In vitro bovine embryo production in a synthetic medium: Embryo development, cryosurvival, and establishment of pregnancy

Mammalian embryo culture media: now and into the future

For over 70years, since the culture of the first mammalian embryo in vitro , scientists have undertaken studies to devise and optimise media to support the manipulation and culture of gametes and embryos. This area of research became especially active in the late 1970s onwards following the successful birth of the first human in vitro fertilised embryo. This review summarises some of the key advances in mammalian embryo culture media over time based on a greater understanding of the biochemical milieu of the reproductive tract. It highlights how learnings from studies in mice and agricultural species have informed human culture media compositions, in particular the inclusion of albumin, growth factors, cytokines, and antioxidants into contemporary culture media formulations, and how these advances may then in turn help to inform and guide development of in vitro culture systems used in other arenas, in particular agriculture. Additionally, it will highlight how the introduction of new technologies, such as timelapse, can influence current trends in media composition and usage that may see a return to a single step medium.

Review of the Current Research on Fetal Bovine Serum and the Development of Cultured Meat

The purpose of this review is to summarize studies that investigate blood and the main components of fetal bovine serum (FBS) in vertebrates, including major livestock, and review the current research on commercializing cultured meat. Detailed research on FBS is still lacking; however, some studies have shown that FBS consists of proteins, carbohydrates, growth factors, cytokines, fats, vitamins, minerals, hormones, non-protein nitrogen, and inorganic compounds. However, there are few studies on how the composition of FBS differs from blood or serum composition in adult animals, which is probably one of the main reasons for not successfully replacing FBS. Moreover, recent studies on the development of FBS replacers and serum-free media have shown that it is difficult to conclude whether FBS has been completely replaced or serum-free media have been developed successfully. Our review of the industrialization of cultured meat reveals that many basic studies on the development of cultured meat have been conducted, but it is assumed that the study to reduce or replace ingredients derived from fetuses such as FBS has not yet been actively developed. Therefore, developing inexpensive and edible media is necessary for the successful industrialization of cultured meat.

Molecular and cellular effects of insulin-like growth factor-1 and LongR3-IGF-1 on in vitro maturation of bovine oocytes: comparative study

Addition effects of insulin-like growth factor-1 (IGF-1) and its synthetic analogue insulin-like growth factor-1 recombinant-3 (LongR3-IGF-1) after in vitro maturation (IVM) of cattle cumulus-oocyte complexes (COCs) were compared and evaluated on meiotic progression, apoptosis and profile genes of oocyte competence (GDF9, BMP15, BAX, BCL2, OOSP1, IGFBP2, IGBFP4 and IGFBP5), and their respective cumulus cells (AREG, EGFR, FSHR, COX2, BAX, BCL2, IGFBP2, IGFBP4 and IGFBP5). The 739 COCs (n = 10 pools) of bovine ovaries were collected, selected and matured with IGF-1 (100 ng/mL), LongR3-IGF-1 (100 ng/mL), and in two control groups with 0.1% polyvinyl alcohol (PVA) or 10% fetal bovine serum (FBS), for 22-24 h. The statistical analysis was performed by a linear mixed effects model, ANOVA and Tukey tests. There was no statistical difference between experimental groups taken into account the meiotic progression and apoptosis (P > 0.05). Nevertheless, there were statistical differences (P ≤ 0.05) among FBS, IGF-1 and LongR3-IGF-1 groups for IGFBP4 gene expression, and among PVA, IGF-1 and LongR3-IGF-1 for COX2 gene expression in cumulus cells. Moreover, statistical difference was found for BCL2 gene expression between IGF-1, FBS and PVA groups and for IGFBP4 gene expression between LongR3-IGF-1, PVA and FBS in oocytes. There was no statistical difference between experimental groups for other genes evaluated. These results showed a good performance of IVM of bovine oocytes in the presence of LongR3-IGF-1 and the possibility of replacement of IGF-1 and FBS.

