Oviductal motile cilia are essential for oocyte pickup but dispensable for sperm and embryo transport.

Mammalian oviducts play an essential role in female fertility by picking up ovulated oocytes and transporting and nurturing gametes (sperm/oocytes) and early embryos. However, the relative contributions to these functions from various cell types within the oviduct remain controversial. The oviduct in mice deficient in two microRNA (miRNA) clusters (miR-34b/c and miR-449) lacks cilia, thus allowing us to define the physiological role of oviductal motile cilia. Here, we report that the infundibulum without functional motile cilia failed to pick up the ovulated oocytes. In the absence of functional motile cilia, sperm could still reach the ampulla region, and early embryos managed to migrate to the uterus, but the efficiency was reduced. Further transcriptomic analyses revealed that the five messenger ribonucleic acids (mRNAs) encoded by miR-34b/c and miR-449 function to stabilize a large number of mRNAs involved in cilium organization and assembly and that Tubb4b was one of their target genes. Our data demonstrate that motile cilia in the infundibulum are essential for oocyte pickup and thus, female fertility, whereas motile cilia in other parts of the oviduct facilitate gamete and embryo transport but are not absolutely required for female fertility.

Dynamics of gametes and embryos in the oviduct: what can in vivo imaging reveal?

In brief: In vivo imaging of gametes and embryos in the oviduct enables new studies of the native processes that lead to fertilization and pregnancy. This review article discusses recent advancements in the in vivo imaging methods and insights which contribute to understanding the oviductal function. Abstract: Understanding the physiological dynamics of gametes and embryos in the fallopian tube (oviduct) has significant implications for managing reproductive disorders and improving assisted reproductive technologies. Recent advancements in imaging of the mouse oviduct in vivo uncovered fascinating dynamics of gametes and embryos in their native states. These new imaging approaches and observations are bringing exciting momentum to uncover the otherwise-hidden processes orchestrating fertilization and pregnancy. For mechanistic investigations, in vivo imaging in genetic mouse models enables dynamic phenotyping of gene functions in the reproductive process. Here, we review these imaging methods, discuss insights recently revealed by in vivo imaging, and comment on emerging directions, aiming to stimulate new in vivo studies of reproductive dynamics.

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.

Oviductal sperm storage in the Chinese pond turtle, Mauremys reevesii, depends on androgen-based promotion of the BCL 2 anti-apoptotic pathway.

CONTEXT: Sperm storage is a complex and highly coordinated process that is regulated by a variety of factors. The BCL 2 protein family plays a key role in regulating apoptosis, and determines sperm survival. AIMS: The objective of this study was to explore the correlation between sperm storage and the BCL 2 protein family in the oviduct of Mauremys reevesii . METHODS: Hematoxylin-eosin (HE) staining, immunohistochemistry (IHC) and real-time quantitative polymerase chain reaction (RT-qPCR) techniques were used to investigate three parts of the reproductive tract (isthmus, uterus and vagina) of mated and unmated female M. reevesii . KEY RESULTS: Hematoxylin-eosin staining revealed many sperm stored in the oviduct. IHC showed positive immunostaining for the BCL 2 and BAX proteins in epithelial ciliated and glandular cells. RT-qPCR indicated that the mRNA expressions of anti-apoptotic genes (BCL 2 , MCL 1 , BCL- W , BCL-XL ) and the androgen receptor (AR) were significantly higher in mated turtles than unmated turtles. However, the expression of pro-apoptotic genes (BAX , BAD , BID and CASPASE 3 ) showed the opposite relationship. CONCLUSIONS: These results suggest that sperm entering the oviduct can promote the synthesis of anti-apoptotic genes to protect themselves from various degradation factors. IMPLICATIONS: These findings will help researchers understand the mechanisms of sperm storage.

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.

Cell-type specific analysis of physiological action of estrogen in mouse oviducts.

