Effects of co-culture and embryo number on the in vitro development of bovine embryos

Individually Cultured Bovine Zygotes Successfully Develop to the Blastocyst Stage in an Extremely Confined Environment

The possibility of detecting the developmental competence of individually cultured embryos through analysis of spent media is a major current trend in an ART setting. However, individual embryo culture is detrimental compared with high-density group culture due to the reduced concentration of putative embryotropins. The main aim of this study was to identify an individual culture system that is not detrimental over high-density group culture in the bovine model. Blastocyst rates and competence were investigated in a conventional (GC) group, semi-confined group (MG), and individual culture (MS) in a commercial microwell device. Main findings showed that: (1) individual embryos can be continuously cultured for 7 days in ~70 nL microwells (MS) without detrimental effects compared with the GC and MG; (2) MS and MG blastocysts had a reduced number of TUNEL-positive cells compared to GC blastocysts; (3) though blastocyst mean cell numbers, mitochondrial activity, and lipid content were not different among the three culture conditions, MS blastocysts had a higher frequency of small-sized lipid droplets and a reduced mean droplet diameter compared with GC and MG blastocysts. Overall, findings open the way to optimize the development and competence of single embryos in an ART setting.

Current knowledge and the future potential of extracellular vesicles in mammalian reproduction

Extracellular vesicles (EVs), which contain various functional classes of vesicles, namely exosomes, microvesicles, and apoptotic bodies, represent the major nano-shuttle to transfer bioactive molecules from donor to recipient cells to facilitate cell-to-cell communication in the follicular, oviduct, and uterine microenvironments. In addition to transferring various molecular cargos in the form of miRNAs, mRNAs, proteins, lipids, and DNA molecules, the relative proportion of those molecular cargos in the reproductive fluids can be associated with the physiological and pathological condition of the host animal. Inside the follicle, EV-mediated circulation of miRNAs has been reported to be associated with the growth status of the enclosed oocytes, the metabolic status, and the advanced maternal aging of the animal. Importantly, EVs have the potential to protect their cargo molecules from extracellular degradation or modification while travelling to the recipient cells. This fact together with the enormous availability in almost all biological fluids and spent culture media make them attractive in the search for biomarkers of oocyte/embryo developmental competence, receptive maternal environment and a multitude of reproductive pathophysiological conditions. One of the key factors that have contributed to the lower efficiency of assisted reproductive technologies (ART) is the absence of several maternal in vivo factors in the ART procedures. For this, several studies have been conducted to supplement various components present in the follicular and oviductal fluids into the existing ART procedures and significant positive impacts have been observed in terms of embryo cleavage rate, blastocyst rate, resistance to stress, and survival after cryopreservation. The potential of EVs in shuttling protective messages against environmental and physiological stressors has been evidenced. The effective use of the EV-coupled molecular signals against stress-associated conditions has the potential to pave the path for the application of these protective signals against oxidative stress-associated pathological conditions including PCOS, ageing, and endometritis. In this review, we provide current knowledge and potential future use of EVs as remedies in reproductive pathophysiological conditions, mainly in follicular and oviductal microenvironments.

Human amniotic membrane stem cells' conditioned medium has better support for in-vitro production of bovine embryos than FBS

Apart from oocyte quality, the media used has a significant effect on the production and quality of blastocysts produced in vitro. This study was designed to evaluate the replacement of serum with human amniotic membrane stem cells' conditioned medium (hAMSCs-CM) during bovine embryo culture on the quantity and quality of produced blastocysts. The in-vitro-produced embryos on the third day of IVC were randomly divided into the following culture groups: SOFaa + 5% FBS (Control), SOFaa + 5% hAMSCs-CM (5% CM), SOFaa + 2.5% hAMSCs-CM + 2.5% FBS (2.5% CM) and SOFaa + hAMSC co-culture (co-culture). The blastocyst and hatching rates, blastocyst cells number (the number of trophectoderm, inner cell mass and total cells), and the expression of some developmentally important genes (OCT4, PLAC8 and COX2 genes) in the treated groups, especially in the 5% CM, compared to the control had improved (p < .05). No significant difference was observed between groups for viability and hatching rate in vitrified-warmed blastocysts. Due to the positive effect of hAMSCs' conditioned medium (hAMSCs-CM) on blastocyst production, as well as its ease of preparation and the need to avoid the transmission of microbial contamination to the culture medium, hAMSCs-CM can be used as a suitable alternative to FBS during 3 to 8 days of bovine embryo culture.

Does the number of embryos loaded on a single cryo-carrier affect post-vitrification survival rate?

BACKGROUND

We aimed to assess whether the survival rate of embryos is influenced by the number of embryos/oocytes loaded on a single cryo-carrier during vitrification.

METHODS

This was a retrospective study that included 974 patients who underwent thawing of 1896 embryo-warming cycles between September 2016 and January 2020. A distinct analysis was made for cleavage stage embryos (2-10-cell stage) and blastocysts. For vitrification, embryos were placed in a Cryotop™ open device using a SAGE vitrification kit following the manufacturer's instructions. Warming was carried using a SAGE warming vitrification kit according the manufacturer's instructions.

RESULTS

Total post-vitrification survival rates of embryos at the cleavage stage or blastocyst stage was 94.8%. At the cleavage stage, cryo-preserving three embryos per single cryo-carrier gave the highest full intact embryo survival rate (91.5%) compared with one or two embryo(s) per single cryo-carrier (85.7%, P < 0.0002 and 87.3%, P < 0.004). Conversely, post warmed full intact blastocyst survival rate for two blastocysts was significantly lower compared with one blastocyst (76.7% vs. 87.9%, P < 0.0193) per single cryo-carrier.

CONCLUSION

Post-thawing survival rate following vitrification is affected by the number of embryos per single cryo-carrier undergoing the vitrification equilibration phase, with the optimum number of three cleaved embryos or one blastocyst per single cryo-carrier. Further studies are required to determine the optimum number of cleaved embryos or blastocysts that should be loaded onto a single cryo-carrier vitrification device.

Sex differences in single IVF-derived bovine embryo cultured in chemically defined medium

Single embryo culture is essential for culturing embryos derived from few oocytes obtained from elite cows through ultrasonography guidance. Bovine in vitro fertilization (IVF) and individual embryo culture is a challenge as it generally leads to impaired embryo development. In this study, we explored the embryonic development and the sex ratio of IVF-derived bovine embryo cultured individually in chemically defined two-step culture medium. Total 63 cumulus-oocyte complexes were collected, in vitro matured, in vitro fertilized and the resultant fertilized oocytes were randomly cultured individually (4 trials, 15–16 oocytes each) in microdrops of 5 µL of a chemically defined two-step culture medium. Blastocysts were counted in every trial (n = 32, 50.79%) and all of them were used for both genomic DNA and total RNA extraction, cDNA synthesis and PCR using specific primers for GAPDH, GDP6, XIST and SRY genes. Results showed significant difference in expression of XIST (positive expression in 11 blastocysts) and SRY (positive expression in 21 blastocysts) mRNAs, P < .05. This result supports the hypothesis of sexual dimorphism among the pre-implantation in vitro produced embryos and provides an efficient medium for single bovine embryos in vitro production.

