In vitro development of polyspermic porcine oocytes: Relationship between early fragmentation and excessive number of penetrating spermatozoa

Direct cleavage during the first mitosis is a sign of abnormal fertilization in cattle

Direct cleavage, a type of abnormal cleavage in which one zygote divides into three or more blastomeres, has been reported in mammals. The incidence of direct cleavage increases in zygotes with three or more pronuclei (multi-PN) and those showing abnormal pronuclei migration. However, there are few reports on the relationship between pronuclei and direct cleavage, and the effects of these relationships on subsequent embryogenesis have not been clarified. It is difficult to observe pronuclei under visible light, especially in bovine zygotes, because of abundant dark lipid droplets in the cytoplasm. We visualized pronuclei by removing lipid droplets from bovine zygotes and analyzed the relationship between the number of pronuclei and direct cleavage using time-lapse cinematography. The direct cleavage rate of multi-PN zygotes was 78.6%, which was significantly higher than that of zygotes with one pronucleus (1 PN, 0.0%) and two pronuclei (2 PN, 8.2%). Observation of pronuclei migration in 2 PN zygotes showed that 3.1% of 2 PN zygotes had non-apposed pronuclei. The direct cleavage rate of zygotes with non-apposed pronuclei was 66.7%, which was significantly higher than that of zygotes with apposed pronuclei (6.4%). Among multi-PN zygotes, the proportions of zygotes with apposed pronuclei and non-apposed pronuclei were 37.5% and 64.3%, respectively. The direct cleavage rate of multi-PN zygotes with non-apposed pronuclei was 100.0%, which was significantly higher than that of zygotes with apposed pronuclei (40.0%). Three-dimensional live-cell imaging of bovine zygotes injected with the mRNA-encoding histone H2B-mCherry showed that the direct cleavage rates of 2 PN and multi-PN zygotes bypassing syngamy were 63.2% and 75.5%, respectively. These rates were significantly higher than that of 2 PN and multi-PN zygotes that underwent syngamy (5.6% and 20.0%, respectively). Regardless of the number of pronuclei, a high frequency of direct cleavage was observed in zygotes in which the pronuclei did not migrate inward the cytoplasm and bypassed syngamy. These results suggest that abnormal fertilization such as multi-PN and migration error of pronuclei in cattle is the primary reason for direct cleavage during the first mitosis. Assessment of direct cleavage during the first mitosis allows exclusion of embryos with abnormal fertilization and may contribute to in vitro produced embryo transfer success.

Parental genomes segregate into distinct blastomeres during multipolar zygotic divisions leading to mixoploid and chimeric blastocysts

Background

During normal zygotic division, two haploid parental genomes replicate, unite and segregate into two biparental diploid blastomeres.

Results

Contrary to this fundamental biological tenet, we demonstrate here that parental genomes can segregate to distinct blastomeres during the zygotic division resulting in haploid or uniparental diploid and polyploid cells, a phenomenon coined heterogoneic division. By mapping the genomic landscape of 82 blastomeres from 25 bovine zygotes, we show that multipolar zygotic division is a tell-tale of whole-genome segregation errors. Based on the haplotypes and live-imaging of zygotic divisions, we demonstrate that various combinations of androgenetic, gynogenetic, diploid, and polyploid blastomeres arise via distinct parental genome segregation errors including the formation of additional paternal, private parental, or tripolar spindles, or by extrusion of paternal genomes. Hence, we provide evidence that private parental spindles, if failing to congress before anaphase, can lead to whole-genome segregation errors. In addition, anuclear blastomeres are common, indicating that cytokinesis can be uncoupled from karyokinesis. Dissociation of blastocyst-stage embryos further demonstrates that whole-genome segregation errors might lead to mixoploid or chimeric development in both human and cow. Yet, following multipolar zygotic division, fewer embryos reach the blastocyst stage and diploidization occurs frequently indicating that alternatively, blastomeres with genome-wide errors resulting from whole-genome segregation errors can be selected against or contribute to embryonic arrest.

Conclusions

Heterogoneic zygotic division provides an overarching paradigm for the development of mixoploid and chimeric individuals and moles and can be an important cause of embryonic and fetal arrest following natural conception or IVF.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13059-022-02763-2.

