Extracellular vesicles-coupled miRNAs from oviduct and uterus modulate signaling pathways related to lipid metabolism and bovine early embryo development

BACKGROUND

Extracellular vesicles (EVs) present in oviductal (OF) and uterine fluid (UF) have been shown to enhance bovine embryo quality during in vitro culture by reducing lipid contents and modulating lipid metabolism-related genes (LMGs), while also influencing cell proliferation, suggesting their involvement on the regulation of different biological pathways. The regulation of signaling pathways related to cell differentiation, proliferation, and metabolism is crucial for early embryo development and can determine the success or failure of the pregnancy. Bioactive molecules within EVs in maternal reproductive fluids, such as microRNAs (miRNAs), may contribute to this regulatory process as they modulate gene expression through post-transcriptional mechanisms.

RESULTS

From the 20 differentially expressed miRNAs, 19 up-regulated in UF-EVs (bta-miR-134, bta-miR-151-3p, bta-miR-155, bta-miR-188, bta-miR-181b, bta-miR-181d, bta-miR-224, bta-miR-23b-3p, bta-miR-24-3p, bta-miR-27a-3p, bta-miR-29a, bta-miR-324, bta-miR-326, bta-miR-345-3p, bta-miR-410, bta-miR-652, bta-miR-677, bta-miR-873 and bta-miR-708) and one (bta-miR-148b) in OF-EVs. These miRNAs were predicted to modulate several pathways such as Wnt, Hippo, MAPK, and lipid metabolism and degradation. Differences in miRNAs found in OF-EVs from the early luteal phase and UF-EVs from mid-luteal phase may reflect different environments to meet the changing needs of the embryo. Additionally, miRNAs may be involved, particularly in the uterus, in the regulation of embryo lipid metabolism, immune system, and implantation. This study evaluated miRNA cargo in OF-EVs from the early luteal phase and UF-EVs from the mid-luteal phase, coinciding with embryo transit within oviduct and uterus in vivo, and its possible influence on LMGs and signaling pathways crucial for early embryo development. A total of 333 miRNAs were detected, with 11 exclusive to OF, 59 to UF, and 263 were common between both groups.

CONCLUSIONS

Our study suggests that miRNAs within OF- and UF-EVs could modulate bovine embryo development and quality, providing insights into the intricate maternal-embryonic communication that might be involved in modulating lipid metabolism, immune response, and implantation during early pregnancy.

Extracellular vesicles from oviductal and uterine fluids supplementation in sequential in vitro culture improves bovine embryo quality

Background

In vitro production of bovine embryos is a well-established technology, but the in vitro culture (IVC) system still warrants improvements, especially regarding embryo quality. This study aimed to evaluate the effect of extracellular vesicles (EVs) isolated from oviductal (OF) and uterine fluid (UF) in sequential IVC on the development and quality of bovine embryos. Zygotes were cultured in SOF supplemented with either BSA or EVs-depleted fetal calf serum (dFCS) in the presence (BSA-EV and dFCS-EV) or absence of EVs from OF (D1 to D4) and UF (D5 to D8), mimicking in vivo conditions. EVs from oviducts (early luteal phase) and uterine horns (mid-luteal phase) from slaughtered heifers were isolated by size exclusion chromatography. Blastocyst rate was recorded on days 7–8 and their quality was assessed based on lipid contents, mitochondrial activity and total cell numbers, as well as survival rate after vitrification. Relative mRNA abundance for lipid metabolism-related transcripts and levels of phosphorylated hormone-sensitive lipase (pHSL) proteins were also determined. Additionally, the expression levels of 383 miRNA in OF- and UF-EVs were assessed by qRT-PCR.

Results

Blastocyst yield was lower (P < 0.05) in BSA treatments compared with dFCS treatments. Survival rates after vitrification/warming were improved in dFCS-EVs (P < 0.05). EVs increased (P < 0.05) blastocysts total cell number in dFCS-EV and BSA-EV compared with respective controls (dFCS and BSA), while lipid content was decreased in dFCS-EV (P < 0.05) and mitochondrial activity did not change (P > 0.05). Lipid metabolism transcripts were affected by EVs and showed interaction with type of protein source in medium (PPARGC1B, LDLR, CD36, FASN and PNPLA2, P < 0.05). Levels of pHSL were lower in dFCS (P < 0.05). Twenty miRNA were differentially expressed between OF- and UF-EVs and only bta-miR-148b was increased in OF-EVs (P < 0.05).

Conclusions

Mimicking physiological conditions using EVs from OF and UF in sequential IVC does not affect embryo development but improves blastocyst quality regarding survival rate after vitrification/warming, total cell number, lipid content, and relative changes in expression of lipid metabolism transcripts and lipase activation. Finally, EVs miRNA contents may contribute to the observed effects.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00763-7.

Uterine extracellular vesicles as multi-signal messengers during maternal recognition of pregnancy in the mare

In contrast to other domestic mammals, the embryo-derived signal(s) leading to maternal recognition of pregnancy (MRP) are still unknow in the mare. We hypothesize that these embryonic signals could be packed into uterine extracellular vesicles (uEVs), acting as multi-signal messengers between the conceptus and the maternal tract, and contributing to MRP. To unveil these signals, the RNA and protein cargos of uEVs isolated from uterine lavages collected from pregnant mares (P; day 10, 11, 12 and 13 after ovulation) and cyclic control mares (C; day 10 and 13 after ovulation) were analyzed. Our results showed a fine-tuned regulation of the uEV cargo (RNAs and proteins), by the day of pregnancy, the estrous cycle, and even the size of the embryo. A particular RNA pattern was identified with specific increase on P12 related to immune system and hormonal response. Besides, a set of proteins as well as RNAs was highly enriched in EVs on P12 and P13. Differential abundance of miRNAs was also identified in P13-derived uEVs. Their target genes were linked to down- or upregulated genes in the embryo and the endometrium, exposing their potential origin. Our study identified for first time specific molecules packed in uEVs, which were previously associated to MRP in the mare, and thus bringing added value to the current knowledge. Further integrative and functional analyses will help to confirm the role of these molecules in uEVs during MRP in the mare.

