Role of the oviduct in early embryo development

Effect of the estrous cycle on zinc transporter expression in bovine cumulus-oocyte complexes and oviduct epithelial cells

During the luteal and follicular phases of the estrous cycle, cumulus-oocyte complexes (COC) and oviduct epithelial cells (OEC) undergo notable physiological and morphological changes. Maintaining proper zinc (Zn) homeostasis is crucial in both somatic and germinal mammalian cells. This study aimed to assess the impact of the estrous phase (luteal or follicular) on Zn transporter expression in bovine COC and OEC (BOEC). The expression of Zn transporters Slc39a6 (ZIP6), Slc39a8 (ZIP8), Slc39a14 (ZIP14), Slc30a3 (ZnT3), Slc30a7 (ZnT7), and Slc30a9 (ZnT9) was analyzed in COC and BOEC from cows during the luteal or follicular phases. Gene expression of ZIP6, ZIP14, and ZnT9 was quantified in COC and BOEC. The gene expression in the remaining transporters could not be quantified due to low mRNA levels (ZIP8 and ZnT3 in COC and BOEC; ZnT7 in BOEC) or absence of expression (ZnT7 in COC). In COC, the relative expression (RE) of all three transporters was higher in the luteal phase compared to the follicular phase (P ≤ 0.05). In BOEC, the luteal phase increased the RE of ZIP 6 (P ≤ 0.05), decreased the RE of ZnT9 (P ≤ 0.05), and did not modify the RE of ZIP14 (P > 0.05) compared to the follicular phase. In conclusion, the study reveals differences in the gene expression of ZIP6, ZIP14, and ZnT9 according to the estrous cycle phase in ex vivo samples of bovine COC and OEC.

In Vitro Culture of Mammalian Embryos: Is There Room for Improvement?

Preimplantation embryo culture, pivotal in assisted reproductive technology (ART), has lagged in innovation compared to embryo selection advancements. This review examines the persisting gap between in vivo and in vitro embryo development, emphasizing the need for improved culture conditions. While in humans this gap is hardly estimated, animal models, particularly bovines, reveal clear disparities in developmental competence, cryotolerance, pregnancy and live birth rates between in vitro-produced (IVP) and in vivo-derived (IVD) embryos. Molecular analyses unveil distinct differences in morphology, metabolism, and genomic stability, underscoring the need for refining culture conditions for better ART outcomes. To this end, a deeper comprehension of oviduct physiology and embryo transport is crucial for grasping embryo-maternal interactions' mechanisms. Research on autocrine and paracrine factors, and extracellular vesicles in embryo-maternal tract interactions, elucidates vital communication networks for successful implantation and pregnancy. In vitro, confinement, and embryo density are key factors to boost embryo development. Advanced dynamic culture systems mimicking fluid mechanical stimulation in the oviduct, through vibration, tilting, and microfluidic methods, and the use of innovative softer substrates, hold promise for optimizing in vitro embryo development.

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.

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.

How the Oviduct Lipidomic Profile Changes over Time after the Start of an Obesogenic Diet in an Outbred Mouse Model

We investigated whether a high-fat/high-sugar (HF/HS) diet alters the lipidomic profile of the oviductal epithelium (OE) and studied the patterns of these changes over time. Female outbred Swiss mice were fed either a control (10% fat) or HF/HS (60% fat, 20% fructose) diet. Mice (n = 3 per treatment per time point) were sacrificed and oviducts were collected at 3 days and 1, 4, 8, 12 and 16 weeks on the diet. Lipids in the OE were imaged using matrix-assisted laser desorption ionisation mass spectrometry imaging. Discriminative m/z values and differentially regulated lipids were determined in the HF/HS versus control OEs at each time point. Feeding the obesogenic diet resulted in acute changes in the lipid profile in the OE already after 3 days, and thus even before the development of an obese phenotype. The changes in the lipid profile of the OE progressively increased and became more persistent after long-term HF/HS diet feeding. Functional annotation revealed a differential abundance of phospholipids, sphingomyelins and lysophospholipids in particular. These alterations appear to be not only caused by the direct accumulation of the excess circulating dietary fat but also a reduction in the de novo synthesis of several lipid classes, due to oxidative stress and endoplasmic reticulum dysfunction. The described diet-induced lipidomic changes suggest alterations in the OE functions and the oviductal microenvironment which may impact crucial reproductive events that take place in the oviduct, such as fertilization and early embryo development.

Optical coherence tomography for dynamic investigation of mammalian reproductive processes

The biological events associated with mammalian reproductive processes are highly dynamic and tightly regulated by molecular, genetic, and biomechanical factors. Implementation of live imaging in reproductive research is vital for the advancement of our understanding of normal reproductive physiology and for improving the management of reproductive disorders. Optical coherence tomography (OCT) is emerging as a promising tool for dynamic volumetric imaging of various reproductive processes in mice and other animal models. In this review, we summarize recent studies employing OCT-based approaches toward the investigation of reproductive processes in both, males and females. We describe how OCT can be applied to study structural features of the male reproductive system and sperm transport through the male reproductive tract. We review OCT applications for in vitro and dynamic in vivo imaging of the female reproductive system, staging and tracking of oocytes and embryos, and investigations of the oocyte/embryo transport through the oviduct. We describe how the functional OCT approach can be applied to the analysis of cilia dynamics within the male and female reproductive systems. We also discuss the areas of research, where OCT could find potential applications to progress our understanding of normal reproductive physiology and reproductive disorders.

