Messenger RNA in oocytes and embryos in relation to embryo viability

Desorption electrospray ionization mass spectrometry reveals lipid metabolism of individual oocytes and embryos

Alteration of maternal lipid metabolism early in development has been shown to trigger obesity, insulin resistance, type 2 diabetes and cardiovascular diseases later in life in humans and animal models. Here, we set out to determine (i) lipid composition dynamics in single oocytes and preimplantation embryos by high mass resolution desorption electrospray ionization mass spectrometry (DESI-MS), using the bovine species as biological model, (ii) the metabolically most relevant lipid compounds by multivariate data analysis and (iii) lipid upstream metabolism by quantitative real-time PCR (qRT-PCR) analysis of several target genes (ACAT1, CPT 1b, FASN, SREBP1 and SCAP). Bovine oocytes and blastocysts were individually analyzed by DESI-MS in both positive and negative ion modes, without lipid extraction and under ambient conditions, and were profiled for free fatty acids (FFA), phospholipids (PL), cholesterol-related molecules, and triacylglycerols (TAG). Principal component analysis (PCA) and linear discriminant analysis (LDA), performed for the first time on DESI-MS fused data, allowed unequivocal discrimination between oocytes and blastocysts based on specific lipid profiles. This analytical approach resulted in broad and detailed lipid annotation of single oocytes and blastocysts. Results of DESI-MS and transcript regulation analysis demonstrate that blastocysts produced in vitro and their in vivo counterparts differed significantly in the homeostasis of cholesterol and FFA metabolism. These results should assist in the production of viable and healthy embryos by elucidating in vivo embryonic lipid metabolism.

Developmental kinetics of pig embryos by parthenogenetic activation or by handmade cloning

The developmental kinetics of pig embryos produced by parthenogenetic activation without (PAZF) or with (PAZI) zona pellucida or by handmade cloning (HMC) was compared by time-lapse videography. After cumulus cell removal, the matured oocytes were either left zona intact (PAZI) or were made zona free by pronase digestion (PAZF) before they were activated (PA). Other matured oocytes were used for HMC based on foetal fibroblast cells. On Day 0 (day of PA or reconstruction), the embryos were cultured for 7 days in vitro in our time-lapse system. Pictures were taken every 30 min, and afterwards, each cell cycle was identified for each embryo to be analysed. Results showed that the PA embryos (both PAZF and PAZI) had shorter first cell cycle compared with HMC (17.4. 17.8 vs 23.6 h), but had a longer time length from four cell to morula stages (57.9, 53.8 vs 44.9 h). However, at the second cell cycle, PAZF embryos needed shorter time, while PAZI embryos had similar time length as HMC embryos, and both were longer than PAZF (23.4, 24.8 vs 14.6 h). Both PAZF and PAZI embryos used similar time to reach the blastocyst stage, and this was later than HMC embryos. In addition, when all of these embryos were grouped into viable (developed to blastocysts) and non-viable (not developed to blastocysts), the only difference in the time length was observed on the first cell cycle (18.6 vs 24.5 h), but not on the later cell cycles. In conclusion, our results not only give detailed information regarding the time schedule of in vitro-handled pig embryos, but also indicate that the first cell cycle could be used as a selecting marker for embryo viability. However, to evaluate the effect of the produced techniques, the whole time schedule of the pre-implantation developmental kinetics should be observed.

Epigenetic disturbances in in vitro cultured gametes and embryos: implications for human assisted reproduction

Although assisted reproductive technology (ART) has become a routine practice for human infertility treatment, the etiology of the increased risks for perinatal problems in ART-conceived children is still poorly understood. Data from mouse experiments and the in vitro production of livestock provide strong evidence that imprint establishment in late oocyte stages and reprogramming of the two germline genomes for somatic development after fertilization are vulnerable to environmental cues. In vitro culture and maturation of oocytes, superovulation, and embryo culture all represent artificial intrusions upon the natural development, which can be expected to influence the epigenome of the resultant offspring. However, in this context it is difficult to define the normal range of epigenetic variation in humans from conception throughout life. With the notable exception of a few highly penetrant imprinting mutations, the phenotypic consequences of any observed epigenetic differences between ART and non-ART groups remain largely unclear. The periconceptional period is not only critical for embryonal, placental, and fetal development, as well as the outcome at birth, but suboptimal in vitro culture conditions may also lead to persistent changes in the epigenome influencing disease susceptibilities later in life. The epigenome appears to be most plastic in the late stages of oocyte and the early stages of embryo development; this plasticity steadily decreases during prenatal and postnatal life. Therefore, when considering the safety of human ART from an epigenetic point of view, our main concern should not be whether or not a few rare imprinting disorders are increased, but rather we must be aware of a functional link between interference with epigenetic reprogramming in very early development and adult disease.