Intrafollicular oocyte transfer in cattle – a technical report

The aim of the study was to develop and evaluate the functionality of a new equipment for intrafollicular oocyte transfer (IFOT) in dairy cattle. The new system for IFOT is composed of the applicator, the aspirator, and the injector. After aspiration of oocytes, the IFOT set is inserted into the working tube of the ultrasound transducer holder, the content of the applicator can be injected into the preovulatory follicle via transvaginal ultrasonography by one operator. The function of instruments used for IFOT was firstly verified in laboratory conditions. Slaughterhouse oocytes filled into the instruments were injected into Petri dishes. The highest recovery rates in vitro (97.5%) were achieved when the applicator was stored with the needle in a downward position. Synchronized Holstein heifers were used for in vivo test. Intrafollicular injection of saline (n = 9) was performed to find whether ovulation is affected by the injection. Then IFOTs of phosphate buffered saline with 20 oocytes (n = 21) were performed into the preovulatory follicles followed by 7-day-old embryo collection. Total ovulation rates were 86.7% (26/30). Total recovery rates (oocytes + embryos) were 23.1%, embryo recovery rates were 10.1%. The new instrument allows for the loading of oocytes and easy transportation to recipients, and also allows IFOT to be performed by one person in field conditions. The method does, however, need further investigation.

Hyaluronic acid capacitation induces intracellular signals modulated by membrane-associated adenylate cyclase and tyrosine kinase involved in bovine in vitro fertilization

Heparin is the most commonly used in vitro capacitation inducer in the bovine. However, hyaluronic acid (HA) has been recently used for capacitation induction as well as for other reproductive biotechnologies, such as sperm selection and in vitro fertilization (IVF). Our aim was to induce sperm capacitation with heparin or HA in order to study mAC and TK intracellular signals and their relation with cleavage and blastocyst rates after IVF as well as with the oxidative status of the potential bovine embryos. 2,5-dideoxyadenosine and genistein were used as mAC and TK inhibitors, respectively. Sperm capacitation was analyzed using CTC technique, sperm plasma membrane and acrosome integrity were determined using trypan blue stain and differential interference contrast, and mitochondrial activity was evaluated using fluorochrome JC-1. Cleavage rate was analyzed 48h and blastocyst production 7-8 days after IVF, while cytosolic oxidative activity was determined using RedoxSensor Red CC-1 fluorochrome 7h after IVF. When mAC and TK inhibitors were added to sperm samples, only capacitation decreased significantly both in HA and heparin treated samples (P < 0.05), but plasma membrane and acrosome integrity percentages were not affected in any of these groups (P > 0.05). Sperm mitochondrial membrane potential only decreased in heparin treated samples in the presence of both inhibitors (P < 0.05). Oocytes activated with HA sperm treated samples with the addition of 2,5-dideoxyadenosine and genistein presented a lower cytosolic oxidative status than those activated with sperm treated with HA alone (P < 0.05). On the other hand, oocytes activated with heparin treated sperm samples presented a lower cytosolic oxidative status only in the presence of 2,5-dideoxyadenosine (P < 0.05). Therefore, mAC and TK present a differential participation in heparin and HA sperm induced capacitation and mitochondrial function as well as in IVF.

The Replacement of Fetal Bovine Serum with Bovine Serum Albumin During Oocyte Maturation and Embryo Culture Does Not Improve Blastocyst Quality After Slow Freezing Cryopreservation

