Pronucleus Formation Research Articles

Epigenetic Characteristics of Paternal Chromatin in Interspecies Zygotes

Both the sperm and oocyte are terminally differentiated cells, but within a very short post-fertilization period, their genomes are converted into a totipotent zygote. The process of this transformation has been studied in a number of mammals as well as in the pig, for which very inconsistent results have been published. To clarify these inconsistencies, we have used the interspecies intracytoplasmic sperm injection technique for embryo production and subsequent paternal genome remodeling evaluation. First, we injected boar sperm heads into ovulated and in vitro matured mouse oocytes. The boar spermatozoa consistently decondense in ovulated oocytes and form fully developed pronuclei with demethylated DNA (5-methylcytosine; 5-MeC). Additional labeling against other histone modifications (H3/K9 dimethylation, H3/K4 trimethylation) and HP1 (Heterochromatin Protein 1) revealed similarity to those changes that are typical for natural mouse zygotes. On the other hand, no decondensation and formation of male pronuclei were observed, in spite of obvious oocyte activation, in in vitro matured oocytes. For this reason, we have evaluated the reprogramming parameters of in vitro matured mouse oocytes in more detail. In mouse zygotes (intraspecific), both pronuclei were consistently formed, but no sperm head chromatin demethylation was detected after 5-MeC labeling. Our observations suggest that porcine sperm heads are capable of undergoing active demethylation in in vivo matured mouse oocytes. On the other hand, in vitro matured oocytes possess much lower sperm remodeling capabilities.

Oocyte glutathione and fertilisation outcome of Macaca nemestrina and Macaca fascicularis in in vivo- and in vitro-matured oocytes

Fertilisation and development of IVM non-human primate oocytes is limited compared with that of in vivo-matured (IVO) oocytes. The present study describes the IVM of macaque oocytes with reference to oocyte glutathione (GSH). Timing of maturation, comparison of IVM media and cysteamine (CYS) supplementation as a modulator of GSH were investigated. A significantly greater proportion of oocytes reached MII after 30 h compared with 24 h of IVM. Following insemination, IVM oocytes had a significantly lower incidence of normal fertilisation (i.e. 2PN = two pronuclei and at least one polar body) and a higher rate of abnormal fertilisation (1PN = one pronucleus and at least one polar body) compared with IVO oocytes. Immunofluorescence of 1PN zygotes identified incomplete sperm head decondensation and failure of male pronucleus formation as the principal cause of abnormal fertilisation in IVM oocytes. The IVO oocytes had significantly higher GSH content than IVM oocytes. Cumulus-denuded oocytes had significantly lower GSH following IVM compared with immature oocytes at collection. Cysteamine supplementation of the IVM medium significantly increased the GSH level of cumulus-intact oocytes and reduced the incidence of 1PN formation, but did not improve GSH levels of the denuded oocyte. Suboptimal GSH levels in macaque IVM oocytes may be related to reduced fertilisation outcomes.

279 IMPROVEMENT OF RAT IN VITRO FERTILIZATION PROTOCOL USING CRYOPRESERVED SPERM AND ITS APPLICATION TO OTHER STRAINS: A PRELIMINARY STUDY

In rats, the success of in vitro fertilization (IVF) was reported almost 40 years ago. Although it had been demonstrated in papers that these IVF oocytes using sperm freshly collected from cauda epididymides can be developed to term via embryo transfer, successful IVF with cryopreserved rat sperm has never been reported. Very recently, we reported establishment of a successful IVF system using frozen-thawed spermatozoa treated with a phosphodiesterase inhibitor, 3-isobutyl-1-methyl-xanthin (IBMX), in Wistar rats (Seita et al. 2009 Biol. Reprod.). The objectives in this study were (1) improvement of the IVF system to a more convenient and simple protocol and (2) a preliminary study for applying our IVF system to inbred rat strains Fischer 344 (F344) and Brown-Norway (BN). In experiment 1, we examined the effect of preincubation time for frozen-thawed sperm on fertilization (2 pronuclei formation). Frozen-thawed sperm were preincubated up to 6 h and then used for IVF according to our previous report. Data showed that sperm preincubated for 5 h contributed to higher fertility than those for other preincubation times. In experiment 2, we examined the effect of co-culture time up to 10 h for IVF on fertility and embryonic development in vitro. The oocytes co-cultured with sperm beyond 6 h showed higher fertilization and blastocyst formation rates than those in 2 and 4 h. In experiment 3, we examined the effect of initial culture period in fertilization medium (310 mOsm modified R1ECM; O h et al. 1998 Biol. Reprod.) on embryonic development in vitro. After IVF, oocytes were cultured in fertilization medium for 6, 12, or 24 h and further cultured in R1ECM up to 120 h. Cleavage rates were not affected by initial culture time in fertilization medium. However, oocytes cultured in fertilization medium for 12 h showed higher blastocyst formation rate than those for 0, 6 and 24 h. In experiment 4, we examined whether the IVF protocol can be applied to F344 and BN rats. Fresh and frozen-thawed sperm collected from cauda epididymides in F344 and BN were used for detection of capacitation-associated tyrosine phosphorylation. In fresh F344 sperm, tyrosine phosphorylation was induced in a time-dependent manner. Although tyrosine phosphorylation was inhibited in frozen-thawed F344 sperm, it was dramatically accelerated by IBMX treatment as well as frozen-thawed Wistar sperm. However, tyrosine phosphorylation in fresh and frozen-thawed BN sperm was suppressed and the phosphorylation in frozen-thawed sperm was not improved by IBMX. Our data demonstrate that (1) a more efficient IVF system using frozen-thawed rat sperm was developed and (2) the IVF system can be applied to at least F344 strain. The work was supported in part by Grant-in-Aid for Scientific Research from JSPS (KAKENHI) (21789253) to J.I. This work was also supported in part by the Promotion and Mutual Aid Corporation for Private Schools of Japan through a Grant-in-Aid for Matching Fund Subsidy for Private Universities to J.I. and N.K.

