Set up of a serum-free culture system for bovine embryos: embryo development and quality before and after transient transfer

Developmental Hurdles That Can Compromise Pregnancy during the First Month of Gestation in Cattle

Several key developmental events are associated with early embryonic pregnancy losses in beef and dairy cows. These developmental problems are observed at a greater frequency in pregnancies generated from in-vitro-produced bovine embryos. This review describes critical problems that arise during oocyte maturation, fertilization, early embryonic development, compaction and blastulation, embryonic cell lineage specification, elongation, gastrulation, and placentation. Additionally, discussed are potential remediation strategies, but unfortunately, corrective actions are not available for several of the problems being discussed. Further research is needed to produce bovine embryos that have a greater likelihood of surviving to term.

Simple and Efficient Chemically Defined In Vitro Maturation and Embryo Culture System for Bovine Embryos

Supplementation of the culture media for in vitro production (IVP) of bovine embryos with fetal bovine serum (FBS) is associated with inconsistent outcomes. The present study sought to replace FBS and BSA by insulin-like growth factor 1 (IGF1), fibroblast growth factor 2 (FGF2) and epidermal growth factor (EGF). In Experiment 1, absence of FBS from maturation medium (MM) did not affect the rate of in vitro maturation, as assessed by the extrusion of the first polar body. However, when gonadotropins and FBS were removed from the MM, the maturation rate was significantly reduced even in the presence of growth factors. Therefore, gonadotropin-supplemented MM medium was established as the base medium for the defined maturation condition. In Experiment 2, the addition of growth factors to gonadotropin-supplemented MM medium supported similar maturation (~90%) compared to the undefined condition (FBS-carrying). In Experiment 3, the addition of growth factors to embryo culture medium showed similar in vitro competence compared to the undefined (FBS) control. In Experiment 4, completely defined conditions (absence of FBS and BSA during in vitro maturation and embryo culture) were tested. A higher cleavage was observed with FGF2 (86%) compared to EGF (77%) and the FBS control (77%), but similar blastocyst rates were observed for FGF2 (24%), EGF (19%) and the FBS control (25%). Embryo quality was similar among groups. Finally, post-thawing survival was higher for FGF2 (94%) compared to the FBS control (77%). Thus, we report a simple defined IVP system for bovine species that generates developmental outcomes and embryos of similar quality than those produced under conditions containing FBS.

Serum supplementation during bovine embryo culture affects their development and proliferation through macroautophagy and endoplasmic reticulum stress regulation

Serum supplementation during bovine embryo culture has been demonstrated to promote cell proliferation and preimplantation embryo development. However, these desirable outcomes, have been associated with gene expression alterations of pathways involved in macroautophagy, growth, and development at the blastocyst stage, as well as with developmental anomalies such as fetal overgrowth and placental malformations. In order to start dissecting the molecular pathways by which serum supplementation of the culture medium during the preimplantation stage promotes developmental abnormalities, we examined blastocyst morphometry, inner cell mass and trophectoderm cell allocations, macroautophagy, and endoplasmic reticulum stress. On day 5 post-insemination, > 16 cells embryos were selected and cultured in medium containing 10% serum or left as controls. Embryo diameter, inner cell mass and trophectoderm cell number, and macroautophagy were measured on day 8 blastocysts (BL) and expanded blastocysts (XBL). On day 5 and day 8, we assessed transcript level of the ER stress markers HSPA5, ATF4, MTHFD2, and SHMT2 as well as XBP1 splicing (a marker of the unfolded protein response). Serum increased diameter and proliferation of embryos when compared to the no-serum group. In addition, serum increased macroautophagy of BL when compared to controls, while the opposite was true for XBL. None of the genes analyzed was differentially expressed at any stage, except that serum decreased HSPA5 in day 5 > 16 cells stage embryos. XBP1 splicing was decreased in BL when compared to XBL, but only in the serum group. Our data suggest that serum rescues delayed embryos by alleviating endoplasmic reticulum stress and promotes development of advanced embryos by decreasing macroautophagy.

PGE2 Supplementation of Oocyte Culture Media Improves the Developmental and Cryotolerance Performance of Bovine Blastocysts Derived From a Serum-Free in vitro Production System, Mirroring the Inner Cell Mass Transcriptome

The culture media used throughout the in vitro production (IVP) of bovine embryos remain complex. The serum added to culture media in order to improve embryo development negatively impacts the cryotolerance of blastocysts. Periconceptional prostaglandin E2 (PGE2) signaling is known to exert prosurvival effects on in vitro-generated blastocysts. The purpose of the present study was to evaluate the effects on developmental and cryotolerance performance of a serum-free (SF) IVP system that included defined oocyte culture media supplemented or not with PGE2, versus serum-containing (SC) IVP. RNA-sequencing analysis was used to examine the gene expression of ICM derived under the different IVP conditions. We assessed the degree of cryotolerance of grade-I blastocysts during a three-day post-thaw culture by measuring survival and hatching rates, counting trophectoderm and inner cell mass (ICM) blastomere numbers. We also determined the proportion of ICM cells expressing octamer-binding transcription factor 4 protein (OCT4/POU5F1). We showed that grade-I blastocyst development rates under SF + PGE2 conditions were similar to those obtained under SC conditions, although the cleavage rate remained significantly lower. SC IVP conditions induced changes to ICM gene expression relative to several metabolic processes, catabolic activities, cell death and apoptosis. These alterations were associated with significantly higher levels of ICM cell death at day 7 post-fertilization, and lower survival and hatching rates after thawing. SF IVP conditions supplemented or not with PGE2 induced changes to ICM gene expression related to DNA replication, metabolism and double-strand break repair processes, and were associated with significantly larger ICM cell populations after thawing. SF + PGE2 IVP induced changes to ICM gene expression related to epigenetic regulation and were associated with a significantly higher proportion of ICM cells expressing OCT4. For the first time, our study thus offers a comprehensive analysis of the ICM transcriptome regulated by IVP culture conditions in terms of the cellular changes revealed during culture for three days after thawing.

