Profiling of proteins secreted in the bovine oviduct reveals diverse functions of this luminal microenvironment

The oviductal microenvironment is a site for key events that involve gamete maturation, fertilization and early embryo development. Secretions into the oviductal lumen by either the lining epithelium or by transudation of plasma constituents are known to contain elements conducive for reproductive success. Although previous studies have identified some of these factors involved in reproduction, knowledge of secreted proteins in the oviductal fluid remains rudimentary with limited definition of function even in extensively studied species like cattle. In this study, we used a shotgun proteomics approach followed by bioinformatics sequence prediction to identify secreted proteins present in the bovine oviductal fluid (ex vivo) and secretions from the bovine oviductal epithelial cells (in vitro). From a total of 2087 proteins identified, 266 proteins could be classified as secreted, 109 (41%) of which were common for both in vivo and in vitro conditions. Pathway analysis indicated different classes of proteins that included growth factors, metabolic regulators, immune modulators, enzymes, and extracellular matrix components. Functional analysis revealed mechanisms in the oviductal lumen linked to immune homeostasis, gamete maturation, fertilization and early embryo development. These results point to several novel components that work together with known elements mediating functional homeostasis, and highlight the diversity of machinery associated with oviductal physiology and early events in cattle fertility.

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.

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

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

Oviductal response to gametes and early embryos in mammals

The oviduct is a complex and organized thin tubular structure connecting the ovary with the uterus. It is the site of final sperm capacitation, oocyte fertilization and, in most species, the first 3–4days of early embryo development. The oviductal epithelium is made up of ciliary and secretory cells responsible for the secretion of proteins and other factors which contribute to the formation of the oviductal fluid. Despite significant research, most of the pathways and oviductal factors implicated in the crosstalk between gametes/early embryo and the oviduct remain unknown. Therefore, studying the oviductal environment is crucial to improve our understanding of the regulatory mechanisms controlling fertilization and embryo development. In vitro systems are a valuable tool to study in vivo pathways and mechanisms, particularly those in the oviducts which in livestock species are challenging to access. In studies of gamete and embryo interaction with the reproductive tract, oviductal epithelial cells, oviductal fluid and microvesicles co-cultured with gametes/embryos represent the most appropriate in vitro models to mimic the physiological conditions in vivo.

Extracellular Vesicles from BOEC in In Vitro Embryo Development and Quality

To evaluate the effect of conditioned media (CM) and Extracellular Vesicles (EVs) derived from bovine oviduct epithelial cell (BOEC) lines on the developmental capacity of bovine zygotes and the quality of embryos produced in vitro, presumptive zygotes were cultured under specific conditions. In experiment 1, zygotes were cultured either on monolayers from BOEC extended culture (E), together with fresh BOEC suspension cells, or with BOEC-CM from fresh or E-monolayers. In experiment 2, EVs were isolated from BOEC-CM and characterized (150-200 nm) by Nanosight® and electron microscopy. Zygotes were cultured in the presence of 3x10(5) EVs/mL, 1.5x10(5) EVs/mL or 7.5x10(4) EVs/mL of fresh or frozen BOEC-EVs. In experiment 3, zygotes were cultured in absence of FCS but with EVs from BOEC-E that had been cultured in different culture media. In experiment 4, zygotes were cultured in SOF+5% normal-FCS, or EV-depleted-FCS. In all cases, cleavage rate (Day 2) and blastocyst development (Day 7-9) was assessed. Blastocysts on Days 7/8 were used for quality evaluation through differential cell count, cryotolerance and gene expression patterns. No differences were found among all FCS-containing groups in cleavage rate or blastocyst yield. However, embryos derived from BOEC-CM had more trophectoderm cells, while embryos derived from BOEC-EVs, both fresh and frozen, has more trophectoderm and total cells. More embryos survived vitrification in the BOEC-CM and BOEC-EV groups. In contrast, more embryos survived in the EV-depleted-FCS than in normal-FCS group. Gene expression patterns were modified for PAG1 for embryos cultured with EVs in the presence of FCS and for IFN-T, PLAC8, PAG1, CX43, and GAPDH in the absence of FCS. In conclusion, EVs from FCS have a deleterious effect on embryo quality. BOEC-CM and EVs during in vitro culture had a positive effect on the quality of in vitro produced bovine embryos, suggesting that EVs have functional communication between the oviduct and the embryo in the early stages of development.