Factors affecting oocyte and embryo transcriptomes

The most important factor affecting the oocyte and early embryo transcriptome is the legacy from the follicular environment prior to meiotic resumption. Up to the 8-cell stage, the oocyte responds to maternal instructions stored before resumption of the meiotic division. Recent evidence suggests that properly prepared or programmed oocytes (in vivo) can achieve close to 100% blastocyst rates in standard in vitro conditions/media. Therefore, the optimal oocyte requires perfect follicular timing and differentiation, but the intra-oocyte mechanisms involved in such preparation are not completely understood. In addition, the influence of maternal mRNA storage and degradation, as well as the length of the poly A tail that influences the general pattern of the oocyte/early embryo transcriptome, is an important factor. Several hypotheses have been put forth to explain the depletion of the maternal store, including the potential role of microRNA (miRNA) in this process. The activation of the embryonic genome could be dependent on, or associated with, the process of maternal mRNA degradation, but obviously other functions are being activated at this critical time point. This review will focus on the period from full-size oocytes to the eight-cell stage and will summarize the impact of the important factors, that is, follicle, maternal RNA storage and embryonic genome activation, on the transcriptome.

Zona pellucida birefringence correlates with developmental capacity of bovine oocytes classified by maturational environment, COC morphology and G6PDH activity

In the present study we aimed to analyse structural changes during in vitro maturation of the bovine zona pellucida (ZP) by scanning electron microscopy (SEM) ands zona pellucida birefringence (ZPB). Here we show that alterations during in vitro maturation invasively analysed by SEM are reflected in ZPB. In vivo-matured oocytes displayed significantly lower birefringence parameters and significantly higher blastocyst rates compared with in vitro-derived oocytes (39.1% vs 21.6%). The same was observed for in vitro-matured oocytes with cumulus-oocyte complex (COC) Quality 1 (Q1) compared with Q3-COCs with respect to zona birefringence and developmental capacity. Immature oocytes with Q1-COCs displayed higher ZPB values and a higher developmental capacity to the blastocyst stage (27.7% vs 16.9%) compared with immature Q3-COCs. Considering in vitro-matured oocytes, only those with Q1-COC showed a trend for ZPB similar to in vivo-matured oocytes. Therefore, a decreasing trend for ZPB during in vitro maturation seems to be typical for high-quality oocytes and successful cytoplasmic maturation. In accordance, fully-grown immature oocytes reached significantly higher blastocyst rates (32.0% vs 11.5%) and lower ZPB values compared with still-growing ones. In conclusion, we successfully evaluated the applicability of zona imaging to bovine oocytes: alterations during in vitro maturation invasively analysed by scanning electron microscopy were reflected in the birefringence of the zona pellucida of bovine oocytes affecting developmental capacity at the same value. Therefore ZPB measurement by live zona imaging has potential to become a new tool to assess correctness of in vitro maturation and to predict developmental competence.

Association of the transcription profile of bovine oocytes and embryos with developmental potential

Although improvements in culture system have enhanced in vitro embryo production, success rates are still not adequate. The reasons for developmental arrest of a part of in vitro produced embryos are unknown, but are connected in part with low cytoplasmic competence of oocytes. The immaturity of cytoplasm can negatively influence fertilization efficiency and subsequent progression through embryonic genome activation (EGA), which are necessary steps in further pre-implantation development. A large number of studies have compared mRNA abundance among oocytes with different developmental competence with the aim to find markers of the normal embryo development. The amount of mitochondrial DNA (mtDNA) and mRNA for mitochondrial transcriptional factors directing oxidative phosphorylation belongs to such promising markers. Nevertheless, recently published studies revealed that the mammalian embryo is able to compensate for a reduced level of mtDNA in oocyte during subsequent pre-implantation development. The search for other molecular markers is in progress. Characterization of oocyte and embryonic mRNA expression patterns during the pre-implantation period, and their relationship to the successful in vitro and in vivo development will be essential for defining the optimized culture conditions or the nuclear transfer protocols. Microarrays technology enables us to reveal the differentially expressed genes during EGA, and to compare the expression profile of in vivo and in vitro produced embryos. Recent evidence indicates that the depletion of the pool of stored maternal mRNAs is critical for subsequent embryo development. All these experiments gradually offer a list of possible candidates for quality and developmental competence markers for mammalian oocytes and pre-implantation embryos.