Characterization and profiling analysis of bovine oviduct and uterine extracellular vesicles and their miRNA cargo through the estrous cycle

Extracellular vesicles (EVs) found in various biological fluids and particularly in reproductive fluids, have gained considerable attention for their possible role in cell- to- cell communication. Among, the different bioactive molecules cargos of EVs, MicroRNAs (miRNAs) are emerging as promising diagnostic biomarkers with high clinical potential. Aiming to understand the roles of EVs in bovine reproductive tract, we intended to characterize and profile the EVs of oviduct and uterine fluids (OF-EVs, UF-EVs) and their miRNA across the estrous cycle. Nanoparticle tracking analysis and transmission electron microscopy confirmed the existence of small EV population in OF and UF at all stages, (size between 30 and 200 nm; concentration: 3.4 × 10¹⁰  EVs/ml and 6.0 × 10¹⁰  EVs/ml for OF and UF, respectively, regardless of stage). The identification of EV markers (CD9, HSP70, and ALIX proteins) was confirmed by western blot. The miRNA analysis revealed the abundance of 310 and 351 miRNAs in OF-EVs and UF-EVs, respectively. Nine miRNAs were differentially abundant in OF-EVs between stages of the cycle, eight of them displayed a progressive increase from S1 to S4 (p < .05). In UF-EVs, a total of 14 miRNAs were differentially abundant between stages. Greater differences were observed between stage 1 (S1) and stage 3 (S3), with 11 miRNAs enriched in S3 compared to S1. Functional enrichment analysis revealed the involvement of these miRNAs in relevant pathways such as cell signaling, intercellular junctions, and reproductive functions that may be implicated in oviduct and uterus modulation across the cycle, but also in their preparation for embryo/conceptus presence and development.

Breast Implant-Associated Anaplastic Large Cell Lymphoma (BIA-ALCL): Review of Epidemiology and Prevalence Assessment in Europe

BACKGROUND

Breast implant-associated anaplastic large cell lymphoma (BIA-ALCL) epidemiologic studies focus on incidence and risk estimates.

OBJECTIVES

The aim of this study was to perform a thorough literature review, and to provide an accurate estimate of BIA-ALCL prevalence in Europe.

METHODS

We searched PubMed, Web of Science, SCOPUS, and Google Scholar databases to identify publications reporting BIA-ALCL epidemiology. Research was conducted between November 2019 and August 2020. European prevalence was assessed as the ratio between pathology-confirmed cases and breast implant-bearing individuals. The Committee on Device Safety and Development (CDSD) collected data from national plastic surgery societies, health authorities, and disease-specific registries to calculate the numerator. The denominator was estimated by combining European demographic data with scientific reports.

RESULTS

Our research identified 507 articles: 106 were excluded for not being relevant to BIA-ALCL. From the remaining 401 articles, we selected 35 that discussed epidemiology and 12 reviews. The CDSD reported 420 cases in Europe, with an overall prevalence of 1:13,745 cases in the 28 member states of the European Union (EU-28). Countries where specific measures have been implemented to tackle BIA-ALCL account for 61% of the EU-28 population and actively reported 382 cases with an overall prevalence of 1:9121.

CONCLUSION

Countries where specific measures have been implemented show a higher prevalence of BIA-ALCL compared with the European mean, suggesting that these countries have improved the detection of the condition and reduced underreporting, which affects the numerator value. Other nations should adopt projections based on these measures to avoid underestimating how widespread BIA-ALCL is.

LEVEL OF EVIDENCE: 4

Culture Medium and Sex Drive Epigenetic Reprogramming in Preimplantation Bovine Embryos

Assisted reproductive technologies impact transcriptome and epigenome of embryos and can result in long-term phenotypic consequences. Whole-genome DNA methylation profiles from individual bovine blastocysts in vivo- and in vitro-derived (using three sources of protein: reproductive fluids, blood serum and bovine serum albumin) were generated. The impact of in vitro culture on DNA methylation was analyzed, and sex-specific methylation differences at blastocyst stage were uncovered. In vivo embryos showed the highest levels of methylation (29.5%), close to those produced in vitro with serum, whilst embryos produced in vitro with reproductive fluids or albumin showed less global methylation (25-25.4%). During repetitive element analysis, the serum group was the most affected. DNA methylation differences between in vivo and in vitro groups were more frequent in the first intron than in CpGi in promoters. Moreover, hierarchical cluster analysis showed that sex produced a stronger bias in the results than embryo origin. For each group, distance between male and female embryos varied, with in vivo blastocyst showing a lesser distance. Between the sexually dimorphic methylated tiles, which were biased to X-chromosome, critical factors for reproduction, developmental process, cell proliferation and DNA methylation machinery were included. These results support the idea that blastocysts show sexually-dimorphic DNA methylation patterns, and the known picture about the blastocyst methylome should be reconsidered.

Sire contribution to fertilization failure and early embryo survival in cattle

Despite passing routine laboratory tests of semen quality, bulls used in artificial insemination (AI) exhibit a significant range in field fertility. The objective of this study was to determine whether subfertility in AI bulls is due to issues of sperm transport to the site of fertilization, fertilization failure, or failure of early embryo or conceptus development. In experiment 1, Holstein-Friesian bulls (3 high fertility, HF, and 3 low fertility, LF) were selected from the national population of AI bulls based on adjusted fertility scores from a minimum of 500 inseminations (HF: +4.37% and LF: -12.7%; mean = 0%). Superovulated beef heifers were blocked based on estimated number of follicles at the time of AI and inseminated with semen from HF or LF bulls (n = 3-4 heifers per bull; total 19 heifers). Following slaughter 7 d later, the number of corpora lutea was counted and the uteri were flushed. Recovered structures (oocytes/embryos) were classified according to developmental stage and stained with 4',6-diamidino-2-phenylindole to assess number of cells and accessory sperm. Overall recovery rate (total structures recovered/total corpora lutea) was 52.6% and was not different between groups. Mean (± standard error of the mean) number of embryos recovered per recipient was 8.7 ± 5.2 and 9.4 ± 5.5 for HF and LF, respectively. Overall fertilization rate of recovered structures was not different between groups. However, more embryos were at advanced stages of development (all blastocyst stages combined), reflected in a greater mean embryo cell number on d 7 for HF versus LF bulls. Number of accessory sperm was greater for embryos derived from HF than for LF bulls. The aim of experiment 2 was to evaluate the effect of sire fertility on survival of bovine embryos to d 15. Day 7 blastocysts were produced in vitro using semen from the same HF (n = 3) and LF (n = 3) bulls and transferred in groups of 5-10 to synchronized heifers (n = 7 heifers per bull; total 42 heifers). Conceptus recovery rate on d 15 was higher in HF (59.4%,) versus LF (45.0%). Mean length of recovered conceptuses for HF bulls was not affected by fertility status. In conclusion, while differences in field fertility among AI sires used in this study were not reflected in fertilization rate, differences in embryo quality were apparent as early as d 7. These differences likely contributed to the higher proportion of conceptuses surviving to d 15 in HF bulls.