Isolation and Characterization of Functionally Active Extracellular Vesicles from Culture Medium Conditioned by Bovine Embryos In Vitro

Extracellular vesicles (EVs) play a possible role in cell–cell communication and are found in various body fluids and cell conditioned culture media. The aim of this study was to isolate and characterize EVs in culture medium conditioned by bovine embryos in group and to verify if these EVs are functionally active. Initially, ultracentrifuged bovine serum albumin (BSA) containing medium was selected as suitable EV-free embryo culture medium. Next, EVs were isolated from embryo conditioned culture medium by OptiPrep^TM density gradient ultracentrifugation. Isolated EVs were characterized by nanoparticle tracking analysis, western blotting, transmission, and immunoelectron microscopy. Bovine embryo-derived EVs were sizing between 25–230 nm with an average concentration of 236.5 ± 1.27 × 10⁸ particles/mL. Moreover, PKH67 EV pre-labeling showed that embryo-secreted EVs were uptaken by zona-intact bovine embryos. Since BSA did not appear to be a contaminating EV source in culture medium, EV functionality was tested in BSA containing medium. Individual embryo culture in BSA medium enriched with EVs derived from conditioned embryo culture medium showed significantly higher blastocyst rates at day 7 and 8 together with a significantly lower apoptotic cell ratio. In conclusion, our study shows that EVs play an important role in inter embryo communication during bovine embryo culture in group.

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

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

In vitro production of bovine embryos derived from individual donors in the Corral® dish

Background

Since the identity of the embryo is of outmost importance during commercial in vitro embryo production, bovine oocytes and embryos have to be cultured strictly per donor. Due to the rather low yield of oocytes collected after ovum pick-up (OPU) per individual cow, oocyte maturation and embryo culture take place in small groups, which is often associated with inferior embryo development. The objective of this study was to improve embryonic development in small donor groups by using the Corral^® dish. This commercial dish is designed for human embryo production. It contains two central wells that are divided into quadrants by a semi-permeable wall. In human embryo culture, one embryo is placed per quadrant, allowing individual follow-up while embryos are exposed to a common medium. In our study, small groups of oocytes and subsequently embryos of different bovine donors were placed in the Corral^® dish, each donor group in a separate quadrant.

Results

In two experiments, the Corral^® dish was evaluated during in vitro maturation (IVM) and/or in vitro culture (IVC) by grouping oocytes and embryos of individual bovine donors per quadrant. At day 7, a significantly higher blastocyst rate was noted in the Corral^® dish used during IVM and IVC than when only used during IVM (12.9% ± 2.10 versus 22.8% ± 2.67) (P < 0.05). However, no significant differences in blastocyst yield were observed anymore between treatment groups at day 8 post insemination.

Conclusions

In the present study, the Corral^® dish was used for in vitro embryo production (IVP) in cattle; allowing to allocate oocytes and/or embryos per donor. As fresh embryo transfers on day 7 have higher pregnancy outcomes, the Corral^® dish offers an added value for commercial OPU/IVP, since a higher blastocyst development at day 7 is obtained when the Corral^® dish is used during IVM and IVC.

Combined effects of individual culture and atmospheric oxygen on preimplantation mouse embryos in vitro

Embryos are routinely cultured individually, although this can reduce blastocyst development. Culture in atmospheric (20%) oxygen is also common, despite multiple detrimental effects on embryos. Although frequently occurring together, the consequences of this combination are unknown. Mouse embryos were cultured individually or grouped, under physiological (5%) or atmospheric (20%) oxygen. Embryos were assessed by time-lapse and blastocyst cell allocation. Compared with the control group (5% oxygen group culture), 5-cell cleavage (t5) was delayed in 5% oxygen individual culture and 20% oxygen group culture (59.91 ± 0.23, 60.70 ± 0.29, 63.06 ± 0.32 h post-HCG respectively, P < 0.05). Embryos in 20% oxygen individual culture were delayed earlier (3-cell cleavage), and at t5 cleaved later than embryos in other treatments (66.01 ± 0.40 h, P < 0.001), this delay persisting to blastocyst hatching. Compared with controls, hatching rate and cells per blastocyst were reduced in 5% oxygen single culture and 20% oxygen group culture (134.1 ± 3.4, 104.5 ± 3.2, 73.4 ± 2.2 cells, P < 0.001), and were further reduced in 20% oxygen individual culture (57.0 ± 2.8 cells, P < 0.001), as was percentage inner cell mass. These data indicate combining individual culture and 20% oxygen is detrimental to embryo development.

Molecular markers for oocyte competence in bovine cumulus cells

This study aimed to quantify the expression of candidate genes in cumulus cells (CCs) from cumulus-oocyte complexes (COCs) with high and low potential for in vitro development up to the blastocyst stage. First, the effects of individual culture and biopsy on embryo development were evaluated. Individuals cultured using the well of the well system were compared with individuals cultured in 20 μL droplets (microdroplets) and those cultured in groups (control). Blastocyst rates were lower for the individual culture systems (P < 0.05; well of the well = 17.9%, n = 95; microdrop = 26.3%, n = 95) than for the control group (45.0%, n = 209). Second, the effects of biopsy on embryo production were compared between the control and microdroplet cultures, and no effects (P > 0.05) were observed for either group. Finally, the expression profiles of glypican 4 (GPC4), IGF4-binding protein, follicle-stimulating hormonereceptor, growth hormone receptor, epidermal growth factor receptor, fibroblast growth factor 11, solute carrier family 2 member 1, solute carrier family 2 member 3,sprouty homolog 1, versican, and keratin protein 8 in CCs obtained by biopsy were quantified by real-time polymerase chain reaction. Cumulus cells were categorized on the basis of the fates of the COCs: expanded blastocyst, cleaved and arrested, and uncleaved. The GPC4 gene was overexpressed (P = 0.007) in CCs from oocytes that formed embryos compared with those that produced cleaved and arrested embryos. We concluded that individual culture reduced blastocyst production; however, biopsy did not affect embryo development. The profile of GPC4 expression can be used as a marker to distinguish COCs with potential for embryo development from those with limited developmental potential.

Autocrine embryotropins revisited: how do embryos communicate with each other in vitro when cultured in groups?

In the absence of the maternal genital tract, preimplantation embryos can develop in vitro in culture medium where all communication with the oviduct or uterus is absent. In several mammalian species, it has been observed that embryos cultured in groups thrive better than those cultured singly. Here we argue that group-cultured embryos are able to promote their own development in vitro by the production of autocrine embryotropins that putatively serve as a communication tool. The concept of effective communication implies an origin, a signalling agent, and finally a recipient that is able to decode the message. We illustrate this concept by demonstrating that preimplantation embryos are able to secrete autocrine factors in several ways, including active secretion, passive outflow, or as messengers bound to a molecular vehicle or transported within extracellular vesicles. Likewise, we broaden the traditional view that inter-embryo communication is dictated mainly by growth factors, by discussing a wide range of other biochemical messengers including proteins, lipids, neurotransmitters, saccharides, and microRNAs, all of which can be exchanged among embryos cultured in a group. Finally, we describe how different classes of messenger molecules are decoded by the embryo and influence embryo development by triggering different pathways. When autocrine embryotropins such as insulin-like growth factor-I (IGF-I) or platelet activating factor (PAF) bind to their appropriate receptor, the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) pathway will be activated which is important for embryo survival. On the other hand, the mitogen-activated protein kinase (MAPK) pathway is activated when compounds such as hyaluronic acid and serotonin bind to their respective receptors, thereby acting as growth factors. By activating the peroxisome-proliferator-activated receptor family (PPAR) pathway, lipophilic autocrine factors such as prostaglandins or fatty acids have both survival and anti-apoptotic functions. In conclusion, considering different types of messenger molecules simultaneously will be crucial to understanding more comprehensively how embryos communicate with each other in group-culture systems. This approach will assist in the development of novel media for single-embryo culture.

