Analysis of differential messenger RNA expression between bovine blastocysts produced in different culture systems: implications for blastocyst quality

Effect of long-term culture of mouse embryonic stem cells under low oxygen concentration as well as on glycosaminoglycan hyaluronan on cell proliferation and differentiation

OBJECTIVES

Maintaining undifferentiated stem cells in defined conditions is of critical importance to improve their in vitro culture. We have evaluated the effects of culturing mouse stem (mES) cells under physiological oxygen concentration as well as by replacing fibroblast feeder layer (mEF) with gelatin or glycosaminoglycan hyaluronan (HA), on cell proliferation and differentiation.

MATERIALS AND METHODS

After 3 days culture or after long-term cell culture under different conditions, levels of apoptotic cell death were determined by cell cycle and TUNEL (TdT-mediated dUTP nick end labelling) assays and levels of cell proliferation by CFSE (5-(and-6)-carboxyfluorescein diacetate succinimidyl ester) labelling. We assessed spontaneous differentiation into cardiomyocytes and mRNA expression of pluripotency and differentiation biomarkers.

RESULTS

After 3 days culture under hypoxic conditions, levels of proliferation and apoptosis of mES cells were higher, in correlation with increase in intracellular reactive oxygen species. However, when cells were continuously grown for 1 month under those conditions, the level of apoptosis was, in all cases, under 4%. Hypoxia reduced spontaneous differentiation of mES into cardiomyocytes. Long-term culture on HA was more effective in maintaining the pluripotent state of the mES cells when compared to that on gelatin. Level of terminal differentiation was highest on mEF, intermediate on HA and lowest on gelatin.

CONCLUSIONS

Our data suggest that hypoxia is not necessary for maintaining pluripotency of mES cells and appeared to be detrimental during ES differentiation. Moreover, HA may offer a valuable alternative for long-term culture of mES cells in vitro.

In vivo-derived horse blastocysts show transcriptional upregulation of developmentally important genes compared with in vitro-produced horse blastocysts

In vitro-produced (IVP) equine blastocysts can give rise to successful pregnancies, but their morphology and developmental rate differ from those of in vivo-derived equine blastocysts. The aim of the present study was to evaluate this difference at the genetic level. Suppression subtractive hybridisation (SSH) was used to construct a cDNA library enriched for transcripts preferentially expressed in in vivo-derived equine blastocysts compared with IVP blastocysts. Of the 62 different genes identified in this way, six genes involved in embryonic development (BEX2, FABP3, HSP90AA1, MOBKL3, MCM7 and ODC) were selected to confirm this differential expression by reverse transcription–quantitative real-time polymerase chain reaction (RT-qPCR). Using RT-qPCR, five genes were confirmed to be significantly upregulated in in vivo-derived blastocysts (i.e. FABP3, HSP90AA1 (both P < 0.05), ODC, MOBKL3 and BEX2 (P < 0.005 for all three)), confirming the results of the SSH. There was no significant difference in MCM7 expression between IVP and in vivo-derived blastocysts. In conclusion, five genes that are transcriptionally upregulated in in vivo-derived equine blastocysts compared with IVP blastocysts have been identified. Because of their possible importance in embryonic development, the expression of these genes can be used as a marker to evaluate in vitro embryo production systems in the horse.

Expression of mRNA, before and after freezing, in bovine blastocysts cultured under different conditions

Production methods and culture systems have been shown to affect blastocyst mRNA expression and cryopreservability, which may serve as sensitive indicators of embryo quality and developmental competence. In the present study, the impact of four established culture conditions for producing bovine blastocysts (in vitro production, IVP; gamete intra-fallopian transfer, GIFT; transfer of cleaved stages into the oviduct, CLVT; multiple ovulation embryo transfer, MOET) was assessed, in terms of both cryosurvival and levels of mRNA expression of several selected genes (occludin, desmocollin 2, solute carrier family 2 member 3, BAX, BCL-XL, heat shock protein 1A, aquaporin 3, DNA methyltransferase 1a) detected with RT-qPCR. At 24 hours post-thawing, blastocysts derived from in vitro production showed a significantly higher re-expansion rate compared to the other groups. At later times, this difference was no longer significant. Before freezing, embryos of the MOET group showed significantly more desmocollin 2 mRNA compared to embryos produced using other culture methods. After freezing, significant upregulation was found in transcripts of heat shock protein 1A in embryos of all groups; of solute carrier family 2 member 3, only in IVP derived embryos; of BAX, BCL-XL, occludin, desmocollin 2, only in the MOET and IVP groups. Aquaporin 3 and DNA methyltransferase 1a were neither up- nor downregulated in blastocysts of any group. In conclusion, these findings suggest that, after freezing, embryos seem to have switched on mRNA synthesis, an active metabolism, operational cell connections, and are prepared for hatching and beyond.

