ZP-free Oocytes Research Articles

A NOVEL ZONA PELLUCIDA (ZP)-FREE CULTURE SYSTEM FOR SEVERE CYTOPLASMIC FRAGMENTATION CASES: A PILOT STUDY USING 3PN EMBRYOS AND TIME-LAPSE CINEMATOGRAPHY

A study in 2017 observed perivitelline threads in more than 50% of cleavage-stage human embryos using time-lapse imaging, and the rate of cytoplasmic fragmentation (at the first cleavage) was significantly decreased in embryos without perivitelline threads (P < 0.001). While it is proposed that perivitelline threads play an important role in crosslinking the cumulus cells and oocyte during maturation, the mechanism underlying such a role remains unclear. It is also unknown whether the threads still function in mature MII oocytes. Therefore, in this study, zona pellucida of abnormally-fertilized oocytes which were donated by patients was removed at pronuclear stage. Those ZP-free oocytes were observed in time-lapse culturing system in order to examine developmental morphology. This study used 57 abnormally fertilized (3PN) embryos (cIVF: n = 51, ICSI: n = 6) donated by assisted reproduction technology patients in our clinic with informed consent since 2017. After confirming the three pronuclei, we removed the ZP from each 3PN embryo using a laser, and the resultant ZP-free embryos were cultured and observed in an incubator equipped with a time-lapse imaging system. For ZP removal, 3PN embryos were placed in drops of 0.125M sucrose-containing HEPES media that had been covered with mineral oil and warmed to 37°C. Despite a small reduction in ooplasm size, half of the ZP was removed by laser (Saturn 5; Origio、Lykos; Hamilton Thorne). Subsequently, the ooplasms were completely separated from their ZPs by pipetting, and these ZP-free 3PN embryos were cultured continuously for 5 days with time-lapse imaging. Of 58 ZP-free embryos in total, 54 (94.7%) were cleaved, and there was no significant decrease in cleavage rate compared to 2PN embryos (98%) used routinely in our clinic. Furthermore, 28 of the 54 embryos (51.9%) developed to the morula stage after third cleavage, and 18 embryos (33.3%) formed a blastocoel and became blastocysts. Thus, removing the ZP before cleavage did not adversely affect the embryo development. In terms of the amount of fragmentation, based on the modified Veeck’s criteria, 36 of 54 ZP-free 3PN embryos (66.7%) showed less than 20% of the volume in fragments compared to the total volume of cytoplasm at the first cleavage (Grade 1 and 2), 14 (25.9%) showed 20-40% fragments (Grade 3), and only 4 (7.4%) showed > 40% fragments (Grade 4). These results suggested that the rate of fragmentation was decreased by ZP removal before the first cleavage. This study revealed that the ZP is not always necessary for normal development after the pronuclear stage because the ZP-Free embryos studied herein developed normally, maintained their cell adhesion well, and showed a decreased rate of fragmentation.

Lipofection-Mediated Introduction of CRISPR/Cas9 System into Porcine Oocytes and Embryos.

Simple SummaryLiposome-mediated gene transfer has become an alternative method for establishing a gene targeting framework, and the production of mutant animals may be feasible even in laboratories without specialized equipment. However, whether blastocyst genome editing can be performed by treatment with lipofection reagent, guide RNA, and Cas9, without performing electroporation or microinjection, remains unclear. In this study, we demonstrated that lipofection treatment successfully induced mutation into zygotes during in vitro fertilization and in embryos at the 2- and 4-cell stages. Although liposome-mediated gene editing is a feasible system for use with zona-pellucida-free oocytes/embryos, several challenges must be overcome.Liposome-mediated gene transfer has become an alternative method for establishing a gene targeting framework, and the production of mutant animals may be feasible even in laboratories without specialized equipment. However, how this system functions in mammalian oocytes and embryos remains unclear. The present study was conducted to clarify whether blastocyst genome editing can be performed by treatment with lipofection reagent, guide RNA, and Cas9 for 5 h without using electroporation or microinjection. A mosaic mutation was observed in blastocysts derived from zona pellucida (ZP)-free oocytes following lipofection treatment, regardless of the target genes. When lipofection treatment was performed after in vitro fertilization (IVF), no significant differences in the mutation rates or mutation efficiency were found between blastocysts derived from embryos treated at 24 and 29 h from the start of IVF. Only blastocysts from embryos exposed to lipofection treatment at 29 h after IVF contained biallelic mutant. Furthermore, there were no significant differences in the mutation rates or mutation efficiency between blastocysts derived from embryos at the 2- and 4-cell stages. This suggests that lipofection-mediated gene editing can be performed in ZP-free oocytes and ZP-free embryos; however, other factors affecting the system efficiency should be further investigated.