Postactivation treatment with nocodazole maintains normal nuclear ploidy of cloned pig embryos by increasing nuclear retention and formation of single pronucleus

The objective of this study was to investigate the effects of postactivation treatment with nocodazole on morphologic changes of donor nuclei and in vitro and in vivo development of somatic cell nucleus transfer (SCNT) embryos in pigs (Sus scrofa). Somatic cell nucleus transfer oocytes were either untreated (control) or treated with nocodazole or demecolcine after electric activation, then cultured in vitro or transferred to surrogate pigs. Treatment with nocodazole (30%) and demecolcine (29%) after electric activation improved embryo development to the blastocyst stage compared with the control (16%). The rate of oocytes that formed single clusters of chromosomes or a pronucleus 4 h after activation was higher after treatment with nocodazole (82%) and demecolcine (86%) than under the control conditions (66%), and this tendency was not altered even 12 h after activation. Pseudo-polar body extrusion was inhibited by nocodazole and demecolcine, and the rate of embryos with diploid chromosomes was higher after treatment with nocodazole (86%) and demecolcine (77%) than under control conditions (58%). Nocodazole treatment resulted in a farrowing rate of 50% with a 1.7% efficiency of piglet production, whereas controls showed a farrowing rate of 60% and a production efficiency of 3.8%. Our results demonstrate that postactivation treatment with nocodazole maintains normal nuclear ploidy of cloned embryos likely by increasing nuclear retention and formation of single pronuclei. In vivo development could be achieved from the transfer of nocodazole-treated embryos but showed some defects compared with control.

378 INVOLVEMENT OF THE SPERM TAIL IN TRIGGERING OOCYTE ACTIVATION IN PIGS

In mammals, repetitive increases of the intracellular Ca2+ level, known as Ca2+ oscillations, are observed in oocytes immediately after sperm-oocyte fusion, which is a prerequisite event for oocyte activation. Previous studies indicate that phospholipase C zeta (PLCζ), a strong candidate sperm factor for triggering Ca2+ oscillations, is localized in the sperm head of several mammalian species. We have reported that the rate of pronucleus formation in oocytes injected with a sperm head is lower than that for oocytes injected with a whole spermatozoon (Nakai et al. 2009 IETS). This has given rise to a hypothesis that not only the sperm head but also the tail play a role in inducing oocyte activation in pigs. In this study, we attempted to detect the localization of PLCζ in the pig sperm tail and also its ability to activate porcine oocytes after injection. To clarify the localization of PLCζ in pig sperm, frozen-thawed ejaculated pig sperm were immunostained using an anti-PLCζ antibody that has been reported previously (Kurokawa et al. 2005). Western blotting was also carried out to examine whether PLCζ (72 kDa) was present in the sperm tail. Sperm tails were detached from the head by sonication and then collected after centrifugation in a Percoll density gradient. We also confirmed whether the sperm tail itself had the ability to trigger oocyte activation using the following 4 injection groups: (1)1 sperm head (Head), (2) 1 sperm tail (Tail), (3) 1 sperm head and 1 tail (Head + Tail), and (4) Sham. The nuclear status of the injected oocyte was evaluated at 10 h after injection. In the present study, we used 3 sperm samples that were prepared from different boars. In pig sperm, the acrosome, tail, and post-acrosomal regions were stained by the PLCζ antibody. The signals in both the post-acrosomal and tail regions disappeared after pretreatment with antigenic peptide, but that in the acrosome region was retained. Furthermore, we confirmed the presence of a band of approximately 72 kDa from the sperm tail and also confirmed its disappearance upon pretreatment with antigenic peptide. The rates of oocytes released from metaphase-II arrest in the Head, Tail, and Head+Tail groups were significantly higher than that in the Sham group (P < 0.05 by ANOVA andTukey test). However, most of the oocytes in the Tail group failed to form pronuclei and showed other meiotic stages (anaphase-II, telophase-II, or metaphase-III). In conclusion, we have shown that PLCζ is expressed in the post-acrosomal and tail region of pig sperm. It is suggested that, in the pig, the sperm tail participates in the triggering of oocyte activation. The authors thankRafaelA. Fissore (Department ofVeterinary and Animal Sciences, University of Massachusetts Amherst) for providing the antigenic peptide for PLCζ. This study was supported in part by JSPS Fellowship (71310042 to M.N.) from the Japanese Society for Promotion of Science (JSPS).