Influence of selected (pre-)maturational parameters on in vitro development and sex distribution of bovine embryos

The objectives of this research were to study the influence of a reduced oxygen concentration during in vitro maturation (IVM) and examine the effect of follicular glucose concentration on bovine in vitro development and sex distribution. In the first experiment, abattoir-derived cumulus-oocyte complexes (COC) were matured under 5% O2 or 20% O2. Secondly, COC were isolated and the glucose (G) concentration of each follicle was determined. COC were pooled in groups (G (< 1.1 mMol) or G (≥ 1.1 mMol)) according to the glucose content before being subjected to in vitro production (IVP). Cleavage and development rates were assessed on days 3, 7 and 8 post insemination. Blastocysts of each group were sexed by polymerase chain reaction (PCR). Expanded blastocysts were stained to assess total cell numbers and live-dead cell ratio. Cleavage and development rates stayed similar after reducing the O2 concentration during IVM. The sex ratio of embryos generated from oocytes matured under 5% O2 was shifted in favour of the female (♀: 61.9%), whereas the sex ratio of embryos belonging to the IVM 20% O2 group did not differ significantly from the expected 50:50 ratio. Neither a 'higher' nor a 'lower' intrafollicular glucose concentration influenced cleavage and development rates, cell numbers or live-dead cell ratio. Eighty five per cent (G (<1.1)) and 63.6% (G (≥ 1.1)) of the analysed embryos were female. In summary, neither a reduced O2 concentration during IVM nor selection based on follicular glucose concentrations affected the morphological quality of embryos. Although the sex distribution was shifted in favour of female embryos in all three experimental groups, more male embryos could be seen in the G (≥ 1.1) group compared with the G(<1.1) group.

The fate of follicles after a blood meal is dependent on previtellogenic nutrition and juvenile hormone in Aedes aegypti

Juvenile hormone (JH) mediates the relationship between fecundity and nutrition during the gonotrophic cycle of the mosquito in three ways: (1) by regulating initial previtellogenic development, (2) by mediating previtellogenic resorption of follicles and (3) by altering intrinsic previtellogenic follicle "quality", physiology, and competitiveness thereby predetermining the fate of follicles after a blood meal. To support a role for JH in mediating the response of ovarian follicles after a blood meal, we explored three main questions: (1) Do changes in nutrition during the previtellogenic resting stage lead to relevant biochemical and molecular changes in the previtellogenic ovary? (2) Do hormonal manipulations during the previtellogenic resting stage lead to the same biochemical and molecular changes? (3) Does nutrition and hormones during the previtellogenic resting stage affect vitellogenic resorption and reproductive output? We examined the accumulation of neutral lipids in the previtellogenic ovary as well as the previtellogenic expression of genes integral to endocytosis and oocyte development such as the: vitellogenin receptor (AaVgR), lipophorin receptor (AaLpRov), heavy-chain clathrin (AaCHC), and ribosomal protein L32 (rpL32) under various previtellogenic nutritional and hormonal conditions. mRNA abundance and neutral lipid content increased within the previtellogenic ovary as previtellogenic mosquitoes were offered increasing sucrose concentrations. Methoprene application mimicked the effect of offering the highest sucrose concentrations on mRNA abundance and lipid accumulation in the previtellogenic ovary. These same nutritional and hormonal manipulations altered the extent of vitellogenic resorption. Mosquitoes offered 20% sucrose during the previtellogenic resting stage had nearly 3 times less vitellogenic resorption than mosquitoes offered 3% sucrose despite taking smaller blood meals and developed ∼10% more eggs during the first gonotrophic cycle. Mosquitoes treated with JH III during the previtellogenic resting stage and then offered a blood meal had a ∼40% reduction in the amount of vitellogenic resorption and developed ∼12% more eggs. Taken together, these results suggest that previtellogenic nutrition alters the extent and pattern of resorption after a blood meal through the effect of JH on mRNA abundance and lipid accumulation in previtellogenic follicles.