One of the endogenous estrogens, 17ß-estradiol (E2 ) is a female steroid hormone secreted from the ovary. It is well established that E2 causes biochemical and histological changes in the uterus. However, it is not completely understood how E2 regulates the oviductal environment in vivo. In this study, we assessed the effect of E2 on each oviductal cell type, using an ovariectomized-hormone-replacement mouse model, single-cell RNA-sequencing (scRNA-seq), in situ hybridization, and cell-type-specific deletion in mice. We found that each cell type in the oviduct responded to E2 distinctively, especially ciliated and secretory epithelial cells. The treatment of exogenous E2 did not drastically alter the transcriptomic profile from that of endogenous E2 produced during estrus. Moreover, we have identified and validated genes of interest in our datasets that may be used as cell- and region-specific markers in the oviduct. Insulin-like growth factor 1 (Igf1) was characterized as an E2 -target gene in the mouse oviduct and was also expressed in human fallopian tubes. Deletion of Igf1 in progesterone receptor (Pgr)-expressing cells resulted in female subfertility, partially due to an embryo developmental defect and embryo retention within the oviduct. In summary, we have shown that oviductal cell types, including epithelial, stromal, and muscle cells, are differentially regulated by E2 and support gene expression changes, such as growth factors that are required for normal embryo development and transport in mouse models. Furthermore, we have identified cell-specific and region-specific gene markers for targeted studies and functional analysis in vivo.

Histology, ultrastructure, and differential gene expression in relation to seasonal sperm storage in the oviduct of the Chinese alligator, Alligator sinensis.

Although oviductal sperm storage are essential steps in reproduction for female animals with internal fertilisation, no systematic study on the identification of genes involving sperm storage has been performed in crocodilian species. In the present research, the relationship between morphological variation related to sperm storage in the oviduct and gene expression patterns derived from RNA sequencing analyses between active period (AP), breeding period (BP), and hibernation period (HP) were investigated. The corresponding results indicated that sperm were observed not only in the ciliated cells within infundibulum and mucosal layer of uterus during BP, but also been detected in the spermatosperm storage tube (SST) in the anterior uterus at HP stage. The further transmission electron microscopy analysis indicated that the differences in the number and activity of the secretory cells likely to attributed to the seasonal variation of microenvironment related to the sperm storage. Based on the RNA-sequecing, 13147 DEGs related to the Peroxisome proliferator-activated receptors (PPARs) and FOXO signalling were identified, including these, the down-regulated ATG12 and BCL2L11 in the HP group may thus constitute an important point of convergence between autophagy and apoptosis involving the FOXO1 pathway. The genes involved in the PPARs pathway might modulate the immune response and thereby contribute to prolong the life span of stored spermatozoa in Alligator sinensis . The outcomes of this study provide fundamental insights into the mechanism of sperm storage in A. sinensis .

Sperm migration, selection, survival, and fertilizing ability in the mammalian oviduct†.

In vitro fertilization (IVF) gives rise to embryos in a number of mammalian species and is currently widely used for assisted reproduction in humans and for genetic purposes in cattle. However, the rate of polyspermy is generally higher in vitro than in vivo and IVF remains ineffective in some domestic species like pigs and horses, highlighting the importance of the female reproductive tract for gamete quality and fertilization. In this review, the way the female environment modulates sperm selective migration, survival, and acquisition of fertilizing ability in the oviduct is being considered under six aspects: (1) the utero-tubal junction that selects a sperm sub-population entering the oviduct; (2) the presence of sperm binding sites on luminal epithelial cells in the oviduct, which prolong sperm viability and plays a role in limiting polyspermic fertilization; (3) the contractions of the oviduct, which promote sperm migration toward the site of fertilization in the ampulla; (4) the regions of the oviduct, which play different roles in regulating sperm physiology and interactions with oviduct epithelial cells; (5) the time of ovulation, and (6) the steroid hormonal environment which regulates sperm release from the luminal epithelial cells and facilitates capacitation in a finely orchestrated manner.

Progesterone induces porcine sperm release from oviduct glycans in a proteasome-dependent manner.