EMC10 governs male fertility via maintaining sperm ion balance.

Infertility is a severe public health problem worldwide that prevails up to 15% in reproductive-age couples, and male infertility accounts for half of total infertility. Studies on genetically modified animal models have identified lots of genes involved in the pathogenesis of male infertility. The underlying causes, however, remain largely unclear. In this study, we provide evidence that EMC10, one subunit of endoplasmic reticulum (ER) membrane protein complex (EMC), is required for male fertility. EMC10 is significantly decreased in spermatozoa from patients with asthenozoospermia and positively associated with human sperm motility. Male mice lacking Emc10 gene are completely sterile. Emc10-null spermatozoa exhibit multiple defects including abnormal morphology, decreased motility, impaired capacitation, and impotency of acrosome reaction, thereby which are incapable of fertilizing intact or ZP-free oocytes. However, intracytoplasmic sperm injection could rescue this defect caused by EMC10 deletion. Mechanistically, EMC10 deficiency leads to inactivation of Na/K-ATPase, in turn giving rise to an increased level of intracellular Na+ in spermatozoa, which contributes to decreased sperm motility and abnormal morphology. Other mechanistic investigations demonstrate that the absence of EMC10 results in a reduction of HCO3- entry and subsequent decreases of both cAMP-dependent protein kinase A substrate phosphorylation and protein tyrosine phosphorylation. These data demonstrate that EMC10 is indispensable to male fertility via maintaining sperm ion balance of Na+ and HCO3-, and also suggest that EMC10 is a promising biomarker for male fertility and a potential pharmaceutical target to treat male infertility.

139 Sperm Transmembrane Protein 95 (TMEM95) is Required for Sperm - Oocyte Interaction and Successful Fertilization but not Mucus Penetration in Cattle