Rescue Potential of Supportive Embryo Culture Conditions on Bovine Embryos Derived from Metabolically Compromised Oocytes

Elevated non-esterified fatty acid (NEFA), predominantly palmitic acid (PA), concentrations in blood and follicular fluid are a common feature in maternal metabolic disorders such as obesity. This has a direct negative impact on oocyte developmental competence and the resulting blastocyst quality. We use NEFA-exposure during bovine oocyte in vitro maturation (IVM) as a model to mimic oocyte maturation under maternal metabolic stress conditions. However, the impact of supportive embryo culture conditions on these metabolically compromised zygotes are not known yet. We investigated if the addition of anti-apoptotic, antioxidative and mitogenic factors (namely, Insulin-Transferrin-Selenium (ITS) or serum) to embryo culture media would rescue development and important embryo quality parameters (cell proliferation, apoptosis, cellular metabolism and gene expression patterns) of bovine embryos derived from high PA- or high NEFA-exposed oocytes when compared to controls (exposed to basal NEFA concentrations). ITS supplementation during in vitro culture of PA-exposed oocytes supported the development of lower quality embryos during earlier development. However, surviving blastocysts were of inferior quality. In contrast, addition of serum to the culture medium did not improve developmental competence of PA-exposed oocytes. Furthermore, surviving embryos displayed higher apoptotic cell indices and an aberrant cellular metabolism. We conclude that some supportive embryo culture supplements like ITS and serum may increase IVF success rates of metabolically compromised oocytes but this may increase the risk of reduced embryo quality and may thus have other long-term consequences.

Platelet rich plasma efficiently substitutes the beneficial effects of serum during in vitro oocyte maturation and helps maintain the mitochondrial activity of maturing oocytes

Platelets contain most of the potent mitogenic factors present in serum and follicular fluid and intraovarian injection of autologous platelet rich plasma (PRP) was shown to improve ovarian function and development of preantral follicles. This study evaluated the effect of PRP on caprine oocyte maturation in vitro and subsequent fertilization and embryonic development. Cumulus oocyte complexes were cultured in a maturation medium supplemented with (1) fetal bovine serum (FBS, control), (2) PRP, extracted from healthy female goats, (3) polyvinyl alcohol (PVA), and (4) PVA plus PRP (PVA-PRP). The degree of cumulus expansion was scored, and denuded oocytes were used for assessment of nuclear maturation, mitochondrial activity, lipid content, redox status, yield and quality of in vitro embryo development, and cryosurvival of the resulting blastocysts. PRP supported the same beneficial effects of FBS on cumulus expansion, nuclear maturation, in vitro developmental competence of oocytes, and survival of vitrified-warmed blastocysts. Moreover, PRP protected oocytes from undesirable effects FBS exerted on the mitochondrial activity and intracytoplasmic lipid content of maturing oocyte. Although PVA could support the same beneficial effects of neither FBS nor PRP on oocyte maturation, its combined addition with PRP improved the yield and quality of oocyte maturation at rates closely similar to PRP. PRP efficiently substitutes beneficial effects of serum during in vitro oocyte maturation and helps maintain the mitochondrial activity of maturing oocytes.

Recent progress in bovine in vitro-derived embryo cryotolerance: Impact of in vitro culture systems, advances in cryopreservation and future considerations

Cryopreservation of in vitro-derived bovine embryos is a crucial step for the widespread reproduction and conservation of valuable high-merit animals. Given the current popularity of bovine in vitro embryo production (IVP), there is a demand for a highly efficient ultra-low temperature storage method in order to maximize donor ovum pickup (OPU) turn-over, recipient availability/utilization and domestic/overseas commercial trading opportunities. However, IVP bovine embryos are still very sensitive to chilling and cryopreservation, and despite recent progress, a convenient (simple and robust) protocol has not yet been developed. At the moment, there are two methods for bovine IVP embryo cryopreservation: slow programmable freezing and vitrification. Both of the aforementioned techniques have pros and cons. While controlled-rate slow cooling can easily be adapted for direct transfer (DT), ice crystal formation remains an issue. On the other hand, vitrification solved this problem but the possibility of successful DT commercial incorporation remains to be determined. Moreover, simplification of the vitrification protocol (including warming) through the use of an in-straw dilution without the use of a microscope is a prerequisite for its use under farm conditions. This review summarizes the bovine IVP embryo cryopreservation achievements, strengths and limitations of both freezing systems and prospective improvements to enhance cryosurvival, as well as perspectives on future directions of this assisted reproductive technology.

Developmental potential of buffalo embryos cultured in serum free culture system

The presence of serum in embryo culture medium has been implicated for increased embryo's sensitivity to cryopreservation, compromised viability, abnormal embryo and fetal development. Hence, designing a serum free culture system is indispensable. The present study aims to compare the efficiency of the serum and granulosa cells monolayer free commercial culture system (SFCS) with the conventional serum supplemented co-culture system (SSCS) and optimized culture system (OCS). Generally, SFCS is designed explicitly for bovine oocyte maturation and embryo culture (SF-IVM and SF-IVC), and SSCS (based on M199, SS-IVM, and SS-IVC) is utilized for buffalo in vitro embryo production. However, OCS is a newly designed culture system in which oocyte maturation is performed in serum supplemented maturation medium, and the subsequent embryos are co-cultured with granulosa cells in serum free culture medium. To evaluate the effect of serum on buffalo embryo production, buffalo oocytes, and their subsequent embryos were cultured in SSCS, SFCS, and OCS, simultaneously. The percentage of cleaved embryos cultured in SSCS and OCS was approximately 4% higher as compared to SFCS. However, OCS significantly showed the maximum proportion of embryos that developed to the blastocyst stage (7d) and hatched (6d) as compared to the SFCS and SSCS. Additionally, OCS promoted the expression of developmentally important genes (BCL2-L1 and VEGF-A), cell number, and cryo-survival ability of blastocysts in comparison with SSCS. Taken together, OCS is more suitable for the oocyte maturation and culture of buffalo embryos. However, to design the serum free culture system, it is recommended to find suitable serum alternatives for in vitro oocyte maturation.