The effects of chemical and physical factors on mammalian embryo culture and their importance for the practice of assisted human reproduction

BACKGROUND

Although laboratory procedures, along with culture media formulations, have improved over the past two decades, the issue remains that human IVF is performed in vitro (literally 'in glass').

METHODS

Using PubMed, electronic searches were performed using keywords from a list of chemical and physical factors with no limits placed on time. Examples of keywords include oxygen, ammonium, volatile organics, temperature, pH, oil overlays and incubation volume/embryo density. Available clinical and scientific evidence surrounding physical and chemical factors have been assessed and presented here.

RESULTS AND CONCLUSIONS

Development of the embryo outside the body means that it is constantly exposed to stresses that it would not experience in vivo. Sources of stress on the human embryo include identified factors such as pH and temperature shifts, exposure to atmospheric (20%) oxygen and the build-up of toxins in the media due to the static nature of culture. However, there are other sources of stress not typically considered, such as the act of pipetting itself, or the release of organic compounds from the very tissue culture ware upon which the embryo develops. Further, when more than one stress is present in the laboratory, there is evidence that negative synergies can result, culminating in significant trauma to the developing embryo. It is evident that embryos are sensitive to both chemical and physical signals within their microenvironment, and that these factors play a significant role in influencing development and events post transfer. From the viewpoint of assisted human reproduction, a major concern with chemical and physical factors lies in their adverse effects on the viability of embryos, and their long-term effects on the fetus, even as a result of a relatively brief exposure. This review presents data on the adverse effects of chemical and physical factors on mammalian embryos and the importance of identifying, and thereby minimizing, them in the practice of human IVF. Hence, optimizing the in vitro environment involves far more than improving culture media formulations.

Epidermal growth factor improves developmental competence and embryonic quality of singly cultured domestic cat embryos

This study examined the influence of EGF on the expression of EGF receptors (EGFR) and developmental competence of embryos cultured individually versus those cultured in groups. Cat oocytes were in vitro matured and fertilized (IVM/IVF), and cleaved embryos were randomly assigned to one of seven culture conditions: one group each in which embryos were subjected to group culture supplemented with or without 5 ng/ml EGF and five groups in which embryos were subjected to single-embryo culture supplemented with EGF (0, 5, 25, 50 or 100 ng/ml). Morulae, blastocysts and hatching blastocysts were assessed at days 5 and 7; post IVF, respectively, and total blastocyst cell numbers were assessed at day 7. Relative mRNA expressions of EGFR of 2–4-cell embryos, 8–16-cell embryos, morulae and blastocysts cultured in groups or singly with or without EGF supplementation were examined. OCT3/4 and Ki67 in blastocysts derived from the group or single-embryo culture systems with or without EGF supplementation were localized. A higher rate of embryos cultured in groups developed to blastocysts than individually incubated cohorts. Although EGF increased blastocyst formation in the single-embryo culture system, EGF did not affect embryo development in group culture. Expression levels of EGFR decreased in morulae and blastocysts cultured with EGF. An increased ratio of Ki67-positive cells to the total number of cells in the blastocyst was observed in singly cultured embryos in the presence of EGF. However, EGF did not affect the expression of OCT3/4. These findings indicate that EGF enhanced developmental competence of cat embryos cultured singly by stimulating cell proliferation and modulating the EGFR expression at various developmental stages.

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.

Use of a novel polydimethylsiloxane well insert to successfully mature, culture and identify single porcine oocytes and embryos

The objective of this study was to evaluate the efficacy of a novel polydimethylsiloxane (PDMS) well-insert system for oocyte in vitro maturation (IVM) and in vitro embryo culture (IVC) in pigs. The PDMS well inserts, consisting of multiple microwells with connecting microchannels, resulted in equivalent blastocyst development compared with standard microdrop culture for IVC. These PDMS well inserts were then evaluated for IVM or IVC in a rocking versus static environment. The rocking environment during both oocyte IVM and embryo culture had detrimental effects on oocyte and embryo development compared with a static environment. Importantly, blastocyst development of oocytes and embryos cultured in the PDMS well inserts in the static environment was equivalent to that of standard microdrops. Further analysis of transcript abundance in blastocysts produced from these different environments revealed that the PDMS well-insert system may produce more viable embryos. In conclusion, this PDMS well-insert system can successfully mature oocytes and culture embryos in an individually-identifiable manner without compromising, and perhaps enhancing, developmental potential.

Individual commitment to a group effect: strengths and weaknesses of bovine embryo group culture

Recently, new culture devices such as Corral and Primo Vision dishes have been designed for the culture of human embryos to allow the combination of group culture plus follow-up of individual embryos. Bovine inseminated oocytes were allocated to Primo Vision dishes, Corral dishes, individual culture or classical group culture. Blastocyst development in Primo Vision dishes was similar to classical group culture (34.3 and 39.0% respectively), and better than Corral dishes or individual culture (28.9 and 28.5% respectively). In Primo Vision dishes, a higher number of ‘slow’ embryos developed to the blastocyst stage compared with their individually cultured counterparts, while no differences were observed for ‘fast’ embryos. ‘Slow’ embryos in a ‘standard drop’ had a higher chance of becoming a blastocyst compared with individual culture (OR: 2.3), whereas blastulation of ‘fast’ embryos was less efficient in a ‘delayed drop’ than in individual culture (OR: 0.3). The number of non-cleaved embryos in Primo Vision dishes did not negatively influence blastocyst development. Likewise, removing non-cleaved embryos (NC removed) and regrouping the cleaved embryos afterwards (ReGR) did not affect blastocyst development and quality compared with group culture in Primo Vision dishes (CTRL, 31.6%, NC removed, 29.3% and ReGR, 29.6%). The experiments revealed that group culture of bovine embryos in Primo Vision dishes is superior to individual culture, primarily because of the higher blastocyst rate achieved by slow embryos. Non-cleaved or arrested embryos do not hamper the ability of co-cultured bovine embryos to reach the blastocyst stage in group culture.

The efficacy of the well of the well (WOW) culture system on development of bovine embryos in a small group and the effect of number of adjacent embryos on their development

The aim of the present study was to clarify the efficacy of the well of the well (WOW) culture system for a small number of embryos and the effect of number of adjacent embryos in a WOW dish on blastocyst development. In conventional droplet culture, embryos in the small-number group (5-6 embryos/droplet) showed low blastocyst development compared with a control group (25-26 embryos/droplet). However, small and large numbers of embryos (5-6 and 25 embryos, respectively) in a WOW dish showed no significant differences in cleavage, blastocyst rates, and mean cell number in blastocysts compared with the control group (25-30 embryos/droplet). In addition, the number of adjacent embryos in a WOW dish did not affect the development to blastocysts and cell number in blastocysts. In conclusion, a WOW dish can provide high and stable blastocyst development in small group culture wherever embryos are placed in microwells of the WOW dish.

Identification of bovine embryos cultured in groups by attachment of barcodes to the zona pellucida

The low number of oocytes collected from unstimulated donors by ovum pick-up means that embryos produced from each individual female have to be cultured individually or in very small groups. However, it has been demonstrated that single-embryo culture is less efficient than embryo culture in groups. To overcome this limitation, we developed a direct embryo-tagging system, which allows the collective culture of embryos from different origins whilst preserving their pedigree. Presumptive bovine zygotes were tagged with eight wheat-germ agglutinin biofunctionalised polysilicon barcodes attached to the outer surface of the zona pellucida (ZP). Four different barcodes were used to encode groups of 20–25 embryos, which were then cultured in the same drop. Cleavage, Day-7 and Day-8 blastocysts and barcode retention rates were assessed. In addition, Day-7 blastocysts were vitrified and warmed. Barcode attachment to the ZP of bovine embryos affected neither in vitro embryo development nor post-warming survival of the tagged embryos. All the embryos maintained barcodes attached until Day 8 of culture (3.63 ± 0.37 barcodes per embryo) and could be identified. In conclusion, identification of embryos by barcodes attached to the ZP is feasible and will allow the culture of embryos from different donors in the same drop.