Integrative Proteomics and Transcriptomics Profiles of the Oviduct Reveal the Prolificacy-Related Candidate Biomarkers of Goats (Capra hircus) in Estrous Periods

The oviduct is a dynamic reproductive organ for mammalian reproduction and is required for gamete storage, maturation, fertilization, and early embryonic development, and it directly affects fecundity. However, the molecular regulation of prolificacy occurring in estrous periods remain poorly understood. This study aims to gain a better understanding of the genes involved in regulating goat fecundity in the proteome and transcriptome levels of the oviducts. Twenty female Yunshang black goats (between 2 and 3 years old, weight 52.22 ± 0.43 kg) were divided into high- and low-fecundity groups in the follicular (FH and FL, five individuals per group) and luteal (LH and LL, five individuals per group) phases, respectively. The DIA-based high-resolution mass spectrometry (MS) method was used to quantify proteins in twenty oviducts. A total of 5409 proteins were quantified, and Weighted gene co-expression network analysis (WGCNA) determined that the tan module was highly associated with the high-fecundity trait in the luteal phase, and identified NUP107, ANXA11, COX2, AKP13, and ITF140 as hub proteins. Subsequently, 98 and 167 differentially abundant proteins (DAPs) were identified in the FH vs. FL and LH vs. LL comparison groups, respectively. Parallel reaction monitoring (PRM) was used to validate the results of the proteomics data, and the hub proteins were analyzed with Western blot (WB). In addition, biological adhesion and transporter activity processes were associated with oviductal function, and several proteins that play roles in oviductal communication with gametes or embryos were identified, including CAMSAP3, ITGAM, SYVN1, EMG1, ND5, RING1, CBS, PES1, ELP3, SEC24C, SPP1, and HSPA8. Correlation analysis of proteomics and transcriptomic revealed that the DAPs and differentially expressed genes (DEGs) are commonly involved in the metabolic processes at the follicular phase; they may prepare the oviductal microenvironment for gamete reception; and the MAP kinase activity, estrogen receptor binding, and angiotensin receptor binding terms were enriched in the luteal phase, which may be actively involved in reproductive processes. By generating the proteome data of the oviduct at two critical phases and integrating transcriptome analysis, we uncovered novel aspects of oviductal gene regulation of fecundity and provided a reference for other mammals.

Effects of an obesogenic diet on the oviduct depend on the duration of feeding

Research question

How long does it take for an obesogenic (high-fat/high-sugar, HF/HS) diet to influence the oviductal microenvironment? What are the affected cellular pathways and are they dependent on the genetic background of the mouse model?

Design

Female Swiss (outbred) and C57BL/6N (B6, inbred) mice were fed either a control (10% fat) or HF/HS (60% fat, 20% fructose) diet. Body weight was measured weekly. Mice were sacrificed at 3 days (3d), 1 week (1w), 4w, 8w, 12w and 16w on the diet (n = 5 per treatment per time point). Total cholesterol concentrations and inflammatory cytokines were measured in serum. Oviductal epithelial cells (OECs) were used to study the expression of genes involved in (mitochondrial) oxidative stress (OS), endoplasmic reticulum (ER) stress and inflammation using qPCR.

Results

Body weight and blood cholesterol increased significantly in the HF/HS mice in both strains compared to controls. In Swiss mice, HF/HS diet acutely increased ER-stress and OS-related genes in the OECs already after 3d. Subsequently, mitochondrial and cytoplasmic antioxidants were upregulated and ER-stress was alleviated at 1w. After 4-8w (mid-phase), the expression of ER-stress and OS-related genes was increased again and persisted throughout the late-phase (12-16w). Serum inflammatory cytokines and inflammatory marker-gene expression in the OECs were increased only in the late-phase. Some of the OEC stress responses were stronger or earlier in the B6.

Conclusions

OECs are sensitive to an obesogenic diet and may exhibit acute stress responses already after a few days of feeding. This may impact the oviductal microenvironment and contribute to diet-induced subfertility.

Specific locations and amounts of denatured collagen and collagen-specific chaperone HSP47 in the oviducts and uteri of old cows as compared with those of heifers

Collagen, the most abundant extra-cellular matrix in oviducts and uteri, performs critical roles in pregnancies. We hypothesised that the locations and amounts of both denatured collagen and the collagen-specific molecular chaperone 47-kDa heat shock protein (HSP47) in the oviducts and uteri of old cows are different compared with those of young heifers because of repeated pregnancies. Since detecting damaged collagen in tissues is challenging, we developed a new method that uses a denatured collagen detection reagent. Then, we compared damaged collagen in the oviducts and uteri between post-pubertal growing nulliparous heifers (22.1±1.0months old) and old multiparous cows (143.1±15.6months old). Further, we evaluated the relationship between denatured collagen and HSP47 by combining this method with fluorescence immunohistochemistry. Picro-sirius red staining showed collagen in almost all parts of the oviducts and uteri. Expectedly, damaged collagen was increased in the oviducts and uteri of old cows. However, damaged collagen and HSP47 were not located in the same area in old cows. The number of fibroblasts increased, suggesting the presence of fibrosis in the oviducts and uteri of old cows. These organs of old cows showed higher HSP47 protein amounts than those of heifers. However, the uteri, but not oviducts, of old cows had lower HSP47 mRNA amounts than those of heifers. These findings revealed the specific location and amounts of denatured collagen and HSP47 in the oviducts and uteri of old cows compared with those of heifers.

Fatty Acid Supplementation During in vitro Embryo Production Determines Cryosurvival Characteristics of Bovine Blastocysts

In vitro production (IVP) embryos have a reduced quality and poor cryotolerance in comparison to in vivo embryos. This study investigated whether free fatty acid (FFA) conditions, fatty acid free (FAF)- synthetic oviduct fluid (SOF) without or with 25 μM of saturated stearic (C_18:0) or unsaturated oleic (C_18:1) acid during the first 5 IVP days, relate to quality and cryosurvival of day 8 blastocysts. Apart from the blastocyst scores, both 1) number and size of lipid droplets of fresh blastocysts and 2) total number and apoptotic and necrotic cells, before and after freezing-thawing, were scored by confocal microscopy. Blastocyst rates were significantly lower in the FAF SOF condition in comparison to other groups. Interestingly, blastocysts originating from the C_18:1 group, with a significantly higher lipid content, and blastocysts from the FAF SOF group demonstrated a high cryosurvival rate (70.1 and 67.4%, respectively) comparable with in vivo blastocysts (68%), in contrast to the poor cryosurvival of C_18:0 exposed embryos (17.6%). In all freeze-thawed embryos the average amount of apoptotic and necrotic cells increased albeit that the C_18:0 condition rates were higher (43.2%) when compared to C_18:1 (26.0%) and FAF SOF conditions (26.5%). The current data show that FFA administered during early embryonic development significantly affect the cryotolerance of blastocysts.

