Reduced polyspermic fertilization of porcine oocytes utilizing elevated bicarbonate and reduced calcium concentrations in a single-medium system

Emerging Contributions of Pluripotent Stem Cells to Reproductive Technologies in Veterinary Medicine

The generation of mature gametes and competent embryos in vitro from pluripotent stem cells has been successfully achieved in a few species, mainly in mice, with recent advances in humans and scarce preliminary reports in other domestic species. These biotechnologies are very attractive as they facilitate the understanding of developmental mechanisms and stages that are generally inaccessible during early embryogenesis, thus enabling advanced reproductive technologies and contributing to the generation of animals of high genetic merit in a short period. Studies on the production of in vitro embryos in pigs and cattle are currently used as study models for humans since they present more similar characteristics when compared to rodents in both the initial embryo development and adult life. This review discusses the most relevant biotechnologies used in veterinary medicine, focusing on the generation of germ-cell-like cells in vitro through the acquisition of totipotent status and the production of embryos in vitro from pluripotent stem cells, thus highlighting the main uses of pluripotent stem cells in livestock species and reproductive medicine.

A New Toolbox in Experimental Embryology-Alternative Model Organisms for Studying Preimplantation Development

Preimplantation development is well conserved across mammalian species, but major differences in developmental kinetics, regulation of early lineage differentiation and implantation require studies in different model organisms, especially to better understand human development. Large domestic species, such as cattle and pig, resemble human development in many different aspects, i.e., the timing of zygotic genome activation, mechanisms of early lineage differentiations and the period until blastocyst formation. In this article, we give an overview of different assisted reproductive technologies, which are well established in cattle and pig and make them easily accessible to study early embryonic development. We outline the available technologies to create genetically modified models and to modulate lineage differentiation as well as recent methodological developments in genome sequencing and imaging, which form an immense toolbox for research. Finally, we compare the most recent findings in regulation of the first lineage differentiations across species and show how alternative models enhance our understanding of preimplantation development.

Selection based on morphological features of porcine embryos produced by in vitro fertilization: Timing of early cleavages and the effect of polyspermy

The aim of this study was to examine whether a morphological approach is efficient for selecting high‐quality porcine embryos produced by in vitro fertilization (IVF) under high polyspermy conditions. Frozen‐thawed Meishan epididymal spermatozoa showing moderate and high polyspermy were subjected to IVF (1 × 10⁵ sperms/ml). Under conditions of moderate polyspermy, 4‐cell embryos selected at 48 hr after IVF (single selection) and 8‐cell embryos selected at 79 hr after IVF from the collected 4‐cell embryos (double selection) showed high developmental competence. Likewise, 4‐ and 8‐cell embryos produced by IVF under high polyspermy conditions also showed high competence for development to blastocysts. However, blastocysts derived from high polyspermy conditions had significantly fewer cells than those produced under moderate polyspermy conditions. Furthermore, the frequency of nuclear and chromosomal abnormalities in 4‐ and 8‐cell embryos produced under conditions of high polyspermy was significantly (p < .05) higher in comparison to moderate polyspermy conditions. These findings suggest that although high polyspermy affects the frequency of nuclear and chromosomal anomalies in porcine IVF embryos, subsequent selection based on morphological features of 4‐ and 8‐cell embryos even under high polyspermy conditions, could be an alternative option for selecting porcine IVF embryos with high development ability.

The effects of permeating cryoprotectants on intracellular free-calcium concentrations and developmental potential of in vitro-matured feline oocytes

Embryos produced from vitrified feline oocytes have resulted in pregnancies, but the efficiency of oocyte vitrification in cats is still low. Our objectives were to evaluate the effects of exposing feline oocytes to ethylene glycol (EG), propanediol (PrOH) and dimethyl sulfoxide (DMSO) on changes in intracellular free-calcium concentrations ([Ca2+]i), the time needed for enzymatic digestion of the zona pellucida (ZP), the incidence of parthenogenetic activation and degeneration and embryonic development following in vitro fertilisation (IVF). All of the chemicals tested altered [Ca2+]i, but changes in [Ca2+]i, resistance of the ZP to enzymatic digestion and the incidence of parthenogenetic activation (<5% for all treatments) were not affected (P > 0.05) by extracellular Ca2+. Exposure to EG (>44.1%) and DMSO (19.7%) increased (P < 0.05) oocyte degeneration compared with control oocytes and oocytes exposed to PrOH (≤2.5%). Following exposure to a combination of PrOH and DMSO (10% v/v each), blastocyst development (per cleaved embryo; 52.1%) was similar (P > 0.05) to control oocytes (64.4%). When oocytes were vitrified with PrOH and DMSO, 28.3% of surviving (intact plasma membrane) oocytes cleaved following IVF, but no blastocyst developed. When a non-permeating cryoprotectant (galactose, 0.25 M) was added to the vitrification medium, 47.7% of surviving oocytes cleaved and 14.3% developed to the blastocyst stage.