A novel approach to sexing bovine blastocysts using male-specific gene expression

When examining gene expression profiles for the purposes of assessing embryo quality, it is imperative that sex be considered, because many embryonic transcripts have sex-related expression patterns. The objective of this study was to systematically examine eight Y chromosome linked genes (DDX3Y, EIF1AY, HSFY, SRY, TSPY, USP9Y, ZFY, and ZRSR2Y) to characterize their expression in bovine blastocysts and to examine the usefulness of this expression for the purpose of RNA-based embryo sexing. In order to examine the expression of these genes, pools of blastocysts (groups of 10 and 20) as well as single embryos (N = 50) were analyzed with reverse transcriptase polymerase chain reaction (RT-PCR) and reverse transcriptase quantitative PCR (RT-qPCR). Of the 50 single embryos, 32 were concurrently sexed with DNA-based methods. Transcripts of DDX3Y, EIF1AY, TSPY, USP9Y, ZFY and ZRSR2Y were detected in the pooled and single blastocysts, but no transcripts were detected for HSFY or SRY. After performing DNA-based sexing experiments, we concluded that this expression was restricted to the male embryos. The consistency of the expression varied according to the gene as well as the specific primer set. Three genes were expressed in the full set of male embryos, DDX3Y, USP9Y, and ZRSR2Y and therefore represent good candidates for RNA-based sexing methods.

New challenges in the analysis of gene transcription in bovine blastocysts

In the last years, enormous progress has been made in the analysis of gene transcription at the blastocyst stage. The study of gene expression at this early stage of development is challenging because of the very small amount of starting material, which limits the use of traditional mRNA analysis approaches such as Northern blot. Another problem is the difficulty for data normalization, particularly the identification of the best housekeeping gene with the lowest fluctuation under different developmental conditions. Moreover, the transcriptional analysis of embryo biopsies or individual embryos needs to take into consideration that the blastocyst is a transitional stage of development, which is composed of three different types of cells (trophoblast, epiblast and primitive ectoderm) with different patterns of gene expression, and that there are large differences between male and female blastocysts. In this review, we analyse the different specific and sensitive tools available to compare mRNA expression levels of specific genes at the blastocyst stage, and how the protocol and the analytical method used can influence the results dramatically. Finally, we describe future research challenges to identify candidate genes related to developmental competence of bovine blastocysts, not only in terms of pregnancy rates but also in relation to adverse long-term consequences in the adult animal.

The effect of ovary storage and in vitro maturation on mRNA levels in bovine oocytes; a possible impact of maternal ATP1A1 on blastocyst development in slaughterhouse-derived oocytes

Since BSE testing of slaughtered cattle is obligatory in Japan, storage of ovaries at 15-20 C overnight in phosphate buffered saline has become a routine protocol in in vitro production (IVP) of cattle embryos. Ovary storage is known to reduce developmental competence of oocytes; however, its effects on oocyte gene expression have not been clarified yet. This study compared oocytes collected from stored slaughterhouse-derived ovaries with those collected by Ovum Pick-Up (OPU) in terms of the expression of 20 selected genes to determine if ovary storage affects cellular processes at the molecular level. Expression of mRNA in oocytes was assayed before and after in vitro maturation (IVM) by real-time quantitative PCR. Maternal mRNA levels of genes were investigated in 2-cell stage embryos obtained from slaughterhouse oocytes to assess their roles for blastocyst formation. In immature OPU oocytes, genes related to metabolism (GAPDH), transporters (GLUT8, ATP1A1) and stress resistance protein (HSP70) showed significantly higher expression compared with oocytes derived from stored ovaries. During IVM, the expression of GDF9, GLUT8, CTNNB1 and PMSB1 was significantly decreased irrespective of oocyte source. Two-cell stage embryos cleaving at 22-25 h after in vitro fertilization (IVF) showed a significantly higher blastocyst formation rate and ATP1A1 gene expression level compared with those cleaving at 27-30 h after IVF. Our results reveal that storage of ovaries alters mRNA levels in oocytes. Correlation of Na/K ATPase ATP1A1 expression in IVP embryos at the 2-cell and 8-cell stages with their developmental ability to the blastocyst stage may suggest the importance of maternal mRNA of this gene during blastulation in embryos derived from slaughterhouse oocytes.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Elevated non-esterified fatty acid concentrations during bovine oocyte maturation compromise early embryo physiology

Elevated concentrations of serum non-esterified fatty acids (NEFA), associated with maternal disorders such as obesity and type II diabetes, alter the ovarian follicular micro-environment and have been associated with subfertility arising from reduced oocyte developmental competence. We have asked whether elevated NEFA concentrations during oocyte maturation affect the development and physiology of zygotes formed from such oocytes, using the cow as a model. The zygotes were grown to blastocysts, which were evaluated for their quality in terms of cell number, apoptosis, expression of key genes, amino acid turnover and oxidative metabolism. Oocyte maturation under elevated NEFA concentrations resulted in blastocysts with significantly lower cell number, increased apoptotic cell ratio and altered mRNA abundance of DNMT3A, IGF2R and SLC2A1. In addition, the blastocysts displayed reduced oxygen, pyruvate and glucose consumption, up-regulated lactate consumption and higher amino acid metabolism. These data indicate that exposure of maturing oocytes to elevated NEFA concentrations has a negative impact on fertility not only through a reduction in oocyte developmental capacity but through compromised early embryo quality, viability and metabolism.

