Mimicking the temperature gradient between the sow's oviduct and uterus improves in vitro embryo culture output

This work was designed to determine temperature conditions within the reproductive tract of the female pig and study their impact on ARTs. Temperatures were recorded using a laparo-endoscopic single-site surgery assisted approach and a miniaturized probe. Sows and gilts were used to address natural cycle and ovarian stimulation treatments, respectively. According to in vivo values, IVF was performed at three temperature conditions (37.0°C, 38.5°C and 39.5°C) and presumptive zygotes were cultured in these conditions for 20 h, while further embryo culture (EC) (21-168 h post-insemination) was maintained at 38.5°C. After 20 h, different fertility parameters were assessed. During EC, cleavage and blastocyst stages were evaluated. Sperm membrane fluidity at the experimental temperatures was studied by using differential scanning calorimetry and fluorescence recovery after photobleaching techniques. An increasing temperature gradient of 1.5°C was found between the oviduct and uterus of sows (P < 0.05) and when this gradient was transferred to pig in vitro culture, the number of poly-nuclear zygotes after IVF was reduced and the percentage of blastocysts was increased. Moreover, the temperature transition phase for the boar sperm membrane (37.0°C) coincided with the temperature registered in the sow oviduct, and sperm membranes were more fluid at 37.0°C compared with those of sperm incubated at higher temperatures (38.5°C and 39.5°C). These data suggest that there may be an impact of physiological temperature gradients on human embryo development.

Reproductive fluids, used for the in vitro production of pig embryos, result in healthy offspring and avoid aberrant placental expression of PEG3 and LUM

Background

In vitro embryo production (IVP) and embryo transfer (ET) are two very common assisted reproductive technologies (ART) in human and cattle. However, in pig, the combination of either procedures, or even their use separately, is still considered suboptimal due to the low efficiency of IVP plus the difficulty of performing ET in the long and contorted uterus of the sow. In addition, the potential impact of these two ART on the health of the offspring is unknown. We investigated here if the use of a modified IVP system, with natural reproductive fluids (RF) as supplements to the culture media, combined with a minimally invasive surgery to perform ET, affects the output of the own IVP system as well as the reproductive performance of the mother and placental molecular traits.

Results

The blastocyst rates obtained by both in vitro systems, conventional (C-IVP) and modified (RF-IVP), were similar. Pregnancy and farrowing rates were also similar. However, when compared to in vivo control (artificial insemination, AI), litter sizes of both IVP groups were lower, while placental efficiency was higher in AI than in RF-IVP. Gene expression studies revealed aberrant expression levels for PEG3 and LUM in placental tissue for C-IVP group when compared to AI, but not for RF-IVP group.

Conclusions

The use of reproductive fluids as additives for the culture media in pig IVP does not improve reproductive performance of recipient mothers but could mitigate the impact of artificial procedures in the offspring.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-020-00544-0.

Mimicking physiological O2 tension in the female reproductive tract improves assisted reproduction outcomes in pig

STUDY QUESTION

Is O2 tension in the pig oviduct and uterus affected by the estrous cycle stage and the animal's age, and can the outcome of in vitro embryo development be improved by mimicking these physiological values?

SUMMARY ANSWER

O2 tension within the pig reproductive organs is affected by the animal's age, and values close to those measured in vivo have a positive impact on embryo development and quality when used during IVF and embryo culture (EC).

WHAT IS KNOWN ALREADY

To obtain a healthy embryo in vitro, it is necessary to adopt a culture microenvironment that approximates physiological conditions. Despite advances in surgical procedures and sensitive probes that allow accurate assessment of in vivo O2 tension, few such studies have been conducted recently in mammals. In addition, no reference values of physiological O2 tension in the reproductive tract exist for large animal models such as pig, and the effect of O2 tension on ART outcomes is unknown.

STUDY DESIGN, SIZE, DURATION

This study was conducted in pigs. We measured oviductal and uterine O2 tension (n = 29 and 13, respectively) and then examined how the use of the physiological values in pig IVF and EC affected pig ART output (n = 1447 oocytes).

PARTICIPANTS/MATERIALS, SETTING, METHODS

The oviductal and uterine O2 tension at the different stages of the estrous cycle was monitored using a laparo-endoscopic single-site surgery (LESS) assisted approach along with a flexible and thin miniaturized luminescent probe. Two groups of pigs, Large-white × Landrace breed, were used: for the first group, 16 pre-pubertal gilts (5 months old and 95 kg) were induced to ovulate with equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG); in the second group 13 mature sows (24-48 months and 185 kg) were used. IVF and EC were performed at two different O2 tensions: Atmospheric O2 (20%) and the mean in vivo value measured (7%). At 18-20 h post-insemination (hpi), a small sample of presumptive zygotes were fixed, stained and examined under epifluorescence microscopy to assess the fertilization rates. At 48 hpi, cleavage was evaluated under the stereomicroscope. Finally, at 180 hpi, development to the blastocyst stage was quantified, blastocyst morphology was assessed, and embryos were fixed and stained to count the mean cell number per blastocyst.

MAIN RESULTS AND THE ROLE OF CHANCE

The mean O2 content within the pig oviduct and uterus was always lower than in ambient air. The average O2 percentage was higher in gilts (10.0%) than in sows (7.6%) (P < 0.0001). The cleavage rate of porcine in vitro fertilized embryos maintained under 7% O2 during IVF and EC was significantly higher (60.0 ± 2.3) compared with those cultured under 20% O2 (32.0 ± 2.2) (P < 0.05). An increase in the number of cells in embryos cultured under the low O2 concentration (88.9 ± 5.9) was observed compared to those cultured under 20% O2 (59.0 ± 5.0) (P < 0.05).

LARGE SCALE DATA

None.

LIMITATIONS, REASONS FOR CAUTION

Although minimally invasive surgery was used the effect of anesthesia and manipulations on O2 tension within the organs are unknown.

WIDER IMPLICATIONS OF THE FINDINGS

Using physiological oxygen concentrations in IVF/EC could improve ART outcomes.

STUDY FUNDING AND COMPETING INTEREST(S)

This study was funded by Spanish Ministry of Economy and Competitiveness (MINECO) and European Regional Development Fund (FEDER). Grants AGL2012-40180-C03-01 and AGL2015-66341-R. The authors declare no conflict of interest.