A population of bulls with 1.7% 56-day non-return rate were found to share a 1386 kb segment of homozygosity (Pausch et al. 2014 PLoS Genet. 10, e1004044). That study identified a nonsense mutation in the transmembrane protein 95 (TMEM95)-encoding gene as the most likely candidate for the subfertility phenotype. Sperm from homozygous bulls (mt/mt) exhibit normal motility and morphology. However, they are not as successful as sperm from wildtype (wt/wt) bulls in binding to the zona pellucida (ZP) or penetrating the plasma membrane of oocytes, which results in lower in vitro fertility (Fernandez-Fuertes et al. 2017 Biol. Reprod. 97, 50-60, 10.1093/biolre/iox065). Sperm from mice deficient for another transmembrane protein, TMEM16E, have normal total motility but cannot penetrate the ZP because they have sluggish motility and are not able to swim in a straight line (Gyobu et al. 2015 Mol. Cell. Biol. 36, 645-659). To determine whether this is one reason behind mt/mt bull subfertility, we assessed the ability of sperm from these bulls to migrate through cervical mucus of oestrus cows. In addition, because mt/mt bulls are homozygous for such an extensive chromosomal segment, this study aimed to determine whether TMEM95 alone is responsible for the loss of sperm function. To test this, sperm from a wt/wt bull was incubated in the presence of anti-TMEM95 antibody (Ab; 1:20 dilution) 1 h before fertilization. In all experiments, data were assessed for normality of distribution and analysed using a one-way ANOVA. In experiment 1, bull genotype had no effect on the number of sperm present in mucus-filled capillaries or on their distribution along them, following 30-min incubation. In experiment 2, incubation of sperm from wt/wt bulls with Ab decreased oocyte cleavage rates compared with the untreated control (59 ± 0.3 v. 76 ± 0.9%, respectively; P &lt; 0.05). However, this percentage was still higher than in the mt/mt group (59 ± 0.3 v. 31 ± 2.9% respectively; P &lt; 0.05). Surprisingly, the Ab did not affect the percentage of blastocysts that developed at Day 8 after fertilization. Three hours after fertilization, a lower number of Ab-treated sperm bound to the ZP compared with untreated sperm (4 ± 1.2 v. 9 ± 2.1, respectively; P &lt; 0.05). This number did not differ between the Ab and mt/mt groups. Consistent with the previous results, Ab-treated sperm were less able to penetrate ZP-free oocytes than untreated sperm (47 ± 1.5 and 58 ± 4.2%, respectively; P &lt; 0.05). However, lower penetration rates were observed in the mt/mt than in the Ab-treated group (24 ± 3.9 and 47 ± 1.5%, respectively; P &lt; 0.05). We concluded that sperm from mt/mt bulls could traverse cervical mucus from oestrus cows. Transmembrane protein 95 seems to be directly responsible for the lower ZP binding and, partially, for the lower plasma membrane penetration observed. However, how this protein exerts these functions and what other factors might be involved remain to be determined. Research was supported by the Irish Department of Agriculture, Food and The Marine under the Research Stimulus Programme (Grant No. 11S104).

4 SUBFERTILITY IN BULLS CARRYING A NONSENSE MUTATION IN TMEM95 IS DUE TO FAILURE TO PENETRATE THE ZONA PELLUCIDA

In a recent genome-wide association study, male reproductive ability was assessed for 7962 Fleckvieh sires (Pausch et al. 2014 PLoS Genet. 10, e1004044). Forty bulls in the population with exceptionally poor reproductive performance were found to be homozygous for a nonsense mutation in the transmembrane protein 95 (TMEM95)-encoding gene. Ejaculates from these individuals exhibited normal sperm concentration, morphology, viability, and motility. However, out of 35,671 inseminations with these bulls, only 1.7% resulted in pregnancies. In addition, none of the bulls with normal reproductive performance was homozygous for this mutation. The aim of this study was to examine the effect of this nonsense mutation in TMEM95 on bovine sperm function in vitro. In all experiments, data were assessed for normality of distribution and analysed using a one-way ANOVA. The model included the main effects of treatment, replicate and their interactions. In Experiment 1, the fertilizing ability of sperm, assessed as oocyte cleavage rate, from 5 homozygous (mt/mt), 3 heterozygous (wt/mt), and 2 wildtype (wt/wt) Fleckvieh bulls was assessed. Oocytes fertilised with sperm from mt/mt males had a lower cleavage rate at 48 h post-fertilization than oocytes fertilised with sperm from wt/wt or wt/mt bulls (26 ± 3%, 72 ± 2%, and 79 ± 3%, respectively; P &lt; 0.01). In addition, the kinetics of cleavage were slower in the mt/mt group as evidenced by a lower proportion of embryos beyond the 2-cell stage at 48 h (32 ± 12.6%, 90 ± 3.6%, and 87 ± 0.4%, respectively, P &lt; 0.01). This translated into a lower blastocyst rate at Day 8 in the mt/mt group in comparison with wt/mt and wt/wt groups (2 ± 1%, 27 ± 3%, and 40 ± 2%, respectively, P &lt; 0.01). In Experiment 2, fluorescent staining of oocytes 3 h after fertilization revealed a lower number of sperm from mt/mt bulls bound to the zona pellucida (ZP) in comparison with sperm from wt/wt or wt/mt individuals (3 ± 1.0, 11 ± 2.3, and 24 ± 9.4, respectively; P &lt; 0.05). In order to further study the potential role of TMEM95 in sperm-ZP interaction, in Experiment 3 sperm from the 3 groups were used to fertilize ZP-free oocytes. Consistent with the previous results, sperm from mt/mt bulls were less able to penetrate oocytes with no ZP than sperm from wt/wt or wt/mt bulls (6 ± 2%, 44 ± 8%, and 68 ± 14%, respectively; P &lt; 0.05). In conclusion, these results suggest that TMEM95 is involved in events that take place before ZP binding but are required for sperm to interact normally with the oocyte vestments and, ultimately, to achieve fertilization. Further study of the possible role of this protein in the initiation of sperm capacitation and hypermotility, as well as in early embryo development, will shed more light regarding the crucial role of TMEM95 in sperm function. Supported by the Irish Department of Agriculture, Food and The Marine under the Research Stimulus Programme (Grant No. 11 S 104).