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.

36 Analysis of miRNA content of oviduct and uterine extracellular vesicles across the bovine estrous cycle

With the aim of investigating the possible hormonal regulatory effect of the oestrous cycle on miRNA content in the extracellular vesicles (EVs) of bovine oviducal and uterine fluids (OF, UF), we performed a bioinformatic analysis of these miRNAs, their target genes, and their biological pathways. Reproductive tracts were collected from slaughtered heifers and selected according to their corpus luteum morphology, corresponding to the 4 stages of the oestrous cycle (n=5 per stage; S1: days 1 to 4, S2: days 5–10, S3: days 11–17, S4: days 18–20) and transported to the laboratory on ice. EVs were obtained by size exclusion chromatography (PURE-EVs-Hansa Biomed) from the flushing of 1.2mL and 2.5mL of OF and UF, respectively. To concentrate the EVs, they were ultracentrifuged and suspended in 100µL of PBS. Total RNA extraction was obtained from 70µL of the previous pellet, using miRNeasy Mini Kit (Qiagen). Then, 100 to 200ng of the obtained RNA was reverse transcribed using miScript II RT Kit (Qiagen). MicroRNA (miRNA) expression profiling was done by primer-based real-time quantitative PCR of 383 mature miRNA sequences. Possible miRNA target genes and their biological pathways were predicted using the miRWalk database. Among EV miRNAs in OF, bta-miR-130a, bta-miR-382, and bta-miR-1291 were the most abundant at all stages of the oestrous cycle, displaying a significantly progressive increase from stages 1 to 4 (P&lt;0.05). In UF, bta-miR-17-5p, bta-miR-206, bta-miR-22-5p, bta-miR-502a, and bta-miR-503-3p were the most abundant at all stages of the cycle, showing greater differences between S1 and S3 (P&lt;0.05). Other miRNAs were exclusively present in a specific stage of the oestrous cycle in OF: bta-miR-21-5p (S1), bta-miR-146a (S2), bta-miR-128 (S3), and bta-miR-147 (S4). In UF, bta-miR-218 (S1), bta-miR-208b (S2), bta-miR-340 (S3), and bta-miR-335 (S4) were found. Table 1 presents some of these miRNAs, their predicted target genes, and functional pathways. In conclusion, this study highlights the effect of the oestrous cycle on miRNAs contained in the EVs of OF and UF. These miRNAs are related to relevant biological pathways implicated in oviduct and uterus modulation across the cycle, but they may also prepare those organs for embryo/conceptus presence and development. Table 1. Micro (mi)RNAs of oviductal (OF) and uterine fluid (UF) extracellular vesicles (EVs), their target genes, and biological pathways Reproductive fluid miRNAs Target genes Target pathways OF bta-miR-130a BMPR2, SMAD5, SMAD4 BMP signalling bta-miR-1291 SLC2A1 Glucagon signalling bta-miR-21–5p LIF Pluripotency stem cells regulation UF bta-miR-17-5p STAT3 Prolactin signalling bta-miR-206 ESR1 Oestrogen signalling bta-miR-340 HRAS Ras/MAPK/ERK signalling (embryo implantation) This research was funded by MINECO-Spain AGL2015-70140-R, PID2019-111641RB-I00, RTI2018-093548-B-I00; SENESCYT-Ecuador (YNC); FAPESP-Brazil 2017/20339-3 (CLVL), 2014/22887-0 (JCS), 2019/04981-2 (RM); CNPq-Brazil 304276/2018-9, 420152/2018-0 (CLVL).

Isolation, Characterization, and MicroRNA Analysis of Extracellular Vesicles from Bovine Oviduct and Uterine Fluids

Intercellular communication can be carried out by circulating systemic and/or locally released extracellular vesicles (EVs), produced by nearly every cell type and tissue, and are involved in physiological and pathological processes. In recent years, EVs have been identified in reproductive tissues, such as oviduct and uterus, and have been shown to be related to several events important for reproductive success. The understanding of their functions in reproduction has important implications for assisted reproductive technologies, for the treatment of infertility in humans and improvement of reproduction efficiency in animals. To study such EVs, it is necessary to isolate and concentrate them from fluid samples, which in the case of reproductive tissues, are usually of limited volume. Several methods for EV isolation are available such as chromatography, ultracentrifugation, polymer-based precipitation, and immunoaffinity.Outcomes can be variable in terms of the amount and quality of isolated EVs, due to the type of isolation method. The choice of method, or a different combination of methods, may depend on the type of sample and scientific question to be addressed in a given study. In this chapter, we describe a method for isolation of EVs from bovine oviductal and uterine fluids for use in functional studies. The method combines size exclusion chromatography and ultracentrifugation. We also describe the different protocols for characterization of isolated EVs (transmission electron microscopy, nanoparticle tracking analysis, and western blot), as well as the isolation of RNA content in EVs, and their miRNAs profiling for functional studies.

52 Extracellular vesicles from oviduct and uterus in sequential invitro culture affects mitochondrial activity and lipid metabolism transcripts in bovine embryos