152 SPECIES-SPECIFIC DIFFERENCES IN THE METHYLATION REPROGRAMMING DURING EARLY PRE-IMPLANTATION DEVELOPMENT

Studies in mouse and human have shown extensive DNA methylation reprogramming in pre-implantation development followed by remethylation from implantation. However, the extent to which such reprogramming is conserved in mammals and the timing of demethylation and remethylation are unknown. As part of a major objective to characterise methylation dynamics in the bovine and porcine species from the oocyte to the blastocyst stage, we aimed here to compare the distribution of methylation at single-base resolution in both species at Day 7.5 of development. The DNA methylation profiles were obtained from individual blastocysts at Day 7.5 [pig: 3 in vivo, 3 in vitro; cow: 3 in vivo, 3 in vitro, 3 inner cell mass (ICM) and 3 trophoectoderm (TE) dissected from in vitro blastocysts] using the post-bisulphite adaptor tagging method and Illumina sequencing. For oocytes, data (GEO: GSE63330) from Schroeder et al. 2015 were analysed. Raw sequences were mapped, methylation calls made using Bismark and data analysis and visualisation was done within the SeqMonk platform. Gene expression profiles from individual blastocysts (3 pig, 3 cow) were obtained by RNA-seq. Annotated mRNA features were quantitated in SeqMonk and these were fed into DESeq2 for differential expression analysis (P < 0.05) as previously reported (Love et al. 2014 Genome Biol. 15, 550). Global methylation levels in whole blastocysts differed substantially between porcine and bovine embryos (in vivo: 12.33 ± 3.6 v. 28.33 ± 3.5%; in vitro: 15.02 ± 3.3 v. 24.41 ± 4.1%). In addition, the distribution of methylation differed: the pattern of cytosine methylated seemed random in the porcine genome, but was highly structured in the bovine genome, with methylation predominantly over gene bodies, resembling the profile previously reported in oocytes (Schroeder et al. 2015 PLoS Genet. 11, e1005442). Regarding correlation analysis, gene expression versus methylation were plotted. It suggested that gene body methylation reflected gene expression pattern in oocytes as well as in bovine blastocysts. Pair-wise comparison of isolated ICM and TE was filtered to require 5% change, and replicate set statistics were applied. This revealed very similar total and regional methylation levels in the 2 compartments, indicating that remethylation does not initiate preferentially in one compartment in bovine pre-implantation embryos. This confirms, from a viewpoint of the genome-wide DNA methylation, what has been observed in mouse for specific genes: the trophoblast-specific DNA methylation occurs after the segregation of the TE and ICM (Nakanishi et al. 2012 Epigenetics 7, 173–183). Our study is the first to provide whole genome methylation profiles from single blastocysts of economically important livestock species. Our data demonstrate that methylation reprogramming in early pre-implantation development is species specific. Knowledge of these specific patterns may have high importance when decisions are taken regarding the use of assisted reproductive technologies, cloning, or generation of transgenic animals. This work was funded by AGL2015–66341-R (MINECO-FEDER), PRX14/00348 (MECD), 19595/EE/14 (F. Séneca).

299 EFFECT OF ESTRADIOL-17β AND FOLLICLE STIMULATING HORMONE ON THE IN VITRO MATURATION OF PORCINE OOCYTES DERIVED FROM SMALL FOLLICLES

In porcine cumulus-oocyte complexes (COC) from middle follicles (MF: 3–6 mm in diameter), FSH is known to induce the resumption of meiosis and accompanied by transactivate of the EGF receptor and activation of MAPK3/1 in the cumulus cells. The aim of the current study was to examine the effect of oestradiol-17β (E2: 0.1 μg mL–1) or FSH on in vitro maturation (IVM) of porcine oocytes derived from small follicles (SF: 1–2 mm in diameter). The COC were aspirated from MF of porcine ovaries obtained at slaughterhouse and cultured for IVM in mPOM (with 1 mM dibutyryl cAMP, 10 IU mL–1 of eCG, and 10 IU mL–1 of hCG for 20 h and then without those for 24 h in an atmosphere of 5% CO2 in air at 39°C) after washing 3 times. The COC from SF, which were aspirated at the same time with COC from MF, were precultured in the absence or presence of E2 or E2 plus FSH for 6 h before IVM culture. After the culture, oocytes were denuded from cumulus cells with 0.1% (vol/vol) hyaluronidase and the meiotic stage was observed. Relative transcript abundance of FSH and EGF receptors of CC was also examined by real-time RT–PCR just after preincubation for 6 h. Statistical analysis of data from 3 to 5 replicates was analysed by ANOVA and Tukey's multiple comparison tests. Maturation rate of oocytes from SF (40.6 ± 3.1%) was significantly lower than that of oocytes from MF controls (78.8 ± 2.8%, P < 0.01). Preincubation in the presence of E2 alone and E2 plus 0.005 IU of FSH significantly increases the maturation rate of oocytes from SF (56.8 ± 1.5 and 55.7 ± 3.1%, respectively, P < 0.01), although the rate was still lower than MF controls. However, in the presence of E2 plus a higher concentration of FSH (0.05 and 0.5 IU), oocyte maturation rate was similar (36.3 ± 2.4 and 33.7 ± 1.9%, respectively) to SF controls and lower than those of E2 alone and E2 plus 0.005 IU of FSH groups. Relative transcript abundance of FSH receptor of CC increased (P < 0.01) during preincubation in the presence of E2, but decreased in the presence of 0.05 IU of FSH. There were no significant differences in the transcript abundance of EGF receptors among treatments during preincubation (P = 0.09). In conclusion, preincubation of COC from SF in the presence of E2 alone and E2 plus 0.005 IU of FSH improves the maturation rate of the oocytes, whereas the presence of FSH more than 0.05 IU mL–1 concealed the positive effect. These effects may be yielded by change in the relative transcript abundance of FSH receptor of COC through the treatments.

227 CALRETICULIN, A 60-kDa PROTEIN, PREVENTS POLYSPERMY IN ZONA PELLUCIDA-FREE PIG OCYTES

After gamete membrane fusion or artificial oocyte activation, cortical granules undergo exocytosis and the released content modifies the zona pellucida (ZP), preventing polyspermy. Calreticulin (CRT), a calcium-binding highly conserved protein of 60 kDa, is contained in cortical granules from hamster eggs (Muñoz-Gotera et al. 2001 Mol. Reprod. Dev. 60), and we recently showed it is exocytosed from chemically activated ZP-free pig oocytes (Romar et al. 2012 Reprod. Fertil. Dev. 24). When pig ZP-enclosed oocytes were incubated with CRT, monospermy was not improved (Romar et al. 2011, Maternal communication with gametes and embryo, p. 72), suggesting that the likely role of CRT in preventing polyspermy might be carried out at the oolemma level. Our objective was to evaluate whether CRT prevents polyspermy in pig ZP-free oocytes by treating the cells with this protein before being inseminated. In vitro-matured cumulus–oocyte complexes (44 h, NCSU-37 medium) were decumulated and ZP was digested with Tyrode’s acid. The ZP-free oocytes were incubated for 30 min in TALP medium supplemented with 0, 100, 1000, and 5000 pg of CRT (ab91577, Abcam, Cambridge, MA, USA) per oocyte. After washing, ZP-free oocytes were inseminated (25 000 sperm mL–1) and gametes were co-cultured for 18 h. Putative zygotes were fixed and stained with Hoechst 33342 to analyse the fertilization results. Four replicates with 30 to 35 oocytes per group were done, and results were analysed by one-way ANOVA. A P-value ≤0.05 was taken to denote statistical significance. Incubation with CRT did not affect penetration rates that were similar among groups (77.12 ± 3.88 and 72.73 ± 4.07, respectively, for the 0- and 5000-pg CRT groups). However, the mean number of sperm per penetrated oocyte decreased from 3.01 ± 0.28 (0-pg group) to 2.07 ± 0.16 (5000-pg group), and monospermy rate increased from 30.77 ± 4.87 (0-pg group) to 52.27 ± 5.36 (5000-pg group; P ≤ 0.05). Incubation with CRT did not affect the number of sperm attached to oolemma, which was similar among all groups (11.45 ± 1.16 v. 10.75 ± 1.17, respectively, for 0 and 5000 pg of CRT). These preliminary data suggest that CRT, a protein exocytosed after oocyte activation, participates in the membrane block to polyspermy in pigs. Future studies to describe the exact mechanism of action of this chaperone protein are necessary. Supported by MEC and FEDER (AGL2009-12512-C02-01).