Expression profile of genes as indicators of developmental competence and quality of in vitro fertilization and somatic cell nuclear transfer bovine embryos

Reproductive biotechnologies such as in vitro fertilization (IVF) and somatic cell nuclear transfer (SCNT) enable improved reproductive efficiency of animals. However, the birth rate of in vitro-derived embryos still lags behind that of their in vivo counterparts. Thus, it is critical to develop an accurate evaluation and prediction system of embryo competence, both for commercial purposes and for scientific research. Previous works have demonstrated that in vitro culture systems induce alterations in the relative abundance (RA) of diverse transcripts and thus compromise embryo quality. The aim of this work was to analyze the RA of a set of genes involved in cellular stress (heat shock protein 70-kDa, HSP70), endoplasmic reticulum (ER) stress (immunoglobulin heavy chain binding protein, Bip; proteasome subunit β5, PSMB5) and apoptosis (BCL-2 associated X protein, Bax; cysteine aspartate protease-3, Caspase-3) in bovine blastocysts produced by IVF or SCNT and compare it with that of their in vivo counterparts. Poly (A) ⁺ mRNA was isolated from three pools of 10 blastocysts per treatment and analyzed by real-time RT-PCR. The RA of three of the stress indicators analyzed (Bax, PSMB5 and Bip) was significantly increased in SCNT embryos as compared with that of in vivo-derived blastocysts. No significant differences were found in the RA of HSP70 and Caspase-3 gene transcripts. This study could potentially complement morphological analyses in the development of an effective and accurate technique for the diagnosis of embryo quality, ultimately aiding to improve the efficiency of assisted reproductive techniques (ART).

Molecular signatures of bovine embryo developmental competence

Assessment of the developmental capacity of early bovine embryos is still an obstacle. Therefore, the present paper reviews all current knowledge with respect to morphological criteria and environmental factors that affect embryo quality. The molecular signature of an oocyte or embryo is considered to reflect its quality and to predict its subsequent developmental capacity. Therefore, the primary aim of the present review is to provide an overview of reported correlations between molecular signatures and developmental competence. A secondary aim of this paper is to present some new strategies to enable concomitant evaluation of the molecular signatures of specific embryos and individual developmental capacity.

[Use of an in vitro model in bovine to evidence a functional and molecular dialogue between preimplantation embryo and oviduct epithelial cells]

Beyond being a pipe between ovary and uterus, the oviduct is an active player in different aspects of early reproductive processes, in particular in the transport of embryos to the site of implantation and the regulation of its early development. Different studies evidenced a communication between oviduct and early embryo at the molecular and functional levels. Since the study of these interactions is difficult in vivo, different in vitro systems have been developed to mimic the maternal milieu during early development. These systems allowed to confirm the action of the cells on the quality of early development (blastocyst rate and viability). In turn, the embryos are producing signals that are able to modify and adapt the activity of maternal cells.

Effects of retinoic acid on maturation of immature mouse oocytes in the presence and absence of a granulosa cell co-culture system

PURPOSE

Evaluation of the all-trans retinoic acid (t-RA) effects on in vitro maturation (IVM) and in vitro fertilization (IVF) of immature mouse oocytes in the presence and absence of granulosa cell monolayer.

METHODS

Denuded oocytes isolated from mice ovaries and matured in IVM medium alone (Control I), IVM medium in the presence of granulosa cells (Control II), IVM medium with t-RA (Experimental I) and IVM medium simultaneously with t-RA and granulosa cells (Experimental II). After 24 h, matured oocytes were fertilized in T6 medium and their development was followed until the blastocyst stage. Metaphase II oocytes ploidy were evaluated by chromosome counting.

RESULTS

The t-RA group compared to the control groups showed no obvious abnormalities. Additionally maturation and embryo development rates significantly increased in the t-RA treated granulosa cell co-culture system.

CONCLUSIONS

In conclusion, association of t-RA with granulosa cell co-culture during in vitro maturation increases meiosis resumption, formation of metaphase II oocytes, as well as 2-cell and blastocyst stage embryos.

In vitro systems for intercepting early embryo-maternal cross-talk in the bovine oviduct

A comprehensive understanding of the complex embryo-maternal interactions during the preimplantation period requires the analysis of very early stages of pregnancy. These are difficult to assess in vivo due to the small size of the embryo exerting local paracrine effects. Specifically designed experiments and holistic transcriptome and proteome analyses to address the early embryo-maternal cross-talk in the oviduct require sufficient numbers of well-defined cells in a standardized experimental environment. The pronounced estrous cycle-dependent changes in gene expression and morphology of bovine oviduct epithelial cells (BOECs) clearly show that a precise definition of the stage of estrous cycle is essential for obtaining a well-defined homogenous population of functional cells. The number of intact cells isolated from individual ampullae by solely mechanical means was 10-fold higher than previously reported cell yields after enzymatic treatment, and the purity was comparable. Bovine oviduct epithelial cells have been cultured as monolayers or in suspension. Proliferating cells grown in monolayers dedifferentiated, with a concomitant loss of important morphologic characteristics. After several days in culture, BOECs in monolayers are less likely to mimic the oviduct environment in vivo than BOEC vesicles formed of epithelial sheets in short-term suspension culture. A 24-h culture system for BOECs isolated on Day 3.5 of the estrous cycle showed excellent preservation of morphologic criteria, marker gene expression, and hormone responsiveness. The short-term BOEC culture system provides well-defined and functional BOECs in sufficient quantities for studies of early embryo-maternal interactions in experiments that mimic the environment in the oviduct in vivo.

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.