Oviducal fluid (OF) and uterine fluid (UF) improve the quality of embryos during invitro culture, and their extracellular vesicles (EV) may be involved in such an effect. We aimed to evaluate the effect of EV from OF and UF in sequential invitro culture on the development and quality of bovine embryos. Zygotes were cultured in synthetic oviduct fluid supplemented either with 3mg mL−1 BSA (n=1584) or 5% EV-depleted fetal calf serum (dFCS, n=1594) in absence or presence (BSAEV, n=1853 and dFCSEV, n=1473) of 3×105 EV mL−1 from OF (Day 1 to Day 4) and UF (Day 5 to Day 8), mimicking invivo conditions. EV from oviducts (early luteal phase) and uterine horns (mid luteal phase) from slaughtered heifers were isolated by size exclusion chromatography; size and concentration were assessed by nanotracking analysis (NTA) and morphology by transmission electron microscopy (TEM). Blastocyst rate was recorded on Days 7–8 and their quality was assessed for mitochondrial activity by staining with Mitotracker Deep Red (ThermoFisher Scientific), survival rate after vitrification/warming by invitro culture for up to 72h, and relative mRNA abundance of lipid metabolism-related transcripts by quantitative PCR. Housekeeping genes were H2AFZ and ACTB. Data were analysed by one-way ANOVA and Tukey test. TEM confirmed the presence and morphology of EVs, and NTA indicated mode size and concentration of particles (137.2 and 151.2 nm; 2.97×1010 and 7.98×1010 particles mL−1, for OF and UF, respectively). Blastocyst yield was lower (P&lt;0.05) in BSA groups compared with dFCS groups (BSA: 16.2±1.5 and 31.0±1.9; BSAEV: 14.1±1.6 and 26.2±2.0% vs. dFCS: 30.5±2.0 and 40.6±2.4; dFCSEV: 31.1±2.5 and 39.8±2.7%, Day 7 and Day 8, respectively), irrespective of EV supplementation. Blastocyst mitochondrial activity was increased (P&lt;0.05) by EV in dFCSEV compared with the other groups. No differences in survival rate after vitrification/warming were found (range at 72 h: 67.1±8.1 to 87.8±5.7%). PPARGC1B was downregulated and ACC upregulated by EV, irrespective of protein source in medium (P&lt;0.05). In contrast, EV affected some transcripts depending on the protein source in the medium (CD36 upregulated in dFCSEV, downregulated in BSAEV; PLIN2 downregulated in dFCSEV and ATGL downregulated in BSAEV, P&lt;0.05). In conclusion, mimicking physiological conditions using EV from OF and UF in sequential IVC does not affect development but improves embryo quality by increasing blastocysts’ mitochondrial activity and favours the expression of specific lipid metabolism transcripts. Functional effects of EV may be influenced by the protein source in the medium. This research was funded by MINECO-Spain AGL2015-70140-R, PID2019-111641RB-I00, RTI2018-093548-B-I00; YN Cajas, SENESCYT-Ecuador; CLV Leal, FAPESP-Brazil 2017/20339-3, CNPq-Brazil 304276/2018-9.

A high glucose concentration during early stages of in vitro equine embryo development alters expression of genes involved in glucose metabolism

BACKGROUND

Equine embryos exhibit an unusual pattern of glucose tolerance in vitro and are currently cultured in hyperglycaemic conditions.

OBJECTIVE

Our main objective was to analyse the effect of different glucose concentrations on in vitro-produced equine embryo development and quality.

STUDY DESIGN

Experiments comparing in vitro and in vivo produced embryos.

METHODS

Oocytes (n = 641) were collected from post-mortem ovaries, matured in vitro and fertilised by intracytoplasmic sperm injection (ICSI). Embryo culture was divided from Day 0 to Day 4 and from Day 4 to Day 9 in three groups: 5-10 (5 and 10 mmol/L glucose respectively; n = 87); 5-17 (5 and 17.5 mmol/L; n = 66); and 10-17 (10 and 17.5 mmol/L; n = 117). A control group of 20 in vivo produced blastocysts was included. Cleavage and blastocyst rates were evaluated and embryos were snap-frozen for analysis of the relative mRNA expression of genes related to mitochondrial function, DNA methylation, apoptosis, glucose transport and metabolism.

RESULTS

No differences were observed in the cleavage or blastocyst rates among in vitro groups. Under high glucose conditions in vitro (10-17 group), BAX/BCL2 was higher, and PFKP, LDHA and COX2 were overexpressed compared to all other groups. The two groups with 5 mmol/L glucose concentration during the first culture stage (5-10 and 5-17) displayed similar patterns which differed to the 10-17 group.

MAIN LIMITATIONS

Conclusions related to embryo quality are based on gene expression patterns. Transfer of in vitro-produced embryos would reveal whether the observed differences improve embryo developmental competence.

CONCLUSIONS

Five mM glucose during the first days of culture seems to be preferable to avoid over-activation of embryonic glycolytic pathways. Further studies are necessary to determine whether this improves embryo developmental competence.

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

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

The effect of rapamycin on bovine oocyte maturation success and metaphase telomere length maintenance

Maternal aging-associated reduction of oocyte viability is a common feature in mammals, but more research is needed to counteract this process. In women, the first aging phenotype appears with a decline in reproductive function, and the follicle number gradually decreases from menarche to menopause. Cows can be used as a model of early human embryonic development and reproductive aging because both species share a very high degree of similarity during follicle selection, cleavage, and blastocyst formation. Recently, it has been proposed that the main driver of aging is the mammalian target of rapamycin (mTOR) signaling rather than reactive oxygen species. Based on these observations, the study aimed to investigate for the first time the possible role of rapamycin on oocyte maturation, embryonic development, and telomere length in the bovine species, as a target for future strategies for female infertility caused by advanced maternal age. The 1nm rapamycin in vitro treatment showed the best results for maturation rates (95.21±4.18%) of oocytes and was considered for further experiments. In conclusion, rapamycin influenced maturation rates of oocytes in a concentration-dependent manner. Our results also suggest a possible link between mTOR, telomere maintenance, and bovine blastocyst formation.

76 Extracellular vesicles from oviduct and uterus in sequential culture improve the quality of bovine embryos produced invitro

Extracellular vesicles (EVs) are released by cells and transport cargo that affect functions of other cells. Oviductal fluid (OF) and uterine fluid (UF) have been shown to improve quality of embryos during invitro culture (Hamdi et al. 2017 Reprod. Fertil. Dev. 30, 935-945) which may be due to their content of EV (Lopera-Vásquez et al. 2017 Reproduction 153, 461-470). Thus, the aim of this study was to evaluate the effect of EVs from OF and UF on a sequential invitro culture system on the development and quality of bovine embryos. Zygotes were cultured in synthetic oviduct fluid (SOF) supplemented with 3mgmL−1 bovine serum albumin (BSA; n=1228) or 5% EV-depleted fetal calf serum (dFCS, n=1261) in the presence (BSAEV, n=1265 and dFCSEV, n=1253) or absence of 3×105 EVmL−1 from OF (Day 1 to Day 4) and UF (Day 4 to Day 9), mimicking invivo conditions. The EVs pooled from 5 oviducts (early luteal phase) and 5 uterine horns (middle luteal phase) from slaughtered heifers were isolated by a Size Exclusion Chromatography kit (Hansa BioMed). The EV size and concentration were assessed by the nanotracking analysis system and morphology by transmission electron microscopy. Embryo development was recorded on Days 7/9. Day 7/8 blastocysts were assessed for quality by staining with (a) Hoechst 33342 (10 µgmL−1, 30min) for total cell number, (b) Bodipy 493/503 (20 µgmL−1, 1h) for lipid content (lipid droplet area in µm2), and (c) for survival rate after vitrification/warming. Data were analysed by one-way ANOVA and Tukey test. The EV concentration was 2.97 and 7.98×1010 particlesmL−1, and mode size 137.2 and 151.2nm for OF and UF, respectively. Transmission electron microscopy confirmed EV presence and size, showing typical cup-shaped morphology. Blastocyst yield was lower (P&lt;0.05) on Day 7 in the BSA groups (BSA: 15.7±1.9 and BSAEV: 15.2.4%) compared with serum groups (dFCS: 28.1±2.6 and dFCSEV: 30.1±2.9%) irrespective of EV supplementation; however, these differences were compensated at Days 8 and 9 (range: 30.0±3.2-40.8±3.9%). The EVs increased (P&lt;0.05) blastocyst total cell number in dFCSEV (152.6±2.9) and BSAEV (140.5±1.5) compared with dFCS (117.9±2.0) and BSA groups (122.4±1.1). However, lipid content was decreased (P&lt;0.05) in the presence of EVs only in dFCSEV (0.231±0.05µm2) compared with BSA (0.393±0.03µm2) and BSAEV (0.379±0.03µm2) groups. The dFCS did not differ from any group (0.371±0.05µm2; P&gt;0.05). Blastocyst survival after vitrification/warming was high in all groups up to 72h (range: 80.0±3.8-100%; P&gt;0.05). In conclusion, mimicking physiological conditions using EV from OF and UF during invitro culture does not affect development but improves embryo quality by increasing blastocyst total cell numbers and decreasing lipid contents. These results provide evidence of the association of the reproductive tract environment and developing embryo, confirming embryo-maternal communication. Funding was provided by MINECO-Spain AGL2015-70140-R; Y. N. Cajas, SENESCYT-Ecuador; C. L. V. Leal, FAPESP-Brazil 2017/20339-3.