Investigation of the Efficacy of Dithiothreitol and Glutathione on In Vitro Fertilization of Cryopreserved Large White Boar Semen

The objectives of this study were to evaluate the properties of sperm motility and morphology under induced oxidative stress, compare the antioxidant capacity of dithiothreitol (DTT) and glutathione (GSH) following the cryopreservation of Large White boar semen, investigate the ability of cryopreserved Large White boar semen to fertilize the matured gilts oocytes and compare the efficacy of DTT and GSH antioxidants in improving the oocyte fertilization by cryopreserved Large White boar semen. The semen was collected from three Large White boars (ten ejaculates per boar) and transported (37 °C) to the laboratory. Semen freezing extenders were supplemented with 5 mM DTT, 5 mM GSH and a combination of 2.5 mM DTT + 2.5 mM GSH. A liquid nitrogen vapor method was used to freeze boar semen. Gilts’ ovaries were collected from the local abattoir and transported (37 °C) to the laboratory. The slicing method was used to retrieve the oocytes from the ovaries. Fresh semen and frozen-thawed semen were used for in vitro fertilization (IVF). For frozen-thawed semen, four treatments (control, 5 mM DTT, 5 mM GSH, and a combination of 2.5 mM DTT + 2.5 mM GSH) were used during IVF in order to evaluate the fertilizing ability of the antioxidants. The supplementation of 5 µM DTT to H2O2-treated semen significantly improved progressive motility (PM) by 14.82%. A combination of 2.5 mM DTT + 2.5 mM GSH treatment reduced percentage of sperm total motility (TM) and rapid motility (RAP) following thawing (p < 0.05). Fresh semen and a combination of 2.5 mM DTT + 2.5 mM GSH treatment recorded a higher percentage of zygotes with polyspermy (p < 0.05). The control treatment numerically recorded a high percentage of zygotes with 1 PN, while the 5 mM DTT treatment recorded a high percentage of zygotes with 2 PN.

Excess polyspermy reduces the ability of porcine oocytes to promote male pronuclear formation after in vitro fertilization

Male pronucleus (MPN) formation is a very important physiological event during fertilization, which affects in vitro production of transferrable embryos. The aim of this study was to find out the correlation between the number of penetrated sperm and the occurrence of failure of MPN formation in porcine oocytes. In vitro matured porcine oocytes were fertilized in vitro with frozen epididymal sperm. Two different frozen sperm lots were tested in this study, which were different in terms of polyspermy rates. The numbers and the status of penetrated sperm in oocytes were evaluated 10 h after insemination. Under high polyspermy condition, the polyspermy rate was 83.5% with an average mean of 3.5 sperms per penetrated oocyte, whereas the percentage of polyspermy was 65.5% with an average mean of 2.4 sperms per penetrated oocyte under moderate polyspermic condition. Correlation analysis revealed a negative correlation between the number of penetrated sperm and their MPN formation percentage both in the sperm lot of high polyspermy (R = −0.560, p < 0.05) and in the sperm lot of moderate polyspermy (R = −0.405, p < 0.05) which suggests that penetration of excessive spermatozoa disables the oocyte cytoplasm to promote MPN formation.

Morphokinetic analysis of pronuclei using time-lapse cinematography in bovine zygotes

The morphokinetics of pronuclei (PN) are considered crucial factors affecting embryogenesis in mammals. Whereas, since bovine zygotes contain a large number of cytosolic lipid droplets, detailed observation of PN has not been performed. In this study, we visualized PN using time-lapse cinematography (TLC) with light microscopy for the first time in delipidated bovine zygotes. The proportions of 0 PN, 1PN, 2PN, and multi-PN in delipidated bovine zygotes were 10.1%, 6.5%, 72.7%, and 10.8%, respectively. Abnormal fertilization, including 1 PN and multi-PN, was observed in 15.6% of blastocysts. The times from IVF to PN appearance, PN fading, and first cleavage in 2 PN bovine zygotes that developed into blastocysts were 10.4, 25.5, and 27.6 h, respectively, which were similar to PN morphokinetics in humans. The 2 PN zygotes showed that the prolonged time from IVF to the appearance of PN and from the fading of PN to the first cleavage negatively affected blastocyst formation. The time from appearance to fading of PN in multi-PN zygotes that developed into blastocysts was longer than that in multi-PN zygotes that did not develop into blastocysts. Besides, among zygotes that developed into blastocysts, the time from appearance to fading of PN in multi-PN zygotes was longer than that in 2 PN and 1 PN zygotes. These results suggest that PN morphokinetic abnormalities are associated with subsequent embryonic development. Observation of PN in bovine zygotes by using non-invasive visible light TLC by delipidation could be a powerful tool to clarify the relationship between PN morphokinetics and developmental competence.