Interaction of bovine viral diarrhea virus with bovine cumulus–oocyte complex during IVM: Detection in permissive cells

Structural changes in the zona pellucida (ZP) of bovine oocytes seem to modulate their interaction with various viral agents, facilitating the viral infection in in vitro production systems. To evaluate the susceptibility of bovine oocytes to noncytopathogenic bovine viral diarrhea virus (ncp-BVDV), cumulus–oocyte complexes were exposed to 107 ​tissue culture-infective doses (TCID50)/mL of an ncp-BVDV strain during IVM (in vitro maturation). After that, cumulus cells and the ZP were removed by hyaluronidase and pronase treatment, respectively, and the percentages of oocytes with polar body were analyzed as a sign of nuclear maturation. After passage through cell culture, the virus was isolated from granulosa cells, ZP-free mature oocytes, and ZP-intact mature oocytes. These results were confirmed by reverse transcription–polymerase chain reaction. After consecutive washes, the virus remained associated with ZP-free oocytes, maintaining its replication and infectivity in permissive cells. Based on these findings, it is concluded that the classical viral isolation procedure has a predictive value to detect BVDV associated with ZP-free oocytes and that it was novelty demonstrated that both washing and trypsin treatment of oocytes were ineffective to remove BVDV infection.

Roles of the zona pellucida and functional exposure of the sperm‐egg fusion factor ‘IZUMO’ during in vitro fertilization in pigs

The zona pellucida (ZP) is considered to play important roles in the prevention of polyspermy in mammalian oocytes. However, in pigs we have shown that the presence of the ZP accelerates sperm penetration into the ooplasm during in vitro fertilization (IVF). In the present study, we investigated the effects of the ZP on sperm binding, acrosomal status, and functional exposure of IZUMO, a critical factor involved in sperm-egg fusion, during IVF in pigs. We evaluated the numbers and acrosomal statuses of sperm binding to the ZP and oolemma, and being present in the ZP and perivitelline space (PVS) using ZP-intact and ZP-free oocytes. More sperm bound to the ZP than to the oolemma. The average number of sperm present in the PVS was 0.44-0.51 per oocyte, and all sperm had lost their acrosomes. The proportion of sperm that were immunopositive for anti-IZUMO antibody was significantly higher after they were passing or had passed through the ZP. Furthermore, addition of anti-IZUMO antibody to the fertilization medium significantly inhibited the penetration of sperm into ZP-free oocytes. These results suggest that, in pigs, the ZP induces the acrosome reaction, which is associated with the functional exposure of IZUMO, resulting in completion of fertilization.