183 CALRETICULIN, A 60-kDa PROTEIN, IS EXOCYTOSED AFTER CHEMICAL ACTIVATION OF ZONA PELLUCIDA-FREE PIG OOCYTES

Following gamete membrane fusion or artificial oocyte activation, cortical granules undergo exocytosis and the released content modifies the zona pellucida (ZP), preventing polyspermy. The specific cortical granule-derived proteins responsible for these post-fertilization events are not fully characterized. Calreticulin, a highly conserved ubiquitous protein of 60 kDa, was exocytosed from activated hamster eggs (Muñoz-Gotera et al. 2001 Mol. Reprod. Dev. 60, 405–413). Preliminary results from our laboratory have shown that calreticulin is located in the cortical area of pig oocytes (data not shown). This study was designed to test whether calreticulin is exocytosed after oocyte activation with calcium ionophore. Immature cumulus–oocyte complexes from Landrace × Large White gilts were in vitro matured for 44 h in an NCSU-37 medium. After maturation, the oocytes were stripped of cumulus cells and their ZP were removed with 0.5% pronase in Ca2+-free PBS. After washing, the ZP-free oocytes were incubated with calcium ionophore A23187 (6.5 μM) for 2min, transferred to a 100-μL droplet of exudate medium (Romar et al. 2011 Reprod. Fertil. Dev. 23, 221 abst) and incubated at 38.5°C, 5% CO2 and saturated humidity for 30 min. After incubation, the medium containing the oocyte exudate (n = 1000) was carefully aspirated and run on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS–PAGE). The gel was then electro transferred onto a polyvinylidene fluoride (PVDF) membrane, incubated with an anti-calreticulin rabbit polyclonal antibody (1:1000) and finally conjugated to horseradish peroxidase (1:20 000) for 1 h with a monoclonal anti-rabbit IgG. Membrane visualization was accomplished using the ECL plus method and Typhoon 9410. A control group was performed with exudate collected from non-activated ZP-free oocytes. To verify cortical reaction and calreticulin exocytosis, an aliquot of activated ZP-free oocytes (n = 18) were fixed (3.7% paraformaldehyde for 30 min), permeabilized (0.1% Triton X-100 for 10 min), incubated with anti-calreticulin antibody (1:10 for 1 h) and conjugated to tetramethyl rhodamine isothiocyanate (1:400 for 1 h) with an anti-rabbit IgG. Finally, samples were incubated with peanut agglutinin conjugated to fluorescein isothiocyanate (10 μg mL–1 for 30 min), mounted and examined under a confocal microscope. No statistical analysis was made because the observations were purely qualitative. A Western blot analysis showed an immunoreactive band of ∼60 kDa, consistent with the expected size of calreticulin, in the lane containing the exudate from activated oocytes. No band was observed in the lane with the exudate collected from non-activated oocytes. Observation under confocal microscopy showed no PNA or anti-calreticulin fluorescence in the cortical region, indicating that the activated pig oocytes displayed full cortical reaction and calreticulin exocytosis during incubation time. These results show that calreticulin protein is exocytosed after the chemical activation of ZP-free pig oocytes as well as the disappearance of the cortical granule monolayer. The possible role of calreticulin on preventing polyspermy should be further investigated. Supported by MEC and FEDER (AGL2009-12512-C02-01) and CONACYT (0105961/I0110/194/09).

182 CHEMICAL ACTIVATION OF ZONA PELLUCIDA-FREE OOCYTES PROVOKES FULL CORTICAL REACTION: AN APPROACH TO STUDY CORTICAL GRANULE-DERIVED PROTEINS IN PIGS

The cortical reaction is a mechanism that prevents polyspermy by cortical granule content being released into the periviteline space, modifying the zona pellucida (ZP). Knowledge about specific cortical granule-derived proteins has progressed slowly because these organelles contain only picogram quantities of proteins. An efficient method for collecting cortical granule content would help in its study; chemical activation of ZP-free oocytes has been successfully used in the murine model (Muñoz-Gotera et al. 2001 Mol. Reprod. Dev. 60, 405–413). Calcium ionophore A23187 is an effective chemical stimulator for provoking the cortical reaction in ZP-intact pig oocytes. However, the commonly used protocol (50 μM for 5min) cannot be employed with ZP-free oocytes because the oolemma is damaged, oocyte lysed and medium contaminated with ooplasm content, which is necessary to reduce the time and ionophore concentration (Romar et al. 2011 Reprod. Fertil. Dev. 23, 221 abst). The objective of this study was to evaluate the efficiency of this activation protocol for provoking the cortical reaction in ZP-free oocytes by assessment with confocal and electron microscopy. Immature cumulus–oocyte complexes from Landrace × Large White gilts were in vitro matured for 44 h in an NCSU-37 medium. After maturation, the oocytes were stripped of cumulus cells and their ZP were removed with pronase. Then, the ZP-free oocytes were incubated with calcium ionophore A23187 (6.5 μM for 2min), transferred to an exudate medium and incubated at 38.5°C, 5% CO2 and saturated humidity for 30 min. Control ZP-free oocytes were incubated without being activated. After incubation, ionophore-treated (n = 10) and control oocytes (n = 18) were used to assess the presence of a cortical granule monolayer. An aliquot was fixed, permeabilized (0.1% Triton), incubated with peanut agglutinin lectin conjugated to fluorescein isothiocyanate (10 μg mL–1 for 30 min) and examined under a confocal microscope. Presence or absence of a cortical granule monolayer at the equator level was recorded. Another aliquot was fixed and processed for electron microscopy observation. The cortical granules in the whole oocytes were counted and results are presented as the mean ± standard error of the mean. No cell lysis was observed in control or activated ZP-free oocytes after treatment and incubation time. The confocal study showed that the activation protocol provokes a full cortical reaction in 100% of A23187-treated oocytes, given that no peanut agglutinin labeling was observed in the cortical area. Presence of a cortical granule monolayer under the oolemma was observed in 100% of control oocytes. Cortical granule release was confirmed by electron microscopy. Control oocytes had 5.90 ± 1.78 cortical granules per 5 μm of oolemma, whereas activated oocytes exhibited a significant reduction (P < 0.05) of up to 0.71 ± 0.20. In conclusion, the presented activation protocol by using ZP-free oocytes is a valid method for provoking a complete cortical reaction and could be employed in the future as an efficient method to collect cortical granule-derived proteins in pig oocytes. Supported by CONACYT (0105961/I0110/194/09), MEC and FEDER (AGL2009-12512-C02-01).

Expression of maternal transcripts during bovine oocyte in vitro maturation is affected by donor age

The primary objective of this study was to compare expression of maternal transcripts in bovine oocyte populations with differential developmental competence: oocytes from prepubertal and pubertal animals; and oocytes from small (3-4 mm) and large (6-10 mm) follicles from pubertal animals. All transcripts were examined in oocytes prior to and after in vitro maturation (IVM). Genes were selected based on their known maternal effect in mouse (ZAR1, STELLA, HSF1, MATER/NLRP5 and its paralogue NLRP9), or their identification as markers of oocyte maturation, either involved in redox metabolism (PRDX1, PRDX2) or meiotic progression (AURKA). Total or polyadenylated forms of the transcripts were followed by reverse transcription coupled to real-time PCR. Six polyadenylated transcripts were found significantly reduced after maturation irrespective of donor age or follicle diameter (p<0.05). Within these six polyadenylated transcripts, ZAR1, NLRP9, HSF1, PRDX1 and PRDX2 were significantly reduced in oocytes from prepubertal animals compared to adult animals (p<0.05). A younger age was also associated with lower abundance (total form) of PRDX2/PRDX1 irrespective of maturation. Total HSF1, PRDX1 and polyadenylated NLRP9 showed a tendency (p values from 0.053 to 0.08) for a higher detection in oocytes from small follicles, thus encouraging further investigation of the follicle diameter model. However, at the present time, follicle size did not significantly affect expression of transcripts examined. In conclusion, this study demonstrates differences in the maternal store of RNA and its regulation during IVM which is dependent on donor age.