Production of good-quality porcine blastocysts by in vitro fertilization of follicular oocytes vitrified at the germinal vesicle stage

We investigated survival, meiotic competence, cytoplasmic maturation, in vitro fertilization, and development of immature porcine (Sus scrofa) oocytes cryopreserved by a modified solid surface vitrification protocol. Cumulus-oocyte complexes (COCs) collected from follicles 3 to 6 mm in diameter in abattoir-derived ovaries of prepubertal gilts were either vitrified (Vitrified group), subjected to cryoprotectant treatment (CPA group), or used without any treatment (Control group). Oocyte viability was assayed by staining with fluorescein diacetate. Live oocytes were matured in vitro and their meiotic progression investigated by nuclear staining. In a series of experiments, the glutathione (GSH) content of in vitro–matured oocytes and viability of cumulus cells were assayed simultaneously. The in vitro–matured oocytes were also fertilized and cultured in vitro to assess their ability to be fertilized and to develop to the blastocyst stage, respectively. The proportion of viable oocytes in the Vitrified group was significantly lower than that in the CPA and Control groups (27.7%, 90.4%, and 100%, respectively). Among the three groups, there were no differences in meiotic competence, cumulus viability, and GSH levels at the end of in vitro maturation. Fertilization parameters (i.e., rates of male pronucleus formation, monospermy, and second polar body extrusion) were also similar among groups. However, comparison of the developmental abilities of oocytes in the Vitrified, CPA, and Control groups revealed that the Vitrified group had a significantly reduced ability to undergo first cleavage (34.4%, 63.3%, and 69.0%) and to develop to the blastocyst stage (5.1%, 25.5%, and 34.6%). The mean total cell numbers in blastocysts after 6 d of culture were not significantly different among the Vitrified, CPA, and Control groups (40.3, 42.8, and 43.4). In conclusion, despite low survival rates and impaired development in the Vitrified group, meiotic competence, cytoplasmic maturation, and subsequent fertilization characteristics of surviving germinal vesicle oocytes were unaffected by vitrification, and high-quality blastocysts were produced from vitrified immature oocytes.

Ability of Catalonian donkey sperm to penetrate zona pellucida-free bovine oocytes matured in vitro

An experiment was designed to study the interaction between fresh/frozen-thawed donkey spermatozoa and zona pellucida (ZP)-free bovine oocytes in an attempt to develop a model for assessing cryopreserved Catalonian donkey sperm function. Semen from five donkeys was collected using an artificial vagina. Sperm motility and viability were immediately assessed and the semen sample cryopreserved. Sperm viability and motility were then reassessed immediately after thawing. The motion characteristics of the fresh and frozen-thawed spermatozoa were determined using a computer-assisted sperm analysis system. In vitro-matured cow oocytes were inseminated with different percent live donkey sperm (high (>60%) or low (<40%) viability donkey sperm). After 18 h of co-incubation, the oocytes were fixed, stained with 4′,6-diamidino-2-phenylindole (DAPI) and examined for sperm penetration, the number of penetrated spermatozoa per oocyte, and male pronucleus formation. Frozen-thawed spermatozoa from high viability semen showed significantly lower VCL, VAP and mean ALH values than did high viability fresh spermatozoa. In contrast, frozen-thawed spermatozoa of low viability had significantly higher velocity values than fresh spermatozoa of low viability. A significant positive correlation ( P < 0.01) was detected between percentage fertilization and viability ( r = 0.84), and between percentage fertilization and certain CASA parameters (VAP, r = 0.56; VCL, r = 0.61 and mean ALH, r = 0.68). Fresh or frozen-thawed high viability spermatozoa penetrated 90.1% and 85.4% of bovine oocytes respectively. Lower rates of penetration were observed for fresh and frozen-thawed low viability spermatozoa (34% and 22.5% respectively). The donkey spermatozoa were able to fuse with the oolema and even to decondense and form the male pronucleus (85–94%). Larger numbers of penetrated spermatozoa per oocyte were recorded when high viability sperm samples were used, whether fresh (3.02 vs. 1.12 for low viability sperm) or frozen-thawed (3.41 vs. 1.47). Consequently, low viability sperm samples showed higher percentages of monospermic penetration (91.17% and 61.97% for fresh and frozen-thawed sperm samples respectively). These findings suggest that bovine oocytes provide a useful model for assessing the penetration potential of frozen-thawed donkey sperm.