Gene expression in the in vitro-produced preimplantation bovine embryos

Recent studies have demonstrated the relevance of a gene expression profile as a clinically important key feature determining embryo quality during the in vitro preimplantation period. Although the oocyte origin can play a crucial role in blastocyst yield, the postfertilization culture period has a profound effect in determining the blastocyst quality with particular regard to the relative abundance of many developmentally and clinically important candidate genes. During the preimplantation period, the embryo undergoes several morphogenetic developmental events including oocyte maturation, minor and major forms of embryonic genome activation and transition of transcription from maternal to embryonic control. The effect of an altered gene expression pattern on the in vitro-produced bovine embryos, particularly when cultured under suboptimal conditions, was reflected by the occurrence of clinically important phenomena like apoptosis and the large offspring syndrome. This review attempts to focus on the morphogenetic embryo development and gene expression profile in the in vitro-produced bovine embryos, with special emphasis on the different parameters that may alter gene expression pattern during the critical period of in vitro culture. The effect of the in vitro system, as reflected by some clinically important phenomena like apoptosis, is also discussed.

Expression pattern of oxygen and stress-responsive gene transcripts at various developmental stages of in vitro and in vivo preimplantation bovine embryos

The present study examined the expression pattern of oxygen (O(2)) and stress-responsive gene transcripts at various preimplantation developmental stages of in vitro produced (IVP) and in vivo derived (IVD) bovine embryos. Embryos were produced in vitro from oocytes matured, fertilized and cultured in synthetic oviductal fluid (SOF) medium under low (5%) and high (20%) O(2) concentrations. In vivo embryos were derived from 18 superovulated and artificially inseminated cows. In IVP and IVD groups, embryos were collected at 2-, 4-, 8-, 16-cell morula and blastocyst stages at specific time points for gene expression analysis. The cleavage rates (69.8+/-4.8%) did not differ significantly, but blastocyst rates were significantly higher (28.5+/-3.7%) in low O(2) than those in high O(2) group (18.7+/-3.9%). Mean cell number in low O(2) (145+/-12) and high O(2) (121+/-73) IVP blastocyst were lower (P<0.05) than those of IVD blastocyst (223+/-25). The ICM ratio of IVD blastocyst (26+/-4) was lower (P<0.05) than that of IVP embryos under 5% O(2) (33+/-5) and 20% O(2) (34+/-4) concentrations, respectively. Using real time PCR, for the set of target transcripts (Glut1, Glut5, Sox, G6PD, MnSOD, PRDX5, NADH and Hsp 70.1) analyzed, there were differences in the mRNA expression pattern at 2-, 4-, 8-, 16-cell morula and Day 7 blastocyst stages between the two embryo sources. It can be concluded that, although in vitro bovine embryo culture in SOF medium under low (5%) O(2) concentration provided a more conducive environment in terms of blastocyst formation; differences in the total cell number and gene expression pattern between the IVP and IVD embryos reflected the effect of O(2) concentration.

Maturation medium supplements affect transcript level of apoptosis and cell survival related genes in bovine blastocysts produced in vitro

The aim of the present study was to investigate whether protein or macromolecule supplements to in vitro maturation media affect transcript abundance of seven genes (Bax, Bcl2, Hsp70, IGF1, IGF1R, IGF2, and IGF2R) in oocytes and blastocysts. Cumulus-oocyte complexes aspirated from slaughterhouse ovaries were matured in TCM199 medium supplemented either with 10% FBS, 6% fatty acid free BSA (fafBSA) or 4% PVP40, then inseminated and cultured in vitro for 9 days. Transcript abundance analysis was carried out on immature and in vitro matured oocytes, as well as on blastocysts. Total RNA was isolated from pools of oocytes and embryos, reverse transcribed into cDNA and subjected to transcript analysis by real-time PCR. No transcript of IGF1 gene was detected either in oocytes or in blastocysts. Maturation conditions significantly affected transcript levels of investigated loci in blastocysts but not in matured oocytes, with one exception. Only relative abundance (RA) of IGF2 gene was higher in oocytes matured with fafBSA. Moreover, oocyte maturation with fafBSA elevated transcript abundance of IGF1R, IGF2, and IGF2R genes in resulting blastocysts, whereas Hsp70 transcription was stimulated by FBS supplementation. Thus, under described conditions, fafBSA may be the optimal supplement to IVM medium due to higher transcript level of growth factor coding genes accompanied by a lower transcript level of Hsp70.

Mammalian embryo co-culture: Trials and tribulations of a misunderstood method

Embryo-somatic cell co-culture was devised over 40 years ago in an attempt to improve the development and viability of mammalian preimplantation embryos generated and cultured in vitro. While initial endeavours were successful in this respect, other studies soon highlighted a number of significant long-term detrimental impacts of this approach. Surprisingly little is known about the mechanisms underlying the beneficial effects of co-culture, although the production of embryotrophic compounds, modulation of nutrient profile, protection against culture-induced stress and/or toxin clearance are all contenders. The extent to which the inadvertent exposure of embryos to serum accounts for many of these effects remains open to question. Although the popularity of somatic cell co-culture has recently declined in favour of the use of sequential media due to concerns associated with its risk of disease transmission and long-term sequelae, we argue that complete dismissal of this technique is ill advised, given that our limited understanding of basic somatic cell interactions has prevented us from fully exploiting its potential. In this respect, there is some merit in focussing future research strategies based on reconstructed maternal tract tissue. Although the use of co-culture in clinical practice is unacceptable and its implementation in domestic species for commercial purposes should be viewed with diffidence, this technique can still provide a wealth of information on the development of novel, more physiological embryo in vitro culture systems. The proviso for acquiring such information is to gain a fuller understanding of the culture requirements/biochemistry of somatic cells and their interaction with the early conceptus.