In vitro evaluation of novel low-pressure spark plasma sintered HA–BG composite scaffolds for bone tissue engineering

The low-pressure spark plasma sintering (SPS) technique is adopted to fabricate hydroxyapatite–bioglass (HA–BG) scaffolds while maintaining the physical properties of both components, including their bulk and relative density and hardness. However, prior to their orthopaedic and dental applications, these scaffolds must be validated via pre-clinical assessments. In the present study, scaffolds with different ratios of HA : BG, namely, 100 : 0 (HB 0 S), 90 : 10 (HB 10 S), 80 : 20 (HB 20 S) and 70 : 30 (HB 30 S) were fabricated. These scaffolds were characterized by investigating their physicochemical properties (X-ray diffraction (XRD) and surface wettability), bioactivity in a simulated body fluid (SBF) (field emission scanning electron microscopy (FESEM), Fourier-transform infrared spectroscopy (FTIR) and calcium dissolution), antimicrobial properties, biocompatibility and osteoinduction of human bone marrow-derived mesenchymal stromal cells (hBMSCs) and human monocyte immune cell response. The XRD and surface wettability results confirmed no formation of undesirable phases and the enhanced surface hydrophilicity of the scaffolds, respectively. The bioactivity in SBF indicated the formation of bone-like apatite on the surface of the scaffolds, corresponding to an increase in BG%, which was confirmed through FTIR spectra and the increasing trend of calcium release in SBF. The scaffolds showed inhibition properties against Staphylococcus aureus and Staphylococcus epidermidis. The scanning electron microscopy (SEM) micrographs and Alamar Blue proliferation assay indicated the good attachment and significant proliferation, respectively, of hBMSCs on the scaffolds. Alizarin Red S staining confirmed that the scaffolds supported the mineralisation of hBMSCs. The osteogenic protein secretion (bone morphogenetic protein-2 (BMP2), type-I collagen (COL1) and osterix (OSX)) was significant on the HB 30 S-seeded hBMSCs when compared with that of HB 0 S. The monocyte migration was significantly halted in response to HA–BG-conditioned media when compared with the positive control (monocyte chemoattractant protein-1: MCP-1). In conclusion, the HB 30 S composite scaffold has a greater potential to substitute bone grafts in orthopaedic and dental applications.

HB 30 S composite scaffold inhibits Staphylococcus spp., supports the biocompatibility and osteogenic differentiation of hBMSCs and resists monocyte migration.

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

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

Bovine oviductal and uterine fluid support in vitro embryo development

In order to mimic the maternal oviductal environment, we evaluated the effect of oviductal fluid (OF) and/or uterine fluid (UF) supplementation on in vitro embryo development and quality. In vitro-produced zygotes were cultured with 1.25% OF from Day 1 to Day 4 after insemination (OF group), 1.25% OF from Day 1 to Day 4 followed by 1.25% UF from Day 4 to Day 9 (OF+UF group) or 1.25% UF only from Day 4 to Day 9 (UF group). Control groups were cultured in the presence of synthetic oviduct fluid (SOF) supplemented with 3mgmL-1 bovine serum albumin (BSA) or 5% fetal calf serum (FCS). Supplementation of the culture medium with OF and/or UF (both at 1.25%) supported embryo development (Day 9 blastocyst rate 28.2-30.6%). At 72h after vitrification-warming, the survival of blastocysts from the OF and OF+UF groups was similar to that of blastocysts in the SOF+BSA group (61.0±5.7% and 62.8±6.4% vs 64.8±6.4% respectively), but significantly higher than that of blastocysts from the SOF+FCS group (31.6±4.9%; P<0.001). Blastocysts from the OF group exhibited upregulation of epigenetic genes (i.e. DNA methyltransferase 3α (DNMT3A) and insulin-like growth factor 2 receptor (IGF2R)), compared with expression in the SOF+FCS group (P<0.05). Whereas those from OF+UF and UF groups exhibited downregulation of oxidative stress genes compared to SOF+BSA and OF groups for glutathione peroxidase (GPX1) and to SOF+FCS, SOF+BSA and OF groups for chloride intracellular channel 1 (CLIC1) (P<0.05). In addition, accumulation of reactive oxygen species was lower in blastocysts from the OF, OF+UF and UF groups. In conclusion, the use of low concentrations of OF and UF in in vitro serum-free culture supports embryo development, with OF providing a better control of embryo methylation, whereas UF may have antioxidant activity.

Shape-from-focus for real-time terahertz 3D imaging

Thanks to significant advances in real-time terahertz imaging in terms of resolution and image quality, adapting and extending optical methods for 3D imaging at the millimeter scale is now promising. The shape-from-focus algorithm is a post-processing tool used in optical microscopy to reconstruct the external shape surface of a convex surface object. Images acquired at different distances from the object-side focal plane are implemented in this algorithm. We localize the best focus position in the stack of images for each pixel and then reconstruct the object in 3D due to the short depth of field. In this Letter, we propose an application of this algorithm in active and real-time terahertz imaging. We achieve the experimental reconstruction in 3D with a terahertz waves imaging system composed of a powerful source and a real-time terahertz camera.