245 ANALYSIS OF CORTICAL GRANULE EXUDATE OBTAINED BY CHEMICAL OOCYTE ACTIVATION IN PIGS

Cortical granules (CG) are clue organelles in the mammalian oocyte because once released, their content modifies the zona pellucida (ZP) and oolema, thus preventing polyspermy. However, research on putative CG proteins has progressed slowly because of the picogram amount of proteins contained in CG. Isolation and identification of CG contents in porcine oocytes would help to elucidate the molecular mechanism involved in blocking polyspermic fertilization. Our objective was to study the contents of CG from in vitro-matured (IVM) porcine oocytes, and to achieve this objective, CG exudate was collected after its release from chemically activated oocytes. Oocytes were subjected to IVM in porcine oocyte medium supplemented with 50 μM β-mercaptoethanol for 44 h. After the IVM period, the ZP was removed by protease treatment (0.5% pronase in PBS), and the ZP-free oocytes were activated with calcium ionophore A23187 (6.5 μM, 2 min) in a medium consisting of 114.06 mM NaCl, 3.20 mM KCl, 0.50 mM MgCl2·6H2O, 10.00 mM sodium lactate, 0.35 mM NaH2PO4, 5.00 mM glucose, 25.07 mM NaHCO3, and 8.00 mM calcium lactate·5H2O. After activation, oocytes were transferred to fresh medium without calcium ionophore and kept for 30 min to allow release of the CG content. After this time, medium containing the CG exudate was collected, as well as the activated oocytes, and both samples were stored at –80°C until analysis. Samples were thawed and the CG proteins were concentrated by centrifugation in 10-kDa centrifugal devices (Microcon, Millipore, Billerica, MA) following the manufacturer’s instructions. The CG exudates from activated oocytes (n = 300) and activated oocytes (n = 125) were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions. In brief, 4% stacking and 12% separating gel was used and run using 25 mM Tris–0.2 M glycine buffer, pH 8.6, containing 0.1% SDS for 1.5 h at 150 V and room temperature. After electrophoresis, the gel was silver stained. Thirteen strong bands were identified in the CG exudate lane, with an approximate molecular mass from approximately 45 to 105 kDa. However, the lane for activated oocytes showed faint protein bands. The presence of well-defined bands in the CG exudate lane might correspond to different CG-derived proteins. These preliminary results show a new approach for studying CG content. Further proteomic analysis of the bands will help to describe specific proteins contained in these organelles, shedding light on the role of the cortical reaction in pigs. Supported by MEC and FEDER (AGL2009-12512-C02-01) and Okayama Universit R. R. was granted funding by JSPS (Ref. S-09210).

263 REGULATION OF SEVERAL TRANSCRIPTS DURING IN VITRO MATURATION IN PORCINE OOCYTES COLLECTED FROM DIFFERENT SIZE FOLLICLES

Oocyte-specific transcripts play important roles in oocyte maturation, fertilization, and early embryonic development. Currently, oocytes from medium-size follicles have been used for different assisted reproductive techniques after in vitro maturation (IVM). The aim of this study was to compare the mRNA expression level in porcine oocytes collected from medium (3–6 mm) and small (<2 mm) size follicles. Genes were selected based on their described maternal effect (NALP9, HSF1), their identification as markers of oocyte maturation (AURK-A, AURK-B, MOS, and C-mos), their involvement in fertilization (ZP3, ZP4), and anti-apoptotic effect (Bcl-2). All transcripts were studied in oocytes just after collection [germinal vesicle (GV) stage] and after in vitro maturation (IVM; metaphase II stage). To ensure nuclear stage of immature oocytes, oocytes were mechanically denuded just after collection, centrifuged (10 000 rpm, 5 min, RT), and observed under the microscope (60×). Those oocytes with clear nucleolus and evident nuclear membrane were selected and stored (n = 10) until study. For metaphase II oocytes, only those exhibiting the extrusion of first polar body after IVM (n = 10) were selected. Total RNA was extracted from the pool of 10 immature and mature oocytes. One picogram of luciferase mRNA per oocyte was added as an exogenous standard. Total RNA was extracted from oocytes and cDNA was obtained and used as a template for quantitative PCR to analyse the level of different transcripts. The whole process was replicated 4 times. Data were normalized to the luciferase RNA and analysed by one-way ANOVA with maturational stage (GV or metaphase II) and follicle size (small or medium) as fixed factors. Results show that all transcripts were significantly decreased during IVM (P < 0.05). Therefore, after IVM, NALP9, AURK-A, MOS, C-mos, ZP3, ZP4, and Bcl-2 transcripts were significantly reduced in matured oocytes compared with immature ones irrespective of follicle diameter. Transcripts of AURKAB and HSF1 decreased after IVM in oocytes from medium follicles or small follicles, respectively. A significant effect of follicular size was only detected in MOS transcripts in GV-stage oocytes because those collected from middle follicles had a higher amount than the ones from small follicles (Table 1). These results suggest that the variations in the maternal store of RNA during IVM are not related with follicle diameter for the studied genes. Further investigations are necessary to determinate the developmental competence of oocytes that came from different types of follicles (small and medium follicles). Table 1.Variation of transcripts during in vitro maturation in porcine oocytes collected from small and medium follicles This study was supported by Okayama University. R. Romar was given a grant by JSPS (Ref. S-09210).

204 AMINO-REACTIVE CROSSLINKER BIS(SULFOSUCCINIMIDYL)SUBERATE INDUCES ZONA PELLUCIDA HARDENING AND REDUCES PENETRATION IN PIG IN VITRO FERTILIZATION

Zona pellucida (ZP) hardening is considered to be the final step in the prevention of polyspermy during fertilization in mammals. However, unfertilized pig oviductal oocytes show a resistance of hours or days to pronase digestion (Broermann et al. 1989 J. Anim. Sci. 67, 1324–1329). We previously demonstrated that the amino-reactive crosslinker DSP is effective in inducing ZP hardening and improves the monospermy levels at pig IVF (Coy et al. 2007, Reprod. Dom. Anim., in press). In this study, a different chemical crosslinker, BS3 [bis(sulfosuccinimidyl) suberate], which also forms stable amide bonds among proteins, was used to evaluate its effect on ZP digestion time, penetration, male pronuclear formation and monospermy percentages, and the mean number of sperm per oocyte. In experiment 1, porcine in vitro-matured oocytes (n = 300) were incubated for 30 min at 0, 0.06, 0.30, or 0.60 mg mL–1 of BS3 in TALP medium and assessed for ZP digestion time in 0.5% pronase solution. The results (analyzed by ANOVA in all the experiments) showed a significant (P ≤ 0.01) dose-dependent increase in ZP hardening, from 69.0 s in the control to 426.3, 2028.3, and 2979.2 s, respectively, for the different BS3 concentrations. In experiment 2, oocytes (n = 473) were fertilized in vitro after no treatment or treatment with BS3 at 0.06, 0.30, and 0.60 mg mL–1. Fresh ejaculated spermatozoa were selected by Percoll� gradient 45:90. Oocytes were inseminated with 105 sperm mL–1, which resulted in high penetration and polyspermy percentages in the control group (83.1 and 89.9%, respectively). However, for the BS3-treated oocytes, significant differences compared with the control group (P ≤ 0.001) were observed in all 3 groups, showing penetration percentages of 22.2, 18.1, and 21.5%, respectively, and monospermy percentages of 100, 88.2, and 95.0%, respectively. The mean numbers of sperm per oocyte were 1.0, 1.1, and 1.05 for the BS3 groups, which were significantly different from 5.0 for the control group. In conclusion, BS3 can be used to induce ZP hardening in the pig and regulate polyspermy in IVF systems, although additional experiments are necessary to find the optimal concentration to improve the penetration percentages with high levels of monospermy. Granted by MEC and FEDER (AGL2006-03495).