A combination of bovine serum albumin with insulin-transferrin-sodium selenite and/or epidermal growth factor as alternatives to fetal bovine serum in culture medium improves bovine embryo quality and trophoblast invasion by induction of matrix metalloproteinases

This study investigated the use of bovine serum albumin (BSA) plus insulin-transferrin-sodium selenite (ITS) and/or epidermal growth factor (EGF) as alternatives to fetal bovine serum (FBS) in embryo culture medium. The developmental ability and quality of bovine embryos were determined by assessing their cell number, lipid content, gene expression and cryotolerance, as well as the invasion ability of trophoblasts. The percentage of embryos that underwent cleavage and formed a blastocyst was higher (P<0.01) in medium containing ITS plus EGF and BSA than in medium containing FBS. Culture with ITS plus EGF and BSA also increased the hatching ability of blastocysts and the total cell number per blastocyst. Furthermore, the beneficial effects of BAS plus ITS and EGF on embryos were associated with a significantly reduced intracellular lipid content, which increased their cryotolerance. An invasion assay confirmed that culture with ITS plus EGF and BSA significantly improved the invasion ability of trophoblasts. Real-time quantitative polymerase chain reaction analysis showed that the mRNA levels of matrix metalloproteinase-2 (MMP2) and MMP9, acyl-CoA synthetase long-chain family member 3, acyl-coenzyme A dehydrogenase long-chain and hydroxymethylglutaryl-CoA reductase significantly increased upon culture with ITS plus EGF and BSA. Moreover, protein expression levels of matrix metalloproteinase-2 and -9 increased (P<0.01) in medium supplemented with ITS plus EGF and BSA compared with medium supplemented with FBS. Taken together, these data suggest that supplementation of medium with ITS plus EGF and BSA improves invitro bovine embryo production, cryotolerance and invasion ability of trophoblasts.

Contributions of RNA-seq to improve in vitro embryo production (IVP)

In Vitro Embryo Production (IVP) is widely used to improve the reproductive efficiency of livestock animals, however increasing the embryo development rates and pregnancy outcomes is still a challenge for some species. Thus, the lack of biological knowledge hinders developing specie-specific IVP protocols. Therefore, the contributions of RNA-seq to generate relevant biological knowledge and improve the efficiency of IVP in livestock animals are reviewed herein.

Oocytes, embryos and pluripotent stem cells from a biomedical perspective

The veterinary and animal science professions are rapidly developing and their inherent and historical connection to agriculture is challenged by more biomedical and medical directions of research. While some consider this development as a risk of losing identity, it may also be seen as an opportunity for developing further and more sophisticated competences that may ultimately feed back to veterinary and animal science in a synergistic way. The present review describes how agriculture-related studies on bovine in vitro embryo production through studies of putative bovine and porcine embryonic stem cells led the way to more sophisticated studies of human induced pluripotent stem cells (iPSCs) using e.g. gene editing for modeling of neurodegeneration in man. However, instead of being a blind diversion from veterinary and animal science into medicine, these advanced studies of human iPSC-derived neurons build a set of competences that allowed us, in a more competent way, to focus on novel aspects of more veterinary and agricultural relevance in the form of porcine and canine iPSCs. These types of animal stem cells are of biomedical importance for modeling of iPSC-based therapy in man, but in particular the canine iPSCs are also important for understanding and modeling canine diseases, as e.g. canine cognitive dysfunction, for the benefit and therapy of dogs.

Effect of sex on cryotolerance of bovine embryos produced in vitro

Male and female embryos are known to be different in developmental kinetics, metabolism, gene expression, and epigenetic patterns. Therefore, the objective of this study was to clarify whether the morphological criteria used to select embryos for cryopreservation lead to a deviation in the male:female ratio, and whether vitrification effects vary according to embryo sex. Initially, five sires were tested to evaluate the effect of the bull on embryo development, sex ratio, speed of development, and response to cryopreservation. Results showed that bulls affected (P < 0.05) embryo production, response to cryopreservation, and sex ratio. Then, one bull was selected, and used to produce embryos in vitro to characterize the responses of male and female embryos to vitrification. Results suggested that male and female embryos have the same morphological responses to vitrification, as no differences (P > 0.05) were observed between the two sexes in post-warming survival and re-expansion rates. However, their molecular responses as evaluated by gene expression (FOSL1, HSPB1, CASP3, CASP8, HSPA5, HSPA1A, G6PD, and PGK1) analysis indicated an effect of sex on vitrification; vitrified female embryos exhibited higher mRNA levels of HSPA1A, CASP3, and G6PD compared to their male counterparts. In conclusion, bulls affected embryo production, speed of development, sex ratio, and response to cryopreservation. Male and female embryos differed in their molecular responses to vitrification; and also, deviations in the male:female ratio when selecting embryos for cryopreservation were confirmed.

Effect of macromolecule supplement on nuclear and cytoplasmic maturation, cryosurvival and in vitro embryo development of dromedary camel oocytes

The current evaluation of oocyte vitro maturation (IVM) media has progressed toward more defined conditions in human and livestock. In this study, the replacement of fetal calf serum (FCS) with bovine serum albumin (BSA) and polyvinyl alcohol (PVA) was evaluated during IVM in dromedary camel. Nuclear maturation rates in presence of FCS and PVA were comparable (81.6 ± 1 and 75.5 ± 5%, respectively). BSA, whether used alone or in combination with FCS, significantly reduced nuclear maturation (51.6 ± 3.9 and 54.6 ± 1.1%, respectively), compared to FCS and PVA. BSA also increased the rates of chromosome aberrations compared to FCS and PVA (25.7 ± 7.4, 8.8 ± 2.3 and 6.0 ± 2.0%, respectively). IVM macromolecule differentially affected morphological aspects of cumulus expansion and FCS promoted the highest dissociation of cumulus cells, compared to all the other groups. FCS significantly increased mean lipid intensity of oocytes compared to BSA, FCS-BSA and PVA which could explain the lower cryo-survival of oocytes matured in presence of FCS compared to BSA and PVA (56.1 ± 5.2, 91.0 ± 19.5, and 87.8 ± 6.7%, respectively). Mitochondrial activity was not affected by macromolecules, but oocytes cultured with PVA had the best redox status, compared to other IVM groups. Cleavage was not affected by IVM macromolecule, but FCS promoted significantly higher rate of morula development (51.6 ± 5.2 vs. 33.6 ± 2.9% for PVA) and blastocyst development (36.8 ± 1.4 vs. 20.5 ± 2.0% for BSA). Although adding FCS during IVM supported highest hatching rate of the resulting blastocysts, differential cell number showed no long lasting effect of IVM macromolecules on blastocyst quality. Obtained results suggest the possibility to switch from undefined to more defined IVM systems for efficient in vitro maturation and subsequent vitrification of dromedary camel oocytes. Keywords: camel, oocyte maturation, protein supplement, cryosurvival.