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

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

Disrupted redox homeostasis and aberrant redox gene expression in porcine oocytes contribute to decreased developmental competence

The objective of this study was to identify specific redox-related genes whose function contributes to oocyte quality and to characterize the role of redox homeostasis in oocyte development. We determined the redox genes glutaredoxin 2 (GLRX2), protein disulfide isomerase family A, members 4 and 6 (PDIA4, PDIA6), and thioredoxin reductase 1 (TXNRD1) were differentially expressed between adult (more competent) and prepubertal (less competent) porcine in vitro-matured (IVM) oocytes. The association between these genes and oocyte quality was further validated by comparing transcript abundance in IVM with that in in vivo-matured (VVM) prepubertal and adult oocytes. By maturing oocytes in variable redox environments, we demonstrated that a balanced redox environment is important for oocyte quality, and over-reduction of the environment is as detrimental as excess oxidation. Critical levels of reactive oxygen species (ROS) and glutathione (GSH) are required for oocyte competence. Elevated GSH and lower ROS in prepubertal oocytes suggest disrupted redox homeostasis exists in these cells. By further comparing GLRX2, PDIA4, PDIA6, and TXNRD1 expression levels in oocytes matured under these different redox environments, we found aberrant expression patterns in prepubertal oocytes but not in adult oocytes when the maturation medium contained high concentrations of antioxidants. These results suggest that prepubertal oocytes are less competent in regulating redox balance than adult oocytes, contributing to lower oocyte quality. In conclusion, aberrant redox gene expression patterns and disrupted redox homeostasis contribute to decreased developmental competence in prepubertal and IVM porcine oocytes. The balance between ROS and GSH plays an important role in oocyte quality.

Transient exposure to sodium butyrate after germinal vesicle breakdown improves meiosis but not developmental competence in pig oocytes

Oocyte maturation is a complex process during which epigenetic modifications are dramatically changed, especially histone acetylation and phosphorylation. We have investigated the effects of NaBu (sodium butyrate), a natural HDAC (histone deacetylase) inhibitor, on porcine oocyte maturation at different stages and subsequent embryonic development to improve IVF (in vitro fertilization) and embryo production. COCs (cumulus oocyte complexes) were cultured, IVM (in vitro maturation) supplemented with 1 mM NaBu before or after GVBD [GV (germinal vesicle) breakdown] during maturation. NaBu delayed oocyte meiosis in the GV and GVBD stages in an exposure-dependent manner. However, the short treatment with 1 mM NaBu after GVBD significantly improved the meiotic competence. No positive effects of NaBu on GSH levels and subsequent embryonic development following IVF were seen. Transient exposure to NaBu after GVBD improves meiotic competence, but not subsequently, probably by having an effect on histone acetylation during oocyte maturation.

The effect of leptin on maturing porcine oocytes is dependent on glucose concentration

Increased body weight is often accompanied by increased circulating levels of leptin and glucose, which alters glucose metabolism in various tissues, including perhaps the oocyte. Alteration of glucose metabolism impacts oocyte function and may contribute to the subfertility often associated with obese individuals. The objective of this study was to determine the effect of leptin (0, 10, and 100 ng/ml) on the oocyte and cumulus cells during in vitro maturation under differing glucose concentrations. We examined the effects of leptin on oocyte maturation, blastocyst development, and/or gene expression in oocytes and cumulus cells (IRS1, IGF1, PPARγ, IL6, GLUT1) in a physiological glucose (2 mM) and high glucose (50 mM) environment. We also evaluated the effect of leptin on glucose metabolism via glycolysis and the pentose phosphate pathway. In a physiological glucose environment, leptin did not have an influence on oocyte maturation, blastocyst development, or oocyte gene expression. Expression of GLUT1 in cumulus cells was downregulated with 100 ng/ml leptin treatment, but did not affect oocyte glucose metabolism. In a high glucose environment, oocyte maturation and glycolysis were decreased, but in the presence of 100 ng/ml leptin, these parameters were improved to levels similar to control. This effect is potentially mediated by an upregulation of oocyte IRS1 and a correction of cumulus cell IGF1 expression. The present study demonstrates that in a physiological glucose concentration, leptin plays a negligible role in oocyte function. However, leptin appears to modulate the deleterious impact of a high glucose environment on oocyte function.