222 SPECIES SPECIFICITY OF PORCINE SPERM MOTILITY REDUCTION BY A HIGH MOLECULAR WEIGHT FRACTION OF OVIDUCTAL FLUID

The significance of sperm motility with respect to fertilization is widely recognized and used as a criterion to assess the quality of ejaculates. Observations of sperm behavior in the oviductal isthmus of several species have shown that their motility is suppressed in this physiological environment because the spermatozoa bind to the oviductal epithelial cells, forming a sperm reservoir prior to ovulation (Hunter 1981 J. Reprod. Fertil. 63, 109–117; Hunter and Wilmut 1984 Reprod. Nutr. Dev. 24, 597–608). Once the spermatozoa are released from the reservoir, they progress toward the ampullar region to reach the oocyte, and an increase in motility at this point could, potentially, be crucial. It has been demonstrated that a soluble fraction of oviductal epithelial cell apical plasma membrane proteins (sAPM) suppresses sperm motility and enhances sperm survival (Holt et al. 2005 Reprod. Fertil. Dev. 17, 683–692; Satake et al. 2006 J. Exp. Biol. 209, 1560–1572). However, few studies to date have investigated the influence of oviductal fluid (OF), the natural medium into which spermatozoa are released from the reservoir, on sperm motility. Consequently, this study aimed to determine the effects of different soluble fractions of OF on sperm motility and the species specificity of such effects. OF from pigs and cows was collected and selectively filtered to obtain two different fractions with molecular weights higher or lower than 100 kD. Diluted semen samples from 14 different boars were exposed to bicarbonate/CO2 (to stimulate maximum motility) in the presence or absence of OF fractions. Sperm trajectories were measured using a Hobson Sperm Tracker (Hobson Tracker, Ltd., Sheffield, UK) and analyzed by PATN analysis as described previously to identify subpopulations of high and low motility spermatozoa (Abaigar et al. 1999 Biol. Reprod. 60, 32–41; Satake et al. 2006). The results showed that neither of the bovine OF fractions affected the proportions of the fast linear boar sperm subpopulation in the samples, which was similar to that of the control. However, when the high molecular weight fraction of porcine OF was used, a significant suppression of the fast linear sperm subpopulation was observed (P ≤ 0.05). These data support the hypothesis that species-specific, high molecular weight components in OF are involved in the suppression of sperm motility. Further studies are required to confirm the significance of this finding, although it may not be unreasonable to speculate that the OF, in addition to other sperm selection mechanisms, acts to protect oocytes against fertilization by poor quality spermatozoa (Okada et al. 1986 J. Submicrosc. Cytol. 18, 233–247). In fact, similar results demonstrating that oviductal fluid decreases sperm motility have been obtained in cow (Grippo et al. 1995 J. Reprod. Fertil. 105, 57–64) and rabbit (Overstreet and Cooper 1979 J. Reprod. Fertil. 55, 53–59). This work was supported by MEC and FEDER (PR2006-0506 and AGL2006-03495).

233 STUDY OF CORTICAL GRANULE CONTENT IN IN VITRO-MATURED PORCINE OOCYTES BY MEANS OF PNA LECTIN PRECIPITATION

Cortical granules (CG) are clue organelles in the oocyte since their content is released under oocyte activation (i.e. fertilization) modifying the zona pellucida and thus blocking polyspermy. Once released, CG are not renewed. Research on cortical reaction and putative CG enzymes has progressed slowly because mammalian eggs contain only picogram quantities of CG-derived proteins (Moller and Wassarman 1989 Dev. Biol. 132, 103–112; Green 1997 Rev. Reprod. 2, 147–156), so the protein(s) responsible for the physiological changes in ZP after cortical reaction are not well known. The objective of this project was to study porcine CG content in in vitro-matured porcine oocytes by means of lectin precipitation with peanut agglutinin (PNA), since this lectin binds to porcine CG (Yoshida et al. 1993 Mol. Reprod. Dev. 36, 462–468). Immature porcine cumulus–oocytes complexes (COCs) from Landrace � Large White gilts were in vitro-matured for 44 h in NCSU-37 medium. After IVM period, COCs were stripped of cumulus cells, washed in PBS, and quickly washed through purified water. Then oocytes were lysed in a fresh water droplet by gentle pipetting using a narrow-bore glass pipette. Once lysed, zonae pellucidae were removed and oocyte cytoplasmic content (lysate) collected. Lysate from 1000 IVM-oocytes was incubated under continuous shaking (2 h, room temperature) with 100 µL PNA-agarose (Sigma, St. Louis, MO, USA) so that proteins bound to PNA could be precipitated by centrifugation. After lectin precipitation, proteins were detached from PNA-agarose beads by boiling in reducing sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) loading buffer (5 min, 100�C) (Laemmli 1970 Nature 227, 689). Samples were then centrifuged (5 min, 7000g), the pellet containing PNA-agarose beads was discarded, and the supernatant containing the proteins was collected and further separated by SDS-PAGE. The silver staining of electrophoresis gels revealed eleven bands from 37 to 180 kDa, so a second gel was electrotransferred to a polyvinylidene fluoride (PVDF) membrane (100V, 1 h) and incubated with PNA-horseradish peroxidase (PNA-HRP, 10 µg mL–1) for 1 h. Visualization was accomplished using the enhanced chemiluminiscence (ECL plus) method and Typhoon 9410 following the manufacturer's instructions (Amersham Biosciences, Freiburg, Germany); only four bands of approximately 57 kDa, 60 kDa, 70 kDa, and 80 kDa were observed. These bands will be cut and processed for proteomic analysis for further studies. Preliminary results show that porcine CG-derived proteins can be studied by PNA lectin precipitation. These results could be employed in the future to develop specific antibodies against porcine CG.

198 FUNCTIONAL EVIDENCE FOR THE EXISTENCE OF AN OVIDUCTAL FACTOR THAT INDUCES ZONA PELLUCIDA HARDENING AND REGULATES POLYSPERMY IN THE PIG AND COW

Many differences between in vivo and in vitro fertilization (IVF) efficiency in mammals are related to the differences between IVF media and oviductal fluid. One of the best known examples is the frequency of polyspermy observed under in vitro conditions in cattle (Roh S et al. 2002 J. Vet. Med. Sci. 64, 667–671) and, in particular, in pigs (Coy P and Romar R 2002 Reprod. Fertil. Dev. 14, 275–286). Zona pellucida (ZP) resistance to pronase digestion (ZP hardening) has been considered as a postfertilization event contributing to the block of polyspermy in mammals (Green D 1997 Rev. Reprod. 2, 147–156). However, pig and cow unfertilized ovulated oocytes show a ZP hardening of hours or days (Katska L et al. 1999 Reprod. Dom. Anim. 34, 255–259; Kolbe T and Holtz W 2005 Theriogenology 63, 1695–1705) compared with the minutes or seconds observed in the in vitro-matured oocytes, even after fertilization (Coy P et al. 2002 Reproduction 124, 279–288; Coy P et al. 2005 Reproduction 129, 19–26). Consequently, we propose the existence of an oviductal factor that induces ZP hardening before any contact of the oocyte with the sperm, thus regulating polyspermy. Porcine and bovine oviductal fluid was obtained by aspiration of oviducts collected at the slaughterhouse and stored frozen. In vitro-matured porcine and bovine oocytes were incubated for 30 min in the oviductal fluid, washed thoroughly in fresh medium, and either assessed for ZP digestion time or in vitro fertilized. The results, analyzed by ANOVA, showed a very strong ZP hardening in oviductal-treated oocytes (2866.83 � 94.4 s in the pig and 4301.1 � 441.7 s in the cow) compared with control oocytes (63.5 � 2.9 s in the pig and 124.2 � 5.9 s in the cow). Moreover, the percentage of monospermy for the oviductal-treated oocytes was significantly higher in both species (50.0 � 10.0% in the pig and 91.7 � 3.0% in the cow) compared with the control groups (5.56 � 3.8% in the pig and 80.8 � 3.5% in the cow). Percentage penetration did not change in porcine oocytes but decreased in bovine oocytes (58.1 � 3.3 v. 38.4 � 3.3, P ≤ 0.001), whereas the mean number of sperm per oocyte decreased for the porcine-treated oocytes (2.7 � 0.2 v. 8.2 � 0.4, P ≤ 0.001) and did not change for the bovine oocytes. These results support the hypothesis that an oviductal factor induces ZP hardening, contributing to the control of polyspermy in the pig and cow, and that it could be used to improve the output of IVF. Supported by MEC and FEDER (AGL2006-03495).