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.

Optimization of the in vitro fertilization protocol for frozen epididymal sperm with low fertilization ability in Ban-A native Vietnamese pigs

The aim of the present study was to improve the penetration during in vitro fertilization (IVF) of a frozen lot of epididymal sperm with a notoriously low fertilization ability of a Ban boar which is a native Vietnamese breed by optimizing different parameters of the IVF system. In Experiment 1, we determined that Pig-fertilization medium was superior medium to Tyrode's albumin lactate pyruvate-polyvinyl alcohol medium for IVF and defined the optimum the sperm concentration (1 × 10⁶  sperm/ml). In Experiment 2, we clarified that partial removal of cumulus cells from cumulus-oocyte complexes by hyaluronidase treatment before IVF enhances sperm penetration, whereas complete cumulus removal reduces penetration. Finally, in Experiment 3 the elevation of concentration of caffeine in Pig-fertilization medium from 2 to 5 mmol/L and the prolongation of the co-culture of gametes from 3 to 5 hr significantly increased the total penetration rate from 15.2% to over 50%. In conclusion, the combination of partial oocyte denudation, an elevated caffeine concentration in Pig-fertilization medium and an extended interval of IVF with using an optimized sperm concentration was a potent way to improve the fertilization results for a frozen epididymal Ban sperm lot with low fertility.

Vitrification, not cryoprotectant exposure, alters the expression of developmentally important genes in in vitro produced porcine blastocysts

The vitrification of embryos is common practice in advanced livestock breeding programs and in human fertility clinics. Recent studies have revealed that vitrification results in aberrant expression of a number of stress related genes. However, few studies have examined the effect that vitrification has on developmentally important genes, and none have been conducted in porcine embryos. The aim of this study was to determine the effects that different vitrification procedures and cryoprotectant combinations have on the expression of imprinted genes in in vitro produced (IVP) porcine blastocysts. The transcript levels of insulin-like growth factor 2 (IGF2) were lower in all groups of vitrified blastocysts compared to that in non-vitrified control blastocysts (P < 0.05). Expression levels of IGF2 and IGF2 receptor (IGF2R) in blastocysts that had been exposed to cryoprotectants without being vitrified were similar to that in non-vitrified control blastocysts (P > 0.05). Furthermore, blastocysts vitrified using ethylene glycol and propanediol combined, and those vitrified in a closed device, had IGF2R transcript levels similar to that in non-vitrified control blastocysts (P > 0.05). In conclusion, vitrification, but not exposure to cryoprotectants, caused aberrant expression of the imprinted genes IGF2 and IGF2R. Vitrification protocols that incorporated propanediol or a closed device were found to be least disruptive of gene expression in IVP porcine blastocysts.

Developmental competence of porcine genome-edited zygotes

Genome editing in pigs has tremendous practical applications for biomedicine. The advent of genome editing technology, with its use of site-specific nucleases-including ZFNs, TALENs, and the CRISPR/Cas9 system-has popularized targeted zygote genome editing via one-step microinjection in several mammalian species. Here, we review methods to optimize the developmental competence of genome-edited porcine embryos and strategies to improve the zygote genome-editing efficiency in pigs.

Lack of calcium oscillation causes failure of oocyte activation after intracytoplasmic sperm injection in pigs