The role of the oviduct and extracellular vesicles during early embryo development in bovine

The oviduct is an important reproductive structure that connects the ovary to the uterus and takes place to important events such as oocyte final maturation, fertilization and early embryonic development. Thus, gametes and embryo can be directly influenced by the oviductal microenvironment composed by epithelial cells such secretory and ciliated cells and oviductal fluid. The oviduct composition is anatomically dynamic and is under ovarian hormones control. The oviductal fluid provides protection, nourishment and transport to gametes and embryo and allows interaction to oviductal epithelial cells. All these functions together allows the oviduct to provides the ideal environment to the early reproductive events. Extracellular vesicles (EVs) are biological nanoparticles that mediates cell communication and are present at oviductal fluid and plays an important role in gametes/embryo - oviductal cells communication. This review will present the ability of the oviducts based on its dynamic and systemic changes during reproductive events, as well as the contribution of EVs in this process.

Porcine oviductal extracellular vesicles facilitate early embryonic development via relief of endoplasmic reticulum stress

The key to successful in vitro embryo production (IVEP) is to mimic the natural in vivo oviductal microenvironment. Although the chemically defined media in extensive use for the in vitro culture of mammalian embryos is based on the composition of oviductal fluid, the IVEP systems in current use must still bypass the oviduct to produce embryos in vitro. Extracellular vesicles (EVs) in the oviduct are versatile intercellular delivery vehicles for maternal-embryo communication, and a lack of them can be associated with failed early embryonic development under in vitro culture conditions. Herein, we isolated EVs from porcine oviduct fluid and confirmed that oviductal EV supplementation improves the embryonic development of parthenogenetically activated (PA) embryos in terms of blastocyst formation rates and total cell numbers. Our experiments also revealed that a beneficial effect of oviductal EVs on PA embryos was achievable, at least in part, by relieving endoplasmic reticulum stress. These results suggest that the maternal-embryo communication mediated by oviductal EVs benefits early embryonic development. Given the contribution of oviductal EVs to early embryonic development, these findings offer novel insights for the optimization of current IVEP systems.

Analysis of Expression Profiles of CircRNA and MiRNA in Oviduct during the Follicular and Luteal Phases of Sheep with Two Fecundity (FecB Gene) Genotypes

CircRNA and miRNA, as classes of non-coding RNA, have been found to play pivotal roles in sheep reproduction. There are many reports of circRNA and miRNA in the ovary and uterus, but few in the oviduct. In this study, RNA-Seq was performed to analyze the expression profile of circRNA and miRNA in the oviduct during the follicular phase and luteal phase of sheep with FecB^BB and FecB⁺⁺ genotypes. The results showed that a total of 3223 circRNAs and 148 miRNAs were identified. A total of 15 DE circRNAs and 40 DE miRNAs were found in the comparison between the follicular phase and luteal phase, and 1 DE circRNA and 18 DE miRNAs were found in the comparison between the FecB^BB genotype and FecB⁺⁺ genotype. GO and KEGG analyses showed that the host genes of DE circRNAs were mainly enriched in the Rap1 signaling pathway, PI3K-Akt signaling pathway and neuroactive ligand-receptor interactions. Novel_circ_0004065, novel_circ_0005109, novel_circ_0012086, novel_circ_0014274 and novel_circ_0001794 were found to be possibly involved in the oviductal reproduction process. GO and KEGG analyses showed that the target genes of DE miRNAs were mainly enriched in insulin secretion, the cAMP signaling pathway, the cGMP-PKG signaling pathway, the Rap1 signaling pathway and the TGF-β signaling pathway, and the target genes LPAR1, LPAR2, FGF18, TACR3, BMP6, SMAD4, INHBB, SKP1 and TGFBR2 were found to be associated with the reproductive process. Miranda software was used to identify 27 miRNAs that may bind to 13 DE circRNAs, including miR-22-3p (target to novel_circ_0004065), miR-127, miR-136 (target to novel_circ_0000417), miR-27a (target to novel_circ_0014274) and oar-miR-181a (target to novel_circ_ 0017815). The results of this study will help to elucidate the regulatory mechanisms of circRNAs and miRNAs in sheep reproduction. Our study, although not establishing direct causal relationships of the circRNA and miRNA changes, enriches the sheep circRNA and miRNA database and provides a basis for further studies on sheep reproduction.

In vivo dynamic 3D imaging of oocytes and embryos in the mouse oviduct

Developmental biologists have always relied on imaging to shed light on dynamic cellular events. However, processes such as mammalian fertilization and embryogenesis are generally inaccessible for direct imaging. In consequence, how the oviduct (fallopian tube) facilitates the transport of gametes and preimplantation embryos continues to be unanswered. Here we present a combination of intravital window and optical coherence tomography for dynamic, volumetric, in vivo imaging of oocytes and embryos as they are transported through the mouse oviduct. We observed location-dependent circling, oscillating, and long-distance bi-directional movements of oocytes and embryos that suggest regulatory mechanisms driving transport and question established views in the field. This in vivo imaging approach can be combined with a variety of genetic and pharmacological manipulations for live functional analysis, bringing the potential to investigate reproductive physiology in its native state.

Wang and Larina present in vivo volumetric imaging of oocytes and embryos as they are transported through the mouse oviduct with optical coherence tomography and an intravital microscopy. The study reveals complex dynamics of oocytes and embryos that suggest a regulatory role of cilia and oviductal contractions in driving the transport.