310 DETERMINATION OF THE PORCINE OVIDUCTAL GLYCOSIDASES DURING THE ESTROUS CYCLE

Carbohydrates play a key role in different reproductive events, such as the sperm–oviductal cell interaction and sperm–oocyte recognition. For example, β-d-galactose and α-d-mannose residues contained in the zona pellucida have been identified as sperm receptors in porcine oocytes (Song et al. 1999 J. Mamm. Ova Res. 16). The glycosidases, enzymes that remove carbohydrates, could play an important role in the reproductive tract, modulating decisive physiological events mediated by carbohydrates. However, the enzymatic activity level of these enzymes or their fluctuations throughout the estrous cycle in the porcine oviductal fluid (POF) has not been studied. The objective of this work was to compare the enzymatic activity level of 7 glycosidases in the POF at different stages of the estrous cycle. Oviducts were collected from the abattoir and classified according to the macroscopic aspect of the genital tract (Grippo et al. 1995 J. Reprod. Fertil. 105, 57–64) as early follicular please (presence of growing follicles), late follicular phase (presence of several grown follicles), early luteal phase (ovaries showing corpora hemorrhagica or recent corpora lutea), and late luteal phase (old corpora lutea or corpora albicans). After classification, oviducts were dissected and oviductal fluid samples were collected by aspiration with an automatic pipette while applying manual pressure from the isthmus toward the ampulla. Samples (6 per group) were centrifuged (7000g, 10 min) and the supernatant was stored at −20°C until assay. Total activity levels were measured fluorimetrically at 450 nm with the corresponding substrate conjugated to 4-methylumbelliferyl for each enzyme (Abascal et al. 1998 Biochem. J. 333, 201–207) using a FLUOstar Galaxy fluorometer (BMG Lab Technologies, Offenburg, Germany). Enzymatic assays were done in duplicate for 4 h at 37°C, and the reactions were stopped by adding glycine–calcium carbonate buffer. Fluorescence was corrected for tissue and substrate blanks. Fluorescence results of each enzyme and oviduct phase were analyzed using a one-way ANOVA with estrous cycle phase being the main factor. Results (mean counts of fluorescence, see Table 1) showed that changes of enzymatic activity during the estrous cycle and activity of some enzymes were modified during or after ovulation, suggesting a role of some glycosidases in the fertilization process. Preliminary assays for neuraminidase were negative in all samples. Future studies are necessary to identify the biological role played by the glycosidases present in the POF. Table 1.Changes in porcine oviductal glycosidases during the estrous cycle Supported by Fundacion Seneca (03018/PI/05) and Ministerio de Educacío y Ciencia (Project code 3495).

290 ENZYMATIC ACTIVITY LEVEL OF SOME GLYCOSIDASES IN BOVINE OVIDUCTAL FLUID AT DIFFERENT STAGES OF THE ESTROUS CYCLE

Carbohydrates play a key role in different reproductive events such as the sperm–oviductal cell interaction and sperm–oocyte recognition. In this way, α-d-mannosyl (Amari et al. 2006 Mol. Reprod. Dev. 59, 221–226) and α-2,3-sialic acid (Velasquez et al. 2006 Mol. Reprod. Dev. in press) residues contained in the zona pellucida have been identified as sperm receptors in bovine oocytes. The glycosidases, enzymes that remove carbohydrates, could play an important role in the reproductive tract, modulating decisive physiological events mediated by carbohydrates. However, the enzymatic activity level of these enzymes or its fluctuations throughout the estrous cycle in the bovine oviductal fluid (BOF) has not been studied. The objective of this work was to compare the enzymatic activity level of 7 different glycosidases in the oviductal fluid of cows at different stages of the estrous cycle. Oviducts were collected from the abattoir and classified according to the macroscopic aspect of the genital tract (Grippo et al. 1995 J. Reprod. Fertil. 105, 57–64) as early follicular (presence of growing follicles), late follicular (presence of a dominant follicle), early luteal phase (ovaries showing a corpus hemorrhagicum or a recent corpus luteum), and late luteal phase (old corpus luteum or corpus albicans). Oviductal fluid samples were collected by aspiration with an automatic pipette making simultaneous manual pressure from the isthmus toward the ampulla. Samples (9 per group) were centrifuged (7000g, 10 min) and supernatant was stored at −20°C until assay. Total activity levels were fluorimetrically measured at 450 nm, with the corresponding substrate conjugated to 4-methylumbelliferil for each enzyme (Abascal et al. 1998 Biochem. J. 333, 201–207) using a fluorometer Fluostar Galaxy (BMG LABTECH GmbH, Offenberg, Germany). Enzymatic assays were done in duplicate for 4 h at 37°C, and the reactions were stopped by adding glycine-calcium carbonate buffer. Fluorescences were corrected for tissue and substrate blanks. Fluorescence results of each enzyme and oviduct phase were analyzed using a 1-way ANOVA, with estrous cycle phase being the main factor. Results (mean counts of fluorescence) showed that the level of activity changes during the estrous cycle and the activity of some enzymes increases close to or after ovulation, suggesting a role of some glycosidases in the fertilization process. Preliminary assays for neuraminidase were negative for all samples. Future studies are necessary to identify the biological role played by the glycosidases present in the bovine oviductal fluid. Table 1.Enzymatic activity level of some glycosidases in bovine oviductal fluid at different stages of the estrous cycle This work was supported by Fundación Séneca (03018/PI/05) and MEC (Project code 3495).

Structural, biochemical and functional aspects of sperm-oocyte interactions in pigs

Polyspermic fertilization is still a major issue in porcine IVF systems. New information is available to characterize the zona pellucida (ZP) at different developmental stages by scanning electron microscopy (SEM) and by confocal microscopy to show the distribution of ZP glycoproteins. SEM images indicated no differences between in vivo and in vitro matured oocytes; however a change in the surface structure between immature and matured oocytes, as well as between mature oocytes and preimplantation embryos was obvious. In addition, spermatozoa were more tightly fixed in the ZP of in vivo produced compared to the ZP of in vitro produced embryos. The ZP undergoes biochemical changes during maturation prior to fertilization. The acidity of the ZP increases during maturation as indicated by a shift of 1.3 pl units for ZPB/ZPC and 0.8 pl units for ZPA in 2D gel electrophoresis, which is based on increasing sulfation of the oligosaccharides during maturation. Mass spectrometry in combination with in-gel deglycosylation allowed the mapping of new glycosylation sites. Functionality of the ZP also depends on its maturation status. Induction of the acrosome reaction was delayed when capacitated spermatozoa were exposed to immature oocytes.