Oocyte activation ability correlates with head flatness and presence of perinuclear theca substance in human and mouse sperm

Recent studies indicate that round-headed sperm cannot activate oocytes and lack the postacrosomal sheath (PAS) or perinuclear theca (PT), although normal flat-headed sperm can activate oocytes and do have PAS (PT). In this study, we investigated how oocyte activation ability correlates with sperm head morphology (round and flat) and the presence of PT, by studying MN13, a representative molecule of the PT. We analyzed sperm with flat and round heads from infertile patients with globozoospermia (n = 1) and teratozoospermia (n = 1), and also from GOPC(-/-) mice, an animal model of human globozoospermia. Differential interference contrast image analysis, immunocytochemistry with MN13 antibody, transmission electron microscopy and an oocyte activation assay (assessing pronucleus formation) with ICSI were used. Flat-headed (control) sperm from both a healthy fertile volunteer man and wild-type mice had MN13 and PAS (PT). Flat-headed sperm (<5% of the population) from GOPC(-/-) mice also had both MN13 and PAS (PT), and they showed high oocyte activation ability. In contrast, round-headed sperm from a globozoospermia patient (100%) and GOPC(-/-) mice (>95% of the population) had neither MN13, nor PAS (PT), nor oocyte activation ability. Oocyte activation was higher in flat- versus round-headed sperm from GOPC(-/-) mice (P < 0.05). Oocyte activation ability may be related to sperm head flatness and presence of MN13 and PAS (PT) in human and mouse sperm. This information is a first step towards the possibility of selecting good-quality sperm with high oocyte activation ability for ICSI.

New Insights into the Mechanisms of Fertilization: Comparison of the Fertilization Steps, Composition, and Structure of the Zona Pellucida Between Horses and Pigs1

The mechanism of fertilization remains largely enigmatic in mammals. Most studies exploring the molecular mechanism underlying fertilization have been restricted to a single species, generally the mouse, without a comparative approach. However, the identification of divergences between species could allow us to highlight key components in the mechanism of fertilization. In the pig, in vitro fertilization (IVF) and polyspermy rates are high, and spermatozoa penetrate easily through the zona pellucida (ZP). In contrast, IVF rates are low in the horse, and polyspermy is scarce. Our objective was to develop a comparative strategy between these two divergent models. First, we compared the role of equine and porcine gametes in the following five functions using intraspecific and interspecific IVF: ZP binding, acrosome reaction, penetration through the ZP, gamete fusion, and pronucleus formation. Under in vitro conditions, we showed that the ZP is a determining element in sperm-ZP attachment and penetration, whereas the capacity of the spermatozoa is of less importance. In contrast, the capacity of the spermatozoa is a key component of the acrosome reaction step. Second, we compared the composition and structure of the equine and porcine ZP. We observed differences in the number and localization of the ZP glycoproteins and in the mesh-like structure of the ZP between equine and porcine species. These differences might correlate with the differences in spermatozoal attachment and penetration rates. In conclusion, our comparative approach allows us to identify determining elements in the mechanism of fertilization.

Effects of the conditioned medium of mesenchymal stem cells on mouse oocyte activation and development

Mesenchymal stem cells (MSCs) have been reported to secrete a variety of cytokines and growth factors acting as trophic suppliers, but little is known regarding the effects of conditioned medium (CM) of MSCs isolated from femurs and tibias of mouse on the artificial activation of mouse oocytes and on the developmental competence of the parthenotes. In the current study, we investigated the effect of CM on the events of mouse oocyte activation, namely oscillations of cytosolic calcium concentration ([Ca(2)+]i), meiosis resumption, pronucleus formation, and parthenogenetic development. The surface markers of MSCs were identified with a fluorescence-activated cell sorter. The dynamic changes of the spindle and formation of pronuclei were examined by laser-scanning confocal microscopy. Exposure of cumulus-oocyte complexes to CM for 40 min was optimal for inducing oocyte parthenogenetic activation and evoking [Ca(2)+]i oscillations similar to those evoked by sperm (95 vs 100%; P > 0.05). Parthenogenetically activated oocytes immediately treated with 7.5 microg/mL cytochalasin B (CB), which inhibited spindle rotation and second polar body extrusion, were mostly diploid (93 vs 6%, P < 0.01) while CB-untreated oocytes were mostly haploid (5 vs 83%, P < 0.01). Consequently, the blastocyst rate was higher in the CB-treated than in the CB-untreated oocytes. There was no significant difference in developmental rate between oocytes activated with CM and 7% ethanol (62 vs 62%, P > 0.05), but the developmental competence of the fertilized oocytes was superior to that of the parthenotes (88 vs 62%, P < 0.05). The present results demonstrate that CM can effectively activate mouse oocytes, as judged by the generation of [Ca(2)+]i oscillations, completion of meiosis and parthenogenetic development.