Identification of developmental competence-related genes in mature porcine oocytes

Oocyte competence is a key factor limiting female fertility, yet the underlying molecular mechanisms that contribute to oocyte competence remain unclear. The objective of this study was to elucidate specific genes whose function contributes to oocyte competence. We observed that 6 of 20 target genes examined were differentially expressed between adult (more competent) and prepubertal (less competent) porcine in vitro matured (IVM) oocytes. These genes were the cholesterol synthesis-related gene HMG-CoA reductase (HMGCR), fatty acid oxidation genes acyl-CoA synthetase long-chain family member 3 (ACSL3) and long-chain acyl-CoA dehydrogenase (ACADL), glycolytic genes fructose 1,6 bisphosphate aldolase (ALDOA) and lactate dehydrogenase C (LDHC), and tumor necrosis factor-α (TNF). These 6 genes, as well as 3 other genes [porcine endogenous retrovirus (PERV), transcribed loci 10 (TL10), serine/arginine-rich splicing factor 1 (SRSF1)], were further analyzed by comparing transcript abundance in IVM and in vivo matured (VVM) prepubertal and adult porcine oocytes. Among these 9 target genes, 5 were differentially expressed between IVM and VVM prepubertal oocytes, while 8 genes were differentially expressed between IVM and VVM adult oocytes. No genes were differentially expressed between VVM prepubertal and adult oocytes. A functional study of TNF demonstrated that depletion of endogenous TNF decreased oocyte competence and TNFAIP6 expression in cumulus cells, while TNF in IVM medium regulated TNFAIP6 expression in cumulus cells. Differential expression of the genes identified in this study suggests that these genes may be functionally relevant to oocyte competence.

Efficiency of in vitro fertilization is influenced by the meiotic competence of porcine oocytes and time of their maturation

The effect of meiotic competence of oocytes and time of their maturation on the efficiency of fertilization was studied in pigs. Cycling gilts with synchronized estrous cycles were used as oocyte donors. To obtain oocytes with different meiotic competence, oocytes were recovered separately from small and medium follicles in the early, middle and late luteal or early follicular phase. They were matured for 40 h, 43 h or 47 h and fertilized by spermatozoa of a proven boar. The penetration and monospermy rates, and total efficiency of fertilization were assessed. The same data were related to the follicle size, with or without regard to the phase, and to the maturation time. Regardless of the phase and the time of maturation, the monospermy rate and total efficiency of fertilization were significantly lower for the small follicle-derived oocytes than for the medium follicle-derived oocytes (38.5±10.4% vs 63.1±7.0% and 24.7±6.3% vs 42.5±3.8%). With regard to the phase, in the small follicle-derived oocytes, the monospermy rate increased significantly (P<0.05) from the early luteal to the late luteal phase (from 25.4±2.4% to 46.4±3.9%) and remained unchanged in the early follicular phase. A similar tendency was observed in the total efficiency of fertilization. No differences were found in either of these parameters in medium follicle-derived oocytes in the late luteal and early follicular phase. With regard to the time of maturation, the total efficiency of fertilization was significantly higher (P<0.05) in the small follicle-derived oocytes matured for 47 h than in those matured for 40 h (27.7±7.4% vs. 20.5±6.1%) and in the medium follicle-derived oocytes matured for 40 h as compared with those matured for 47 h (47.1±1.9% vs. 32.7±1.1%). With regard to the phase and the time of maturation, the differences were significant only in the late luteal and early follicular phases. It can be concluded that greater meiotic competence of porcine oocytes positively influences monospermy rate and total efficiency of fertilization process. However adequate time of maturation is an important factor for oocytes with different meiotic competence to improve the IVF procedure.