Effect of oviductal and cumulus cells on zona pellucida and cortical granules of porcine oocytes fertilized in vitro with epididymal spermatozoa

The objective of this study was to evaluate the effects of porcine oviductal epithelial cell (POEC) monolayers and cumulus cells on the zona pellucida (ZP) and cortical granules (CG) of in vitro matured porcine oocytes. Denuded and cumulus-enclosed oocytes were exposed to POEC before or during in vitro fertilization (IVF). The functional effects of the co-culture system were the tested on the ZP resistance, measured by the time necessary to dissolve the ZP with 0.1% pronase, and the distribution and density of the cortical granules. CG density in the equator and cortex of each oocyte was evaluated by confocal microscopy after staining with fluorescein isothiocyanate-labelled peanut agglutinin (FITC-PNA). Both variables were assessed immediately after an in vitro maturation period (IVM group), 3 and 6h after culture with or without (Control) oviductal cells (Experiment 1) and 3h after insemination with frozen-thawed epididymal spermatozoa in the presence or absence (Control) of oviductal cells (Experiment 2). The time to dissolve the ZP of oocytes from IVM group was 440.4 +/- 61.7 s and no difference was observed among groups in Experiment 1. In contrast, the density of CG was affected; oocytes pre-incubated for 6h had a higher density than those pre-incubated for 3 h (P <0.001). Oocytes fertilized in vitro in the presence of POEC (Experiment 2) had a similar ZP digestion time as control oocytes 3 h after insemination. The presence of POEC during IVF as well as the presence of cumulus cells had no effect on the density and distribution of CG. However, a significant decrease in the density of CG was observed in the fertilized oocytes compared to in vitro matured oocytes (P <0.001). It is concluded that under the conditions employed the oviductal and cumulus cells in the perifertilization period had no effect on ZP hardening and CG density. However, an increase in CG density was observed when oocytes were maintained in culture. In addition, no hardening of ZP was observed after IVF, and denuded and cumulus-enclosed oocytes showed similar cortical reactions after insemination with epididymal spermatozoa regardless of the presence of POEC.

Analysis of in vitro fertilizing capacity to evaluate the freezing procedures of boar semen and to predict the subsequent fertility

A porcine in vitro fertilization (IVF) system and seminal quality parameters of frozen-thawed boar semen were used to assess the effectiveness of two different thawing rates of frozen boar semen, and to address the question of whether differences between fertility of ejaculates could be predicted in a limited field trial. In the first experiment, two thawing procedures were analysed (37 degrees C, 30 s; 50 degrees C, 12 s) and no differences in sperm quality were found. However, when the procedure was 50 degrees C, 12 s the IVF results showed a higher number of sperm per penetrated oocyte and a near 10 points higher rate of pronuclear formation. In the second experiment, the fertility results obtained in the limited field trial show to be efficient enough for application in a commercial use, especially for three of the employed boars (fertility > or = 80%). In this limited study, the conventional seminal parameters are not accurate enough to discriminate good and bad boars in relation to fertility. On the contrary, parameters of in vitro penetrability are more precise to predict subsequent fertilities. As conclusion, the IVF fertilization system seems to be a good tool to evaluate the quality of frozen-thawed boar semen previous to its commercial way, to verify the bank semen storage quality and a good way to assay new sperm freezing procedures, as it is the more precise evaluating method in estimating the potential fertilizing ability.

Effects of oviductal and cumulus cells on in vitro fertilization and embryo development of porcine oocytes fertilized with epididymal spermatozoa

This study was designed to evaluate the effects of adding porcine oviductal epithelial cell (POEC) monolayers before or during the fertilization of denuded or cumulus-enclosed oocytes, in terms of fertilization results and subsequent embryo development. The variables determined were: penetration rate, mean number of spermatozoa per oocyte, male pronucleus formation rate, monospermy rate, cleavage rate after 48 h of fertilization, blastocyst rate, and mean number of nuclei per blastocyst. We used cumulus-free and cumulus-enclosed oocytes preincubated or fertilized in the presence of POEC, once the purity in epithelial cells of these cultures had been assessed. All the experiments involved the use of frozen-thawed epididymal spermatozoa to avoid replicate variability. The POEC cultures prepared showed a high proportion of epithelial cells (over 95%). Preincubation of oocytes with POEC before fertilization showed no effects on the fertilization variables determined. In contrast, during IVF under our experimental conditions, these cells attached to the cumulus cells and their interaction had a significant effect on some of the fertilization variables analyzed. The presence of POEC and cumulus cells during IVF increased oocyte penetrability. Moreover, in the absence of POEC, cumulus cells resulted in a reduced monospermy rate. On subsequent embryo culture, a lower cleavage and blastocyst formation rate were recorded when the oocytes had been preincubated with POEC before IVF.

Effect of sperm preparation method on in vitro fertilization in pigs

This study was designed to determine the effect of different sperm preparation treatments before IVF on the acrosome reaction, oocyte penetration time, early embryo development and timing of female and male pronucleus formation. Pooled sperm-rich fractions were (i) washed in PBS, (ii) left unwashed, or (iii) layered in a Percoll gradient. In Expt 1, the proportion of acrosome-reacted spermatozoa, determined by staining with fluorescein isothyocyanate-labelled peanut agglutinin lectin and propidium iodide, was highest after treatment with Percoll (P < 0.001). In Expt 2, oocytes matured in vitro were co-cultured with spermatozoa for 2, 4 or 6 h. Attached spermatozoa were then removed and the oocytes were cultured in fresh IVF medium for 16 h. Both sperm treatment and co-culture time were found to affect penetrability and monospermy rates (P < 0.001); spermatozoa treated with Percoll showed fastest oocyte penetration and highest penetrability. In Expt 3, matured oocytes were co-incubated with spermatozoa pretreated by the three above mentioned procedures (i, ii, iii) for 2, 6 and 2 h respectively. Putative zygotes were then washed and transferred to medium NCSU-23 until the blastocyst stage. In this experiment, sperm treatment had a significant effect on the cleavage rate (P < 0.001) and rate of blastocyst formation (P < 0.05); the group treated with Percoll showed the highest rate of blastocyst formation. Finally, in Expt 4, timing of female and male pronucleus formation for each sperm treatment was determined 4, 6 and 8 h after insemination. The time of female and male pronucleus formation was affected by the sperm treatment and was faster for the Percoll group (P < 0.05). The findings of the present study indicate that treatment with Percoll yields the best results in this in vitro pig embryo production system.

Effect of in vitrofertilization medium on the acrosome reaction, cortical reaction, zona pellucida hardening and in vitro development in pigs

Physiological events at the time of fertilization of pig oocytes may differ in vitro depending on the in vitro fertilization (IVF) medium. This hypothesis was tested by in vitro maturation of pig oocytes for 44 h in NCSU-37 medium and thereafter fertilization with frozen-thawed ejaculated spermatozoa. Three different IVF media (TCM-199, Tyrode's albumin lactate pyruvate (TALP) and Tris-buffered medium (TBM)) were used. For the acrosome reaction test, spermatozoa were incubated for 0-150 min in the three IVF media, and the proportion of live acrosome-reacted and acrosome-intact cells was determined by fluorescein isothiocyanate-labelled peanut agglutinin (FITC-PNA) and propidium iodide (PI) staining. The cortical granule density of oocytes was evaluated by confocal microscopy, 2.5 and 5.0 h after culture in each medium in the presence or absence of spermatozoa. Zona pellucida resistance to pronase digestion was also determined in the same groups. The percentages of penetration, monospermy, male pronucleus formation, cleavage and blastocyst formation, and the number of cells per blastocyst after culture were determined. The results indicate that the acrosome reaction occurred much faster in TBM than in TCM-199 or TALP medium. Continuous cortical granule synthesis was observed in the three media when oocytes were incubated in the absence of spermatozoa. The presence of spermatozoa triggered the cortical reaction in a large proportion of oocytes fertilized in TCM-199 and TALP media. On the basis of the duration of pronase digestion, the zona pellucida of oocytes incubated in TCM-199 was harder (407.7 +/- 35.5 s) than that of oocytes cultured in TALP (235.4 +/- 18.2 s) or TBM (189.1 +/- 16.8 s). No zona pellucida hardening was noted in oocytes after insemination in any of the media. The percentages of penetration and cleavage were higher in oocytes cultured in TCM-199 and TALP than in TBM. The percentage of monospermy was higher in TCM-199 and TBM than in TALP. No effect of the medium was shown on the percentage of blastocyst formation or on the number of cells per blastocyst. In conclusion, the results highlight how differently the fertilization events take place in each IVF medium and how far these IVF media still are from achieving biological properties of gametes close to those observed in the physiological setting.