Fetal calf serum enhances in vitro production of Bos taurus indicus embryos

The objective of this study was to determine the effect of fetal calf serum (FCS) on the quality of in vitro produced bovine embryos. Cumulus oocyte-complexes (COCs, n = 2 449) recovered by ovum pick-up from Bos taurus indicus donors were randomly assigned to experimental groups. Sperm selected by Percoll gradient was used for in vitro fertilization (insemination = Day 0). In Experiment 1 (n = 1 745 COCs), zygotes were cultured in vitro in Synthetic Oviduct Fluid + 4 mg/mL of bovine serum albumin (BSA), or BSA + 2% FCS (BSA+FCS). In Experiment 2 (n = 704 COCs), the COCs were cultured in SOF + BSA, BSA + 2% FCS, or BSA + 2% FCS on D4 (BSA + FCSD4). In Experiment 1, blastocyst yield (51%) and Quality I blastocysts (41%) at Day 7 were higher (P < 0.05) in the BSA + FCS treatment than in BSA (42 and 30%, respectively). In Experiment 2, blastocyst yield was higher (P < 0.05) in the BSA+FCS (47%) treatment. Quality I blastocyst yield was higher (P < 0.05) for BSA + FCS (34%) and BSA+FCSD4 (32%) compared to the BSA treatment (20%). A total of 820 embryos were transferred, with no significant differences among groups in pregnancy rates. In conclusion, in vitro culture in SOFaaci + BSA + FCS enhanced blastocyst yield and Quality I blastocysts; adding FCS to the culture medium increased the efficiency of IVP of bovine embryos.

Comparison of mRNA expression levels of selected genes in the brain stem of cattle naturally infected with classical and atypical BSE

Since 2004 cases of atypical bovine spongiform encephalopathy (BSE) in older cattle are recorded on the basis of aberrant glycoprofiles of prion protein resistant to proteolysis (PrP(res)). The nature of those types of PrP(res) is still not fully understood but the epidemiological data indicate that their occurrence is rare. Hitherto, most BSE cases were studied on the basis of the features of pathological form of prion protein (PrP(Sc)) or lesions observed in the gray matter of the brain. Here we propose the gene expression profiling as a method to characterize and distinguish BSE types. Thus, the aim of the study was to compare the activity of some genes which are known to play a role in the pathogenesis of transmissible spongiform encephalopathies (TSEs). Significant differences in the expression level of the selected genes in the brain stem were observed for 7 out of 11 genes tested when the results for BSE affected and healthy control animals were compared. Significant up-regulation of caspase 3, Bax and 14-3-3 protein encoding genes was apparent in the obex of all BSE affected cattle regardless of the prion type. Significant and unique to BSE H-type up-regulation was detected in prion and SOD1 genes, while BSE C-type was characterized by higher Bcl-2 and Fyn gene expression levels in respect to other BSE types and control animals. Different gene expression profiles of bovine brains infected with classical and atypical BSE indicate possible different pathogenesis or origin of the disease.

Oviductal secretions: will they be key factors for the future ARTs?

A variety of evolutionary processes has led to the development of different organs to ensure that internal fertilization occur successfully. Fallopian tubes are a particularly interesting example of such organs. Some of the key events during fertilization and early embryo development occur in the oviduct. Knowledge of the different components described in the oviduct is extensive. Oviductal components include hormones, growth factors and their receptors that have important roles in the physiology of the oviduct and embryo development. Other oviductal factors protect the gamete and the embryos against oxidative stress and pathogens. Different proteins and enzymes are present in the oviductal fluid and have the ability to interact with the oocyte and the sperm before the fertilization occurs. Of special interest is the oviduct-specific glycoprotein (OVGP1), a glycoprotein that is conserved in different mammals, and its association with the zona pellucida (ZP). Interaction of the oocyte with oviductal secretions leads us to emphasize the concept of 'ZP maturation' within the oviduct. The ZP changes produced in the oviduct result in an increased efficiency of the in vitro fertilization technique in some animal models, contributing in particular to the control of polyspermy and suggesting that a similar role could be played by oviductal factors in human beings. Finally, attention should be given to the presence in the oviductal fluid of several embryotrophic factors and their importance in relation to the in vivo versus in vitro developmental ability of the embryos.