In pigs, the efficiency of embryo production after intracytoplasmic sperm injection (ICSI) is still low because of frequent failure of normal fertilization, which involves formation of two polar bodies and two pronuclei. To clarify the reasons for this, we hypothesized that ICSI does not properly trigger sperm-induced fertilization events, especially intracellular Ca²⁺ signaling, also known as Ca²⁺ oscillation. We also suspected that the use of in vitro-matured oocytes might negatively affect fertilization events and embryonic development of sperm-injected oocytes. Therefore, we compared the patterns of Ca²⁺ oscillation, the efficiency of oocyte activation and normal fertilization, and embryo development to the blastocyst stage among in vivo- or in vitro-matured oocytes after ICSI or in vitro fertilization (IVF). Unexpectedly, we found that the pattern of Ca²⁺ oscillation, such as the frequency and amplitude of Ca²⁺ rises, in oocytes after ICSI was similar to that in oocytes after IVF, irrespective of the oocyte source. However, half of the oocytes failed to become activated after ICSI and showed no Ca²⁺ oscillation. Moreover, the embryonic development of normal fertilized oocytes was reduced when in vitro-matured oocytes were used, irrespective of the fertilization method employed. These findings suggest that low embryo production efficiency after ICSI is attributable mainly to poor developmental ability of in vitro-matured oocytes and a lack of Ca²⁺ oscillation, rather than the pattern of oscillation.

Porcine oocyte maturation in vitro: role of cAMP and oocyte-secreted factors - A practical approach

Polyspermy or the penetration of more than one sperm cell remains a problem during porcine in vitro fertilization (IVF). After in vitro culture of porcine zygotes, only a low percentage of blastocysts develop and their quality is inferior to that of in vivo derived blastocysts. It is unknown whether the cytoplasmic maturation of the oocyte is sufficiently sustained in current in vitro maturation (IVM) procedures. The complex interplay between oocyte and cumulus cells during IVM is a key factor in this process. By focusing on this bidirectional communication, it is possible to control the coordination of cumulus expansion, and nuclear and cytoplasmic maturation during IVM to some extent. Therefore, this review focuses on the regulatory mechanisms between oocytes and cumulus cells to further the development of new in vitro embryo production (IVP) procedures, resulting in less polyspermy and improved oocyte developmental potential. Specifically, we focused on the involvement of cAMP in maturation regulation and function of oocyte-secreted factors (OSFs) in the bidirectional regulatory loop between oocyte and cumulus cells. Our studies suggest that maintaining high cAMP levels in the oocyte during the first half of IVM sustained improved oocyte maturation, resulting in an enhanced response after IVF and cumulus matrix disassembly. Recent research indicated that the addition of OSFs during IVM enhanced the developmental competence of small follicle-derived oocytes, which was stimulated by epidermal growth factor (EGF) via developing EGF-receptor signaling.

The effect of temperature during liquid storage of in vitro-matured bovine oocytes on subsequent embryo development

The aim of the present study was to optimize the temperature for the temporal storage of matured bovine oocytes. In vitro-matured bovine oocytes were preserved in HEPES-buffered TCM199 medium supplemented with 10% newborn calf serum at different temperatures (4 °C, 15 °C, 25 °C, and 38.5 °C) for 20 hours. Embryo development and blastocyst quality after in vitro fertilization, cytoplasmic ATP and glutathione levels in oocytes, and the frequency of apoptotic oocytes were compared among storage groups and a control group without storage. Among the storage groups, those at 25 °C and 38.5 °C showed the highest rates of blastocyst development (19.3% and 24.5%, respectively) compared with those stored at 4 °C and 15 °C (8.5% and 14.9%, respectively); however, blastocyst formation rates in all storage groups were lower than that in the control group (39.8%; P < 0.05). Storage at 38.5 °C and 15 °C was associated with reduced cell numbers in resultant blastocysts compared with the control and the 25 °C storage groups. Storage at 4 °C reduced metabolic activity of oocytes characterized by their lower ATP levels compared with the other groups. Storage for 20 hours significantly reduced the glutathione content in oocytes in all groups in a similar manner, irrespective of the temperature. Storage at 4 °C or 15 °C but not at 25 °C and 38.5 °C significantly increased the percentage of apoptotic oocytes compared with the control group. In conclusion, 25 °C was found to be the most suitable temperature for the temporal storage of matured bovine oocytes regarding both the developmental competence of oocytes and the quality of resultant blastocysts.

A high incidence of chromosome abnormalities in two-cell stage porcine IVP embryos

In pigs, in vitro production is difficult with a high occurrence of polyspermy and low blastocyst formation rates. To test the hypothesis that this may, at least in part, be due to chromosomal errors, we employed whole genome amplification and comparative genomic hybridization, performing comprehensive chromosome analysis to assess both cells of the two-cell stage in vitro porcine embryos. We thus described the incidence, nature and origin of chromosome abnormalities, i.e. whether they derived from incorrect meiotic division during gametogenesis or aberrant mitotic division in the zygote. We observed that 19 out of 51 (37%) of two-cell stage early pig IVP embryos had a chromosome abnormality, mostly originating from an abnormal division in the zygote. Moreover, we frequently encountered multiple aneuploidies and segmental chromosome aberrations. These results indicate that the pig may be particularly sensitive to in vitro production, which may, in turn, be due to incorrect chromosome segregations during meiosis and early cleavage divisions. We thus accept our hypothesis that chromosome abnormality could explain poor IVP outcomes in pigs.