Development and pattern of mRNA relative abundance of bovine embryos cultured in the isolated mouse oviduct in organ culture

The aim of this study was to examine the development of bovine zygotes in isolated mouse oviducts (IMO) and the quality of the blastocysts produced. In vitro produced bovine zygotes were transferred into the ampullae of the IMO and cultured in SOF or KSOM. Control embryos were cultured in droplets of the same media. Following 6 days of culture, blastocysts were processed for nuclei counts or mRNA abundance. Culture in the IMO did not affect the proportion of zygotes developing to the blastocyst stage compared to the respective control droplets (SOF: 17.7 +/- 3.2% vs. 18.8 +/- 2.7%; KSOM: 20.7 +/- 2.6% vs. 22.2 +/- 2.8%). Culture in the IMO in KSOM resulted in an increased number of inner cell mass (ICM) nuclei; however, total nuclei number or incidence of apoptosis was unaffected. Culture in the IMO in SOF resulted in an increase (P < 0.05) in abundance of transcripts in blastocysts for Oct-4 and SOX, and reduced abundance of Glut-1, Na/K, Cx43, and survivin compared to blastocysts derived from culture in SOF alone. In contrast, culture in the IMO in KSOM resulted in increased abundance of transcripts for Glut-1, Cx43, Oct-4, and survivin and reduced expression of Na/K and SOX compared to KSOM alone. Transcripts for G6PDH, IFN-tau, and E-Cad were unaffected. These data confirm that the IMO is capable of supporting development of bovine embryos. Depending on the basal medium used, the pattern of transcript abundance in embryos derived from the IMO is similar to that of in vivo derived embryos.

A bovine oviduct epithelial cell suspension culture system suitable for studying embryo–maternal interactions: morphological and functional characterization

We established a short-term (24 h) culture system for bovine oviduct epithelial cells (BOECs), obtained on day 3.5 of the estrous cycle and evaluated the cells with respect to morphological criteria, marker gene expression, and hormone responsiveness. BOEC sheets were isolated mechanically from the ampulla with similar yields from oviducts ipsi- and contralateral to the ovulation site (57.9 ± 4.6 and 56.4 ± 8.0 × 106cells). BOECs showed > 95% purity and cells cultured for 24 h maintained morphological characteristics presentin vivo, as determined by light microscopy, scanning electron microscopy, and transmission electron microscopy. Both secretory cells with numerous secretory granules and ciliated cells with long, well-developed, and vigorously beating kinocilia were visible. Quantitative real-time PCR failed to detect significant differences in transcript levels between ipsi-and contralateral BOECs for the majority of marker genes (estrogen receptors α and β (ESR1andESR2), 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR), oviductal glycoprotein 1 (OVGP1), progesterone receptor (PGR), and tumor rejection antigen 1 (TRA1)) throughout the 24 h culture period. However, the combined data of all time points for glutathione peroxidase 4 (GPX4), a gene previously shown to be expressed at higher levels in the ipsilateral oviductin vivo, also indicated significantly different mRNA levelsin vitro. The expression of marker genes remained stable after 6 h cell culture, indicating only a short adaptation period. Western blot analysis confirmed ESR1 and PGR protein expression throughout the culture period. In agreement with cyclic differencesin vivo, estradiol-17β stimulation increasedPGRtranscript abundance in BOECs. Our novel culture system provides functional BOECs in sufficient quantities for holistic transcriptome and proteome studies, e.g. for deciphering early embryo–maternal communication.

Effect of embryo developmental stage and culture conditions on number and quality of ovine in vitro produced blastocysts

This study evaluated the final output and quality of in vitro produced blastocysts derived from in vivo recovered sheep embryos cultured at various early developmental stages to blastocyst. A total of 270 embryos were recovered from the oviduct, at different days of the early luteal phase, and were classified into three different developmental stages: 2- to 4-cell (n = 93); 5- to 8-cell (n = 92) and 9- to 12-cell (n = 85). The effect of culture conditions was studied, at the same time, by randomly allocating the embryos to one of four groups: three groups of culture with fresh oviduct monolayers (2, 4 and 5 days old) and a fourth group with 2-day monolayers derived from frozen-thawed oviduct cells. Two control groups were established: first, embryos cultured in semi-defined medium (n = 29) and, second, blastocysts obtained in vivo and cryopreserved (n = 43). Influence on blastocyst yield of embryo developmental stage at the start of culture was statistically significant (p < 0.001). Two- to four-cell embryos showed a significantly lower developmental rate (67.7%) than the 5- to 8-cell (83.6%; p < 0.001) and 9- to 12-cell groups (90.5%; p < 0.0001) and lower quality in terms of blastocyst cryotolerance (56.0 vs. 83.7%; p < 0.005). There were no detected effects relating to the age or handling of the monolayer on the embryo developmental rate, but the day of blastocyst appearance was different between embryos cultured on monolayers derived from fresh or frozen-thawed cells (p < 0.0001); the main influence was on the group of 9- to 12-cell embryos (p < 0.0001). Current results confirm the temporal sensitivities of sheep embryos to in vitro culture, regardless of the culture conditions.