Effect of co-culture with intact embryos on development of bovine separated blastomeres

To improve embryo development in bovine separated blastomeres, we evaluated applicability of co-culture with intact embryos. The morphological quality of blastocysts derived from separated blastomeres and rate of blastocyst formation were only slightly increased when the cells were co-cultured with intact embryos, which did not provide significant differences when statistically analyzed. However, the cell count of inner cell mass (ICM), trophectoderm (TE) and total number of cells in Day 8 blastocysts were significantly higher when the cells were co-cultured with the intact embryos than those with the cells cultured individually (P<0.05). Transfer of four monozygotic pairs of blastocysts derived from the cells co-cultured with intact embryos led to three pregnancies even when the blastomeres were produced by in vitro maturation and in vitro fertilization of oocytes collected by ovum pick-up from elite cows. These results suggest that co-culturing with intact embryos may enhance development of bovine separated blastomere.

Development of a single bovine embryo improved by co-culture with trophoblastic vesicles in vitamin-supplemented medium

To improve the development of singly cultured bovine embryos, we developed a co-culture method with trophoblastic vesicles. The growth of trophoblastic cells was markedly increased in vitamin-supplemented medium 199 compared with medium 199. Upon co-culture of a single embryo with trophoblastic vesicles in vitamin-supplemented medium 199, embryo development to the blastocyst stage was significantly higher than in embryos co-cultured with trophoblastic vesicles in RPMI 1640 or with cumulus cells in medium 199 (control). In the absence of the vitamin cocktail, co-culture with trophoblastic vesicles in medium 199 did not improve embryo development compared with that of the control. The vitamin cocktail was effective in embryo development when co-cultured with trophoblastic vesicles, but not with cumulus cells. Embryo development was not improved in the absence of co-cultured trophoblastic vesicles, even in the presence of vitamin cocktail. In conclusion, the co-culture system with trophoblastic vesicles in vitamin-supplemented medium 199 efficiently enhances the development of singly cultured embryos.

Effect of sericin on preimplantation development of bovine embryos cultured individually

The silk protein sericin has been identified as a potent antioxidant in mammalian cells. This study was conducted to examine the effects of sericin on preimplantation development and quality of bovine embryos cultured individually. When two-cell-stage embryos were cultured individually for 7 days in CR1aa medium supplemented with 0, 0.1, 0.5, or 1% sericin, rates of total blastocyst formation and development to expanded blastocysts from embryos cultured with 0.5% sericin were higher (P < 0.05) than those from embryos cultured with 0 or 1% sericin. When embryos were cultured individually for 7 days in the CR1aa medium supplemented with 0 or 0.5% sericin under two oxidative stress conditions (50 or 100 μm H(2)O(2)), the addition of sericin significantly improved the blastocyst formation rate of embryos exposed to 100 μm H(2)O(2). However, the protective effect of sericin was not observed in development of embryos exposed to 50 μm H(2)O(2). When embryos were exposed to 100 μm H(2)O(2) during culture, the DNA fragmentation index of total blastocysts from embryos cultured with 0.5% sericin was lower than blastocysts derived from embryos cultured without sericin (4.4 vs. 6.8%; P < 0.01). In conclusion, the addition of 0.5% sericin to in vitro culture medium improved preimplantation development and quality of bovine embryos cultured individually by preventing oxidative stress.

Effect of culture medium volume and embryo density on early mouse embryonic development: tracking the development of the individual embryo

PURPOSE

To determine the optimal volume or density of embryos for the well-of-the-well (WOW) system in order to track the development of individual embryos and to determine whether the WOW system can reverse the negative impact of culturing embryos singly.

METHODS

(1) Mouse embryos (groups of nine at the 2-cell stage) were cultured in 6.25 μl, 12.50 μl, 25.00 μl and 50.00 μl of droplets of culture medium under paraffin oil; (2) Groups of three, six, nine and twelve embryos at the 2-cell stage were cultured in 50 μl of droplet of culture medium under paraffin oil; (3) Groups of nine embryos at the 2-cell stage were cultured in 50 μl of droplet under paraffin oil with or without nine micro-wells made on the bottom of the Petri dish into each of which were placed one of the nine embryos (WOW system). Also single 2-cell stage embryos was cultured individually in 5.5 μl of droplet of culture medium under paraffin oil with or without a single micro-well made on the bottom of the Petri dish (WOW system for single culture). At the end of culture, the percentages of blastocyst development, hatching and hatched blastocysts were compared in each group. The blastocysts were fixed for differential staining.

RESULTS

The blastocyst development was significantly higher (P < 0.05) when nine embryos were cultured in 50 μl of droplet of culture medium compared with other volumes. The blastocyst development was significantly reduced (P < 0.05) in single embryo culture compared to group embryo culture with or without the WOW system. The blastocyst development was not improved when single embryo cultured individually in a micro-well was compared to single embryo cultured individually without micro-well. The total cell numbers of blastocysts were significantly higher in group embryo culture than single embryo culture regardless of whether the WOW system was used. In addition, the total cell numbers of blastocysts were significantly higher (P < 0.05) in single embryo culture with the WOW system than without.

CONCLUSIONS

Group embryo culture is superior to single embryo culture for blastocyst development. The WOW system with 50 μl of droplet of culture medium can be used to track the individual development of embryo cultured in groups while preserving good embryonic development. The reduced embryonic development with single embryo culture cannot be ameliorated by the WOW system.

Rethinking in vitro embryo culture: new developments in culture platforms and potential to improve assisted reproductive technologies

The preponderance of research toward improving embryo development in vitro has focused on manipulation of the chemical soluble environment, including altering basic salt composition, energy substrate concentration, amino acid makeup, and the effect of various growth factors or addition or subtraction of other supplements. In contrast, relatively little work has been done examining the physical requirements of preimplantation embryos and the role culture platforms or devices can play in influencing embryo development within the laboratory. The goal of this review is not to reevaluate the soluble composition of past and current embryo culture media, but rather to consider how other controlled and precise factors such as time, space, mechanical interactions, gradient diffusions, cell movement, and surface interactions might influence embryo development. Novel culture platforms are being developed as a result of interdisciplinary collaborations between biologists and biomedical, material, chemical, and mechanical engineers. These approaches are looking beyond the soluble media composition and examining issues such as media volume and embryo spacing. Furthermore, methods that permit precise and regulated dynamic embryo culture with fluid flow and embryo movement are now available, and novel culture surfaces are being developed and tested. While several factors remain to be investigated to optimize the efficiency of embryo production, manipulation of the embryo culture microenvironment through novel devices and platforms may offer a pathway toward improving embryo development within the laboratory of the future.