A new rolling culture-based in vitro fertilization system capable of reducing polyspermy in porcine oocytes

The high incidence of polyspermy is one of the major obstacles during in vitro fertilization (IVF) in pigs. To overcome this, we developed a novel IVF method, which involves constant rotation. Oocytes matured in vitro were mixed with spermatozoa (0.2 × 10(5) sperm/mL) in an IVF medium (200 μL) using a 200 μL PCR tube. This tube was then rotated at 1 rpm for 6 h at 38.5°C in a rotation mixer (experimental group). A second PCR tube was simultaneously cultured without rotation (control group). The rate of polyspermy was evaluated 12 h after insemination and was significantly (P < 0.05; 21.0% vs. 48.3%) lower in the experimental group than in the control group. Sperm penetration rate was similar in oocytes from the experimental and control groups (75.2% vs. 83.1%). However, monospermic fertilization rate of the oocytes was significantly (P < 0.05; 44.8% vs. 21.2%) higher in the experimental group than in the control group. Furthermore, the rate of blastocyst formation (30.1% vs. 20.8%) increased in the experimental group, as compared to the control group. This present system will contribute to increase the efficacy of blastocyst production through reduction of polyspermic penetration.

Increasing the cAMP concentration during in vitro maturation of pig oocytes improves cumulus maturation and subsequent fertilization in vitro

Porcine IVF faces various problems such as incomplete cytoplasmic maturation of the oocyte and polyspermy. Previous studies proved the importance of cAMP in regulating nuclear and cytoplasmic maturation of oocytes. This study investigated the effect of the cAMP-modulating agents 3-isobutyl-1-methylxanthine (IBMX) and dibutyryl cAMP sodium salt (dbcAMP) on several parameters during in vitro production of porcine embryos. First, we wanted to see if oocyte collection in IBMX could meiotically arrest oocytes and, as such, improve synchronization of nuclear and cytoplasmic maturation. To this end, cumulus-oocyte complexes (COCs) were collected from gilts in HEPES-buffered Tyrode balanced salt solution medium with 0.5-mM IBMX or without IBMX. At the end of oocyte collection, the effect of IBMX on chromatin configuration was evaluated. However, no differences could be observed in nuclear configuration between IBMX- and IBMX+ oocytes (P > 0.05). Second, we added dbcAMP during IVM to improve cytoplasmic maturation and evaluated cumulus expansion (lack of adhesion), a disintegrin and metalloproteinase with thrombospondin-like repeats (ADAMTS-1) levels in cumulus cells, fertilization, and blastocyst rates. Cumulus-oocyte complexes were matured in modified North Carolina State University medium 37 with or without 1-mM dbcAMP. Frozen-thawed, epididymal, boar spermatozoa were used for IVF. After IVF, presumed zygotes were cultured for 7 days in North Carolina State University medium 23. Penetration rate decreased in dbcAMP+ (57.3%) compared with dbcAMP- (67.8%), but the polyspermy rate also decreased (43.3% vs. 53.4%, respectively) leading to an increased normal fertilization rate (56.7% vs. 46.6%, respectively; P < 0.05). Only 7.2% of the COCs showed adhesion in dbcAMP+ which was lower than 15.7% in dbcAMP- (P < 0.05) probably because of an upregulation of the ADAMTS-1 protein by dbcAMP. When the adherent oocytes were removed during maturation, no difference could be detected between the blastocyst rate of dbcAMP- and dbcAMP+ (17.1% and 21.0% on Day 7, respectively; P > 0.05). In conclusion, the use of IBMX during collection did not cause a meiotic arrest. Using dbcAMP during IVM caused a greater normal fertilization rate, a lower rate of adherent COCs during IVM, higher levels of ADAMTS-1 in cumulus cells, and an equal blastocyst rate after screening out adherent COCs. These findings contribute to a better understanding of cAMP involvement in porcine oocyte maturation and provide a basis to develop an improved system with less polyspermy and higher blastocyst rates.