Intracellular localisation of platelet-activating factor during mammalian embryo development in vitro: a comparison of cattle, mouse and human

Platelet-activating factor (PAF) is a well-known marker for embryo quality and viability. For the first time, we describe an intracellular localisation of PAF in oocytes and embryos of cattle, mice and humans. We showed that PAF is represented in the nucleus, a signal that was lost upon nuclear envelope breakdown. This process was confirmed by treating the embryos with nocodazole, a spindle-disrupting agent that, as such, arrests the embryo in mitosis, and by microinjecting a PAF-specific antibody in bovine MII oocytes. The latter resulted in the absence of nuclear PAF in the pronuclei of the zygote and reduced further developmental potential. Previous research indicates that PAF is released and taken up from the culture medium by preimplantation embryos invitro, in which bovine serum albumin (BSA) serves as a crucial carrier molecule. In the present study we demonstrated that nuclear PAF does not originate from an extracellular source because embryos cultured in polyvinylpyrrolidone or BSA showed similar levels of PAF in their nuclei. Instead, our experiments indicate that cytosolic phospholipase A2 (cPLA2) is likely to be involved in the intracellular production of PAF, because treatment with arachidonyl trifluoromethyl ketone (AACOCF3), a specific cPLA2 inhibitor, clearly lowered PAF levels in the nuclei of bovine embryos.

Oxidative stress differentially impacts male and female bovine embryos depending on the culture medium and the stress condition

Male and female embryos are known to differ for their metabolism and response to environmental factors very early in development. The present study aimed to evaluate the response to oxidative stress of male and female bovine embryos at the morula-blastocyst stages in terms of developmental rates, total cell number and apoptotic rates in two culture conditions. Embryos where cultured in a medium supplemented with either 5% fetal calf serum (FCS) or 4 mg/mL bovine serum albumin and a mixture of insulin, transferrin and selenium (BSA-ITS). Oxidative stress was applied at Day-5 post insemination (pi) by adding either AAPH or menadione to the culture medium, and blastocysts were analyzed at Day-7pi. The impact on development and blastocyst quality was dependent on the culture medium and the stress inducer but differed between male and female embryos. Male embryos resisted better to oxidative stress in FCS supplemented medium, no matter the stress inducer. Accordingly, the impact on blastocyst cell number tended to be higher in female blastocysts after stress induction with AAPH in FCS supplemented medium. On the other hand, in BSA-ITS supplemented medium, female embryos were more resistant to AAPH induced stress, while menadione had no impact on sex ratio. The weaker resistance of males to AAPH in this medium is in accordance with their trend to show a higher increase in apoptotic rates than females in this condition. In conclusion, this study shows that oxidative stress has differential impact on male and female bovine blastocysts depending on the culture condition and on the way oxidative stress is induced.

Choosing a culture medium for SCNT and iSCNT reconstructed embryos: from domestic to wildlife species

Over the past decades, in vitro culture media have been developed to successfully support IVF embryo growth in a variety of species. Advanced reproductive technologies, such as somatic cell nuclear transfer (SCNT), challenge us with a new type of embryo, with special nutritional requirements and altered physiology under in vitro conditions. Numerous studies have successfully reconstructed cloned embryos of domestic animals for biomedical research and livestock production. However, studies evaluating suitable culture conditions for SCNT embryos in wildlife species are scarce (for both intra- and interspecies SCNT). Most of the existing studies derive from previous IVF work done in conventional domestic species. Extrapolation to non-domestic species presents significant challenges since we lack information on reproductive processes and embryo development in most wildlife species. Given the challenges in adapting culture media and conditions from IVF to SCNT embryos, developmental competence of SCNT embryos remains low. This review summarizes research efforts to tailor culture media to SCNT embryos and explore the different outcomes in diverse species. It will also consider how these culture media protocols have been extrapolated to wildlife species, most particularly using SCNT as a cutting-edge technical resource to assist in the preservation of endangered species.

Modification of mitochondrial function, cytoplasmic lipid content and cryosensitivity of bovine embryos by resveratrol

Resveratrol is a potent activator of NAD-dependent deacetyltransferase sirtuin-1 (SIRT1) and affects lipid metabolism and ATP generation in somatic cells. In the present study, the effects of supplementing culture medium with resveratrol on lipid metabolism, ATP generation, and cryosensitivity of bovine in vitro produced embryos were investigated. Bovine early cleaved-stage embryos were cultured in medium containing 0 or 0.5 µM resveratrol for 1 or 5 days. Resveratrol treatment for both 1 day and 5 days increased the expression levels of SIRT1 and phosphorylated AMP-activated protein kinase (pAMPK) in the embryos. Furthermore, resveratrol treatment was effective to increase ATP generation and reduce lipid content of the embryos. The effects of resveratrol treatment were diminished by the SIRT1 inhibitor “EX527”, and the reduced lipid content was reversed by treatment with etomoxir (a potent inhibitor of beta-oxidation). Blastocysts developed after resveratrol treatment showed low levels reactive oxygen species and increased cryotolerance. These results demonstrate that resveratrol improves in vitro development of bovine embryos, while reducing cytoplasmic lipid content through activation of beta-oxidation, thereby effective for production of bovine blastocysts with enhanced cryotolerance.

Dynamic Pattern of HOXB9 Protein Localization during Oocyte Maturation and Early Embryonic Development in Mammals

Background

We previously showed that the homeodomain transcription factor HOXB9 is expressed in mammalian oocytes and early embryos. However, a systematic and exhaustive study of the localization of the HOXB9 protein, and HOX proteins in general, during mammalian early embryonic development has so far never been performed.

Results

The distribution of HOXB9 proteins in oocytes and the early embryo was characterized by immunofluorescence from the immature oocyte stage to the peri-gastrulation period in both the mouse and the bovine. HOXB9 was detected at all studied stages with a dynamic expression pattern. Its distribution was well conserved between the two species until the blastocyst stage and was mainly nuclear. From that stage on, trophoblastic cells always showed a strong nuclear staining, while the inner cell mass and the derived cell lines showed important dynamic variations both in staining intensity and in intra-cellular localization. Indeed, HOXB9 appeared to be progressively downregulated in epiblast cells and only reappeared after gastrulation had well progressed. The protein was also detected in the primitive endoderm and its derivatives with a distinctive presence in apical vacuoles of mouse visceral endoderm cells.