Effect of in vitrofertilization medium on the acrosome reaction, cortical reaction, zona pellucida hardening and in vitro development in pigs

Physiological events at the time of fertilization of pig oocytes may differ in vitro depending on the in vitro fertilization (IVF) medium. This hypothesis was tested by in vitro maturation of pig oocytes for 44 h in NCSU-37 medium and thereafter fertilization with frozen-thawed ejaculated spermatozoa. Three different IVF media (TCM-199, Tyrode's albumin lactate pyruvate (TALP) and Tris-buffered medium (TBM)) were used. For the acrosome reaction test, spermatozoa were incubated for 0-150 min in the three IVF media, and the proportion of live acrosome-reacted and acrosome-intact cells was determined by fluorescein isothiocyanate-labelled peanut agglutinin (FITC-PNA) and propidium iodide (PI) staining. The cortical granule density of oocytes was evaluated by confocal microscopy, 2.5 and 5.0 h after culture in each medium in the presence or absence of spermatozoa. Zona pellucida resistance to pronase digestion was also determined in the same groups. The percentages of penetration, monospermy, male pronucleus formation, cleavage and blastocyst formation, and the number of cells per blastocyst after culture were determined. The results indicate that the acrosome reaction occurred much faster in TBM than in TCM-199 or TALP medium. Continuous cortical granule synthesis was observed in the three media when oocytes were incubated in the absence of spermatozoa. The presence of spermatozoa triggered the cortical reaction in a large proportion of oocytes fertilized in TCM-199 and TALP media. On the basis of the duration of pronase digestion, the zona pellucida of oocytes incubated in TCM-199 was harder (407.7 +/- 35.5 s) than that of oocytes cultured in TALP (235.4 +/- 18.2 s) or TBM (189.1 +/- 16.8 s). No zona pellucida hardening was noted in oocytes after insemination in any of the media. The percentages of penetration and cleavage were higher in oocytes cultured in TCM-199 and TALP than in TBM. The percentage of monospermy was higher in TCM-199 and TBM than in TALP. No effect of the medium was shown on the percentage of blastocyst formation or on the number of cells per blastocyst. In conclusion, the results highlight how differently the fertilization events take place in each IVF medium and how far these IVF media still are from achieving biological properties of gametes close to those observed in the physiological setting.

Effect of co-culture of porcine sperm and oocytes with porcine oviductal epithelial cells on in vitro fertilization

This study was designed to determine the effect of co-culture with porcine oviductal epithelial cell (POEC) monolayers on in vitro fertilization of pig oocytes. The in vitro penetrability of mature (experiment 1) or immature (experiment 2) oocytes was studied in presence or absence of POEC during IVF with fresh semen. In experiment 3, boar and POEC effects were analyzed but in this case with frozen-thawed spermatozoa. In experiment 4, the spermatozoa were pre-incubated before IVF with or without POEC in order to assess their effect on IVF sperm-related parameters. In experiment 5, the effect of POEC was studied by co-culturing them with oocytes before IVF to determine if monospermy was improved. The results showed that high sperm concentration and POEC increase oocyte penetrability (P<0.01) and decrease monospermy rate (P<0.01), in both mature and immature oocytes (P<0.01) with fresh semen and a 18 h culture time. With frozen semen was detected a boar and POEC effect (P<0.01) on penetration rate. The sperm pre-culture 2 h with POEC also resulted in an increase of sperm penetration in terms of number of sperm per oocyte (P<0.01) and this treatment did not increase monospermy when contact time between gametes was limited to 6 h although monospermy was higher when POEC were present during IVF. Finally, exposure of oocytes to POEC for 4 h before IVF facilitated monospermic penetration to over 70% (P<0.01). In conclusion, the use of POEC in porcine IVF systems provides the possibility of working with low sperm concentrations and the effect of POEC on monospermy depends on sperm concentration, boar and contact time between gametes. Moreover, the exposure of oocytes to POEC before IVF improves the rate of monospermy.

Effects of maturational stage, cumulus cells and coincubation of mature and immature cumulus-oocyte complexes on in vitro penetrability of porcine oocytes

The in vitro penetrability of porcine oocytes is conditioned by several factors, some of which remain unclear. Knowledge of the different effects of the cellular components involved in penetrability would no doubt serve to simplify laboratory IVF methods. This study was designed to evaluate the effects of the following factors on penetrability: oocyte maturational stage, the presence of isolated or oocyte-attached cumulus cells, and coincubation of in vitro-matured and immature oocytes. Immature oocytes and oocytes matured in Waymouth medium were obtained from non atretic follicles and fertilized in TCM 199 medium. Sperm-rich fractions were collected by the gloved hand method and semen was used for IVF at a final concentration of 1 x 10(6) cells/mL in all experiments. Under the same conditions of IVF, the penetrability of the immature cumulus-oocyte complexes (COCs) was significantly lower than that of mature COCs, in terms of penetration rate and mean number of sperm per penetrated oocyte. This difference was abolished when the oocytes were denuded, leading to similar penetration rates. Coincubation of mature and immature COCs reduced the penetrability of immature COCs compared with that observed when these were incubated in isolation. However, neither the addition of isolated cumulus cells from decumulated mature oocytes nor the addition of denuded mature oocytes to immature COCs modified the penetration rate. These findings suggest that the presence of surrounding cumulus cells is mainly responsible for the differences observed in penetrability, regardless of the maturational stage of the oocyte. Moreover, when mature and immature COCs are coincubated, penetrability of immature COCs is diminished by the effects of the mature COC and not by the independent actions of the cellular components.

Maturation, fertilization and complete development of porcine oocytes matured under different systems

This study was designed 1) to determine the effectiveness of 2 in vitro maturation systems commonly employed to produce nuclear and cytoplasmically mature pig oocytes, 2) to assess the effects of boar, sperm concentration and maturation system on oocyte penetrability and male pronucleus formation and 3) to determine the ability of the in vitro matured oocytes to be fertilized in vivo by artificial insemination (AI) of sows. The differences examined between the 2 maturation systems included the culture medium (Waymouth vs TCM199), hormones, additives, culture conditions (static vs gentle agitation) presence or absence of porcine follicular fluid (PFF) and presence or absence of follicular shells. The results showed that nuclear maturation rate was similar in both systems (83.3 +/- 3.5 vs 86.4 +/- 2.5%), and intracellular content of glutathione was 5.21 +/- 0.73 vs 3.5 +/- 0.39 pmol/oocyte, although no correlation between these parameters was observed. The penetration rate and number of sperm cells per oocyte were dependent on the boar, maturation system and sperm concentration, but the rate of male pronuclear formation seemed to be influenced only by the boar and the maturation system but not by sperm concentration. In vivo fertilization of in vitro matured oocytes showed that both maturation systems could yield viable oocytes since 3 of 4 gilts and 2 of 4 gilts, respectively, became pregnant. Failure to become pregnant was not associated with inadequate oocyte maturation since control gilts, which received their own ovulated oocytes rather than in vitro matured oocytes at transfer, also did not become pregnant. We conclude that polyspermy may be an inherent problem in the IVF but not in the IVM systems.