Effect of different culture systems on mRNA expression in developing rabbit embryos

The rate of zygotes in vitro developed to hatched blastocyst stage was evaluated between two different commercial media (TCM-199 and Ham's F10) and two different culture systems (renewal and non-renewal single medium) to determine the effects of culture conditions on rabbit embryo preimplantation development. The relative transcript abundances of OCT4, vascular endothelial growth factor (VEGF) and epidermal growth factor receptor 3 (erbB3) of resultant blastocysts were also analysed and compared with in vivo developed blastocysts. Results showed an important divergence in mRNA expression between embryos developed under in vivo and in vitro conditions despite there being no significant difference in hatching blastocyst rates between different culture systems and different media. For OCT4, transcript abundance of in vitro culture embryos differs from their in vivo chronological counterparts, but, when the medium is renewed, mRNA expression seemed similar to in vivo developed 4-day-old embryos. In addition, VEGF and erbB3 expression showed marked variation between different in vitro conditions. Therefore, the study of specific transcript abundance in rabbit blastocyst provides a more detailed description of which alterations in gene expression occur due in vitro conditions, and further studies should be carried out to reduce current limitations of long-term culture of rabbit pre-implantation embryos.

Pluripotent stem cells and reprogrammed cells in farm animals

Pluripotent cells are unique because of their ability to differentiate into the cell lineages forming the entire organism. True pluripotent stem cells with germ line contribution have been reported for mice and rats. Human pluripotent cells share numerous features of pluripotentiality, but confirmation of their in vivo capacity for germ line contribution is impossible due to ethical and legal restrictions. Progress toward derivation of embryonic stem cells from domestic species has been made, but the derived cells were not able to produce germ line chimeras and thus are termed embryonic stem-like cells. However, domestic animals, in particular the domestic pig (Sus scrofa), are excellent large animals models, in which the clinical potential of stem cell therapies can be studied. Reprogramming technologies for somatic cells, including somatic cell nuclear transfer, cell fusion, in vitro culture in the presence of cell extracts, in vitro conversion of adult unipotent spermatogonial stem cells into germ line derived pluripotent stem cells, and transduction with reprogramming factors have been developed with the goal of obtaining pluripotent, germ line competent stem cells from domestic animals. This review summarizes the present state of the art in the derivation and maintenance of pluripotent stem cells in domestic animals.

Differential gene expression and developmental competence in in vitro produced bovine embryos

The embryonic developmental block occurs at the 8-cell stage in cattle and is characterized by a lengthening of the cell cycle and an increased number of embryos that stop development. The maternal-embryonic transition arises at the same stage resulting in the transcription of many genes. Gene expression studies during this stage may contribute to the understanding of the physiological mechanisms involved in the maternal-embryonic transition. Herein we identified genes differentially expressed between embryos with high or low developmental competence to reach the blastocyst stage using differential display PCR. Embryos were analysed according to developmental kinetics: fast cleavage embryos showing 8 cells at 48 h post insemination (hpi) with high potential of development (F8), and embryos with slow cleavage presenting 4 cells at 48 hpi (S4) and 8 cells at 90 hpi (S8), both with reduced rates of development to blastocyst. The fluorescence DDPCR method was applied and allowed the recovery of 176 differentially expressed bands with similar proportion between high and low development potential groups (52% to F8 and 48% in S4 and S8 groups). A total of 27 isolated fragments were cloned and sequenced, confirming the expected primer sequences and allowing the identification of 27 gene transcripts. PI3KCA and ITM2B were chosen for relative quantification of mRNA using real-time PCR and showed a kinetic and a time-related pattern of expression respectively. The observed results suggest the existence of two different embryonic genome activation mechanisms: fast-developing embryos activate genes related to embryonic development, and slow-developing embryos activate genes related to cellular survival and/or death.