Metatranscriptome analysis of the human fecal microbiota reveals subject-specific expression profiles, with genes encoding proteins involved in carbohydrate metabolism being dominantly expressed

The human gastrointestinal (GI) tract provides home to a complex microbial community, collectively termed microbiota. Although major efforts have been made to describe the diversity and stability of the microbiota, functional studies have been largely restricted to intestinal isolates and include few community studies. The aim of this study was to explore the in situ gene expression of the fecal microbiota and to evaluate the RNA fingerprinting method cDNA-AFLP (cDNA amplified fragment length polymorphism) for this purpose. To this end, cDNA-AFLP analysis of enriched mRNA revealed that two healthy subjects showed highly divergent expression profiles with considerable fluctuations in time. Subsequent excision and sequence determination of bands from the mRNA-enriched profiles resulted in 122 identifiable sequences (transcripts and rRNAs). The classification of retrieved transcripts into functional clusters based on COG (cluster of orthologous genes) annotation showed that most assigned transcripts belonged to the metabolism cluster (26% of all sequences), underlining that even at the very end of the intestinal tract the microbiota is still very active. This study furthermore revealed that cDNA-AFLP is a useful tool to compare gene expression profiles in time in complex microbial communities.

Effects of gamete source and culture conditions on the competence of in vitro-produced embryos for post-transfer survival in cattle

One limitation to the use of in vitro-produced embryos in cattle production systems is the fact that pregnancy rates after transfer to recipients are typically lower than when embryos produced in vivo are transferred. Conceptually, the oocyte and spermatozoon from which the embryo is derived could affect competence for post-transfer survival. There are sire differences in embryonic survival after transfer, but there is little evidence that an embryo's ability to establish pregnancy is determined by sex sorting of spermatozoa by flow cytometry. The role of the source of the oocyte as a determinant of embryonic survival after transfer has not been examined carefully. Conditions for embryo culture after fertilisation can have an impact on the ability of the embryo to establish pregnancy following transfer. Among the specific molecules produced in the reproductive tract of the cow that have been shown to improve competence of in vitro-produced embryos for post-transfer survival are colony-stimulating factor 2, insulin-like growth factor-1 (for recipients exposed to heat stress) and hyaluronan (for less-advanced embryos). There is also a report that embryo competence for post-transfer survival can be improved by inclusion of a carbon-activated air filtration system in the incubator used to culture embryos. Progress in developing culture systems to improve embryonic competence for survival after transfer would be hastened by the development of in vitro assays that accurately predict the potential of an embryo to establish pregnancy after transfer. A group of 52 genes has been identified that are differentially expressed in embryos that developed to term v. embryos that did not establish pregnancy. Perhaps a gene microarray consisting of these genes, alone or in combination with other genes, could be used to screen embryos for competence to establish pregnancy.

Effects of histone hyperacetylation on the preimplantation development of male and female bovine embryos

Trichostatin A (TSA) induces histone hyperacetylation by inhibiting histone deacetylases and consequently increasing gene expression. The hypothesis was that TSA supplementation during the in vitro culture (IVC) of bovine embryos would increase the blastocyst rate, particularly in low-quality and female embryos. Oocytes were fertilised separately with X and Y spermatozoa and, 70 h after IVF, the IVC medium was supplemented with 5 nM and 15 nM TSA for 48 or 144 h. Incubation of female embryos with 5 nM and 15 nM TSA resulted in similar increases in acetylated histone H3K9 levels. However, to see comparable effects on acetylated histone H3K9 levels in male embryos, the culture medium needed to be supplemented with 15 nM TSA (as opposed to 5 nM TSA for female embryos). Treatment of male and female embryos with 5 nM TSA for 48 h or female embryos with 5 nM for 144 h had no effect on blastocyst rates, although 15 nM TSA compromised embryonic development. The terminal deoxyribonucleotidyl transferase-mediated dUTP–digoxigenin nick end-labelling (TUNEL) assay revealed increased apoptosis in female embryos treated with 5 nM TSA for 144 h, as well as in male and female embryos treated with 15 nM TSA for 48 h, but this increase in apoptosis was not observed in low-quality embryos. The results of the present study suggest that TSA treatment promotes histone hyperacetylation, but has no beneficial effects on the in vitro production of male and female bovine embryos during preimplantation development.

Colony-stimulating factor 2 (CSF-2) improves development and posttransfer survival of bovine embryos produced in vitro

In this study, we tested the role of colony-stimulating factor 2 (CSF2) as one of the regulatory molecules that mediate maternal effects on embryonic development during the preimplantation period. Our objective was to verify effects of CSF2 on blastocyst yield, determine posttransfer survival, and evaluate properties of the blastocyst formed after CSF2 treatment. In vitro, CSF2 increased the percentage of oocytes that became morulae and blastocysts. Blastocysts that were treated with CSF2 tended to have a greater number of inner cell mass cells and had a higher ratio of inner cell mass to trophectoderm cells. There was no effect of CSF2 on the incidence of apoptosis. Treatment with CSF2 from d 5 to 7 after insemination increased embryonic survival as indicated by improved pregnancy rate at d 30-35 of gestation. Moreover, treatment with CSF2 from either d 1-7 or 5-7 after insemination reduced pregnancy loss after d 30-35. Results indicate that treatment with CSF2 can affect embryonic development and enhance embryo competence for posttransfer survival. The fact that treatment with CSF2 during such a narrow window of development altered embryonic function much later in pregnancy suggests that CSF2 may exert epigenetic effects on the developing embryo that result in persistent changes in function during the embryonic and fetal periods of development.