In mammals, the oviduct retains sperm, forming a reservoir from which they are released in synchrony with ovulation. However, the mechanisms underlying sperm release are unclear. Herein, we first examined in greater detail the release of sperm from the oviduct reservoir by sex steroids, and secondly, if the ubiquitin-proteasome system (UPS) mediates this release in vitro. Sperm were allowed to bind to oviductal cells or immobilized oviduct glycans, either bi-SiaLN or a suLeX, and channeled with steroids in the presence or absence of proteasome inhibitors. Previously, we have demonstrated progesterone-induced sperm release from oviduct cells and immobilized glycans in a steroid-specific manner. Herein, we found that the release of sperm from an immobilized oviduct glycan, a six-sialylated branched structure, and from immobilized fibronectin was inhibited by the CatSper blocker NNC 055-0396, akin to the previously reported ability of NNC 055-0396 to inhibit sperm release from another oviduct glycan, sulfated Lewis-X trisaccharide. Thus, CatSper may be required for release of sperm from a variety of adhesion systems. One possible mechanism for sperm release is that glycan receptors on sperm are degraded by proteasomes or shed from the sperm surface by proteasomal degradation. Accordingly, the inhibition of proteasomal degradation blocked sperm release from oviduct cell aggregates both immobilized oviduct glycans as well as fibronectin. In summary, progesterone-induced sperm release requires both active CatSper channels and proteasomal degradation, suggesting that hyperactivation and proteolysis are vital parts of the mechanism by which sperm move from the oviduct reservoir to the site of fertilization.

Possibility of Undeveloped Egg Absorption during Embryogenesis: A Unique Phenomenon Observed in the Ovoviviparous Mayfly Cloeon dipterum.

Oviparous, ovoviviparous and viviparous reproduction are interesting subjects for understanding animals' evolutionary pathways and adaptation to their life history and habitat conditions. In this study, we examined the reproductive mode of the ovoviviparous mayfly Cloeon dipterum, particularly comparing embryogenesis between hand-pairing and unmated females' common oviduct. Our study suggested that the high developmental rate of C. dipterum observed in a recent study could be ascribed to their absorption of unfertilized eggs. The developmental rates of hand-paired females were almost 100%, while their egg-bearing numbers were lower than those of virgin females. Thus, such reduced egg numbers suggest the maternal absorption of unfertilized eggs. This trait is thought to have evolved with the ovoviviparous characteristics of C. dipterum. We identified the basis of the irregularity of this species exhibiting such a high (i.e., 100%) developmental rate in our previous recent study.

Mimicking the temperature gradient between the sow's oviduct and uterus improves in vitro embryo culture output.

This work was designed to determine temperature conditions within the reproductive tract of the female pig and study their impact on ARTs. Temperatures were recorded using a laparo-endoscopic single-site surgery assisted approach and a miniaturized probe. Sows and gilts were used to address natural cycle and ovarian stimulation treatments, respectively. According to in vivo values, IVF was performed at three temperature conditions (37.0°C, 38.5°C and 39.5°C) and presumptive zygotes were cultured in these conditions for 20 h, while further embryo culture (EC) (21-168 h post-insemination) was maintained at 38.5°C. After 20 h, different fertility parameters were assessed. During EC, cleavage and blastocyst stages were evaluated. Sperm membrane fluidity at the experimental temperatures was studied by using differential scanning calorimetry and fluorescence recovery after photobleaching techniques. An increasing temperature gradient of 1.5°C was found between the oviduct and uterus of sows (P < 0.05) and when this gradient was transferred to pig in vitro culture, the number of poly-nuclear zygotes after IVF was reduced and the percentage of blastocysts was increased. Moreover, the temperature transition phase for the boar sperm membrane (37.0°C) coincided with the temperature registered in the sow oviduct, and sperm membranes were more fluid at 37.0°C compared with those of sperm incubated at higher temperatures (38.5°C and 39.5°C). These data suggest that there may be an impact of physiological temperature gradients on human embryo development.

Canine oviductal exosomes improve oocyte development via EGFR/MAPK signaling pathway.

Oviduct cells produce a favorable environment for the development of gametes by generating multiple growth factors. Particularly, in canine species, immature oocytes undergo serial maturation processes in the oviduct, while the other mammals already possess matured oocytes in ovulatory follicles. However, little is known about the potential effect exhibited by the components released from canine oviduct cells (OCs) for modulating the biological function of oocytes. Recently, exosomes are regarded as promising extracellular vesicles because they represent considerable data for molecular cargo. Therefore, we first investigated the effect of canine oviductal exosomes (OC-Exo) on oocyte development via EGFR/MAPK pathway. Our results showed that OC-Exo labeled with PHK67 are successfully incorporated with cumulus cells and oocytes during IVM. Also, OC-Exo markedly increased the proportion of cumulus-oocyte complexes (COCs) exhibiting cumulus expansion as well as cumulus cell proliferation and maturation rate of oocytes (P < 0.05). Furthermore, gene expression patterns related with EGFR/MAPK pathway including EGFR, PKA, TACE/ADAM17, MAPK1/3, MAPK14, PTGS2, TNFAIP6, GDF9, and BMP15 were positively modified in COCs cultured with OC-Exo (P < 0.05). In addition, OC-Exo significantly up-regulated the protein expression levels of p-EGFR, p-MAPK1/3, GDF9 and BMP15 in COCs (P < 0.05). Consequently, the current study provides a model for understanding the roles of OC-Exo as bioactive molecules for canine oocyte maturation via EGFR/MAPK pathway, which would open a new avenue for the application of exosomes to improve assisted reproductive technology in mammals, including humans.