Effect of ammonium during in vitro maturation on oocyte nuclear maturation and subsequent embryonic development in pigs

The effects of ammonium in a chemically defined maturation medium on oocyte nuclear maturation and subsequent embryonic development of pigs after in vitro fertilization (IVF) and parthenogenetic activation (PA) were examined. Cumulus-oocyte complexes were matured in Purdue Porcine Medium (PPM) supplemented with 0mM, 0.02mM, 0.2mM, 2mM, or 20mM ammonium chloride, or TCM199 with 10% porcine follicle fluid (TCM+pFF; positive control) at 38.7 degrees C in 7% CO(2) in air for 40-44h. No significant difference (P>0.05) in nuclear maturation was found between oocytes matured in TCM+pFF or PPM with 0mM, 0.02mM and 0.2mM ammonium chloride. However, nuclear maturation was decreased (P<0.05) in oocytes matured in PPM with 2mM or 20mM ammonium. After IVF, oocytes matured in PPM with 20mM ammonium resulted in embryos with reduced (P<0.05) embryonic cleavage and blastocyst development than all other treatment groups. After PA, oocytes matured in PPM with 20mM ammonium resulted in embryos with lesser (P<0.05) embryonic cleavage compared to TCM+pFF. However, PA embryos derived from oocytes matured in PPM with both 2mM and 20mM ammonium had reduced (P<0.05) blastocyst development compared with TCM+pFF. These results demonstrate the detrimental effect of ammonium during in vitro oocyte maturation on nuclear progression to metaphase II. Additionally, the presence of ammonium during in vitro maturation negatively influences subsequent embryonic development, although PA embryos appear to be more sensitive to the negative effects of ammonium during oocyte maturation than do IVF embryos.

In vitro fertilization in inbred BALB/c mice I: isotonic osmolarity and increased calcium-enhanced sperm penetration through the zona pellucida and male pronuclear formation

To optimize IVF conditions for BALB/c mice, which are known to have poor in vitro fertilizability, the requirements for sperm–ova interaction were studied by use of modified simplex optimization medium (mKSOM) as a basic medium. Modified human tubal fluid (mHTF) was used for sperm preincubation and acted as a positive control. When the two media were compared, neither capacitation nor fertilization was supported in mKSOM. Increasing the calcium concentration in mKSOM to 5 mM or more during sperm: ova coincubation improved zona penetration but not male pronuclear (MPN) formation to the same level as those cells incubated in mHTF. When medium osmolarity was varied from 230–305 mOsmol by NaCl at 5 mM CaCl2, MPN formation improved at 280 mOsmol or higher osmolarity to the same level as that found when using mHTF. When NaCl equivalent to 25–75 mOsmol was substituted with trehalose, no significant reduction in fertilization was observed. Substitution of NaCl equivalent to 75 mOsmol with other osmotic reagents (sucrose, choline chloride and sorbitol) resulted in similar levels of fertilization as found with mHTF, except for sorbitol, which reduced fertilization significantly caused by its detrimental effect on sperm viability. At isotonic osmolarity (305 mOsmol), maximum fertilization was observed at 5 mM CaCl2; lower or higher concentrations of CaCl2 resulted in reduced fertilization. Calcium and osmolarity, therefore, are important for sperm : ova interaction in BALB/c mice and the increases in calcium to 5 mM and osmolarity to 305 mOsmol are optimal for BALB/c sperm to penetrate through the zona and to form MPN.

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.

A comparative analysis of metabolism and viability in porcine oocytes during in vitro maturation

The importance of oocyte quality cannot be overstated, because it impacts all subsequent events during development of the embryo, the fetus and even the resulting offspring. Oocyte metabolism plays a critical role in supporting developmental competence via multiple mechanisms. It is beginning to be understood that metabolic pathways not only affect cytoplasmic maturation but may control nuclear maturation as well. A complete understanding of the precise roles that metabolism plays in determining oocyte quality is crucial for developing efficient in vitro maturation systems to support acquisition of oocyte competence. To date, this pursuit has not been entirely successful. Work in our laboratory on porcine oocyte metabolism has elucidated some of the intricate control mechanisms at work within the oocyte, not only for energy production, but also encompassing progression of nuclear maturation, mitochondrial activity and distribution, and oxidative and ionic stresses. We hypothesize that by utilizing oocyte metabolic data, we can develop more appropriate in vitro maturation systems that result in increased oocyte and embryo developmental competence.