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

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

Epigenetic profile of developmentally important genes in bovine oocytes

Assisted reproductive technologies are associated with an increased incidence of epigenetic aberrations, specifically in imprinted genes. Here, we used the bovine oocyte as a model to determine putative epigenetic mutations at three imprinted gene loci caused by the type of maturation, either in vitro maturation (IVM) in Tissue Culture Medium 199 (TCM) or modified synthetic oviduct fluid (mSOF) medium, or in vivo maturation. We applied a limiting dilution approach and direct bisulfite sequencing to analyze the methylation profiles of individual alleles (DNA molecules) for H19/IGF2, PEG3, and SNRPN, which are each associated with imprinting defects in humans and/or the mouse model, and are known to be differentially methylated in bovine embryos. Altogether, we obtained the methylation patterns of 203 alleles containing 4,512 CpG sites from immature oocytes, 213 alleles with 4,779 CpG sites from TCM-matured oocytes, 215 alleles/4,725 CpGs in mSOF-matured oocytes, and 78 alleles/1,672 CpGs from in vivo-matured oocytes. The total rate of individual CpGs and entire allele methylation errors did not differ significantly between the two IVM and the in vivo group, indicating that current IVM protocols have no or only marginal effects on these critical epigenetic marks. Furthermore, the mRNA expression profiles of the three imprinted genes and a panel of eight other genes indicative of oocyte competence were determined by quantitative real-time PCR. We found different mRNA expression profiles between in vivo-matured oocytes versus their in vitro-matured counterparts, suggesting an influence on regulatory mechanisms other than DNA methylation.

Expression of enzymes involved in the synthesis of prostaglandin E2 in bovine in vitro-produced embryos

Prostaglandin E2 (PGE2) may play a major role in embryo development and the establishment of pregnancy in cattle. The biosynthesis of PGE2 implies the sequential transformation of arachidonic acid to PGH2 by cyclooxygenases (COXs), then the conversion of PGH2 to PGE2 by prostaglandin E synthases (PGESs). Quantitative RT-PCR was used to examine the expression of COX-1, COX-2, microsomal PGES-1 (mPGES-1), microsomal PGES-2 (mPGES-2) and cytosolic PGES (cPGES) mRNAs in day 7 in vitro-produced (IVP) embryos from oocytes collected by ovum pick-up in Holstein heifers. Transcripts for COX-2 and mPGES-1 were detected in all embryos, whereas transcripts for COX-1 and mPGES-2 were not detected and cPGESs were at the limit of detection in 40% of embryos. Levels of COX-2 and mPGES-1 mRNAs were significantly higher in blastocysts and expanded blastocysts than in morulae and early blastocysts. Furthermore, excellent-quality embryos (grade 1) displayed higher levels of both COX-2 and mPGES-1 than did embryos of good and medium qualities (grades 2-3). Our results suggest that bovine IVP embryos at the morula and blastocyst stages use exclusively the COX-2/mPGES-1 pathway for PGE2 biosynthesis, and that PGE2 is potentially involved in blastocyst expansion and developmental competence.

Real-time qRT-PCR analysis of EGF receptor in cumulus-oocyte complexes recovered by laparoscopy in hormonally treated goats

Ovarian stimulation with exogenous follicle stimulating hormone (FSH) has been used to increase the number of viable oocytes for laparoscopic oocyte recovery (LOR) in goats. The aim of this study was to evaluate the effect of two FSH protocols for ovarian stimulation in goats on the expression pattern of epidermal growth factor (EGF) receptor (EGFR) in cumulus–oocyte complexes (COCs) recovered by LOR. After real-time qRT-PCR analysis, expression profiles of morphologically graded COCs were compared prior to and after in vitro maturation (IVM) on a FSH protocol basis. The use of a protocol with higher number of FSH injections at a shorter interval resulted in GI/GII COCs with a higher level of EGFR expression in cumulus cells, but not in the oocyte, which was correlated with an elevated meiotic competence following IVM. Based on the maturation profile and EGFR expression patterns observed between groups, the morphological selection of COCs prior to IVM was not a good predictor of oocyte meiotic competence. Therefore, EGFR may be a good candidate marker for indirect prediction of goat oocyte quality. The IVM process of goat COCs increased the EGFR expression in oocytes and cumulus cells, which seemed to be strongly associated with the resumption of meiosis. In summary, differential EGFR expression in goat cumulus cells was associated with the in vivo prematuration process, and in turn, the upregulation in the entire COC was associated with IVM. Cause-and-effect relationships between such increased expression levels, particularly in the oocyte, and oocyte competence itself still need to be further investigated.