YAP and TAZ are required for the postnatal development and the maintenance of the structural integrity of the oviduct.

The development of the Müllerian ducts into the female reproductive tract requires the coordination of multiple signaling pathways that regulate proliferation, apoptosis and differentiation. The Hippo pathway has been reported to interact with several pathways with established roles in Müllerian duct development; yet, its potential roles in reproductive tract development and function remain mostly uncharacterized. The objective of this study was therefore to characterize the roles of the Hippo transcriptional coactivators YAP and TAZ in the female reproductive tract using transgenic mouse models. This report shows that the concomitant conditional inactivation of Yap and Taz in the mouse Müllerian duct mesenchyme results in postnatal developmental defects of the oviduct. Most notably, discontinuities in the myosalpinx layer lead to the progressive formation of cystic dilations of the isthmus. These defects prevented embryo transport and subsequent implantation in older animals, causing infertility. The loss of YAP/TAZ did not appear to affect other biological processes known to be required for the maintenance of oviductal wall integrity, such as TGF-ß/SMAD and Notch signaling and the biogenesis of miRNA, suggesting that the Hippo pathway acts independently of these processes to direct oviduct development. Taken together, these results suggest redundant and essential roles for YAP and TAZ in the postnatal development of the oviduct and the maintenance of its structural integrity.

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.

Analysis of ciliogenesis process in the bovine oviduct based on immunohistochemical classification.

The oviductal epithelium is composed of ciliated and non-ciliated cells. The proportions of these cells change during the estrous cycle. However, the mechanism underlying this cyclic change in the cell proportions remains unclear. Our previous study indicated that ciliated cells are derived from non-ciliated cells. Here, we aimed to investigate the mechanism regulating the changes in the populations of ciliated and non-ciliated cells during the estrous cycle. To this end, we examined the numbers of cells that were positive for acetylated-α-tubulin (cilia marker), Ki67 (proliferation marker), PAX8 (non-ciliated cell marker), and FOXJ1 and MYB (ciliogenesis markers) in the epithelial cells at four different estrous stages (Stage I: days 1-4 after ovulation, Stage II: days 5-10, Stage III: days 11-17, and Stage IV: days 18-20) by immunohistochemistry. The oviductal epithelial cells expressed either FOXJ1 or PAX8. All the acetylated-α-tubulin+ cells were positive for FOXJ1, although there were a few acetylated-α-tubulin-/FOXJ1+ cells. MYB was expressed in both the FOXJ1+ and PAX8+ cells, but it was not expressed in the Ki67+ cells. The numbers of Ki67+ and MYB+ cells were the highest in Stage IV, while the numbers of FOXJ1+ and acetylated-α-tubulin+ cells were the highest in the following Stage I, suggesting that ciliogenesis is associated with the estrous cycle. Thus, based on immunological classification, the oviductal epithelium contains at least seven types of cells at different translational/transcriptional states, and their number is regulated by the estrous cycle. This cyclic event might provide an optimal environment for gamete transport, fertilization, and embryonic development.

Asynchrony between the early embryo and the reproductive tract affects subsequent embryo development in cattle.

The aim of this study was to determine the effect of maternal-embryonic asynchrony in the reproductive tract (oviduct and uterus) on subsequent embryo development in cattle. Fifty Day 1invitro-produced zygotes were transferred endoscopically into the oviduct ipsilateral to the corpus luteum of heifers (n=40) that were either synchronous with the embryos (Day 1 after ovulation) or asynchronous and ahead of the embryo (Day 3 after ovulation). A subset of heifers was killed in a commercial abattoir 3, 6 or 14 days after embryo transfer. Location within the reproductive tract, developmental stage and the quality of embryos were recorded. Transfer of embryos to an advanced (asynchronous) oviduct resulted, on Day 4, in fewer embryos at the expected location (oviduct), and a greater number of degenerated and retarded embryos with a lower total cell number than for embryos in the synchronous group. Similarly, on Day 7, asynchrony led to a greater number of degenerated and retarded embryos compared with the synchronous group. Total embryo cell number was similar among groups. Although Day 15 conceptuses were longer following asynchronous transfer, only 50% of the asynchronous heifers yielded conceptuses, compared with 100% in the synchronous group. In conclusion, asynchrony between the developing embryo and the reproductive tract has a negative effect on embryo development.