Effects of culture medium and protein supplementation on mRNA expression of in vitro produced bovine embryos

Numerous studies have reported aberrant gene expression levels attributed to suboptimal in vitro culture conditions. This study investigated the effects of different culture systems and protein sources on the developmental competence of in vitro production (IVP) embryos measured by cleavage and blastocyst rates, cell number, and relative abundance of POU5F1 (OCT4), nanog, GJA1 (connexin 43), and SLC2A1 (GLUT1) transcripts when compared to in vivo embryos. Experiment 1 compared IVP embryos cultured in either synthetic oviductal fluid (SOFaa) or potassium simplex optimized medium supplemented with amino acids (KSOMaa). Experiment 2 compared the same two culture systems with and without the addition of calf serum (CS). Results from both experiments indicated that despite similar developmental rates, significant differences were observed at the mRNA level. In Experiment 1, OCT4 was the only transcript to have a mean abundance level significantly higher in KSOMaa blastocysts when compared with both SOFaa and in vivo embryos. The same pattern of upregulation of OCT4 mRNA was noted in Experiment 2. There were no significant alterations of the ICM specific transcript nanog in either experiment. In contrast to reports by others, connexin 43 mRNA was not expressed at detectable levels in in vivo embryos analyzed in our studies. Blastocysts cultured in SOFaa with CS or KSOMaa had a significant upregulation of GLUT1 mRNA when compared with other treatments and in vivo embryos. Until differences between IVP and in vivo embryos are minimized, aberrations in IVP will continue to arise.

Analysis of gene transcription alterations at the blastocyst stage related to the long-term consequences of in vitro culture in mice

We have reported thatin vitroculture (IVC) of preimplantation mouse embryos in the presence of FCS produces long-term effects (LTE) on development, growth and behaviour of the offspring at adult age. To analyse the mechanisms underlying this phenomenon, we have examined development and global alterations in gene expression in the mouse blastocysts produced in the presence of FCS, conditions known to be suboptimal and that generate LTE. Embryos culturedin vitroin KSOM and in KSOM+FCS had a reduced number of cells in the inner cell mass at the blastocyst stage compared within vivoderived embryos; however, only culture in KSOM+FCS leads to a reduction in the number of trophoblast cells. Gene expression levels were measured by comparison among three groups of blastocysts (in vivo, IVC in KSOM and IVC in KSOM+FCS). Different patterns of gene expression and development were found between embryos culturedin vitroorin vivo. Moreover, when we compared the embryos produced in KSOM versus KSOM+FCS, we observed that the presence of FCS affected the expression of 198 genes. Metabolism, proliferation, apoptosis and morphogenetic pathways were the most common processes affected by IVC. However, the presence of FCS during IVC preferentially affected genes associated with certain molecular and biological functions related to epigenetic mechanisms. These results suggest that culture-induced alterations in transcription at the blastocyst stage related to epigenetic mechanisms provide a foundation for understanding the molecular origin at the time of preimplantation development of the long-term consequences of IVC in mammals.

Effects of oviductal fluid on the development, quality, and gene expression of porcine blastocysts produced in vitro

In mammals, fertilization and early pre-implantation development occur in the oviduct. Previous results obtained in our laboratory have identified specific molecules in the oviduct that affect porcine sperm-egg interactions. The aim of the present study was to determine whether the contact between oocytes and oviductal fluid also affect embryo development, quality, and gene expression. In vitro matured porcine oocytes were exposed to bovine oviductal fluid (bOF) for 30 min prior to fertilization. Cleavage and blastocyst development rates were significantly higher from bOF-treated oocytes than from untreated oocytes. Blastocysts obtained from bOF-treated oocytes had significantly greater total cell numbers than those obtained from untreated oocytes. Using real-time PCR, grade 1 (very good morphological quality) and grade 2 (good morphological quality) blastocysts were analyzed for gene transcripts related to apoptosis (BAX, BCL2L1), mitochondrial DNA (mtDNA) transcription/replication (POLG, POLG2, and TFAM), blastomere connection and morula compaction (GJA1), and blastocyst formation and pluripotency (POU5F1). We found that the entire set of genes analyzed was differentially expressed between grade 1 and 2 blastocysts. Furthermore, bOF treatment reduced the ratio of BAX to BCL2L1 transcripts and enhanced the abundance of TFAM transcripts in grade 2 blastocysts. Not only do these findings demonstrate that factors within the bOF act on porcine oocytes both quickly and positively, but they also suggest that such factors could promote embryo development and quality by protecting them against adverse impacts on mtDNA transcription/replication and apoptosis induced by the culture environment.