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.

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.

Extracellular vesicles and domestic animal reproduction

Embryo implantation is a complex process in which significant changes occur continually in both the corpora lutea and in the endometrium of females and which varies depending on the embryonic, pre-implantation, or fetal stages. However, at all stages, correct maternal-embryonic communication is essential. In the last few years, a new intercellular communication tool, mediated by extracellular vesicles (EVs), has emerged. Many authors agree on the relevant role of EVs in correct communication between the mother and the embryo, as a fundamental system for the pregnancy to reach term and embryonic development to occur correctly. This review analyzes current information on known EVs, their main functions, and their role in implantation and embryonic development in domestic animals.

Anti-Müllerian hormone receptor type 2 (AMHR2) expression in bovine oviducts and endometria: comparison of AMHR2 mRNA and protein abundance between old Holstein and young and old Wagyu females

Anti-Müllerian hormone (AMH) is a glycoprotein produced by granulosa cells of preantral and small antral follicles that has multiple important roles in the ovaries. Recent studies have revealed extragonadal AMH regulation of gonadotrophin secretion from bovine gonadotrophs. In this study we investigated whether the primary receptor for AMH, AMH receptor type 2 (AMHR2), is expressed in bovine oviducts and endometria. Reverse transcription-polymerase chain reaction detected expression of AMHR2 mRNA in oviductal and endometrial specimens. Western blotting and immunohistochemistry were performed to analyse AMHR2 protein expression using anti-bovine AMHR2 antibody. Immunohistochemistry revealed robust AMHR2 expression in the tunica mucosa of the ampulla and isthmus, as well as in the glandular and luminal epithelium of the endometrium. AMHR2 mRNA (measured by real-time polymerase chain reaction) and AMHR2 protein expression in these layers did not significantly differ among oestrous phases in adult Wagyu cows (P>0.1). In addition, AMHR2 mRNA and protein expression in these layers did not differ among old Holsteins (mean (±s.e.m.) age 91.9±6.4 months) and young (26.6±0.8 months) and old (98.8±10.2 months) Wagyu cows. Therefore, AMHR2 is expressed in bovine oviducts and endometria.

Oviduct as a sensor of embryo quality: deciphering the extracellular vesicle (EV)-mediated embryo-maternal dialogue

Embryo-derived extracellular vesicles (EVs) may play a role in mediating the embryo-maternal dialogue at the oviduct, potentially carrying signals reflecting embryo quality. We investigated the effects of bovine embryo-derived EVs on the gene expression of bovine oviductal epithelial cells (BOECs), and whether these effects are dependent on embryo quality. Presumptive zygotes were cultured individually in vitro in culture medium droplets until day 8 while their development was assessed at day 2, 5 and 8. Conditioned medium samples were collected at day 5 and pooled based on embryo development (good quality embryo media and degenerating embryo media). EVs were isolated from conditioned media by size exclusion chromatography and supplemented to primary BOEC monolayer cultures to evaluate the effects of embryo-derived EVs on gene expression profile of BOEC. Gene expression was quantified by RNA-seq and RT-qPCR. A total of 7 upregulated and 18 downregulated genes were detected in the BOECs supplemented with good quality embryo-derived EV compared to the control. The upregulated genes included interferon-τ-induced genes, such as OAS1Y, MX1 and ISG15, which have previously been reported as upregulated in the oviductal epithelial cells in the presence of embryos. Of the upregulated genes, OAS1Y and MX1 were validated with RT-qPCR. In contrast, only one differentially expressed gene was detected in BOECs in response to degenerating embryo-derived EVs, suggesting that oviductal responses are dependent on embryo quality. Our results support the hypothesis that embryo-derived EVs are involved in embryo-maternal communication at the oviduct and the oviductal response is dependant on the embryo quality. KEY MESSAGES: • Extracellular vesicles (EVs) released by individually cultured pre-implantation bovine embryos can alter the gene expression of primary oviductal epithelial cells. • The oviductal response, in terms of gene expression, to the bovine embryo-derived EVs varied depending on the embryo quality. • In vivo, the oviduct may have the ability to sense the quality of the pre-implantation embryos. • The observed effect of embryo-derived EVs on oviductal epithelial cells could serve as a non-invasive method of evaluating the embryo quality.

The proteome of human Fallopian tube lavages during the phase of embryo transit reveals candidate proteins for the optimization of preimplantation embryo culture

STUDY QUESTION

Are there phase-specific changes in the early secretory (ES) phase human tubal lavage proteome that can inform and potentially optimize IVF culture media?

SUMMARY ANSWER

The human tubal lavage proteome during the ES phase relative to the menstrual phase reveals substantial differential protein abundance in pathways such as glycolysis, redox homeostasis and activation of 14-3-3 zeta-mediated signaling.

WHAT IS KNOWN ALREADY

The Fallopian tube is uniquely suited to the development of the preimplantation embryo as it transits the tube during the ES phase of the menstrual cycle. Euploid cleavage-stage embryo arrest may reflect incomplete recapitulation of in-vivo conditions by current media formulations.

STUDY DESIGN, SIZE, DURATION

Proteome-wide analysis of distal tubal lavage specimens collected from 26 healthy women undergoing open microtubal anastomosis surgery from January 2013 to January 2018 was performed. Specimens were grouped by menstrual cycle phase in order to analyze phase-specific differences in protein abundance. For the murine embryo assay, single-cell embryos (N = 482) were collected from superovulated wild type C57BL/6 female mice and cultured in microdrops over 5 days for the assessment of blastocyst development.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Human tubal lavage specimens were processed for label-free mass spectrometry. Reported menstrual cycle day was confirmed by measuring serum hormones. Key protein targets in the ES phase were validated via immunoblot. The ES phase-specific increase in 14-3-3 zeta protein was confirmed via ELISA of conditioned media obtained from primary human Fallopian tube epithelial cell culture. A murine embryo assay was performed to investigate the impact of graduated concentrations of 14-3-3 zeta on the blastocyst development rate.

