal treatment for at least 3 months prior to surgery. CD1 female mice were used for ovarian follicle isolation. The human fallopian epithelium layers were either co-cultured with five murine multilayer secondary follicles (150-180 μm follicles, encapsulated in one alginate gel bead) for 15 days or received stepwise steroid hormone additions for 13 days. The fallopian tissue morphology and cilia beating rate, as measured by an Andor Spinning Disk Confocal, were investigated. Oviduct-specific glycoprotein 1 (OVGP1), human insulin-like growth factor 1 (hIGF1), vascular endothelial growth factor A (VEGF-A) and interleukin 8 (IL8) as biological functional markers were measured either by ELISA or western blot to indicate dynamic changes in the fallopian epithelium during the reproductive cycle generated by mouse follicles or by stepwise steroid hormone induction. Three or four patients in each experiment were recruited for replicates. Data were presented as mean ± SD and further analyzed using one-way ANOVA followed by Tukey's multiple comparisons test.

MAIN RESULTS AND THE ROLE OF CHANCE

The cultured fallopian tube epithelium responded to exogenous steroid hormone stimulation, as demonstrated by enhanced cilia beating rate (~25% increase, P = 0.04) and an increase in OVGP1 secretion (P = 0.02) in response to 1 nM estradiol (E₂) treatment when compared with 0.1 nM E₂. Conversely, 10 nM progesterone plus 1 nM E₂ suppressed cilia beating rate by ~30% (P = 0.008), while OVGP1 secretion was suppressed by 0.1 nM E₂ plus 50 nM progesterone (P = 0.002 versus 1 nM E₂ alone). Human fallopian tube epithelium was co-cultured with murine secondary follicles to mimic the human menstrual cycle. OVGP1 and VEGF-A secretion from fallopian tissue was similar with stepwise hormone treatment and when cultured with murine follicles. However, the secretion patterns of hIGF1 and IL8 differed in the luteal phase when comparing steroid treatment with follicle co-culture. In co-culture, hIGF1 secretion was suppressed in the luteal versus follicular phase (P = 0.005) but stepwise hormone treatment had no effect on hIGF1. In co-culture, IL8 secretion was also suppressed on luteal phase day 15 (P = 0.013) versus follicular phase day 7, but IL8 secretion increased continuously under high E₂/progesterone treatment (P = 0.003 for D13 versus D3). In the co-culture system, the corpus luteum continuously produced progesterone in the presence of fallopian tube tissue until Day 18 while, without fallopian tissue, progesterone started to drop from Day 13.

LIMITATIONS, REASONS FOR CAUTION

One limitation of this study is that murine follicles were used to mimic the human menstrual cycle. However, although secretion patterns of peptide hormones such as inhibins and activins differ in mice and humans, the co-culture system used here did reveal interactions between the tissues that govern reproductive function.

WIDER IMPLICATIONS OF THE FINDINGS

In vitro co-culture models of fallopian reproductive tissues with ovarian follicles can provide an important tool for understanding fertility and for uncovering the mechanisms responsible for reduced fertility. In addition, the role of oviductal secretions and how they influence ovarian function, such as the production of progesterone during the menstrual cycle, can be uncovered using this model.

LARGE-SCALE DATA

None.

STUDY FUNDING AND COMPETING INTERESTS

This work was funded by grants from the NIH (UH3TR001207), the American Cancer Society (RSG-12-230-01-TBG) and NIH (R01EB014806). The authors declare no competing financial interest.