Sterile filtered paraffin oil supports in vitro developmental competence in bovine embryos comparable to co-culture

PURPOSE

To investigate whether sterile filtered light paraffin oil (SPO) overlaying is superior to washed light mineral oil (WMO) in supporting the in vitro developmental competence of bovine follicular oocytes. In addition, the effects of the two types of oil overlaying were compared with oil overlaying plus co-culture (CC) on bovine embryo development in vitro.

METHODS

Bovine follicular oocytes retrieved from abattoir-derived ovary were in vitro matured, fertilized and cultured in 50 microL drops overlayed with WMO or SPO and were subsequently evaluated for development rates. In second experiment, day 2 embryos grown under WMO overlaying were further cultured for 6 days in the presence (WMO+CC and SPO+CC) or absence of adult ear skin fibroblast-based co-culture system overlaid with WMO or SPO. Blastocysts from each group were evaluated for total nuclei number or were further cultured for 48 h to evaluate post-hatching development.

RESULTS

SPO overlaying resulted in significant higher (p < 0.05) development rate to morula (44.8% versus 30.6%) and blastocyst (32.8% versus 21.7%) than WMO. Also, treatment of the day 2 embryo cultures with SPO overlaying or oil plus CC (WMO+CC or SPO+CC groups) reached significantly higher development rates from the morula stage compared to embryo cultures treated with the WMO overlaying (p < 0.05). However, the development rates of the SPO treatment group (morula: 72.7%; blastocyst: 53.1%) were slightly high compared to development of the culture treated with WMO+CC (69.6 and 50.4%, respectively). This similar developmental competence pattern was also observed in cell number and embryo hatching rate.

CONCLUSION

SPO overlaying is superior to WMO and WMO+CC in supporting in vitro development of bovine embryos. The development rates are further enhanced when embryos are cultured in co-culture system overlaid with SPO. Thus, these data suggest that overlaying oil can significantly influence the pre-implantation embryo development in vitro.

Messenger RNA expression patterns in bovine embryos derived from in vitro procedures and their implications for development

The preimplantation bovine embryo is initially under the control of maternal genomic information that is accumulated during oogenesis. The genetic programme of development soon becomes dependent on new transcripts derived from activation of the embryonic genome. The early steps in development, including the timing of the first cleavage, activation of the embryonic genome, compaction and blastocyst formation, can be affected by the culture media and conditions, as well as the production procedure itself. These perturbations can possibly result in a marked decrease in the quality of the resulting blastocysts and may even affect the viability of offspring born after transfer. In vitro procedures such as in vitro production and somatic nuclear transfer of bovine embryos have been shown to be correlated with significant up- or downregulation, de novo induction or silencing of genes critical for undisturbed fetal and neonatal development. These alterations are likely to be caused by epigenetic modifications, such as DNA methylation and histone modifications. Analysis of perturbed epigenetic reprogramming and of the related phenomena, such as genomic imprinting and X-chromosome inactivation, in bovine embryos is promising for understanding the underlying mechanisms of developmental abnormalities, such as large offspring syndrome.

Gene Expression and Developmental Competence of Bovine Embryos Produced In Vitro with Different Serum Concentrations

The objective of this study was to determine the developmental rates and relative abundance of Hsp 70.1 and Glut-1 transcripts in in vivo- and in vitro-produced (IVP) bovine embryos in media supplemented with bovine serum albumin (BSA) or different oestrous cow serum concentrations. In experiment 1, in vitro maturation and culture media were supplemented with 0.4% BSA or 1, 5, 10 or 20% of oestrous cow serum (ECS). The analysis of the expression of Hsp 70.1 and Glut-1 was carried out in individual days 7 and 8 embryos by a semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) assay. In experiment 2, in vivo-produced morulae were collected on day 7 of the oestrous cycle and employed for the comparison of the relative abundances of Hsp 70.1 and Glut-1 transcripts with IVP morulae produced using two protein sources (10% ECS or 0.4% BSA). No differences were observed in cleavage rate among groups, but blastocyst formation (27%) and hatching rates (78%) were significantly higher in IVP embryos produced with 20% ECS than the other groups (p<0.05). No significant differences were observed in the relative abundances of Hsp 70.1 and Glut-1 mRNA in days 7 and 8 blastocysts expanded blastocysts between groups. The abundances of mRNA for those genes were similar between IVP and in vivo-produced morulae. In spite of the alterations observed in embryonic development, the presence of serum at distinct concentrations did not appear to alter the relative abundance profiles of Hsp 70.1 and Glut-1 compared with controls or the BSA supplementation to the IVP media.