MAIN RESULTS AND THE ROLE OF CHANCE

Comparison of the ES and menstrual phase human tubal lavage proteomes revealed 74 differentially expressed proteins with enrichment of pathways and biological processes involved in the regulation of carbohydrate metabolism, oxidative stress and cell survival. The adapter-regulator protein 14-3-3 zeta was among the most significantly increased in the ES phase. Supplementation of embryo culture media with 14-3-3 zeta at concentrations tested did not significantly improve the murine blastocyst development.

LIMITATIONS, REASONS FOR CAUTION

Although select associations were recapitulated in the conditioned media from sex steroid exposed primary human tubal epithelial cells, cell culture represents an in-vitro approximation. Changes to embryo culture media, such as protein supplementation, must undergo rigorous preclinical safety testing prior to adoption for human use.

WIDER IMPLICATIONS OF THE FINDINGS

This study represents the first description of the human Fallopian tube lavage proteome across the menstrual cycle, revealing a unique proteomic signature during the ES phase. Although supplementation of culture media with 14-3-3 zeta at appropriate concentrations showed no significant impact on the murine blastocyst development rate, other biologically plausible candidate proteins for individual or high throughput testing strategies are identified.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded in part by an Army Medical Department Advanced Medical Technology Initiative grant from the United States Army Medical Research and Materiel Command's Telemedicine and Advanced Technology Research Center. There are no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Influence of metabolic status and genetic merit for fertility on proteomic composition of bovine oviduct fluid†

The oviduct plays a crucial role in fertilization and early embryo development providing the microenvironment for oocyte, spermatozoa, and early embryo. Since dairy cow fertility declined steadily over the last decades, reasons for early embryonic loss have gained increasing interest. Analyzing two animal models, this study aimed to investigate the impact of genetic predisposition for fertility and of metabolic stress on the protein composition of oviduct fluid. A metabolic model comprised maiden Holstein heifers and postpartum lactating (Lact) and non-lactating (Dry) cows, while a genetic model consisted of heifers from the Montbéliarde breed and Holstein heifers with low- and high-fertility index. In a holistic proteomic analysis of oviduct fluid from all groups using nano-liquid chromatography tandem-mass spectrometry analysis and label-free quantification, we were able to identify 1976 proteins, among which 143 showed abundance alterations in the pairwise comparisons within both models. Most differentially abundant proteins were revealed between low fertility Holstein and Montbéliarde (52) in the genetic model and between lactating and maiden Holstein (19) in the metabolic model, demonstrating a substantial effect of genetic predisposition for fertility and metabolic stress on the oviduct fluid proteome. Functional classification of affected proteins revealed actin binding, translation, and immune system processes as prominent gene ontology (GO) clusters. Notably, Actin-related protein 2/3 complex subunit 1B and the three immune system-related proteins SERPIND1 protein, immunoglobulin kappa locus protein, and Alpha-1-acid glycoprotein were affected in both models, suggesting that abundance changes of immune-related proteins in oviduct fluid play an important role for early embryonic loss.

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.

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.

Oviductal extracellular vesicles interact with the spermatozoon's head and mid-piece and improves its motility and fertilizing ability in the domestic cat

Fertilization and early embryo development are regulated by a unique maternal-gamete/embryo cross-talk within the oviduct. Recent studies have shown that extracellular vesicles (EVs) within the oviduct play important roles in mediating this developmental process. Here, we examined the influence of oviductal EVs on sperm function in the domestic cat. We demonstrated that (1) EVs are enriched in proteins related to energy metabolism, membrane modification, and reproductive function; (2) EVs bound and fused with the membranes of the acrosome and mid piece; and (3) incubating sperm with EVs improved motility, fertilizing capacity of cat spermatozoa and prevented acrosomal exocytosis in vitro. These findings indicated that oviductal EVs mediate sperm function and fertilization in the cat and provides new insights to improve sperm cryopreservation and in vitro fertilization in the domestic and wild felids and human.

Effect of porcine uterus as ex vivo model of fertilizing ability and gene expression pattern on blastocysts

The success of in vitro embryo production demonstrates that the oviduct can be bypassed during early embryonic development. Using an ex vivo model of porcine uterus is one of the strategies used to investigate fertilization within the oviductal environment. In this study, in vitro-matured porcine oocytes (MII) were fertilized with 7.5 × 10⁷, 15 × 10⁷, or 30 × 10⁷ sperm cells for 20 min in the oviduct of a porcine uterine ex vivo model. MII oocytes used for in vitro fertilization (IVF) served as control 1; those cultured in the oviduct of the ex vivo model for 20 min before IVF served as control 2. In present study, the penetration rate, polyspermy, and fertilization efficiency, and accumulated reactive oxygen species (ROS) levels in the treatment groups were significantly decreased compared to those in the control 1 group. During embryonic development, the cleavage rates in the treatment groups were significantly lower than those in the control groups. The cleavage rate in the 30 × 10⁷ sperm cell-treated group was higher than that in the 7.5 × 10⁷ sperm cell-treated group. The blastocyst formation rate in control 1 and 2, and 30 × 10⁷ sperm cell-treated groups increased compared to that in the 7.5 and 15 × 10⁷ sperm cell-treated groups. PCNA, HSP70.2, and GLUT1 were upregulated in the treatment groups and POU5F1, BAX, GPX1 were upregulated in the treatment and control 2 groups, compared to the control 1 group. These results suggest that an ex vivo model may decrease the penetration rate and fertilization efficiency by increasing the accumulated ROS levels and inducing the expression of apoptosis- and stress-related genes. However, the model improved the monospermy rate and expression of embryo developmental competence genes. This is the first study that evaluates the effect of an ex vivo model of porcine uterus on fertilization parameters, and the development of porcine embryos.