Post‐activation treatment with demecolcine improves development of somatic cell nuclear transfer embryos in pigs by modifying the remodeling of donor nuclei

The objective of this study was to examine the effect of cytochalasin B (CB) and/or demecolcine (Dc) on the remodeling of donor nuclei, nuclear ploidy, and development of somatic cell nuclear transfer (SCNT) and parthenogenetic (PA) pig embryos. SCNT and PA oocytes were either untreated (control), or treated with CB, Dc, or both CB and Dc after electric activation, and then cultured or transferred to surrogates. In SCNT, blastocyst formation was higher after treatment with CB and/or Dc (26-28%) than in the controls (16%). The number of oocytes that formed a single pronucleus (PN) was higher after treatment with Dc (86%) and CB + Dc (86%) than under control conditions (44%) or after treatment with CB (63%). In PA, blastocyst formation was higher after CB treatment (47%) than under control conditions (28%), while the formation of a single PN was higher after treatment with Dc (88%) and CB + Dc (84%) compared to controls (34%). The rate of formation of diploid embryos was higher after treatment with Dc and CB + Dc than under control conditions. Dc treatment resulted in a farrowing rate of 50% with 1.1% production efficiency, while controls showed a farrowing rate of 37.5% and a production efficiency of 0.7%. The results of our study demonstrate that post-activation treatment with Dc improves preimplantation development and supports normal in vivo development of SCNT pig embryos, probably because Dc induces formation of a single PN and this leads to normal nuclear ploidy.

Association of human sperm nuclear decondensation and in vitro penetration ability.

Sperm nuclear decondensation is an integral step in fertilization which leads to the formation of the male pronucleus. The association between the in vitro spontaneous nuclear decondensation of human sperm and its fertilizing ability was studied in infertile male patients. The ability of sperm to fertilize an egg using the discontinuous two-layer Percoll method was significantly correlated to the percentage of decondensed swollen head (r = 0.43; P less than 0.005). The fertilizing ability of sperm processed with Test-Yolk buffer was correlated with the percentage of sperm at the fully decondensed stalk stage (r = 0.51; P less than 0.05). There were insignificant correlations for the whole-wash centrifugation, cryopreserved-thawed and swim-up methods. Samples of sperm that were positive (greater than 0% fertilization) in the sperm penetration assay had a higher percentage of decondensed sperm heads (66.7% vs. 20.6%) after Percoll wash or whole-wash centrifugation (60.5% vs. 44.3%) treatments compared with samples with no fertilization. Treatments that included Test-Yolk resulted in high percentages of decondensed swollen heads. The results suggest a positive association between sperm nuclear decondensation and the fertilizing ability of sperm, and affirm the importance of nuclear decondensation to the study of fertilization events.

Separation of a pronucleus by premature cytokinesis: a mechanism for immediate diploidization of tripronuclear oocytes?

To describe an oocyte with a peculiar combination of abnormalities in terms of cytoplasmic fragmentation and formation of pronuclei. Case report. University-based IVF unit. A chromosomally normal couple undergoing the third treatment by assisted reproduction. Controlled ovarian hyperstimulation, follicular aspiration, testicular sperm extraction, intracytoplasmic sperm injection (ICSI), and oocyte fixation. Assessment of pronuclear formation and cytogenetic analysis of a tripronuclear fragmented oocyte. The described oocyte revealed two polar body-like structures after follicular aspiration and developed three pronuclei after ICSI, accompanied by extrusion of another polar body-like globule. Moreover, the pronuclear stage had undergone a premature irregular cytokinesis, including one of the pronuclei in the smaller half of the divided cytoplasm. Cytogenetic analysis showed a triploid karyotype (23,X/23,X,ace/23,Y) commonly found in digynic ICSI zygotes. The chromosomal constitution suggests that the third globule represents another cytoplasmic fragment and no regular second polar body. Separation of a supernumerary pronucleus by premature cytokinesis might be relevant for the discussion on diploidization of triploid zygotes.