Ascorbic acid-cyclodextrin complex alters the expression of genes associated with lipid metabolism in bovine in vitro produced embryos

Ascorbic acid (AC) used as antioxidant in embryo culture is very sensitive and degrades unavoidably in aqueous solution. Methyl-β-cyclodextrin (CD) improved the stability of AC in solution to elevated temperature, light, humidity and oxidation. The aim of this study was to evaluate the effect of the complex AC-CD during in vitro maturation (IVM) or in vitro culture (IVC) on oocyte developmental competence and subsequent embryo development and quality. AC-CD (100 µM) was added to IVM media, and maturation level and embryo development were examined. Matured oocytes, their cumulus cells and produced blastocysts were snap-frozen for gene expression analysis by RT-qPCR. Besides, in vitro-produced zygotes were cultured with 100 µM of AC-CD and blastocysts were as well snap-frozen for gene expression analysis. A group without AC-CD (control^- ) and other with CD (control⁺ ) were included. No differences were found on maturation, cleavage or blastocyst rates. However, in matured oocytes, AC-CD downregulated BAX, GPX1 and BMP15. In cumulus cells, AC-CD downregulated BAX/BCL2 and GSTA4 while upregulated BCL2 and CYP51A1. The expression of SL2A1, FADS1, PNPLA and MTORC1 was downregulated in blastocysts derived from oocytes matured with AC-CD, while in blastocysts derived from zygote cultured with AC-CD, CYP51A1 and IGF2R were downregulated and PNPLA2 was upregulated. In conclusion, AC-CD in both IVM and IVC media may reduce accumulated fat by increasing lipolysis and suppressing lipogenesis in blastocysts derived from both oocytes and zygotes cultured with AC-CD, suggesting that CD improves the quality of embryos and bioavailability of AC during IVM and IVC.

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.

Cultured bovine embryo biopsy conserves methylation marks from original embryo

A major limitation of embryo epigenotyping by chromatin immunoprecipitation analysis is the reduced amount of sample available from an embryo biopsy. We developed an in vitro system to expand trophectoderm cells from an embryo biopsy to overcome this limitation. This work analyzes whether expanded trophectoderm (EX) is representative of the trophectoderm (TE) methylation or adaptation to culture has altered its epigenome. We took a small biopsy from the trophectoderm (30-40 cells) of in vitro produced bovine-hatched blastocysts and cultured it on fibronectin-treated plates until we obtained ∼4 × 104 cells. The rest of the embryo was allowed to recover its spherical shape and, subsequently, TE and inner cell mass were separated. We examined whether there were DNA methylation differences between TE and EX of three bovine embryos using whole-genome bisulfite sequencing. As a consequence of adaptation to culture, global methylation, including transposable elements, was higher in EX, with 5.3% of quantified regions showing significant methylation differences between TE and EX. Analysis of individual embryos indicated that TE methylation is more similar to its EX counterpart than to TE from other embryos. Interestingly, these similarly methylated regions are enriched in CpG islands, promoters and transcription units near genes involved in biological processes important for embryo development. Our results indicate that EX is representative of the embryo in terms of DNA methylation, thus providing an informative proxy for embryo epigenotyping.

116 In Vitro Transcriptomic Response of Bovine Oviduct Epithelial Cells to Direct or Indirect Embryo Contact

We observed that in vitro transcriptomic response of bovine oviduct epithelial cells (BOEC) to the early embryo could be the result of a contact-dependent signalling effect or interactions with embryo secretions. In order to determine this, BOEC were co-cultured directly with embryos or indirectly with embryo-conditioned media (CM); BOEC from the isthmus of oviducts at early luteal phase were cultured with TCM-199+10% fetal calf serum (FCS) in 4-well plates in 5% CO2 in air at 38.5°C for 6 days until confluence. In vitro 2- and 8-cell embryos as well as their CM were produced in parallel. A day before co-culture, BOEC medium was replaced with SOF+10% FCS. Groups for 2- and 8-cell embryos were established: BOEC in direct contact with embryos; BOEC in the same well as embryos but not in indirect contact; BOEC with embryo CM; and BOEC without embryos, as a control. Polyester mesh was used to maintain embryos position on top of the cells. After 48 h of co-culture, BOEC were recovered for gene expression analysis (4 replicates). The relative abundance of candidate genes previously shown to be affected by the presence of embryo in vivo (Maillo et al. 2015 Biol Reprod. 92, 144) [SMAD6 (BMP signalling pathway); ROCK1, ROCK2 (cytokinesis); SOCS3 (inflammatory response); PRELP (extracellular matrix)] or in vitro (Schmaltz-Panneau et al. 2014 Anim. Reprod. Sci. 149, 103-106) [GPX4, NFE2L2 (oxidative stress); SCN9A (sodium ion binding); EPSTI1 (tissue remodelling); IGFBP3 (insulin-like growth factor binding); TDGF1 (BMP signalling pathway); AGR3 (regulation of ciliary beating)] was assessed by RT-qPCR. H2A.Z and ACTG1 were used as housekeeping genes. Statistical analysis was assessed by ANOVA. The BOEC responded to the presence of 2-cell embryos only when in direct contact by significantly decreasing abundance of NFE2L2. Both direct and indirect embryo contact or culture with CM significantly decreased GPX4, ROCK2, and SCN9A transcripts compared with control. The presence of 2-cell embryos irrespective of being in direct or indirect contact reduced the expression of SMAD6 compared with the control and CM groups. In the case of CM, expression of IGFBP3 was enhanced compared with the control but was similar to the presence of the 2-cell embryos. In the presence of 8-cell embryos, direct contact with BOEC significantly down-regulated the expression for GPX4 and SOCS3, whereas expression of SCN9A was up-regulated. The opposite was observed when compared with control. The presence of 8-cell embryos down-regulated the expression of SMAD6 and ROCK2 compared with the CM group, whereas direct or indirect contact with BOEC or culture with CM down-regulated the expression of PRELP compared to control. In conclusion, these results provide evidence for a differential affect on the transcriptome of BOEC in vitro depending on embryo stage. These changes may be related either with direct embryo contact or embryo secretions released into the media. Research supported by Spanish MINECO-AGL2015-70140-R; AGL2015-66145-R; OECD-Co-operative Programme TAD/CRP JA00092482.