Ontology groups representing angiogenesis and blood vessels development are highly up-regulated during porcine oviductal epithelial cells long-term real-time proliferation – a primary cell culture approach

The morphological and biochemical modification of oviductal epithelial cells (OECs) belongs to the group of compound processes responsible for proper oocyte transport and successful fertilization. The cellular interactions between cumulus-oocyte complexes (COCs) and oviductal epithelial cells (OECs) are crucial for this unique mechanism. In the present study we have analyzed angiogenesis and blood vessel development processes at transcript levels. By employing microarrays, four ontological groups associated with these mechanisms have been described. Differentially expressed genes belonging to the “angiogenesis”, “blood circulation”, “blood vessel development” and “blood vessel morphogenesis” GO BP terms were investigated as a potential markers for the creation of new blood vessels in cells under in vitro primary culture conditions.

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.

Differential integrin expression in pre-implantation embryos developing under in vivo and in vitro conditions

Implantation failure is a major problem in human assisted reproduction, which persists regardless the optimization of endometrial receptivity and selection of genetically and morphologically healthy embryos. Since embryo-endometrium interaction depends on cell junctional, cell adhesion and cell-substratum adhesion molecules, the present study inquired whether in vitro growing murine embryos display similar to the in vivo growing embryos patterns of adhesion molecules. To this extend aVb3 expression and distribution in zygotes and 2-cell stage embryos were studied. The results demonstrated that only the in vivo growing embryos displayed specifically polarized aVb3 distribution, indicating their potential successful interaction with endometrium. Based on previous studies showing that L-carnitine (L-Cn) could affect embryonic development, it was demonstrated that the addition of L-Cn to the culture medium, could lead the in vitro growing embryos to acquire aVb3 expression and distribution similar to the in vivo growing embryos. Visualization of the effect of L-Cn using third harmonic generation imaging showed decreased lipid droplet levels in 2-cell-stage embryos, observation that correlates with an active energetic state of the growing embryos. Thus, the application of L-Cn to the culture medium could assist pre-implantation-state embryos to acquire aVb3 expression and distribution similar to the in vivo developing conditions.

Expression of macrophage migration inhibitory factor (MIF) in bovine oviducts is higher in the postovulatory phase than during the oestrus and luteal phase

Whether macrophage migration inhibitory factor (MIF) in the bovine oviduct is important for early embryogenesis has not been well substantiated. The aim of the present study was to test the hypothesis that bovine oviduct expresses higher levels of MIF during the post-ovulation phase. Both ampullary and isthmic samples were collected from Japanese black heifers during oestrus (Day 0; n=5), postovulation (Day 3; n=6) and luteal phase (Days 9-12; n=5). MIF mRNA and protein were extracted from the ampullary and isthmic samples and their levels measured by real-time polymerase chain reaction and western blot analysis respectively. Fluorescent immunohistochemistry was performed on frozen ampullary and isthmic sections using antibodies against MIF. MIF mRNA and protein expression was higher in the postovulatory phase than during oestrus and the luteal phase (P<0.05). Fluorescent immunohistochemistry confirmed that in all phases of the oestrous cycle evaluated, the primary site of MIF expression in the ampulla and isthmus was the tunica mucosa. In conclusion, the bovine ampulla and isthmus have higher MIF expression during the postovulatory phase. Further studies are needed to clarify the role of MIF in bovine oviducts.

Effect of bovine oviductal fluid on development and quality of bovine embryos produced in vitro

To evaluate the effect of bovine oviductal fluid (OF) supplementation during in vitro culture of bovine embryos on their development and quality, in vitro-produced zygotes were cultured in synthetic oviductal fluid (SOF; negative control; C^-) supplemented with OF or 5% fetal calf serum (positive control; C⁺). Embryo development was recorded on Days 7-9 after insemination and blastocyst quality was assessed through cryotolerance, differential cell counting of the inner cell mass and trophectoderm, and gene expression. OF was added to the culture medium at concentrations ranging from 0.625% to 25%. The higher OF concentrations (5%, 10% and 25%) had a detrimental effect on embryo development. Lower OF concentrations (1.25% and 0.625%) supported embryo development until Day 9 (27.5%) and produced higher-quality blastocysts, as reflected by their cryotolerance (53.6% and 57.7% survival at 72h, respectively, vs 25.9% in C⁺) and total cell number (mean (± s.e.m.) 165.1±4.7 and 156.2±4.2, respectively, vs 127.7±4.9 in C^- and 143.1±4.9 in C⁺). Consistent with these data, upregulation of the water channel aquaporin 3 (AQP3) mRNA was observed in blastocysts supplemented with 1.25% OF compared with C^- and C⁺. Serum supplementation resulted in a reduction in the expression of glucose and lipid metabolism-related genes and downregulation of the epigenetic-related genes DNA methyltransferase 3A (DNMT3A) and insulin-like growth factor 2 receptor (IGF2R). In conclusion, in vitro culture with low concentrations of OF has a positive effect on the development and quality of bovine embryos.

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.

Prolonged in vivo functional assessment of the mouse oviduct using optical coherence tomography through a dorsal imaging window

The oviduct (or fallopian tube) serves as an environment for gamete transport, fertilization and preimplantation embryo development in mammals. Although there has been increasing evidence linking infertility with disrupted oviduct function, the specific roles that the oviduct plays in both normal and impaired reproductive processes remain unclear. The mouse is an important mammalian model to study human reproduction. However, most of the current analyses of the mouse oviduct rely on static histology or 2D visualization, and are unable to provide dynamic and volumetric characterization of this organ. The lack of imaging access prevents longitudinal live analysis of the oviduct and its associated reproductive events, limiting the understanding of mechanistic aspects of fertilization and preimplantation pregnancy. To address this limitation, we report a 3D imaging approach that enables prolonged functional assessment of the mouse oviduct in vivo. By combining optical coherence tomography with a dorsal imaging window, this method allows for extended volumetric visualization of the oviduct dynamics, which was previously not achievable. The approach is used for quantitative analysis of oviduct contraction, spatiotemporal characterization of cilia beat frequency and longitudinal imaging. This new approach is a useful in vivo imaging platform for a variety of live studies in mammalian reproduction.