Single or Group Culture of Mammalian Embryos: The Verdict of the Literature

During infertility treatment with IVF, embryos are cultured either in groups or individually. Each approach has potential benefits and detriments, and the purpose of this review is to try to come to a consensus based on the literature as to which approach yields superior results. Group culture of embryos may produce better quality embryos via secretion of embryotrophic factors, while opponents of the approach argue that embryos cultured together may either deplete the media of substrates or negatively affect nearby embryos via the transmission of other secreted factors. In these cases, quantity of embryos, volume of media and proximity and quality of companion embryos are also important factors to consider. While it has long been accepted that group culture is beneficial for embryos from various animal species, emerging data also suggest a similar benefit in the human. Conversely, embryos cultured individually avoid potential substrate depletion, negative impact from factors secreted from companion embryos, while more practically permitting the ability to monitor and track the embryo for identification via morphology or molecular analysis to select and transfer potentially superior embryos. Importantly, advancements in embryo culture platforms now permit tracking of individual embryos, while also offering ability to reap the benefits of group culture. These approaches utilize confined microenvironments immediately surrounding the embryos that may be conducive for periodic sampling/analysis, while also allowing access to a larger media reservoir to avoid substrate depletion. Thus, though questions remain as to optimal embryo density and volume of culture media, group embryo culture in the correct culture platform is likely to be superior to individual embryo culture.

Improved blastocyst development of single cow OPU-derived presumptive zygotes by group culture with agarose-embedded helper embryos

BACKGROUND

The in vitro culture of presumed zygotes derived from single cow ovum pick-up (OPU) is important for the production of quality blastocysts maintaining pedigree. The aim of the present study was to evaluate the agar chip-embedded helper embryo coculture system for single cow OPU-derived zygotes by assessing embryo quality.

METHODS

Cumulus oocyte complexes (COCs) were collected from Hanwoo cows with high genetic merit twice a week using the ultra-sound guided OPU technique and from slaughterhouse ovaries. The Hanwoo cow COCs and slaughterhouse ovaries were matured in vitro, fertilized in vitro with thawed Hanwoo sperm and cultured for 24 h. The presumed zygotes were subsequently placed in three different culture systems: (1) control OPU (controlOPU) with single cow OPU-derived presumed zygotes (2~8); (2) agar chip-embedded slaughterhouse helper embryo coculture (agarOPU) with ten presumed zygotes including all presumed zygotes from a cow (2~8) and the rest from agar chip-embedded slaughterhouse presumed zygotes (8~2); and (3) slaughterhouse in vitro embryo production (sIVP) with ten slaughterhouse ovary-derived presumed zygotes, each in 50 μL droplets. Day 8 blastocysts were assayed for apoptosis and gene expression using real time PCR.

RESULTS

The coculture system promoted higher blastocyst development in OPU zygotes compared to control OPU zygotes cultured alone (35.2 vs. 13.9%; P < 0.01). Genes predicted to be involved in implantation failure and/or embryo resorption were down-regulated (P < 0.05) in control OPU zygotes (CD9, 0.4-fold; AKRAB1, 0.3-fold) and in cocultured zygotes (CD9, 0.3-fold; AKRAB1, 0.3-fold) compared to sIVP blastocysts (1.0-fold). Moreover, genes involved in implantation and/or normal calf delivery were up-regulated (P < 0.05 to P < 0.01) in control OPU zygotes (PGSH2, 5.0-fold; TXN, 4.3-fold; PLAU, 1.7-fold) and cocultured zygotes (PGSH2, 14.5-fold; TXN, 3.2-fold; PLAU, 6.8-fold) compared to sIVP (1.0-fold) blastocysts. However, the expression of PLAC8, TGF-β1, ODC1, ATP5A1 and CASP3 did not differ between the three culture groups.

CONCLUSIONS

Results show that the agar chip-embedded helper embryo coculture system enhances developmental competence and embryo quality in cultures of limited numbers of high pedigree single cow OPU presumed zygotes.

Equine bone marrow mesenchymal or amniotic epithelial stem cells as feeder in a model for the in vitro culture of bovine embryos

Various studies have shown that the in vitro culture environment is one of the key determinants of the blastocyst output. In the present study we investigated the effects of co-culturing bovine embryos with equine bone marrow mesenchymal stem cells (BM-MSCs) or equine amniotic epithelial stem cells (AE-SCs) on in vitro blastocysts development. BM specimens were obtained aseptically from sternal aspirates of horses under local anaesthesia and the isolated cells were resuspended in Dulbecco Modified Earle's Medium supplemented with 10 ng/ml of basic fibroblast growth factor (bFGF). Amniotic membranes were obtained from fresh placentas and, to release the AE cells, amniotic fragments were incubated with 0.05% trypsin for 45 min. Separated AE cells were plated in standard culture medium containing 10 ng/ml epidermal growth factor (EGF). Seven hundred and five cumulus–oocyte complexes were used and, after IVM and IVF, cumulus-free presumptive zygotes were randomly transferred into one of three co-culture systems in which they were cultured up to day 7: (1) co-culture with cumulus cells (control); (2) co-culture with BM-MSCs; and (3) co-culture with AE-SCs. Statistical analyses were performed by ANOVA. Blastocyst developmental rates were significantly different (p < 0.001) between control, AE-SCs and BM-MSCs (respectively 35.45, 41.84 and 30.09%). In conclusion, the AE-SC monolayer create a more suitable microenvironment necessary for inducing local cell activation and proliferation of the growing embryos in comparison with BM-MSCs and cumulus cells. It can be suggested that these cells secrete biologically active substances, including signalling molecules and growth factors of epithelial nature, different to those of the BM cells of mesenchymal origin.

Oocyte source and hormonal stimulation for in vitro fertilization using sexed spermatozoa in cattle

The aim of this study was to investigate the efficiency of in vitro embryo production in cattle utilizing sexed sperm from two bulls and oocytes recovered by OPU. Twenty donor animals were employed in eight OPU replicates: the first four OPU trials were conducted on animals without hormone treatment, and the last four were run on the same animals, following FSH subcutaneous and intramuscular administration. A higher rate of blastocyst development was recorded in stimulated, as compared to nonstimulated animals, (25.2% versus 12.8%, P = .001). Ocytes derived from slaughterhouse (SH) ovaries were also fertilized with sperm from the same bulls. Overall, non-sexed sperm used with oocytes derived from SH ovaries was significantly more efficient for blastocyst development than was sexed sperm with these same SH derived oocytes and sexed sperm with stimulated donor oocytes (39.8% versus 25.0% and 25.2%, P = .001). In conclusion, the use of sexed sperm with OPU-derived oocytes resulted in a significantly higher blastocyst development when donors were hormonally stimulated; furthermore, the level of efficiency achieved was comparable to that attained when the same sexed sperm was tested on oocytes derived from SH ovaries.

Improved in vitro development of OPU-derived bovine (Bos taurus) embryos by group culture with agarose-embedded helper embryos

The average number of oocytes collected by ovum pick up (OPU) from Bos taurus cattle is <8 per live donor. The objective was to determine whether development of small numbers of cattle embryos (produced by OPU and IVF), was enhanced by including "helper" embryos, produced from abbatoir-derived oocytes and embedded in agarose. Oocytes were from abbatoir-derived ovaries (Experiments 1 and 2) or OPU of elite donors (Experiment 3). In Experiment 1, cleaved embryos (2-8 cells), were randomly allocated. Controls were groups of 1, 3, 5, 10, and 20 cleaved embryos cultured in 50 μL serum-free SOF, whereas treatments were groups of 1, 3, and 5 embryos freely cultured along with helpers in groups of either 9, 7 or 5 embedded in agarose per droplet. Therefore, there were 10 cleaved embryos per droplet in combinations of 1 + 9, 3 + 7 or 5 + 5 (free + helper), respectively. There was an increase in the progression to blastocyst for 1-5 embryos per droplet, compared to 10 and 20 (6.6-24.2% vs. 39.2-43.3%, P < 0.05). For the tested free embryos, those cultured with helpers had increased blastocyst development over their control counterparts (39.3-49.5% vs. 6.6-24.2%, P < 0.05). When the number of embryos per droplet was 10 or 20, blastocyst percentage was similar (39.2-49.5%, P > 0.05). In Experiment 2, addition of an agarose chip to the culture medium did not significantly affect development to the blastocyst stage. In Experiment 3, after fertilizing OPU oocytes with sorted X-sperm, a group of three cleaved embryos were cultured in a droplet with either seven helpers (3 + 7) or alone (3 + 0). Blastocyst development of OPU oocytes in the 3 + 7 group was 37.1%, higher than that in the 3 + 0 group (11.8%, P < 0.05). In conclusion, limited numbers of OPU/IVF oocytes had competent development when cultured with helpers (embedded in agarose to provide physical separation).