Effects of bovine Herpesvirus Type 5 on development of in vitro-produced bovine embryos

Bovine (Bos indicus) herpesviruses have been associated with reproductive disease. Type 1, the most studied species, is best known for its reproductive and respiratory effects. Type 5 (BoHV-5) has been detected in bull semen and aborted fetuses but not in oocytes and embryos. This study consisted of three experiments that evaluated (1) BoHV-5-infected oocytes matured in medium with fetal bovine serum (BoHV-FBS) or polyvinyl alcohol (BoHV-PVA) and fertilized by noninfected sperm; (2) noninfected oocytes fertilized by BoHV-5-infected sperm; and (3) infection of presumptive zygotes by BoHV-5. Each treatment involved nine drops of 15 to 20 oocytes. Infection with BoHV-5 was detected by polymerase chain reaction and in situ hybridization assay, and fertilization capacity and embryonic development were assessed using in vitro culture. Experimentally induced infection was obtained in all experiments, and vertical transmission of BoHV-5 by gametes was confirmed. The cleavage rate was reduced (P=0.0201) in BoHV-FBS (80.4+/-8.9%; mean+/-SD) compared with that of noninfected oocytes (89.9+/-6.5%); neither differed from BoHV-PVA (87.3+/-7.1%), and the resulting embryo production rate was not significantly different among groups. Rates of cleavage (87.5+/-7.5% vs. 92.2+/-5.5%, control vs. infected) and development of embryos (41.7+/-9.9% vs. 44.3+/-7.7% to morula/blastocyst/expanded blastocyst [M/B/EB] and 39.6+/-10.3% vs. 40.8+/-9.2% to blastocyst/expanded blastocyst/hatching blastocyst [B/EB/HB] stages) were not compromised by infected sperm (P=0.1462, P=0.5402, and P=0.8074, respectively). However, presumptive zygotes directly infected 1 d after fertilization produced a lower number (P=0.0140 to M/B/EB and P=0.002 to B/EB/HB stages) of in vitro-produced embryos (31.6+/-4.6 vs. 25.0+/-5.5 and 31.6+/-4.6 vs. 20.2+/-5.4; control vs. infected). In conclusion, BoHV-5 infected gametes and was transmissible to the embryo during in vitro development. As zygotes infected 1 d after fertilization had compromised development, BoHV-5 has the potential to be a pathogen with economic consequences.

In vitro production and cryotolerance of prepubertal and adult goat blastocysts obtained from oocytes collected by laparoscopic oocyte-pick-up (LOPU) after FSH treatment

This study compares the developmental capacity and cryotolerance of embryos produced from oocytes of stimulated prepubertal and adult Sarda goats. Twelve prepubertal and 13 adult goats were each given 110 and 175 IU FSH, respectively, and cumulus-oocyte complexes (COCs) were collected by laparoscopic oocyte-pick-up (LOPU). After in vitro maturation, fertilisation and culture (IVMFC), blastocysts were vitrified, warmed and blastocoel re-expansion and gene expression were evaluated. Prepubertal goats produced a higher COCs number than adults (mean +/- s.e.m., 89.67 +/- 5.74 and 26.69 +/- 3.66, respectively; P < 0.01). Lower developmental competence was demonstrated in the prepubertal oocytes as shown by a higher number of COCs discarded before IVM (21.1% and 14.7% for prepubertals and adults, respectively; P < 0.01) and IVF (23.4% v. 9.1%; P < 0.01) and by the lower cleavage (55.6% and 70.3%, respectively; P < 0.01) and blastocyst rates (24.2% and 33.9%, respectively; P < 0.05). Compared with the adult, prepubertal vitrified/warmed blastocysts showed significantly (P < 0.05) lower in vitro viability, as determined by the re-expansion rate (62.5% and 40.3%). No differences were observed in the time required for blastocoel re-expansion or in cyclin B1, E-cadherin, Na/K ATPase, HSP90beta and aquaporin 3 messenger RNA quantity. These results show that in vitro-produced embryos produced from prepubertal goat oocytes have a lower developmental rate and cryotolerance compared with their adult counterparts. However, we can assume that the quality of re-expanded embryos does not differ between the two groups.

Single embryo and oocyte lipid fingerprinting by mass spectrometry

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

Messenger RNA expression of Pabpnl1 and Mbd3l2 genes in oocytes and cleavage embryos

OBJECTIVE

To identify genes specifically expressed in mammalian oocytes using an in silico subtraction, and to characterize the mRNA patterns of selected genes in oocytes, embryos, and adult tissues.

