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The oviduct provides optimum physiological and biochemical milieu essential for successful fertilization, early embryo development and facilitates functional maturation of spermatozoa. A study has revealed that spermatozoa alters the gene expression in bovine oviductal epithelial cells (BOECs) remotely via bio-active particles, thus acting as a cue to the oviduct prior to their arrival. However, very little attention has been paid to the question of whether spermatozoa could alter the cargo of extracellular vesicles (EVs) derived from BOECs. Therefore, the aim of this study was to investigate the alterations in small non-coding RNAs in EVs cargo derived from BOECs when incubated with spermatozoa in contact and non-contact co-culture models. After 4 h of incubation the EVs were isolated from the conditioned media, followed by small non-coding sequencing of the BOEC derived EVs. Our results revealed that EVs from both co-culture models contained distinct cargo in form of miRNA, fragmented mRNA versus control. The pathway enrichment analysis revealed that EV miRNA from direct co-culture were involved in the biological processes associated with phagocytosis, macroautophagy, placenta development, cellular responses to TNF and FGF. The mRNA fragments also varied within the different groups and mapped to the exonic regions of the transcriptome providing vital insights regarding the changes in cellular transcriptome on the arrival of spermatozoa. The findings of this study suggest that spermatozoa, in contact as well as remotely, alter the EV cargo of female reproductive tract epithelial cells which might be playing an essential role in pre and post-fertilization events. Graphical abstract

Simple Summary Before the union of an egg and spermatozoon, several vital processes occur for fertilization in the female reproductive system. One of these processes is the maturation of spermatozoa which occurs in the female reproductive tract. Spermatozoa not undergoing maturation in the female reproductive tract are unable to penetrate the egg. Many reports have suggested the involvement of different factors in mediating the functional maturation of spermatozoa. Follicular fluid (FF) is named as one of those factors. FF is an ovarian fluid that plays an essential role in egg maturation and sources extracellular vesicles (EVs). EVs are nano-containers that are released from different cells and are present in all body fluids. Several studies have reported that FF supports the functional maturation of spermatozoa. Therefore, we hypothesized that FF EVs might have a role in inducing functional maturation in spermatozoa. Surprisingly, the FF-derived EVs were able to aid vital functional parameters of spermatozoa and the effects from EVs were species- and source-specific. Therefore, deciphering the cargo of FF EVs responsible for modulating spermatozoa’s functions can potentially prove beneficial in diagnosing and treating male infertility and improving the current assisted reproductive technology protocols. Abstract While follicular fluid (FF) is known to enhance the functional properties of spermatozoa, the role of FF-derived extracellular vesicles (EVs) in this respect is unknown. We hypothesized that bovine FF EVs convey signals to spermatozoa supporting sperm viability, inducing sperm capacitation and acrosome reaction. In this study, the effects of bovine FF EVs on sperm functions are evaluated. Irrespective of the size of the follicles which FF EVs had originated from, they were capable of supporting sperm viability, inducing capacitation and acrosome reaction. These effects were specific to the source of bovine FF EVs, as human-cell-line-derived or porcine FF EVs did not affect spermatozoa viability or induced capacitation and acrosome reaction. A minimum of 5 × 105 EVs/mL was adequate to maintain sperm viability and induce capacitation and acrosome reaction in spermatozoa. Interestingly, with FF EV trypsin treatment, FF EVs lost their ability to support sperm functions. In conclusion, this study demonstrates that bovine FF EVs can support spermatozoa function and may contribute to a favorable periconceptional microenvironment. This is an important aspect of the interactions between different sexes at the earliest stages of reproduction and helps to understand molecular mechanisms modulating processes such as sperm competition and female cryptic choice.

The capability of spermatozoa to directly influence maternal gene expression is already established. Indeed, some of the changes induced by spermatozoa may have a direct functional importance in the pre-conceptional period. Although the mechanisms underlying these sperm-maternal interactions are not well characterized, it is possible that they could involve ligands that are released from the spermatozoa. This study therefore aimed to test whether physical contact between bovine spermatozoa and bovine oviductal epithelial cells (BOECs) is a prerequisite for spermatozoa-induced gene expression changes. We used two co-culture models: a contact co-culture model in which spermatozoa interact directly with BOECs, and a non-contact co-culture model in which an insert with the pore size of 0.4 μm was placed between spermatozoa and BOECs. Messenger RNA sequencing analysis of BOECs by RNA-seq revealed ten differentially expressed genes in contact system and 108 differentially expressed genes in the non-contact system after 10 h of co-culture. Retinol metabolism pathway and ovarian steroidogenesis pathway were significantly enriched in the non-contact co-culture system. Q-PCR analysis revealed that transcriptional responses can be rapid, with increased expression of four genes (DHRS3, CYP1B1, PTGS2, and ATF3) detectable within just 90 min of co-incubation, but with expression levels highly dependent on the type of co-culture system. The findings from our study demonstrate that direct contact with spermatozoa is not necessary to induce changes in gene expression of oviductal epithelial cells, suggesting that spermatozoa may be able to signal to maternal tissues in advance of their arrival. Electronic supplementary material The online version of this article (10.1007/s12079-020-00575-2) contains supplementary material, which is available to authorized users.

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.

While follicular fluid (FF) is well known to provide an optimal environment for oogenesis, its functional roles following its release into the oviduct during ovulation are currently elusive. We hypothesized that FF and FF-derived extracellular vesicles (EVs) may be conveyors of signals capable of inducing functionally-relevant transcriptional responses in oviductal cells. The aim of this study was, therefore, to evaluate the effect of FF and FF-derived EVs on the transcriptome of primary bovine oviductal epithelial cells (BOECs). We examined the gene expression of BOECs in three conditions: BOECs cultured with FF, FF-derived EVs, and without supplementations. For each condition, cells were cultured for 6 and 24 h. RNA sequencing results revealed that FF had a stronger effect on BOECs gene expression compared to EVs. We detected 488 and 1998 differentially expressed genes (DEGs) with FF treatment in 6 and 24 h, respectively, whereas only 41 DEGs were detected at 6 h following EV treatment. Pathway analysis of the FF-induced DEGs showed that several pathways were highly enriched, notably oxidative phosphorylation, thermogenesis, arachidonic acid metabolism, and steroid hormone biosynthesis. Some of these pathways have a role in sperm survival, fertilization, and early embryo development. In conclusion, the findings of our study demonstrate for the first time that bovine FF and FF-derived EVs can induce changes in the gene expression of the bovine oviductal cells which, although observed in vitro, may be reflective of in vivo responses which may contribute to a favorable periconceptional microenvironment for sperm survival, fertilization, and early embryo development.