Quantitative analysis of messenger RNA abundance for ribosomal protein L-15, cyclophilin-A, phosphoglycerokinase, β-glucuronidase, glyceraldehyde 3-phosphate dehydrogenase, β-actin, and histone H2A during bovine oocyte maturation and early embryogenesis in vitro

Real-time reverse transcription PCR has greatly improved the ease and sensitivity of quantitative gene expression studies. However, measurement of gene expression generally requires selection of a valid reference (housekeeping gene) for data normalization to compensate for inherent variations. Given the dynamic nature of early embryonic development, application of this technology to studies of oocyte and early embryonic development is further complicated due to limited amounts of starting material and a paucity of information on constitutively expressed genes for data normalization. We have validated quantitative procedures for real-time reverse transcription polymerase chain reaction (RT-PCR) analysis of mRNA abundance during bovine meiotic maturation and early embryogenesis and utilized this technology to determine temporal changes in mRNA abundance for ribosomal protein L-15, cyclophilin-A, phosphoglycerokinase, beta-glucuronidase, glyceraldehyde-3-phosphate dehydrogenase, beta-actin, and histone H2A. Quantification of amounts of specific exogenous RNAs added to samples revealed acceptable rates of RNA recovery and efficiency of reverse transcription with minimal variation. Progression of bovine oocytes to metaphase II resulted in reduced abundance of polyadenylated, but not total transcripts for majority of above genes; however phosphoglycerokinase exhibited a significant decline in both RNA populations. Abundance of mRNAs for above genes in early embryos generally remained low until the blastocyst stage, but abundance of ribosomal protein L-15 mRNA was increased at the morula stage and histone H2A mRNA showed dynamic changes prior to embryonic genome activation. Results demonstrate a valid approach for quantitative analysis of mRNA abundance in oocytes and embryos, but do not support constitutive expression of above genes during early embryonic development.

Can Vero cell co-culture improve in-vitro maturation of bovine oocytes?

This study was carried out to evaluate the effect of Vero cell co-culture on developmental competence of immature oocytes. Bovine cumulus-oocyte complexes (COC) were matured in presence or absence of Vero cells. Matured oocytes were inseminated and cultured for up to 9 days. Cleavage percentages were recorded on day 2 after insemination and embryos were evaluated on a daily basis. Expanding/expanded and hatching/hatched blastocysts were used for cell number assay. Results indicated a significantly greater cleavage percentage in oocytes matured in presence of Vero cells than control (86% versus 76%, P < or = 0.05). The percentages of advanced embryos appear to be greater on a daily basis in COC matured in presence of Vero cells compared with control. However, these differences were not significant. Blastocysts derived from COC matured in the presence of Vero cells had a significantly higher (P < or = 0.05) number of inner cell mass, trophectoderm and total cell number in expanding/expanded (65.25, 224.5 and 289.7 respectively) and hatching/hatched (67.75, 289.75 and 357.5) embryos in comparison to the control (42, 203.5, 245.5 and 51.3, 265, 316.3 respectively). Results confirm that co-culture of bovine COC during in-vitro maturation, enhances their ability for cleavage and for producing blastocysts with higher quality.

Culture of early stage ovine embryos to blastocyst enhances survival rate after cryopreservation

The current study assessed both the effects of in vitro culture and developmental stage of early stage in vivo produced ovine embryos on their ability to survive cryopreservation. Early stage embryos (n=226) were recovered from the oviduct, at different days of the early luteal phase, at three different developmental stages: 2- to 4-cell, 5- to 8-cell and 9- to 12-cell. For each stage, half of the embryos were cultured to the blastocyst stage and frozen thereafter (CF), while the remainder was frozen just after recovery (EF). A third experimental group (BF; n=43) included blastocysts obtained from the uterus and frozen immediately after recovery. Embryo viability post-thawing was determined by assessing their rate of development to the hatched blastocyst stage following in vitro culture. Culture negatively affected embryo viability, since survival rate was higher in blastocysts obtained from the uterus than in those from culture (83.7% versus 66.1%; P<0.05); also the cryosurvival of cultured embryos was lower when the timing of blastocyst formation was extended (P<0.01). However, survival following freezing-thawing of early developmental stages was significantly lower when compared to viability of their counterparts cultured to the blastocyst stage (23.1% versus 66.1%, P<0.0001). In conclusion, our results indicate that, despite the deleterious effects of culture per se, the culture of early in vivo produced ovine embryos to the blastocyst stage prior to be frozen improves their survival after thawing.