The evolution of porcine embryo in vitro production

The in vitro production of porcine embryos has presented numerous challenges to researchers over the past four decades. Some of the problems encountered were specific to porcine gametes and embryos and needed the concerted efforts of many to overcome. Gradually, porcine embryo in vitro production systems became more reliable and acceptable rates of blastocyst formation were achieved. Despite the significant improvements, the problem of polyspermic fertilization has still not been adequately resolved and the embryo in vitro culture conditions are still considered to be suboptimal. Whereas early studies focused on increasing our understanding of the reproductive processes involved, the technology evolved to the point where in vitro-matured oocytes and in vitro-produced embryos could be used as research material for developing associated reproductive technologies, such as SCNT and embryo cryopreservation. Today, the in vitro procedures used to mature oocytes and culture embryos are integral to the production of transgenic pigs by SCNT. This review discusses the major achievements, advances, and knowledge gained from porcine embryo in vitro production studies and highlights the future research perspectives of this important technology.

Delay in cleavage of porcine embryos after intracytoplasmic sperm injection (ICSI) shows poorer embryonic development

In pigs, the embryonic developmental ability after intracytoplasmic sperm injection (ICSI) is inferior to that resulting from in vitro fertilization (IVF). We evaluated the timing of cell division up to blastocyst formation on embryonic development after ICSI using either whole sperm (w-ICSI) or the sperm head alone (h-ICSI) and IVF as a control. At 10 h after ICSI or IVF, we selected only zygotes, and each of the zygotes/embryos was evaluated for cleavage every 24 h until 168 h. We then observed a delay in the 1st and 2nd cleavages of h-ICSI embryos and also in blastocoele formation by w-ICSI embryos in comparison with IVF embryos. The rate of blastocyst formation and the quality of blastocysts in both ICSI groups were inferior to those in the IVF group. In conclusion, the delay in cleavage of porcine ICSI embryos shows poorer embryonic development.

Comparisons of the effects of long-acting and short-acting GnRH agonists on embryo quality, endometrial thickness and pregnancy rate in human in vitro fertilization

INTRODUCTION

The aim was to compare the efficacy of long-acting and short-acting gonadotropin-releasing hormone (GnRH) agonists by long protocol on embryo quality, endometrial thickness and pregnancy rate in in vitro fertilization.

MATERIAL AND METHODS

In this retrospective study, long-term pituitary downregulation, achieved with long- and short-acting GnRH agonists (GnRHa), was performed for patients undergoing in vitro fertilization (n = 175).

RESULTS

There were no significant differences between the long and short-acting GnRH group (63.16% vs. 66.26%, p > 0.05), and the secondary and primary infertility group (63.47% vs. 66.86%, p > 0.05) in embryo quality. Logistic regression analysis showed that type of infertility and endometrial thickness were significantly associated with pregnancy outcome. Patients in the long-acting GnRHa group had a thicker endometrium on the day of human chorionic gonadotrophin (hCG) administration (10.79 ±2.62 mm vs. 9.64 ±1.97 mm, p < 0.01), lower serum luteinizing hormone (LH) concentration (1.21 ±1.13 vs. 2.53 ±3.39) and a higher pregnancy rate (59.60% vs. 43.42%, p < 0.05) than those of patients in the short-acting GnRHa group.

CONCLUSIONS

This work suggests that types of agonist protocol and infertility may not affect embryo quality. Type of infertility and endometrial thickness may be positive predictors for clinical pregnancy, but the key finding is that the long-acting GnRHa protocol may be an effective method of improving endometrial thickness, endometrial receptivity and pregnancy rate in in vitro fertilization.