Changes in acetylation on lysine 12 of histone H4 (acH4K12) of murine oocytes during maternal aging may affect fertilization and subsequent embryo development

To compare acH4K12 levels in oocytes during mouse aging and then assess how such changes might affect the developmental potential of oocytes. Experimental animal study. State key laboratory and university research laboratory. Kunming white strain mice. Oocytes obtained from TSA treated group or aging mouse group were fertilized and the formation of pronuclei and subsequently developmental potential in vitro or in vivo were assessed. AcH4K12 levels in oocytes were assessed using fluorescence staining, and confocal microscopy and oocyte developmental potentials were determined by in vitro or in vivo methods. The AcH4K12 levels in oocytes statistically significantly increased during mouse aging. When histone acetylation of oocytes of young mice was artificially increased by trichostatin A (TSA) treatment, the acH4K12 levels in male and female pronuclei in fertilized oocytes showed statistically significant changes. About 38.9% of TSA-treated oocytes failed to form pronuclei or formed morphologically abnormal pronuclei 6 hours after fertilization, which statistically significantly decreased the blastocyst rate of TSA-treated oocytes when compared with the control group (41.5% vs. 60.5%). A similar reduction in blastocyst development was also observed when oocytes collected in older mice were compared with younger mice (17.3% vs. 69.4%). The AcH4K12 levels in oocytes statistically significantly increased during the aging process in mice, and such changes may affect the acetylation patterns and morphology of pronuclei during fertilization and lead to a reduction in oocyte developmental potential.

Reorganisation of human sperm nuclear architecture during formation of pronuclei in a model system

By fertilisation, two terminally differentiated cells, namely the egg and spermatozoon, are combined to create a totipotent zygote. During this process, the inactive sperm nucleus is transformed into a functional male pronucleus. Recent studies demonstrate that human sperm chromatin has an elaborate multilevel organisation, but almost nothing is known about how sperm chromosomes are transformed during fertilisation. Because of ethical reasons and technical complications, experimentation with human embryos is generally unworkable and adequate model systems are necessary to study the formation of male pronuclei. Here, we analyse remodelling of human sperm chromatin and chromosome architecture in Xenopus egg extracts using immunofluorescent localisation of protamines and centromere protein A, as well as fluorescence in situ hybridisation localisation of major alpha-satellite DNA and whole chromosome territory (CT). We demonstrate noticeable relocalisation of centromeres and remodelling of CT during the decondensation-recondensation cycle, mimicking cellular events that occur in the paternal genome in vivo during fertilisation.

Effects of Cysteine During In Vitro Maturation of Porcine Oocytes Under Low Oxygen Tension on Their Subsequent In Vitro Fertilization and Development

In this study, we evaluated the effect of different concentrations of cysteine in in vitro maturation (IVM) medium during IVM under low oxygen tension (5% O(2)) of porcine oocytes on the intracellular content of glutathione (GSH) and subsequent in vitro fertilization (IVF) and development. Cumulus oocyte complexes (COCs) were collected from ovaries obtained at a local slaughterhouse, cultured in IVM medium supplemented with 0 (control), 0.05, 0.1, 0.2 or 0.6 mM cysteine for 44-46 h, fertilized in vitro and subsequently cultured for 6 days in total. The GSH content of the IVM oocytes exposed to 0, 0.05, 0.1, 0.2 or 0.6 mM cysteine increased significantly (P<0.05) as the concentration of cysteine increased (12.2, 14.0, 15.1, 16.4 and 16.4 pmol/oocyte, respectively). However, the rates of oocyte maturation, sperm penetration, male pronuclear formation, monospermy and even cleavage on Day 2 (the day of IVF was defined as Day 0) and blastocyst formation on Day 6 did not differ among the groups. Moreover, the cell numbers of blastomeres in blastocysts were uniform among the groups. These results indicate that supplementation with 0.05-0.6 mM cysteine during IVM under 5% O(2) tension significantly increased the intracellular GSH contents of IVM oocytes; however, it had no promoting effects on nuclear maturation, fertilization, male pronucleus formation and subsequent embryonic development to the blastocyst stage.

Nuclear Replacement ofIn Vitro-Matured Porcine Oocytes by a Serial Centrifugation and Fusion Method