Calreticulin from suboolemmal vesicles affects membrane regulation of polyspermy

This study was designed to determine whether calreticulin (CRT), a chaperone protein, is present in in vitro-matured (IVM) pig oocytes and to study its potential role in the block to polyspermy. Western blot analysis, using an anti-CRT antibody, of oocyte lysate showed an immunoreactive band of ∼60 kDa. Simultaneous labeling of IVM oocytes with anti-CRT antibody and peanut agglutinin lectin (PNA lectin, a porcine cortical granules (CG)-specific binding lectin) revealed localization of CRT in the subplasmalemmal region with a 27.7% colocalization with PNA staining. After IVF, PNA labeling was not observed and anti-CRT labeling decreased significantly in zygotes and disappeared in two-cell embryos. Western blot analysis of oocyte exudate obtained from zona pellucida (ZP)-free oocytes activated with calcium ionophore confirmed the presence of a band that reacted with an anti-CRT antibody. Anti-CRT antibody and PNA labeling were not observed in activated oocytes despite being detectable in non-activated oocytes. The presence of CRT in vesicles located under the oolemma was demonstrated using immunogold cytochemistry at the ultrastructural level. To study the role of CRT in fertilization, ZP-enclosed and ZP-free oocytes were incubated with exogenous CRT and then inseminated. Whereas ZP-free oocytes showed fewer penetrating sperm and lower polyspermy rates than untreated oocytes, the opposite effect was observed in ZP-enclosed oocytes. In conclusion, CRT is confined to subplasmalemmal vesicles partially overlapping with CG contents. Its exocytosis after the oocyte activation seems to participate in the membrane block to polyspermy in pigs but is not involved in the ZP block.

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).

38 GENERATION OF INTERSPECIFIC CLONED BLASTOCYSTS BY ZONA PELLUCIDA-FREE NUCLEAR TRANSFER IN WILD FELIDS

Somatic cell nuclear transfer is an assisted reproductive technique that could help to preserve endangered species. Because it is difficult to obtain wild felid oocytes, interspecific cloning using domestic cat (DC) oocytes is an alternative to produce cloned embryos in these species. The aim of this study was to evaluate different cloning strategies in the DC (Felis silvestris catus) and to use the most efficient strategy to generate wild felid embryos by interspecific cloning. First, we evaluated 3 different cloning strategies: (1) enucleation of DC oocytes with zona pellucida (ZP) followed by fusion of a DC fibroblast that was injected into the perivitelline space (ZP-enclosed group), (2) the same enucleation procedure followed by intracytoplasmic injection of a DC fibroblast (ZPi group), and (3) enucleation of ZP-free oocytes followed by adhesion and fusion of a DC fibroblast (ZP-free group). After 2 h of nuclear reprogramming, the reconstructed embryos were activated with 5 µM ionomycin and 1.9 mM DMAP, and cultured in SOF. The ZP-free embryos were cultured in wells of the well system. Embryo development among treatment groups was compared by the Fisher exact test (P ≤ 0.05). The blastocyst rates were similar among the 3 groups: 11.1% (2/18), 11.1% (5/45), and 12.7% (9/71), for ZP-enclosed, ZPi, and ZP-free, respectively. However, the quantity of reconstructed embryos after the procedure was higher in the ZP-free clones because of a higher fusion rate (82.7 vs. 25.4%) and the use of a less-invasive technique than the injection. Moreover, the percentage of expanded blastocysts was also higher (0, 16.2, and 77.8% for ZP-enclosed, ZPi, and ZP-free, respectively). Parthenogenetic controls, with and without ZP, did not differ in blastocyst rates: 47.7% (42/88) and 49.4% (38/77), respectively. After this, the ZP-free strategy was chosen for the successive experiment. In experiment 2, the wild felid species selected for interspecific cloning were Bengal (a hybrid between Felis silvestris and Prionailurus bengalensis; FP group), cheetah (Acinonyx jubatus; AJ group), and tiger (Panthera tigris; PT group). The morula and blastocyst rates were higher in the FP group: 34.3% (36/105), 16.2% (16/99), and 17.5% (11/63) for morulae, and 33.3% (35/105), 1% (1/99), and 3.2% (2/63) for blastocysts of FP, AJ, and PT, respectively. Additionally, total cell number and the expression pattern of octamer-binding transcription factor 4 (Oct-4) were examined in the blastocysts by immunocytochemistry. The mean total cell number in DC, FP, AJ, and PT blastocysts was 177.9 ± 53, 229 ± 40, 53, and 41, respectively. All blastocysts expressed Oct-4 but in different proportions. The percentage of cells expressing Oct-4 in DC, FP, AJ, and PT blastocysts was 48, 66, 100, and 98%, respectively. In summary, ZP-free cloning was found to be an efficient technique in DC, with potential to be used in wild felid species. We also demonstrated that DC oocytes were able to reprogram cells of other genera. This is the first report of felid ZP-free cloning and also the first time that tiger and cheetah embryos were produced by interspecific cloning.