Suitability and effectiveness of single layer centrifugation using Androcoll-P in the cryopreservation protocol for boar spermatozoa

The goal of the present experiment was to evaluate the suitability and effectiveness of single layer centrifugation (SLC), using the pig-specific colloid Androcoll-P, as a routine procedure for selecting boar spermatozoa for cryopreservation. The study focuses special attention on the effectiveness of SLC for processing a whole sperm rich ejaculate fraction and the fertilizing ability of frozen-thawed (FT) sperm selected using SLC prior to freezing. Thirteen sperm rich ejaculate fractions (one per boar) were split into three aliquots. Two aliquots of 15 and 150mL were SLC-processed (500×g for 20min) using 15 and 150mL (v/v) of Androcoll-P-Large and Androcoll-P-XL, respectively. The third aliquot remained un-processed as a control. The percentages of spermatozoa that were morphologically normal and showed rapid and progressive motility (assessed by CASA) spermatozoa were higher (P<0.01) and those with fragmented nuclear DNA (sperm chromatin dispersion test) were lower (P<0.01) after SLC than control semen samples, regardless of the Androcoll-P used. The recovery rates of total, motile, viable (flow cytometric evaluated after staining with H-42, PI and FITC-PNA) and morphologically normal spermatozoa ranged between 20 and 100% and those with intact nuclear DNA ranged between 60 and 100%, irrespective of the Androcoll-P used. Thereafter, the semen samples were cryopreserved using a standard 0.5-mL straw freezing protocol. Post-thaw percentages of sperm motility (both total motility and rapid progressive motility), viability and intact nuclear DNA were higher (P<0.05) in SLC-processed than in control semen samples, irrespective of the Androcoll-P used. SLC-processing also improved the in vitro fertilizing ability of FT-sperm (679 in vitro matured oocytes inseminated with a viable sperm:oocyte ratio of 300:1 and coincubated for 6h), measured as the percentage of penetrated oocytes and the mean number of swollen sperm heads and/or male pronuclei in penetrated oocytes. However, there was no effect of SLC-processing on the in vitro ability of putative zygotes to develop to blastocysts. Overall these results indicate that SLC-processing of boar ejaculates using Androcoll-P improves the quality and fertilizing ability of cryosurvival boar sperm. However, efforts should be made to ensure continued high recovery yields before considering the inclusion of SLC as a routine procedure in the cryopreservation protocol of boar ejaculates.

Evaluation of zona pellucida function for sperm penetration during in vitro fertilization in pigs

In porcine oocytes, the function of the zona pellucida (ZP) with regard to sperm penetration or prevention of polyspermy is not well understood. In the present study, we investigated the effects of the ZP on sperm penetration during in vitro fertilization (IVF). We collected in vitro-matured oocytes with a first polar body (ZP+ oocytes). Some of them were freed from the ZP (ZP− oocytes) by two treatments (pronase and mechanical pipetting), and the effects of these treatments on sperm penetration parameters (sperm penetration rate and numbers of penetrated sperm per oocyte) were evaluated. There was no evident difference in the parameters between the two groups. Secondly, we compared the sperm penetration parameters of ZP+ and ZP− oocytes using frozen-thawed epididymal spermatozoa from four boars. Sperm penetration into ZP+ oocytes was found to be accelerated relative to ZP− oocytes. Thirdly, we evaluated the sperm penetration of ZP+ and ZP− oocytes at 1−10 h after IVF (3 h gamete co-incubation). The proportions of oocytes penetrated by sperm increased significantly with time in both groups; however, the number of penetrated sperm per oocyte did not increase in ZP− oocytes. Finally, we performed IVF using ZP− oocytes divided into control (3 h) and prolonged gamete co-incubation (5 h) groups. Greater numbers of sperm penetrated in the 5 h group than in the control group. These results suggest that the ZP and oolemma are not competent factors for prevention of polyspermy in our present porcine IVF system. However, it appears that ZP removal is one of the possibilities for reducing polyspermic penetration in vitro in pigs.

In vitro production of porcine embryos: current status, future perspectives and alternative applications

The pig is considered to be a suitable source of cells and organs for xenotransplants, as well as a transgenic animal to produce specific proteins, given the biological similarities it shares with human beings. However, the in vitro embryo production system in pigs is inefficient compared with those in other mammals, such as cattle or mice. Although numerous modifications have been applied to improve the efficiency of in vitro embryo production systems in pigs, not much progress has been made to overcome the problem of polyspermy, and low developmental ability due to insufficient cytoplasmic abilities of in vitro matured oocytes and improper culture conditions for the in vitro produced embryos. Recent achievements, such as the establishment of chemically defined medium and utilization of 'zona hardening' technique, have gained some success. However, further research for the reduction of polyspermy and detrimental effects of the culture systems in pigs is still needed.