Towards the use of microfluidics for individual embryo culture

Mammalian embryo development is still relatively inefficient in vitro. Much research has been conducted on the chemical environment, or culture medium, surrounding the embryo, but little attention has been given to the actual physical culture environment, which has changed very little over the years. The application of microfluidics to embryo production in vitro is a tantalising approach that may alleviate some of the limits that traditional microdrop culture places on embryo development and research into gamete and embryo physiology. These devices may lead to enhanced in vitro embryo development and quality by more closely mimicking the in vivo environment. Initial work in this area is promising and gives us proof-of-principle that these unique microfluidic systems may indeed be applicable to in vitro culture of gametes and embryos. The present paper reviews the advantages of microfluidics for in vitro embryo production: how the platforms are manufactured, the current uses of microfluidics in assisted reproduction, static v. dynamic culture environments, individual gamete and embryo culture and the future directions of microfluidic application to in vitro embryo production and manipulation. Finally, preliminary data from our laboratory using a new microfluidic well insert for porcine, bovine and murine embryo culture is discussed.

On-chip single embryo coculture with microporous-membrane-supported endometrial cells

In vitro culture (IVC) of the mammalian embryo is an essential technique in reproductive technology and other related life science disciplines. Although embryos are usually cultured in groups, a single embryo culture has been highly desired for IVC to investigate developmental processes. In this study, we proposed and developed the first single embryo coculture device, which allows making an array of a single embryo coculture with endometrial cells by controlling the culture environment in a microfluidic device. To realize this concept, we investigated three key issues: selection of a culture medium for the embryo coculture with endometrial cells using a mouse embryo and endometrial cells, evaluation of an on-microporous-membrane coculture of endometrial cells and an embryo to control the polarization of endometrial cells on the membrane, and evaluation of the coculture of endometrial cells and the embryo in the microfluidic device. We successfully obtained an array of a single coculture of embryo with endometrial cells in a microfluidic device. This concept will open and enhance the management of an individual embryo for assisted reproductive technology, livestock breeding, and fundamental stage research by further development.

Maturation, fertilisation and culture of bovine oocytes and embryos in an individually identifiable manner: a tool for studying oocyte developmental competence

The ability to successfully culture oocytes and embryos individually would facilitate the study of the relationship between follicle parameters and oocyte developmental competence, in order to identify markers of competent oocytes, as well as the ability to use small numbers of oocytes from an individual donor such as when ovum pick-up is carried out. Using a total of 3118 oocytes, the aim of the present study was to develop a system capable of supporting the development of immature bovine oocytes to the blastocyst stage in an individually identifiable manner. Initially, post-fertilisation embryo culture in the Well-of-the-Well (WOW) system, on the cell adhesive Cell-Tak or in polyester mesh was tested and shown to result in similar development to embryos cultured in standard group culture. The results demonstrate that it is possible to culture bovine oocytes to the blastocyst stage in an individually identifiable manner in all three culture systems with comparable success rates. This permits the localisation and identification of individual embryos throughout preimplantation development in vitro while retaining the developmental benefits of group culture. In terms of ease of preparation and use, culture in isolation within the strands of a polyester mesh is preferable.

Embryo culture: can we perform better than nature?

Culture of preimplantation-stage embryos has always been a key element of laboratory embryology and has contributed substantially to the success of many assisted reproduction procedures. During the past decade, its importance has increased as extended in-vitro embryo culture and single blastocyst transfer have become indispensable parts of the approach to decreasing the chance of multiple pregnancy while preserving the overall efficiency of the treatment. However, in spite of the scientific and commercial challenge stimulating research worldwide to optimize embryo culture conditions, a consensus is missing even in the basic principles, including composition and exchange of media, the required physical and biological environment and even the temperature of incubation. This review attempts to summarize the controversies, demonstrate the fragility of some widely accepted dogmas and generate an open-minded debate towards rapid and efficient optimization. New approaches expanding the traditional frames of mammalian embryo culture are also discussed. Although some researchers suppose that the efficiency of the presently applied in-vitro culture systems have already approached the biological limits, authors are confident that substantial improvement may be achieved that may expand considerably the possibilities of future assisted reproduction in humans.

Effect of culture system on survival rate of vitrified bovine embryos produced in vitro

This study was designed to evaluate the effect of in vitro culture system on bovine blastocyst yield and quality after vitrification. In Experiment 1, IVM/IVF zygotes were allocated to three culture conditions: (I) Oviductal cells-SOF (OCM-SOF); (II) Oviductal cells-TCM (OCM-TCM); and (III) SOF for 8 days. There was no significant difference between blastocyst rates among groups. In Experiment 2, the IVP-blastocysts in three above culture conditions were vitrified within groups segregated according to age (Day 7 and 8) and blastocoelic cavity size (early and expanded blastocysts). A trend of higher survival rate was obtained in vitrified/warmed early blastocysts compared with expanded ones, so that the difference in OCM-TCM group was significant (P<0.001). Higher survival and hatching rates (P<0.001) were obtained in OCM-SOF and OCM-TCM groups (co-culture) compared with SOF group and the age of blastocyst had no effect on post-thaw survival and hatching rates. In Experiment 3, after staining of blastocysts, in fresh blastocysts the highest number of trophectoderm cells was observed in OCM-TCM group and the number of inner cell mass (ICM) was higher in co-culture groups than SOF group (P<0.001). In vitrified/warmed blastocysts the number of ICM and trophectoderm cells in co-culture groups was higher than SOF group (P<0.001) except for the ICM of expanded blastocysts. In conclusion, in our culture conditions, the blastocyst yield is not influenced by culture system, while the cryotolerance of IVP-blastocysts is positively influenced by the presence of somatic cells. Moreover, the expanded blastocysts are more susceptible to cryoinjury than early blastocysts.

Nuclear maturation and development of IVM/IVF canine embryos in synthetic oviductal fluid or in co-culture with buffalo rat liver cells

In vitro embryo production in the domestic bitch can provide valuable insights for conservation of endangered canids. In the present study, canine oocytes underwent in vitro maturation (IVM) in simple or complex media, with production of in vitro matured and fertilized (IVM/IVF) canine embryos. Cumulus-oocyte complexes (COCs) were harvested from ovaries by slicing and subjected to IVM in four media (SOF, TCM 199, Ham-F10, and DMEM/F12). After culture for 48h, oocytes were stained and examined for nuclear maturation. There were no significant differences in the mean (+/-S.D.) percentage of nuclear maturation (metaphase II) of oocytes cultured in SOF (18.6+/-7.6%), TCM 199 (18.3+/-4.5%), Ham-F10 (13.9+/-8.2%), or DMEM/F12 (11.9+/-4.2%). For assessment of embryo development, oocytes were matured for 48h in synthetic oviductal fluid (SOF), fertilized with frozen-thawed sperm, and presumptive zygotes were cultured for 7 d, either in SOF or as co-cultures with BRL cells in TCM 199. Percentages of IVM/IVF oocytes that developed to the 2-cell, 3-4-cell, and 5-7-cell stages were higher (P<0.05) following culture in SOF versus BRL cell co-cultures (33.6+/-1.2% vs 13.7+/-1.2%, 24.7+/-0.5% vs 8.7+/-1.1%, and 15.1+/-2.2% vs 4.3+/-1.3%, respectively). However, none of the embryos developed beyond the 8-16-cell stage. In conclusion, simple or complex media successfully induced resumption of meiosis and nuclear maturation of canine oocytes. Furthermore, SOF supported in vitro development of IVM/IVF canine embryos to the 8-16-cell stage.