Effects of bovine oviduct epithelial cells, fetal calf serum and bovine serum albumin on gene expression in single bovine embryos produced in the synthetic oviduct fluid culture system

In this study the synthetic oviduct fluid (SOF) system with bovine oviduct epithelial cell (BOEC) co-culture is compared with an SOF system with common protein supplements. One thousand six hundred bovine embryos were cultured in SOF media supplemented with BOEC, fetal calf serum (FCS) and bovine serum albumin (BSA). Eight different culture groups were assigned according to the different supplementation factors. Developmental competence and the expression levels of five genes, namely glucose transporter-1 (Glut-1), heat shock protein 70 (HSP), connexin43 (Cx43), β-actin (ACTB) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), analysed as mRNA by using reverse transcription–polymerase chain reaction, were measured on bovine embryos cultured for 9 days. Gene expression of these in vitro-produced embryos was compared with the gene expression of in vivo-produced embryos. There was no significant difference found in embryo developmental competence between the Day 9 embryos in BOEC co-culture, FCS and BSA supplements in SOF media. However, differences in gene expression were observed. With respect to gene expression in in vivo and in vitro embryos, BOEC co-culture affected the same genes as did supplementation with FCS and BSA. HSP was the only gene that differed significantly between in vitro and in vivo embryos. When the different in vitro groups were compared, a significant difference between the BOEC co-culture and the FCS supplementation groups due to Glut-1 expression was observed.

Predicting embryo quality: mRNA expression and the preimplantation embryo

To overcome the low implantation rate (10-20%) following IVF in humans, more than two embryos are commonly replaced, potentially leading to high order multiple pregnancies with associated significantly elevated risks. Selecting the most viable embryos and transferring fewer of them could reduce this risk. Prolonged culture of embryos in vitro to the blastocyst stage may expose the embryo to hazards not normally encountered in the female reproductive tract. Recent studies comparing bovine oocyte maturation, fertilization and embryo culture in vivo and in vitro have demonstrated that the origin of the oocyte is the main factor affecting blastocyst yield, while the post-fertilization culture environment is crucial in determining blastocyst quality, measured in terms of cryotolerance and relative transcript abundance, irrespective of the origin of the oocyte. Production of embryos in vitro, particularly when using an extended period of in-vitro culture may predispose the embryo to phenomena such as 'large offspring syndrome', which is probably linked to altered gene expression, particularly of imprinted genes. Post-fertilization culture environment clearly has a profound effect on the relative abundance of gene transcripts within the embryo. Culture under sub-optimal conditions for even one day can lead to perturbations in the pattern of expression.

A Comparative Expression Analysis of Gene Transcripts in Post-fertilization Developmental Stages of Bovine Embryos Produced in Vitro or in Vivo

This study was carried out to examine the temporal variation in the relative abundance of transcripts during the post-fertilization stages of bovine embryos derived from in vitro or in vivo culture. For this purpose, cumulus-oocyte complexes obtained from ovaries from slaughterhouses were matured, fertilized and cultured in vitro. The in vitro culture was carried out using CR1 medium. In vivo embryos were derived from superovulated and artificially inseminated Simmental heifers and cows. Embryos were recovered from both systems approximately at day 1 (two-cell), day 2 (four-cell), day 3 (eight-cell), day 4 (16-cell), day 5 (morula) and day 7 (blastocyst) after insemination. Relative abundance of target transcripts was performed using real-time PCR. The transcripts studied were the nucleosome assembly protein, mRNA for alivin 1, Pleckstrin homology Sec7 coiled domain, polyadenylate binding protein, NADH dehydrogenase subunit 2, high-mobility group transcription factor, cytokine-like nuclear factor, NY-REN-58 antigen mRNA, mRNA for KIAA1764 and one novel transcript. These transcripts were derived from our previous study conducted using mRNA differential display reverse transcription-polymerase chain reaction (DDRT-PCR) between in vitro-produced bovine eight-, 16-cell, morula and blastocyst-stage embryos. The results of the present study have demonstrated the temporal variation in the relative abundance of these transcripts between in vitro and in vivo culture systems. Such variation in the relative abundance of transcripts during the post-fertilization developmental stages of in vitro and in vivo embryos may reflect the effect of the in vitro culture condition on the transcriptional activity thereby on the developmental competence of the resulting embryos.

Effect of culture environment on embryo quality and gene expression - experience from animal studies

Recent studies comparing bovine oocyte maturation, fertilization and embryo culture in vivo and in vitro have demonstrated that the origin of the oocyte is the main factor affecting blastocyst yield, while the post-fertilization culture environment is critical in determining blastocyst quality, measured in terms of cryotolerance and relative transcript abundance, irrespective of the origin of the oocyte. Production of embryos in vitro, particularly when using an extended period of in-vitro culture, may predispose the embryo to phenomena such as the large offspring syndrome, which is likely to alter gene expression, particularly of imprinted genes. It is clear now that the post-fertilization culture environment has a profound effect on the relative abundance of gene transcripts within the embryo, and culture under suboptimal conditions for as little as 1 day can lead to perturbations in the pattern of expression.