The objective of the present study was to establish a method for nuclear replacement in metaphase-II (M-II) stage porcine oocytes. Karyoplasts containing M-II chromosomes (K) and cytoplasts without chromosomes (C) were produced from in vitro-matured oocytes by a serial centrifugation method. The oocytes were then reconstructed by fusion of one karyoplast with 1, 2, 3 or 4 cytoplasts (K + 1C, K + 2C, K + 3C and K + 4C, respectively). Reconstructed oocytes, karyoplasts without fusion of any cytoplast (K) and zona-free M-II oocytes (control) were used for experiments. The rates of female pronucleus formation after parthenogenetic activation in all groups of reconstructed oocytes (58.2-77.4%) were not different from those of the K and control groups (58.2% and 66.0%, respectively). In vitro fertilization was carried out to assay the fertilization ability and subsequent embryonic development of the reconstructed oocytes. The cytoplast : karyoplast ratio did not affect the fertilization status (penetration and male pronuclear formation rates) of the oocytes. A significantly high monospermy rate was found in K oocytes (p < 0.05, 61.6%) compared with the other groups (18.2-32.8%). Blastocyst formation rates increased significantly as the number of the cytoplasts fused with karyoplasts increased (p < 0.05, 0.0-15.3%). The blastocyst rate in the K + 4C group (15.3%) was comparable with that of the control (17.8%). Total cell numbers in both the K + 3C and K + 4C groups (16.0 and 15.3 cells, respectively) were comparable with that of the control (26.2 cells). Our results demonstrate that a serial centrifugation and fusion (Centri-Fusion) is an effective method for producing M-II chromosome transferred oocytes with normal fertilization ability and in vitro development. It is suggested that the number of cytoplasts fused with a karyoplast plays a critical role in embryonic development.

229 INFLUENCE OF SPERM TREATMENT ON SPERM HEAD DECONDENSATION FERTILIZING WITH EJACULATED AND EPIDIDYMAL PORCINE SPERM BY ICSI

Intracytoplasmic sperm injection (ICSI) provides a possible remedy to produce high numbers of monospermic zygotes. However, the efficiency of ICSI in pigs is low, mainly due to a failure of oocyte activation and low incidence of sperm head decondensation. The persistence of an intact sperm acrosome, plasma membrane, and perinuclear theca, which are removed during the process of sperm penetration in natural fertilization, are considered major reasons for low male pronuclear formation after ICSI in the oocytes, which are capable of supporting male pronuclear formation after IVF. Failure of male pronucleus formation is the major fertilization defect causing embryo development failure in pig oocytes subjected to ICSI (Lee JW et al. 2003 Theriogenology 59, 305). The main objective of this experiment was to determine the effect of sperm treatment on sperm head decondensation for ejaculated and epididymal spermatozoa used with ICSI. We divided ejaculated (EJ) and epididymal (EP) sperm into 3 treatment groups: 1) sperm without any treatment (control = C), 2) spermatozoa washed through a Percoll® gradient (P), and 3) spermatozoa washed through Percoll® followed by 30 min of incubation in porcine oviductal fluid (POF). Oocytes were matured in vitro 44 h in NCSU-37 and microinjected with sperm from the different treatment. Four hours after injection, the putative zygotes were stained with Hoescht and classificated as: (i) intact, (ii) low level of decondensation, and (iii) high level of decondensation and male pronuclei. A total of 461 oocytes were injected in 6 replicates. Sperm head decondensation (categorical data) was modeled using a binomial model of parameters and analyzed by ANOVA. The EP-C treatment showed a higher level of intact sperm (21.95 ± 3.4) than the other treatments (EP-P: 16 ± 3.6; EP-POF: 6.58 ± 3.6; EJ-C: 12.33 ± 3.7; EJ-P 5 ± 3.5; EJ-POF: 5.3 ± 3.6). Ejaculated sperm showed lower decondensation levels (C: 49.32 ± 5.7; P: 38.75 ± 5.4; POF: 32.00 ± 5.6) compared to epididymal sperm (C: 67.07 ± 5.4; P: 64 ± 5.6; POF: 61.84 ± 5.6). Sperm decondensation and male pronuclear formation were higher in EJ-P (56.25 ± 5.0) and EJ-POF (62.67 ± 5.2) compared to other groups (EP-C: 10.89 ± 4.9; EP-P: 20.00 ± 5.2; EP-POF: 31.58 ± 5.1; EJ-C: 38.36 ± 5.2). In conclusion, the EJ sperm exhibited higher levels of head sperm decondensation and pronuclei formation than EP sperm; the modification of sperm membrane mediated by washing sperm through Percoll® or incubating with POF induced faster decondensation than sperm without any treatment. Supported by MEC (AGL2006-03495).