DESIGN

Comparison between oocyte groups and between early embryo stages.

SETTING

Laboratories of embryo manipulation and molecular biology from Departamento de Genética (FMRP) and Departamento de Ciências Básicas (FZEA)--University of São Paulo.

SAMPLE(S)

Oocytes were collected from slaughtered cows for measurements, in vitro fertilization, and in vitro embryo culture. Somatic tissue, excluding gonad and uterus tissue, was collected from male and female cattle.

MAIN OUTCOME MEASURE(S)

Messenger RNA levels of poly(A)-binding protein nuclear-like 1 (Pabpnl1) and methyl-CpG-binding domain protein 3-like 2 (Mbd3l2).

RESULT(S)

Pabpnl1 mRNA was found to be expressed in oocytes, and Mbd3l2 transcripts were present in embryos. Quantification of Pabpnl1 transcripts showed no difference in levels between good- and bad-quality oocytes before in vitro maturation (IVM) or between good-quality oocytes before and after IVM. However, Pabpnl1 transcripts were not detected in bad-quality oocytes after IVM. Transcripts of the Mbd3l2 gene were found in 4-cell, 8-cell, and morula-stage embryos, with the highest level observed in 8-cell embryos.

CONCLUSION(S)

Pabpnl1 gene expression is restricted to oocytes and Mbd3l2 to embryos. Different Pabpnl1 mRNA levels in oocytes of varying viability suggest an important role in fertility involving the oocyte potential for embryo development.

A retrospective model of oocyte competence: global mRNA and housekeeping transcripts are not associated with in vitro developmental outcome

Oocyte developmental competence depends on maternal stores that support development throughout a transcriptionally silent period during early embryogenesis. Previous attempts to investigate transcripts associated with oocyte competence have relied on prospective models, which are mostly based on morphological criteria. Using a retrospective model, we quantitatively compared mRNA among oocytes with different embryo development competence. A cytoplasm biopsy was removed from in vitro matured oocytes to perform comparative analysis of amounts of global polyadenylated (polyA) mRNA and housekeeping gene transcripts. After parthenogenetic activation of biopsied oocytes, presumptive zygotes were cultured individually in vitro and oocytes were classified according to embryo development: (i) blocked before the 8-cell stage; (ii) blocked between the 8-cell and morulae stages; or (iii) developed to the blastocyst stage. Sham-manipulated controls confirmed that biopsies did not alter development outcome. Total polyA mRNA amounts correlate with oocyte diameter but not with the ability to develop to the 8-cell and blastocyst stages. The last was also confirmed by relative quantification of GAPDH, H2A and Hprt1 transcripts. In conclusion, we describe a novel retrospective model to identify putative markers of development competence in single oocytes and demonstrate that global mRNA amounts at the metaphase II stage do not correlate with embryo development in vitro.

An in vivo culture system for human embryos using an encapsulation technology: a pilot study

BACKGROUND

Animal studies have demonstrated better embryo development in vivo than in vitro. This pilot study tested the feasibility of using a novel in utero culture system (IUCS) to obtain normal human fertilization and embryo development.

METHODS

The IUCS device comprised a perforated silicone hollow tube. The study included 13 patients (<36 years) undergoing a first intracytoplasmic sperm injection (ICSI) treatment and 167 metaphase II oocytes in three groups. In Group 1, 1-2 h after ICSI, sibling oocytes were assigned to IUCS or conventional in vitro culture. The device was retrieved on Day 1, and all zygotes were cultured in vitro till Day 5. In Group 2, fertilized oocytes were assigned on Day 1, embryos retrieved on Day 3 and all embryos cultured till Day 5. In Group 3, after Day 0 assignment, embryos were retrieved on Day 3 for blastomere biopsy and fluorescence in situ hybridization (FISH) and cultured until Day 5. The highest quality blastocysts were transferred on Day 5.

RESULTS

Fertilization and embryo development were comparable in the in vitro and IUCS arms, with a tendency towards better embryo quality in the IUCS. FISH analysis in Group 3 revealed more normal embryos using the IUCS (P = 0.049). Three clinical pregnancies and live births were obtained: two from the IUCS arm and one from the in vitro arm.

CONCLUSIONS

Our pilot study shows that this new IUCS appears to be feasible and safe, supporting normal fertilization, embryo development and normal chromosomal segregation. Furthermore, live births are possible after the transient presence of a silicone device in the uterus. Clinicaltrials.gov: NCT00480103.

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.