Steroid hormones in bovine oviductal fluid during the estrous cycle

Ovarian steroid hormones are major regulators of the physiology of the oviduct and reproductive events occurring within the oviduct. To establish a whole steroid profiling of the bovine oviductal fluid (OF) during the estrous cycle, contralateral and ipsilateral (to the corpus luteum or preovulatory follicle) oviducts were classified into four stages of the estrous cycle (n = 18-27 cows per stage): postovulatory (Post-ov), mid-luteal (Mid-lut), late luteal (Late-lut), and preovulatory on the basis of the ovarian morphology and intrafollicular steroid concentrations. Steroids were extracted from pools of 150 to 200 μL OF (three to 10 cows per pool; three to four pools per "stage × side" group), purified, fractioned by high-performance liquid chromatography, and analyzed by gas chromatography coupled with tandem mass spectrometry. The concentrations of progesterone (P4) in ipsilateral OF increased from Post-ov (56.9 ± 13.4 ng/mL) to Mid-lut (120.3 ± 34.3 ng/mL), then decreased from Late-lut (76.7 ± 1.8 ng/mL) to Pre-ov (6.3 ± 1.7 ng/mL), and were four to 16 times higher than in contralateral OF. Most P4 metabolites followed similar patterns of variation. Concentrations of 17beta-estradiol (E2) were significantly higher at Pre-ov (290.5 ± 63.2 pg/mL) compared with all other stages (<118.3 pg/mL), with no difference regarding the side of ovulation. Concentrations of androstenedione displayed a pattern similar to that of E2, whereas other androgens, estrone, and corticoids did not vary between stages or sides. In conclusion, a highly concentrated and fluctuating hormonal environment was evidenced in the bovine OF. These results could be useful to improve media for IVF, embryo development, and culture of oviductal cells.

Spatial differences in gene expression in the bovine oviduct

The aim of this study was to compare the transcriptome of the oviductal isthmus of pregnant heifers with that of cyclic heifers as well as to investigate spatial differences between the transcriptome of the isthmus and ampulla of the oviduct in pregnant heifers. After synchronizing crossbred beef heifers, those in standing oestrus (=Day 0) were randomly assigned to cyclic (non-bred, n=6) or pregnant (artificially inseminated, n=11) groups. They were slaughtered on Day 3 and both oviducts from each animal were isolated and cut in half to separate ampulla and isthmus. Each portion was flushed to confirm the presence of an oocyte/embryo and was then opened longitudinally and scraped to obtain epithelial cells which were snap-frozen. Oocytes and embryos were located in the isthmus of the oviduct ipsilateral to the corpus luteum Microarray analysis of oviductal cells revealed that proximity to the corpus luteum did not affect the transcriptome of the isthmus, irrespective of pregnancy status. However, 2287 genes were differentially expressed (P<0.01) between the ampulla and isthmus of the oviduct ipsilateral to the corpus luteum in pregnant animals. Gene ontology revealed that the main biological processes overrepresented in the isthmus were synthesis of nitrogen, lipids, nucleotides, steroids and cholesterol as well as vesicle-mediated transport, cell cycle, apoptosis, endocytosis and exocytosis, whereas cell motion, motility and migration, DNA repair, calcium ion homeostasis, carbohydrate biosynthesis, and regulation of cilium movement and beat frequency were overrepresented in the ampulla. In conclusion, large differences in gene expression were observed between the isthmus and ampulla of pregnant animals at Day 3 after oestrus.

Proteomes of the Female Genital Tract During the Oestrous Cycle

The female genital tract includes several anatomical regions whose luminal fluids successively interact with gametes and embryos and are involved in the fertilisation and development processes. The luminal fluids from the inner cervix, the uterus and the oviduct were collected along the oestrous cycle at oestrus (Day 0 of the cycle) and during the luteal phase (Day 10) from adult cyclic ewes. The proteomes were assessed by GeLC-MS/MS and quantified by spectral counting. A set of 940 proteins were identified including 291 proteins differentially present along the cycle in one or several regions. The global analysis of the fluid proteomes revealed a general pattern of endocrine regulation of the tract, with the cervix and the oviduct showing an increased differential proteins abundance mainly at oestrus while the uterus showed an increased abundance mainly during the luteal phase. The proteins more abundant at oestrus included several families such as the heat shock proteins (HSP), the mucins, the complement cascade proteins and several redox enzymes. Other proteins known for their interaction with gametes such as oviductin (OVGP), osteopontin, HSPA8, and the spermadhesin AWN were also overexpressed at oestrus. The proteins more abundant during the luteal phase were associated with the immune system such as ceruloplasmin, lactoferrin, DMBT1, or PIGR, and also with tissue remodeling such as galectin 3 binding protein, alkaline phosphatase, CD9, or fibulin. Several proteins differentially abundant between estrus and the luteal phase, such as myosin 9 and fibronectin, were also validated by immunohistochemistry. The potential roles in sperm transit and uterine receptivity of the proteins differentially regulated along the cycle in the female genital tract are discussed.