Consequences of in vitro culture conditions on embryo development and quality

Despite major efforts directed at improving the yield of blastocysts from immature oocytes in vitro, the quality of such blastocysts continually lags behind that of blastocysts produced in vivo. These differences are manifested at the level of morphology, metabolism, gene expression and cryotolerance, and may have a knock-on effect further along the developmental axis. Evidence suggesting that in vitro culture conditions, while capable of producing blastocysts in relatively high numbers, are far from optimal with deficiencies being manifested in terms of abnormally large offspring. It is clear nowadays that modification of the post-fertilization culture environment in vitro can improve blastocyst quality to some extent.

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

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

Early apoptosis is associated with improved developmental potential in bovine oocytes

The poor quality of oocytes may be the main reason for the low efficiency of the current in vitro embryo production. However, efforts are required to understand the mechanisms of oocyte development, which is believed to be largely regulated by apoptosis in vivo. The aim of this study was to investigate the levels of apoptosis in bovine immature oocytes with different developmental potentials and to determine whether early apoptosis in bovine oocytes is correlated with their subsequent development. Cumulus-oocyte complexes (COCs) were selected and classified into four groups according to oocyte cytoplasm and cumulus status. Early and late stages of apoptosis were detected by Annexin-V and TUNEL staining, respectively. Developmental competence was evaluated by nuclear maturation (MII) after in vitro maturation and development rates in different stages following in vitro fertilization. Meanwhile, the transcripts of Bcl-2 and Bax genes were carried out in immature oocytes by real-time RT-PCR. Results indicated that Annexin-V-positive oocytes were detected in various groups at different percentages, and Group III showed the highest positive ratio. No TUNEL-positive oocytes were found in any immature COCs. Group III oocytes demonstrated the highest nuclear maturation, cleavage, blastocyst, and hatching blastocyst rates. Meanwhile, Group III oocytes exhibited the highest Bax (initiating apoptosis) transcriptional level and the lowest Bcl-2 (preventing apoptosis) transcriptional level. Taken together, Annexin-V and quantitative PCR results indicated that early apoptosis was beneficial for developmental competence, while TUNEL staining showed that none of the immature oocytes were undergoing late-stage apoptosis. This is the first time that Bax and Bcl-2 transcripts were characterized in the immature bovine oocyte, and results indicated that the genes are good markers of early apoptosis and embryo development. This research overthrows the traditional view that oocytes undergoing apoptosis have poor developmental competence, and the findings will facilitate oocyte selection and improvement of in vitro embryo production.

Preimplantation embryo programming: transcription, epigenetics, and culture environment

Preimplantation development directs the formation of an implantation- or attachment-competent embryo so that metabolic interactions with the uterus can occur, pregnancy can be initiated, and fetal development can be sustained. The preimplantation embryo exhibits a form of autonomous development fueled by products provided by the oocyte and also from activation of the embryo's genome. Despite this autonomy, the preimplantation embryo is highly influenced by factors in the external environment and in extreme situations, such as those presented by embryo culture or nuclear transfer, the ability of the embryo to adapt to the changing environmental conditions or chromatin to become reprogrammed can exceed its own adaptive capacity, resulting in aberrant embryonic development. Nuclear transfer or embryo culture-induced influences not only affect implantation and establishment of pregnancy but also can extend to fetal and postnatal development and affect susceptibility to disease in later life. It is therefore critical to define the basic program controlling preimplantation development, and also to utilize nuclear transfer and embryo culture models so that we may design healthier environments for preimplantation embryos to thrive in and also minimize the potential for negative consequences during pregnancy and post-gestational life. In addition, it is necessary to couple gene expression analysis with the investigation of gene function so that effects on gene expression can be fully understood. The purpose of this short review is to highlight our knowledge of the mechanisms controlling preimplantation development and report how those mechanisms may be influenced by nuclear transfer and embryo culture.