Conclusions

Together, these results could suggest the existence of unsuspected functions for HOXB9 during early embryonic development in mammals.

Effect of insulin-transferrin-selenium (ITS) and l-ascorbic acid (AA) during in vitro maturation on in vitro bovine embryo development

The aim of this study was to evaluate the effect of adding a combination of insulin, transferrin and selenium (ITS) and l-ascorbic acid (AA) during in vitro maturation (IVM) and in vitro culture (IVC) on in vitro embryo production. To verify the effect of the supplements, cleavage and blastocyst rates, embryo size and total cell number were performed. Embryonic development data, embryo size categorization and kinetics of maturation were analyzed by chi-squared test, while the total cell number was analyzed by a Kruskal-Wallis test (P < 0.05). When ITS was present during IVM, IVC or the entire culture, all treatments had a cleavage and blastocyst rates and embryo quality, similar to those of the control group (P < 0.05). Supplementation of IVM medium with ITS and AA for 12 h or 24 h showed that the last 12 h increased embryo production (51.6%; n = 220) on D7 compared with the control (39.5%; n = 213). However, no improvement was observed in blastocyst rate when less competent oocytes, obtained from 1-3 mm follicles, were exposed to ITS + AA for the last 12 h of IVM, with a blastocyst rate of 14.9% (n = 47) compared with 61.0% (n = 141) in the control group. The results suggest that the addition of ITS alone did not affect embryo production; however, when combined with AA in the last 12 h of maturation, there was improvement in the quantity and quality of embryos produced. Furthermore, the use of ITS and AA during IVM did not improve the competence of oocytes obtained from small follicles.

Effect of supplemented sericin on the development, cell number, cryosurvival and number of lipid droplets in cultured bovine embryos

Sericin was investigated as an alternative to fetal bovine serum (FBS) for bovine embryo culture. In vitro matured oocytes were developed using 0.05%, 0.1% or 0.15% sericin. The developmental rate, cryosurvival rate and blastulation time of these embryos were compared with those of embryos developed using 5% FBS. The number of lipid droplets was compared among the blastocysts developed using 5% FBS, using 0.05% sericin and in vivo. The rate of cleavage and blastocyst formation was similar among all groups. Blastulation occurred significantly earlier in the embryos developed using 5% FBS than in those developed using sericin at any concentration (P < 0.05). At 72 h after thawing, the cryosurvival rate of the blastocysts developed using 5% FBS and 0.05% sericin were significantly higher compared with those developed using 0.1% and 0.15% sericin (P < 0.05). The blastocysts developed using 0.05% sericin and in vivo produced a significantly fewer number of medium and large lipid droplets than those developed using 5% FBS. These results suggest that the blastocysts developed using 0.05% sericin show characteristics similar to those of the blastocysts developed in vivo and that the use of sericin as an alternative to FBS is feasible.

Suboptimal culture conditions induce more deviations in gene expression in male than female bovine blastocysts

Background

Since the development of in vitro embryo production in cattle, different supplements have been added to culture media to support embryo development, with serum being the most popular. However, the addition of serum during embryo culture can induce high birthweights and low viability in calves (Large Offspring Syndrome). Analysis of global gene expression in bovine embryos produced under different conditions can provide valuable information to optimize culture media for in vitro embryo production.

Results

We used RNA sequencing to examine the effect of in vitro embryo production, in either serum-containing or serum-free media, on the global gene expression pattern of individual bovine blastocysts. Compared to in vivo derived embryos, embryos produced in serum-containing medium had five times more differentially expressed genes than embryos produced in serum-free conditions (1109 vs. 207). Importantly, in vitro production in the presence of serum appeared to have a different impact on the embryos according to their sex, with male embryos having three times more genes differentially expressed than their female counterparts (1283 vs. 456). On the contrary, male and female embryos produced in serum-free conditions showed the same number (191 vs. 192) of genes expressed differentially; however, only 44 of those genes were common in both comparisons. The pathways affected by in vitro production differed depending on the type of supplementation. For example, embryos produced in serum-containing conditions had a lower expression of genes related to metabolism while embryos produced in serum-free conditions showed aberrations in genes involved in lipid metabolism.

Conclusions

Serum supplementation had a major impact on the gene expression pattern of embryos, with male embryos being the most affected. The transcriptome of embryos produced in serum-free conditions showed a greater resemblance to that of in vivo derived embryos, although genes involved in lipid metabolism were altered. Male embryos appeared to be most affected by suboptimal in vitro culture, i.e. in the presence of serum.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2393-z) contains supplementary material, which is available to authorized users.

Size of the Ovulatory Follicle Dictates Spatial Differences in the Oviductal Transcriptome in Cattle

In cattle, molecular control of oviduct receptivity to the embryo is poorly understood. Here, we used a bovine model for receptivity based on size of the pre-ovulatory follicle to compare oviductal global and candidate gene transcript abundance on day 4 of the estrous cycle. Growth of the pre-ovulatory follicle (POF) of Nelore (Bos indicus) cows was manipulated to produce two groups: large POF large corpus luteum (CL) group (LF-LCL; greater receptivity) and small POF-small CL group (SF-SCL). Oviductal samples were collected four days after GnRH-induced ovulation. Ampulla and isthmus transcriptome was obtained by RNA-seq, regional gene expression was assessed by qPCR, and PGR and ERa protein distribution was evaluated by immunohistochemistry. There was a greater abundance of PGR and ERa in the oviduct of LF-LCL animals thus indicating a greater availability of receptors and possibly sex steroids stimulated signaling in both regions. Transcriptomic profiles indicated a series of genes associated with functional characteristics of the oviduct that are regulated by the periovulatory sex steroid milieu and that potentially affect oviductal receptivity and early embryo development. They include tissue morphology changes (extra cellular matrix remodeling), cellular changes (proliferation), and secretion changes (growth factors, ions and metal transporters), and were enriched for the genes with increased expression in the LF-LCL group. In conclusion, differences in the periovulatory sex steroid milieu lead to different oviductal gene expression profiles that could modify the oviductal environment to affect embryo survival and development.