115 In Vivo Transcriptomic Response of Bovine Oviduct Epithelial Cells to the Early Embryo

The presence of a single 8-cell embryo does not alter the transcriptome of the cells of the oviducal isthmus, although a local effect at the precise position of the embryo cannot be ruled out. Thus, we aimed to study the local embryo effect on the transcriptomic response of the epithelial cells of the oviduct in vivo. Fifteen heifers were synchronized and all showed standing heat and were artificially inseminated. All heifers were slaughtered on Day 2.5 after oestrus. The oviducts from 13 animals (with a corpus luteum, CL) were isolated, trimmed free of tissue and divided between ampulla and isthmus. The ipsilateral isthmus was then divided into smaller sections (2 cm). Each section was sequentially flushed until the embryo was located and was then opened and scraped longitudinally to obtain the epithelial cells. Cells were snap-frozen in LN2 for gene expression analysis. All recovered embryos were found at the beginning of the isthmus of the oviduct ipsilateral to the CL. Three at 2-cell stage and 1 at 8-cell stage. The recovery rate was 30.8% (4/13) and only samples from these 4 animals were used for analysis. The 2-cm sections selected for the transcriptomic analysis were embryo section (ES), in which the embryo was found; proximal section (PS), through which the embryo had passed; distal section (DS), on the uterine side of the embryo; and contralateral section (CS), section from the contralateral isthmus. The expression pattern of 10 differentially expressed genes between the isthmus of pregnant and cyclic heifers (Maillo et al. 2015 Biol Reprod. 92, 144) were assessed by RTq-PCR relative to 2 housekeeping genes, H2A.Z and ACTG. Five up-regulated genes (STK32A, SLC26A3, KERA, QRFPR, MCTP1) and 5 down-regulated (SOD3, PRELP, VAT1L, SOCS3, CCL20) were analysed. One-way ANOVA and t-test was used for statistical analysis. Comparison between ES and the CS revealed one significantly altered gene (VAT1L). This is in agreement with our in vivo results in which VAT1L was also down-regulated in the presence of embryos. Comparison within the ipsilateral oviduct of ES and PS samples revealed STK32A, SLC26A3, QRFPR, MCTP1, and SOCS3 transcripts significantly down-regulated compared with DS samples, whereas the expression for CCL20 was different between ES and DS but similar to the PS. In conclusion, the fact that 5 out of 10 transcripts were different between the segment where the embryo was collected and other locations in the oviduct suggests the presence of embryo site-specific signal. However, comparison between the ipsilateral embryo site with the contralateral site revealed that only one transcript was different. Moreover, the similarities in the ipsilateral oviduct between embryo and proximal site may be due to the passage of the embryo. Furthermore, the location of the embryo close to the ampullary-isthmic junction may mask the effect due to the spatial differences of the bovine oviduct. Research supported by EU, Horizon 2020 Marie Sklodowska-Curie, REPBIOTECH 675526; Spanish MINECO AGL2015-70140-R & AGL2015-66145-R; OECD-CoOperative Prog TAD/CRP JA00092482.

Embryo culture in presence of oviductal fluid induces DNA methylation changes in bovine blastocysts

During the transit through the oviduct, the early embryo initiates an extensive DNA methylation reprogramming of its genome. Given that these epigenetic modifications are susceptible to environmental factors, components present in the oviductal milieu could affect the DNA methylation marks of the developing embryo. The aim of this study was to examine if culture of bovine embryos with oviductal fluid (OF) can induce DNA methylation changes at specific genomic regions in the resulting blastocysts. In vitro produced zygotes were cultured in medium with 3 mg/mL bovine serum albumin (BSA) or 1.25% OF added at the one- to 16-cell stage (OF1–16), one- to 8-cell stage (OF1–8) or 8- to 16-cell stage (OF8–16), and then were cultured until Day 8 in medium with 3 mg/mL BSA. Genomic regions in four developmentally important genes (MTERF2, ABCA7, OLFM1, GMDS) and within LINE-1 retrotransposons were selected for methylation analysis by bisulfite sequencing on Day 7–8 blastocysts. Blastocysts derived from OF1–16 group showed lower CpG methylation levels in MTERF2 and ABCA7 compared with the BSA group. However, CpG sites within MTERF2, ABCA7 and OLFM1 showed higher methylation levels in groups OF1–8 and OF8–16 than in OF1–16. For LINE-1 elements, higher CpG methylation levels were observed in blastocysts from the OF1–16 group than in the other experimental groups. In correlation with the methylation changes observed, mRNA expression level of MTERF2 was increased, while LINE-1 showed a decreased expression in blastocysts from OF1–16 group. Our results suggest that embryos show transient sensitivity to OF at early stages, which is reflected by specific methylation changes at the blastocyst stage.

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

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

Effect of bovine oviductal extracellular vesicles on embryo development and quality in vitro

The aim of this study was to evaluate the effect of extracellular vesicles (EV) from oviductal fluid (OF), either from the ampulla or isthmus, on the development and quality of in vitro-cultured bovine embryos. Zygotes were cultured in synthetic oviduct fluid (SOF + 3 mg/mL BSA) without calf serum (C- group), in the presence of 3 × 10⁵ EV/mL from ampullary or isthmic OF at either 1 × 10⁴g (10 K) or 1 × 10⁵ g (100 K), and compared with SOF + 5% FCS (C+ group). OF-EV size and concentration were assessed by electron microscopy and nanotracking analysis system. Embryo development was recorded on Days 7-9, and blastocyst quality was assessed through cryotolerance and gene expression analysis. Lower blastocyst yield was observed on Day 7 in the C- and OF-EV groups (12.0-14.3%) compared with C+ (20.6%); however, these differences were compensated at Days 8 and 9 (Day 9: 28.5-30.8%). Importantly, the survival rate of blastocysts produced with isthmic 100 K OF-EV was higher than that of C+ and C- group at 72 h after vitrification and warming (80.1 vs 34.5 and 50.5% respectively, P < 0.05). In terms of gene expression, blastocysts produced in the presence of 100 K isthmic OF-EV upregulated the water channel AQP3 and DNMT3A and SNRPN transcripts compared with the C+, with the expression in C- being intermediate. The lipid receptor LDLR was downregulated in C+ compared with all other groups. In conclusion, the addition of oviductal fluid extracellular vesicles from isthmus, to in vitro culture of bovine embryos in the absence of serum improves the development and quality of the embryos produced.