Kinetic effect of oestrogen on secretion of prostaglandins E2 and F2α in bovine oviduct epithelial cells

This study aimed to investigate the effect of oestrogen on prostaglandin E2 (PGE₂) and prostaglandin F2α (PGF_2α) secretion in bovine oviduct epithelial cells. Bovine oviduct epithelial cells were obtained from the lumen of fresh bovine oviducts. Quantitative real-time polymerase chain reaction and in-cell western assays were used to measure PGE₂ and PGF_2α synthase activity and enzyme-linked immunosorbent assays were used to detect the concentrations of the two prostaglandins in extracellular fluid. We observed that oestradiol caused a short-term increase in cyclo-oxygenase-2 (COX-2), which stimulated PGE₂ and PGF_2α secretion, and that a subsequent decrease in COX-2 and an increase in cyclo-oxygenase-1 (COX-1) produced a high PGE₂:PGF_2α ratio. These findings reflect the dynamic change in PGE₂ and PGF_2α levels under the influence of oestrogen, which may be essential for fertilisation.

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.

In Vivo Imaging of the Mouse Reproductive Organs, Embryo Transfer, and Oviduct Cilia Dynamics Using Optical Coherence Tomography

The oviduct (or fallopian tube) serves as the site where a number of major reproductive events occur for the start of a new life in mammals. Understanding the oviduct physiology is essential to uncover hidden mechanisms of the human reproduction and its disorders, yet the current analysis of the oviduct that is largely limited to in vitro imaging is a significant technical hurdle. To overcome this barrier, we have recently developed in vivo approaches based on optical coherence tomography for structural and functional imaging of the mouse oviduct. In this chapter, we describe the details of such live imaging methods that allow for three-dimensional visualization of the oviduct wall morphology, microscale mapping of the oviduct cilia beat frequency, and high-resolution observation of the cumulus-oocyte complex at the cellular level. We expect this set of imaging tools will enable novel studies toward a comprehensive knowledge of the mammalian reproduction.

Emerging role of extracellular vesicles in communication of preimplantation embryos in vitro

In vitro, efficient communication between mammalian embryos in groups or between embryos and cocultured somatic cells implies that there is a sender, a message and a receiver that is able to decode the message. Embryos secrete a variety of autocrine and paracrine factors and, of these, extracellular vesicles have recently been implicated as putative messengers in embryo-embryo communication, as well as in communication of the embryo with the maternal tract. Extracellular vesicles (EVs) are membrane-bound vesicles that are found in biofluids and in culture media conditioned by the presence of embryos or cells. EVs carry and transfer regulatory molecules, such as microRNAs, mRNAs, lipids and proteins. We conducted a systematic search of the literature to review and present the currently available evidence regarding the possible roles of EVs in in vitro embryo communication and embryo development. It is important to note that there is limited information available on the molecular mechanisms and many of the biologically plausible functions of EVs in embryo communication have not yet been substantiated by conclusive experimental evidence. However, indirect evidence, such as the use of media conditioned by embryos or by somatic cells with improved embryo development as a result, may indicate that EVs can be an important asset for the development of tailor-made media, allowing better embryo development in vitro, even for single embryo culture.

Metabolite availability as a window to view the early embryo microenvironment in vivo

A preimplantation embryo exists independent of blood supply, and relies on energy sources from its in vivo environment (e.g., oviduct and uterine fluid) to sustain its development. The embryos can survive in this aqueous environment because it contains amino acids, proteins, lactate, pyruvate, oxygen, glucose, antioxidants, ions, growth factors, hormones, and phospholipids-albeit the concentration of each component varies by species, stage of the estrous cycle, and anatomical location. The dynamic nature of this environment sustains early development from the one-cell zygote to blastocyst, and is reciprocally influenced by the embryo at each embryonic stage. Focusing on embryo metabolism allowed us to identify how the local environment was deliberately selected to meet the dynamic needs of the preimplantation embryo, and helped reveal approaches to improve the in vitro culture of human embryos for improved implantation rates and pregnancy outcome.

Sex steroids modulate morphological and functional features of the bovine oviduct

In cattle, the oviduct plays a major role in the reproductive process; however, molecular control of oviduct receptivity to the embryo is poorly understood. A model for receptivity based on size of the pre-ovulatory follicle (POF) was used to compare oviductal morphology, cellular proliferation, and candidate transcript abundance. Growth of the POF of Nelore (Bos indicus) cows was manipulated to produce two groups: a large POF-large corpus luteum (CL) group (LF-LCL; greater receptivity) and a small POF-small CL group (SF-SCL). Samples of the ampulla and isthmus ipsilateral and contralateral to CL were collected 4 days after GnRH-induced ovulation. Tissues were either embedded in paraffin for Harris-Hematoxylin and Eosin and periodic acid-Schiff staining and KI67 immunostaining, followed by morphological analyses, or stored at -80 °C for RNA extraction, cDNA synthesis, and qPCR analyses. The effects of group (LF-LCL and SF-SCL), region (ampulla and isthmus), and side (ipsilateral and contralateral) were analyzed using three-way nested ANOVA. The ipsilateral ampulla of the LF-LCL group presented more primary mucosal folds, a greater mucosal-folding grade and luminal perimeter, and more secretory cells and proliferating cells when compared with the ampulla of the SF-SCL group and with the contralateral ampulla of both groups. There were no morphological differences in the isthmus between groups and sides. Changes in transcript abundance are suggestive of LF-LCL-stimulated secretory activity. In summary, ovulation of a larger POF generates a periovulatory endocrine milieu that modulates morphological and functional features of the bovine oviduct which may support embryo survival and development.