Maturation and fertilisation of sheep oocytes cultured in serum-free medium containing silk protein sericin

Sericin is a water-soluble component of silk and has been used as a biomaterial due to its antibacterial and ultraviolet radiation-resistant properties. This study was designed to evaluate the effect of sericin supplementation in a maturation medium on the meiotic competence and fertilisability of sheep oocytes. Cumulus-oocyte complexes (COCs) were cultured in TCM199 supplemented with sericin at various concentrations of 0 (control), 0.1, 0.25 and 0.5%, either with or without bovine serum albumin (BSA). When the COCs were matured without BSA, the supplementation of 0.1% sericin significantly increased the rates of maturation to metaphase II and the total fertilisation of oocytes compared with the other concentrations of sericin. When the COCs were matured with BSA, the beneficial effects of 0.1% sericin supplementation on the maturation and fertilisation of oocytes were not observed. Our findings indicate that supplementation with 0.1% sericin during maturation culture may improve the nuclear maturation and fertilisability of sheep oocytes. Moreover, it may be possible to replace BSA with sericin in chemically defined media without the risk of disease transmission.

Replacing serum in culture medium with albumin and insulin, transferrin and selenium is the key to successful bovine embryo development in individual culture

Individual culture of bovine embryos is usually associated with low blastocyst development. However, during preliminary experiments in our laboratory we observed high blastocyst development after individual embryo culture in a serum-free culture system. We therefore hypothesised that serum has a negative effect on embryos cultured individually whereas embryos in groups can counteract this. First, we determined whether the timing of removal of serum (during maturation or culture) had an influence on individual embryo development. The results clearly showed that removal of serum during embryo culture was the main contributing factor since high blastocyst development was observed after individual culture in synthetic oviductal fluid supplemented with bovine serum albumin (BSA) and insulin, transferrin and selenium (ITS), independent of the maturation medium. Second, we investigated whether an individual factor of the ITS supplement was essential for individual embryo development. We demonstrated that repeatable high blastocyst percentages were due to the synergistic effect of ITS. Finally, we investigated if a group-culture effect can still be observed under serum-free conditions. Group culture generated blastocysts with higher total cell numbers and less apoptosis. These data show that individual culture in serum-free conditions leads to high blastocyst development, but group culture still improves blastocyst quality.

Effect of resveratrol supplementation during culture on the quality and cryotolerance of bovine in vitro produced embryos

The aim of the study was to evaluate whether resveratrol supplementation of bovine culture medium improves in vitro blastocyst development, embryo cryotolerance and cell numbers. Abattoir-derived oocytes were matured and fertilized in vitro according to standard procedure. Twenty hours after IVF, zygotes were cultured in SOF medium, supplemented with 0 (control, n=439), 0.25μM (n=422), 0.5μM (n=447) and 1μM resveratrol (n=416). On Day 7 (IVF=Day 0) blastocysts were vitrified by cryotop in 16.5% ethylene glycol, 16.5% dimethyl sulfoxide and 0.5M sucrose. Development rate, i.e. the percentage of embryos resuming development to reach a more advanced stage, and hatching rate were evaluated after 24 and 48h culture. Blastocysts cultured with (0.5μM) and without resveratrol underwent differential staining to count inner cell mass (ICM) and trophectoderm (TE) cells. Resveratrol during culture did not increase blastocyst yields (57.1, 57.7, 59.2 and 46.6%, respectively in 0, 0.25, 0.5 and 1μM resveratrol). However, 0.5μM resveratrol improved embryo cryotolerance compared to the control, as indicated by higher development rates (67.3% vs 50.3%, respectively; P<0.01) and hatching rates (58.9% vs 30.9%, respectively; P<0.01) recorded after 48h post-warming culture. Blastocysts produced in the control and in 0.5μM resveratrol groups had similar numbers of ICM (34.1 and 36.4, respectively), TE (88.1 and 85.3, respectively) and total (122.2 and 121.7, respectively) cells. In conclusion, low levels of resveratrol during in vitro culture improve the quality of IVP bovine embryos, as indicated by their increased resistance to cryopreservation.

A chemically defined medium for rabbit embryo cryopreservation

This study evaluates a new synthetic substitute (CRYO3, Ref. 5617, Stem Alpha, France) for animal-based products in rabbit embryo cryopreservation solutions. This evaluation was performed using two approaches: a thermodynamic approach using differential scanning calorimetry and a biological approach using rabbit embryo slow-freezing. During the experiment, foetal calf serum (FCS) was used as a reference. Because FCS varies widely by supplier, three different FCS were selected for the thermodynamic approach. The rabbit embryo slow-freezing solutions were made from Dulbecco's phosphate buffer saline containing 1.5 M Dimethyl Sulfoxide and 18% (v.v(-1)) of CRYO3 or 18% (v.v(-1)) of FCS. These solutions were evaluated using four characteristics: the end of melting temperature, the enthalpy of crystallisation (thermodynamic approach) and the embryo survival rates after culture and embryo transfer (biological approach). In the thermodynamic approach, the solutions containing one of the three different FCS had similar mean thermodynamic characteristics but had different variabilities in the overall data with aberrant values. The solution containing CRYO3 had similar thermodynamic properties when compared to those containing FCS. Moreover, no aberrant value was measured in the solution containing CRYO3. This solution appears to be more stable than the solutions containing a FCS. In the biological approach, the in vitro embryo survival rates obtained with the solution containing CRYO3 (73.7% and 81.3%) and with the solution containing a FCS (77.6% and 71.9%) were similar (p = 0.7). Nevertheless, during the in vivo evaluation, the implantation rate (21.8%) and the live-foetuses rate (18.8%) of the CRYO3 group were significantly higher than the implantation rate (7.1%, p = 0.0002) and the live-foetuses rate (5.3%, p = 0.0002) of the FCS group. The pregnancy rate was also higher in the CRYO3 group compared to the FCS group (81.3% and 43.8%, respectively, p = 0.066). We conclude that CRYO3 can be used as a chemically defined substitute for animal-based products in rabbit embryo cryopreservation solutions.