Chemical manipulation of glucose metabolism in porcine oocytes: effects on nuclear and cytoplasmic maturation in vitro

The objectives of this study were to manipulate metabolism of glucose through glycolysis and the pentose phosphate pathway (PPP) in porcine oocytes during in vitro maturation, and determine the effects of this manipulation on meiotic progression, intracellular glutathione (GSX) concentrations and embryonic development. Cumulus-oocyte complexes isolated from abattoir ovaries were matured (40–44 h) in Purdue Porcine Medium for maturation alone (control) or supplemented with pyrroline-5 carboxylate (PC, 0.1 μM; PPP stimulator), diphenyleneiodonium (DPI, 0.1 μM; PPP inhibitor), dinitrophenol (DNP, 10 μM; glycolytic stimulator), hexametaphosphate (HMP, 100 μM; glycolytic inhibitor), PC + HMP or DNP + DPI. At the conclusion of in vitro maturation, cumulus cells were removed and oocytes were randomly allocated for analysis of GSX, metabolism and nuclear maturation, or in vitro fertilization and embryo culture. Both DPI and DNP + DPI decreased (P ≤ 0.05) the activity of glycolysis and the PPP, increased (P ≤ 0.05) the percentage of immature oocytes, and decreased (P ≤ 0.05) the proportion of mature oocytes compared with control oocytes and oocytes from the other treatments. Embryonic development (cleavage and blastocyst stage) and the intracellular content of GSX were also decreased (P ≤ 0.05) following exposure to DPI or DNP + DPI compared with control oocytes and oocytes from the other treatments. Oocyte metabolism, nuclear maturation, GSX content and embryonic development were unaffected (P > 0.05) following exposure to PC, DNP, HMP or PC + HMP. Our results suggest that metabolism of glucose through the PPP and/or glycolysis plays a key role in the control of nuclear and cytoplasmic maturation of porcine oocytes in vitro.

Defending the zygote: search for the ancestral animal block to polyspermy

Fertilization is the union of a single sperm and an egg, an event that results in a diploid embryo. Animals use many mechanisms to achieve this ratio; the most prevalent involves physically blocking the fusion of subsequent sperm. Selective pressures to maintain monospermy have resulted in an elaboration of diverse egg and sperm structures. The processes employed for monospermy are as diverse as the animals that result from this process. Yet, the fundamental molecular requirements for successful monospermic fertilization are similar, implying that animals may have a common ancestral block to polyspermy. Here, we explore this hypothesis, reviewing biochemical, molecular, and genetic discoveries that lend support to a common ancestral mechanism. We also consider the evolution of alternative or radical techniques, including physiological polyspermy, with respect to our ability to describe a parsimonious guide to fertilization.

Effect of short periods of sperm-oocyte coincubation during in vitro fertilization on embryo development in pigs

The present study was conducted to determine if the efficiency of in vitro pig embryo production could be improved by a reduction in the period of time that oocytes are exposed to sperm during in vitro fertilization. A total of 1596 immature cumulus-oocyte complexes from five replicates were matured in vitro and inseminated with frozen-thawed spermatozoa (2000 spermatozoa/oocyte) for 10, 30, 60 min or 6h (control group). The oocytes from short coincubation times were washed three times in fertilization medium to remove spermatozoa not bound to the zona and transferred to another droplet of the same medium (containing no sperm) for 6h. After 6h, the oocytes from each group were cultured in embryo culture medium for another 6h to assess fertilization parameters and for 7 days to assess embryo development. After each period of coincubation, some oocytes were stained with Hoechst-33342 to count zona-bound sperm. Although the number of zona-bound sperm increased with the coincubation time (34.1 +/- 1.7, 46.8 +/- 2.8, 62.8 +/- 3.8 and 139.5 +/- 6.1 for 10, 30, 60 min and 6h, respectively, P < 0.02), the penetration rate was not significantly different among groups (61.3-68.2%). However, the efficiency of fertilization (number of monospermic oocytes/total number of inseminated oocytes) increased (P < 0.04) as the coincubation time was increased (26.6 +/- 2.9%, 29.0 +/- 4.4%, 39.5 +/- 6.2%, and 49.3 +/- 3.0% for 10, 30, 60 min and 6h, respectively). Nevertheless, there were no significant differences among groups in blastocyst formation rates (17.5-25.5%). These results demonstrate that although a sperm-oocyte coincubation time of as little as 10 min results in fertilization rates similar to a 6-h coincubation, the reduction in the period of time of sperm-oocyte coincubation does not improve the efficiency of in vitro pig embryo production.