Oxygen tension during in vitro culture of bovine embryos: Effect in production and expression of genes related to oxidative stress

In vitro bovine embryos production and quality was evaluated in two culture systems, which utilize different oxygen tension. After IVM/IVF presumptive zygotes were cultured in either one of the two systems. The culture systems evaluated were-high O2: SOFaaci medium and culture for 7 d under 5% CO2 in air, at 39 degrees C in the presence of cumulus cells (control); low O2: SOFaaci medium and culture for 7 d under 5% CO2 and 5% O2 at 39 degrees C. In low O2 system the zygotes were denuded by successive pipetting before being transferred to culture medium, while in the high O2 zygotes kept the cumulus cells that remained after IVF. Cleavage rates were evaluated 48 h post-insemination (hpi) and the blastocyst rates at D6 and D7 post-insemination (pi). From both groups a total of 94 expanded blastocysts, from D7 of culture, were fixed and stained with aceto-orcein to evaluate cell numbers. Seven pools of 15 embryos from each treatment were frozen for gene expression evaluation. The abundance of transcripts for genes related to oxidative stress, superoxide dismutase (Mn-SOD), catalase, gluthatione peroxidase (GPX) and for embryo quality, interferon-tau (IFN-tau) were determined using a semi-quantitative RT-PCR. Cleavage rate was similar (P>0.05) for both groups. The blastocyst rate at D6 pi was greater (P<0.05) in the group cultured under low O2 tension (37.4%) than in the high O2 tension (21.9%). However, blastocyst rate and total cell number at D7 were similar (P>0.05) between groups. No change (P>0.05) in transcript amount between treatments was observed for GPX, catalase and IFN-tau genes. However, the relative abundance of transcripts for Mn-SOD gene was greater (P<0.05) for embryos cultured in high O2 tension system. The results suggest that bovine embryos can be cultured either in SOFaaci medium under greater O2 tension in the presence of cumulus cells, or in SOFaaci medium under less O2 tension, without affecting embryo production or quality.

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

It is well known that serum in culture medium negatively affects blastocyst quality. The objective of this work was to develop and test a serum-free culture medium which could improve embryo quality, measured by the resistance to freezing, lipid and glutathione content of the resulting blastocysts, as well as the ability of the blastocysts to elongate after transient transfer to recipient cows. In a first experiment we showed that adding a mixture of insulin, transferrin and selenium to serum-free Synthetic Oviduct Fluid medium (SOF-ITS) improved embryo development and quality. In the second experiment, the addition of BSA to SOF-ITS further improved blastocyst development. Moreover, a reduction in lipid content of morulae was observed in SOF-ITS-BSA by comparison with morulae cultured with serum (SOF-FCS). The resistance to freezing measured by hatching rates 24h post-thawing was also improved for blastocysts with a diameter between 160 and 180 microm cultured in SOF-ITS-BSA by comparison to those produced with serum. In order to evaluate the redox potential of the embryos, reduced glutathione content (GSH) was evaluated both before and after cryopreservation. A significant decrease in glutathione was observed after freezing, whatever the culture medium, but no difference was observed between culture conditions. Transient transfers were performed and elongated D-13 embryos were recovered. Elongation was more pronounced and the embryonic disk more often visible in embryos cultured in SOF-ITS-BSA than in embryos cultured with FCS. In conclusion, the serum-free system we developed to produce in vitro bovine embryos meets the developmental and qualitative requirements for a large-scale use.

Influence of in vitro oxygen concentrations on preimplantation embryo development, gene expression and production of hanwoo calves following embryo transfer

This study evaluated the effects of two different oxygen (O2) concentrations on in vitro embryo development, embryo quality, and gene expression and the in vivo development following embryos transfer to recipients of natural and synchronized estrus in bovines. Cumulus oocyte complexes were in vitro matured in TCM199 supplemented with FSH (10 microg/ml), LH (10 microg/ml), and 10% (v/v) FBS. Presumptive zygotes were cultured in SOF medium either under 5% (low) or 20% (high) O2 in air. Cleavage rates did not differ between groups. Blastocyst and hatched blastocyst development in 5% O2 were significantly (P < 0.05) higher than in 20% O2. Total cell number of in vivo blastocyst was significantly (P < 0.05) higher than that of in vitro blastocyst. ICM ratio and apoptosis of in vivo blastocyst were significantly (P < 0.05) lower than that of in vitro blastocyst. Using real time PCR, we have found that for the set of genes (GLUT-1, MnSOD, VEGF, Bax, and Bcl-2) analyzed, there were differences in mRNA expression between in vitro produced (IVP) and in vivo produced embryos. Interestingly, the abundance of transcript for IFN-tau in IVP embryos produced under 5% O2 concentration was similar to in vivo counterparts. The pregnancy and twin rates of natural recipients were significantly (P < 0.05) higher than those of synchronized counterparts. No significant difference in the offspring sex was observed. In conclusion, low (5%) O2 concentration during IVC was beneficial for enhancing the embryo quality and recipients of natural estrus were more suitable than synchronized estrus for stable production of Hanwoo calves.

Modifications to Improve the Efficiency of Zona-Free Mouse Nuclear Transfer

In the present study, some modifications were made to the zona-free nuclear transfer technique in the mouse in order to achieve greater efficiency. Firstly, a 1-h interval was allowed between cumulus removal and zona pellucida digestion. Secondly, acid Tyrode's was selected for zona pellucida removal, because contrary to pronase, it allows embryo survival during parthenogenic activation in the absence of calcium. Even when the exposure time to pronase was reduced to as little as 1 min or washed with fetal calf serum to inhibit the enzyme, the percentage of lysis during activation in the absence of calcium was still very high. Thirdly, electrofusion was performed at room temperature (21 degrees C), instead of 30 degrees C as in our previous experiments. Finally, embryos were cultured in groups of 12-15, instead of individually, using a "well of the wells" system during activation and culture. When compared, parthenogenic activated control embryos showed an increase in the development to blastocyst when cultured in pairs instead of individually. By the end of the experiments and using embryonic stem (ES) cells, there was a significant increase in fusion rate (1.5-fold increase) and in development to morula/blastocyst from cleaved reconstructed embryos (1.5-fold increase) when compared with the results before the modifications. A 2.4-fold increase in overall efficiency was achieved from the oocyte to morula/blastocyst stages.

Development of porcine embryos in vivo and in vitro; evidence for embryo 'cross talk' in vitro

The in vitro development of zygotes of domestic species to the blastocyst stage is facilitated by culture in groups, suggesting a role for autocrine/paracrine factors. A novel method was used to investigate the potential role of such factors using in-vitro-produced and in-vivo-derived porcine embryos. The development of individual zygotes to the blastocyst stage was optimal when they were cultured 81-160 mum apart. As the distance between the embryos was increased, blastocyst rates declined significantly, reaching zero beyond 640 mum. Blastocyst volume and cell number (both inner cell mass and trophectoderm) were also increased when the distance apart was between 81 and 160 mum. Culturing embryos in groups at different stages of development suggested that group culture confers a greater advantage to development after the activation of the genome. Group culture of in-vivo-derived embryos showed a weak distance effect. The results suggest a role for as yet unknown diffusible paracrine/autocrine factors released by early porcine embryos in promoting the growth of neighbouring embryos in vitro. This advantage is observed to a lesser extent by in-vivo-derived zygotes which are likely to have been better conditioned for development in vitro by being conceived in the female reproductive tract.