Defined media optimization for in vitro culture of bovine somatic cell nuclear transfer (SCNT) embryos

The objective was to establish an efficient defined culture medium for bovine somatic cell nuclear transfer (SCNT) embryos. In this study, modified synthetic oviductal fluid (mSOF) without bovine serum albumin (BSA) was used as the basic culture medium (BCM), whereas the control medium was BCM with BSA. In Experiment 1, adding polyvinyl alcohol (PVA) to BCM supported development of SCNT embryos to blastocyst stage, but blastocyst formation rate and blastocyst cell number were both lower (P < 0.05) compared to the undefined group (6.1 vs. 32.6% and 67.3 ± 3.4 vs. 109.3 ± 4.5, respectively). In Experiment 2, myo-inositol, a combination of insulin, transferrin and selenium (ITS), and epidermal growth factor (EGF) were added separately to PVA-supplemented BCM. The blastocyst formation rate and blastocyst cell number of those three groups were dramatically improved compared with that of PVA-supplemented group in Experiment 1 (18.5, 23.0, 24.1 vs. 6.1% and 82.7 ± 2.0, 84.3 ± 4.2, 95.3 ± 3.8 vs. 67.3 ± 3.4, respectively, P < 0.05), but were still lower compared with that of undefined group (33.7% and 113.8 ± 3.4, P < 0.05). In Experiment 3, when a combination of myo-inositol, ITS and EGF were added to PVA-supplemented BCM, blastocyst formation rate and blastocyst cell number were similar to that of undefined group (30.4 vs. 31.1% and 109.3 ± 4.4 vs. 112.0 ± 3.6, P > 0.05). In Experiment 4, when blastocysts were cryopreserved and subsequently thawed, there were no significant differences between the optimized defined group (Experiment 3) and undefined group in survival rate and 24 and 48 h hatching blastocyst rates. Furthermore, there were no significant differences in expression levels of H19, HSP70 and BAX in blastocysts derived from optimized defined medium and undefined medium, although the relative expression abundance of IGF-2 was significantly decreased in the former. In conclusion, a defined culture medium containing PVA, myo-inositol, ITS, and EGF supported in vitro development of bovine SCNT embryos.

Beneficial effect of two culture systems with small groups of embryos on the development and quality of in vitro-produced bovine embryos

Currently, in vitro-produced embryos derived by ovum pick up (OPU) and in vitro fertilization (IVF) technologies represent approximately one-third of the embryos worldwide in cattle. Nevertheless, the culture of small groups of embryos from an individual egg donor is an issue that OPU-IVF laboratories have to face. In this work, we tested whether the development and quality of the preimplantation embryos in vitro cultured in low numbers (five embryos) could be improved by the addition of epidermal growth factor, insulin, transferrin and selenium (EGF-ITS) or by the WOW system. With this aim, immature oocytes recovered from slaughtered heifers were in vitro matured and in vitro fertilized. Presumptive zygotes were then randomly cultured in four culture conditions: one large group (LG) (50 embryos/500 μl medium) and three smaller groups [five embryos/50 μl medium without (control) or with EGF-ITS (EGF-ITS) and five embryos per microwell in the WOW system (WOW)]. Embryos cultured in LG showed a greater ability to develop to blastocyst stage than embryos cultured in smaller groups, while the blastocyst rate of WOW group was significantly higher than in control. The number of cells/blastocyst in LG was higher than control or WOW, whereas the apoptosis rate per blastocyst was lower. On the other hand, the addition of EGF-ITS significantly improved both parameters compared to the control and resulted in similar embryo quality to LG. In conclusion, the WOW system improved embryo development, while the addition of EGF-ITS improved the embryo quality when smaller groups of embryos were cultured.

Forskolin effect on the cryosurvival of in vitro-produced bovine embryos in the presence or absence of fetal calf serum

The objective of this study was to assess the viability and cryotolerance of zebu embryos produced in vitro with or without the addition of fetal calf serum (FCS) and forskolin (F). Embryos produced in vivo were used as a control. Presumptive zygotes were cultured in modified synthetic oviductal fluid supplemented with amino acids (SOFaa), bovine serum albumin (BSA) and with (2.5%) or without (0%) FCS. On day 6 of growth, the embryos from each group were divided into treatments with or without 10 μM F to induce embryonic lipolysis, comprising a total of four experimental groups: 2.5% FCS, 0% FCS, 2.5% + F and 0% + F. For vitrification, embryos were exposed to vitrification solution 1 (5 M EG (ethylene glycol)) for 3 min and then transferred to vitrification solution 2 (7 M EG, 0.5 M galactose solution and 18% (w/v) Ficoll 70) before being introduced to liquid nitrogen. The presence of FCS in the culture medium resulted in the production of embryos with a similar rate of damaged cells compared with in vivo-produced embryos. After vitrification, the 2.5% FCS group had a significantly higher rate of damaged cells when compared with the other groups (P < 0.05). The results of this experiment indicated that the omission of FCS and the addition of forskolin do not have deleterious effect on embryo production rates. In addition, embryos produced in the presence of FCS had greater sensitivity to cryopreservation, but this effect was reversed when forskolin was added to the medium, which improved embryo survival without affecting embryo development and quality after vitrification.

Crucial surviving aspects for vitrified in vitro-produced bovine embryos

The objective of the present study was to correlate some parameters (cleavage, blastocyst production, quality degree score, total cell number, fresh apoptosis and lipid content) with embryo survival after cryopreservation. A total of 1727 in vitro-produced bovine blastocysts were used to establish the parameters (mean ± standard error of the mean (SEM)) for cleavage (85.6 ± 0.8), blastocyst production (39.9 ± 1.4), quality degree score (1.6 ± 0.1), total cell number (140.1 ± 2.9), fresh apoptosis (20.8 ± 1.1) and lipid content (21.3 ± 0.8 droplets). On the same way 1316 blastocysts were vitrified for the determination of post-cryopreservation embryo survival (49.4 ± 1.9). Fresh apoptosis rate and total lipid droplets value were correlated (P < 0.05) with embryo survival after cryopreservation (r = 0.91 and r = 0.59; respectively). However, cleavage, blastocyst production, quality degree score and total cell number were not correlated (P > 0.05) with embryo cryotolerance (r = 0.23, r = 0.38, r = 0.22 and r = 0.28; respectively). Therefore, the increased lipid content was moderately correlated with apoptosis in vitrified blastocysts. On the other hand, increased apoptosis in fresh blastocysts was strongly correlated with apoptosis in vitrified blastocysts, which indicated that the apoptosis rate in fresh embryos was a better parameter than the lipid content to predict post-vitrification embryo survival.