Suppressed expression of macrophage migration inhibitory factor in the oviducts of lean and obese cows

Oviducts synthesise macrophage migration inhibitory factor (MIF) to promote sperm capacitation and embryogenesis. This study aimed to test a hypothesis that the oviducts of obese cows may express MIF at a lower level than those of normal and lean cows. Ampullar and isthmic oviduct sections were collected from lean (n=5; body condition score (BCS) on a 5-point scale, 2.5), normal (n=6; BCS, 3.0) and obese (n=5; BCS, 4.0) Japanese Black cows. MIF mRNA and protein were extracted from ampullae and isthmuses and their levels measured by real-time polymerase chain reaction or western blot. Immunohistochemistry was performed on frozen sections of ampullae and isthmuses by using antibodies to MIF. MIF mRNA and protein expression were lower in the obese and lean groups than in the normal group (P<0.05). Immunohistochemistry revealed that the primary site of MIF expression in the ampulla and isthmus is the tunica mucosa. In conclusion, obese cows have suppressed MIF expression in the ampullae and isthmuses of their oviducts, as hypothesised, but, unexpectedly, MIF expression was also lower in lean cows.

Improved bovine embryo production in an oviduct-on-a-chip system: prevention of poly-spermic fertilization and parthenogenic activation

The oviduct provides the natural micro-environment for gamete interaction, fertilization and early embryo development in mammals, such as the cow. In conventional culture systems, bovine oviduct epithelial cells (BOEC) undergo a rapid loss of essential differentiated cell properties; we aimed to develop a more physiological in vitro oviduct culture system capable of supporting fertilization. U-shaped chambers were produced using stereo-lithography and mounted with polycarbonate membranes, which were used as culture inserts for primary BOECs. Cells were grown to confluence and cultured at an air-liquid interface for 4 to 6 weeks and subsequently either fixed for immune staining, incubated with sperm cells for live-cell imaging, or used in an oocyte penetration study. Confluent BOEC cultures maintained polarization and differentiation status for at least 6 weeks. When sperm and oocytes were introduced into the system, the BOECs supported oocyte penetration in the absence of artificial sperm capacitation factors while also preventing polyspermy and parthenogenic activation, both of which occur in classical in vitro fertilization systems. Moreover, this "oviduct-on-a-chip" allowed live imaging of sperm-oviduct epithelium binding and release. Taken together, we describe for the first time the use of 3D-printing as a step further on bio-mimicking the oviduct, with polarized and differentiated BOECs in a tubular shape that can be perfused or manipulated, which is suitable for live imaging and supports in vitro fertilization.

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.

Expression and localization of ARTEMIN in the bovine uterus and embryos

Artemin a member of the glial cell line-derived neurotrophic factor (GDNF) family is present in mice and human preimplantation embryos, and reproductive tract, during early pregnancy promoting embryo development in vitro. The presence of artemin in cattle embryos and reproductive tract, however, is unknown. In the present work we identified for first time artemin in bovine uterine fluid (UF) (Western blot), endometrium (RT-PCR, Western blot and immunohistochemistry) and embryos (RT-PCR and immunohistochemistry) during early preimplantation development. In addition, GFRalpha3, a component of the artemin receptor was localized in blastocysts produced in vitro. Individually developing embryos released ARTEMIN in culture medium and triggered ARTEMIN mRNA down-regulation in epithelial cells from endometrial cell cultures. Our results suggest that ARTEMIN derived from early embryos and maternal reproductive tract may exert important roles during early development in cattle.

Designing 3-Dimensional In Vitro Oviduct Culture Systems to Study Mammalian Fertilization and Embryo Production

The oviduct was long considered a largely passive conduit for gametes and embryos. However, an increasing number of studies into oviduct physiology have demonstrated that it specifically and significantly influences gamete interaction, fertilization and early embryo development. While oviduct epithelial cell (OEC) function has been examined during maintenance in conventional tissue culture dishes, cells seeded into these two-dimensional (2-D) conditions suffer a rapid loss of differentiated OEC characteristics, such as ciliation and secretory activity. Recently, three-dimensional (3-D) cell culture systems have been developed that make use of cell inserts to create basolateral and apical medium compartments with a confluent epithelial cell layer at the interface. Using such 3-D culture systems, OECs can be triggered to redevelop typical differentiated cell properties and levels of tissue organization can be developed that are not possible in a 2-D culture. 3-D culture systems can be further refined using new micro-engineering techniques (including microfluidics and 3-D printing) which can be used to produce ‘organs-on-chips’, i.e. live 3-D cultures that bio-mimic the oviduct. In this review, concepts for designing bio-mimic 3-D oviduct cultures are presented. The increased possibilities and concomitant challenges when trying to more closely investigate oviduct physiology, gamete activation, fertilization and embryo production are discussed.

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.

Ethanol impedes embryo transport and impairs oviduct epithelium

Most studies have demonstrated that alcohol consumption is associated with decreased fertility. The aim of this study was to investigate the effects of alcohol on pre-implantation embryo transport and/or early embryo development in the oviduct. We reported here that ethanol concentration-dependently suppressed the spontaneous motility of isolated human oviduct strips (EC50 50±6mM), which was largely attenuated in the present of L-NAME, a classical nitric oxide synthase(NOS) competitive inhibitor. Notably, either acute or chronic alcohol intake delayed egg transport and retarded early development of the embryo in the mouse oviduct, which was largely rescued by co-administration of L-NAME in a acute alcohol intake group but not in chronic alcohol intake group. It is worth mentioning that the oviductal epithelium destruction was verified by scanning electron microscope (SEM) observations in chronic alcohol intake group. In conclusion, alcohol intake delayed egg transport and retarded early development of the embryo in the oviduct by suppressing the spontaneous motility of oviduct and/or impairing oviductal epithelium. These findings suggested that alcohol abuse increases the incident of ectopic pregnancy.

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.