In the present study, four experimental groups were used: fresh embryos, cultured during in vitro maturation and in vitro culture in media supplemented with bovine serum albumin (BSA) (fresh BSA) or fetal bovine serum (FBS) (fresh FBS); and two groups of cryopreserved and thawed embryos, produced under the same conditions (frozen BSA and frozen FBS). Experiment 1 evaluated the protein source effect on embryo development and response to cryopreservation. At day 7, half of the expanded blastocysts (Bx) from each group were cryopreserved and warmed and the other half were used as controls. After warming, embryos were incubated under the same conditions for 48 hours, and the hatching rate was measured at 24 and 48 hours. The total and the apoptotic cell numbers were measured in a subset of Bx after 24 hours. Experiment 2 used the Bx of experiment 1 to compare the expression of KRT8, PLAC8, FOSL1, HSP1A1, and HSPA5 genes in hatched blastocysts at 24 and 48 hours for all groups. The FBS group showed a higher percentage (p < 0.05) of embryos (42.8% vs. 27.9%) and higher rates of Bx (75.0% vs. 63.8%) on day 7, compared with the BSA group. At 24 hours postwarming, the fresh FBS group showed the highest hatching rate (p < 0.05) in comparison with other treatments. However, at 48 hours, the hatching rate was similar (p > 0.05) among groups: fresh FBS (68.1% ± 23.3%), fresh BSA (70.0% ± 31.0%), frozen FBS (39.2 ± 27.1), and frozen BSA (38.2 ± 23.9). After 24 hours, frozen BSA showed a higher number of cells compared with frozen FBS (p < 0.05). The expression of the PLAC8 gene was higher (p < 0.05) in fresh BSA embryos compared with frozen FBS embryos at 24 hours. In the present study, BSA replacement reduced embryo development, but did not affect the response to cryopreservation. However, upregulation of the PLAC8 gene suggests that embryos cultured in BSA might have better quality to support further development.

The cytokine platelet factor 4 successfully replaces bovine serum albumin for the in vitro culture of porcine embryos

The cytokine platelet factor 4 (PF4) enhances differentiation and cell viability of different stem cells lines in vitro. This study investigated whether PF4 addition to customary pig embryo semi-defined culture media can improve their developmental outcome (Experiment 1) and ultimately replace the need for bovine serum albumin (BSA, Experiment 2). Experiment 1 added PF4 (100-1000 ng/mL, 0 = control) to NCSU-23 with 0.4 mg/mL BSA culturing 3430 presumptive zygotes. Experiment 2 added PF4 (100-1000 ng/mL, 0 = Control-PVA) to a BSA-free medium (NCSU-23 with 0.3 mg/mL PVA) culturing 3820 presumptive zygotes. Zygote culture in NCSU-23 with 0.4 mg/mL BSA was used as overall control. All groups of Experiment 1 displayed similar rates of day 2-cleavage (range: 65.0 ± 10.9 to 70.0 ± 5.8%); of day 7-blastocyst rates (range: 46.6 ± 10.0 to 56.4 ± 8.2%) and of total day 7-blastocyst efficiency (range: 32.3 ± 8.3 to 37.2 ± 7.3%). Addition of PF4 did not affect total cell numbers of day 7 blastocysts (range: 44.1 ± 23.2 to 50.5 ± 26.4). In Experiment 2, PF4 accelerated embryo development, increasing (P < 0.01) blastocyst yield compared to 0-PF4, and blastocyst formation by day 5 adding PF4 100-500 ng/mL (range: 29.9 ± 7.8 to 31.8 ± 5.5%; P < 0.05) compared with BSA-control (17.2 ± 8.2%) and PF4 1000 ng/mL (15.5 ± 7.9%); showing similar blastocyst rates (range: 42.0 ± 11.5 to 49.3 ± 10.0%), total efficiency (28.0 ± 8.2 to 32.3 ± 7.1%) total cell numbers (range: 42.6 ± 19.3 to 45.7 ± 23.9) as BSA-controls. In conclusion, although PF4 did not show additive improvement under usual semi-defined, BSA-supplemented embryo media, it successfully replaced BSA sustaining porcine blastocyst production in chemically defined conditions.