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 &lt; 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).

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).

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).

Birth of piglets by in vitro fertilization of zona-free porcine oocytes

The present experiments were conducted to optimize in vitro fertilization conditions for zona pellucida-free (ZP-free) oocytes and their subsequent development. The results demonstrated that: (1) maximal fertilization efficiency was achieved at 200 spermatozoa per ZP-free oocyte. At this sperm dose, there were no significant differences in penetration rates and polyspermy rates from controls (zona-intact oocytes with 1000 spermatozoa/oocyte), indicating that ZPs of in vitro matured pig oocytes failed to block polyspermy during in vitro fertilization. (2) In vitro development of zygotes from ZP-free oocytes showed that there was no difference in cleavage rates. The blastocyst rate was slightly lower in the ZP-free group than the control. However, there was no difference in cell number per blastocyst between the control and the ZP-free group. (3) Examination of acrosome status by a specific fluorescein isothiocyanate-conjugated peanut agglutinin (FITC-PNA) staining procedure revealed that frozen–thawed pig spermatozoa could undergo acrosome reaction and penetrate oocytes without induction by ZP. These data suggested that there are alternative mechanistic pathways for acrosome reaction induction during the fertilization process than the widely accepted sperm–zona receptor models. Finally, the viability of ZP-free derived embryos was demonstrated by full-term development and the delivery of healthy piglets following embryo transfer. In conclusion, the present experiments showed for the first time in farm animals, that normal embryos could be produced by in vitro fertilization of ZP-free oocytes in optimized conditions and that they could develop normally to full-term.

Parthenogenetic activation of pig oocytes with calcium ionophore and the block to sperm penetration after activation.

Calcium ionophore A23187 can parthenogenetically activate oocytes in many animals. The present study was designed to analyze functionally the mechanism of A23187 activation of pig oocytes matured in vitro. In experiment 1, effects of the concentration of A23187 on intracellular calcium transients, cortical granule (CG) exocytosis, nuclear activation, and zona reaction, which was determined by zona hardening and sperm penetrability, were examined. Cumulus-free oocytes were exposed to 0-100 microM A23187 for 5 min. It was found that the amplitude of the intracellular calcium transients, percentage of CG exocytosis, and percentage of pronuclear formation were increased in a concentration-dependent manner. The time for dissolution of zona pellucida (ZP) was increased in the oocytes treated with 25-100 microM A23187. Penetration of ZP-intact oocytes by spermatozoa was decreased and only 3-4% of oocytes were penetrated by spermatozoa after 50-100 microM A23187 treatment. In experiment 2, oocytes were treated with 100 microM A23187 for 5 min and then cultured for 10 min or 3.5 h before insemination. No difference in penetration rates was observed between the two groups of oocytes (12.0% vs. 12.2%), but the penetration rates were significantly lower than those in controls (85.2% vs. 82.4%). In experiment 3, treatment of oocytes with 100 microM A23187 for 5 min was followed by removal of the ZP from a portion of the oocytes. ZP-intact and ZP-free oocytes were then inseminated for examination of sperm penetration. One of 65 (2%) oocytes with ZP and 48 of 52 (92%) oocytes without ZP were penetrated by spermatozoa. These results indicate that activation of pig oocytes by A23187 is the result of A23187-induced intracellular calcium increase and that A23187-induced cortical reaction can prevent sperm penetration of ZP-intact oocytes, but not ZP-free oocytes.