Unravelling the needs of singly in vitro-produced bovine embryos: from cumulus cell co-culture to semi-defined, oil-free culture conditions

Producing bovine in vitro embryos individually is a challenge as it generally leads to impaired embryo development. Earlier research optimised a single embryo in vitro production (IVP) protocol using serum, cumulus cells and oil during culture. As some of these factors are undesirable in certain circumstances, the present study investigated their necessity and possible interactions, and defined their role during single-embryo culture. Although the cumulus cell monolayer produced progesterone, it appeared not to be a key factor in supporting single-embryo development. Because in vitro culture in large medium volumes was shown to impair single-embryo development, two new oil-free culture protocols were tested. Using a 30-µL droplet of medium in 96-well plates with a small surface area resulted in comparable blastocyst rates to those obtained under oil. When serum was used, co-culture with cumulus cells seems necessary, leading to consistently high blastocyst rates. Finally, a serum-free, oil-free culture system using insulin, transferrin, selenium and BSA resulted in embryos with similar total cell numbers and apoptotic cell ratios, but blastocyst rates did not equal those obtained with serum and co-culture. This research additionally stresses the fact that specific interaction mechanisms between somatic cells and a developing in vitro embryo are far from unravelled.

Effects of different cryopreservation methods on post-thaw culture conditions of in vitro produced bovine embryos

The aim of this work was to evaluate the effect of cryopreservation protocols on subsequent development of in vitro produced bovine embryos under different culture conditions. Expanded in vitro produced blastocysts (n = 600) harvested on days 7-9 were submitted to controlled freezing [slow freezing group: 10% ethylene glycol (EG) for 10 min and 1.2°C/min cryopreservation]; quick-freezing [rapid freezing group: 10% EG for 10 min, 20% EG + 20% glycerol (Gly) for 30 s]; or vitrification [vitrification group: 10% EG for 10 min, 25% EG + 25% Gly for 30 s] protocols. Control group embryos were not exposed to cryoprotectant or cryopreservation protocols and the hatching rate was evaluated on day 12 post-insemination. In order to evaluate development, frozen-thawed embryos were subjected to granulosa cell co-culture in TCM199 or SOFaa for 4 days. Data were analyzed by PROC MIXED model using SAS Systems for Windows®. Values were significant at p < 0.05. The hatching rate of the control group was 46.09%. In embryos cultured in TCM199, slow freezing and vitrification group hatching rates were 44.65 ± 5.94% and 9.43 ± 6.77%, respectively. In embryos cultured in SOFaa, slow freezing and vitrification groups showed hatching rates of 11.65 ± 3.37 and 8.67 ± 4.47%, respectively. In contrast, the rapid freezing group embryos did not hatch, regardless of culture medium. The slow freezing group showed higher hatching rates than other cryopreservation groups. Under such conditions, controlled freezing (1.2°C/min) can be an alternative to cryopreservation of in vitro produced bovine embryos.

Single embryo and oocyte lipid fingerprinting by mass spectrometry

Methods used for lipid analysis in embryos and oocytes usually involve selective lipid extraction from a pool of many samples followed by chemical manipulation, separation and characterization of individual components by chromatographic techniques. Herein we report direct analysis by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) of single and intact embryos or oocytes from various species. Biological samples were simply moisturized with the matrix solution and characteristic lipid (represented by phosphatidylcholines, sphingomyelins and triacylglycerols) profiles were obtained via MALDI-MS. As representative examples, human, bovine, sheep and fish oocytes, as well as bovine and insect embryos were analyzed. MALDI-MS is shown to be capable of providing characteristic lipid profiles of gametes and embryos and also to respond to modifications due to developmental stages and in vitro culture conditions of bovine embryos. Investigation in developmental biology of the biological roles of structural and reserve lipids in embryos and oocytes should therefore benefit from these rapid MALDI-MS profiles from single and intact species.

Elongation and gene expression in bovine cloned embryos transferred to temporary recipients

Elongated embryos provide a unique source of information about trophoblastic differentiation, gene expression and maternal-embryonic interactions; however they are difficult and costly to obtain, especially elongated cloned embryos. One alternative is their production in heterologous temporary recipients such as sheep and goats. We aimed to produce elongated bovine cloned embryos using heterologous transfer to temporary recipients. Day-7 cloned cattle blastocysts were transferred to the uteri of ewes and goats and recovered as elongated structures at day 17. We evaluated elongation, length, presence of embryonic disc and expression of several important genes for embryonic development. We also produced homologous (cloned cattle embryos transferred into cattle uteri). Cloned bovine blastocysts were able to proceed with preimplantation development through elongation with high efficiency despite the species to which they were transferred. In qualitative and quantitative RT-PCR experiments we found differences in the pattern of gene expression among embryos recovered from different species. Sox2, Nanog and FGF-4 were markedly deregulated. No previous reports about the expression pattern of the studied genes had been published for elongated bovine cloned embryos produced in intermediate recipients, furthermore, the pattern of expression of Nanog, Oct4, Eomes, Cdx2, IFN-tau, Dicer, FGF-4 and Sox2 shown here are novel for elongated cloned bovine embryos created by hand-made cloning. Our data confirmed that sheep and goats can be used as temporary recipients. This model could serve as a basis for further research on gene expression and cellular changes during bovine peri-implantation development.

Plant protein hydrolysates (plant peptones) as substitutes for animal proteins in embryo culture medium

The aim of the present study was to improve the sanitary quality of in vitro-produced bovine embryos by using plant protein hydrolysates (plant peptones) as substitutes for animal proteins. Peptones were compared with bovine serum albumin (BSA) as the protein source in synthetic oviduct fluid medium and the quality of the resulting embryos was determined. Two batches of peptones (wheat and cotton) were selected on the basis of their anti-oxidant properties. When added to the culture medium, both peptones (at 0.56 mg mL–1 for cotton peptone and at 0.18 mg mL–1 for wheat peptone) led to similar developmental and hatching rates compared with 4 mg mL–1 BSA and embryos were equally resistant to freezing and able to elongate after transfer. Surprisingly, a significant decrease in reduced glutathione (GSH) content was observed when embryos were produced with plant peptone instead of BSA. Supplementation of the culture medium with precursors of GSH (cysteine and β-mercaptoethanol) significantly increased the GSH content. A shift of the sex ratio towards male embryos was seen for Day 8 embryos cultured with wheat peptone, whereas no shift was observed for embryos cultured in the presence of BSA or polyvinylpyrrolidone. In conclusion, culture with plant peptones enables embryos to be obtained at a similar rate and of similar quality to that seen following the use of BSA. The use of the plant peptones increased the sanitary quality of the embryos and decreased the cost of embryo production.