C-kit signaling promotes human pre-implantation 3PN embryonic development and blastocyst formation

BACKGROUND

Although in vitro culture system has been optimized in the past few decades, the problem of few or no high quality embryos has been still not completely solved. Accordingly, fully understanding the regulatory mechanism of pre-implantation embryonic development would be beneficial to further optimize the in vitro embryo culture system. Recent studies have found the expression of c-kit in mouse embryo and its promotion effects on mouse embryonic development. However, it is unclear the expression, the role and the related molecular regulatory mechanism of c-kit in human pre-implantation embryo development. Therefore, the present study is to determine whether c-kit is expressed in human pre-implantation embryos, and to investigate the possible regulatory mechanism of c-kit signaling in the process of embryonic development.

METHODS

The present study includes human immature oocytes and three pronucleus (3PN) embryos collected from 768 women (28-32 ages) undergoing IVF, and normal 2PN embryos collected from ICR mice. Samples were distributed randomly into three different experimental groups: SCF group: G-1™ (medium for culture of embryos from the pro-nucleate stage to day 3) or G-2™ (medium for culture of embryos from day3 to blastocyst stage) + HSA (Human serum album) solution + rhSCF; SCF + imanitib (c-kit inhibitor) group: G-1™ or G-2™ + HSA solution + rhSCF + imanitib; SCF + U0126 (MEK/ERK inhibitor) group: G-1™ or G-2™ + HSA solution + rhSCF + U0126; Control group: G-1™ or G-2™ + HSA solution + PBS; The rate of good quality embryos at day 3, blastulation at day 6 and good quality blastulation at day 6 were analysis. RT-PCR, western blot and immunofluorescence staining were applied to detect the target genes and proteins in samples collected from human or mice, respectively.

RESULTS

c-kit was expressed ubiquitously in all human immature oocytes, 3PN embryos and 3PN blastocysts. In the experiment of human 3PN embryos, compared with other groups, SCF group showed obviously higher rate of good quality at day 3, better rate of blastocyst formation at day 6 and higher rate of good quality blastocyst formation at day 6. Furthermore, we observed a higher ETV5 expression in SCF group than that in other groups. Similar results were also found in animal experiment. Interestingly, we also found a higher phosphorylation level of MEK/ERK signal molecule in mice embryos from SCF group than those from other groups. Moreover, inhibition of MEK/ERK signaling would remarkably impeded the mice embryonic development, which might be due to the reduced ETV5 expression.

CONCLUSIONS

The present study firstly revealed that c-kit signaling might promote the human pre-implantation embryonic development and blastocyst formation by up-regulating the expression of ETV5 via MEK/ERK pathway. Our findings provide a new idea for optimizing the in vitro embryo culture condition during ART program, which is beneficial to obtain high quality embryos for infertile patients.

The protective effect of melatonin on the in vitro development of yak embryos against hydrogen peroxide-induced oxidative injury

SummaryMelatonin plays a critical role in several types of cells as an antioxidant to protect intracellular molecules from oxidative stress. The anti-oxidation effect of melatonin in yak embryos is largely unknown. We report that melatonin can protect the development of yak preimplantation embryos against oxidative stress induced by hydrogen peroxide (H2O2). Therefore, the quality of blastocysts developed from zygotes exposed to H2O2 was promoted. In addition, we observed that melatonin reduced H2O2-induced intracellular reactive oxygen species (ROS) levels and prevented mitochondrial dysfunction in zygotes. These phenomena revealed the effective antioxidant activity of melatonin to prevent oxidative stress in yak embryos. To determine the underlying mechanism, we further demonstrated that melatonin protected preimplantation embryos from oxidative damage by preserving antioxidative enzymes. Collectively, these results confirmed the anti-oxidation effect of melatonin in yak embryos that significantly improved the quantity and quality of blastocysts in the in vitro production of embryos in yaks.