Comparative transcriptome analysis of in vivo- and in vitro-produced porcine blastocysts by small amplified RNA-serial analysis of gene expression (SAR-SAGE)

Production of embryos in vitro has enormous potential for research and commercial applications. Unfortunately, in vitro production of porcine embryos is extremely inefficient. Despite the characterization of distinct phenotypes, little is known about the molecular mechanisms and altered physiological processes of in vitro-produced embryos. The objective of this study was to compare global gene expression patterns from in vivo- (IVO) and in vitro-produced (IVP) porcine embryos using small amplified RNA-serial analysis of gene expression (SAR-SAGE). Whole-cell RNA from pools of Day 6 IVO and IVP blastocysts was used to construct SAR-SAGE libraries. Sequence analysis of the IVO and IVP libraries yielded 98,771 and 98,408 tags, respectively. A total of 20,029 and 23,453 putative transcripts were detected in the IVO and IVP libraries, respectively. Statistical analyses of SAGE tag frequencies between the IVO and IVP libraries indicated that 938 and 193 tags were differentially expressed at a P < 0.05 and P < 0.001 level of significance, respectively, suggesting significant deviations in transcriptome profiles from IVO and IVP embryos. Categorization of differentially expressed transcripts into functional groupings indicated a significant deviation in gene expression from IVP blastocysts compared with IVO blastocysts for a number of biological processes including cellular metabolism, organization, and response to stress. Real-time PCR confirmed differential expression for several transcripts from independent IVO and IVP blastocysts. These results demonstrate compromised gene expression in IVP blastocysts compared with IVO blastocysts for a number of biological processes, particularly processes involved in mitochondrial function; thereby providing potential target pathways for improvement of IVP methods.

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.

Development, molecular composition and freeze tolerance of bovine embryos cultured in TCM-199 supplemented with hyaluronan

Hyaluronan (HA) is glycosaminoglycan that is present from the start of embryonic development and its role and concentration increases with embryo development. The objective of this study was to evaluate if the presence of HA in TCM-199 culture medium had an effect on the development and quality of bovine embryos. There was no effect of HA on the total number of zygotes developing to blastocysts on day 7, however more expanded and hatched blastocyst stages were observed on days 8 and 9 in the group supplemented with HA (p< 0.05). Following freeze/thawing, significantly more (p< 0.05) embryos cultured in medium supplemented with HA hatched than those cultured in TCM-199 alone or those with BSA. Medium supplemented with HA and BSA significantly increased the level of expression of glucose metabolismGlut-1gene and embryo compactionCx43gene (p< 0.05), and had no effect onGlut-5andIGF-IIexpression. In addition, HA presence in culture decreased the level of expression of apoptosisBaxand oxidative stressSOXgenes (p< 0.05). There was significant difference in total number of nuclei between TCM-199 medium only and the remaining media containing BSA or HA plus BSA, between which there was no difference. In summary, our results indicate that the addition of high molecular weight HA to TCM-199 medium that contains BSA on day 4 of culture improved embryo development to hatching and hatched blastocysts and the quality of produced embryos, which were superior to embryos cultured without HA addition.

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.

Epigenetic differences between male and female bovine blastocysts produced in vitro

Epigenetic differences between male and female bovine blastocysts provide a plausible link between physiological and gene transcription differences observed between male and female embryos. The aim of this study was to examine sex-related epigenetic differences in bovine blastocysts produced in vitro. Oocytes were matured in vitro and inseminated with frozen-thawed sex-sorted (X or Y) and unsorted (control) bull sperm. Zygotes were cultured to blastocyst stage and were analyzed for embryo sexing, mtDNA content, telomere lengths, methylation analysis, and quantification of mRNA transcripts of DNA methyltransferases (Dnmt1, Dnmt3a, Dnmt3b) HMT1 hnRNP methyltransferase-like 2 (Hmt1), and interleukin enhancer binding factor 3 (Ilf3). There was a difference (P < 0.05) in the mean mtDNA copy number between male (410,000 +/- 23,000) and female (360,000 +/- 21,000) blastocysts. Telomere length was shorter in male blastocysts (P < 0.01). The level of methylation in a sequence near a variable number of tandem repeats minisatellite region [variable number of tandem repeats (VNTR)] in males (39.8% +/- 4.8) was higher than in females (23.7% +/- 3.1) (P < 0.05); however, no differences were found in other regions analyzed. Moreover, transcription differences between sexes were observed for Dnmt3a, Dnmt3b, Hmt1, and Ilf3. These results provide evidence of epigenetic differences between male and female bovine in vitro produced embryos and suggest that before initiation of gonadal differentiation, epigenetic events may modulate the difference between speed of development, metabolism, and transcription observed during preimplantation development between male and female embryos.