Oviduct fluid extracellular vesicles regulate polyspermy during porcine in vitro fertilisation.

High polyspermy is one of the major limitations of porcine invitro fertilisation (IVF). The addition of oviductal fluid (OF) during IVF reduces polyspermy without decreasing the fertilisation rate. Because extracellular vesicles (EVs) have been described as important OF components, the aim of this study was to evaluate the effect of porcine oviductal EVs (poEVs) on IVF efficiency compared with porcine OF (fresh and lyophilised). OF was collected from abattoir oviducts by phosphate-buffered saline flush, and poEVs were isolated by serial ultracentrifugation. Four IVF treatments were conducted: poEVs (0.2mgmL-1), OF (10%), lyophilized and reconstituted pure OF (LOF; 1%) and IVF without supplementation (control). Penetration, monospermy and IVF efficiency were evaluated. Transmission electron microscopy showed an EVs population primarily composed of exosomes (83%; 30-150nm). Supplementation with poEVs during IVF increased monospermy compared with control (44% vs 17%) while maintaining an acceptable penetration rate (61% vs 78% respectively) in a similar way to OF and LOF. Western blotting revealed poEVs proteins involved in early reproductive events, including zona pellucida hardening. In conclusion, our finding show that poEVs are key components of porcine OF and may play roles in porcine fertilisation and polyspermy regulation, suggesting that supplementation with poEVs is a reliable strategy to decrease porcine polyspermy and improve invitro embryo production outcomes.

Spermatozoa produced during winter are superior in terms of phenotypic characteristics and oviduct explants binding ability in the water buffalo (Bubalus bubalis).

Although reduced reproductive efficiency during summer has been well documented in buffaloes, the reason for the same is yet to be understood. The present study was conducted to identify the subtle differences in sperm phenotypic characteristics (motility, membrane integrity, acrosome reaction and lipid peroxidation status), oviduct binding ability and expression of fertility-associated genes (AK 1, ATP5D, CatSper 1, Cytochrome P450 aromatase, SPP1 and PEBP1) between winter and summer seasons in buffaloes. Cryopreserved spermatozoa from 6 Murrah buffalo bulls (3 ejaculates/bull/season) were utilized for the study. Real-time quantitative PCR was performed for assessing the expression patterns of select fertility-associated genes. The proportion of motile and membrane intact spermatozoa was significantly higher (p < .05) in winter as compared to summer ejaculates. The proportion of moribund and lipid peroxidized spermatozoa was significantly lower (p < .05) in winter ejaculates as compared to summer. The sperm-oviduct binding index was significantly lower (p < .01) when spermatozoa from summer ejaculates were used as compared to winter ejaculates. The expression of fertility-associated genes did not differ significantly between the two seasons except for PEPB1; the transcriptional abundance of PEPB1 was significantly (p < .05) lower in summer as compared to winter season. It was inferred that buffalo spermatozoa produced during winter season were superior in terms of cryotolerance, membrane and acrosome integrity, lipid peroxidation status and the ability to bind with oviduct explants.

Embryo-Maternal Interactions Underlying Reproduction in Mammals.

This Special Issue, "Embryo-Maternal Interactions Underlying Reproduction in Mammals", gathers a collection of 23 articles, 16 original research articles and 7 up-to-date reviews, providing new findings or summarizing current knowledge on embryo-maternal interactions in seven different mammalian species including humans. Considering the different players involved in these embryo-maternal interactions, articles are mainly focused on one of these different players: the oviduct, the uterus, the embryo or the emergent extracellular vesicles. Additionally, a few articles bring up the impact of reproductive, but also non-reproductive, diseases, as well as stress factors, on the establishment of pregnancy. We hope the readers enjoy this collection of articles and that the knowledge assembled here will support and inspire current and future research investigations. We would like to thank all authors for their contributions to this Special Issue.

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.