Evaluation of developmental competence of in vitro-produced porcine embryos based on the timing, pattern and evenness of the first cleavage and onset of the second cleavage

The following selection markers for in vitro-produced porcine embryos were investigated: the timing, pattern and evenness of the first cleavage and the timing of the second cleavage. The embryos that cleaved by 30 h post-insemination (hpi) developed to blastocysts at a significantly higher rate (60.9%) and with a significantly higher cell number (33.6 cells) than those of embryos cleaved by 36 hpi (26.4% and 23.6 cells, respectively, P<0.05). Blastocyst proportions derived from 2- and 3-cell embryos cleaved by 30 hpi (68.2 and 65.3%, respectively) were significantly higher than those of 4- and >4-cell embryos (46.3 and 42.6%, respectively, P<0.05). The cell number per blastocyst generated from 2-cell embryos was significantly greater (37.3 cells) than those from 3-, 4- and >4-cell embryos (23.6-27.8 cells, P<0.05). Among embryos cleaved by 30 hpi, the blastocysts derived from evenly cleaved embryos (40.6 cells) were of significantly better quality than those derived from unevenly cleaved embryos (33.2 cells, P<0.05), although their blastocyst rates did not differ. The evenly cleaved embryos that underwent subsequent cleavage within 18 h had significantly higher blastocyst rates (72.7-81.0%) and quality (36.2-40.9 cells) than those without subsequent cleavage (48.3% and 22.5 cells, respectively, P<0.05) during the same period. In conclusion, the timing, pattern and evenness of the first cleavage and the timing of the second cleavage affected the developmental competence and quality of in vitro-produced porcine embryos.

Transplantation of adult fibroblast nuclei into the central region of metaphase II eggs resulted in mid-blastula transition embryos

Recently, a novel technical method to perform somatic nuclear transplantation (NT) in zebrafish using nonactivated eggs as recipients without the need to detect the micropyle was developed in our lab. However, the use of spermatozoa as an activating agent prevented to know whether the inserted nucleus compromised embryonic and early larval developmental ability. The aim of the present work was to test the developmental ability of the embryos reconstructed by transplanting adult fibroblast nuclei into the central region of the metaphase II egg but subsequently activated by only water. In addition, because an oocyte aging facilitates the activation in mammalian oocytes, this work also pursued to test whether the use of limited-aged eggs (2 h) as recipients improved the activation process in zebrafish NT. The adult somatic nucleus located in the central region of the nonactivated egg resulted in the 12% of mid-blastula transition embryos versus the 20% when the transplant is in the animal pole (p >or= 0.05). This suggests that the central region of the nonactivated metaphase II eggs can be a suitable place for nucleus deposition in NT in zebrafish. These results reinforce the possibility to use nonactivated metaphase II eggs in subsequent reprogramming studies by adult somatic NT in zebrafish. Unfortunately, in contrast to mammals, a limited egg aging (2 h) did not improve the activation process in zebrafish NT.

Generation of porcine diploid blastocysts after injection of spermatozoa grown in nude mice

It is anticipated that the utilization of spermatogonia through testicular xenografting will open new avenues for the conservation of male gametes. With the aim of establishing this new technique for genetic preservation of pigs, we used it in combination with intracytoplasmic sperm injection (ICSI). Testicular tissues derived from neonatal piglets, which contained seminiferous cords consisting of only gonocytes/spermatogonia, were transplanted under the back skin of castrated nude mice. Between 125 and 192 d after xenografting, sperm (morphologically similar to epididymal sperm) were recovered from 41 of the 65 host mice (63.1%). Testicular spermatozoa from adult boars were used as a positive control. A single spermatozoon was injected into an in vitro matured porcine oocyte, and the oocytes were electro-stimulated and cultured (graft-ICSI and testis-ICSI, respectively). Blastocyst rates in both ICSI groups (24.9% and 37.4%, respectively) were higher (P<0.05) than those without the injection procedure (parthenogenetic; 12.7%) and after injection of a small amount of injection buffer (sham; 13.0%). Rates of diploid blastocysts in both graft-ICSI and testis-ICSI groups (48.9% and 60.6%) were higher (P<0.05) than those in the parthenogenetic and sham groups (13.5% and 28.0%). Therefore, we demonstrated that porcine oocytes injected with xenogeneic sperm have in vitro developmental ability to the blastocyst stage.