Effect of duration of oocyte maturation on the kinetics of cleavage, embryo yield and sex ratio in cattle

The aim of the present study was to examine the effect of maturation for 16 v. 24 h on the kinetics of development and the sex ratio of bovine embryos. Oocytes were inseminated at 16 or 24 h after the beginning of maturation using frozen–thawed bull semen. Two-cell embryos at 24, 28, 32, 36, 40, 44 and 48 h post-insemination (hpi) and blastocysts at Days 6, 7 and 8 from both groups were snap-frozen individually and stored at –80°C until determination of embryo sex. Insemination at 16 h resulted in a lower cleavage rate at 48 hpi than insemination at 24 h (70.6% v. 77.1%, respectively, P < 0.05). In terms of the evolution of cleavage divisions, insemination at 24 h resulted in a typical pattern of cleavage such that by 32 hpi, ~58% of presumptive zygotes had cleaved. In contrast, first cleavage following insemination at 16 h was significantly slower such that by 32 hpi, ~35% of presumptive zygotes had cleaved. Duration of IVM did not affect blastocyst yield (~37%). The overall sex ratio of 2-cell embryos at 48 hpi differed from 1 : 1 in favour of males in both groups (24 h: 55.9 v. 44.1%; 16 h: 59.1 v. 40.9%, P < 0.05). Similarly, the overall sex ratio of blastocysts differed from 1 : 1 in both groups (24 h: 59.7 v. 40.3%; 16 h: 58.5 v. 41.5%, P < 0.05). In conclusion, timing of gamete interaction and maturity of the oocyte at the time of the interaction can affect the kinetics of the early cleavage divisions but has no effect on the sex ratio of the embryos produce.

Selective degradation of transcripts in mammalian oocytes and embryos

During the last decade several gene expression analysis studies have been carried out to investigate the transcriptional profile of bovine embryos in response to various culture and treatments conditions. Despite this fact, the function of a large number of genes in mammalian embryogenesis has not yet been investigated or is not known. The conventional gene-knockout experiments have been used extensively to study the function of genes in mammalian embryogenesis. However, these studies are relatively slow and cannot keep pace with the rapid accumulation of new sequence information produced by various genome projects. For this, the posttranscriptional gene silencing (PTGS) by double-stranded RNA (dsRNA), or RNA interference (RNAi), has emerged as a new tool for studying gene function in an increasing number of organisms. The present review will focus on recent developments in the use of RNAi for selective degradation of transcripts in mammalian embryos to elucidate their function in early development.

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.

Nuclear reprogramming in embryos generated by the transfer of yak (Bos grunniens) nuclei into bovine oocytes and comparison with bovine–bovine SCNT and bovine IVF embryos

Although inter-species SCNT may be useful for increasing and preserving populations of endangered species, there are many reports that inter-species nuclear transfer embryos only develop to the blastocyst stage. In this study, yak-bovine SCNT blastocysts were successfully implanted in the surrogate bovine uterus but failed to develop to term or aborted. To clarify the reasons, we examined yak-bovine SCNT blastocyst development, total cell number, inner cell mass (ICM) number, trophoblast (TE) cell number and relative gene expression in yak fibroblast cells and yak-bovine SCNT embryos at various stages. The potential for development of yak-bovine SCNT embryos to blastocysts was 30+/-5.7% (mean+/-S.E.M.); the total cell number was 85.3+/-16.3, fewer than in IVF bovine embryos (106.2+/-18.2) but within the reported range (60-300). The yak-bovine SCNT blastocysts had a lower ratio of TE cells to total cells (43.9+/-8.7%) than bovine IVF embryos (59.4+/-3.4%; P<0.05) or bovine-bovine SCNT (69.5+/-5.4%; P<0.05). Also, several yak-bovine SCNT embryos had abnormal initiation of expression of both Mash2 and IL6. However, expression of vimentin, collagen, Cx43 and PSMC3 were normal in yak fibroblast cells and yak-bovine SCNT embryos. In conclusion, we inferred that the normal allocation of ICM and TE cells in yak-bovine SCNT embryos and embryo-specific gene reprogramming may be important for successful inter-species animal cloning.

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.

Impact of in vitro production techniques on the expression of X-linked genes in bovine (bos taurus) oocytes and pre-attachment embryos

Our previous studies showed that expression patterns of X-linked genes in cultured cells are different from those of their tissues of origin. This investigation analyses the transcription pattern of the X-linked genes BIRC4, GAB3, MECP2, RPS4X, SLC25A6, and XIST in bovine in vitro matured oocytes and in vitro fertilized embryos, and their in vivo counterparts. In vitro-derived pools of mature oocytes and pre-attachment embryos were obtained by: (a) TCM-199/serum with bovine oviductal epithelial cells as co-culture, and (b) synthetic oviductal fluid/BSA. Pools of in vivo-derived morulae and blastocysts were provided by a commercial embryo transfer operation. Total RNA was extracted for quantification of gene-specific transcript levels using real-time quantitative PCR. Statistical analysis was performed using a mixed model factorial ANOVA with alpha = 0.05. The effect of the in vitro environmental conditions on X-linked gene transcription was most evident during the fourth cell cycle, at the period of activation of the embryonic genome, and seemed to be less pronounced at later developmental stages, with the exception of BIRC4. The levels of X-linked genes transcripts in in vivo-derived embryos were lower relative to their in vitro counterparts for all genes tested. Finally, the pattern of expression of XIST in bovine oocytes and embryos was similar to that reported in humans. These results highlight the possibility that X-linked gene expression analysis is a useful tool to monitor the impact of reproductive biotechnologies on the developmental potential of embryos and aid in their improvement.