Temporal divergence in the pattern of messenger RNA expression in bovine embryos cultured from the zygote to blastocyst stage in vitro or in vivo

The objective of this study was to examine the time during the postfertilization period that gene expression patterns in in vitro-cultured bovine embryos diverge from those of their in vivo-cultured counterparts. Presumptive bovine zygotes were produced by in vitro maturation and fertilization of immature oocytes collected from the ovaries of slaughtered animals. Approximately 20 h post insemination (hpi), zygotes were denuded and randomly divided into two groups for culture either in vitro, in synthetic oviduct fluid medium, or in vivo, in the ewe oviduct. Embryos were recovered from both systems at approximately 30 hpi (2-cell), 2 (4-cell), 3 (8-cell), 4 (16-cell), 5 (early morula), 6 (compact morula), or 7 (blastocyst) days post insemination. On recovery, they were examined for stage of development and snap frozen in liquid nitrogen for the analysis of transcript abundance using real-time polymerase chain reaction. The transcripts studied were glucose transporter 5, sarcosine oxidase, mitochondrial Mn-superoxide dismutase, connexin 43, interferon tau, insulin-like growth factor II, apoptosis regulator box-alpha and insulin-like growth factor-I receptor, most of which are known from our previous work to differ in terms of transcript abundance in blastocysts derived from culture in vitro or in vivo. The results demonstrate that the relative abundance of the transcripts studied varies throughout the preimplantation period and is strongly influenced by the culture environment. In addition, the data demonstrate that changes in transcript abundance in blastocyst stage embryos are in many cases a consequence of perturbed transcription earlier in development. Depending on the transcript, these differences may be evident by as little as 10 h of initiation of culture. Such information has implications not only for basic biology but also for human assisted reproduction in which there is a move toward culturing embryos to the blastocyst stage, necessitating prolonged culture in vitro under potentially deleterious conditions.

Oocyte and embryo quality: effect of origin, culture conditions and gene expression patterns

In general, the majority of immature bovine oocytes fail to develop to the blastocyst stage following maturation, fertilization and culture in vitro. The evidence suggests that while culture conditions during in vitro embryo production can impact on the developmental potential of the early embryo, the intrinsic quality of the oocyte is the key factor determining the proportion of oocytes developing to the blastocyst stage. In addition, evidence suggests that the period of post-fertilization embryo culture is the most critical in determining blastocyst quality. This paper reviews the current literature, with emphasis on the bovine model, demonstrating evidence for an effect of oocyte origin and/or in vitro maturation conditions on the developmental capacity and gene expression patterns in the oocyte. Furthermore, the well-documented effects of post-fertilization culture environment on embryo gene expression and quality are highlighted.

Embryo-maternal communication in bovine - strategies for deciphering a complex cross-talk

Early embryonic development, implantation and maintenance of a pregnancy are critically dependent on an intact embryo-maternal communication. So far, only few signals involved in this dialogue have been identified. In bovine and other ruminants, interferon tau is the predominant embryonic pregnancy recognition signal, exhibiting antiluteolytic activity. However, this is just one aspect of the complex process of embryo-maternal signalling, and a number of other systems are more likely to be involved. To gain a more comprehensive understanding of these important mechanisms, integrated projects involving specialists in embryology, reproductive biotechnology and functional genome research are necessary to perform a systematic analysis of interactions between pre-implantation stage embryos and oviduct or uterine epithelial cells, respectively. State-of-the-art transcriptomic and proteomic technologies will identify reciprocal signals between embryos and their maternal environment and the respective downstream reaction cascades. For in vivo studies, the use of monozygotic twins as recipient animals provides elegant model systems, thus eliminating genetic variability as a cause of differential gene expression. In addition, suitable systems for the co-culture of oviduct epithelial or endometrium cells with the respective embryonic stages need to be established for functional validation of candidate genes potentially involved in the dialogue between embryos and their maternal environment. The knowledge of these mechanisms should help to increase the pregnancy rate following embryo transfer and to avoid embryonic losses. Candidate genes involved in embryo-maternal communication will also be used to define new quality criteria for the selection of embryos for transfer to recipients. Another application is the supplementation of embryotrophic factors or components of embryo-maternal signalling in optimized formulations, such as bioartificial matrices. As a long-term goal, signalling mechanisms identified in bovine will also be functionally evaluated in other species, including the human.

Regulation of ipsilateral and contralateral bovine oviduct epithelial cell function in the postovulation period: a transcriptomics approach

We studied differential gene expression in ipsilateral and contralateral bovine oviduct epithelial cells using a combination of subtracted cDNA libraries and cDNA array hybridization. Four Simmental heifers were synchronized and slaughtered 3.5 days after they entered standing heat. Epithelial cells were isolated from ipsilateral and contralateral oviducts. To identify genes that are differentially regulated in ipsilateral and contralateral epithelium, subtracted cDNA libraries were produced by suppression subtractive hybridization and analyzed by cDNA array hybridization. Sequencing of cDNAs showing differential expression levels in ipsilateral and contralateral epithelium revealed 35 different cDNAs, 30 of which matched genes with known functions and 5 of which matched genes without a known function. The majority of genes (n = 27) were expressed at a higher level in the ipsilateral oviduct, but for some genes (n = 8), mRNA abundance was higher in the contralateral oviduct. The regulated genes or their products include a variety of functional classes such as cell-surface proteins, cell-cell interaction proteins, members of signal transduction pathways, immune-related proteins, and enzymes. Identification of genes differentially regulated in ipsilateral and contralateral oviduct epithelial cells is the first step toward a systematic analysis of local mechanisms that regulate the function of the bovine oviduct epithelium in the postovulation period.