Rapid cooling of rabbit embryos in a synthetic medium

Embryo cryopreservation media usually contain animal-derived products, such as bovine serum albumin (BSA). These products present two major disadvantages: an undefined variable composition and a risk of pathogen transmission. We aimed to evaluate the effect of replacing BSA in rabbit embryo rapid cooling "freezing" and warming media with a chemically defined medium with no animal-derived products: STEM ALPHA. Cryo3 ("Cryo3"). A total of 1540 rabbit morulae were divided into three cryopreservation groups (group 1: BSA, group 2: 20% Cryo3 and group 3: 100% Cryo3) and a fresh controls group. After rapid cooling, embryos were cultured (in vitro approach), or transferred into synchronized does (in vivo approach). In the in vitro approach, post-warm survival rates obtained with 100% Cryo3 (94.9%) were superior to BSA (90.8%) and 20% Cryo3 (85.6%). The blastocyst formation rate was similar between BSA, 20% Cryo3 and 100% Cryo3 groups (85.1, 77.9 and 83.3%, respectively), as was the expansion/hatching rate (63.1, 63.4 and 58.0%, respectively) and embryo mitochondrial activity. In the in vivo approach, pregnancy (80.0, 68.0 and 95.2%, respectively), implantation (40.5, 45.9 and 44.8%, respectively), and live-foetus rates (35.6, 35.5 and 38.1%, respectively) were similar between the three groups. To conclude, Cryo3 can replace BSA in rabbit embryo rapid cooling "freezing" and warming media.

Effect of exogenous transforming growth factor β1 (TGF-β1) on early bovine embryo development

During preimplantation development, embryos are exposed and have the capacity to respond to different growth factors present in the maternal environment. Among these factors, transforming growth factor β1 (TGF-β1) is a well known modulator of embryonic growth and development. However, its action during the first stages of development, when the embryo transits through the oviduct, has not been yet elucidated. The objective of the present study was to examine the effect of early exposure to exogenous TGF-β1 on embryo development and expression of pluripotency (OCT4, NANOG) and DNA methylation (DNMT1, DNMT3A, DNMT3B) genes in bovine embryos produced in vitro. First, gene expression analysis of TGF-β receptors confirmed a stage-specific expression pattern, showing greater mRNA abundance of TGFBR1 and TGFBR2 from the 2- to the 8-cell stage, before embryonic genome activation. Second, embryo culture for the first 48 h in serum-free CR1aa medium supplemented with 50 or 100 ng/ml recombinant TGF-β1 did not affect the cleavage and blastocyst rate (days 7 and 8). However, RT-qPCR analysis showed a significant increase in the relative abundance of NANOG and DNMT3A in the 8-cell stage embryos and expanded blastocysts (day 8) derived from TGF-β1 treated embryos. These results suggest an early action of exogenous TGF-β1 on the bovine embryo, highlighting the importance to provide a more comprehensive understanding of the role of TGF-β signalling during early embryogenesis.

Different co-culture systems have the same impact on bovine embryo transcriptome

During the last few years, several co-culture systems using either BOEC or VERO feeder cells have been developed to improve bovine embryo development and these systems give better results at high oxygen concentration (20%). In parallel, the SOF medium, used at 5% O2, has been developed to mimic the oviduct fluid. Since 2010s, the SOF medium has become popular in improving bovine embryo development and authors have started to associate this medium to co-culture systems. Nevertheless, little is known about the putative benefit of this association on early development. To address this question, we have compared embryo transcriptomes in four different culture conditions: SOF with BOEC or VERO at 20% O2, and SOF without feeders at 5% or 20% O2. Embryos have been analyzed at 16-cell and blastocyst stages. Co-culture systems did not improve the developmental rate when compared to 5% O2. Direct comparison of the two co-culture systems failed to highlight major differences in embryo transcriptome at both developmental stages. Both feeder cell types appear to regulate the same cytokines and growth factors pathways, and thus to influence embryo physiology in the same way. In blastocysts, when compared to culture in SOF at 5% O2, BOEC or VERO seems to reduce cell survival and differentiation by, at least, negatively regulating STAT3 and STAT5 pathways. Collectively, in SOF medium both blastocysts rate and embryo transcriptome suggest no influence of feeder origin on bovine early development and no beneficial impact of co-culture systems when compared to 5% O2.