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.

Suppression of connexin 43 and E-cadherin transcripts in in vitro derived bovine embryos following culture in vitro or in vivo in the homologous bovine oviduct

In this study, a combination of RNAi and endoscopic transfer to the oviduct of synchronized heifers has been used to investigate the effect of suppression of Cx43 and E-cadherin on the development, mRNA and protein expression of bovine blastocysts cultured in vitro or in vivo. In vitro matured and fertilized bovine zygotes were randomly assigned to one of four groups namely: Connexin43 dsRNA-injected (n = 790), E-cadherin dsRNA-injected (n = 775), water-injected (n = 774), and noninjected controls (n = 652). Following 2 days in vitro culture, 4- and 8-cell stage embryos from each treatment group were used for culture in vitro or in vivo. About half of the 4-8-cell stage embryos from each treatment group were transferred to the oviduct of synchronized heifers, while the remainder were further cultured in vitro. Embryos from in vivo culture were flushed from recipients on the fourth day post transfer (= Day 7 post insemination). Blastocyst stage embryos from both culture systems were used for mRNA and protein expression analysis. Irrespective of treatment or culture conditions, microinjection resulted in a decline in the proportion of embryos reaching the blastocyst stage. Significantly, lower blastocyst development was observed in E-cadherin and water-injected embryos following in vivo culture compared to the noninjected controls, while intermediate results were obtained following injection with Cx43 dsRNA. Both mRNA and protein products of the target genes were suppressed but the efficiency of suppression of the target genes varied depending on the initial level of transcript abundance, which is known to be greatly affected by the culture environment.

Embryo culture and long-term consequences

The development of pre-elongation (ruminants) and preimplantation (e.g. mouse and humans) embryos ex vivo has evolved over the past four decades into a reliable technology that is used as a research tool in developmental biology, as well as other embryo technologies, for application in infertility treatment, species conservation and selective breeding. It is clear from a variety of embryo culture studies that adaptive responses by embryos during culture can lead to significant alterations in subsequent developmental profiles, the mechanisms of which are not entirely clear but are unlikely to be limited to a single mechanism because this does not account for the variability seen in responses and the emerging list of specific cellular stressors that cause long-term deviations in fetal development. Epigenetic mechanisms, especially deviation of methylation patterns, and adaptation via causal pathways linking gene expression signalling with critical developmental time points, especially of placental development, are two candidates. Observational studies on post-transfer consequences must now be designed so that specific candidate pathways are followed to elucidate their role in perturbed development following transfer.

Temporal expression of transcripts related to embryo quality in bovine embryos cultured from the two-cell to blastocyst stage in vitro or in vivo

The post-fertilization embryo culture environment can have a dramatic effect on the pattern of gene expression in the embryo and it is widely acknowledged that bovine embryos derived from in vitro culture are of inferior quality to those derived in vivo. The objective of this study was to examine temporal variation in the mRNA abundance of several transcription and translation factors known to differ between blastocysts produced following culture in vitro and in vivo. Embryos were recovered from two in vitro culture systems SOF1 or SOF2 at five developmental stages: 2- to 4-cell, 8-cell, 16-cell, morula, and blastocyst. In vivo embryos were produced from superovulated and artificially inseminated heifers and recovered at approximately 40 hr or 3, 4, 5, and 7 days postinsemination. Blastocysts were also produced following in vitro maturation, in vitro fertilization and culture in the ewe oviduct. Analysis of relative transcript abundance for FOXO3A, EEF1G, HMG2, and REA was performed using quantitative real-time PCR. Irrespective of culture environment each transcript followed, approximately the same general pattern of expression where relative abundance decreased dramatically from the 2- to 4-cell stage to 8-cell stage and increased from the morula to blastocyst stage (P < 0.05). Transcripts for GNBL2 were not observed between the 2- and 16-cell stage of development. Relatively high expression at the 2- to 4-cell indicated that these transcripts are most likely of maternal origin produced in the oocyte during growth and final maturation. A culture-induced change in mRNA abundance of transcription and translation factors was evident in embryos that were produced not only between in vivo and in vitro culture environments but also between different in vitro culture systems.

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.