80 EFFECT OF BOVINE OVIDUCTAL FLUID ON DNA METHYLATION OF BOVINE BLASTOCYSTS PRODUCED IN VITRO

During the transit through the oviduct, the early embryo undergoes an epigenetic reprogramming of its genome, which induces changes in DNA methylation pattern. Given that epigenetic modifications are susceptible to environmental influence, the oviducal milieu may affects DNA methylation marks in the developing embryo. The aim of this study was to evaluate whether bovine oviducal fluid (OF) exerts an effect on methylation status of genomic regions at different time points of embryo development. In vitro-produced zygotes were cultured in SOF + 3 mg mL−1 BSA (control, C) or in SOF + 1.25% OF at 3 different time points: until 98 h post-insemination (hpi) (OF1–16: 1–16 cell), 52 hpi (OF1–8: 1–8 cell), or from 52 until 98 hpi (OF8–16: 8–16 cell). The OF used was acquired from Embryocloud (Murcia, Spain) from cow oviducts at the early luteal phase (Day 1–4). After, embryo culture took place in control medium up to Day 8. For all the groups, the speed of development was considered, and normal developing embryos that reached ≥6 cells at 52 hpi and ≥16 cells at 98 hpi were selected and separately cultured from slow developing embryos. Cleavage (52 hpi) and blastocyst yield (Day 7–8) were analysed by ANOVA (8 replicates). Expanding blastocysts (Day 7–8) from the normal developing groups were collected for bisulfite sequencing analysis. The DNA bisulfite conversion was performed with a MethylEdge Bisulfite Conversion System kit (Promega, WI, USA) in groups of 20 blastocysts obtained from 5 replicates. Methylation status was analysed on regions localised in 4 developmental important genes (MTERF2, ABCA7, OLFM1, and GMDS) and within 2 LINE L1 elements located on chromosomes 9 (L9) and 29 (L29). Methylation percentages (10 sequenced clones/group) were compared using statistical z-test. No significant differences were found on cleavage rate (C: 89.7 ± 1.0, OF1–16: 84.9 ± 1.7; OF1–8: 85.4 ± 1.9; OF8–16: 89.1 ± 1.9%) and blastocyst yield between normal developing embryos (C: 36.8 ± 5.3; OF1–16: 34.7 ± 3.7; OF1–8: 41.0 ± 3.8; OF8–16: 43.9 ± 5.1%). Blastocysts derived from all OF groups showed the CpG region of MTERF2 hypomethylated compared with C group (20.0, 26.2, and 32.9% v. 56.2%, respectively; P < 0.001). The CpG sequence of ABCA7 exhibited significant hypomethylation in embryos from OF1–16 group compared with OF1–8, OF8–16, and C groups (31.1 v. 56.8, 57.9, and 65.8%, respectively; P < 0.001). Although the methylation of the CpG region within OLFM1 did not differ between OF1–16 and C groups (24.1 v. 19.4%, respectively), embryos from OF1–8 group showed a highly methylated region (47.1%) compared with OF1–16 and C groups (P < 0.001). The CpG sequence on L9 showed a high methylation level in blastocysts derived from OF1–16 group compared with OF8–16 and C groups (36.4 v. 14.5 and 20.0%, respectively; P < 0.05). There were no differences in methylation marks between groups examined for CpG regions of GMDS and L29. These results indicated that embryos exhibit a temporal sensitivity to OF at early embryonic stages, which is reflected by DNA methylation changes of specific genes at blastocyst stage. This is the first report describing that OF could modify specific epigenetic marks of the bovine embryonic genome.

83 BONE MORPHOGENETIC PROTEIN SIGNALING DURING INTERACTION OF THE BOVINE EMBRYO WITH OVIDUCTAL EPITHELIAL CELLS IN VITRO

In previous studies, we have demonstrated that different signalling components of bone morphogenetic proteins (BMP) are expressed in an anatomically and temporally regulated fashion in the bovine oviduct. However, a local response of this signalling to the embryo presence has not been elucidated yet. The aim of the present study was to evaluate whether the interaction of the embryo with the oviduct can induce changes in the gene expression of BMP signalling components. For this purpose, we used an in vitro co-culture system of a bovine oviducal epithelial cell (BOEC) monolayer with pre-implantation embryos in 2 developmental time points: before and during the main phase of embryonic genome activation (EGA). Isthmus epithelial cells from post-ovulatory stage oviducts (Day 2–4) were cultured in 500 μL of SOF + 10% FCS in 4-well plates at 38.5°C, 5% CO2, 5% O2, and 90% N2. On Day 6 of culture, medium was replaced with SOF + 5% FCS, and 24 h later BOEC monolayer was cultured in the absence or presence of in vitro-produced embryos from 2- to 8-cell stage [G1 BOEC; 33–54 h post-insemination (hpi)] or from 8- to 16-cell stage (G2 BOEC; 54–98 hpi) in the same conditions. In both groups, a polyester mesh was used to define a local co-culture area, and 30 embryos per well were placed in a 6 × 5 grid over the monolayer. In addition, as control groups, embryos in both developmental stages were cultured either in SOF + 5% FCS (G1 FCS and G2 FCS) or in SOF + 3 mg mL−1 BSA (G1 BSA and G2 BSA). At 54 hpi (G1 BOEC/BSA/FCS) or 98 hpi (G2 BOEC/BSA/FCS), embryos that reached 8- or 16-cell stage, respectively, were transferred to SOF + BSA and cultured until Day 9. The mRNA expression levels of 3 BMP receptors (BMPRIA/IB/II), 2 signalling proteins (SMAD1/5), 1 inhibitor (SMAD6), and 1 target gene (ID2) were analysed by qPCR in 5 samples of BOEC cultured with or without embryos before or during EGA, and in 3 pools of 10 embryos at 8 (54 hpi), 16 (98 hpi), and blastocyst stage (Day 7–8) from all groups. Genes H2A.Z and ACTG1 were used as housekeeping genes, and statistical differences were assessed by ANOVA. The presence of the embryo, irrespective the stage, significantly reduced the expression levels of BMPRIB, BMPRII, SMAD1, SMAD6, and ID2 in BOEC. Embryos that interacted with BOEC before EGA (G1 BOEC) showed a significant increase in the relative abundance of SMAD1 at the 8-cell stage compared with controls. Moreover, embryos that interacted with BOEC during EGA (G2 BOEC) showed a significant increase in the relative abundance of BMPRIB, BMPRII, and ID2 at the 16-cell stage when compared with controls. However, no differences were observed in the mRNA expression levels of BMP signalling components in the blastocysts between groups. In conclusion, local embryo-oviduct interaction in vitro induces changes in the transcriptional levels of BMP signalling, causing a bidirectional response that reduces the expression levels of this signalling in the oviducal cells while increases them in the embryo at early stages. This suggests that BMP signalling pathway could be involved in an early cross-talk between the bovine embryo and the oviduct during first stages of development.

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.