233 DEHIDROLEUCODINE INDUCES PARTHENOGENETIC ACTIVATION OF BOVINE OOCYTES

Dehydroleucodine (DhL) is a sesquiterpene lactone that inhibits germinal vesicle breakdown in Bufo arenarum oocytes. Its action takes place over early stages of the cdc25 activation cascade (Bühler MI et al. 2007 Zygote 15, 183–187). The aim of this study was to evaluate the potential of DhL to induce parthenogenetic activation by observing nuclear dynamics and second polar body (2PB) extrusion of bovine oocytes, in the presence or absence of Cytochalasin B (CB), comparing these treatments with 6-Dimethylaminopurine (DMAP), an activation agent widely used. Cumulus–oocyte complexes were collected from cow ovaries obtained from a slaughterhouse. They were matured in TCM 199, supplemented with 5% FCS, 10 UI mL–1 penicillin, 10 μg mL–1 FSH, 100 μM cysteamine, 0.3 mm sodium pyruvate and 2 mm glutamine, at 39°C under 6% CO2 in air for 24 h. After removal of cumulus cells, metaphase II (MII) oocytes were selected and treated with 5 μm ionomycin (Io) for 4 min. Afterwards, oocytes were randomly allocated into one of the following treatments: a) incubation with 2 mm DMAP for 3 h (DMAP); b) incubation with 5 μm DhL for 3 h (DhL); and c) incubation with 5 μm DhL and 5 μg mL–1 CB, for 3 h (DhL-CB). A control group was only treated with Io. Activated oocytes were cultured in the maturation medium during 4, 11 or 17 h (Io exposure = 0 h), stained with Hoechst 33342 and analyzed under fluorescence microscope to evaluate nuclear stage and 2PB extrusion. Activation data are presented in Table 1. Oocytes with two extruded polar bodies and a metaphase plate were considered as partially activated (PA) and those exhibiting one pronucleus (PN) or already cleaved, as fully activated (FA). Oocytes that remained arrested at MII were not included in the table. Rates of 2PB emission were 98.3, 4.9, 83.6 and 61.5% for Io, DMAP, DhL and DhL-CB, respectively. These percentages were determined over total number of activated oocytes (PA and FA) within each group, including results from all evaluation times because no differences were found between them. Nuclear evaluation suggests that DhL is as effective as DMAP to induce full activation when combined with CB, and its use does not induce the early PN formation observed with DMAP at 4 h post Io. Most of the oocytes activated with DhL extruded a 2PB; these results were statistically different from those observed for other groups. These results indicate that DhL might be a useful agent to induce parthenogenesis, allowing 2PB extrusion and avoiding early PN formation in bovine oocytes. Table 1.Partial and full activation of bovine oocytes at 4, 11 and 17 h post treatments

Reduced developmental competence of immature, in-vitro matured and postovulatory aged mouse oocytes following IVF and ICSI

BackgroundThe present study highlights basic physiological differences associated with oocyte maturation and ageing. The study explores the fertilizing capacity and resistance to injury of mouse oocytes at different stages of maturation and ageing following IVF and ICSI. Also, the study examines the developmental competence of embryos obtained from these oocytes. The outcome of the study supports views that the mouse can be a model for human IVF suggesting that utilizing in-vitro matured and failed fertilized oocytes to produce embryos mainly when limited number of oocytes is retrieved in a specific cycle, should be carefully considered.MethodsHybrid strain mouse oocytes were inseminated by in-vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI). Oocytes groups that were used were germinal vesicle (GV) in-vitro matured metaphase II (IVM-MII), freshly ovulated MII (OV-MII), 13 hrs in-vitro aged MII (13 hrs-MII) and 24 hrs in-vitro aged MII (24 hrs-MII). Fertilization and embryo development to the blastocyst stage were monitored up to 5 days in culture for IVF and ICSI zygotes. Sperm head decondensation and pronuclear formation were examined up to 9 hrs in oocytes following ICSI. Apoptotic events in blocked embryos were examined using the TUNNEL assay. Differences between females for the number and quality of GV and OV-MII oocytes were examined by ANOVA analyses. Differences in survival after ICSI, fertilization by IVF and ICSI and embryo development were analysed by Chi-square test with Yates correction.ResultsNo differences in number and quality of oocytes were identified between females. The findings suggest that inability of GV oocytes to participate in fertilization and embryo development initiates primarily from their inability to support initial post fertilization events such as sperm decondensation and pronuclei formation. These events occur in all MII oocytes in similar rates (87–98% for IVF and ICSI). Following ICSI, pronuclei appeared in IVM and freshly ovulated oocytes by 8–9 hrs after insemination. In comparison, pronuclei appeared in 13 hrs aged oocytes by 4–5 hrs. Significantly higher proportions (P < 0.001) of blastocysts resulted from OV-MII oocytes than the other groups examined with 75% and 71% for IVF and ICSI, respectively. The 13 hrs-MII oocytes resulted in 47 and 40% blastocysts, while IVM-MII and 24 hrs-MII oocytes resulted in 38% and 0% blastocysts from IVF and 5% and 5% from ICSI, respectively. In addition, anucleate cells and DNA fragments were observed in retarded embryos derived from IVM and aged oocytes, however, apoptotic events were similar for all groups.ConclusionThe data suggests that the use of oocytes other than freshly ovulated MII should be carefully considered for assisted reproduction.