Is apoptosis in bovine in vitro produced embryos related to early developmental kinetics and in vivo bull fertility?

Although several studies have indicated a paternal effect on bovine embryo development, no conclusive data exist on the effect of in vivo bull fertility on apoptosis. Therefore, it was the main objective of this study to compare the apoptotic cell ratio (ACR) in embryos originating from bulls with different in vivo fertility. However, since it is has been demonstrated before that bulls with different in vivo fertility differ in timing of first cleavage, it was necessary to investigate first the effect of timing of development on apoptosis in vitro in order to get an unbiased insight in the contribution of in vivo bull fertility on apoptosis in bovine blastocysts. In the first experiment, bovine embryos (n = 939) were allocated to different groups according to cleavage rate at 30, 36 and 48 hpi and blastocysts were selected at 7 and 8 dpi. The blastocyst rate at 7 dpi was significantly lower in embryos which had first cleaved at 48 hpi than in embryos from the 30 and 36 hpi group (P < 0.05). The ACR after TUNEL in day 7 blastocyst was significantly lower in the 30 hpi group in comparison with the 36 and 48 hpi group (P < 0.05) and lower in day 7 blastocysts than in day 8 blastocysts. In the second experiment, sperm of eight bulls with different non return rates was used for in vitro bovine embryo production (n = 3820 oocytes). Cleavage rates (30, 36 and 48 hpi) and blastocyst rate (7 dpi) were determined. Only very low negative correlations could be found between in vivo and in vitro bull fertility and ACR did not differ between groups derived from sires with either low or normal fertility (P > 0.05). Further research in serum free conditions is needed to confirm that the lower ACR in early cleaved embryos could be mediated by the cooperative interaction of embryos of good quality cultured in group. In vivo bull fertility could hardly be correlated with in vitro blastocyst yield and could not be correlated with appearance of apoptosis.

Gene expression and developmental competence of bovine embryos produced in vitro under varying embryo density conditions

The objective of this study was to determine the effects of oocyte/embryo density (embryo number:medium volume ratio) on developmental competence and relative transcription of developmentally important genes in in vitro-produced bovine embryos. Using standard procedures, bovine oocytes were matured, fertilized and cultured in vitro in groups of 5, 10, 20 or 30 oocytes/embryos per 100 microL medium drop (embryo number/medium volume ratios of 1:20, 1:10, 1:5 and 1:3.3, respectively). A semi-quantitative RT-PCR assay was used to determine the relative abundance of Hsp 70.1 and Glut-1 transcripts in Day-6 morulae, and in Day-7 and Day-8 blastocysts and expanded blastocysts. Cleavage rates (55.9, 49.1, 47.1 and 34.6%, respectively) and blastocyst developmental rates (24.1, 18.9, 20.4 and 12.6%, respectively) were higher in groups containing 5, 10 and 20 embryos versus 30 embryos per drop, but there were no significant differences among groups in hatching rates. The relative abundance of Hsp 70.1 transcripts in Day-7 blastocysts was higher in embryos produced in the 20-embryo than in the 5-embryo groups. There were no differences among embryos from all groups in the amount of Glut-1 mRNA (regardless of embryonic stage). However, there were differences in the pattern of Hsp 70.1 gene expression between distinct stages of embryo development and embryo density; these dissimilarities appeared to be associated with compromised development at higher embryo densities. In conclusion, the increase in embryo density during IVM, IVF, and IVC phases of in vitro embryo production might negatively affect embryo development and the pattern of gene expression of in vitro-produced bovine embryos.

Evaluation of different culture systems on the in vitro production of bovine embryos

The objective of this study was to determine the development potential and quality of in vitro produced bovine embryos cultured individually or in groups. After IVM and IVF, presumptive zygotes were cultured in groups or individually, either in drops or in the modified "well of the well" (mWOW) system. In Experiment 1, four culture systems were utilized: T1: drop in group (control); T2: mWOW in groups; T3: mWOW individually; and T4: drop individually. Cleavage and blastocyst rates at Days 6, 7 and 8 and total cell number of Day 6 blastocysts were similar (P > 0.05) for all treatments. However, in Day 7 blastocysts, total cell number was lower (P < 0.05) in embryos cultured individually in a small drop than those cultured in the mWOW. In Experiment 2, blastocysts of T1, T2 and T3 were allocated into two groups, control and vitrified. After warming, the vitrified embryos were cultured for 72 h. At 48 h, the development of the Days 6 and 7 embryos was similar (P > 0.05) for all treatments in the control group. For the vitrified embryos, lower hatching rates (P < 0.05) were observed in the T3 group. In conclusion, embryos cultured in groups in the mWOW system had the same blastocyst rates but better quality (measured by their survival after vitrification) than those cultured individually in the mWOW system.

Efeito de sistema de cultivo, célula somática e soro em co-cultura sobre o desenvolvimento de embriões bovinos fecundados in vitro

O objetivo deste experimento foi o de avaliar o efeito de sistemas de cultivo e de diferentes células somáticas e soro bovino na co-cultura sobre a produção de embriões bovinos fecundados in vitro. No experimento um avaliou-se o efeito do sistema de co-cultura com células da tuba uterina e do sistema "definido". No experimento dois utilizaram-se células da granulosa ou da tuba uterina para a co-cultura em meio CR1aa (Charles Rosenkrans). No experimento três utilizou-se soro de vaca em cio (SVC) ou soro fetal bovino (SFB), ambos em co-cultura com células da granulosa em CR1aa. Os ovócitos utilizados foram obtidos de ovários colhidos em matadouro e maturados in vitro em meio 199 com soro de vaca em cio e FSH por 24h. Após a maturação, os ovócitos foram fecundados in vitro por 22h e posteriormente divididos aleatoriamente nos tratamentos. Avaliaram-se a taxa de clivagem no dia três do cultivo, a produção de blastocistos nos dias sete e oito, e de blastocistos eclodidos nos dias nove e dez. Não houve diferença entre os sistemas em co-cultura e "definido" quanto à taxa de clivagem (80,7% e 75,4%) e de produção de blastocisto (19,4% e 17,7%). Entretanto, a taxa de blastocistos eclodidos foi superior para o sistema em co-cultura (37,5%) quando comparado com o sistema "definido" (8,7%). O cultivo embrionário em células da tuba uterina ou da granulosa resultaram em taxas de clivagem, produção de blastocisto e blastocistos eclodidos semelhantes entre si (65,5% e 66,7% de clivagem, 11,6% e 13,7% de blastocistos e 23,1% e 50,0% de blastocistos eclodidos; P>0,05), bem como o cultivo com SFB ou SVC (63,9% e 70,2% de clivagem, 14,3% e 8,7% de blastocisto e 41,2% e 33,3% de blastocistos eclodidos; P>0,05). Conclui-se que o sistema de cultivo "definido" pode ser utilizado para estudos com cultivo de embriões in vitro, no entanto, os resultados quanto à taxa de eclosão ainda são inferiores ao sistema em co-cultura. As células da granulosa e da tuba uterina possuem efeito semelhante sobre o desenvolvimento embrionário, assim como o soro de vaca em cio e o soro fetal bovino, quando em co-cultura.